Serotonergic modulation of spinal ascending activity and sacral reflex activity evoked by pelvic nerve stimulation in cats

Clozapine inhibits micturition parameters and the external urethral sphincter during cystometry in anesthetized rats

Clozapine therapy has been associated with a high degree of urinary disturbances. The purpose of this study is to examine the effect of clozapine on urodynamic parameters and on the activity of the external urethral sphincter in anesthetized rats. Single cystometrograms (CMG) were performed on urethane-anesthetized female Sprague-Dawley rats, while also recording the EMG from the external urethral sphincter. Clozapine (0, 0.1, 1, 10 mg/kg) was administered intravenously. In addition, the peripheral end of the pudendal nerve was stimulated in order to determine if clozapine was exerting peripheral effects directly on the external urethral sphincter. Clozapine increased the bladder capacity while reducing the micturition volume thus resulting in a marked increase in the residual volume. The pressure threshold was increased but the peak pressure during contraction remained unchanged. The expulsion time and contraction time were decreased and the amplitude of the high frequency oscillations (HFO) seen during the expulsion phase were markedly reduced and even abolished. The EMG from the external urethral sphincter also showed marked decreases after clozapine, and the bursting pattern seen during HFO was abolished. Clozapine had no effect on the activity elicited from electrical stimulation of the pudendal nerve. Clozapine inhibits several urodynamic parameters and inhibits the activity of the external urethral sphincter in anesthetized rats. These effects may help explain the urinary disturbances reported in the clinical literature.

Effects of WAY100635, a selective 5-HT1A-receptor antagonist on the micturition-reflex pathway in the rat

5-Hydroxytryptamine (5-HT) receptors in the central nervous system have been implicated in the control of micturition. The present study was undertaken to evaluate the effects of a selective 5-HT1A-receptor antagonist [N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexanecarboxamide trihydrochloride (WAY100635)] on the micturition-reflex pathway in urethane-anesthetized female Wistar rats. Rhythmic isovolumetric bladder contractions evoked by bladder distension were abolished by 0.3- to 3-mg/kg iv or 30- to 100-microg intrathecal (it) administration of WAY100635 in a dose-dependent manner for periods of 3-15 min. Intrathecal injection of WAY100635 was effective only if injected at the L6-S1 spinal cord level, but not at the thoracic or cervical cord levels. WAY100635 (30-100 microg it) significantly reduced the amplitude of bladder contractions evoked by electrical stimulation of the pontine micturition center. However, the field potentials in the rostral pons evoked by electrical stimulation of pelvic nerve were not affected by intrathecal or intravenous injection of WAY100635. These results suggest that 5-HT1A receptors at the L6-S1 level of the spinal cord have an important role in the tonic control of the descending limb of the micturition-reflex pathway in the rat.

Coordination of the bladder detrusor and the external urethral sphincter in a rat model of spinal cord injury: effect of injury severity

Recovery of urinary tract function after spinal cord injury (SCI) is important in its own right and may also serve as a model for studying mechanisms of functional recovery after injury in the CNS. Normal micturition requires coordinated activation of smooth muscle of the bladder (detrusor) and striated muscle of the external urethral sphincter (EUS) that is controlled by spinal and supraspinal circuitry. We used a clinically relevant rat model of thoracic spinal cord contusion injury to examine the effect of varying the degree of residual supraspinal connections on chronic detrusor-EUS coordination. Urodynamic evaluation at 8 weeks after SCI showed that detrusor contractions of the bladder recovered similarly in groups of rats injured with a 10 gm weight dropped 12.5, 25, or 50 mm onto the spinal cord. In contrast, the degree of coordinated activation of the EUS varied with the severity of initial injury and the degree of preservation of white matter at the injury site. The 12.5 mm SCI resulted in the sparing of 20% of the white matter at the injury site and complete recovery of detrusor-EUS coordination. In more severely injured rats, the chronic recovery of detrusor-EUS coordination was very incomplete and correlated to decreased innervation of lower motoneurons by descending control pathways and their increased levels of mRNA for glutamate receptor subunits NR2A and GluR2. These results show that the extent of recovery of detrusor-EUS coordination depends on injury severity and the degree of residual connections with brainstem control centers.

Non-linear membrane properties of sacral sphincter motoneurones in the decerebrate cat

1. Responses to pudendal afferent stimulation and depolarizing intracellular current injection were examined in sacral sphincter motoneurones in decerebrate cats. 2. In 16 animals examined, 2-10 s trains of electrical stimulation of pudendal afferents evoked sustained sphincter motoneurone activity lasting from 5 to >50 s after stimulation. The sustained response was observed in: 11 animals in the absence of any drugs; two animals after the intravenous administration of 5-hydroxytryptophan (5-HTP; <= 20 mg kg-1); one animal in which methoxamine was perfused onto the ventral surface of the exposed spinal cord; and two animals following the administration of intravenous noradrenergic agonists. 3. Extracellular and intracellular recordings from sphincter motoneurones revealed that the persistent firing evoked by afferent stimulation could be terminated by motoneurone membrane hyperpolarization during micturition or by intracellular current injection. 4. Intracellular recordings revealed that 22/40 sphincter motoneurones examined displayed a non-linear, steep increase in the membrane potential in response to depolarizing ramp current injection. The mean voltage threshold for this non-linear membrane response was -43 +/- 3 mV. Five of the 22 cells displaying the non-linear membrane response were recorded prior to the administration of 5-HTP; 17 after the intravenous administration of 5-HTP (<= 20 mg kg-1). 5. It is concluded that sphincter motoneurones have a voltage-sensitive, non-linear membrane response to depolarization that could contribute to sustained sphincter motoneurone firing during continence.

Transmission of afferent information from urinary bladder, urethra and perineum to periaqueductal gray of cat

The micturition reflex pathway is a supraspinal pathway. Anatomical tracing evidence is compatible with an involvement of the periaqueductal gray (PAG) in the ascending limb of this reflex. We tested the involvement of the PAG in receiving urinary tract- or perineum-related information and attempted to characterize this ascending path in terms of what type of information is being conveyed. Electrical stimulation of the pelvic nerves, which carry afferent information from the urinary bladder, evoked maximum field potentials in the caudal third of the PAG, primarily in the dorsal part of the lateral PAG and in the ventrolateral PAG. Since the regions activated by pelvic nerve stimulation differed from those activated by stimulation of the sensory pudendal or superficial perineal nerves, it is possible that specific pathways for different nerve inputs to the PAG exist. Sacral spinal cord neurons ascending to the PAG were identified by antidromic activation and then tested for inputs from pelvic, sensory pudendal or superficial perineal nerves. Of 18 units identified, only five received inputs from any of the peripheral nerves tested and only two projecting neurons received a pelvic nerve input. Thus the PAG may receive inputs from bladder and perineum, but the small proportion of cells with direct projections to the PAG receiving inputs from our test nerves implies that the major part of this pathway is not directly related to lower urinary tract function.