John W. Downie

Effect of anesthetics on reflex micturition in the chronic cannula-implanted rat.

It is well known that urethane is a suitable anesthetic for acute studies and has been extensively recommended for investigations related to micturition physiology. This is mainly because of the capability of urethane anesthesia to spare reflex micturition as well as its easily established long‐lasting and stable anesthetic level. However, urethane anesthesia is usually restricted to acute experiments due to its potential toxicity. This study searched for an alternative to urethane that would be suitable for studies in which recovery from anesthesia was needed. The list of administered drugs was as follows: pentobarbital, thiobutabarbital, ketamine‐acepromazine, ketamine‐diazepam, tiletamine‐zolazepam, fentanyl‐droperidol, alphaxalone‐alphadolone, propofol, isoflurane, methoxyflurane, azaperone, tribromoethanol, and buprenorphine. Among these drugs, only tiletamine‐zolazepam spared the reflex micturition contractions. However, the duration of this anesthesia was too short (approximately 30 minutes) to complete the necessary testing and additional dosing of the anesthetic generally obliterated the micturition reflex. On the other hand, rats given i.v. urethane infusion (10% solution in 0.9% saline, 3.2–4.0 mg/kg/min, total dose 0.56–1.03 g/kg) maintained a stable anesthesia that permitted both reflex micturition and stereotaxic procedures. Rats moved spontaneously 3–16 hours after cessation of i.v. urethane anesthesia and completely recovered in 2 days without significant after‐effects. Bladder function was normal. No pathological changes were seen 1 week later. The present results suggest that urethane is the most suitable anesthetic for acute and chronic physiological experiments that require demonstration of reflex micturition. Neurourol. Urodynam. 19:87–99, 2000.

Experimental evidence for a central nervous system site of action in the effect of alpha-adrenergic blockers on the external urinary sphincter

The present study was done to test the hypothesis that alpha-adrenoceptor blocking drugs (phentolamine and prazosin) could interfere with somatic control of the external sphincter through an action in the central nervous system. Stimulation of the hypogastric nerve in the chloralose-anesthetized cat caused a urethral constriction which could be antagonized by alpha-receptor blockers. However, the constriction produced by stimulation of the S1 or S2 ventral root was completely resistant to alpha blockade. The drugs therefore had the expected action against sympathetic stimulation of the urethra but had no peripheral effect on the somatic component. The central effect of these drugs was investigated by recording urethral perfusion pressure responses, or compound action potentials on the central cut end of the pudendal nerve, evoked by stimulation of the contralateral pudendal or pelvic nerve. The urethral constriction produced by stimulation of the central cut end of 1 pudendal nerve was antagonized by both prazosin and phentolamine. Action potentials evoked on the pudendal nerve by stimulation of the central cut end of the contralateral pudendal or pelvic nerve were substantially inhibited by prazosin. Phentolamine produced a more variable blockade of the pudendal-pudendal reflex. The results strongly indicate that these alpha-adrenoceptor antagonists and especially prazosin can influence pudendal nerve-dependent urethral responses through a central nervous system action and not through a peripheral mechanism.

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

Serotonin (5-HT) may be inhibitory to micturition at a spinal level. A potential mechanism of action for serotonergic inhibition of bladder function is a depression of the ascending limb of the supraspinal reflex mediating micturition. Ascending activity evoked by pelvic nerve stimulation was recorded in the thoracic spinal cord of anesthetized cats. For comparison, spinal reflex activity evoked by pelvic nerve stimulation was recorded on the pudendal nerve. The effects of intrathecal administration of serotonergic agents were examined to determine whether spinal and supraspinal responses to bladder afferent activation were modulated by 5-HT. Methysergide (60 nmol), a non-selective serotonergic antagonist, increased ascending activity by 61+/-7% and depressed spinal reflex activity by 38+/-6%. Zatosetron (10 nmol), a 5-HT3 antagonist had a similar effect on both activities (increased by 93+/-24% and decreased by 77+/-7%, respectively). The effect on ascending activity of blocking 5-HT3 receptors was also confirmed with ICS 205930 and MDL 72222. 2-Methyl-5-HT (800 nmol), a 5-HT3 agonist, depressed ascending activity to 46+/-9% of control, but enhanced spinal reflex activity by 73+/-92%. These results demonstrate that stimulation of 5-HT3 and methysergide-sensitive 5-HT receptors can inhibit ascending activity and facilitate spinal reflex activity elicited by activation of bladder afferents. It is suggested that descending serotonergic pathways may participate in the spinal coordination of urinary continence.

