Responses of Medullary Reticular Formation Neurons to Input from the Male Genitalia. Hubscher, Charles H. and Richard D. Johnson. Department of Physiological Sciences, College of Veterinary Medicine and University of Florida Brain Institute, University of Florida, Gainesville, FL 32610-0144.
APStracts 3:0110N, 1996.
SUMMARY AND CONCLUSIONS
1. The medullary reticular formation (MRF) is known to be involved in the modulation of certain reproductive behaviors. Ejaculation in the male, disrupted after spinal transection, may depend on a spinal-bulbo-spinal connection. To determine if single neurons in the MRF receive sensory input from the male genitalia, the present study was undertaken using electrophysiological techniques. 2. The MRF of 14 urethane-anesthetized mature male rats was searched for single neurons responsive to bilateral electrical stimulation of the dorsal nerve of the penis (DNP). In addition, each DNP- responsive neuron was tested for responsiveness to bilateral electrical stimulation of the pelvic nerve (PN) and to mechanical stimulation (gentle touch, pressure, pinch) of the external genitalia, anus, urethra and skin over most regions of the body. 3. A total of 165 single neurons responsive to bilateral electrical stimulation of the DNP were isolated and characterized throughout the MRF. All neurons responded to both ipsilateral and contralateral DNP stimulation. The majority of responses were excitatory and most neurons had no background activity. Some neurons required wind-up with bilateral electrical stimulation of the DNP in order to respond. 4. About half of the neurons were located in the nucleus reticularis gigantocellularis (Gi); the remainder were located in surrounding (dorsal, ventral, lateral) regions of the MRF. Variations in response properties were found among neurons located in different MRF regions. 5. Eighty-eight DNP-responsive neurons were additionally responsive to bilateral electrical stimulation of the PN. None of the responses to bilateral PN were stronger than those for bilateral DNP and many (48%) were weaker. 6. Of the 165 DNP-responsive neurons, all were responsive to pressure/pinching of the penis; 16% responded to gentle stroking of the glans. Most of these neurons were additionally responsive (bilaterally) to pinching more than one (often all) of the following areas: perineum, scrotum, anus, ears, and toes (forefoot and hindfoot). 7. In conclusion, neurons located in the MRF of male rats are involved in the processing of bilaterally convergent inputs from multiple cutaneous and visceral regions of the body, including the penis and male urogenital tract. These neurons likely exert their effects by directly and/or indirectly activating (i) ascending pathways to rostral regions of the brain important for somatovisceral sensation and motor behavior, and (ii) descending pathways to the spinal cord for modulation of segmental sexual reflexes. Contributions are likely for a wide spectrum of sensations and reproductive behaviors.

Received 21 February 1996; accepted in final form 14 May 1996.
APS Manuscript Number J136-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 17 June 96