Participation of hippocampal formation in negative feedback inhibition of penile erection in the rat

Detailed information on how the central nervous system regulates penile erection, particularly the inhibitory aspect, is sparse. We observed in Sprague-Dawley rats anesthetized and maintained with chloral hydrate that administration of papaverine (400 μg) directly into the corpora cavernosum of the penis produced an increase in intracavernous pressure (ICP). This elicited experimental index for penile erection was accompanied by a transient increase in the root mean square values, concurrent with a shift in the contribution of Θ (increase) and δ (decrease) power to the hippocampal electroencephalographic (hEEG) activity. Reversal blockade of these hEEG responses with xylocaine, given either intrathecally at the L6-S1 spinal levels or unilaterally to the hippocampal formation, significantly heightened and prolonged the ICP response. Pretreatment with xylocaine by itself, however, did not alter appreciably the baseline ICP or hEEG activity. These results suggest the presence of a novel negative feedback inhibitory mechanism in the hippocampal formation, which is triggered by ascending sensory inputs initiated by tumescence of the penis during normal erectile processes.