The administration of GABA-transaminase inhibitors (GABA-TIs) to male rats reduces the proportion of mounts that result in intromissions. Copulatory pelvic thrusting remains normal, despite the fact that animals treated with GABA-TIs show gross deficiencies in other motor acts. In order to determine whether altered sexual behavior produced by GABA-TI could be due to deficiencies in activity of striated penile muscles, we recorded the electromyographic (EMG) activity of the ischiocavernosus (IC) muscle during copulation in male rats treated with sodium valproate. The duration of IC EMG bursts was reduced by sodium valproate in separate tests that allowed or prevented intromission. There was no effect on EMG amplitude or frequency. It is suggested that insufficient activity of the IC muscles reduces the likelihood of vaginal penetration. The actions of GABA may be localized to hypothalamic or brain stem nuclei with GABAergic projections to the spinal motoneurons controlling the IC muscles, or GABA may act directly on these neurons.
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