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Role of nigral dopamine in amphetamine-induced locomotor activity
366
Brain Research, 278 (1983) 366-369
Elsevier
Role of nigral dopamine in amphetamine-induced locomotor activity E. AMANDA JACKSON and PETER H. KELLY* Department (ff'Phys'iology and Biophysi(w, University of Southern California School of Medicine, 2025 Zonal A venue, Los Angeles, CA 90033 (U.S.A. )
(Accepted June 30th, 19831 Key words: dopamine - - dendrites - - substantia nigra - - locomotor activity - - amphetamine
Dopamine ( 11)0ug) injected into the substantia nigra pars reticulata of rats pretreatcd with the monoamine oxidase inhibitor, pargyline, resulted in a stimulation of locomotor activity. Bilateral injection of the dopamine antagonist haloperidol (5 ug) into the substantia nigra pars rcticulata resulted in a reduction of the locomotor activity evoked by a low dose of amphetamine ( 1.25 mg/kg s.c.). These results suggest that the release of dopamine from nigral dendrites is involved in amphetamine-induced locomotor activity.
The mechanisms involved in the stimulation of locomotor activity by psychostimulants such as amphetamine are of relevance to theories of psyehostimulant action and m o t o r function, and have been the subject of considerable study H.2:. The view that dopamine release from mesolimbic d o p a m i n e terminals in the nucleus accumbens is involved in this effect, is supported by the l o c o m o t o r stimulation resulting from injection of d o p a m i n e into the nucleus accumbens of n i a l a m i d e - p r e t r e a t e d rats 3-~,27, and by the reduction of a m p h e t a m i n e - i n d u c e d locomotor activity after selective destruction of mesolimbic dopaminergic neurons by 6-hydroxydopamine 1~.15-1s,3~. In further support, a m p h e t a m i n e results in no further stimulation of locomotor activity in rats ~3-j7 and mice 4,3~, made hyperactive by large electrolytic or radiofrequency lesions of the nucleus accumbens. On the basis of these observations it has been suggested that neural activity in efferents of the nucleus accumbens inhibits locomotor activity, and that the activity of these efferents is decreased by the action of dopamine in this nucleus LT. Recently we have found that the hyperactivity produced by electrolytic lesions of the nucleus accumbens is not permanent, declining to normal levels around two months after the lesion (Kelly and Schultz, in preparation). Moreover, at this time am* To whom correspondence should be addressed. 0006-8993/83/$03.00 © 1983 Elsevier Science Publishers B.V.
phetamine is able to cause a large stimulation of locomotor activity which is blocked by a-methyl-p-tyrosine p r e t r e a t m e n t or by d o p a m i n e antagonists, but only weakly affected by adrenergic a- and fl-antagonists. These observations have led us to investigate the possibility that d o p a m i n e release at some site other than the nucleus accumbens may also be involved in a m p h e t a m i n e - i n d u c e d l o c o m o t o r activity. In support of this possibility we report here that d o p a m i n e elicits locomotor activity when injected into the substantia nigra of p a r g y l i n e - p r e t r e a t e d rats, and that bilateral injection of haloperidol into the substantia nigra reduces the l o c o m o t o r stimulation e v o k e d by systemic amphetamine. Adult male S p r a g u e - D a w l e y rats were anesthetized with Equithesin (3.5 ml/kg) and stereotaxically implanted with bilateral 23 gauge stainless-steel guide cannulae aimed at a point 2 mm above the substantia nigra pars reticulata. Coordinates of the guide cannulae tips were 4.0 mm posterior to bregma, 2.0 mm lateral and 7.2 mm below dura according to the atlas of Pellegrino et al. 26. The cannulae were cemented to screws in the skull and when not in use were occluded by wire stylets. Six days after surgery the rats were injected with pargyline hydrochloride (Sigma, 50 mg/kg i.p.) and placed individually in previously described 1° photocell activity cages for 1 h ha-
