Cocaine-induced sex differences in D1 dopamine receptor mRNA levels after acute cocaine administration.

INTRODUCTION: Although it is known that female rats have a more robust behavioral response to acute cocaine administration than male rats, the neurobiological mechanisms underlying these differences remain unclear. The purpose of the present study was to determine if there are sex differences in cocaine's regulation of dopamine D1 and D2 receptor mRNA levels.
METHODS: Male and female Fischer rats received acute cocaine (20 mg/kg, intraperitoneal) or saline. Ambulatory activity was recorded one hour post drug treatment. Rats were then sacrificed either 1 or 24 hours post drug treatment and D1/D2 DA receptor mRNA levels were measured via solution hybridization assay.
RESULTS: Cocaine-induced ambulatory activity was greater in female than male rats. There were no sex differences in baseline levels of D1 and D2 receptor mRNA in the caudate putamen (CPu) or the nucleus accumbens (NAc). Cocaine administration reduced levels of D1 mRNA in the NAc only in male rats.
CONCLUSION: Our findings suggest that the regulation of striatal D1 mRNA levels after acute cocaine administration is a sexually dimorphic process. We also hypothesize that the D1 receptor may be an important substrate in the regulation of sex differences in cocaine-induced locomotor activity.