Micturition In Cats Research Articles

Effect of 5-serotonin 1 receptor agonists on acetic acid stimulated micturition in chronic spinal cord injury cats

Objective To evaluate the effects of 5-serotonin 1 (5-HT1) receptor agonists on acetic acid stimulated micturition in cats with chronic spinal cord injury (SCI).Methods Chloralose-anesthetized SCI cats were catheterized through the bladder dome for filling cystometry during 0.5％ acetic acid infusion.Dose-response curves for ( R)-8-OH-DPAT (0.30-30.00 μg/kg,i.v.) or GR 46611 (0.03-300.00 μg/kg,i.v.) were followed by 5-HT1A antagonist WAY-100635 (300.00 μg/kg).Threshold volume,bladder capacity,residual volume,micturition volume,and arterial pressure were measured and the external urethral sphincter electromyogram (EUS-EMG) was recorded.Results Acid-infused SCI cats responded to (R)-8-OH-DPAT but not GR-46611 with dose-dependent increases in threshold volume,capacity,and residual volume,significantly at the dose above 10 μg/kg.Effects of (R)-8-OH-DPAT were largely reversed by WAY 100635.Neither (R)-8-OH-DPAT nor GR-46611 augmented EUS-EMG activity.Conclusion Because 5-HT1A receptor agonists increase bladder capacity under either saline or acid infused conditions,they are promising candidates for reducing bladder hyperactivity and increasing bladder capacity in patients with chronic SCI. Key words: Spinal cord injury; Micturition; 5-serotonin receptor; Cat

Studies on thyrotropin-releasing hormone-induced micturition in cats.

In unanaesthetized cats micturition produced by thyrotropin-releasing hormone (TRH) was investigated after its injection into the cerebral ventricles through chronically implanted cannulae. TRH in doses from 0.1 to 1.0 mg evoked dose-dependent micturition. In cats treated with intracerebroventricular (i.c.v.) reserpine and 6-hydroxydopamine, but not with i.c.v. 5,6-dihydroxytryptamine and hemicholinium, the micturition caused by i.c.v. TRH was abolished. Chlorpromazine and antazoline injected into the cerebral ventricles prevented the micturition induced by i.c.v. TRH. On the other hand, mecamylamine, yohimbine, propranolol, atropine and methysergide injected i.c.v. had virtually no effect or partially antagonized the micturition evoked by TRH similarly injected. It is apparent therefore that centrally induced TRH micturition could be related to central catecholaminergic mechanisms.

Effect of 5-Hydroxytryptamine 1 Serotonin Receptor Agonists on Noxiously Stimulated Micturition in Cats With Chronic Spinal Cord Injury

The serotonin 5-hydroxytryptamine(1A/7) receptor agonist (R)-8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin) (Sigma) and the 5-hydroxytryptamine(1A/1B/1D) agonist GR-46611 (3-[3-(2-dimethylaminoethyl)-1H-indol-5-yl]-N-(4-methoxybenzyl)acrylamide) (Tocris Cookson, Ellisville, Missouri) inhibit bladder activity during saline infusion into the bladder of cats with chronic spinal cord injury (saline infused, spinal cord injured cats), suggesting an effect on mechanosensitive bladder afferent C fibers or their targets. We investigated the effects of (R)-8-OH-DPAT and GR-46611 on bladder activity in chronic spinal cord injured cats during infusion of dilute acetic acid into the bladder to stimulate chemosensitive bladder afferent C fibers (acid infused, spinal cord injured cats). Chloralose anesthetized, spinal cord injured cats were catheterized through the bladder dome for filling cystometry during 0.5% acetic acid infusion. Dose-response curves for (R)-8-OH-DPAT (0.3 to 30 microg/kg intravenously) or GR-46611 (0.03 to 300 microg/kg intravenously) were followed by the 5-hydroxytryptamine(1A) antagonist WAY-100635 (N-tert-butyl-3-(4-(2-methoxyphenyl)-piperazin-1-yl)-2-phenylpropanamide) (Sigma) (300 microg/kg). Threshold volume, bladder capacity, residual volume, micturition volume and arterial pressure were measured and external urethral sphincter electromyogram was recorded. Acid infused, spinal cord injured cats responded to (R)-8-OH-DPAT but not to GR-46611 with dose dependent increases in threshold volume, capacity and residual volume (significant above 3 microg/kg). Effects of (R)-8-OH-DPAT were largely reversed by WAY-100635. Neither (R)-8-OH-DPAT nor GR-46611 augmented external urethral sphincter electromyogram activity. Based on differences in the response to GR-46611 in saline vs acid infused, spinal cord injured animals it is tempting to speculate that 2 distinct populations of bladder afferent C fibers (1 chemosensitive and 1 mechanosensitive) can initiate spinal bladder reflexes. Because 5-hydroxytryptamine(1A) receptor agonists increased bladder capacity under saline or acid infused conditions, they are promising candidates for decreasing bladder hyperactivity and increasing bladder capacity in patients with chronic spinal cord injury.

