Acquisition of a Fixed Ratio Schedule in Adult Male Rats Neonatally Exposed to Ethanol and/or Cocaine

Abstract

Acquisition of an operant learning task for sucrose reinforcement was examined in rats after neonatal exposure to ethanol and/or cocaine. Subjects were raised using an artificial rearing procedure from postnatal days 4 to 11 and were intragastrically fed a milk diet containing either ethanol (6 g/kg/day), cocaine (60 mg/kg/day), the combination (6 g/kg/day + 60 mg/kg/day), or an isocaloric control diet. There was also a suckled sham control. Adult male offspring (postnatal day 65 to postnatal day 68) were shaped to lever press for sucrose reinforcement and then began daily 15-min sessions of fixed ratio (FR) training. The number of days to acquire an FR 20 was measured. Neonatal exposure to the ethanol/cocaine combination significantly increased the number of days to reach the FR 20. There was also a trend for fewer of these subjects to reach the FR 20, although this difference was not statistically significant. These results suggest that subjects neonatally exposed to the ethanol/cocaine combination have difficulty learning an operant task. This impairment was unique to the ethanol/cocaine combination group and suggests that polydrug exposure during development may have a more adverse outcome than exposure to ethanol or cocaine alone.