REDUCTION OF PERINEAL EVOKED EXCITATORY POSTSYNAPTIC POTENTIALS IN CAT LUMBAR AND SACRAL MOTONEURONS DURING MICTURITION

These experiments were undertaken to examine whether both premotoneuro nal mechanisms and direct actions on motoneurons could contribute to s uppression of excitatory perineal reflex pathways during micturition. Intracellular recordings were obtained from motoneurons innervating th e external urethral sphincter (EUS), external anal sphincter (EAS), an d selected hindlimb muscles in decerebrate male cats. The peak amplitu des of EPSPs evoked by electrical stimulation of peripheral cutaneous afferents were measured during micturition. In the EUS, EAS, and hindl imb motoneurons examined, EPSPs produced by stimulation of perineal af ferents (superficial perineal or sensory pudendal nerves) were reduced in amplitude during micturition. The sample of PSPs evoked by stimula tion of hindlimb cutaneous nerves recorded in hindlimb motoneurons rev ealed that these PSPs could also be reduced. In contrast, no changes w ere seen in monosynaptic EPSPs evoked by muscle afferent stimulation. The present study demonstrates that during micturition there is a stro ng suppression of perineal reflexes to both sphincter and hindlimb mot oneurons. Since reduced EUS activity is required for efficient micturi tion, suppression of the strong excitatory perineal input to EUS moton eurons likely contributes to decreased EUS activity during the bladder contraction. It appears that the micturition circuitry utilizes both premotoneuronal mechanisms and direct motoneuronal inhibition to achie ve this reflex suppression. The function of the micturition-related re duction of perineal reflexes to hindlimb or EAS motoneurons is not kno wn at this time and further investigations are required to elucidate t he interaction between micturition circuitry and hindlimb cutaneous pa thways.