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Expression of testosterone conditioned place preference is blocked by peripheral or intra-accumbens injection of
M G Packard1, J P Schroeder, G M Alexander
1Department of Psychology, University of New Orleans, Louisiana 70148, USA.
Abstract:
Previous evidence indicates that peripheral and intranucleus accumbens injections of testosterone have rewarding effects in male rats as measured in a conditioned place preference (CPP) paradigm. The present study investigated the neurochemical bases of the rewarding properties of testosterone by examining the effect of peripheral and intranucleus accumbens injection of the dopamine receptor antagonist alpha-flupenthixol on expression of testosterone-induced CPP. On alternating days, adult male Long-Evans rats received peripheral injections of testosterone in a water-soluble hydroxypropyl-beta-cyclodextrin (HBC) inclusion complex (0.8 mg/kg) or saline-HBC immediately prior to being confined for 30 min to one of two compartments of a place preference apparatus. All rats received 8 days of pairings (four hormone pairings, four saline pairings). On day 9 the rats were given a 20-min test session during which they had access to all compartments of the apparatus. No hormone was injected prior to the test session; however, rats received a peripheral (20 min prior; 0.2, 0.3 mg/kg) or intra-accumbens (2 min prior, 5.0 micrograms) injection of alpha-flupenthixol or saline. On the test day, rats receiving saline injections spent significantly more time in the compartment previously paired with injections of testosterone than in the compartment previously paired with vehicle injections. In contrast, rats receiving peripheral or intra-accumbens alpha-flupenthixol injections did not spend significantly more time in the compartment previously paired with testosterone. The blockade of testosterone CPP was not due to an effect of alpha-flupenthixol on motor behavior. The findings provide further evidence of the rewarding affective properties of testosterone and indicate that peripheral administration and intra-accumbens administration of alpha-flupenthixol block expression of testosterone CPP. The rewarding affective properties of testosterone are mediated, at least in part, via an interaction with the mesolimbic dopamine system.