Reflexes evoked by electrical stimulation of afferent axons in the pudendal nerve under empty and distended bladder conditions in urethane-anesthetized rats

Abstract

This study examined reflex mechanisms that mediate urinary bladder and external urethral sphincter (EUS) coordination in female Sprague-Dawley urethane-anesthetized rats under empty and distended bladder conditions. The bladder was distended either by a small balloon or a saline filled catheter inserted through the body of the bladder. Stimulation of the entire pudendal nerve elicited short latency (8-12 ms) responses in the EUS and short (3-8 ms) and long latency responses (16-20 ms) in contralateral pudendal nerve. The long latency pudendal-pudendal reflex was reduced by 36.7% in area during bladder distension with the balloon catheter. However, there was no significant change in the area of pudendal-EUS reflex during bladder distension. Peak amplitudes of both reflexes were reduced 32% by bladder distension. The effects of glutamatergic receptor antagonists on the reflexes were also examined. MK801 (0.3-5 mg/kg, i.v.), an N-methyl-D-aspartate glutamatergic receptor antagonist, markedly depressed the pudendal-pudendal reflex, but LY215490 (3 mg/kg, i.v.), an alpha-amino-5-methyl isoxazole-4-propionate antagonist, had a minimal inhibitory effect. Both glutamatergic receptor antagonists significantly suppressed the pudendal-EUS reflex. These results indicate that the EUS is innervated by multiple pathways and that glutamatergic excitatory transmission is important in the neural mechanisms underlying bladder-sphincter coordination in the rat.

Serotonergic drugs and spinal cord transections indicate that different spinal circuits are involved in external urethral sphincter activity in rats

“…Asynchronous tonic and bursting EUS EMG activity and pelvic-EUS reflexes were rectified and measured by integrating the area under the curve (AUC) (mV-ms or V-ms) with a personal computer (2,3,12,24). The tonic and bursting EUS EMG activity were measured over the same length of time (1 s) in every experiment.…”

“…The ER also has a short central delay (3-4 ms) (1), comparable to that of the spinal micturition reflex. Similarly, EUS reflex activity and reflexes in pudendal nerve motor axons elicited by electrical stimulation of afferent axons in the pudendal nerve (i.e., the pudendal-EUS reflex) also occur after a short central delay (4.5-8.5 ms) (3,23). Thus the long central delay of the spinal LR stands in marked contrast to the short central delays of other spinal reflexes involved in LUT function.…”

“…8-OH-DPAT (Sigma, St. Louis, MO) and WAY100635 (Sigma) were dissolved in normal saline for intravenous administration. Drug doses were calculated for the base of each compound and selected based on results from previous experiments (2,3,14,27). Single doses of 8-OH-DPAT (1 mg/kg) and WAY100635 (1 mg/kg) were administered intravenously.…”

“…The large-amplitude tonic activity was reduced and the EUS bursting during voiding was eliminated. Trace 3 is a fast sweep of the period (3) showing that EUS bursting was eliminated by WAY100635, leaving only tonic EUS activity when the bladder pressure increased during a micturition reflex. C2: after WAY100635 the burst firing of the LR was suppressed.…”

Spinal neurons activated in response to pudendal or pelvic nerve stimulation in female rats

“…The pelvic nerve regulates bladder contractions and the pudendal motor nerve controls external urethral sphincter activity. Recent studies have suggested that the pudendal sensory nerve can modulate micturition, possibly through a positive feedback loop by regulating the excitatory drive of the parasympathetic neurons [11,16]. Stimulation of the pudendal sensory nerve also increases vaginal blood flow (author's unpublished observations).…”