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Locomotor activation induced by MK-801 in the rat: postsynaptic interactions with dopamine receptors in the ventral striatum
European Journal of Pharmacology, 251 (1994) 229-236 © 1994 Elsevier Science B.V. All rights reserved 0014-2999/94/$07.00
229
EJP 53467
Locomotor activation induced by MK-801 in the rat: postsynaptic interactions with dopamine receptors in the ventral striatum Abdel-mouttalib Ouagazzal, Andr6 Nieoullon and Marianne Arnalric * Laboratoire de Neurobiologie Cellulaire et Fonctionnelle ~, CNRS, 31 Chemin J. Aiguier, 13402 Marseille Cedex 20, France Received 3 June 1993, revised MS received 22 September 1993, accepted 22 October 1993
The effects of bilateral 6-hydroxydopamine-induced destruction of the dopamine nerve terminals in the ventral striatum (nucleus accumbens) or pharmacological blockade of dopamine receptors with haloperidol injected locally into this area were examined on the locomotor hyperactivity induced by systemic administration of the non-competitive NMDA receptor antagonist, MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d) cyclohepten-5,10-imine hydrogen maleate salt). The locomotor stimulation induced by two doses of MK-801 (0.15 and 0.3 mg/kg, i.p.) was not attenuated by 6-hydroxydopamine bilateral lesions to the ventral striatum, either 7 or 14 days after the operation. The same lesion however reduced the locomotor activation induced by 0.5 m g / k g d-amphetamine 14 days after surgery. Bilateral intra-accumbens injection of haloperidol at a dose (2.5 p~g/side) that blocked d-amphetamine-induced hypermotility did not reduce the locomotor response to 0.3 m g / k g MK-801, while 5/xg/side haloperidol decreased the MK-801-induced locomotor stimulation. These results suggest that the locomotor response to MK-801 is dependent on an interaction between dopaminergic and excitatory amino acid transmission occurring postsynaptically rather than presynaptically in the ventral striatum. NMDA receptor antagonist; MK-801 (( + )-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine); 6-Hydroxydopamine; Haloperidol; Nucleus accumbens; Locomotion; (Rat)
1. Introduction The results of numerous studies have demonstrated that stimulation of mesolimbic dopaminergic transmission within the ventral striatum (nucleus accumbens and olfactory tubercle) increases locomotor activity in the rat (for review, see Le Moal and Simon, 1991). Microinjections of dopamine or dopaminergic agonists into the nucleus accumbens-olfactory tubercle area produces robust locomotor stimulation in rodents, for instance (Pijnenburg and Van Rossum, 1973). Furthermore, either the pharmacological blockade of dopamine receptors in the nucleus accumbens (Pijnenburg et al., 1975; Boss et al., 1988; Plaznic et al., 1989) or the selective destruction of mesolimbic dopaminergic neurons, performed by locally injecting the neurotoxin, 6-hydroxydopamine, into the ventral striatum (Kelly et al., 1975; Kelly and Iversen, 1976), reduces the locomotor hyperactivity induced by systemic administration of psychostimulant drugs such as d - a m p h e t a m i n e and cocaine.
* Corresponding author. Tel. 33 91 16 42 66, fax 33 91 77 50 83. 1 Laboratoire associ6 ~ l'Universit~ Aix-Marseille II.
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Blocking excitatory amino acid transmission at the N-methyl-D-aspartate ( N M D A ) receptor complex has also been found to elicit motor effects. Systemic administration of N M D A receptor antagonists produces locomotor hyperactivity, stereotyped behaviours and ataxia in rodents (for review, see Schmidt et al., 1992). Subsequent studies have provided evidence that the nucleus accumbens and the antero-dorsal striatum are involved in the mediation of this motor syndrome. Local injections of N M D A receptor antagonists into the nucleus accumbens induce locomotor stimulation in the rat (Donzanti and Uretsky, 1984; Raffa et al., 1989), while similar injections into the antero-dorsal striatum mainly result in stereotyped behaviours (Schmidt, 1986). The fact that pharmacological blockade of dopamine receptors can reduce the locomotor activity and stereotypies induced by the systemic injection of N M D A receptor antagonists (Clineschmidt et al., 1982; Dall'Olio et al., 1992; Hoffman, 1992; Ouagazzal et al., 1993) suggests that these behavioural effects may be dopamine-mediated. The exact nature and the site of this interaction between dopamine and excitatory amino acid still remain to be determined, however. On the basis of neurochemical data showing that N M D A receptor antagonists, at doses inducing behavioural
230 activation, enhance dopamine release in the nucleus accumbens and dorsal striatum (Imperato et al., 1990; Moghaddam and Gruen, 1991; L6scher et al., 1991; Liljequist et al., 1991), it has been suggested that the behavioural effects of N M D A receptor antagonists may be mediated by an increase in the dopamine release within these brain structures. Conflicting results obtained by other groups showed, however, that N M D A receptor antagonist administration either has no effect or even inhibits dopamine release in the striatum (Kashihara et al., 1990; Weihmuller, et al., 1991). Furthermore, behavioural experiments showing that N M D A receptor antagonists can elicit a marked locomotor stimulation in monoamine-depleted mice (Carlsson and Carlsson, 1989; Svensson and Carlsson, 1992) have led to the hypothesis that they may also act via a dopamine-independent mechanism. The present study was conducted to further elucidate the role of the mesolimbic dopaminergic system in mediating the locomotor stimulation induced by systemic administration of the non-competitive N M D A receptor antagonist, MK-801 (( + )-5-methyl-10,11-dihydro-5H-dibenzo (a,d) cyclohepten-5,10-imine hydrogen maleate salt). For this purpose, in the first experiment we studied the influence of the destruction of the dopaminergic nerve terminals in the ventral striatumnucleus accumbens after local bilateral injection of the neurotoxin, 6-hydroxydopamine, on MK-801- and damphetamine-induced locomotor stimulation. In the second experiment, the effects of local bilateral microinjections of the dopamine receptor antagonist, haloperidol, into the nucleus accumbens on MK-801and d-amphetamine-induced activation were tested.
2. Materials and methods
2.1. Subjects Male albino Wistar rats (Iffa-Credo) weighing 280300 g at the start of the experiment were housed in groups of three per cage with food and water available at libitum. They were maintained under temperaturecontrolled conditions with an alternating 12-h light-dark cycle.
2.2. Stereotaxic surgery and injection procedure Stereotaxic surgery was performed under xylazine (15 m g / k g , i.m.) and ketamine (100 m g / k g , i.m.) anaesthesia. In the first experiment, the rats received a bilateral injection of either a 6-hydroxydopamine (4 gg//xl, expressed as free base; nucleus accumbens-lesioned rats n = 29) or a vehicle solution (0.9% saline containing 1 m g / m l ascorbic acid; sham rats n = 29) into the nucleus accumbens area. The coordinates were
as follows: AP + 3.2 mm, L _+1.7 ram, from the bregma, DV - 7 . 8 mm from the skull surface with the incisor bar set at +5.0 mm (according to the atlas of Pellegrino et al., 1979). Intracerebral injection of the solution was performed with a pump-driven 10-/xl Hamilton syringe through 30-gauge stainless steel injection needles. A total volume of 2 ~l was injected on each side, at a rate of 1 /xl/3 rain. After the drug injection, the injection needles were left in situ for 3 min to allow the drug to diffuse away from the tips. In the second experiment, rats (n = 35) were implanted with bilateral stainless steel guide cannulas (23-gauge) positioned 3 mm above the nucleus accumbens (same coordinates as for the lesion except the dorso-ventral ones, which were - 4 . 8 mm from the skull). Wire stylets were inserted into the cannulas to prevent occlusion. One week after implantation, a bilateral 30-gauge injection needle was inserted through the guide to 3 mm beyond its tip and a volume of 0.5 or 1/zl was infused at a rate of 0 . 5 / . d / 3 min with a Hamilton syringe mounted on a microdrive pump. Injectors remained in place for 2 min to allow the drug to diffuse. Each rat was used only once.
2.3. Drugs 6-Hydroxydopamine hydrochloride (Sigma) was dissolved in 0.9% saline solution containing ascorbic acid (1 m g / m l ) as an antioxidant, d-Amphetamine was dissolved in physiological saline. Haloperidol (Haldol, injectable solution, Janssen) was injected at two doses: 2 . 5 / z g / 0 . 5 / x l or 5 ~ g / # l . Control injections using the vehicle (solvent of the commercial preparation for haloperidol) were tested. MK-801 ((+)-5-methyl10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine hydrogen maleate salt) (a generous gift from Merck Sharp and Dohme Research Laboratories, U.K.) was dissolved in a physiological saline solution, and the pH was adjusted to 6.5 with the minimum quantity of N a O H (0.1 N). D-Amphetamine was injected subcutaneously (s.c.) and MK-801 intraperitoneally (i.p.), in a volume of 1 m l / k g .
2.4. BehaL'ioural testing Locomotor activity was measured in 16 wire (top, floor and front door) and Plexiglass cages (side walls) 40 X 25 x 23 cm, with two horizontal infrared photocell beams located across the long axis of the cage (Imetronic, France). Beam interruptions were accumulated over 1-min intervals and recorded in minute bins by means of a microcomputer (Tandon PCA 12 SL). The operated animals were subdivided into four groups. Group A [sham (n = 6), lesioned (n = 10)] and group B [sham (n = 8), lesioned (n = 10)] received an injection of MK-801 at 0.15 and 0.3 m g / k g , i.p., respectively.
