Increased sensitivity to d-and l-amphetamine action after midbrain raphe lesions as measured by locomotor activity

Nr?rrophur~nu~r~k,~ Vol. 18. pp. 243 fo 249 0 Pergamon Press Ltd 1979.Printed in Great Britain

INCREASED SENSITIVITY TO dAND ~-AMPHETAMINE ACTION AFTER MIDBRAIN RAPHE LESIONS AS MEASURED BY LOCOMOTOR ACTIVITY I. LUCKI and J. A. Department of Psychology,

HARVEY

The University of Iowa. Iowa City, IA 52242. U.S.A. (Accepted 17 August 1978)

Summary--This study examined the effects of d- and I-amphetamine on locomotor activity and stereotyped behavior in control rats and rats with lesions in the raphe nuclei (RN) and dorsolateral tegmenturn (DLT). Raphe nuclei lesions produced a large (93%) and selective depletion of the tetencephafic content of serotonin and an enhancement of both d- and ~-amphetamine action on locomotor activity that was characterized by a shift in the dose-effect curve to the left of controls. The ED50 for the locomotor increasing effects of both d- and j-amphetamine was significantly reduced by the RN lesions to approximately one-third of control values. In addition. RN lesions significantly increased the maximum levels of locomotor responding to d- but not I-amphetamine. Finally, rats with RN lesions demonstrated a significantly greater incidence of stereotyped behavior at lower dosages of d- but not Camphetamine than did controls. Dorsolateral tegmentum lesions that produced a selective but small (54%) decrease in the telenccphahc content of norepinephrine had no effect on either d- or ~-amphetamine

A number of investigators have reported an enhancement of amphetamine action in the rat as measured by locomotor activity when the brain content of serotonin is decreased by injection of d,l-p-cholorophenylalanine (p-CP), a tryptophan-free diet, lesions of the midline raphe nuclei (RN lesions), or injections of the serotonin neurotoxin, 5,6-dihydroxytryptamine (Neill, Grant and Grossman, 1972; Mabry and Campbell, 1973; Breese, Cooper and Mueller, 1974; Carey, 1976; Geyer, Puerto, Menkes, Segal and Mandell, 1976; Hollister, Breese, Kuhn, Cooper and Schanberg, 1976; Segal, 1976). However, none of these studies has examined whether the enhancement of the amphetamine action was due to a decrease in EDSO’s or an increase in the magnitude of drug effect, or both. Moreover, Jacobs, Wise and Taylor (1975) have questioned these findings by pointing to the methodological problems involved in comparing drug effects between groups of animals having unequal baselines. Both pCP and RN lesions, by themselves, produce large increases in locomotor activity above that of controls. Jacobs et al. (1975) found no difference in the dose-effect curves of pCP injected, RN lesioned or control rats when the increase in locomotor activity produced by d-amphetamine was calculated as a percent change from each animal’s activity baseline. There is also no agreement concerning the effect of serotonin depletion on ~phet~ne-indu~d stereotyped behavior. Raphe nuclei lesions have been reported to produce an enhancement of stereotyped Key words: d-amphetamine, l-amphetamine, serotonin, norepinephrine, locomotor activity, stereotyped behavior. raphe nuclei. r&h I8,13--s

243

behavior (Gum&a, Kostowski and Czlonkowski, 1973) while p-CP has been reported to produce an enhan~ment (Swonger and Rech, 1972; Ernst, 1972) no effect (Breese rt al., 1974) or a decrease in stereotyped behavior (Gumulka rt al., 1973; Segal, 1976). The present study was designed to obtain more detailed information concerning the role of serotonin in the action of amphetamine as measured by locomotor activity and stereotyped behavior. To this end, an activity chamber was employed that provided a measure of the maximum increase in locomotor activity produced by amphetamine and thus allowed for a determination of EDSO’s. These measures, along with determinations of stereotyped behavior, were obtained for both d- and ~-~ph~amine in control rats and rats with RN lesions that produced a selective decrease in the telencephalic content of serotonin.