367 bituation. After this period, the rats were removed from the cages, injected intranigrally and returned to the activity cages for 4 h. The intranigral injections were made through 30 gauge stainless-steel injection cannulae protruding 2 mm beyond the tips of the guide cannulae. Half of the rats received 100 pg per side of dopamine hydrochloride (Sigma) in 0.5 pl of nitrogen-bubbled 0.9% saline, delivered at the rate of 0.11 pl/min, while the other animals received a similar injection of vehicle. Injection cannulae were left in place an additional 2.5 min before replacing the wire stylets. Two days later the treatments were reversed. In addition to recording photocell beam interruptions, 4 categories of behavior were rated on a 3-point scale every 10 min for 2.5 h beginning 1 h after intranigral injections. These categories were locomotor activity, rearing, sniffing and licking/gnawing. A rating of zero was given if the behavior was absent, 1 if it was intermittent and 2 if it was continuous. Twenty-eight days after surgery the rats, except for one whose implant became dislodged, were placed individually in the activity cages and habituated for 1 h. They were then removed and injected bilaterally in the substantia nigra with haloperidol (Janssen) or vehicle immediately before D-amphetamine sulfate (Sigma, 1.25 mg/kg s.c.), and then returned to the activity cages for 150 min. Haioperidol was dissolved in 1% lactic acid and brought to pH 4.5 with NaOH. 5 pg of haloperidol were injected per side in a volume of 1 pl, delivered at the rate of 0.22 pl/min. The injection cannulae were left in place an additional 2.5 min before replacing the wire stylets. Two days later the treatments were reversed. On day 34 post-surgery the animals were habituated in the activity cages for 1 h, injected with saline s.c. and returned to the cages to determine the baseline level of activity. At the termination of these experiments the animals were deeply anesthetized with Equithesin and perfused intracardially with buffered (pH 7.4) 10% formalin. Forty-eight micron frozen sections of brain were cut in a cryostat and stained with cresyl violet. All injection sites were localized in the substantia nigra pars reticulata. The effect of intranigral dopamine injection on photocell beam interruptions is shown in Fig. 1. During the 4 h following dopamine injection photocell beam interruptions were 1797 + 357 (mean +
E O
la
O
O
E
80 I~
Oopamine
40
S~line
O ..I
0
1
2
3
4
Hours Fig. 1. Locomotor counts (mean + S.E.M.) in a group of 6 rats after the bilateral injection of dopamine hydrochloride (100pg) or nitrogen-bubbled saline (0.5/~1) 1 h after pargyline injection (50 mg/kg i.p.).
S.E.M.), and following vehicle injection were 480 + 116. These values were significantly different (P < 0.01, t-test). In 3 animals the locomotor response showed no obvious directional component, while two animals walked in wide circles and one showed tight circling. Table I shows the distribution of behavior ratings obtained in this experiment. Median scores per rat per behavior for each treatment were compared using the Mann-Whitney U-test as suggested by Robbins 30. These comparisons confirmed that dopamine resulted in an increase in locomotor activity (P < 0.05), but no significant alteration in the other categories of behavior. The effect of intranigral haloperidol on amphetamine-induced locomotor activity is shown in Fig. 2. Photocell beam interruptions in the 150 min following amphetamine injection were 2243 + 421 (mean + S.E.M.) after intranigral vehicle and 1293 + 221 afTABLE I Distribution of ratings of specific behaviors after intranigral injections of saline or dopamine into pargyline-pretreated rats Behavior category
Frequency of rating score After saline
Locomotor activity Rearing Sniffing Licking/gnawing
After doparnine
0
1
2
0
1
2
58 86 41 39
20 4 30 41
12 0 19 10
4 89 56 72
14 1 18 17
72 0 16 1
368
240. E o
180
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120.
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150
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Fig. 2. Locomotor counts (mean + S.E.M., n = 5) evoked by n-amphetamine sulfate (1.25 mg/kg s.c.) administered immediately after bilateral intranigral injection of 5/~g of haloperidol (O) or vehicle (0). For comparison the spontaneous level of activity after subcutaneous injection of saline (A) is also shown.
