Brain Research, 84 (1975) 195-205
195
© Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
THE EFFECTS OF PSYCHOMOTOR STIMULANTS ON STEREOTYPY AND LOCOMOTOR ACTIVITY IN SOCIALLY-DEPRIVED AND CONTROL RATS
B. J. S A H A K I A N , T. W. ROBBINS, M. J. M O R G A N AND S. D. IVERSEN
Department of Experimental Psychology, University of Cambridge, Cambridge (Great Britain) (Accepted September 26th, 1974)
SUMMARY
Using measures of locomotor activity and stereotypy, dose-response curves to several psychomotor stimulant drugs were obtained on rats reared in deprived or normal environments. At both 0.5 and 1.5 mg/kg D-amphetamine, the deprived rats exhibited more intense stereotyped behavior than the control rats. At 5.0 mg/kg, both groups showed maximum response. However, there was no significant difference between the two groups in locomotor response. A similar pattern of results was found for pipradrol, cocaine, and apomorphine. The findings show that different social and environmental experience can modify the response to dopaminergic stimulating agents. The results also suggest that stereotyped behavior should not be considered on the same continuum as locomotor activity. These two behaviors may be mediated by different mechanisms.
INTRODUCTION
Rearing conditions can influence subsequent behavior4,25. In addition to these effects on behavior, rearing conditions have been shown to affect the responseto drugs 17,19,~4 and the chemistry and morphology of the brain 15,~°,~2,ea,zg. In many of these studies, the experimental animals have been reared in social isolation, by being housed individually. There are species differences in the isolation phenomenon. Rats, for example, must be isolated for longer periods than mice al, and in dogs, the effects of isolation persist for yearsZL In novel environments, isolated animals are generally more active than control animals, though these results appear to be species and situation dependent31. However, this effect has been substantiated for rats in an open field 25,al. Differences have also been found in reversal discrimination problems zl, maze learning6, and persistence in operant tasks zS.
196 Valzelli a~ has neatly delineated some social behaviors that characterize isolated mice, such as a generally more exaggerated response to the environment, 'high degree of tension', and an increase in spontaneous locomotor activity. In rats, amphetamine increases locomotor activity and induces stereotyped behavior, effects generally ascribed to the interaction of the drug with amine neurotransmitters (noradrenaline (NA) and dopamine (DA)) in the brainS,9,16,27. Since impoverished environment rats show more locomotor activity25, 28 and persistence z~ and since isolated and control rodents are differentially affected by drugsS,35, a6, it is possible that rats reared in impoverished environments may develop with different responsiveness in their amine transmitter systems. A behavioral examination of this hypothesis was undertaken by observing the response differences between sociallydeprived and control rats to psychomotor stimulants. The expectation was that isolated rats would show greater sensitivity than control rats to the psychomotor stimulating action of D-amphetamine. It was predicted that with increasing drug doses, stereotyped behavior would appear earlier in the isolated animals, and would remain more intense, until a ceiling level would be reached. By comparing the action of the psychomotor stimulants which produced the effect with those that did not, it was hoped to characterize any neuropharmacological differences between isolated and control rats. METHODS
Subjects The subjects were 12 individually reared and environmentally impoverished and 12 socially reared and environmentally enriched adult female hooded rats. All rats were born and housed in the laboratory, and the individually reared rats had been socially-deprived since weaning (16 days). For details of the rearing conditions see Morgan 25. During the experiment, the only housing difference between the two groups was that socially-deprived rats were housed one rat per cage (38 cm × 26 cm × 19 cm) and control rats were housed 4 rats per cage (38 cm × 26 cm × 19 cm). All rats were able to see, smell, and hear other rats.
Procedure Locomotor activity was measured by means of photocell cages. Each of the 12 wire cages (40 cm × 25 cm × 20 cm) had 2 horizontal photocell beams spaced equally along the long axis. During each experimental session, the rats were habituated to the photocell cages for 0.5 h, injected i.p., and returned immediately to the photocell cages for the testing session. The testing sessions were l h long for 5.0 mg/kg cocaine and 0.1 mg/kg apomorphine, and 2 h for all other doses and drugs. The number of interruptions of photocell beams was recorded and stereotypy ratings taken for each 10-min period. Stereotypy was rated on a 0-6 point scale adapted from Creese and Iversen 9. The two lowest ratings, 0, inactive or asleep, and 1, active, were intended for saline control animals or drug animals exhibiting normal behavior. The other categories
197 described increasing intensities of stereotyped behavior; 2, predominantly locomotor activity with bursts of stereotyped sniffing or rearing; 3, stereotyped behavior maintained over a wide area of the cage; 4, stereotyped sniffing or rearing maintained in one location of the cage; 5, stereotyped behavior in one location with licking or gnawing; 6, assumption of a bizarre posture, 'awkward disjunctive posture' (see ref. 11, p. 221). The experimenter's ratings given to the rats were confirmed by independent observers on a blind basis. Subjects were used as their own controls, and were tested on two days per dose of the drug, with at least one intervening recovery day. The order of injection of a particular dose or saline was counterbalanced so that half the animals received the drug on the first test day and saline on the second, whereas the other half received the reverse. Experimental sessions allowed at least one recovery day between injections. At least 3 days separated injection of the next drug in the series. The series order was D-amphetamine, apomorphine, cocaine, and pipradrol and the dose order was random. The photocell cages were housed in a separate room. The background noise level, produced by the ventilation fan, was 67-68 dB; this masked entraneous sounds. The illumination level immediately outside the photocell cages was approximately 0.14 ft. lamberts. Temperature was held constant at 20 °C. Testing sessions were scheduled between 9 a.m. and 4 p.m.