231
Group C [sham (n = 7), lesioned (n = 9)] received an injection of 0.5 m g / k g , s.c., d-amphetamine. A control group [sham (n = 8)] received an injection of saline (i.p.) only. The behavioural responses of the various experimental groups to MK-801, d-amphetamine and saline were measured 7 and 14 days after surgery. In the second experiment, one group of rats was given an injection of 0.3 m g / k g MK-801 15 min after bilateral microinjections of haloperidol 2.5 /xg/0.5 /xl (n = 8) or 5/xg/pA (n = 8) or vehicle (n = 7) into the nucleus accumbens. A second group was given an injection of 0.5 m g / k g d-amphetamine 15 min after bilateral microinjections of haloperidol 2.5 Fzg/0.5 /xl (n = 6) or vehicle (n = 6) into the nucleus accumbens. On the test days, spontaneous locomotor activity was recorded for 90 min prior to any drug treatment and immediately after d-amphetamine or MK-801 administration for 120 min.
2.5. Biochemical assays At the end of experiment 1, the rats were killed by decapitation. Their brains were rapidly removed and the nucleus accumbens, olfactory tubercle, anterior striatum and posterior striatum were dissected out and stored at -80°C. The levels of dopamine and its metabolite, D O P A C (3,4-dihydroxyphenylacetic acid), were determined by high performance reverse phase liquid chromatography (HPLC) coupled with electrochemical detection of the compounds (Dusticier and Nieoullon, 1987). The values obtained for the lesioned groups are expressed as percentages of those obtained for the sham-operated animals.
2. 6. Histology At the end of experiment 2, the rats were perfused with a 10% formalin solution through the left cardiac
ventricle under chloral anesthesia. The brains were removed and kept in a 10% formalin solution. The brains were then sectioned and colored with cresyl in order to verify the location of the injection sites.
2. Z Data analysis The effects of 6-hydroxydopamine lesion on locomotor activity induced by MK-801 and d-amphetamine were analyzed by subjecting the total number of beam interruptions recorded per 10-rain period to a two-factor analysis of variance (ANOVA) with the lesion and control groups forming the independent factor and time, the repeated measure. The effects of haloperidol infusion on MK-801- and d-amphetamine-induced locomotor activation were also analyzed by means of A N O V A with the vehicle and the various drug doses forming the independent factor. Individual group comparisons were carried out using the Newman-Keuls test. The biochemical results were analyzed using Student's t-test. The significance level was taken to be P < 0.05.
3. Results
3.1. Neurochemical results The regional brain dopamine concentrations determined in 6-hydroxydopamine and vehicle-injected animals are shown in table 1. Eight animals with a dopamine depletion of less than 70% in the ventral striatum area were excluded from the behavioural analysis. The neurochemical assay data on the remaining animals from groups A and B showed that 6-hydroxydopamine infusion into the nucleus accumbens produced a substantial, significant depletion of dopamine in the ventral striatum (nucleus accumbens
TABLE 1 Effects of 6-hydroxydopamine (6-OHDA) treatment on regional dopa mi ne (DA) and 3,4-dihydroxyphenylacetic acid ( D O P A C ) concentrations. Dopam ine and D O P A C levels in n g / m g protein for groups A, B and C. Values shown are m e a n s ± S.E.M. Groups
Ventral striatum
Antero-dorsal striatum
Posterior striatum
DA
DOPAC
DA
DOPAC
DA
DOPAC
5.53 ± 0.86 0.66±0.15 a 88
1.36 ± 0.11 0.38±0.09 a 72
6.42 ± 1.54 2.25 ± 0.28 a 65
1.69 _+0.35 0.81 ±0.11 a 52
7.83 ± 0.69 5.87±0.54 ~ 25
1.37 _+0.22 0.78±0.07 a 43
8.38 ± 1.06 1.52 ± 0.26 ~ 82
1.84 ± 0.34 0.42 ± 0.12 " 77
7.26 ± 0.58 2.07 ± 0,70 ~ 71
1.43 ± 0.21 0.50 ± 0.13 a 65
8,75 + 0.37 7.09 _+0.74 ~ 19
1.09 ± 0.10 0.85 ± 0.10 21
5.43 ± 0.42 1.27± 0.39 ~ 77
1.58 ± 0.28 0.35 ± 0.06 a 78
7.29 ± 1.16 3.42± 1.15 a 53
1.78 ± 0.40 0.69±0.13 ~ 61
7.97 ± 1.20 5.74 ± 0.70 a 28
1.74 + 0.30 1.01 +0.20 ~ 42
(A) Sham (n = 6) 6 - O H D A (n = 8) % Depletion
(B) Sham (n = 8) 6 - O H D A (n = 7) % Depletion
(c) Sham (n = 7) 6 - O H D A (n = 6) % Depletion
Significantly different from sham group, P < 0.05, Student's t-test.
232
and olfactory tubercle) and the antero-dorsal striatum, but smaller depletions in the posterior striatum. Groups A and B exhibited reductions of 88 and 82% in the ventral striatum, 65 and 71% in the antero-dorsal striaturn and 25 and 19% in the posterior striatum, respectively. These values were comparable to, although higher than, those measured in group C, which were 77, 53 and 28% respectively. As shown in table 1, the D O P A C decreases were found to parallel those of dopamine in the same striatal regions after 6-hydroxydopamine infusion into the nucleus accumbens. The D O P A C levels in the ventral striatum (which decreased by more than 70%) were lower than in the antero-dorsal and posterior striatum.
3.2. Effects of MK-801- and d-amphetamine-induced locomotor stimulation in animals with 6-hydroxydopamine lesions Administration of MK-801 (0.15 and 0.3 m g / k g , i.p.) resulted in dose-dependent locomotor stimulation in the intact rats (sham animals). As shown in fig. 1A, the locomotor stimulation induced by the injection of 0.15 m g / k g MK-801 in intact rats differed significantly from the locomotor activity of the vehicle-injected animals. The two-factor A N O V A showed a significant main effect of drug [F(1,12) = 7.57, P < 0.05], time [F(11,132) = 4.41, P < 0.05] and the drug × time interaction was found to be significant [F(11,132)= 3.23, P < 0.05] (fig. 1A). The administration of 0.3 m g / k g MK-801 to sham animals resulted in greater locomotor activation than 0.15 m g / k g MK-801 (fig. 1B). In line with this trend, the two-factor A N O V A revealed a significant main effect of drug [F(1,14) = 8.7, P < 0.05], time [F(11,154) = 2.78, P < 0.05] and a significant drug × time interaction [F(11,154) = 2.72, P < 0.05]. This locomotor activation was comparable in intensity to that observed after administration of 0.5 m g / k g damphetamine s.c.: the mean photocell counts during the total 120 min was 1 2 9 6 + 3 9 8 with 0.3 m g / k g MK-801 and 1037 + 266 with d-amphetamine. As previously mentioned, d-amphetamine injected at a dose of 0.5 r a g / k g enhanced locomotor activity, for a period of 90-120 min (fig. 1C). In keeping with this trend, the two-factor A N O V A showed a significant main effect of drug [F(1,13)= 13.25, P < 0 . 0 5 ] , time [F(11,143)= 13.49, P < 0.05] and the drug × time interaction was found to be significant [F(11,143) = 8.23, P < 0.05]. Seven days post-operatively, the 6-hydroxydopamine-injected animals showed enhanced locomotion after either MK-801 (0.15 or 0.3 m g / k g ) or 0.5 m g / k g d-amphetamine injection (fig. 1A, B and C, respectively). The two-factor A N O V A showed that the lesion had no significant effect on MK-801 or amphetamineinduced locomotion. When retested 14 days after surgery (fig. 2A and B), there was still no significant
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Time (min) Fig. 1. Locomotor response to MK-801 0.15 mg/kg (A) and 0.3 mg/kg (B) i.p. injection and 0.5 mg/kg d-amphetamine s.c. (C) in sham animals (o) and animals with 6-hydroxydopamine lesion to the nucleus accumbens (e) 7 days after surgery. Locomotor response to vehicle (A, B and C) in sham-operated animals (zx). The mean number of photocell counts is plotted on the ordinate in 10-min periods. Insert refers to mean total photocell counts_+ S.E.M. during the 120-min test. * Significantly different from sham-operated animals injected with vehicle, P < 0.05.
difference between the locomotor responses of the 6-hydroxydopamine lesion and sham groups to MK-801, 0.15 and 0.3 m g / k g , since the two-factor A N O V A showed no main lesion effect, [F(1,12)= 0.32, N.S.,
233
and F(1,13)= 1.36, N.S.]. However, the 6-hydroxydopamine-lesioned animals showed an attenuated locomotor response to d-amphetamine as compared to the sham animals (fig. 2C). In line with this trend, a twofactor A N O V A revealed a significant main lesion effect [F(1,11) = 13.05, P < 0.05].