ter intranigral haloperidol. These values differed significantly (P < 0.05, t-test) from each other and from the saline-evoked activity (199 _+ 41, P < 0.01 in each case). Thus intranigral haloperidol reduced the amphetamine-induced locomotor activity but did not completely block it. Recently, convincing evidence has accumulated that dopamine is released from nigral dendrites I. Dopamine can be released from slices of the substantia nigra by depolarizing stimuli 5,6, by other neurotransmitters ~9,> and by amphetamine 24,33. Moreover, amphetamine-induced release of nigral dopamine has been demonstrated in vivo by the use of push-pull cannulae 21. Since the substantia nigra contains few, if any, dopaminergic nerve terminals 5,12.25,32y it is probable that the nigral dopamine release occurs from dendrites. The results of the present study suggest that amphetamine-induced dopamine release from nigral dendrites is involved in the locomotor stimulant action of amphetamine. In view
1 Cheramy, A., Leviel, V. and Glnwinski, J., Dendritic release of dopamine in the substantia nigra, Nature (Lond.), 289 (1981) 537-542. 2 Conrad, L. C. A. and Pfaff, D. W., Autoradiographic tracing of nucleus accumbens efferents in the rat, Brain Research, 113 (1976) 589-596. 3 Costall, B. and Naylor, R. J., Antagonism of the hyperactivity induced by dopamine applied intracerebrally to the nucleus accumbens septi by typical neuroleptics and by clo-
of the role of dopamine release in the nucleus accumbens in locomotor activity, and the well-established anatomical projection from the nucleus accumbens to the substantia nigra 2.23,2s,35.38 a possibility is that, through these efferents, dopaminergic activity in the nucleus accumbens stimulates locomotor activity at least partly by enhancing nigral dopamine release. Further experiments examining a number of predictions of this scheme are necessary to provide evidence on this issue, However, such a view is consistent with the results of Heal et al.L who found that the locomotor activity elicited by the injection of dibutyryl cyclic A M P into the nucleus accumbens was antagonized by low systemic doses of haloperidol, but not by haloperidol injected into the nucleus accumbens. They suggested that this effect of systemic haloperidol was mediated at a dopaminergic synapse beyond the nucleus accumbens. Though the phenomenon of dendritic dopamine release has been known for several years, initial studies showed no behavioral effect when apomorphine or amphetamine were unilaterally injected into the substantia nigra 7,16. Subsequent studies showed contralateral rotation after the injection of apomorphine into a dopamine-depleted substantia nigra 20.34, and provided evidence that this effect requires the presence of striatonigral terminals 20. Together with the present study these studies therefore provide evidence for a role of nigral dopamine receptors in certain behavioral actions of directly- and indirectly-acting dopamine agonists. It will be of interest to determine the relative importance of terminal regions and dendritic mechanisms in the behavioral actions of other types of drugs affecting dopaminergic, and possibly other, neurotransmitter systems. This work was supported by N I N C D S Grant NS 16175. We thank Mrs. Linda Schultz for her excellent assistance.
zapine, sulpiride and thioridazine, Europ. J. Pharmacol., 35 (1976) 161-168. 4 Costall, B., Naylor, R. J. and Nohria, V., Hyperactivity response to apomorphine and amphetamine in the mouse: the importance of the nucleus accumbens and caudate-putamen, J. Pharm. Pharmacol., 31 (1979)25%261. 5 Cuello, A. C. and Iversen, L. L., Interactions of dopamine with other neurotransmitters in the rat substantia nigra: a possible functional role of dendritic dopamine. In S. Garat-
