Effects of acute and chronic midthoracic spinal cord injury on neural circuits for male sexual function. I. Ascending pathways.

Normal male reproductive function, particularly ejaculation, requires the integrity of urogenital sensory input and its ascending spinal projections. After midthoracic chronic spinal cord injury, sexual dysfunction occurs in both rats and humans. Neurons in the medullary reticular formation (MRF) are involved in the processing of bilaterally convergent sensory inputs from multiple cutaneous, mucocutaneous, and visceral regions of the body, including the penis and male urogenital tract. A variety of acute and chronic lesions were used to determine the midthoracic location of ascending spinal pathways conveying sensory input from the penis and male urogenital tract to MRF. A total of 371 single neurons were recorded in the MRF of 34 urethan-anesthetized mature male rats. Twenty-seven rats received a chronic T8 dorsal (DHx) or lateral (LHx) hemisection or contusion (Cx) injury 30 days before the terminal electrophysiological experiments. In addition, nine dorsal nerve of the penis (DNP)-responsive MRF neurons in seven intact control animals were tested completely both before and after various select acute spinal cord lesions. The chronic lesion data indicate that low and high threshold input from the penis (mucocutaneous) and male urogenital tract (visceral) ascend bilaterally within the dorsal quadrant at T8 as opposed to high threshold input from the hindpaws (cutaneous), which ascends unilaterally in the ventrolateral quadrant (VLQ). The acute lesion data indicate that the low-threshold information conveyed from the penis and male urogenital tract ascends in the dorsal columns, as opposed to the high-threshold nociceptive inputs that ascend bilaterally in the dorsolateral quadrant (DLQ). These results, as well as previous data on ascending projections from female reproductive organs within the dorsal columns and DLQ to other caudal brain stem nuclei, provide evidence for ascending pathways conveying nociceptive information centrally via the DLQ. This spinal gray-DLQ pathway(s) conveying information from mucocutaneous/pelvic/visceral territories therefore differs from the traditionally recognized spinal gray-VLQ pathway(s), which is known to convey nociceptive information from cutaneous regions of the body.