Mediation of rat postejaculatory 22 kHz ultrasonic vocalization by dopamine D2 receptors

Abstract

We investigated the role of dopamine receptor subtypes in the regulation of ultrasonic vocalization and masculine copulatory behavior. Intact sexually experienced male Long-Evans rats were treated with saline, selective dopamine D1 (SKF 38393) and D2 (LY 171555) receptor agonists and with selective dopamine D1 (SCH 23390) and D2 (raclopride) receptor antagonists 15 and 30 min before the 30-min test session, respectively. Mating stimuli were ovariectomized female rats injected SC with estradiol benzoate (8 μg/0.1 ml/rat) and progesterone (200 μg/0.1 ml/rat), 48 and 4 hr before the test session, respectively. We found a decrease in the number of intromissions required to reach ejaculation in animals treated with SKF 38393 (10 mg/kg/IP), LY 171555 (doses ranging from 0.01 to 0.5 mg/kg/SC) and with raclopride (0.1 mg/kg/SC). LY 171555 reduced the postejaculatory vocalization (PEV) in a dose-dependent fashion with complete suppression at the highest dose. No other parameters of sexual behavior were affected by this treatment. Raclopride, a dopamine D2 receptor antagonist, antagonized the suppressive effects of the D2 agonist LY 171555 on the PEV (and also decreased the number of intromissions to reach ejaculation), whereas SCH 23390, a dopamine D1 receptor antagonist, did not. Raclopride, given alone at the dose of 0.5 mg/kg/SC, almost completely suppressed all behavioral activity, whereas the lower dose (0.1 mg/kg) decreased intromission frequency and increased the length of the 22 kHz PEV. Therefore, we suggest that 22 kHz PEV is under the control of dopamine D2 receptors.