369 tini, J. F. Pujol and R. Samanin (Eds.), Interactions Between Putative Neurotransmitters in the Brain, Raven, New York, 1978, pp. 127-149. 6 Geffen, L. B., Jessell, T. M., Cuello, A. C. and Iversen, L. L., Release of dopamine from dendrites in rat substamia nigra, Nature (Lond.), 260 (1976) 258-260. 7 Glick, S. D. and Crane, L. A., Function of nigral dopamine receptors? Brain Research, 156 (1978) 380-381. 8 Heal, D. J., Phillips, A. G. and Green, A. R., Studies on the locomotor activity produced by injection of dibutyryl cyclic Y5'-AMP into the nucleus accumbens of rats, Neuropharmacology. 17 (1978) 265-270. 9 Jackson. D. M., Anden, N.-E. and Dahlstr6m, A., A functional effect of dopamine in the nucleus accumbens and in some other dopamine-rich parts of the rat brain, Psychopharmacologia, 45 (1975) 139-149. 10 Jackson, E. A., Neumeyer, J. L. and Kelly, P. H., Behavioral activity of some novel aporphines in rats with 6-hydroxydopamine lesions of caudate or nucleus accumbens, Europ. J. Pharmacol., 87 (1983) 15-23. 11 Jeste, D. V. and Smith, G. P., Unilateral mesolimbicortical dopamine denervation decreases locomotion in the open field and after amphetamine, Pharm. Biochem. Behav., 12 (1980) 453-457. 12 Juraska, J. M., Wilson, C. J. and Groves, P. M., The substantia nigra of the rat: a Golgi study, J. comp. Neurol., 172 (1977) 585-600. 13 Kehne. J. H., Sant, W. W. and Sorenson, C. A., The effects of radio-frequency lesions of the nucleus accumbens on D-amphetamine-induced locomotor and rearing behavior in rats, Psychopharmacology, 75 (1981) 363-367. 14 Kelly, P.H., Drug-induced motor behavior. In L. L. Iversen, S. D. Iversen and S. H. Snyder (Eds.), Handbook of Psychopharmacology, Vol. 8, Plenum, New York, 1977, pp. 295-311. 15 Kelly, P. H. and Iversen, S. D., Selective 6OHDA-induced destruction of mesolimbic dopamine neurons: abolition of psychostimulant-induced locomotor activity in rats, Europ. J. Pharmacol., 40 (1976) 45-56. 16 Kelly, P. H. and Moore, K. E., Dopamine concentrations in the rat brain following injections into the suhstantia nigra of baclofen, 7-aminobutyric acid, 7-hydroxybutyric acid, apomorphine and amphetamine, Neuropharmacology, 17 (1978) 169-174. 17 Kelly, P. H. and Roberts, D. C. S., Effects of amphetamine and apomorphine on locomotor activity after 6-OHDA and electrolytic lesions of the nucleus accumbens septi, Pharm. Biochem. Behav., in press. 18 Kelly, P. H., Seviour, P. W. and Iversen, S. D., Amphetamine and ap0morphine responses in the rat following 6OHDA lesions of the nucleus accumbens septi and corpus striatum, Brain Research, 94 (1975) 507-522. 19 Kerwin, R. W. and Pycock, C. J., Specific stimulating effect of glycine on 3H-dopamine efflux from substantia nigra slices of the rat, Europ. J. Pharmacol., 54 (1979) 93-98. 20 Kozlowski, M. R., Sawyer, S. and Marshall, J. F., Behavioural effects and supersensitivity following nigral dopamine receptor stimulation, Nature (Lond.), 287 (1980) 52-54. 21 Leviel, V., Cheramy, A. and Glowinski, J., Role of the dendritic release of dopamine in the reciprocal control of the two nigro-striatal dopaminergic pathways, Nature (Lond.), 280 (1979) 236--239. 22 Moore, K. E., The actions of amphetamine on neurotrans-
mitters: a brief review, Biol. Psychiat., 12 (1977) 451--462. 23 Nauta, W. J. H., Smith, G. P., Faull, R. L. M. and Domesick, V. B., Efferent connections and nigral afferents of the nucleus accumbens septi in the rat, Neuroscience, 3 (1978) 385--401. 24 Paden, C., Wilson, C. J. and Groves, P. M., Amphetamine-induced release of dopamine from the substantia nigra in vitro, Life Sci., 19 (1976) 1499--1506. 25 Parizek, J., Hassler, R. and Bak, I. J., Light and electron microscopic autoradiography of substantia nigra of rat after intraventricular administration of tritium labelled norepinephrine, dopamine, serotonin and the precursors, Z. Zellforsch. Mikrosk. Anat., 115 (1971) 137-148. 26 Pellegrino, L. J., Pellegrino, A. S. and Cushman, A. J., A Stereotaxic Atlas of the Rat Brain, Plenum, New York, 1979, 158 pp. 27 Pijnenburg, A. J. J. and Van Rossum, J. M., Stimulation of locomotor activity following injection of dopamine into the nucleus accumbens, J. Pharm. Pharmacol., 25 (1973) 1003-1005. 28 Powell, E. W. and Leman, R. B., Connections of the nucleus accumbens,, Brain Research, 105 (1976) 389-403. 29 Reubi, J. C., Emson, P. C., Jessell, T. M. and Iversen, L. L., Effects of GABA, dopamine and substance P on the release of newly synthesized 3H-5-hydroxytryptamine from rat substantia nigra in vitro, Naunyn-Schmiederberg's Arch. Pharmacol., 304 (1978) 271-275. 