From M.A. Bozarth & C.M. Pudiak (1996). Intravenous nicotine self-administration in laboratory animals: Chasing the enigma. Society for Neuroscience Abstracts, 22, 163.
INTRAVENOUS NICOTINE SELF-ADMINISTRATION IN LABORATORY ANIMALS: CHASING THE ENIGMA. M.A. Bozarth* & C.M. Pudiak. Addiction Research Unit, Department of Psychology, University at Buffalo, Buffalo, NY 14260.
Two standard intravenous self-administration procedures effective in demonstrating cocaine and heroin reinforcement were used to assess the reinforcing effect of nicotine—direct acquisition and cross-substitution procedures. The first experiment examined the ability of nicotine to establish self-administration behavior. Experimentally naive rats were tested using 10-hr sessions for a total of 20 days. Manipulations which enhance responding were not used, e.g., lever training, food deprivation. The second experiment examined the ability of nicotine to maintain responding in animals previously trained to intravenously self-administer cocaine (1 mg/kg/inf). Various nicotine doses were substituted for the reinforcing cocaine injections during 3-hr self-administration tests; each nicotine dose was tested for 5 consecutive days. Both studies used nicotine bitartrate (10, 30, or 100 mg/kg/inf; dose expressed as free-base weight; solution pH adjusted to 7 ± 0.2) infused in a 0.25 ml/500 g volume over 30 sec/500 g.
In the direct acquisition study, several rats showed periodic response levels suggesting nicotine self-administration during some days of testing. However, nicotine intake was erratic both across days and within sessions even for these subjects. When tested for cocaine self-administration after completion of the nicotine tests, all subjects showed reliable cocaine self-administration. In the cross-substitution study, response rates for 10 and 30 mg/kg/inf nicotine unit-doses exceeded saline response rates. However, both nicotine doses produced nearly identical intake patterns decreasing across the 5-day tests. The 100 mg/kg/inf nicotine dose failed to maintain responding above saline levels.
These data suggest that nicotine does not serve as an effective reinforcer when tested using standard procedures that readily demonstrate intravenous cocaine and heroin reinforcement. Unlike the self-administration of highly addictive drugs, nicotine self-administration appears enigmatic, requiring special testing conditions. This finding is consistent with other tests suggesting the reinforcing efficacy of nicotine is very low.
Supported by Philip Morris Research Center (Richmond, VA).
© 1997 Addiction Research Unit/University at Buffalo
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