[Pontine control of the internal urethral sphincter activity on decerebrate dogs]

The present study was performed to investigate the pontine control of the internal urethral sphincter (IUS) activity using 13 supracolicular decerebrate female dogs. The lower urinary tract function was evaluated by measuring the bladder and the IUS pressure and the external urethral sphincter (EUS) EMG. Bilateral ureters were cannulated and urine was drained extracorporeally. The bladder neck was ligated to induce a isovolumetric bladder contraction, and the urethra was separated from the bladder to evaluate the function of the bladder and the urethra separately. Electrical stimulation (ES) (0.3 m sec. pulse, 50 Hz, 10-100 microA, 3 sec.) in the pontine micturition center (PMC) was carried out using a microelectrode (10-30 microns in tip diameter). The sympathetic chains, hypogastric nerves and pelvic nerves were identified for preparing the nerve transection. 1) ES in the PMC evoked a bladder contraction and a relaxation of the IUS and EUS. This response was similar to the micturition reflex induced by slow filling of the bladder with saline. 2) The threshold intensity for evoking the IUS pressure drop (i.e. IUS relaxation) was equal to or lower than that for the bladder contraction. The latencies from the ES in the PMC to the IUS relaxation and to the bladder contraction were 0.24 +/- 0.14 sec. (mean +/- S.D.) and 0.42 +/- 0.08 sec., respectively. 3) ES in the PMC evoked the IUS relaxation even when the bladder was empty. 4) Transection of the sympathetic chains had no influence on the IUS relaxation by ES in the PMC. Transection of the hypogastric nerves not only decreased the urethral resting pressure but also reduced the urethral pressure drop by ES. Transection of the pelvic nerves abolished the IUS relaxation as well as the bladder contraction by ES. 5) Phentolamine decreased the urethral pressure between ESs and reduced the degree of the urethral pressure drop to the ES. Phenylephrine increased not only the urethral pressure between ESs but also the degree of the pressure drop by the ES. Propranolol and atropine die not affect the urethral pressure changes to the ESs. Hexamethonium abolished the urethral responses. These results indicate that the PMC regulates the IUS activity as well as the bladder activity. These results also suggest that the excitation of the PMC produces the IUS relaxation through the pelvic nerve pathway as well as the hypogastric nerve pathway. The IUS relaxation through the pelvic nerve pathway is mediated by non-adrenergic and non-cholinergic mechanisms.