The activation of gamma aminobutyric acid(A) receptors in the paraventricular nucleus of the hypothalamus reduces non-contact penile erections in male rats

Male rats show 4-6 penile erection episodes when put in the presence of an inaccessible receptive female. These noncontact penile erections were reduc ed dose-dependently by muscimol, a gamma aminobutyric acid (GABA)A receptor agonist, when given into the paraventricular nucleus of the hypothalamus ( 0.1, 0.5, 1 and 2 mug). In contrast, baclofen, a GABAB receptor agonist (2 mug) was ineffective. Muscimol reduction of non-contact penile erections wa s not seen when male rats were pretreated with bicuculline methiodide (2 mu g) given 5 min before muscimol into the paraventricular nucleus. Since musc imol injected into the paraventricular nucleus also prevents penile erectio n induced by drugs (e.g. apomorphine, oxytocin or N-methyl-D-aspartic acid) , the present results show that an increased GABAergic activity in the para ventricular nucleus can impair the expression of penile erection induced no t only by drugs but also by sexual physiological stimuli. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.