30 Robhins, T. W., A critique of the methods available for the measurement of spontaneous motor activity. In L. L. Iversen, S. D. Iversen and S. H. Snyder (Eds.), Handbook o] Psychopharmacology, Vol. 7, Plenum, New York, 1977, pp. 37-82. 31 Segal, D. S., Kelly, P. H,, Koob, G. and Roberts, D. C. S., Nonstriatal dopamine mechanisms in the response to repeated amphetamine administration. In E. Usdin and J. D. Barchas (Eds.), Catecholamines: Basic and Clinical Frontiers, Pergamon, New York, 1979, pp. 1672-1674. 32 Sotelo, C., The fine structural localization of norepinephrine-3H in the substantia nigra and area postrema of the rat. An autoradiographic study, J. UItrastruct. Res., 36 (1971) 824-841. 33 Starr, M. S., G A B A potentiates potassium-stimulated 3Hdopamine release from slices of rat substantia nigra and corpus striatum, Europ. J. Pharmacol., 48 (1978) 325-328. 34 Starr, M. S. and Summerhayes, M., Multifocal brain sites for apomorphine-induced circling and other stereotyped motor behavior in the 6-hydroxydopamine-lesioned rat, Neurosci. Lett., 34 (1982) 277-282. 35 Swanson, L. W. and Cowan, W. M., A note on the connections and development of the nucleus accumbens, Brain Research, 92 (1975) 324-330. 36 Teitelbaum, H., Giammateo, P. and Mickley, G. A., Differential effects of localized lesions of n. accumbens on morphine- and amphetamine-induced locomotor hyperactivity in the C57 BL/6J mouse, J. comp. Physiol. Psychol., 93 (1979) 745-751. 37 Wassef, M., Berod, A. and Sotelo, C., Dopaminergic dendrites in the pars reticulata of the rat substantia nigra and their striatal input. Combined immunocytochemical localization of tyrosine hydroxylase and anterograde degeneration, Neuroscience, 6 (1981) 2125-2139. 38 Williams, D. J., Crossman, A. R. and Slater, P., The efferent projections of the nucleus accumbens in the rat, Brain Research, 130 (1977) 217-227.
Brain Research, 278 (1983) 366-369
Elsevier
Role of nigral dopamine in amphetamine-induced locomotor activity E. AMANDA JACKSON and PETER H. KELLY* Department (ff'Phys'iology and Biophysi(w, University of Southern California School of Medicine, 2025 Zonal A venue, Los Angeles, CA 90033 (U.S.A. )
(Accepted June 30th, 19831 Key words: dopamine - - dendrites - - substantia nigra - - locomotor activity - - amphetamine
Dopamine ( 11)0ug) injected into the substantia nigra pars reticulata of rats pretreatcd with the monoamine oxidase inhibitor, pargyline, resulted in a stimulation of locomotor activity. Bilateral injection of the dopamine antagonist haloperidol (5 ug) into the substantia nigra pars rcticulata resulted in a reduction of the locomotor activity evoked by a low dose of amphetamine ( 1.25 mg/kg s.c.). These results suggest that the release of dopamine from nigral dendrites is involved in amphetamine-induced locomotor activity.
The mechanisms involved in the stimulation of locomotor activity by psychostimulants such as amphetamine are of relevance to theories of psyehostimulant action and m o t o r function, and have been the subject of considerable study H.2:. The view that dopamine release from mesolimbic d o p a m i n e terminals in the nucleus accumbens is involved in this effect, is supported by the l o c o m o t o r stimulation resulting from injection of d o p a m i n e into the nucleus accumbens of n i a l a m i d e - p r e t r e a t e d rats 3-~,27, and by the reduction of a m p h e t a m i n e - i n d u c e d locomotor activity after selective destruction of mesolimbic dopaminergic neurons by 6-hydroxydopamine 1~.15-1s,3~. In further support, a m p h e t a m i n e results in no further stimulation of locomotor activity in rats ~3-j7 and mice 4,3~, made hyperactive by large electrolytic or radiofrequency lesions of the nucleus accumbens. On the basis of these observations it has been suggested that neural activity in efferents of the nucleus accumbens inhibits locomotor activity, and that the activity of these efferents is decreased by the action of dopamine in this nucleus LT. Recently we have found that the hyperactivity produced by electrolytic lesions of the nucleus accumbens is not permanent, declining to normal levels around two months after the lesion (Kelly and Schultz, in preparation). Moreover, at this time am* To whom correspondence should be addressed. 0006-8993/83/$03.00 © 1983 Elsevier Science Publishers B.V.