METHODS

Male albino rats (Hohzman Co., Madison, WI), 53 days old on arrival, were housed two per cage and allowed free access to food (Purina Laboratory Chow) and water in a room maintained on a 12-hour lightdark cycle. Locomotor activity of all rats was measured one week later by the method of Mabry and Campbell (1973) in four stabilimeter cages housed in separate sound attenuated chambers illuminated by a 6-watt light bulb and containing a Plexiglas window for observation of the animal. Ventilation and background noise was provided by a Pentaflow Whisper Fan (Pamotor, 3urling~e, CA) attached to

244

I. LUCKI and J. A. HARVEY

each chamber. The stabilimeter cages were constructed of stainless-steel mesh and measured 36 x 23 x 19 cm. Each cage was mounted on a ccntral fulcrum which allowed it to be tilted as the animal moved from one end of the cage to the other. The tilting of the cage, through a distance of 0.6cm. closed or opened a microswitch located at one end of the cage and this was recorded as an upward or downward deflection of a pen by means of a Grass model 7 polygraph. Short latency pen deflections of less than 250msec were not recorded as locomotor activity counts since these were observed in preliminary experiments to be caused by the animal pivoting at the center of the stabilimeter cage. Locomotor activity was recorded during light hours in four 20-min sessions spaced 48 hr apart until activity levels had stabilized (4 days). The mean activity score for the last three sessions was calculated for each animal and served as the baseline measure for preoperative activity. One week later all animals underwent surgery. Surgery Destruction of the raphe nuclei (RN) was produced by placement of two midline lesions aimed at the dorsal and medial raphe nuclei by means of the apparatus and co-ordinate system of Krieg (1946). A 24gauge nichrome electrode, insulated except for the cross-sectional diameter of the tip, was set at a 10” angle to the midline in order to avoid damage to the midsagittal sinus. The placement of each lesion was 1 mm anterior to lambda. The dorsal raphe lesion was produced by lowering the electrode 6.7 mm below the surface of the skull from a point 1.2 mm lateral to the midline and passing a 2ma cathodal current for 20sec. The medial raphe lesion was produced by lowering the electrode 8.6mm below the surface of the skull from a point 1Smm lateral to the midline and passing a 2 ma current for 25 sec. Destruction of the dorsolateral tegmentum (DLT) was accomplished by means of a Kopf stereotaxic instrument and the co-ordinate system of Konig and Klippel(1963). Bilateral lesions were aimed at a point 0.2 mm anterior and 3.1 mm dorsal to ear bar zero and 1.5 mm to each side of the midline. Each lesion was produced by passage of a 2 mA current for 20 sec. Surgical controls were treated in an identical manner except that the electrode was not lowered into the brain. All surgery was under ether anesthesia and was followed by an intramuscular injection of 75,000 units of penicillin. Postoperative measurement of drug effects LocomDtor activity. Postoperative measures of locomotor activity began six weeks after surgery, and continued over a 16-week period. Locomotor activity was measured during 20-minute sessions on Monday, Wednesday and Friday of each week. d- or I-Amphetamine sulfate (Smith, Kline & French Laboratories, Philadelphia, PA) was dissolved in sterile physiological saline and the dosage is expressed as the salt form.