Micturition and the soul

There is a close connection between micturition and emotion. Several species use micturition to signal important messages as territorial demarcation and sexual attraction. For this reason, micturition is coordinated not in the spinal cord but in the brainstem, where it is closely connected with the limbic system. In cat, bladder afferents terminate in a cell group in the lateral dorsal horn and lateral part of the intermediate zone. Neurons in this cell group project to supraspinal levels, not to the thalamus but to the central periaqueductal gray (PAG). Neurons in the lateral PAG, not receiving direct sacral cord afferents, project to the pontine micturition center (PMC). The PMC projects directly to the parasympathetic bladder motoneurons and to sacral GABA-ergic and glycinergic premotor interneurons that inhibit motoneurons in Onuf's nucleus innervating the external striated bladder sphincter. Thus, PMC stimulation causes bladder contraction and bladder sphincter relaxation, i.e., complete micturition. Other than the PAG, only the preoptic area and a cell group in the caudal hypothalamus project directly to the PMC. The ventromedial upper medullary tegmentum also sends projections to the PMC, but they are diffuse and also involve structures that adjoin the PMC. Neuroimaging studies in humans suggest that the systems controlling micturition in cat and human are very similar. It seems that the many structures in the brain that are known to influence micturition use the PAG as relay to the PMC. This basic organization has to be kept in mind in the fight against overactive bladder (OAB) and urge-incontinence.

Sacral dorsal horn neurone activity during micturition in the cat.

The excitability of two groups of neurones located in different parts of the sacral spinal cord were examined during micturition in decerebrate adult cats. One group of cells, characterized by their activation by pudendal cutaneous afferents, was located in the dorsal commissure of the first and second sacral spinal segments. The second group, located in the dorsal horn of the first sacral spinal segment, was excited by group II muscle and cutaneous afferents. Micturition was evoked by distension of the urinary bladder or by electrical stimulation of the pontine micturition centre. Tonic firing was induced in the neurones by ejection of DL-homocysteic acid from the recording extracellular micropipette. The instantaneous firing frequency of 11/17 sacral dorsal grey commissure neurones was decreased from 7 to 100 % during micturition, and on average was about half of the prevoid firing frequency. It is hypothesized that these sacral neurones are interposed in polysynaptic excitatory pathways from sacral perineal afferents to sphincter motoneurones and that they are subject to direct postsynaptic inhibition during micturition. One other cell showed no change in firing during micturition, two displayed complex patterns of modulation, while 3/17 of the dorsal grey commissure neurones increased their firing rate 30 to 1000 % during micturition. It is hypothesized that the excited neurones may be part of the inhibitory pathways mediating postsynaptic inhibition of sphincter motoneurones or sacral primary afferent depolarization during micturition. Alternatively, they may be part of the excitatory urethral-bladder reflex circuitry. A small (5-15 %) but significant decrease in firing was observed in 4/5 of the group II rostral sacral neurones examined; the firing of a fifth neurone was unchanged. The depression of group II neurones may serve to suppress unwanted hindlimb reflexes that could disrupt micturition.

