Effects of nicotine on schedule-controlled behaviour: Role of fixed-interval length and modification by mecamylamine and chlorpromazine

The effects of nicotine, alone and in combination with mecamylamine and chlorpromazine, were studied in one group of rats exposed to a fixed-interval 30 sec schedule of food reinforcement, and a second group exposed to a fixed-interval 120 sec schedule. For both groups nicotine increased overall response rates in a dose-related fashion up to a maximum at 0.3 mg/kg. Examination of the within-interval response patterns showed that nicotine tended to increase the low level response rates in the early and middle parts of the interval and decrease, or increase to a proportionally smaller extent, the higher level response rates at the end of the interval. The response rate and pattern of the animal, rather than the schedule to which it was exposed, was found to be the main determinant of the effects of nicotine. Mecamylamine (1.0 mg/kg) blocked most of the changes in rate produced by nicotine, although in the group exposed to the fixed-interval 30 sec schedule, the increases in response rate tended to predominate after combined administration of mecamylamine and nicotine. Chlorpromazine (1.0 mg/kg) failed to block the effects of nicotine in either group. Instead, the effects of combined administration of nicotine and chlorpromazine were similar to the added effects of the two compounds given alone. It appears that the behavioural effects of nicotine are not mediated through catecholaminergic systems.