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Fig. 3. Effects of haloperidol on the locomotor activation induced by 0.3 m g / k g MK-801 i.p. (A) and 0.5 m g / k g d - a m p h e t a m i n e s.c. (B). Rats were injected bilaterally into the nucleus accumbens with 1 pA of vehicle (©), 2 . 5 / x g / 0 . 5 / z l (o) or 5 # g / / x l haloperidol (z~) 15 rain before the MK-801 or d - a m p h e t a m i n e injection. Coordinates as in fig. 1. Insert refers to mean total photocell counts_+S.E.M, during the 120-rain test. * Significantly different from controls, P < 0.05, Newman-Keuls test after significant A N O V A .
3.3. Effects of haloperidol infusion into the nucleus accumbens on MK-801- and d-amphetamine-induced activation
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Time (min) Fig. 2. Locomotor response to MK-801 0.15 m g / k g (A) and 0,3 m g / k g (B) i.p. and 0.5 m g / k g d - a m p h e t a m i n e s.c. (C) in sham animals (©) and animals with 6-hydroxydopamine lesion to the nucleus aecumbens (e) 14 days after surgery. Coordinates as in fig. 1. Insert refers to m e a n total photocell c o u n t s ± S . E . M , during the 120-rain test. * Significantly different from sham animals, P < 0.05.
Local infusion of haloperidol into the nucleus accumbens reduced the locomotor stimulation induced by 0.3 m g / k g MK-801 (fig. 3A). The two-factor A N O V A showed a main effect of dose [F(2,20) = 6.56, P < 0.05] and a dose × time interaction [F(22,220)= 2.30, P < 0.05]. Individual comparisons based on the Newman-Keuls test showed that only the rats injected with highest dose of haloperidol (5 /zg//xl) had a significantly decreased locomotor response to MK-801 as compared to the vehicle-injected animals (graph insert, Newman-Keuls test, P < 0.05). Bilateral infusion of the lowest dose of haloperidol (2.5 /~g/0.5 tzl) into the nucleus accumbens markedly reduced the damphetamine-induced locomotor activation (fig. 3B).
234 The two-factor A N O V A showed a significant main treatment effect [F(1,10)= 10.86, P < 0 . 0 5 ] and revealed that the treatment × time interaction was significant [ F ( l l , l l 0 ) = 5.32, P < 0.05].
4. Discussion The results of the present study showed that destruction of the mesolimbic dopamine terminals within the ventral striatum (nucleus accumbens and olfactory tubercle) failed to block the MK-801-induced locomotor stimulation. The behavioural response to systemic injection of 0.15 or 0.3 m g / k g MK-801 was not altered in animals with 6-hydroxydopamine lesions on either postoperative day (days 7 and 14). In agreement with results of numerous previous studies, however, the same 6-hydroxydopamine lesion markedly reduced the locomotor stimulation induced by d-amphetamine (0.5 m g / k g ) , confirming that the locomotor stimulatory effects of indirect dopamine agonists are mediated mainly via facilitation of mesolimbic dopaminergic neurotransmission. Interestingly, 7 days after the surgery, no significant difference between the locomotor responses to d-amphetamine of the nucleus accumbens-lesioned and sham animals could be observed. In fact, the suggestion is that 1 week after local injection of 6-hydroxydopamine into the nucleus accumbens, dopamine fiber degeneration may not be complete. As previously reported by Kelly et al. (1975), the blockade of the locomotor response to d-amphetamine injection was maximal around 14 days after 6-hydroxydopamine lesion. On the same post-operative day, however, the 6-hydroxydopamine lesion of the nucleus accumbens had no effect on the MK-801-induced locomotion. Twenty one days after the surgery, the lesion still had no effect on MK-801-induced hyperactivity (data not shown). These results therefore suggest that unlike d-amphetamine-induced locomotor activation, the locomotor stimulatory effects of MK-80I may be not mediated mainly via facilitation of mesolimbic dopaminergic neurotransmission. In contrast, French et al. (1985), have previously observed that 6-hydroxydopamine lesion of the nucleus accumbens depressed the locomotor activity induced by systemic administration of the non-competitive N M D A receptor antagonist, phencyclidine. These results suggested that the behavioural effects of phencyclidine may be mediated by an increase of the dopamine release from mesolimbic dopaminergic terminals. Neurochemical experiments have shown however that, unlike MK-801, phencyclidine also has potent ability to inhibit dopamine uptake (Snell et al., 1988; Maurice et al., 1991). It is therefore possible that the discrepancy between our data and those of French et al. (1985) may be due to the fact that the be-
havioural effects of phencyclidine result from its simultaneous interactions with dopamine uptake processes and the N M D A receptor complex, while the pharmacological effects of MK-801 may result mainly from its interaction with the N M D A receptor complex alone. As reported previously (Clineschmidt et al., 1982; Dall'Olio et al., 1992; Hoffman, 1992) systemic injection of dopamine receptor antagonists has been shown to attenuate the hypermotility induced by MK-801, so that the dopaminergic system may be involved in this stimulatory effect. In the present study, the finding that local infusion of 5 / x g / / x l of the dopamine receptor antagonist, haloperidol, into the nucleus accumbens markedly reduced the locomotor activity induced by 0.3 m g / k g MK-801 suggests that the MK-801 effects involve the activation of dopamine receptors in the nucleus accumbens. In agreement with this idea, Wallace et al. (1992) have recently reported that local injection of either dopamine D~ or D 2 receptor antagonists into the nucleus accumbens reduced the locomotor response to MK-801 administration. However, lower doses of haloperidol (2.5 /xg/0.5 /xl) blocking damphetamine-induced locomotor activity failed to reduce the locomotor stimulation induced by MK-801. These data confirm those obtained by Raffa et al. (1989), showing that intra-accumbens infusion of haloperidol (2.5/xg/side) failed to block the locomotor stimulation induced by local injection of MK-801 into the nucleus accumbens. As compared to that with amphetamine, the locomotor response to MK-801 may thus be less sensitive to dopamine receptor blockade in the ventral striatum. In line with these data, we recently reported that systemic blockade of dopamine D~ or D 2 receptor subtypes had differential effects on the locomotor activity induced by MK-801 and damphetamine. The doses of the dopamine D l or D 2 receptor antagonists needed to block MK-801-induced locomotor stimulation were higher than those blocking the locomotor activity produced by d-amphetamine (Ouagazzal et al., 1993). It therefore appears likely that the attenuation of MK-801 behavioural effects may occur only when dopaminergic transmission is largely blocked. These results further support the idea that the mechanisms involved in the behavioural effects of MK801 and d-amphetamine may be different. In view of all the data described above, it appears that the locomotor stimulatory effects of MK-801 may be not mediated via an enhancement of the dopamine release from dopaminergic terminals within the ventral striatum but may well result from interactions between the dopaminergic and excitatory amino acid systems occurring postsynaptically. Possible postsynaptic interactions between dopamine and N M D A receptors have been suggested previously by results showing that the concomitant administration of subthreshold doses o[ an N M D A receptor antagonist and a dopamine recep-
235 tor agonist resulted in synergistic m o t o r stimulatory effects in m o n o a m i n e - d e p l e t e d mice a n d in m a r m o s e t s exposed to 1 - m e t h y l - 4 - p h e n y l - l , 2 , 3 , 6 - t e t r a h y d r o p y r i dine ( M P T P ) (Svensson et al., 1992; Wfillner et al., 1992). W e have o b t a i n e d f u r t h e r s u p p o r t for the above hypothesis in s u b s e q u e n t p r e l i m i n a r y e x p e r i m e n t s showing that systemic injection of h a l o p e r i d o l at low doses can reduce the l o c o m o t o r activity i n d u c e d by MK-801 in a n i m a l s with a 6 - h y d r o x y d o p a m i n e lesion (data not shown). I n this context, the a t t e n u a t i o n of MK-801 effects may well be due to the blockade of mesolimbic d o p a m i n e r g i c n e u r o t r a n s m i s s i o n . In this case, a l t h o u g h the d e p l e t i o n of v e n t r a l striatal d o p a m i n e exceeded 80% in the p r e s e n t e x p e r i m e n t , the residual d o p a m i n e a n d the adaptive striatal synaptic c h a n g e s occurring after l o n g - t e r m d o p a m i n e depletion might suffice to facilitate the expression of MK-801 effects. For example, l o n g - t e r m striatal d o p a m i n e dep l e t i o n has b e e n r e p o r t e d to i n d u c e postsynaptic d o p a m i n e r e c e p t o r supersensitivity, as established biochemically from the increase in the d o p a m i n e r e c e p t o r B .... r e c o r d e d in the s t r i a t u m ( S t a u n t o n et al., 1982), a n d b e h a v i o u r a l l y from the ' s u p e r s e n s i t i v e ' l o c o m o t o r r e p o n s e i n d u c e d by the direct d o p a m i n e r e c e p t o r agonist, a p o m o r p h i n e (Kelly a n d Iversen, 1976). Striatal d o p a m i n e d e a f f e r e n t a t i o n has b e e n f o u n d to also induce o t h e r complex changes, such as an increase in the n u m b e r of striatal N M D A receptors ( S a m u e l et al., 1990), which may lead to c h a n g e s in excitatory a m i n o acid transmission. O t h e r structures c o n t a i n i n g b o t h d o p a m i n e a n d N M D A receptors might also be involved, however, in the m e d i a t i o n of l o c o m o t o r responses to MK-801. In this respect, it is of interest to note that p h a r m a c o l o g i c a l b l o c k a d e of excitatory a m i n o acid t r a n s m i s s i o n at the level of the ventral t e g m e n t a l area, s u b s t a n t i a nigra or i n t e r n a l globus pallidus in the rat also i n d u c e d locomotor activity ( D a w b a r n a n d Pycock, 1981; Brotchie et al., 1991). T h e f u n c t i o n a l role of the N M D A - d o p a m i n e i n t e r a c t i o n s putatively involved at these levels in the expression of the MK-801 effects still r e m a i n s to be d e t e r m i n e d , however. In conclusion, the p r e s e n t study showed that 6-hyd r o x y d o p a m i n e n u c l e u s a c c u m b e n s lesions failed to block the M K - 8 0 1 - i n d u c e d locomotor s t i m u l a t i o n in rats whereas p h a r m a c o l o g i c a l blockade of d o p a m i n e receptors in this area r e d u c e d the MK-801 b e h a v i o u r a l effects. T h e s e data suggest that the l o c o m o t o r stimulatory effects of MK-801 may result mainly, within the v e n t r a l s t r i a t u m , from i n t e r a c t i o n s b e t w e e n the d o p a m i n e r g i c a n d excitatory a m i n o acid t r a n s m i s s i o n occurring postsynaptically r a t h e r t h a n presynaptically.