All injections of drug or saline were intraperitoneal and of equal volume (1 ml/kg). Animals were injected every Friday, 30min prior to behavioral testing, in the following sequence: saline; d-amphetamine, 0.5, 1.0, 2.0 and 4.0mg/kg; saline; d-amphetamine 0.25 mg/kg; I-amphetamine, 2.0, 4.0. 8.0, 1.0, and 0.5 mg/kg; d-amphetamine, 0.125 and 0.062 mg/kg; saline; I-amphetamine, 16.0 mg/kg. Thus, all injections of drug or saline were spaced one week apart. The average locomotor activity obtained on Monday and Wednesday of each week (days on which neither drug nor saline were injected) provided 16 measures of activity which were averaged for each animal to provide a measure of postoperative baseline activity. Since the locomotor activity obtained after each of the three injections of saline did not differ significantly for the RN, DLT or control groups, these were averaged for each group to provide a measure of saline baseline activity. The effects of d- or I-amphetamine were expressed in three ways: (1) as the actual locomotor activity following each dosage of drug; (2) as a difference score (D-score) obtained by subtracting the saline baseline activity of each animal from the activity following each dosage of drug; and (3) as an output ratio obtained by dividing activity after drug by saline baseline activity. An ED50 was calculated for each animal as the dosage of drug required to produce a half-maximal increase in locomotor activity. This was done by estimating the regression line of D-scores as a function of dosage when plotted on semi-logarithmic paper (Goldstein. 1964). The maximum D-score of each animal (regardless of dosage) also provided a measure of the maximum increase in activity prodaced by d- or I-amphetamine above the animals saline baseline. Low baseline activity. One week after the above sequence of drug testing, the locomotor activity of RN lesioned and control rats was measured during two 140-min sessions spaced one week apart. In this procedure, animals were placed in the chambers for 90min in order to reduce their baseline activity, then injected with drug or saline and placed back into the chambers. Thirty minutes later the locomotor activity of each rat was recorded for 20min. The sequence of injections was: saline; and 0.50mg/kg d-amphetamine. Stereotyped behavior. After each injection of drug or saline, animals were rated for the presence of stereotyped behaviors (Randrup and Munkvad. 1970; Schiorring. 1971) as reflected by: (1) intense sniffing in one area of the cage; (2) rapid repetitive head movements; or (3) licking or gnawing of the grid floor. Each animal was observed five times (i.e. every 4min) for 30sec. An animal was classified as being in stereotopy if it demonstrated stereotyped behavior during at least one of the five observations. Assay of monoamines Telencephalic content of serotonin, norepinephrine and dopamine was determined six weeks after the last

245

Raphe lesions and amphetamine action day of behavioral testing. Brains were removed after decapitation and dissected on an ice-cold surface. The telencephalon was peeled forward until the columns of the fornix were visible and cuts were then made through the anterior commissure and the coronal radiations on each side. Monoamines were determined spectrophotofluorometrically in separate a& quots of telencephalon following the procedure of Green and Harvey (1974), by the butanol extraction method for serotonin (Bogdanski, Pletscher, Brodie and Udenfriend, 1956), and the alumina column method of Crout, Creveling and Udenfriend (1961) followed by the oxidation procedure of Chang (1964) for norepinephrine and dopamine. Monoamine content was calculated as nmol of amine/g tissue, fresh weight. The brainstems of all lesioned rats were placed in a 3.7% (w/v) formaldehyde solution for subsequent

histological

examination.

Histology

Frozen, 40pm thick, coronal sections through the extent of the RN and DLT lesions were stained for cell bodies and fiber tracts by the method of Kliiver and Barrera (1953). The extent of each lesion was then determined by microscopic examination of the histological material. Raphe nuclei lesions produced maximal damage at the level of the decussation of the superior cerebellar peduncle and destroyed the rostra1 portions of the three major groups of cells known to contain serotonin cell bodies that project rostrally to forebrain: the dorsal raphe nucleus (B-7); the medial raphe nucleus (B-8) and the ventromedial tegmentum (B-9) as described by Dahlstriim and Fuxe (1964). In addition, the placement of the lesions would have interrupted virtually all of the ascending serotonergic fibers projecting from more caudal portions of these nuclei which were themselves not damaged. Some damage also occurred to the ventromedial periventricular gray area, the medial longitudinal fasciculus, the trochlear nuclei, the decussation of the superior cerebellar peduncle, the tectospinal tracts and the dorsal portions of the medial lemniscus. Rostrally, damage occurred to the dorsal two-thirds of the interpeduncular nucleus, nucleus linearis caudalis, nucleus linearis

