Social and environmental influences on opioid sensitivity in rats: importance of an opioid's relative efficacy at the mu-receptor.

Rationale: Evidence indicates that social and environmental enrichment can influence the functional maturation of the central nervous system and may affect an organism's sensitivity to centrally acting drugs.

Objective: The purpose of the present study was to examine the effects of social and environmental enrichment on sensitivity to mu-opioids possessing a range of relative efficacies at the mu-receptor.

Methods: Rats were obtained at weaning (21 days) and divided into two groups immediately upon arrival.

Effects of positive allosteric modulators of the GABAB receptor on cocaine self-administration in rats.

Rationale: Previous studies have strongly implicated a role for GABA(B) receptors in modulating the reinforcing effects of cocaine.

Objective: The purpose of the present study was to examine the efficacy of two novel positive allosteric modulators of the GABA(B) receptor, CGP7930 and GS39783, to decrease cocaine self-administration in rats responding under various schedules of reinforcement.

Methods: Rats were trained to self-administer cocaine under progressive ratio (PR), fixed ratio (FR) and discrete trials (DT) schedules of reinforcement, and the ability of CGP7930 and GS39783 to decrease cocaine-maintained responding was examined.

Sensitivity to the effects of opioids in rats with free access to exercise wheels: mu-opioid tolerance and physical dependence.

Rationale: Exercise stimulates the release of endogenous opioid peptides and increases nociceptive (i.e. pain) thresholds in both human and animal subjects.