Acknowledgements This study was supported by grants from the CNRS, the University of Aix-Marseille II (Direction de la Recherche et des Etudes
Doctorales) and DRET (convention No. 91.34.157.00.470.75.01.). A. Ouagazzal was supported by a grant from the Moroccan Governemerit. The authors thank Nicole Dusticier for performing the H.P.L.C. measurements and Mrs. J. Blanc for English corrections to the manuscript.
References Boss, R., A. Cools and S. Ogen, 1988, Differential effects of the selective D2-antagonist raclopride in the nucleus accumbens of the rat on spontaneous and d-amphetamine-induced activity. Psychopharmacology 95, 447. Brotchie, J.M., l.J. Mitchell, M.A. Sambrook and A.R. Crossman, 1991, Alleviation of parkinsonism by antagonism of excitatory amino acid transmission in the medial segment of the globus pallidus in rat and primate, Movement Disord. 6, 113. Carlsson, M. and A. Carlsson, 1989, The NMDA antagonist MK-801 causes marked locomotor stimulation in monoamine-depleted mice, J. Neural Transm. 75, 221. Clineschmidt, B.V., G.E. Martin, P.R. Bunting and N.L. Papp, 1982, Central sympathomimetic activity of ( + )-5-methyl-10,11-dihydro5H-dibenzo [a,d] cyclohepten-5,10-imine (MK-801), a substance with potent anticonvulsant, central sympathomimetic and apparent anxiolytic properties, Drug. Dev. Res. 2, 135. Dall'Olio, R., O. Gandolfi and N. Montarano, 1992, Effect of chronic treatment with dizocilpine (MK-801) on the behavioral response to dopamine receptor agonist in the rat, Psyehopharmacology 107, 591. Dawbarn, D. and C.J. Pycock, 1981, Motor effects following application of putative excitatory amino acid antagonists to the region of the mesencephalic dopamine cell bodies in the rat, NaunynSchmied. Arch. Pharmacol. 318, 100. Donzanti, B.A. and N.J. Uretsky, 1984, Antagonism of the bypermotility response induced by excitatory amino acids in the rats nucleus accumbens, Naunyn-Schmied. Arch. Pharmacol. 325, 1. Dusticier, N. and A. Nieoullon, 1987, Comparative analysis of the effects of in vivo electrical stimulation of the frontal cortex and gamma-butyrolactone administration on dopamine and dihydroxyphenyl acetic acid (DOPAC) striatal contents in the rat, Neurochem. Int. 10, 275. French, E.D., C. Pilapil and R. Quirion, 1985, Phencyclidine binding sites in the nucleus accumbens and phencyclidine induced hyperactivity are decreased following lesions of the mesolimbic dopamine system, Eur. J, Pharmacol. 116, l. Hoffman, D.C., 1992, Typical and atypical neuroleptics antagonize MK-801-induced locomotion and stereotypy in rats, J. Neural Transm. 89, 1. Imperato, A., M.G. Scrocco, S. Bacchi and L. Angelucci, 1990, NMDA receptors and in vivo dopamine release in the nucleus accumbens and caudatus, Eur. J. Pharmacol. 187, 555. Kashihara, K., T. Hamamura, K. Okumura and S. Otsuki, 1990, Effect of MK-801 on endogenous dopamine release in vivo, Brain Res. 528, 80. Kelly, P.H. and S.D. Iversen, 1976, Selective 6-hydroxydopamine-induced destruction of mesolimbic dopamine neurons: abolition of psychostimulant-induced locomotor activity in rats, Eur. J. Pharmacol. 40, 45. Kelly, P.H., P.W. Seviour and S.D. Iversen, 1975, Amphetamine and apomorphine responses in the rat following 6-hydroxydopamine lesions of the nucleus accumbens septi and corpus striatum, Brain Res. 94, 507. Le Moal, M. and H. Simon, 1991, Mesocorticolimbic dopaminergic network, functional and regulatory roles, Physiol. Rev. 71, 155. Liljequist, S., K. Ossowska, M. Grabowska-And6n and N. And6n,1991, Effect of the NMDA receptor antagonist, MK-801.
236 on locomotor activity and on the metabolism of dopamine in various brain areas of mice, Eur. J. Pharmacol. 195, 55. L6scher, W., R. Armies and D. H6nack, 1991, The N-methyl-Daspartate receptor antagonist MK-801 induces increases in dopamine and serotonine metabolism in several brain regions of rats, Neurosci. Lett. 198, 191. Maurice, T., J. Vigon, J. Kameuka and R. Chicheportiche, 1991, Differential interaction of phencyclidine-like drugs with the dopamine uptake complex in vivo, J. Neurochem. 56, 553. Moghaddam, B. and R.J. Gruen, 1991, Do endogenous excitatory amino acids influence striatal dopamine release?, Brain Res. 544, 329. Ouagazzal, A., A. Nieoullon and M. Amalric, 1993, Effects of dopamine D1 and D2 receptor blockade on MK-801-induced hyperlocomotion in rats, Psychopharmacology 111,427. Pellegrino, L.J., A.S. Pellegrino and A.J. Cushman, 1979, A Stereotaxic Atlas of the Rat Brain (Plenum Press, New York). Pijnenburg, A.J.J. and J.M. Van Rossum, 1973, Stimulation of locomotor activity following injections of dopamine into the nucleus accumbens, J. Pharmacol. 25, 1003. Pijnenburg, A.J.J., W.M. H6nig and J.M. Van Rossum, 1975, Inhibition of d-amphetamine-induced locomotor activity by injection of haloperidol into the nucleus accumbens of the rat, Psychopharmacologia (Berlin) 41, 87. Plaznic, A., R. Stefanski and W. Kostowski, 1989, Interaction between accumbens D1 and D2 receptors regulating rat locomotor activity, Psychopharmacology 99, 558. Raffa, R.B., M.E. Ortegon, D.M. Robisch and G.E. Martin, 1989, In vivo demonstration of the enhancement of MK-801 by L-glutamate, Life Sci. 44, 1593. Samuel, D., M. Errami and A. Nieoullon, 1990, Localization of N-methyl-o-aspartate receptors in the rat striatum: effects of specific lesions on the [3H]3-(2-carboxypiperazin-4-yl) propyl-1phosphonic acid binding, J. Neurochem. 54, 1926. Schmidt, W.J., 1986, lntrastriatal injection of DL-2- amino-5-phos-
phonovaleric acid (AP-5) induces sniffing stereotypy that is antagonized by haloperidol and clozapine, Psychopharmacology 90, 123. Schmidt, W.J., M. Bubser and W. Hauber, 1992, Behavioural pharmacology of glutamate in the basal ganglia, J. Neural Transm. 38, 65. Snell, LD., S. Yi and K.M. Johnson, 1988, Comparison of the effects of MK-801 and phencyclidine on catecholamine uptake and NMDA-induced norepinerphrine release, Eur. J. Pharmacol. 145, 223. Staunton, D.A., P,J. Magistretti, G.F. Koob, W.J. Shoemaker and F.E. Bloom, 1982, Dopaminergic supersensitivity induced by denervation and chronic receptor blockade is additive, Nature 229, 72. Svensson, A. and M.L. Carlsson, 1992, Injection of the competitive NMDA receptor antagonist AP-5 into the nucleus accumbens of monoamine-depleted mice induces pronounced locomotor stimulation, Neuropharmacology 31,513. Svensson, A., A. Carlsson and M.L. Carlsson, 1992, Differential locomotor interactions between dopamine D 1 / D 2 receptor agonists and NMDA antagonist dizocilpine in monoamine-depleted mice, J. Neural Transm. 90, 199. Wallace, L.J., D.L Willins and N.J. Uretsky, 1992, MK-801-induced hypermotility is dependent on dopaminergic neurotransmission in the nucleus accumbens (NA), Soc. Neurosci. Abstr. 18 No. 19114. Weihmuller, F.B., S.J. O'Dell, B.N. Cole and J.F. Marshall, 1991, MK-801 attenuates the dopamine-releasing but not the behavioral effects of methamphetamine: an in vivo microdialysis study, Brain Res. 549, 230. Wiillner, V., A. Kupsch, G. Arnold, P. Renner, C. Scheid, R. Scheid, W. Oertel and T. Klockgether, 1992, The competitive NMDA antagonist CGP40.116 enhances L-DOPA response in the MPTP-treated marmosets, Neuropharmacology 31, 713.
