Mechanisms of penile erection during REM sleep regulated by the hypothalamo-limbic system.

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To elucidate the mechanisms involved in regulation of penile erection during REM sleep, we electrically stimulated the proptic/hypothalamic areas, in and around the brainstem cholinergic neurons (larerodorsal tegmental nucleus, LDT) and recorded the neuronal activity in the LDT.Spontaneous normal penile erection pattern is composed of slow increase of pressure in corpus spongeneosum of the penis (CSP) and sharp increase in CSP pressure synchronized with burstic bulbospongiosus (BS) muscle activity. In unanesthetized, head-restrained rats, penile erection which was almost similar to the normal spontaneous one was evoked after the electrical stimulation to the medial preoptic area (MPOA), lateral preoptic area (LPOA), paraventricular nucleus (PVN) or bed nucleus of stria terminalis (BST). Among them, latency of the response was shorter in the PVN. In urethane anesthetized rats, erection was evoked only from the MPOA and PVN. Erection was evoked also in and around the LDT. In some areas, the evoked erection pattern was almost normal, while in other areas only the slow increase in CSP pressure or sharp increase of CSP pressure and BS muscle activity was observed. Some of the the cholinergic neurons in the LDT showed phasic firing before the sharp CSP increase, while others showed tonic increase for several seconds before the initiation of erection.These results indicate that lateral part and medial part of the preoptic area are involved in penile erection in different way. PVN is the final out put in the hypothalamus for penile erection. The LDT contains systems which selectively activate the component of penile erection and those which inhibit penile erection.