Response properties and anatomical organization of pontine and medullary units responsive to vaginal stimulation in the cat.

The response properties and anatomical organization in the brain stem of 234 pontine and 60 medullary genitally sensitive (GS) neurons were studied by single-unit recording in acutely prepared estrous and anestrous cats which were decerebrated under sodium pentothal or anesthetized with urethane. Pontine unit responses to vaginal probing were very pronounced and stimulus-bound, and involved a variety of response patterns. Most of the pontine GS neurons also responded to nociceptive stimuli and to a lesser degree, to innocuous somatic, extragenital visceral, and auditory stimuli. Among pontine GS cells recorded in estrous cats, responsiveness to innocuous somatosensory stimuli was more prevalent than among units in anestrous preparations (71% vs. 40%), and on the average, the units in estrous cats responded to stimulation of more regions of the body than did comparable units in anestrous animals. In recordings from the medulla in the decerebrate preparations, exclusive responsiveness to vaginal stimulation was observed in 22% of the GS neurons, contrasting with earlier results from urethane-anesthetized animals in which a greater degree of specificity was found. A close anatomical proximity existed between some medullary GS neurons and cells of nucleus ambiguus, including antidromically identified recurrent laryngeal nerve motor neurons, and between pontine cells and the trigeminal motor nuclei. Antidromic responses of GS neurons to stimulation of the brain stem revealed a projection from medullary GS neurons to the lateral tegmental field of the pons. Relatively few pontine GS neurons projected to the ipsilateral medulla. A strong synaptic influence upon medullary GS neurons, possibly or midbrain origin, descends from the lateral tegmental field of the pons.