229
EJP 53467
Locomotor activation induced by MK-801 in the rat: postsynaptic interactions with dopamine receptors in the ventral striatum Abdel-mouttalib Ouagazzal, Andr6 Nieoullon and Marianne Arnalric * Laboratoire de Neurobiologie Cellulaire et Fonctionnelle ~, CNRS, 31 Chemin J. Aiguier, 13402 Marseille Cedex 20, France Received 3 June 1993, revised MS received 22 September 1993, accepted 22 October 1993
The effects of bilateral 6-hydroxydopamine-induced destruction of the dopamine nerve terminals in the ventral striatum (nucleus accumbens) or pharmacological blockade of dopamine receptors with haloperidol injected locally into this area were examined on the locomotor hyperactivity induced by systemic administration of the non-competitive NMDA receptor antagonist, MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d) cyclohepten-5,10-imine hydrogen maleate salt). The locomotor stimulation induced by two doses of MK-801 (0.15 and 0.3 mg/kg, i.p.) was not attenuated by 6-hydroxydopamine bilateral lesions to the ventral striatum, either 7 or 14 days after the operation. The same lesion however reduced the locomotor activation induced by 0.5 m g / k g d-amphetamine 14 days after surgery. Bilateral intra-accumbens injection of haloperidol at a dose (2.5 p~g/side) that blocked d-amphetamine-induced hypermotility did not reduce the locomotor response to 0.3 m g / k g MK-801, while 5/xg/side haloperidol decreased the MK-801-induced locomotor stimulation. These results suggest that the locomotor response to MK-801 is dependent on an interaction between dopaminergic and excitatory amino acid transmission occurring postsynaptically rather than presynaptically in the ventral striatum. NMDA receptor antagonist; MK-801 (( + )-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine); 6-Hydroxydopamine; Haloperidol; Nucleus accumbens; Locomotion; (Rat)
1. Introduction The results of numerous studies have demonstrated that stimulation of mesolimbic dopaminergic transmission within the ventral striatum (nucleus accumbens and olfactory tubercle) increases locomotor activity in the rat (for review, see Le Moal and Simon, 1991). Microinjections of dopamine or dopaminergic agonists into the nucleus accumbens-olfactory tubercle area produces robust locomotor stimulation in rodents, for instance (Pijnenburg and Van Rossum, 1973). Furthermore, either the pharmacological blockade of dopamine receptors in the nucleus accumbens (Pijnenburg et al., 1975; Boss et al., 1988; Plaznic et al., 1989) or the selective destruction of mesolimbic dopaminergic neurons, performed by locally injecting the neurotoxin, 6-hydroxydopamine, into the ventral striatum (Kelly et al., 1975; Kelly and Iversen, 1976), reduces the locomotor hyperactivity induced by systemic administration of psychostimulant drugs such as d - a m p h e t a m i n e and cocaine.
* Corresponding author. Tel. 33 91 16 42 66, fax 33 91 77 50 83. 1 Laboratoire associ6 ~ l'Universit~ Aix-Marseille II.
SSDI 0 0 1 4 - 2 9 9 9 ( 9 3 ) E 0 7 8 1 - M
Blocking excitatory amino acid transmission at the N-methyl-D-aspartate ( N M D A ) receptor complex has also been found to elicit motor effects. Systemic administration of N M D A receptor antagonists produces locomotor hyperactivity, stereotyped behaviours and ataxia in rodents (for review, see Schmidt et al., 1992). Subsequent studies have provided evidence that the nucleus accumbens and the antero-dorsal striatum are involved in the mediation of this motor syndrome. Local injections of N M D A receptor antagonists into the nucleus accumbens induce locomotor stimulation in the rat (Donzanti and Uretsky, 1984; Raffa et al., 1989), while similar injections into the antero-dorsal striatum mainly result in stereotyped behaviours (Schmidt, 1986). The fact that pharmacological blockade of dopamine receptors can reduce the locomotor activity and stereotypies induced by the systemic injection of N M D A receptor antagonists (Clineschmidt et al., 1982; Dall'Olio et al., 1992; Hoffman, 1992; Ouagazzal et al., 1993) suggests that these behavioural effects may be dopamine-mediated. The exact nature and the site of this interaction between dopamine and excitatory amino acid still remain to be determined, however. On the basis of neurochemical data showing that N M D A receptor antagonists, at doses inducing behavioural
230 activation, enhance dopamine release in the nucleus accumbens and dorsal striatum (Imperato et al., 1990; Moghaddam and Gruen, 1991; L6scher et al., 1991; Liljequist et al., 1991), it has been suggested that the behavioural effects of N M D A receptor antagonists may be mediated by an increase in the dopamine release within these brain structures. Conflicting results obtained by other groups showed, however, that N M D A receptor antagonist administration either has no effect or even inhibits dopamine release in the striatum (Kashihara et al., 1990; Weihmuller, et al., 1991). Furthermore, behavioural experiments showing that N M D A receptor antagonists can elicit a marked locomotor stimulation in monoamine-depleted mice (Carlsson and Carlsson, 1989; Svensson and Carlsson, 1992) have led to the hypothesis that they may also act via a dopamine-independent mechanism. The present study was conducted to further elucidate the role of the mesolimbic dopaminergic system in mediating the locomotor stimulation induced by systemic administration of the non-competitive N M D A receptor antagonist, MK-801 (( + )-5-methyl-10,11-dihydro-5H-dibenzo (a,d) cyclohepten-5,10-imine hydrogen maleate salt). For this purpose, in the first experiment we studied the influence of the destruction of the dopaminergic nerve terminals in the ventral striatumnucleus accumbens after local bilateral injection of the neurotoxin, 6-hydroxydopamine, on MK-801- and damphetamine-induced locomotor stimulation. In the second experiment, the effects of local bilateral microinjections of the dopamine receptor antagonist, haloperidol, into the nucleus accumbens on MK-801and d-amphetamine-induced activation were tested.
2. Materials and methods
2.1. Subjects Male albino Wistar rats (Iffa-Credo) weighing 280300 g at the start of the experiment were housed in groups of three per cage with food and water available at libitum. They were maintained under temperaturecontrolled conditions with an alternating 12-h light-dark cycle.
2.2. Stereotaxic surgery and injection procedure Stereotaxic surgery was performed under xylazine (15 m g / k g , i.m.) and ketamine (100 m g / k g , i.m.) anaesthesia. In the first experiment, the rats received a bilateral injection of either a 6-hydroxydopamine (4 gg//xl, expressed as free base; nucleus accumbens-lesioned rats n = 29) or a vehicle solution (0.9% saline containing 1 m g / m l ascorbic acid; sham rats n = 29) into the nucleus accumbens area. The coordinates were
as follows: AP + 3.2 mm, L _+1.7 ram, from the bregma, DV - 7 . 8 mm from the skull surface with the incisor bar set at +5.0 mm (according to the atlas of Pellegrino et al., 1979). Intracerebral injection of the solution was performed with a pump-driven 10-/xl Hamilton syringe through 30-gauge stainless steel injection needles. A total volume of 2 ~l was injected on each side, at a rate of 1 /xl/3 rain. After the drug injection, the injection needles were left in situ for 3 min to allow the drug to diffuse away from the tips. In the second experiment, rats (n = 35) were implanted with bilateral stainless steel guide cannulas (23-gauge) positioned 3 mm above the nucleus accumbens (same coordinates as for the lesion except the dorso-ventral ones, which were - 4 . 8 mm from the skull). Wire stylets were inserted into the cannulas to prevent occlusion. One week after implantation, a bilateral 30-gauge injection needle was inserted through the guide to 3 mm beyond its tip and a volume of 0.5 or 1/zl was infused at a rate of 0 . 5 / . d / 3 min with a Hamilton syringe mounted on a microdrive pump. Injectors remained in place for 2 min to allow the drug to diffuse. Each rat was used only once.
2.3. Drugs 6-Hydroxydopamine hydrochloride (Sigma) was dissolved in 0.9% saline solution containing ascorbic acid (1 m g / m l ) as an antioxidant, d-Amphetamine was dissolved in physiological saline. Haloperidol (Haldol, injectable solution, Janssen) was injected at two doses: 2 . 5 / z g / 0 . 5 / x l or 5 ~ g / # l . Control injections using the vehicle (solvent of the commercial preparation for haloperidol) were tested. MK-801 ((+)-5-methyl10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine hydrogen maleate salt) (a generous gift from Merck Sharp and Dohme Research Laboratories, U.K.) was dissolved in a physiological saline solution, and the pH was adjusted to 6.5 with the minimum quantity of N a O H (0.1 N). D-Amphetamine was injected subcutaneously (s.c.) and MK-801 intraperitoneally (i.p.), in a volume of 1 m l / k g .
