MORPHOLOGICAL AND ELECTROPHYSIOLOGICAL ANALYSIS OF THE PERIPHERAL ANDCENTRAL AFFERENT PATHWAYS FROM THE CLITORIS OF THE CAT

Afferent neurons projecting to the clitoris of the cat were identified by WGA-HRP tracing in the S1 and S2 dorsal root ganglia. An average o f 433 cells were identified on each side of the animal. 85% and 15% of the labeled cells were located in the S1 and S2 dorsal root ganglia, respectively. The average cross sectional area of clitoral afferent ne uron profiles was 1,479 +/- 627 mu m(2). Unilateral transection of the pudendal nerve reduced the number of labeled cells to 1% of that on t he control side. Central projections of clitoral afferents were identi fied in the lumbo-sacral segments (L7-S3) of the spinal cord. HRP labe led fibers were located in the marginal zone on the medial side of dor sal horn and extended into the dorsal half of the dorsal gray commissu re. Electrophysiological recordings detected axonal volleys in the pud endal nerve and S1 dorsal root in response to electrical stimulation ( threshold, 1-4 V) of the clitoral surface. Estimated axonal conduction velocities at the two sites ranged from 7-27 m/s and 0.6-30 m/s, resp ectively. Multi-unit recordings from dorsal roots in the lumbo-sacral segments revealed that non-noxious pressure stimulation of the clitori s evoked discharges in the 81 dorsal root. Small increases were also d etected in the S2 and L7 roots. Single unit discharges recorded from 1 dorsal roots were activated by electrical stimulation of the clitoral surface at thresholds of 0.6-1.2 V and latencies of 1.5-1.8 ms (estim ated conduction velocities of 24-30 m/s). Light constant pressure on t he clitoris produced an initial burst of single unit firing (maximum f requencies 170-255 Hz) followed by rapid adaptation and a sustained fi ring (maximum 30 Hz) which was maintained during the stimulation, Toni c firing increased to an average maximum of 145 Hz at 6-8 g/mm(2) pres sure. These results indicate that the clitoris is innervated by mechan o-sensitive myelinated afferent fibers in the pudendal nerve which pro ject centrally to the region of the dorsal commissure in the L7-S1 spi nal cord.