Forebrain muscarinic control of micturition reflex in rats

Liberation of Serotonin Is Not Unaffected by Acetylcholine in Rat Hippocampus

Purpose

Raised cerebral titers of acetylcholine have notable links with storage symptomatology related to lower urinary tract symptoms. The hippocampus contributes to the normal control of continence in the majority of instances (circuit 3). Owing to synaptic connections with other nerve cells, acetylcholine affects the micturition pathway via the liberation of additional cerebral neurotransmitters. Despite the fact that cerebral serotonin is a key inhibitor of reflex bladder muscle contractions, the influence of acetylcholine on its liberation is poorly delineated. The current research was conducted in order to explore the role of acetylcholine in serotonin liberation from sections of rat hippocampus in order to improve the comprehension of the relationship between cholinergic and serotonergic neurons.

Methods

Hippocampal sections from 6 mature male Sprague-Dawley rats were equilibrated over a 30-minute period in standard incubation medium so as to facilitate [³H]5-hydroxytryptamine (5-HT) uptake. The cerebral neurotransmitter, acetylcholine, was applied to the sections. Aliquots of drained medium solution were utilized in order to quantify the radioactivity associated with [³H]5-HT liberation; any alterations in this parameter were noted.

Results

When judged against the controls, [³H]5-HT liberation from the hippocampal sections remained unaltered following the administration of acetylcholine, implying that this agent has no inhibitory action on this process.

Conclusions

Serotonin liberation from murine hippocampal sections is unaffected by acetylcholine. It is postulated that the bladder micturition reflex responds to acetylcholine through its immediate cholinergic activity rather than by its influence on serotonin release. These pathways are a promising target for the design of de novo therapeutic agents.

Change in the central control of the bladder function of rats with focal cerebral infarction induced by photochemically-induced thrombosis

The photochemically-induced thrombosis (photothrombosis) method can create focal cerebral infarcts anywhere in the relatively superficial layers of the cerebrum; it is easy to implement and minimally invasive. Taking advantage of this versatility, we aimed to establish a new rat model of urinary frequency with focal cerebral infarction, which was characterized by its simplicity, nonlethal nature, and high reproducibility. The prefrontal cortex and the anterior cingulate cortex, which are involved in lower urinary tract control, were targeted for focal cerebral infarction, and urinary parameters were measured by cystometrogram. Cystometric analysis indicated that micturition intervals significantly shortened in photothrombosis-treated rats compared with those in the sham operative group on Days 1 and 7 (P < 0.01), but prolonged after 14 days, with no difference between the two groups. Immunopathological evaluation showed an accumulation of activated microglia, followed by an increase in reactive astrocytes at the peri-infarct zone after photothrombotic stroke. Throughout this study, all postphotothrombosis rats showed cerebral infarction in the prefrontal cortex and anterior cingulate cortex; there were no cases of rats with fatal cerebral infarction. This model corresponded to the clinical presentation, in that the micturition status changed after stroke. In conclusion, this novel model combining nonlethality and high reproducibility may be a suitable model of urinary frequency after focal cerebral infarction.

Stem Cell Therapy for Neurogenic Bladder Dysfunction in Rodent Models: A Systematic Review

PURPOSE

Neurogenic bladder dysfunction (NGB) has an impact on the quality of life, which made it an important research subject in preclinical studies. The present review investigates the effect of stem cell (SC) therapy on bladder functional recovery after the onset of spinal cord injury (SCI), multiple sclerosis (MS), Parkinson disease (PD), and stroke in rodent models.

METHODS

All experiments evaluated the regenerative potential of SC on the management of NGB in rodent models up to June 2019, were included. From 1,189 relevant publications, 20 studies met our inclusion criteria of which 15 were conducted on SCI, 2 on PD, 2 on stroke, and 1 on MS in the rodent models. We conducted a meta-analysis on SCI experiments and for other neurological diseases, detailed urodynamic findings were reported.