intermedius, the Edinger-Westphall nuclei and the principle oculomotor nucleus. Caudally, there was damage extending to the level of the ventral tegmental nucleus of Gudden but sparing the caudal portions of the dorsal and medial raphe nuclei. Dorsolateral tegmentum lesions produced their maximum bilateral damage at the level of the dorsal and ventral tegmental nuclei of Gudden in the region. through which the dorsal and ventral noradrenergic bundles are known to pass (Palkovits and Jacobowitz, 1974). There was always some damage to the superior cerebellar peduncle, nucleus parabrachialis dorsalis and ventralis as well as the dorsal mesencephalic nucleus and tract of the trigeminal nerve. There was also some damage to the trochlear nerve, locus coeruleus, nucleus tegmenti lateralis but this was primarily unilateral. The lesions extended rostrally to the level of the trochlear nucleus where damage bordered the lateral lemniscus laterally and included the ventrolateral periaqueductal gray area. Caudally, the lesion extended along the dorsal surface of the pontile tegmentum. Statistics All statistical comparisons of locomotor activity were carried out by means of Student’s t-test, two tailed. Comparisons of stereotyped behaviors were carried out by means of 2 x 2 contingency tables (Finney, 1948). RESULTS

Effect of lesions on locomotor activity

Table 1 presents the baseline preoperative locomotor activity, the baseline postoperative locomotor activity obtained during the 16 weeks of drug testing, and the saline baseline activity for the three groups of rats. There were no significant differences in the baseline locomotor activity of the three groups of rats prior to surgery. Postoperatively, RN lesions produced an 8.5 fold increase in baseline locomotor activity while the activity of rats with DLT lesions was reduced to approximately one-half that of controls. All groups demonstrated a small and comparable decrease in activity when injected with saline.

Table 1. Effect of brainstem lesions on locomotor activityt

Group Control DLT lesion RN lesion

N

Preoperative Baseline activity3

8 7 8

23.8 f 2.6 28.5 + 2.8 28.2 + 3.3

Postoperative Baseline Saline baseline activity5 activity11 18.6 & 2.1 10.3 & 1.7* 157.3 + 27.6**

15.4 * 2.1 8.2 + 1.2* 151.2 i 30.7**

t All values are mean + S.E.M. activity counts/20 min. 1 Mean is based on each animal’s average activity over three preoperative sessions. g Mean is based on each animal’s average activity over 16 weeks of testing. 11 Mean is based on each animal’s average activity over three separate saline injection sessions conducted at the beginning, middle and end of the 16 weeks of testing. Asterisk indicates a significant difference between the mean values of lesioned and control groups as calculated by Student’s t-test. two tailed: *P < 0.01; **P < 0.001.

246

1. Luctct and J.

A. HARVEY

5 F u *

_ I,_____-__

w

E

_

____

_______

_-___

-

CONTROL \

CONTROL

w

DLT

CI

RN LESION

LESION

o

6

.06

,125

.2-5

.j

;

2

SULFATE (mglkg)

D-AMPHETAMINE

of lesions on

a~~~eta~ine action

Both d-amphetamine (Fig. 1) and /-amphetamine (Fig. 2) produced a dose-dependent increase in the locomotor activity of all three groups of rats followed by a decrease in activity at higher dosages. The peak increase in activity for control and DLT-lesioned rats occurred at 2.0mg,kg of d-amphetamine and at 4.0mg/kg of ~-amphetamine. In contrast, the doseeffect curve for the RN-lesioned animals was shifted to the left with peak increases in activity occurring at 0.5 mg/kg d-amphetamine and 2.0 mg/kg I-amphetamine. In agreement with the dose-effect curves of Figures I and 2, RN lesions produced a significant decrease in the ED50 for both d- and &hetamine as compared with control rats (Table 2). Based on the ratio of EDSO’s, the RN lesioned rats were 3.3 and 2.4 times more sensitive than controls

0.5

1

L-AMPHETAMINE

Fig. 1. Effect of d-amphetamine on locomotor activity of rats with DLT lesions (n = 7). RN lesions (n = 8) and Controls (n = 8). The points at the extreme left of the Figure at the zero dosage, and the extended dotted lines. represent the mean saline baseline activity of each group with vertical lines representing 1 S.E.M. The absence of a vertical line indicates that I S.E.M. is contained within the width of the symbol. The asterisk indicates that the peak locomotor activity of each group was significantly different from its respective saline baseline (P < 0.05) as calculated by Student’s t-test. two tailed.

