Time-dependent changes in nicotine behavioral responsivity during early withdrawal from chronic cocaine administration and attenuation of cocaine sensitization by mecamylamine.
Cocaine abuse is associated with a high prevalence of nicotine dependence. In animals, nicotinic antagonists have been reported to block the development of cocaine behavioral sensitization and to attenuate cocaine place preference or self-administration. In the present study, we have determined: (1) changes in the locomotor responses to nicotine challenge during the first week of withdrawal from daily cocaine pretreatment; and (2) effects of the non-selective nicotinic acetylcholine receptor (nAChR) antagonist mecamylamine given during the first 5 days of cocaine withdrawal on the maintenance of cocaine behavioral sensitization. Male Sprague-Dawley rats were pretreated with daily saline (SI) or cocaine (CI) injections for 14 days. In Experiment 1, separate animals in the SI and CI groups received a single nicotine challenge on day 1, 3, or 7 of withdrawal from their respective pretreatments. The CI group displayed enhanced locomotor responses to nicotine as compared to SI controls on days 3 and 7 of withdrawal, but not day 1. In Experiment 2, SI and CI animals were treated once a day with either saline or mecamylamine during the first 5 days of withdrawal, and were subsequently challenged with single cocaine injections on both withdrawal days 7 and 14. Mecamylamine treatment significantly attenuated expression of cocaine behavioral sensitization on both withdrawal days 7 and 14. Time-dependent changes in nicotinic responses occur during the first week of cocaine withdrawal, and intact nAChR neurotransmission during this period may be necessary for maintenance of cocaine behavioral sensitization.
Szabo, ST; Fowler, JC; Froeliger, B; Lee, TH
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