Effects of housing conditions and social behavior on methamphetamine self-administration in male and female rats
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Social support is a potentially protective factor against substance use disorders (SUDs). Previous studies in animal models for SUDs have shown that when females are pair housed, they have lower motivation for cocaine and methamphetamine (METH) than females who are single housed. In males, however, social housing has not had the same beneficial effect. This study investigates effects of social housing on METH self-administration in females or males when both cage mates are self-administering METH. The study also investigated how the quality of the relationships changed after METH self-administration. The results show that singly housed females self-administered more METH than socially housed females, while males in both social housing conditions self-administered METH at the same rate. The social behavior data showed that females given saline spent more time apart, however the females given METH spent more time together, suggesting that their social behavior may play a role in the attenuation of METH self-administration. Males’ social behavior remained unchanged after METH and the dominant male in a pair self-administered more METH than the non-dominant male. Females’ self-administration was not affected by dominance. The results of this study show that social housing provides some protective benefits to females, but not males, for METH self-administration. Further, the type of relationship between cage mates affects males’ self-administration and may explain why social housing with a same sex mate is not beneficial for males.
STRUCTURED ABSTRACT
Background
Social support is a potentially protective factor against substance use disorders (SUDs). Previous studies in rats have shown that when females are pair housed, they have lower motivation for drugs such as cocaine and methamphetamine (METH), than females who are single housed. In males, however, socially housed and singly housed males both have the same motivation for drugs such as cocaine.
Purpose
The aim of this study was to investigate if social housing would attenuate METH self-administration in females or males when both cage mates are self-administering METH on an intermittent access schedule (IntA). The study also investigated how the quality of those relationships changed after METH self-administration, if dominance played a role in the rate of self-administration, and the extent to which the quality of the relationships was related to METH self-administration.
Methods
Male and female rats were individually housed or housed in same sex pairs from around day 42, then animals underwent self-administration of METH (0.3 mg/kg/inf) on an IntA schedule of reinforcement. Both animals in a pair self-administered METH. Social behavior was evaluated prior to and throughout the period when animals were self-administering METH.
Results
The results showed that in females, single housed females self-administered more METH than pair housed females, while males in both housing conditions self-administered METH at the same rate. More singly housed females on day one of the IntA had high rates of self-administration, compared to socially housed females. Differences attenuated after the first session, but singly housed females still self-administered METH to a greater extent than pair housed females overall. The social behavior data showed that females given saline spent more time apart while the females given METH spent more time together. This suggested that social behavior may contribute to the attenuation of self-administration in females. Males’ social behavior largely remained unchanged after METH and males continued to exhibit dominance behaviors. Furthermore, males’ METH self-administration was affected by dominance, with dominant males exhibiting greater responding for METH than non-dominant males.
Conclusions
Social housing provides some protective benefits to females, but not males, for METH self-administration. Further, the type of relationship between cage mates affects males’ self-administration and may explain why social housing with a same sex mate is not beneficial for males.
HIGHLIGHTS
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Pair housing in female rats resulted in less methamphetamine self-administration compared with individually housed females.
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Pair housing in male rats did not attenuate methamphetamine self-administration compared with single housing.
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Females self-administering methamphetamine spent more time together.
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Males’ self-administration of methamphetamine was affected by dominance status.