The central nervous system control of micturition in cats and humans

Recent findings concerning the central control of micturition in cats are compared to findings obtained from dynamic imaging studies in humans. In the cat, three areas in the brainstem and diencephalon are specifically implicated in the control of micturition: (1) Barrington’s nucleus or the pontine micturition center in the dorsomedial pontine tegmentum directly excites bladder motoneurons and indirectly inhibits, via inhibitory interneurons in the medial sacral cord, urethral sphincter motoneurons; (2) the periaqueductal grey receiving bladder filling information; and (3) the pre-optic area of the hypothalamus possibly involved in determining the beginning of micturition. According to PET-scan studies, in humans the same supraspinal regions are active during micturition. In the cat another area, located in the ventrolateral pontine tegmentum and is called the L-region, which controls the motoneurons of the pelvic floor, including the external urethral sphincter. This region might be considered as the pontine storage center. In humans the L-region is especially active in volunteers who tried but did not succeed to micturate. The results suggest that in cats and humans at the brainstem and diencephalic levels micturition is organized in the same way.

Evidence for a strychnine-sensitive mechanism and glycine receptors involved in the control of urethral sphincter activity during micturition in the cat.

Micturition in the decerebrate cat is characterized by a coordinated bladder contraction and a simultaneous decrease in external urethral sphincter (EUS) efferent activity. Without the suppression of EUS activity, voiding is significantly impaired, resulting in a state sometimes referred to as bladder-sphincter dyssynergia. The aim of the present study was to determine whether glycinergic inhibition contributes to the suppression of EUS activity during micturition evoked by bladder distension or electrical stimulation of the pontine micturition center (PMC) in decerebrate cats. Using subconvulsive intravenous doses of strychnine (0.1-0.24 mg/kg), we examined changes in bladder and EUS electroneurographic (ENG) activity during micturition. Following subconvulsive doses of strychnine, tonic EUS ENG activity increased during bladder filling in five of six animals. In the presence of strychnine, it was possible to evoke reflex bladder contractions of similar duration and peak pressure to those observed before strychnine administration. However, there was an absence of suppression of EUS ENG activity during the bladder contractions in all the animals. To determine whether the changes in sphincter activity could be due to strychnine acting at glycine receptors on EUS motoneurons, sacral spinal tissue was processed for a structural protein (gephyrin) associated with the glycine receptor. Motoneurons in Onufs nucleus in S1 were identified using choline acetyltransferase immunohistochemistry and subsequently processed with a gephyrin monoclonal antibody. Abundant gephyrin labeling was evident throughout Onufs nucleus. Since Onufs nucleus is made up of EUS and other motoneuron populations, a sample of antidromically identified urethral and anal sphincter motoneurons were intracellularly labeled with tetramethylrhodamine dextran (TMR-D) and then processed with the gephyrin antibody. Using dual-beam confocal microscopy, gephyrin immunoreactivity was observed on the soma and proximal processes of individual EUS motoneurons in both male and female animals. It was concluded that a strychnine-sensitive mechanism contributes to the suppression of sphincter activity normally observed during voiding. Although glycinergic inhibition may affect several components of the circuitry responsible for micturition, it appears that the suppression of EUS motoneurons during micturition may be partly due to a direct glycinergic inhibition of the EUS motoneurons.

Micturition control by microstimulation of the sacral spinal cord of the cat: acute studies

The feasibility of using microstimulation of neural elements in the sacral spinal cord to effect micturition in cats has been assessed in acute experiments. Previous attempts at intramedullary stimulation have been limited by unwanted cocontraction of the bladder and the external urethral sphincter (EUS) or by side effects. Using microstimulation of parasympathetic preganglionic neurons or their efferent axons, the authors were able to repeatably elevate bladder pressure without simultaneously increasing EUS tone or eliciting undesired somatic contractions. Both stimulus amplitude and pulse width were effective in modulating bladder contractions but the stimulus frequency was not. Use of an interrupted duty cycle was helpful in preventing detrusor muscle fatigue during sustained periods of stimulation. Pulsing multiple microelectrodes implanted in the sacral spinal cord (especially bilateral pairs) enhanced elevation of bladder pressure over that elicited by stimulation with an individual electrode, but the effect was less than additive. These results have provided a basis for the development of a chronic spinal cord stimulation system suitable for controlling micturition. >

Mechanisms underlying the recovery of urinary bladder function following spinal cord injury