phetamine is able to cause a large stimulation of locomotor activity which is blocked by a-methyl-p-tyrosine p r e t r e a t m e n t or by d o p a m i n e antagonists, but only weakly affected by adrenergic a- and fl-antagonists. These observations have led us to investigate the possibility that d o p a m i n e release at some site other than the nucleus accumbens may also be involved in a m p h e t a m i n e - i n d u c e d l o c o m o t o r activity. In support of this possibility we report here that d o p a m i n e elicits locomotor activity when injected into the substantia nigra of p a r g y l i n e - p r e t r e a t e d rats, and that bilateral injection of haloperidol into the substantia nigra reduces the l o c o m o t o r stimulation e v o k e d by systemic amphetamine. Adult male S p r a g u e - D a w l e y rats were anesthetized with Equithesin (3.5 ml/kg) and stereotaxically implanted with bilateral 23 gauge stainless-steel guide cannulae aimed at a point 2 mm above the substantia nigra pars reticulata. Coordinates of the guide cannulae tips were 4.0 mm posterior to bregma, 2.0 mm lateral and 7.2 mm below dura according to the atlas of Pellegrino et al. 26. The cannulae were cemented to screws in the skull and when not in use were occluded by wire stylets. Six days after surgery the rats were injected with pargyline hydrochloride (Sigma, 50 mg/kg i.p.) and placed individually in previously described 1° photocell activity cages for 1 h ha-
367 bituation. After this period, the rats were removed from the cages, injected intranigrally and returned to the activity cages for 4 h. The intranigral injections were made through 30 gauge stainless-steel injection cannulae protruding 2 mm beyond the tips of the guide cannulae. Half of the rats received 100 pg per side of dopamine hydrochloride (Sigma) in 0.5 pl of nitrogen-bubbled 0.9% saline, delivered at the rate of 0.11 pl/min, while the other animals received a similar injection of vehicle. Injection cannulae were left in place an additional 2.5 min before replacing the wire stylets. Two days later the treatments were reversed. In addition to recording photocell beam interruptions, 4 categories of behavior were rated on a 3-point scale every 10 min for 2.5 h beginning 1 h after intranigral injections. These categories were locomotor activity, rearing, sniffing and licking/gnawing. A rating of zero was given if the behavior was absent, 1 if it was intermittent and 2 if it was continuous. Twenty-eight days after surgery the rats, except for one whose implant became dislodged, were placed individually in the activity cages and habituated for 1 h. They were then removed and injected bilaterally in the substantia nigra with haloperidol (Janssen) or vehicle immediately before D-amphetamine sulfate (Sigma, 1.25 mg/kg s.c.), and then returned to the activity cages for 150 min. Haioperidol was dissolved in 1% lactic acid and brought to pH 4.5 with NaOH. 5 pg of haloperidol were injected per side in a volume of 1 pl, delivered at the rate of 0.22 pl/min. The injection cannulae were left in place an additional 2.5 min before replacing the wire stylets. Two days later the treatments were reversed. On day 34 post-surgery the animals were habituated in the activity cages for 1 h, injected with saline s.c. and returned to the cages to determine the baseline level of activity. At the termination of these experiments the animals were deeply anesthetized with Equithesin and perfused intracardially with buffered (pH 7.4) 10% formalin. Forty-eight micron frozen sections of brain were cut in a cryostat and stained with cresyl violet. All injection sites were localized in the substantia nigra pars reticulata. The effect of intranigral dopamine injection on photocell beam interruptions is shown in Fig. 1. During the 4 h following dopamine injection photocell beam interruptions were 1797 + 357 (mean +
E O
la
O
O
E
80 I~
Oopamine
40
S~line
O ..I
0
1
2
3
4
Hours Fig. 1. Locomotor counts (mean + S.E.M.) in a group of 6 rats after the bilateral injection of dopamine hydrochloride (100pg) or nitrogen-bubbled saline (0.5/~1) 1 h after pargyline injection (50 mg/kg i.p.).
S.E.M.), and following vehicle injection were 480 + 116. These values were significantly different (P < 0.01, t-test). In 3 animals the locomotor response showed no obvious directional component, while two animals walked in wide circles and one showed tight circling. Table I shows the distribution of behavior ratings obtained in this experiment. Median scores per rat per behavior for each treatment were compared using the Mann-Whitney U-test as suggested by Robbins 30. These comparisons confirmed that dopamine resulted in an increase in locomotor activity (P < 0.05), but no significant alteration in the other categories of behavior. The effect of intranigral haloperidol on amphetamine-induced locomotor activity is shown in Fig. 2. Photocell beam interruptions in the 150 min following amphetamine injection were 2243 + 421 (mean + S.E.M.) after intranigral vehicle and 1293 + 221 afTABLE I Distribution of ratings of specific behaviors after intranigral injections of saline or dopamine into pargyline-pretreated rats Behavior category
Frequency of rating score After saline
Locomotor activity Rearing Sniffing Licking/gnawing
After doparnine
0
1
2
0
1
2
58 86 41 39
20 4 30 41
12 0 19 10
4 89 56 72
14 1 18 17
72 0 16 1
368
240. E o
180
° o
120.
