Disruptive effects of d-amphetamine on conditioned sexual inhibition in the male rat.

Rationale: Male rats trained to associate a neutral odor (almond) with nonreceptive females during their initial sexual experiences develop a conditioned sexual inhibition (CSI) toward the female bearing the olfactory cue when given a choice in a final copulatory preference test between two receptive females (one unscented and one scented) in an open field. We have previously shown that this CSI can be abolished by acute alcohol before the final copulatory preference test.

Objective: To examine whether acute treatment with d-amphetamine could also disrupt CSI.

Methods: Male rats received 20 alternating conditioning sessions with an unscented receptive female or an almond-scented non-receptive female. Forty minutes prior to the copulatory preference test with two receptive females, one unscented and the other scented (almond extract), males were injected with saline or one of three doses of d-amphetamine (d- 0.5, 1.0, or 2.0 mg/kg). After two reconditioning trials, males were injected with d-amp or saline and exposed to the olfactory cue alone for 1 h. Brains were fixed and processed for immunohistochemical analysis of Fos protein as a marker of neuronal activation. Fos expression was assessed in several brain regions involved in male sexual behavior.

Results: Saline-treated males displayed inhibition of copulatory behavior directed toward the scented female. In contrast, and regardless of the dose, males treated with d-amp prior to the final test copulated with both scented and unscented females, indicating that d-amp disrupted the CSI. Exposure to d-amphetamine and the odor alone induced a differential pattern of Fos expression in several brain areas involved in the expression and/or the regulation of male sexual behavior.

Conclusions: As observed previously with alcohol, a low dose of d-amphetamine disrupted the display of a CSI by acting on brain regions mediating sexual behavior.