Interactive effects of diazepam and ethanol on baboon match-to-sample performance

Abstract

Four juvenile male baboons were trained to perform a match-to-sample (MTS) discrimination task. Diazepam (DZ) at doses of 0.5, 1.0, 2.0, 4.0, or 6.0 mg/kg resulted in a significant ( p<0.05) increase in the mean response times (MRT) during the 2 hr test session in terms of percent change from baseline performance under nondrug conditions measured the day prior to drug treatment. Effects were maximal at 2.0 mg/kg diazepam and no further effects were observed at 4.0 or 6.0 mg/kg. Administration of 0.25 mg/kg of diazepam had no effect on MTS performance. Exposure to 0.5 g/kg of ethanol (EtOH) had no effect on response time, while 1.0 g/kg EtOH significantly ( p<0.05) increased response time. Baboons receiving combined treatment with 0.5 or 1.0 g/kg EtOH plus 1.0 mg/kg diazepam displayed a significant ( p<0.05) percent increase in mean response time compared to that observed under baseline conditions on the day prior to drug treatment. The 0.5 g/kg EtOH and 1.0 mg/kg diazepam combination increased MRT to an extent comparable to the effect observed at the same dose of diazepam alone. Effects observed with 1.0 mg/kg diazepam and 1.0 g/kg EtOH were similar to those produced by the DZ alone. Combinations of 0.5 g/kg EtOH and 0.5 mg/kg diazepam, 1.0 g/kg EtOH and 0.25 mg/kg diazepam, and 1.0 g/kg EtOH and 0.5 mg/kg diazepam had no significant effect on response times. However, combined treatment with 0.25 mg/kg of diazepam and 1.0 g/kg EtOH resulted in a complete elimination of the increase in MRT observed previously with the EtOH alone and administration of 0.5 g/kg EtOH combined with 0.5 mg/kg diazepam eliminated the increase in response time produced by 0.5 mg/kg diazepam alone. These results indicate that EtOH or diazepam increase the time required for baboons to respond to the correct stimuli in an MTS discrimination task. However, significant interactive effects were observed, since the administration of a combination of a low dose of DZ with EtOH appeared to prevent the increases in response time observed with either drug alone.