o '~
/emph
l 0
i
30
"4-~. ~ . , _ a-,a-
90
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120
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150
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Fig. 2. Locomotor counts (mean + S.E.M., n = 5) evoked by n-amphetamine sulfate (1.25 mg/kg s.c.) administered immediately after bilateral intranigral injection of 5/~g of haloperidol (O) or vehicle (0). For comparison the spontaneous level of activity after subcutaneous injection of saline (A) is also shown.
ter intranigral haloperidol. These values differed significantly (P < 0.05, t-test) from each other and from the saline-evoked activity (199 _+ 41, P < 0.01 in each case). Thus intranigral haloperidol reduced the amphetamine-induced locomotor activity but did not completely block it. Recently, convincing evidence has accumulated that dopamine is released from nigral dendrites I. Dopamine can be released from slices of the substantia nigra by depolarizing stimuli 5,6, by other neurotransmitters ~9,> and by amphetamine 24,33. Moreover, amphetamine-induced release of nigral dopamine has been demonstrated in vivo by the use of push-pull cannulae 21. Since the substantia nigra contains few, if any, dopaminergic nerve terminals 5,12.25,32y it is probable that the nigral dopamine release occurs from dendrites. The results of the present study suggest that amphetamine-induced dopamine release from nigral dendrites is involved in the locomotor stimulant action of amphetamine. In view
1 Cheramy, A., Leviel, V. and Glnwinski, J., Dendritic release of dopamine in the substantia nigra, Nature (Lond.), 289 (1981) 537-542. 2 Conrad, L. C. A. and Pfaff, D. W., Autoradiographic tracing of nucleus accumbens efferents in the rat, Brain Research, 113 (1976) 589-596. 3 Costall, B. and Naylor, R. J., Antagonism of the hyperactivity induced by dopamine applied intracerebrally to the nucleus accumbens septi by typical neuroleptics and by clo-
of the role of dopamine release in the nucleus accumbens in locomotor activity, and the well-established anatomical projection from the nucleus accumbens to the substantia nigra 2.23,2s,35.38 a possibility is that, through these efferents, dopaminergic activity in the nucleus accumbens stimulates locomotor activity at least partly by enhancing nigral dopamine release. Further experiments examining a number of predictions of this scheme are necessary to provide evidence on this issue, However, such a view is consistent with the results of Heal et al.L who found that the locomotor activity elicited by the injection of dibutyryl cyclic A M P into the nucleus accumbens was antagonized by low systemic doses of haloperidol, but not by haloperidol injected into the nucleus accumbens. They suggested that this effect of systemic haloperidol was mediated at a dopaminergic synapse beyond the nucleus accumbens. Though the phenomenon of dendritic dopamine release has been known for several years, initial studies showed no behavioral effect when apomorphine or amphetamine were unilaterally injected into the substantia nigra 7,16. Subsequent studies showed contralateral rotation after the injection of apomorphine into a dopamine-depleted substantia nigra 20.34, and provided evidence that this effect requires the presence of striatonigral terminals 20. Together with the present study these studies therefore provide evidence for a role of nigral dopamine receptors in certain behavioral actions of directly- and indirectly-acting dopamine agonists. It will be of interest to determine the relative importance of terminal regions and dendritic mechanisms in the behavioral actions of other types of drugs affecting dopaminergic, and possibly other, neurotransmitter systems. This work was supported by N I N C D S Grant NS 16175. We thank Mrs. Linda Schultz for her excellent assistance.
zapine, sulpiride and thioridazine, Europ. J. Pharmacol., 35 (1976) 161-168. 4 Costall, B., Naylor, R. J. and Nohria, V., Hyperactivity response to apomorphine and amphetamine in the mouse: the importance of the nucleus accumbens and caudate-putamen, J. Pharm. Pharmacol., 31 (1979)25%261. 5 Cuello, A. C. and Iversen, L. L., Interactions of dopamine with other neurotransmitters in the rat substantia nigra: a possible functional role of dendritic dopamine. In S. Garat-
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