Reinforcing effect as a function of infusion speed in intravenous self-administration of nicotine in rhesus monkeys.

The influence of infusion speed on the reinforcing effect of nicotine (NIC) 30 micrograms/kg/infusion was studied in rhesus monkeys using intravenous self-administration at infusion speeds of 5.2, 1.3, and 0.3 micrograms/s under a fixed-ratio 5 schedule with a 15-min time-out after each intake. The 24-h self-administration rate was observed in 3 periods of 8 days each for each speed, separated by saline self-administration periods of 2 weeks each. As a result, when a fixed infusion speed of 5.2 micrograms/s was used throughout the 3 periods, the average rates of NIC were not significantly different each other, but when the infusion speed was changed from 5.2 to 1.3, and then to 0.3 micrograms/s, the average rates significantly decreased. The plasma level following a single-dose infusion of NIC 30 micrograms/kg positively correlated with the infusion speeds. These results indicate that the reinforcing effect of NIC is a function of the infusion speed, most likely through elevation of the peak level of NIC in the plasma.