Objective: In this study, the effects of bilateral injections of nicotinic cholinergic agents into the hippocampal CA1region of Wistar rats on morphine-induced conditioned place preference (CPP) was studied.
Method: All animals were canulated in the CA1 area of dorsal hippocampus by stereotaxic instrument. Each animal was allowed to recover 1-week before CPP induction. We used a 5-day schedule for CPP with three distinct phases: first, the preconditioning phase, second, the conditioning phase and finally, the testing or the expression phase.
Results: Subcutaneous administration of different doses of morphine sulphate (0.5-6mg/kg) produced a dose-dependent CPP. Using a 3-day schedule of conditioning, it was found that intra-CA1 administration of nicotine (0.5, 0.75, and 1mg/rat) with an ineffective dose of morphine (0.5mg/kg) elicited a significant CPP. Bilateral injections of different doses of the nicotinic receptor antagonist, mecamylamine (2, 4, and 8mg/rat) into the CA1 regions significantly inhibited the morphine (6mg/kg)-induced CPP. Moreover mecamylamine (8mg/rat, intra-CA1) decreased the effect of nicotine-induced potentiation of the morphine response.
Conclusion: Intra-CA1 injections of nicotine or mecamylamine alone did not induce a significant place preference or place aversion. It may be concluded that the nicotinic receptors of the hippocampal CA1 regions play an important role in morphine reward.
Type of Study:
Research |
Subject:
Special Received: 2007/03/14 | Accepted: 2007/04/21 | Published: 2007/06/22