Electrophysiological techniques were used to examine the asynchronous and evoked activity on postganglionic nerves to the urinary bladder in the urethananesthetized rat. Distension of the bladder (0.4-0.6 ml) evoked reflex contractions of the bladder (mean intravesical pressure 28 cmH2O) and efferent firing on postganglionic nerves. Electrical stimulation of afferent and efferent axons in the pelvic nerve elicited short-latency (0.3-11 ms) responses and long-latency (45-170 ms) reflexes on the nerves. The short-latency responses consisted of nonsynaptic axonal volleys with conduction velocities ranging from 0.5 to 11 m/s and synaptic responses with latencies of 6-11 ms. Stimulation of the pelvic nerve elicited late supraspinal reflexes (mean latency 122 +/- 28 ms) in 60% of normal rats and an early reflex (mean latency 56 +/- 5 ms) in 25% of those animals in which a late reflex was also identified. Early reflexes (mean latency 50 +/- 9 ms) were elicited in 100% of chronic spinal animals. The conduction time for the afferent and efferent limbs of the reflexes was calculated to be 7 and 58 ms, respectively, with a central delay of 57 ms for the late and less than 5 ms for the early reflex. It is concluded that sacral parasympathetic input to the urinary bladder of the rat is mediated by supraspinal and spinal reflex pathways. It is likely that in normal animals the late-occurring supraspinal reflex mediates micturition. The significance of the spinal reflex in the normal animals is uncertain; however, this reflex is essential for the generation of automatic micturition in chronic spinal preparations.

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Electrophysiological techniques were used to examine the axonal composition and reflex activity of the penile nerve of the rat. Stimulation of either the pelvic nerve, hypogastric nerve, or sympathetic chain elicited synaptic and axonal volleys in the penile nerve. Synaptic responses were suppressed by nicotinic ganglionic blockade, indicating that they were mediated by cholinergic transmission in peripheral ganglia. Axonal volleys represented in part afferent pathways from receptors in the pelvic muscles, perineum, and anus. Stimulation of the penile or pelvic nerves increased intracavernous pressure. Stimulation of the dorsal nerve of the penis elicited central reflexes (50- to 150-ms latencies) in the penile nerve. Those reflexes were not eliminated by acute or chronic spinalization (T8) but were abolished by transection of preganglionic nerves, indicating an origin in the lumbosacral spinal cord. Thus the penile nerves are composed of a heterogenous population of afferent and efferent axons. Reflex activity elicited in these nerves by stimulation of pathways from the penis is probably involved in the initiation of penile erection.

Micturition, which is mediated by a spinobulbospinal reflex pathway, can be modulated by various spinal and supraspinal mechanisms. This study examined modulation of the micturition reflex in decerebrate unanesthetized cats. Electrical stimulation of the pontine micturition center (PMC) elicited two types of bladder responses: small-amplitude short-duration responses due to direct activation of the bulbospinal pathway (PS-direct contractions) and large-amplitude long-duration reflex responses induced by PS-direct contractions but maintained by afferent feedback (PS-reflex contractions). Rectal and vaginal-cervical stimulation inhibited the PS-direct contractions, indicating inhibition of the descending or efferent limb of the micturition pathway. Stimulation of the central end of a transected S2 ventral root elicited recurrent inhibition of PS-reflex contractions but not of PS-direct contractions, indicating that recurrent inhibition does not directly affect the descending pathway. Continuous electrical stimulation (20 Hz) of the PMC decreased (53 +/- 21%) bladder capacity, presumably by affecting transmission in the pons or ascending input to the pons. Thus the micturition reflex could be modulated at several sites: the pons, the ascending or descending pathways, or spinal interneuronal sites.

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