Micturition in cats and rats with an intact neuraxis is dependent upon a spinobulbospinal reflex activated by Aδ bladder afferents. This report describes changes in micturition reflexes 2 h to 14 weeks following spinal cord transection at the lower thoracic level. In acute spinal cats micturition reflexes were blocked, however, several weeks after transection, a long latency (180–200 ms) spinal reflex could be activated by C-fiber bladder afferents. This reflex was blocked by capsaicin in doses (20–30 mg/kg, s.c.) that did not affect micturition reflexes in intact cats. Micturition reflexes were unmasked in acute spinal and facilitated in chronic spinal cats by naloxone, an opioid antagonist. Spinal neurons and axons containing opioid peptides were more prominent below the level of transection in chronic spinal cats. VIP, a putative neurotransmitter in C-fiber bladder afferents, inhibited micturition reflexes when injected intrathecally (2–10 μg) in intact cats but facilitated micturition reflexes in spinal cats (doses 0.1–1 μg, i.t.). VIP-containing C-fiber afferent projections to lamina 1 of the sacral spinal cord expanded in spinal cats. Thus VIP afferents may have an important role in the recovery of bladder reflexes after spinal injury. Paraplegic animals also exhibit bladder-sphincter dyssynergia, which causes functional outlet obstruction. Studies in rats have revealed that outlet obstruction induced by partial urethral ligation facilitates spinal micturition reflex pathways and causes an expansion of HRP-labelled bladder afferent projections in the spinal cord. These findings raise the possibility that the alterations in central reflex connections in paraplegic animals may be induced in part by changes in peripheral afferent input secondary to outlet obstruction. In summary, recovery of bladder function in paraplegic animals is associated with a major reorganization of reflex connections and neurotransmitter mechanisms in the spinal cord. It appears that this reorganization involves morphological as well as functional changes.

Organization of the sacral parasympathetic reflex pathways to the urinary bladder and large intestine.

Electrophysiological and horseradish peroxidase (HRP) techniques have provided new insights into the organization of the sacral parasympathetic reflex pathways to the large intestine and urinary bladder. The innervation of the two organs arises from separate groups of sacral preganglionic cells: (1) a dorsal band of cells in laminae V and VI providing an input to the intestine; and (2) a lateral band of cells in lamina VII providing an input to the bladder. These two groups of cells were separated by an interband region containing tract cells and interneurons. Neurons in the interband region received a visceral afferent input and exhibited firing correlated with the activity of intestine and urinary bladder. It seems reasonable therefore to consider the interband region as a third component of the sacral parasympathetic nucleus. Anterograde transport of HRP revealed that visceral afferents from the intestine and bladder projected into the parasympathetic nucleus. Most of the projections were collaterals from afferent axons in Lissauer's tract that passed in lamina I laterally and medially around the dorsal horn. These afferent collaterals were located in close proximity to preganglionic perikarya and dendrites in laminae I, V and VI. The proximity of visceral afferents and efferents in the sacral cord probably reflects the existence of polysynaptic rather than monosynaptic connections since electrophysiological studies revealed that both the defecation and micturition reflexes occurred with very long central delays (45-70 msec). The reflex pathways mediating defecation and micturition in cats with an intact neuraxis were markedly different. Defecation was dependent upon a spinal reflex with unmyelinated (C-fiber) peripheral afferent and efferent limbs. On the other hand, micturition was mediated by a spinobulbospinal pathway with myelinated peripheral afferent (A-fiber) and efferent axons (B-fiber). Transection of the spinal cord at T12-L2 blocked the micturition reflex but only transiently depressed the defecation reflex. In chronic spinal cats the micturition reflex recovered 1-2 weeks after spinalization; however, in these animals bladder-to-bladder micturition reflexes were elicited by C-fiber rather than A-fiber afferents. The C-fiber afferent-evoked reflex was weak or undetectable in animals with an intact neuraxis. Transection of the spinal cord also changed the micturition reflex in neonatal kittens (age 5-28 days). In neonates with an intact neuraxis bladder-to-bladder reflexes occurred via a long latency spinobulbospinal pathway (325-430 msec). The long latency is attributable to the slow conduction velocity in immature unmyelinated peripheral and central axons. In chronic spinal kittens (3-7 days after spinalization) the long latency reflex was abolished and a shorter latency (90-150 msec) bladder reflex was unmasked. The emergence of this spinal pathway may reflect axonal sprouting and the formation of new reflex connections within the sacral parasympathetic nucleus.