Nicotine conditions place preferences after intracerebral administration in rats

Abstract

A single-trial place conditioning procedure, one treatment and one non-treatment during two daily conditioning sessions followed by a single test session on the 3rd day, was used to examine the place conditioning effects of intracerebrally administered nicotine. In the first series of experiments, Sprague-Dawley male rats were implanted unilaterally with guide cannulas aimed at the lateral ventricle. After 1 week, rats received either “treatment” (nicotine in 2 µl phosphate buffer or 2 µl of buffer alone) or “no treatment” (no injections) before being placed in the black or white compartment of a three-compartment place-conditioning apparatus for 20 min. The next day the rats received the opposite treatment before being conditioned in the opposite compartment. On day 3, animals had free access to the entire apparatus for 15 min and the time spent in each compartment was recorded automatically. Even though the rats exhibited a baseline bias for the black compartment, intracerebroventricular nicotine induced positive place preferences relative to buffer control, i.e. if treatments were paired with the black compartment, nicotine enhanced the preference for the black compartment, and if the treatments were paired with the white compartment, nicotine induced a preference for the white compartment. In addition, the nicotine-induced preference response was antagonized by the co-intraventricular administration of mecamylamine. In a second series of experiments, animals were implanted unilaterally with guide cannulas aimed at the pendunculopontine tegmental nucleus of the mesopontine tegmentum. Nicotine microinjection, 1.2–18.5 nmol in 0.5 µl buffer, induced a dose-dependent positive place preference response. The place preference induced by 18.5 nmol nicotine was antagonized by co-administering 0.8 nmol mecamylamine; 0.8 nmol mecamylamine had no effects of its own. Finally, microinjections of 18.5 nmol nicotine 2 mm dorsal to the pedunculopontine tegmental nucleus did not condition place preferences. These data demonstrate that a sensitive site of action of the nicotine-conditioned place preference response in rats is within the mesopontine tegmentum.