2.4. BehaL'ioural testing Locomotor activity was measured in 16 wire (top, floor and front door) and Plexiglass cages (side walls) 40 X 25 x 23 cm, with two horizontal infrared photocell beams located across the long axis of the cage (Imetronic, France). Beam interruptions were accumulated over 1-min intervals and recorded in minute bins by means of a microcomputer (Tandon PCA 12 SL). The operated animals were subdivided into four groups. Group A [sham (n = 6), lesioned (n = 10)] and group B [sham (n = 8), lesioned (n = 10)] received an injection of MK-801 at 0.15 and 0.3 m g / k g , i.p., respectively.
231
Group C [sham (n = 7), lesioned (n = 9)] received an injection of 0.5 m g / k g , s.c., d-amphetamine. A control group [sham (n = 8)] received an injection of saline (i.p.) only. The behavioural responses of the various experimental groups to MK-801, d-amphetamine and saline were measured 7 and 14 days after surgery. In the second experiment, one group of rats was given an injection of 0.3 m g / k g MK-801 15 min after bilateral microinjections of haloperidol 2.5 /xg/0.5 /xl (n = 8) or 5/xg/pA (n = 8) or vehicle (n = 7) into the nucleus accumbens. A second group was given an injection of 0.5 m g / k g d-amphetamine 15 min after bilateral microinjections of haloperidol 2.5 Fzg/0.5 /xl (n = 6) or vehicle (n = 6) into the nucleus accumbens. On the test days, spontaneous locomotor activity was recorded for 90 min prior to any drug treatment and immediately after d-amphetamine or MK-801 administration for 120 min.
2.5. Biochemical assays At the end of experiment 1, the rats were killed by decapitation. Their brains were rapidly removed and the nucleus accumbens, olfactory tubercle, anterior striatum and posterior striatum were dissected out and stored at -80°C. The levels of dopamine and its metabolite, D O P A C (3,4-dihydroxyphenylacetic acid), were determined by high performance reverse phase liquid chromatography (HPLC) coupled with electrochemical detection of the compounds (Dusticier and Nieoullon, 1987). The values obtained for the lesioned groups are expressed as percentages of those obtained for the sham-operated animals.
2. 6. Histology At the end of experiment 2, the rats were perfused with a 10% formalin solution through the left cardiac
ventricle under chloral anesthesia. The brains were removed and kept in a 10% formalin solution. The brains were then sectioned and colored with cresyl in order to verify the location of the injection sites.
2. Z Data analysis The effects of 6-hydroxydopamine lesion on locomotor activity induced by MK-801 and d-amphetamine were analyzed by subjecting the total number of beam interruptions recorded per 10-rain period to a two-factor analysis of variance (ANOVA) with the lesion and control groups forming the independent factor and time, the repeated measure. The effects of haloperidol infusion on MK-801- and d-amphetamine-induced locomotor activation were also analyzed by means of A N O V A with the vehicle and the various drug doses forming the independent factor. Individual group comparisons were carried out using the Newman-Keuls test. The biochemical results were analyzed using Student's t-test. The significance level was taken to be P < 0.05.
3. Results
3.1. Neurochemical results The regional brain dopamine concentrations determined in 6-hydroxydopamine and vehicle-injected animals are shown in table 1. Eight animals with a dopamine depletion of less than 70% in the ventral striatum area were excluded from the behavioural analysis. The neurochemical assay data on the remaining animals from groups A and B showed that 6-hydroxydopamine infusion into the nucleus accumbens produced a substantial, significant depletion of dopamine in the ventral striatum (nucleus accumbens
TABLE 1 Effects of 6-hydroxydopamine (6-OHDA) treatment on regional dopa mi ne (DA) and 3,4-dihydroxyphenylacetic acid ( D O P A C ) concentrations. Dopam ine and D O P A C levels in n g / m g protein for groups A, B and C. Values shown are m e a n s ± S.E.M. Groups
Ventral striatum
Antero-dorsal striatum
Posterior striatum
DA
DOPAC
DA
DOPAC
DA
DOPAC
5.53 ± 0.86 0.66±0.15 a 88
1.36 ± 0.11 0.38±0.09 a 72
6.42 ± 1.54 2.25 ± 0.28 a 65
1.69 _+0.35 0.81 ±0.11 a 52
7.83 ± 0.69 5.87±0.54 ~ 25
1.37 _+0.22 0.78±0.07 a 43
8.38 ± 1.06 1.52 ± 0.26 ~ 82
1.84 ± 0.34 0.42 ± 0.12 " 77
7.26 ± 0.58 2.07 ± 0,70 ~ 71
1.43 ± 0.21 0.50 ± 0.13 a 65
8,75 + 0.37 7.09 _+0.74 ~ 19
1.09 ± 0.10 0.85 ± 0.10 21
5.43 ± 0.42 1.27± 0.39 ~ 77
1.58 ± 0.28 0.35 ± 0.06 a 78
7.29 ± 1.16 3.42± 1.15 a 53
1.78 ± 0.40 0.69±0.13 ~ 61
7.97 ± 1.20 5.74 ± 0.70 a 28
1.74 + 0.30 1.01 +0.20 ~ 42
(A) Sham (n = 6) 6 - O H D A (n = 8) % Depletion
(B) Sham (n = 8) 6 - O H D A (n = 7) % Depletion
(c) Sham (n = 7) 6 - O H D A (n = 6) % Depletion
Significantly different from sham group, P < 0.05, Student's t-test.
232
and olfactory tubercle) and the antero-dorsal striatum, but smaller depletions in the posterior striatum. Groups A and B exhibited reductions of 88 and 82% in the ventral striatum, 65 and 71% in the antero-dorsal striaturn and 25 and 19% in the posterior striatum, respectively. These values were comparable to, although higher than, those measured in group C, which were 77, 53 and 28% respectively. As shown in table 1, the D O P A C decreases were found to parallel those of dopamine in the same striatal regions after 6-hydroxydopamine infusion into the nucleus accumbens. The D O P A C levels in the ventral striatum (which decreased by more than 70%) were lower than in the antero-dorsal and posterior striatum.
3.2. Effects of MK-801- and d-amphetamine-induced locomotor stimulation in animals with 6-hydroxydopamine lesions Administration of MK-801 (0.15 and 0.3 m g / k g , i.p.) resulted in dose-dependent locomotor stimulation in the intact rats (sham animals). As shown in fig. 1A, the locomotor stimulation induced by the injection of 0.15 m g / k g MK-801 in intact rats differed significantly from the locomotor activity of the vehicle-injected animals. The two-factor A N O V A showed a significant main effect of drug [F(1,12) = 7.57, P < 0.05], time [F(11,132) = 4.41, P < 0.05] and the drug × time interaction was found to be significant [F(11,132)= 3.23, P < 0.05] (fig. 1A). The administration of 0.3 m g / k g MK-801 to sham animals resulted in greater locomotor activation than 0.15 m g / k g MK-801 (fig. 1B). In line with this trend, the two-factor A N O V A revealed a significant main effect of drug [F(1,14) = 8.7, P < 0.05], time [F(11,154) = 2.78, P < 0.05] and a significant drug × time interaction [F(11,154) = 2.72, P < 0.05]. This locomotor activation was comparable in intensity to that observed after administration of 0.5 m g / k g damphetamine s.c.: the mean photocell counts during the total 120 min was 1 2 9 6 + 3 9 8 with 0.3 m g / k g MK-801 and 1037 + 266 with d-amphetamine. As previously mentioned, d-amphetamine injected at a dose of 0.5 r a g / k g enhanced locomotor activity, for a period of 90-120 min (fig. 1C). In keeping with this trend, the two-factor A N O V A showed a significant main effect of drug [F(1,13)= 13.25, P < 0 . 0 5 ] , time [F(11,143)= 13.49, P < 0.05] and the drug × time interaction was found to be significant [F(11,143) = 8.23, P < 0.05]. Seven days post-operatively, the 6-hydroxydopamine-injected animals showed enhanced locomotion after either MK-801 (0.15 or 0.3 m g / k g ) or 0.5 m g / k g d-amphetamine injection (fig. 1A, B and C, respectively). The two-factor A N O V A showed that the lesion had no significant effect on MK-801 or amphetamineinduced locomotion. When retested 14 days after surgery (fig. 2A and B), there was still no significant
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difference between the locomotor responses of the 6-hydroxydopamine lesion and sham groups to MK-801, 0.15 and 0.3 m g / k g , since the two-factor A N O V A showed no main lesion effect, [F(1,12)= 0.32, N.S.,
233
and F(1,13)= 1.36, N.S.]. However, the 6-hydroxydopamine-lesioned animals showed an attenuated locomotor response to d-amphetamine as compared to the sham animals (fig. 2C). In line with this trend, a twofactor A N O V A revealed a significant main lesion effect [F(1,11) = 13.05, P < 0.05].
