Effects of lesions in the lateral medulla on mating and responses to genital stimulation in female cats

Forebrain influences on brainstem and spinal mechanisms of copulatory behavior: a current perspective on Frank Beach's contribution

In a 1967 Physiological Reviews paper, Frank Beach put forth four propositions regarding forebrain and hormonal control of brainstem-spinal mechanisms of copulatory behavior. Simply stated, he proposed that: 1) the forebrain exerted an inhibitory control over species-typical copulatory reflexes through descending effects on brainstem-spinal mechanisms and 2) gonadal hormones influence these reflexes largely by actions on forebrain control processes rather than by direct effects on the brainstem or spinal cord. This theoretical scheme was of great heuristic significance during the subsequent two decades of research, which has largely supported and delineated in greater mechanistic detail the processes Beach hypothesized to exist. This subsequent research has also shown the central nervous system actions of gonadal hormones to be more widespread and complex than Beach proposed. Some of these recent research findings are presented, with emphasis on neurophysiological studies which have identified hormone-induced functional changes in forebrain and brainstem neurons. It is proposed that these functional changes may represent a mechanism for the behavior-controlling actions of hormones that were hypothesized by Beach.

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.