Sacro-lumbar Intersegmental Spinal Reflex in Autonomic Pathways Mediating Female Sexual Function

Introduction. Autonomic neurons in paracervical ganglia mediating vasodilation in the female reproductive tract receive inputs from both midlumbar and sacral spinal levels. However, it is not known how the lumbar pathways are activated. Aim. This study tested whether stimulation of pudendal sensory nerve could activate lumbar spinal outflows to paracervical ganglia via a spinal reflex pathway. Methods. Isolated spinal cords with attached peripheral nerves were removed from urethane-anesthetized female guinea pigs and perfused via the aorta with physiological salt solution. Spinal pathways to midlumbar preganglionic neurons were tested by recording extracellular compound action potentials (CAPs) in lumbar splanchnic or distal hypogastric nerves after electrical stimulation of thoracic spinal cord or the pudendal nerve. CAPs also were recorded from pelvic nerves after pudendal nerve stimulation. Sensory neurons were retrogradely traced from the pudendal nerve and characterized immunohistochemically. Main Outcome Measures. Activation of preganglionic neurons projecting from midlumbar spinal cord to paracervical ganglia following stimulation of pudendal sensory nerves in isolated preparations. Results. Thoracic spinal cord stimulation produced CAPs in hypogastric nerves that were abolished by transection of L3 lumbar splanchnic nerves. Pudendal nerve stimulation produced CAPs in L3 lumbar splanchnic, hypogastric, and pelvic nerves, demonstrating an ascending intersegmental spinal circuit to midlumbar levels in addition to the sacral spinal circuit. These CAPs in hypogastric nerves were enhanced by bicuculline (10μM), blocked by tetrodotoxin (1μM) but were not affected by hexamethonium (200μM). Retrograde axonal tracing revealed four groups of sensory neurons in S3 dorsal root ganglia that were distinguished immunohistochemically. Conclusion. Midlumbar preganglionic neurons projecting to paracervical ganglia regulating blood flow and motility in the female reproductive tract can be activated by an ascending intersegmental spinal pathway from pudendal sacral inputs, which is inhibited by local spinal circuits. This pathway will help understand pathological conditions affecting reproductive function.