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Fig. 3. Effects of haloperidol on the locomotor activation induced by 0.3 m g / k g MK-801 i.p. (A) and 0.5 m g / k g d - a m p h e t a m i n e s.c. (B). Rats were injected bilaterally into the nucleus accumbens with 1 pA of vehicle (©), 2 . 5 / x g / 0 . 5 / z l (o) or 5 # g / / x l haloperidol (z~) 15 rain before the MK-801 or d - a m p h e t a m i n e injection. Coordinates as in fig. 1. Insert refers to mean total photocell counts_+S.E.M, during the 120-rain test. * Significantly different from controls, P < 0.05, Newman-Keuls test after significant A N O V A .
3.3. Effects of haloperidol infusion into the nucleus accumbens on MK-801- and d-amphetamine-induced activation
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Local infusion of haloperidol into the nucleus accumbens reduced the locomotor stimulation induced by 0.3 m g / k g MK-801 (fig. 3A). The two-factor A N O V A showed a main effect of dose [F(2,20) = 6.56, P < 0.05] and a dose × time interaction [F(22,220)= 2.30, P < 0.05]. Individual comparisons based on the Newman-Keuls test showed that only the rats injected with highest dose of haloperidol (5 /zg//xl) had a significantly decreased locomotor response to MK-801 as compared to the vehicle-injected animals (graph insert, Newman-Keuls test, P < 0.05). Bilateral infusion of the lowest dose of haloperidol (2.5 /~g/0.5 tzl) into the nucleus accumbens markedly reduced the damphetamine-induced locomotor activation (fig. 3B).
234 The two-factor A N O V A showed a significant main treatment effect [F(1,10)= 10.86, P < 0 . 0 5 ] and revealed that the treatment × time interaction was significant [ F ( l l , l l 0 ) = 5.32, P < 0.05].
4. Discussion The results of the present study showed that destruction of the mesolimbic dopamine terminals within the ventral striatum (nucleus accumbens and olfactory tubercle) failed to block the MK-801-induced locomotor stimulation. The behavioural response to systemic injection of 0.15 or 0.3 m g / k g MK-801 was not altered in animals with 6-hydroxydopamine lesions on either postoperative day (days 7 and 14). In agreement with results of numerous previous studies, however, the same 6-hydroxydopamine lesion markedly reduced the locomotor stimulation induced by d-amphetamine (0.5 m g / k g ) , confirming that the locomotor stimulatory effects of indirect dopamine agonists are mediated mainly via facilitation of mesolimbic dopaminergic neurotransmission. Interestingly, 7 days after the surgery, no significant difference between the locomotor responses to d-amphetamine of the nucleus accumbens-lesioned and sham animals could be observed. In fact, the suggestion is that 1 week after local injection of 6-hydroxydopamine into the nucleus accumbens, dopamine fiber degeneration may not be complete. As previously reported by Kelly et al. (1975), the blockade of the locomotor response to d-amphetamine injection was maximal around 14 days after 6-hydroxydopamine lesion. On the same post-operative day, however, the 6-hydroxydopamine lesion of the nucleus accumbens had no effect on the MK-801-induced locomotion. Twenty one days after the surgery, the lesion still had no effect on MK-801-induced hyperactivity (data not shown). These results therefore suggest that unlike d-amphetamine-induced locomotor activation, the locomotor stimulatory effects of MK-80I may be not mediated mainly via facilitation of mesolimbic dopaminergic neurotransmission. In contrast, French et al. (1985), have previously observed that 6-hydroxydopamine lesion of the nucleus accumbens depressed the locomotor activity induced by systemic administration of the non-competitive N M D A receptor antagonist, phencyclidine. These results suggested that the behavioural effects of phencyclidine may be mediated by an increase of the dopamine release from mesolimbic dopaminergic terminals. Neurochemical experiments have shown however that, unlike MK-801, phencyclidine also has potent ability to inhibit dopamine uptake (Snell et al., 1988; Maurice et al., 1991). It is therefore possible that the discrepancy between our data and those of French et al. (1985) may be due to the fact that the be-
havioural effects of phencyclidine result from its simultaneous interactions with dopamine uptake processes and the N M D A receptor complex, while the pharmacological effects of MK-801 may result mainly from its interaction with the N M D A receptor complex alone. As reported previously (Clineschmidt et al., 1982; Dall'Olio et al., 1992; Hoffman, 1992) systemic injection of dopamine receptor antagonists has been shown to attenuate the hypermotility induced by MK-801, so that the dopaminergic system may be involved in this stimulatory effect. In the present study, the finding that local infusion of 5 / x g / / x l of the dopamine receptor antagonist, haloperidol, into the nucleus accumbens markedly reduced the locomotor activity induced by 0.3 m g / k g MK-801 suggests that the MK-801 effects involve the activation of dopamine receptors in the nucleus accumbens. In agreement with this idea, Wallace et al. (1992) have recently reported that local injection of either dopamine D~ or D 2 receptor antagonists into the nucleus accumbens reduced the locomotor response to MK-801 administration. However, lower doses of haloperidol (2.5 /xg/0.5 /xl) blocking damphetamine-induced locomotor activity failed to reduce the locomotor stimulation induced by MK-801. These data confirm those obtained by Raffa et al. (1989), showing that intra-accumbens infusion of haloperidol (2.5/xg/side) failed to block the locomotor stimulation induced by local injection of MK-801 into the nucleus accumbens. As compared to that with amphetamine, the locomotor response to MK-801 may thus be less sensitive to dopamine receptor blockade in the ventral striatum. In line with these data, we recently reported that systemic blockade of dopamine D~ or D 2 receptor subtypes had differential effects on the locomotor activity induced by MK-801 and damphetamine. The doses of the dopamine D l or D 2 receptor antagonists needed to block MK-801-induced locomotor stimulation were higher than those blocking the locomotor activity produced by d-amphetamine (Ouagazzal et al., 1993). It therefore appears likely that the attenuation of MK-801 behavioural effects may occur only when dopaminergic transmission is largely blocked. These results further support the idea that the mechanisms involved in the behavioural effects of MK801 and d-amphetamine may be different. In view of all the data described above, it appears that the locomotor stimulatory effects of MK-801 may be not mediated via an enhancement of the dopamine release from dopaminergic terminals within the ventral striatum but may well result from interactions between the dopaminergic and excitatory amino acid systems occurring postsynaptically. Possible postsynaptic interactions between dopamine and N M D A receptors have been suggested previously by results showing that the concomitant administration of subthreshold doses o[ an N M D A receptor antagonist and a dopamine recep-
235 tor agonist resulted in synergistic m o t o r stimulatory effects in m o n o a m i n e - d e p l e t e d mice a n d in m a r m o s e t s exposed to 1 - m e t h y l - 4 - p h e n y l - l , 2 , 3 , 6 - t e t r a h y d r o p y r i dine ( M P T P ) (Svensson et al., 1992; Wfillner et al., 1992). W e have o b t a i n e d f u r t h e r s u p p o r t for the above hypothesis in s u b s e q u e n t p r e l i m i n a r y e x p e r i m e n t s showing that systemic injection of h a l o p e r i d o l at low doses can reduce the l o c o m o t o r activity i n d u c e d by MK-801 in a n i m a l s with a 6 - h y d r o x y d o p a m i n e lesion (data not shown). I n this context, the a t t e n u a t i o n of MK-801 effects may well be due to the blockade of mesolimbic d o p a m i n e r g i c n e u r o t r a n s m i s s i o n . In this case, a l t h o u g h the d e p l e t i o n of v e n t r a l striatal d o p a m i n e exceeded 80% in the p r e s e n t e x p e r i m e n t , the residual d o p a m i n e a n d the adaptive striatal synaptic c h a n g e s occurring after l o n g - t e r m d o p a m i n e depletion might suffice to facilitate the expression of MK-801 effects. For example, l o n g - t e r m striatal d o p a m i n e dep l e t i o n has b e e n r e p o r t e d to i n d u c e postsynaptic d o p a m i n e r e c e p t o r supersensitivity, as established biochemically from the increase in the d o p a m i n e r e c e p t o r B .... r e c o r d e d in the s t r i a t u m ( S t a u n t o n et al., 1982), a n d b e h a v i o u r a l l y from the ' s u p e r s e n s i t i v e ' l o c o m o t o r r e p o n s e i n d u c e d by the direct d o p a m i n e r e c e p t o r agonist, a p o m o r p h i n e (Kelly a n d Iversen, 1976). Striatal d o p a m i n e d e a f f e r e n t a t i o n has b e e n f o u n d to also induce o t h e r complex changes, such as an increase in the n u m b e r of striatal N M D A receptors ( S a m u e l et al., 1990), which may lead to c h a n g e s in excitatory a m i n o acid transmission. O t h e r structures c o n t a i n i n g b o t h d o p a m i n e a n d N M D A receptors might also be involved, however, in the m e d i a t i o n of l o c o m o t o r responses to MK-801. In this respect, it is of interest to note that p h a r m a c o l o g i c a l b l o c k a d e of excitatory a m i n o acid t r a n s m i s s i o n at the level of the ventral t e g m e n t a l area, s u b s t a n t i a nigra or i n t e r n a l globus pallidus in the rat also i n d u c e d locomotor activity ( D a w b a r n a n d Pycock, 1981; Brotchie et al., 1991). T h e f u n c t i o n a l role of the N M D A - d o p a m i n e i n t e r a c t i o n s putatively involved at these levels in the expression of the MK-801 effects still r e m a i n s to be d e t e r m i n e d , however. In conclusion, the p r e s e n t study showed that 6-hyd r o x y d o p a m i n e n u c l e u s a c c u m b e n s lesions failed to block the M K - 8 0 1 - i n d u c e d locomotor s t i m u l a t i o n in rats whereas p h a r m a c o l o g i c a l blockade of d o p a m i n e receptors in this area r e d u c e d the MK-801 b e h a v i o u r a l effects. T h e s e data suggest that the l o c o m o t o r stimulatory effects of MK-801 may result mainly, within the v e n t r a l s t r i a t u m , from i n t e r a c t i o n s b e t w e e n the d o p a m i n e r g i c a n d excitatory a m i n o acid t r a n s m i s s i o n occurring postsynaptically r a t h e r t h a n presynaptically.
