These experiments were undertaken to examine whether both premotoneuronal mechanisms and direct actions on motoneurons could contribute to suppression of excitatory perineal reflex pathways during micturition. Intracellular recordings were obtained from motoneurons innervating the external urethral sphincter (EUS), external anal sphincter (EAS), and selected hindlimb muscles in decerebrate male cats. The peak amplitudes of EPSPs evoked by electrical stimulation of peripheral cutaneous afferents were measured during micturition. In the EUS, EAS, and hindlimb motoneurons examined, EPSPs produced by stimulation of perineal afferents (superficial perineal or sensory pudendal nerves) were reduced in amplitude during micturition. The sample of PSPs evoked by stimulation of hindlimb cutaneous nerves recorded in hindlimb motoneurons revealed that these PSPs could also be reduced. In contrast, no changes were seen in monosynaptic EPSPs evoked by muscle afferent stimulation. The present study demonstrates that during micturition there is a strong suppression of perineal reflexes to both sphincter and hindlimb motoneurons. Since reduced EUS activity is required for efficient micturition, suppression of the strong excitatory perineal input to EUS motoneurons 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 achieve this reflex suppression. The function of the micturition-related reduction of perineal reflexes to hindlimb or EAS motoneurons is not known at this time and further investigations are required to elucidate the interaction between micturition circuitry and hindlimb cutaneous pathways.

The musculotropic action of dicyclomine hydrochloride in bladder muscle has been attributed to its local anesthetic activity. In this study rabbit detrusor strips were depleted of calcium by incubation in Ca2+-free solution containing ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA). Contractions elicited by replacement of Ca2+ during depolarization with 80 mM K+ were only slightly affected by atropine or scopolamine but were antagonized in a noncompetitive manner by dicyclomine and rociverine (pD2' = 4.89 and 4.61, respectively). These contractions were also blocked with greater potency by nifedipine (pD2' = 8.50) and with lesser potency by lidocaine (pD2' = 2.52). Procaine was ineffective up to 1 mM. Comparison of the antagonism produced by dicyclomine and rociverine with that produced by nifedipine or lidocaine did not help to define the mechanism of the musculotropic drugs. However, as rociverine is not a local anesthetic and procaine was not effective, it appears that the "local anesthetic" property is not sufficient to explain the action of these musculotropic drugs.

No abstract