Drugs and doses D-Amphetamine sulfate (Smith, Kline, and French), 0.5, 1.5, 5.0 mg/kg; 0.9 70 saline for control injections. Pipradrol hydrochloride (Merrell), 3.0, 5.0, 10.0 mg/kg; polyethylene glycol 400 (British Drug House) and distilled water (2; 1)for control injections. Cocaine hydrochloride (May and Baker Ltd.), 5.0, 10.0, 15.0, 20.0 mg/kg; 0.9 7o saline for control injections. Apomorphine hydrochloride (MacFarlan Smith), 0.1, 0.5, 1.5 mg/kg; 0.9% saline with 1 mg/ml ascorbic acid as an antioxidant for control injections. Biochemical methods At the end of the experiment, 12 rats (6 socially-deprived and 6 control) were killed, the brain extracted and placed on ice. Whole brain noradrenaline and dopamine were then assayed using catechol-O-methyl-transferase for the enzyme radiochemical assay of these amines 1°. RESULTS
The results for locomotor activity were analyzed by analysis of variance. The habituation data were analyzed by a 2-way analysis of variance with animals nested within groups. The main effect of the drug on locomotor activity were analyzed on a split plot design with 5 factors. Three factors, animals within groups, rearing condition and period were orthogonal to the other two, drug treatment and time course. The factor period refers to the counterbalanced sequence of administration of drug or saline. Since the stereotypy rating scale did not constitute an interval or ratio scale of
198 TABLE I LEVEL OF SIGNIFICANCE FOR MAIN AND INTERACTION EFFECTS FOR LOCOMOTOR ACTIVITY
Drugs and doses'
Treatment Periods'
Time
F=17.30
F--2.81 df=11,473 P
195
© Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
THE EFFECTS OF PSYCHOMOTOR STIMULANTS ON STEREOTYPY AND LOCOMOTOR ACTIVITY IN SOCIALLY-DEPRIVED AND CONTROL RATS
B. J. S A H A K I A N , T. W. ROBBINS, M. J. M O R G A N AND S. D. IVERSEN
Department of Experimental Psychology, University of Cambridge, Cambridge (Great Britain) (Accepted September 26th, 1974)
SUMMARY
Using measures of locomotor activity and stereotypy, dose-response curves to several psychomotor stimulant drugs were obtained on rats reared in deprived or normal environments. At both 0.5 and 1.5 mg/kg D-amphetamine, the deprived rats exhibited more intense stereotyped behavior than the control rats. At 5.0 mg/kg, both groups showed maximum response. However, there was no significant difference between the two groups in locomotor response. A similar pattern of results was found for pipradrol, cocaine, and apomorphine. The findings show that different social and environmental experience can modify the response to dopaminergic stimulating agents. The results also suggest that stereotyped behavior should not be considered on the same continuum as locomotor activity. These two behaviors may be mediated by different mechanisms.
INTRODUCTION
Rearing conditions can influence subsequent behavior4,25. In addition to these effects on behavior, rearing conditions have been shown to affect the responseto drugs 17,19,~4 and the chemistry and morphology of the brain 15,~°,~2,ea,zg. In many of these studies, the experimental animals have been reared in social isolation, by being housed individually. There are species differences in the isolation phenomenon. Rats, for example, must be isolated for longer periods than mice al, and in dogs, the effects of isolation persist for yearsZL In novel environments, isolated animals are generally more active than control animals, though these results appear to be species and situation dependent31. However, this effect has been substantiated for rats in an open field 25,al. Differences have also been found in reversal discrimination problems zl, maze learning6, and persistence in operant tasks zS.
