PRIMARY AFFERENT DEPOLARIZATION OF CAT PUDENDAL AFFERENTS DURING MICTURITION AND SEGMENTAL AFFERENT STIMULATION

1. This investigation examined primary afferent depolarization (PAD) o f perineal afferents during micturition and evoked by electrical stimu lation of perineal, hindlimb cutaneous and muscle-nerves. PAD was infe rred from changes in excitability of spinal terminals of single affere nts in decerebrate and chloralose-anaesthetized paralysed male cats. O bservations were made on perineal afferent fibres travelling in the se nsory branch of the pudendal (SPud) and superficial perineal (SPeri) n erves. 2. Micturition was evoked by distension of the bladder and exci tability changes were measured in twenty-seven SPud afferents. In ten afferents, there was evidence of PAD during micturition. The time cour se of PAD was similar to the period of decreased activity in sphincter muscle efferents during micturition. In four afferents, there was dec reased excitability during voiding that was interpreted as removal of tonic PAD. In the remaining thirteen afferents there were no detectabl e changes in excitability. Bladder distension in the absence of mictur ition failed to change the excitability of any SPud afferents tested. 3. Almost all SPud afferents were subject to PAD upon stimulation of c utaneous nerves. Superficial perineal, long saphenous, caudal cutaneou s sural and the predominantly cutaneous posterior tibial nerves were p articularly effective in evoking PAD. While group I strength stimulati on of hindlimb muscle-nerves produced PAD of some SPud fibres, group I I stimulation often increased the magnitude or incidence of PAD. The p atterns and magnitude of PAD observed in SPeri afferents were similar to those observed in SPud afferents. 4. Since some SPud afferents were subject to PAD during micturition, PAD is probably one mechanism resp onsible for suppression of sphincter reflexes during micturition. Addi tional roles of PAD of perineal afferents evoked by activation of hind limb cutaneous and muscle afferents are discussed.