Effects

0

4

to d: and I-amphetamine,

2

4

8

Fig. 2. Effect of ~-amphetamine on locomotor activity. See legend of Figure I for details.

respectively. The ED50 of DLT-lesioned rats did not differ from that of controls for either stereoisomer of amphetamine. Raphe nuclei-lesioned rats demonstrated a greater maximum increase in activity than controls for both stereoisomers of amphetamine: however, this was only significant for d-amphetamine (Table 2). There was no significant difference between the maximum increase in activity demonstrated by DLT-lesioned and control rats after d- or ~-amphetamine. For all three groups of rats, the ED50 for l-amphetamine was significantly and approximately three times greater than for d-amphetamine (P < 0.01 for each comparison). Also, for DLT-lesioned and control rats, the maximum increase in activity produced by d-amphet~ine was si~ificantly and approximately two times greater than that produced by l-amphetamine (P < 0.05 for each comparison). Although RNlesioned animals also demonstrated a greater maximum increase to d- as compared with I-amphetamine this difference was not significant. E#ect of RN Iesions on d-u~~~eta~ine action under reduced baseline conditions The RN-lesioned rats demonstrated a greater maximum increase in activity after d-amphetamine than did controls when changes in activity were calculated

Table 2. Effects of d- and ~-amphetamine on locomotor activity?

Group

N

Control DLT lesion RN lesion

8 7 8

d-Amphetamine ED50 Maximum change in activityt Ow/kg) 1.02 + 0.08 1.26 f 0.10 0.31 &-0.09**

16

SULFATE (mglkg)

93.2 + 7.7 88.1 f 21.4 172.5 f 35.2**

I-Amphetamine Maximum change ED50 in activityt (mg/kg) 2.90 + 0.24 3.00 * 0.51 1.19 f 0.25**

49.1 f 12.3 32.7 + 4.5 104.2 k 32.1

t All values given as mean k S.E.M. $ Maximum change in activity was calculated for each animal as its maximum activity after drug minus its saline baseline activity. Asterisk indicates a significant difference between the mean of the lesioned and control groups as calculated by Student’s f-test, two tailed: *P c 0.05; **P < 0.001.

Raphe lesions and amphetamine Table 3. Effect of 0.50 mg/kg d-amphetamine

on locomotor activity under high and low baseline conditions? Activity after (0.50 mg/kg)S

Saline baseline activityS

247

action

D-score9

Output ratioi!