196 Valzelli a~ has neatly delineated some social behaviors that characterize isolated mice, such as a generally more exaggerated response to the environment, 'high degree of tension', and an increase in spontaneous locomotor activity. In rats, amphetamine increases locomotor activity and induces stereotyped behavior, effects generally ascribed to the interaction of the drug with amine neurotransmitters (noradrenaline (NA) and dopamine (DA)) in the brainS,9,16,27. Since impoverished environment rats show more locomotor activity25, 28 and persistence z~ and since isolated and control rodents are differentially affected by drugsS,35, a6, it is possible that rats reared in impoverished environments may develop with different responsiveness in their amine transmitter systems. A behavioral examination of this hypothesis was undertaken by observing the response differences between sociallydeprived and control rats to psychomotor stimulants. The expectation was that isolated rats would show greater sensitivity than control rats to the psychomotor stimulating action of D-amphetamine. It was predicted that with increasing drug doses, stereotyped behavior would appear earlier in the isolated animals, and would remain more intense, until a ceiling level would be reached. By comparing the action of the psychomotor stimulants which produced the effect with those that did not, it was hoped to characterize any neuropharmacological differences between isolated and control rats. METHODS
Subjects The subjects were 12 individually reared and environmentally impoverished and 12 socially reared and environmentally enriched adult female hooded rats. All rats were born and housed in the laboratory, and the individually reared rats had been socially-deprived since weaning (16 days). For details of the rearing conditions see Morgan 25. During the experiment, the only housing difference between the two groups was that socially-deprived rats were housed one rat per cage (38 cm × 26 cm × 19 cm) and control rats were housed 4 rats per cage (38 cm × 26 cm × 19 cm). All rats were able to see, smell, and hear other rats.
Procedure Locomotor activity was measured by means of photocell cages. Each of the 12 wire cages (40 cm × 25 cm × 20 cm) had 2 horizontal photocell beams spaced equally along the long axis. During each experimental session, the rats were habituated to the photocell cages for 0.5 h, injected i.p., and returned immediately to the photocell cages for the testing session. The testing sessions were l h long for 5.0 mg/kg cocaine and 0.1 mg/kg apomorphine, and 2 h for all other doses and drugs. The number of interruptions of photocell beams was recorded and stereotypy ratings taken for each 10-min period. Stereotypy was rated on a 0-6 point scale adapted from Creese and Iversen 9. The two lowest ratings, 0, inactive or asleep, and 1, active, were intended for saline control animals or drug animals exhibiting normal behavior. The other categories
197 described increasing intensities of stereotyped behavior; 2, predominantly locomotor activity with bursts of stereotyped sniffing or rearing; 3, stereotyped behavior maintained over a wide area of the cage; 4, stereotyped sniffing or rearing maintained in one location of the cage; 5, stereotyped behavior in one location with licking or gnawing; 6, assumption of a bizarre posture, 'awkward disjunctive posture' (see ref. 11, p. 221). The experimenter's ratings given to the rats were confirmed by independent observers on a blind basis. Subjects were used as their own controls, and were tested on two days per dose of the drug, with at least one intervening recovery day. The order of injection of a particular dose or saline was counterbalanced so that half the animals received the drug on the first test day and saline on the second, whereas the other half received the reverse. Experimental sessions allowed at least one recovery day between injections. At least 3 days separated injection of the next drug in the series. The series order was D-amphetamine, apomorphine, cocaine, and pipradrol and the dose order was random. The photocell cages were housed in a separate room. The background noise level, produced by the ventilation fan, was 67-68 dB; this masked entraneous sounds. The illumination level immediately outside the photocell cages was approximately 0.14 ft. lamberts. Temperature was held constant at 20 °C. Testing sessions were scheduled between 9 a.m. and 4 p.m.
Drugs and doses D-Amphetamine sulfate (Smith, Kline, and French), 0.5, 1.5, 5.0 mg/kg; 0.9 70 saline for control injections. Pipradrol hydrochloride (Merrell), 3.0, 5.0, 10.0 mg/kg; polyethylene glycol 400 (British Drug House) and distilled water (2; 1)for control injections. Cocaine hydrochloride (May and Baker Ltd.), 5.0, 10.0, 15.0, 20.0 mg/kg; 0.9 7o saline for control injections. Apomorphine hydrochloride (MacFarlan Smith), 0.1, 0.5, 1.5 mg/kg; 0.9% saline with 1 mg/ml ascorbic acid as an antioxidant for control injections. Biochemical methods At the end of the experiment, 12 rats (6 socially-deprived and 6 control) were killed, the brain extracted and placed on ice. Whole brain noradrenaline and dopamine were then assayed using catechol-O-methyl-transferase for the enzyme radiochemical assay of these amines 1°. RESULTS
The results for locomotor activity were analyzed by analysis of variance. The habituation data were analyzed by a 2-way analysis of variance with animals nested within groups. The main effect of the drug on locomotor activity were analyzed on a split plot design with 5 factors. Three factors, animals within groups, rearing condition and period were orthogonal to the other two, drug treatment and time course. The factor period refers to the counterbalanced sequence of administration of drug or saline. Since the stereotypy rating scale did not constitute an interval or ratio scale of
198 TABLE I LEVEL OF SIGNIFICANCE FOR MAIN AND INTERACTION EFFECTS FOR LOCOMOTOR ACTIVITY
Drugs and doses'
Treatment Periods'
Time
F=17.30
F--2.81 df=11,473 P
