In precollicular decerebrate cats and dogs the intravenous administration of naloxone reduced urinary bladder capacity. Successive cystometrograms revealed that naloxone in doses of 10–100 µg/kg i. v. reduced the volume necessary to evoke micturition by 21–67% (mean 48%) in cats and 15–81% (mean 43%) in dogs, respectively. Microinjection of fentanyl (0.4–10 nM) into the pontine micturition center (PMC) increased the bladder capacity by 4–46% (mean 18%) in cats. Naloxone injected into the same site reversed the effect of fentanyl. Microinjection of naloxone (40–120 nM) into the PMC reduced the bladder capacity by 17–57% (mean 34%) in cats. These data indicate that endogenous opioid peptides may have a role in controlling micturition in both decerebrate cat and dog, and that the enkephalinergic inhibitory mechanisms are important in modulating the micturition reflex at the level of the pontine micturition center.
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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