17.1 f 5.4 101.4 f 38.8*

2.1 f 0.3 1.9 & 0.3

7.8 + 3.2 131.9 + 34.9*

7.4 + 3.0 137.0 f 32.3*

High baseline condition

Control RN lesion

15.4 f 2.1 151.2 +_30.7*

Control RN lesion

2.0 t 0.4 5.2 k 4.2

32.5 + 6.5 252.6 j, 49.S LOWhasrline condition 9.8 &-3.0 137.1 i 32.2*

t All values are given as mean & S.E.M. and are based on 8 rats per group. i Activity per 20-min period. 9 D-scores were calculated for each animal as its activity after drug minus its saline baseline activity. 11 Output ratios were calculated for each animal as its activity after drug divided by its saline baseline activity. Asterisk indicates a significant difference between the mean of RN-lesioned and control group (*P < 0.05) as calculated by Student’s I-test, two-tailed. i.e. activity after drug minus saline baseline activity (see Table 2). However, because of the differences in the saline baseline activity between RNlesioned and control rats (see Table l), the reverse would appear to be true if drug effects are expressed as an output ratio, i.e. activity after drug divided by the saline baseline activity. Using output ratios, the maximum increase in activity after d-amphetamine for the three groups of rats was (mean f S.E.M.): control, 8.8 & 1.9; DLT lesion, 12.2 rfr 2.6; RN lesion, 2.6 + 0.4. Thus, when calculated as an output ratio, the RN-lesioned rats demonstrated a significantly smaller maximum increase in activity than either the DLT-lesioned or control rats (P < 0.01 for each comparison). The same results are obtained if one examines the effects of OSOmg/kg d-amphetamine, the dosage of drug that produced the peak increase in the locomotor activity of the RN-lesioned rats (see Fig. 1). The top portion of Table 3 (high baseline condition) presents the data obtained when the saline baseline activity of RN-lesioned rats was significantly higher than that of control. Under these conditions, 0.50 mg/kg d-amphetamine produced a significantly greater increase in the activity of the RN-lesioned rats as compared with controls when the data were calculated as a D-score, but not when calculated as an output ratio. Therefore, the baseline activity of RN-lesioned and control rats was equated by extended exposure of the animals (90-min) to the locomotor activity chambers prior to saline or drug injections. These data are presented in the bottom portion of Table 3 (low baseline as D-scores,

condition). In spite of the equal saline baselines, RNlesioned animals again demonstrated a significantly greater increase in locomotor activity after 0.50 mg/kg d-amphetamine than controls when the data were calculated as a D-score. More importantly, under these conditions, the RN-lesioned rats also demonstrated a si~i~cantly greater increase in activity than controls when the data were calculated as an output ratio. Stereotyped

behavior

Both DLT-lesioned and control rats first demonstrated stereotyped behavior at 4.0 mg,kg d-amphetamine (Table 4). In contrast, five RN-lesioned animals demonstrated stereotyped behavior at 2.0 mg/kg, and this represented a significantly greater incidence of stereotyped behavior as compared with DLT-lesioned or control rats (P < 0.02 for each comparison). Althou~ more RN-lesioned rats (4 out of 8) demonstrated stereotyped behavior after 4.0 mg/kg I-amphetamine than did controls (1 out of 8), this difference. was not significant. Comparison of the data presented in Table 4 with the data of Figures 1 and 2, suggests that decreases in locomotor activity for all three groups of rats were associated with dosages of d- or ~-amphetamine that began to elicit stereotyped behaviors. Eflect

of lesions

on brain

monoamines

In agreement with the histological localization of lesions (see Histology ‘in Methods Section), RN lesions produced a significant and large (93%) de-

Table 4. Effect of d- and I-amphetamine on stereotyped behavior

Group

Iv

Control DLT lesion

8 7

RN lesion

8

Number of animals demonstrating syndrome /-amphetamine (mg/kg) d-amphetamine (mgjkg) 4.0 4.0 8.0 16.0 1.0 2.0 0 0 I

0 0 5*

5 5 6

0 0

1

I 2 4

7 6 6

* Indicates that the number of RN-lesioned rats demonstrating stereotyped behavior is significantly greater than for control or DLT-lesioned groups. P < 0.02 as calculated by a 2 x 2 contingency table (Finney. 1948).

248

I. LUCKI and J. A. HARVEY Table 5. Effect of brainstem lesions on monoamine content of telencephalon Group

N

Control DLT lesion RN lesion

8 7 7

Monoamine content (nmol/g & S.E.M.) Serotonin Norepinephrine Dopamine 3.92 f 0.11 3.64 k 0.23 0.28 k 0.17*

1.92 & 0.07 0.89 * 0.12* 1.71 _t 0.12

4.79 f 0.13 6.85 F 0.33 6.40 + 0.26

* Mean value significantly different from the mean of controls (P < 0.001) as calculated bv Student’s t-test. two tailed.

