RESPONSES OF MEDULLARY RETICULAR-FORMATION NEURONS TO INPUT FROM THE MALE GENITALIA

1. The medullary reticular formation (MRF) is known to be involved in the modulation of certain reproductive behaviors. Ejaculation in the m ale, disrupted after spinal transection, may depend on a spinal-bulbo- spinal connection. To determine whether single neurons in the MRF rece ive sensory input from the male genitalia, the present study was under taken using electrophysiological techniques. 2. The MRF of 14 urethan- anesthetized mature male rats was searched for single neurons responsi ve to bilateral electrical stimulation of the dorsal nerve of the peni s (DNP). In addition, each DNP-responsive neuron was tested for respon siveness to bilateral electrical stimulation of the pelvic nerve (PN) and to mechanical stimulation (gentle touch, pressure, pinch) of the e xternal genitalia, anus, urethra, and skin over most regions of the bo dy. 3. A total of 165 single neurons responsive to bilateral electrica l stimulation of the DNP were isolated and characterized throughout th e MRF. All neurons responded to both ipsilateral and contralateral DNP stimulation. The majority of responses were excitatory, and most neur ons had no background activity. Some neurons required wind-up with bil ateral electrical stimulation of the DNP to respond. 4. About half of the neurons were located in the nucleus reticularis gigantocellularis (Gi); the remainder were located in surrounding (dorsal, ventral, late ral) regions of the MRF. Variations in response properties were found among neurons located in different MRF regions. 5. Eighty-eight DNP-re sponsive neurons were additionally responsive to bilateral electrical stimulation of the PN. None of the responses to bilateral PN were stro nger than those for bilateral DNP and many (48%) were weaker. 6. Of th e 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 m ore than one (often all) of the following areas: perineum, scrotum, an us, ears, and toes (forefoot and hindfoot). 7. In conclusion, neurons located in the MRF of male rats are involved in the processing of bila terally convergent inputs from multiple cutaneous and visceral regions of the body, including the penis and male urogenital tract. These neu rons likely exert their effects by directly and/or indirectly activati ng ascending pathways to rostral regions of the brain important for so matovisceral sensation and motor behavior, and descending pathways to the spinal cord for modulation of segmental sexual reflexes. Contribut ions are likely for a wide spectrum of sensations and reproductive beh aviors.