[Rapid establishment of nicotine intravenous self-administration behavior in rats]

The reinforcing effect of nicotine was investigated using the intravenous self-administration method in rats. After forced iv injection of nicotine (3, 10 and 30 micrograms/kg/inj) at 1-hr intervals for 3 days in 3 dose-level groups, self-administration sessions under the continuous reinforcement schedule were carried out for 15 days. Rats initiated self-administration of nicotine rapidly in 10 and 30 micrograms/kg/inj groups. Daily self-administration responses by nicotine (30 micrograms/kg/inj) were 3-10 times the control levels. Total self-administration responses for 15 days increased in a dose dependent manner. When the fixed ratio was increased from 1 to 4 and 8 after the 15 days self-administration session in the nicotine (10 and 30 micrograms/kg/inj) groups, lever press responses increased only about 2 times, and self-administration responses decreased in the both groups. These findings suggest that nicotine becomes a reinforcer rapidly, but the magnitude of reinforcing effect is relatively week after the acquisition of nicotine for a short period.