RESULTS

The common SC sources used for therapeutical purposes were neural progenitor cells, bone marrow mesenchymal SCs, human amniotic fluid SCs, and human umbilical cord blood SCs. There was a significant improvement of micturition pressure in both contusion and transaction SCI models 4 and 8 weeks post-SC transplantation. Residual urine volume, micturition volume, and bladder capacity were improved 28 days after SC transplantation only in the transaction model of SCI. Nonvoiding contraction recovered only in 56 days post-cell transplantation in the contusion model.

CONCLUSION

Partial bladder recovery has been evident after SC therapy in SCI models. Due to limitations in the number of studies in other neurological diseases, additional studies are necessary to confirm the detailed mechanism for bladder recovery.

Bladder Transplantation of Amniotic Fluid Stem Cell may Ameliorate Bladder Dysfunction After Focal Cerebral Ischemia in Rat

The objective is to investigate whether human amniotic fluid stem cells (hAFSCs) grafting into the bladder may influence bladder functional and molecular changes in an animal stroke model. Female rats were divided into three groups: sham, middle cerebral artery occlusion (MCAO) alone, and MCAO plus 1 × 10⁶ hAFSCs transplanting into bladder wall. Bladder function was analyzed by cystometry at days 3 and 10 after MCAO. The expressions of bladder nerve growth factor (NGF), M2‐muscarinic, M3‐muscarinic, and P2X1 receptors were measured by immunohistochemistry and real‐time polymerase chain reaction. When compared with sham‐operated group, MCAO alone rats had significant increase in residual volume and decrease in voided volume and intercontraction interval; however, these bladder dysfunctions were improved following hAFSCs transplantation. The immunoreactivities of NGF, M3, and P2X1 significantly decreased at days 3 and 10, but M2 increased at day 3 after MCAO. Following hAFSCs transplantation, the immunoreactivities of NGF and P2X1 significantly increased at day 3, and M2 increased at day 10 after MCAO. The mRNAs of NGF, M2, and M3 significantly increased at day 3, but NGF and M2 decreased at day 10 after MCAO. Following hAFSCs transplantation, there was significant decrease in M2 mRNA at day 3 and increase in P2X1 mRNA at days 3 and 10 after MCAO. Bladder dysfunction caused by MCAO can be improved by hAFSCs transplanting into bladder which may be related to the expressions of bladder NGF, and muscarinic and P2X1 receptors. Stem Cells Translational Medicine2017;6:1227–1236

Neural control of the lower urinary tract

This article summarizes anatomical, neurophysiological, pharmacological, and brain imaging studies in humans and animals that have provided insights into the neural circuitry and neurotransmitter mechanisms controlling the lower urinary tract. The functions of the lower urinary tract to store and periodically eliminate urine are regulated by a complex neural control system in the brain, spinal cord, and peripheral autonomic ganglia that coordinates the activity of smooth and striated muscles of the bladder and urethral outlet. The neural control of micturition is organized as a hierarchical system in which spinal storage mechanisms are in turn regulated by circuitry in the rostral brain stem that initiates reflex voiding. Input from the forebrain triggers voluntary voiding by modulating the brain stem circuitry. Many neural circuits controlling the lower urinary tract exhibit switch-like patterns of activity that turn on and off in an all-or-none manner. The major component of the micturition switching circuit is a spinobulbospinal parasympathetic reflex pathway that has essential connections in the periaqueductal gray and pontine micturition center. A computer model of this circuit that mimics the switching functions of the bladder and urethra at the onset of micturition is described. Micturition occurs involuntarily in infants and young children until the age of 3 to 5 years, after which it is regulated voluntarily. Diseases or injuries of the nervous system in adults can cause the re-emergence of involuntary micturition, leading to urinary incontinence. Neuroplasticity underlying these developmental and pathological changes in voiding function is discussed.

Effects of cholinesterase inhibition in supraspinal and spinal neural pathways on the micturition reflex in rats

OBJECTIVE

To investigate whether activation of brain and spinal cholinergic pathways affects the micturition reflex in rats.