Effect of 5-HT receptor and adrenoceptor antagonists on micturition in conscious cats

Micturition was induced in awake cats by infusing saline into the bladder at a physiological filling rate. Methysergide, a serotonergic antagonist given intrathecally, decreased the volume at which micturition occurred. Phentolamine, a non-specific alpha-adrenoceptor antagonist, also decreased volume threshold. Prazosin, an alpha 1-adrenoceptor antagonist, was without effect on micturition. These results imply that 5-HT receptors and alpha 2-adrenoceptors may be inhibitory to micturition at a spinal level.

Characteristics of K+- and veratridine-induced release of ATP from synaptosomes prepared from dorsal and ventral spinal cord.

K+ and veratridine released 2-3 times more ATP from dorsal than from ventral spinal cord synaptosomes (P2). K+-induced release of ATP was Ca2+-dependent whereas veratridine-induced release was augmented in a Ca2+-free medium. Twenty-one to 24 days after section of the right sciatic nerve of the rat the evoked release of ATP from right dorsal synaptosomes was indistinguishable from release from left dorsal synaptosomes. Although these latter results suggest that ATP may not be a transmitter at primary afferent synapses in the spinal cord, it is possible that sciatic nerve section does not deplete the releasable pool of ATP in primary afferent terminals the releasable pool of ATP in primary afferent terminals or that ATP is also released from interneurons in the dorsal spinal cord.

External sphincter dyssynergia: an abnormal continence reflex.

Some of the characteristics of detrusor-external sphincter dyssynergia were examined in 14 patients with traumatic upper motor neuron lesions within 44 weeks of injury. The sacral evoked response latencies of the male patients were shortened at any time after injury. A continence reflex could be demonstrated in most patients at any time after injury. Comparing averaged values for the group at 4-week intervals, resting pressure at the external urethral sphincter and post-void residual volumes reached nadirs at 12 weeks while voiding efficiency peaked at this time. Thus, voiding function appears to be optimal 12 weeks after injury. During reflex detrusor activity, increases in external urethral sphincter electromyographic activity and external urethral sphincter pressure were associated clearly with a positive slope of the intravesical pressure trace, whereas decreases in both parameters were associated with a negative slope. Voiding occurred only during a negative slope. Although propantheline induced detrusor areflexia, episodic peaks in external urethral sphincter pressure and electromyographic activity continued to occur. We propose that external sphincter dyssynergia, which is independent of detrusor contraction, is the continence reflex exaggerated owing to the loss of supraspinal influences. We believe that the multiple patterns of dyssynergia described previously by others are variations, largely owing to technique, of the single pattern we have observed. The observation of synergic-like urethral responses in some patients during a negative slope of the intravesical pressure, even with complete suprasacral spinal lesions, implies existence of a pathway for synergic-like voiding in the spinal cord.

Serotonergic modulation of cat bladder function before and after spinal transection

Micturition was evoked in conscious cats by infusing saline into the bladder at a physiological rate. Drugs were administered intrathecally. Micturition volume threshold was increased by 5-hydroxytryptamine (5-HT, serotonin) and decreased by zatosetron, a 5-HT3 receptor antagonist, in spinally intact cats. Thus 5-HT3 receptors inhibit micturition. After complete spinal transection, serotonin reduced volume threshold in 3 of 4 cats, indicating an alteration in serotonergic control. However, 2-methyl-5-HT, a 5-HT3 receptor agonist, increased volume threshold. Thus 5-HT3 receptor-mediated inhibition of bladder function remains after spinal transection. We conclude that some, but not all, serotonergic modulation of bladder function is altered after spinal transection.