crease in the serotonin content of telencephalon without significantly affecting content of norepinephrine or dopamine (Table 5). Dorsolateral tegmentum lesions had no significant effect on either the serotonin or dopamine content of telencephalon but did significantly decrease norepinephrine by 54%. DISCUSSION The results of the present study indicate that RN lesions produce a shift to the left in the dose-effect curve for both d- and f-amphetamine as measured by locomotor activity. This increased sensitivity of RN-lesioned animals to the locomotor increasing effects of both d- and I-amphetamine was reflected by a significant decrease in their EDSO’s as compared with control animals. In agreement with Jacobs rr al. (1975) it was also found that the increased baseline locomotor activity of RN-iesioned animals as compared with controls made it difficult to determine whether these lesions had also affected the magnitude by which d-amphetamine increased locomotor activity. For example, when drug effect was calculated as a difference score (locomotor activity after drug minus saline baseline activity), d-amphetamine appeared to produce a greater increase in locomotor activity of RN-lesioned as compared with control rats. However, when drug effect was calculated as an output ratio (locomotor activity after drug divided by saline baseline activity), d-amphetamine appeared to produce a smatler increase in activity of RN-lesioned animals as compared with controls. The inverse relationship between baseline activity levels and amphetamine action has been well documented by Dews and Wenger (1977). Amphetamine-induced increases in the rate of lever pressing, as calculated by output ratios, show a systematic decrease as baseline rates of responding increase. Hence, one can only determine whether the magnitude of amphetamine action has been affected by RN lesions if one compares drug effects under equal baseline conditions with those of controls. This was accomplished in the present experiments by extended exposure of both RN-lesioned animals and controls to the activity chambers prior to injection of saline or d-amphetamine. Under these conditions, when the saline baseline activity of RN-lesioned and control animals were equalized, 0.5 mg/kg d-amphetamine produced a significantly greater increase in the locomotor activity of RN-lesioned animals as com-

pared with controls whether activity was measured by a difference score or an output ratio. Thus, RN lesions appear to produce both an increased sensitivity and an increased magnitude of responding to d-amphetamine. Raphe nuclei lesions also produced a si~ificantly increased sensitivity to d-amphetamine’s ability to elicit stereotyped behaviors, though this effect was not as prominent after I-amphetamine. These results are in agreement with Gumulka rt al. (1973) who reported that stereotyped behavior produced by 5 mg/kg d,~-amphetamine was intensified in rats with RN lesions. Segal(l976) has pointed out that activity representing locomotion is first increased by a given dosage of amphetamine and then decreased, with the decrease being due to the onset of stereotyped behaviors. The dose-effect curves of the present study are in full agreement with these observations of Segal (1976). With increasing dosages of d- or I-amphetamine, locomotor activity first increased and then decreased for all groups of animals with the decreases occurring at dosages that were observed to elicit stereotyped behaviors. The decreases in locomotor activity of RN-Iesioned animals occurred at lower dosages of amphetamine as compared with controls (see Figs 1 and 2). This would appear to be another reflection of the greater sensitivity of RN-lesioned rats to amphetamine’s ability to induce stereotyped behavior. ior. The absence of any alteration in either d- or ~-amphetamine action after DLT lesions may be due to the incomplete interruption of the ascending noradrenergic pathways as reflected by only a 54% decrease in the telencephalic content of norepinephrine. However, the absence of any effect of selective norepinephrine depletion on amphetamine action is in agreement with the results of others (Hollister, Breese and Cooper, 1974; Roberts, Zis and Fibiger, 1975; Creese and Iversen, 1975; Kostowski, Jerhcz, Bidzinski and Hauptmann, 1977). In agreement with many studies demonstrating that amphetamine action is mediated by dopamine, selective depletion of dopamine in brain blocks the ability of amphetamine to produce increases in locomotor activity or stereotyped behaviors (Holhster et al., 1974; Roberts et al., 1975; Creese and Iversen, 1975). Since RN lesions, in the present study, produced a seieetive and large (93%) depletion of telencephalic serotonin along with an increased sensitivity to

Raphe amphetamine, normally

it would

involved

Acknow/edgements-We Kenny Simansky and assistance and Smith, viding us with both study was supported

appear

that

in the actions

lesions

serotonin

and amphetamine

is also

of amphetamine.

thank Arthur J. Schlosberg, Scott E. McMaster for their valuable Kline & French for generously prod- and I-amphetamine sulfate. This by U.S.P.H.S. Grant MH-16841. REFERENCES

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