Acknowledgements This study was supported by grants from the CNRS, the University of Aix-Marseille II (Direction de la Recherche et des Etudes
Doctorales) and DRET (convention No. 91.34.157.00.470.75.01.). A. Ouagazzal was supported by a grant from the Moroccan Governemerit. The authors thank Nicole Dusticier for performing the H.P.L.C. measurements and Mrs. J. Blanc for English corrections to the manuscript.
References Boss, R., A. Cools and S. Ogen, 1988, Differential effects of the selective D2-antagonist raclopride in the nucleus accumbens of the rat on spontaneous and d-amphetamine-induced activity. Psychopharmacology 95, 447. Brotchie, J.M., l.J. Mitchell, M.A. Sambrook and A.R. Crossman, 1991, Alleviation of parkinsonism by antagonism of excitatory amino acid transmission in the medial segment of the globus pallidus in rat and primate, Movement Disord. 6, 113. Carlsson, M. and A. Carlsson, 1989, The NMDA antagonist MK-801 causes marked locomotor stimulation in monoamine-depleted mice, J. Neural Transm. 75, 221. Clineschmidt, B.V., G.E. Martin, P.R. Bunting and N.L. Papp, 1982, Central sympathomimetic activity of ( + )-5-methyl-10,11-dihydro5H-dibenzo [a,d] cyclohepten-5,10-imine (MK-801), a substance with potent anticonvulsant, central sympathomimetic and apparent anxiolytic properties, Drug. Dev. Res. 2, 135. Dall'Olio, R., O. Gandolfi and N. Montarano, 1992, Effect of chronic treatment with dizocilpine (MK-801) on the behavioral response to dopamine receptor agonist in the rat, Psyehopharmacology 107, 591. Dawbarn, D. and C.J. Pycock, 1981, Motor effects following application of putative excitatory amino acid antagonists to the region of the mesencephalic dopamine cell bodies in the rat, NaunynSchmied. Arch. Pharmacol. 318, 100. Donzanti, B.A. and N.J. Uretsky, 1984, Antagonism of the bypermotility response induced by excitatory amino acids in the rats nucleus accumbens, Naunyn-Schmied. Arch. Pharmacol. 325, 1. Dusticier, N. and A. Nieoullon, 1987, Comparative analysis of the effects of in vivo electrical stimulation of the frontal cortex and gamma-butyrolactone administration on dopamine and dihydroxyphenyl acetic acid (DOPAC) striatal contents in the rat, Neurochem. Int. 10, 275. French, E.D., C. Pilapil and R. Quirion, 1985, Phencyclidine binding sites in the nucleus accumbens and phencyclidine induced hyperactivity are decreased following lesions of the mesolimbic dopamine system, Eur. J, Pharmacol. 116, l. Hoffman, D.C., 1992, Typical and atypical neuroleptics antagonize MK-801-induced locomotion and stereotypy in rats, J. Neural Transm. 89, 1. Imperato, A., M.G. Scrocco, S. Bacchi and L. Angelucci, 1990, NMDA receptors and in vivo dopamine release in the nucleus accumbens and caudatus, Eur. J. Pharmacol. 187, 555. Kashihara, K., T. Hamamura, K. Okumura and S. Otsuki, 1990, Effect of MK-801 on endogenous dopamine release in vivo, Brain Res. 528, 80. Kelly, P.H. and S.D. Iversen, 1976, Selective 6-hydroxydopamine-induced destruction of mesolimbic dopamine neurons: abolition of psychostimulant-induced locomotor activity in rats, Eur. J. Pharmacol. 40, 45. Kelly, P.H., P.W. Seviour and S.D. Iversen, 1975, Amphetamine and apomorphine responses in the rat following 6-hydroxydopamine lesions of the nucleus accumbens septi and corpus striatum, Brain Res. 94, 507. Le Moal, M. and H. Simon, 1991, Mesocorticolimbic dopaminergic network, functional and regulatory roles, Physiol. Rev. 71, 155. Liljequist, S., K. Ossowska, M. Grabowska-And6n and N. And6n,1991, Effect of the NMDA receptor antagonist, MK-801.
236 on locomotor activity and on the metabolism of dopamine in various brain areas of mice, Eur. J. Pharmacol. 195, 55. L6scher, W., R. Armies and D. H6nack, 1991, The N-methyl-Daspartate receptor antagonist MK-801 induces increases in dopamine and serotonine metabolism in several brain regions of rats, Neurosci. Lett. 198, 191. Maurice, T., J. Vigon, J. Kameuka and R. Chicheportiche, 1991, Differential interaction of phencyclidine-like drugs with the dopamine uptake complex in vivo, J. Neurochem. 56, 553. Moghaddam, B. and R.J. Gruen, 1991, Do endogenous excitatory amino acids influence striatal dopamine release?, Brain Res. 544, 329. Ouagazzal, A., A. Nieoullon and M. Amalric, 1993, Effects of dopamine D1 and D2 receptor blockade on MK-801-induced hyperlocomotion in rats, Psychopharmacology 111,427. Pellegrino, L.J., A.S. Pellegrino and A.J. Cushman, 1979, A Stereotaxic Atlas of the Rat Brain (Plenum Press, New York). Pijnenburg, A.J.J. and J.M. Van Rossum, 1973, Stimulation of locomotor activity following injections of dopamine into the nucleus accumbens, J. Pharmacol. 25, 1003. Pijnenburg, A.J.J., W.M. H6nig and J.M. Van Rossum, 1975, Inhibition of d-amphetamine-induced locomotor activity by injection of haloperidol into the nucleus accumbens of the rat, Psychopharmacologia (Berlin) 41, 87. Plaznic, A., R. Stefanski and W. Kostowski, 1989, Interaction between accumbens D1 and D2 receptors regulating rat locomotor activity, Psychopharmacology 99, 558. Raffa, R.B., M.E. Ortegon, D.M. Robisch and G.E. Martin, 1989, In vivo demonstration of the enhancement of MK-801 by L-glutamate, Life Sci. 44, 1593. Samuel, D., M. Errami and A. Nieoullon, 1990, Localization of N-methyl-o-aspartate receptors in the rat striatum: effects of specific lesions on the [3H]3-(2-carboxypiperazin-4-yl) propyl-1phosphonic acid binding, J. Neurochem. 54, 1926. Schmidt, W.J., 1986, lntrastriatal injection of DL-2- amino-5-phos-
phonovaleric acid (AP-5) induces sniffing stereotypy that is antagonized by haloperidol and clozapine, Psychopharmacology 90, 123. Schmidt, W.J., M. Bubser and W. Hauber, 1992, Behavioural pharmacology of glutamate in the basal ganglia, J. Neural Transm. 38, 65. Snell, LD., S. Yi and K.M. Johnson, 1988, Comparison of the effects of MK-801 and phencyclidine on catecholamine uptake and NMDA-induced norepinerphrine release, Eur. J. Pharmacol. 145, 223. Staunton, D.A., P,J. Magistretti, G.F. Koob, W.J. Shoemaker and F.E. Bloom, 1982, Dopaminergic supersensitivity induced by denervation and chronic receptor blockade is additive, Nature 229, 72. Svensson, A. and M.L. Carlsson, 1992, Injection of the competitive NMDA receptor antagonist AP-5 into the nucleus accumbens of monoamine-depleted mice induces pronounced locomotor stimulation, Neuropharmacology 31,513. Svensson, A., A. Carlsson and M.L. Carlsson, 1992, Differential locomotor interactions between dopamine D 1 / D 2 receptor agonists and NMDA antagonist dizocilpine in monoamine-depleted mice, J. Neural Transm. 90, 199. Wallace, L.J., D.L Willins and N.J. Uretsky, 1992, MK-801-induced hypermotility is dependent on dopaminergic neurotransmission in the nucleus accumbens (NA), Soc. Neurosci. Abstr. 18 No. 19114. Weihmuller, F.B., S.J. O'Dell, B.N. Cole and J.F. Marshall, 1991, MK-801 attenuates the dopamine-releasing but not the behavioral effects of methamphetamine: an in vivo microdialysis study, Brain Res. 549, 230. Wiillner, V., A. Kupsch, G. Arnold, P. Renner, C. Scheid, R. Scheid, W. Oertel and T. Klockgether, 1992, The competitive NMDA antagonist CGP40.116 enhances L-DOPA response in the MPTP-treated marmosets, Neuropharmacology 31, 713.