Pharmacological analysis of the responses of the feline urethra to autonomic nerve stimulation

The effects of sympathetic and parasympathetic nerve stimulation on resistance to flow in the proximal urethra was examined in male, chloralose-anesthetized cats. Hypogastric (sympathetic) nerve stimulation increased urethral resistance, an effect that was blocked by the alpha-adrenergic antagonist prazosin (0.1 mg/kg), reduced 50% by ganglionic blockade with hexamethonium (0.4 to 0.6 mg/min) and potentiated by the beta-adrenergic antagonist sotalol (5 mg/kg). In the presence of phenylephrine-induced constrictions of the urethra, hypogastric nerve stimulation decreased resistance by a sotalol-sensitive, hexamethonium-resistant mechanism. The results imply that sympathetic stimulation can either raise or lower urethral resistance under different conditions, and that the organization of the nerves mediating the two types of response differs. Because pelvic nerve stimulation produced small and inconsistent responses, the parasympathetic input was instead activated by sacral ventral root stimulation. Sacral stimulation produced an atropine-sensitive constriction when basal urethral resistance was low, and dilatation when resistance was high. The latter response was reduced by atropine, but was resistant to sotalol. However, the decrease in resistance produced by acetylcholine in the presence of PE was not reduced by atropine, implying that acetylcholine-induced dilatation of the urethra is not due to activation of muscarinic receptors on smooth muscle. It is hypothesized that parasympathetic dilatation of the urethra may be mediated by a non-cholinergic, non-adrenergic inhibitory transmitter released from post-ganglionic neurons. A muscarinic mechanism may be involved in this response either to potentiate the action of the unknown transmitter or to facilitate the ganglionic excitation of these neurons. Parasympathetic constrictor responses can be attributed to activation of postganglionic cholinergic neurons.

α2-Adrenoceptors not imidazole receptors mediate depression of a sacral spinal reflex in the cat

In chloralose-anaesthesized cats, clonidine, an alpha 2-adrenoceptor agonist with an imidazole ring, depressed pudendal nerve reflex activity. Clonidines inhibitory action on this compound action potential response was mimicked by guanabenz, a non-imidazole alpha 2-adrenoceptor agonist, and was reversed by SK & F 86466, a non-imidazole alpha 2-adrenoceptor antagonist. These results imply that clonidines action on this reflex related to urinary sphincter function is mediated by alpha 2-adrenoceptors and is not dependent on an imidazole structure.

Bladder and Urethral Function and Supersensitivity to Subcutaneously Administered Bethanechol in Cats with Chronic Cauda Equina Lesions

The failure of bethanechol chloride to induce voiding in patients with neurogenic bladder, despite a positive bethanechol test, is being reported more frequently. An experimental model was designed in the cat to study the response of the bladder and urethra to subcutaneous and intraarterial bethanechol after complete and partial sacral decentralization. Complete sacral rhizotomy abolished the micturition reflex. Basal urethral perfusion pressure was not affected by complete sacral rhizotomy and a significant part of this basal urethral pressure remained sympathetically mediated. However, the urethral constriction response to bladder filling was lost in half the cats with complete lesions. Bladder and urethral supersensitivity to bethanechol chloride in cats with complete lesions was characterized by a shift to the left of the i.a. dose-response curve, and by the presence of responses to doses of s.c. bethanechol chloride which are subthreshold in normal cats. The urethra also showed exaggerated constriction responses to i.a. and s.c. bethanechol. After complete lesions a part of the bladder and urethral responses to s.c. bethanechol was adrenergically mediated and exerted through the vesicourethral short neuron system. The rest of the response was due to stimulation of urethral muscarinic receptors. Partial sacral lesions were compatible with a micturition reflex and the urethra retained its reflex response to bladder distension. After partial decentralization the bladder and urethra also showed responses to subthreshold doses of s.c. bethanechol. While the bladder response to s.c. bethanechol did not show a significant adrenergic component in cats with partial lesions, most of the urethral response was sympathetically mediated. In conclusion, complete cauda equina lesions result in an areflexic detrusor with frequent loss of the urethral responsiveness to bladder filling. Urethral supersensitivity to s.c. bethanechol might be responsible for a non-voiding outcome after bethanechol injection in patients with complete cauda equina lesions, despite a positive bethanechol test. Because the detrusor reflex is preserved and the urethra is less supersensitive to bethanechol after partial cauda equina lesions, these may represent a better indication for bethanechol therapy than do complete ones.