Vesicourethral Function in Mice With Genetic Disruption of Neuronal Nitric Oxide Synthase:

Effects of anaesthesia on the nitrergic pathway during the micturition reflex in rats

OBJECTIVE

To investigate the effects of anaesthesia on the nitrergic pathway during the micturition reflex in rats.

MATERIALS AND METHODS

The effects of N(G)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthase, on bladder and urethral activities were evaluated by infusion cystometrography (CMG) and urethral perfusion pressure under isovolumetric conditions in awake or urethane-anaesthetized rats. L-NAME was administered intravenously (i.v.), intrathecally (i.t.), intracerebroventriculary (i.c.v.) or intravesically in normal rats or rats pre-treated with resiniferatoxin, a potent C-fibre afferent neurotoxin.

RESULTS

L-NAME injected i.v. decreased the intercontraction interval (ICI) in the awake but increased it in the anaesthetized rats. L-NAME injected i.t. increased the ICI in both states and these effects were not apparent after pre-treatment with resiniferatoxin. L-NAME injected i.c.v. decreased the ICI in the awake but increased i.t. in the anaesthetized rats. Intravesical L-NAME decreased the ICI in the awake but not in the anaesthetized rats. L-NAME administered i.v., but not i.t. or i.c.v., increased bladder contraction during CMG. Under isovolumetric conditions, L-NAME administered i.v., but not i.t. or i.c.v., reduced the urethral relaxation without changing bladder contraction.

CONCLUSIONS

These results indicate that spinal NO release facilitates the mechanoceptive C-fibres, and this facilitatory effect is masked by supraspinal (possibly forebrain) and local inhibitory effects of NO during the micturition reflex in awake rats. Urethane seems to inhibit the supraspinal and local inhibitory effects of NO, resulting in unmasking the facilitatory effect of NO in the spinal cord and brain stem. During the voiding phase, urethral relaxation depends on the peripheral but not the central NO system.

Interaction between neurotransmitter antagonists and effects of sacral neuromodulation in rats with chronically hyperactive bladder

OBJECTIVE

To investigate to what extent antagonists of spinal neurotransmitters interact with the effects of sacral neuromodulation in a rat model of a chronically hyperactive urinary bladder.

MATERIALS AND METHODS

In female rats the urinary bladder was instilled with turpentine oil 2.5% to induce cystitis. After surviving for 10 days the rats were anaesthetized with urethane, the bladder catheterized and connected to a pressure transducer. Stimulating electrodes were placed in the sacral foramina bilaterally. The spinal cord was exposed by a laminectomy, and a small pool was placed on the cord for intrathecal administration of neurotransmitter antagonists. Sacral neuromodulation was applied before and after administering the antagonists. The antagonists used were: memantine, an antagonist for N-methyl-D-aspartate (NMDA) receptors; CNQX, an antagonist for non-NMDA receptors, and L-NAPNA, a blocker of nitric oxide synthase.

RESULTS

With no electrical neuromodulation, memantine and L-NAPNA abolished the cystitis-induced bladder contractions for approximately 4 and approximately 37 min, respectively. The effect of CNQX was similar to that of artificial cerebrospinal fluid. Electrical sacral modulation with no antagonists also transiently abolished the bladder contractions; at the highest intensity used, the pause was 2-3 min. Superfusion of the spinal cord with CNQX reduced this effect of neuromodulation significantly, whereas memantine had no influence, and L-NAPNA increased the neuromodulation-induced pause.

CONCLUSIONS

The results suggest that non-NMDA receptors are involved in the effects of sacral neuromodulation, whereas NMDA receptors appear to have no role. Nitric oxide is essential for maintaining the chronic hyperactive state of the urinary bladder.

A rat model for studying effects of sacral neuromodulation on the contractile activity of a chronically inflamed bladder

OBJECTIVE

To develop an animal model in which the effects of electrical stimulation of the sacral nerves (sacral neuromodulation) on a chronic hyperactive urinary bladder can be studied.

MATERIALS AND METHODS

In female rats the urinary bladder was instilled with mustard oil (0.4%); after 10 days the animals were anaesthetized with intraperitoneal urethane, the bladder catheterized and connected to a pressure transducer. Stimulating electrodes were placed into the sacral foramina bilaterally. The intensity and duration of sacral electrical stimulation was varied systematically to determine the effects of the sacral neuromodulation on bladder contractions.

RESULTS

The main effect of the neuromodulation was an increase in the interval between contractions, i.e. during and for some time after the stimulation the contractions were completely abolished. The duration of the pause increased with the intensity and duration of stimulation. After the contractions had reappeared the frequency of contractions was reduced for a long period. In animals with chronic cystitis the effects of neuromodulation tended to be stronger (the pauses were longer) than in control animals with an intact bladder, but only in one test (increase of pause length with stimulus duration) was the difference statistically significant.

CONCLUSIONS

The results show that this animal model is suitable for studying the effects and mechanisms of sacral neuromodulation on a chronic hyperactive urinary bladder.