Effects of Nicotine and Cytisine on the Formation and Extinction of the Conditioned Active Avoidance Reflex in Rats

We studied the effects of nicotine and cytisine injected i.p. in equimolar doses (0.5 mu mol/kg) on the formation and extinction of the conditioned active avoidance reflex (AAR) in rats; a combination of conditioning acoustic stimulation and unconditioned nociceptive electrocutaneous stimulation was used for training. A stable AAR was formed more rapidly in the case of nicotine injections; the corresponding effect of cytisine injections did not attain a significance level (probably because of the weak effect of this cholinomimetic on AAR formation in slowly trained animals present in the tested group). Injections of both nicotine and cytisine in the course of formation of a stable AAR led to a significantly slower extinction of the conditioned reflex habit. Both cholinomimetics demonstrated such an effect with respect to both the entire animal population and rats with rapid extinction of the habit. Cytisine-induced slowing down of extinction of the AAR was more significant than the corresponding effect of nicotine. We postulate that the positive effects of cytisine and nicotine on maintenance of the AAR are mediated by activation of neuronal nicotine cholinoreceptors having the alpha 3 beta 4 subunit structure.