MATERIALS AND METHODS

The effects of intracerebroventricular (i.c.v.) or intrathecal (i.t.) administration of neostigmine as a cholinesterase inhibitor and oxotremorine-M (OXO-M) as a muscarinic acetylcholine receptor (mAChRs) agonist, on the micturition reflex were evaluated by infusion cystometrography (CMG) in urethane-anaesthetized untreated rats or rats pretreated with capsaicin.

RESULTS

Neostigmine injected i.c.v. increased bladder capacity (BC) and pressure threshold (PT) dose-dependently, with an increase in maximum voiding pressure (MVP) and a decrease in voiding efficiency (VE) at higher doses. Also, neostigmine injected i.t. increased the BC and PT dose-dependently without changing MVP or VE, and these effects were not apparent in capsaicin-pretreated rats. In both routes, atropine as an antagonist of mAChRs, but not mecamylamine as a nicotinic-AChR antagonist, almost completely antagonized the effects of neostigmine. The rank order of potencies of the antagonists for increasing effects of BC induced by 1 nmol of neostigmine was: pirenzepine (an M(1) mAChR antagonist) = atropine > 4-DAMP (an M(3) mAChR antagonist) " methoctramine (an M(2) mAChR antagonist) and tropicamide (an M(4) mAChR antagonist) via the i.c.v. route; and atropine > methoctramine > pirenzepine > tropicamide and 4-DAMP via the i.t. route, respectively. OXO-M injected via i.c.v. and i.t. had the same effects on BC, PT, MVP and VE as neostigmine by i.c.v. and i.t., respectively.

CONCLUSIONS

These results indicate that activation of muscarinic cholinergic mechanisms by the cholinesterase inhibitor in the brain and spinal cord can inhibit the micturition reflex, mainly by affecting afferent pathways. These mAChR-induced inhibitory effects seem to be mediated through M(1)/M(3) receptor subtypes in the brain, while in the spinal cord, the M(1)/M(2) receptor subtypes might be involved in inhibitory effects, which are mediated via inhibition of mechanoceptive C-fibre afferent pathways.

Effects of antimuscarinics on voiding function after cerebral infarction in a rat model of overactive bladder

Muscarinic receptor antagonists are used clinically for their therapeutic peripheral effects on bladder function. However, these agents may also act on central muscarinic receptors, especially in individuals with compromised blood-brain barrier function. We compared the effects of atropine and tolterodine, agents that do and do not readily cross the blood-brain barrier, respectively, administered peripherally (intravenous [i.v.]) and centrally (intracerebroventricular [i.c.v.]) on cystometrography in conscious rats after cerebral infarction induced by middle cerebral artery occlusion or sham surgery. We hypothesized that tolterodine would produce greater improvement in bladder capacity and less impairment in bladder contractility and that the effects of both agents would be greater in rats with cerebral infarction and sham-operated rats after peripheral administration, but that tolterodine and atropine would exert similar effects after central administration. Bladder capacity was markedly reduced following cerebral infarction. Low-dose i.v. tolterodine (<or=20 nmol/kg) significantly reversed this effect without altering residual volume or bladder contraction pressure. Low-dose i.v. atropine (2 nmol/kg) had no effect on bladder capacity but significantly decreased bladder contraction pressure. Higher doses of i.v. atropine (>or=20 nmol/kg) significantly increased bladder capacity but also significantly increased residual volume and decreased bladder contraction pressure. Tolterodine was significantly more efficacious than atropine in increasing bladder capacity, whereas atropine produced significantly greater increases in residual volume and reductions in bladder contraction pressure; these treatment group differences were also observed in sham-operated animals. Tolterodine and atropine administered i.c.v. significantly increased bladder capacity following cerebral infarction or sham surgery; however, this was accompanied by significantly increased residual volume and decreased bladder contraction time. The decrease in bladder contraction time was significantly smaller after tolterodine vs atropine. Peripherally acting muscarinic receptor antagonists may be preferable to centrally acting agents for minimizing adverse events, such as incomplete bladder emptying, even in individuals with compromised blood-brain barrier function.

Mild brain ischemia produces bladder hyperactivity without brain damage in rats

INTRODUCTION

The influence of brain ischemia without cerebral infarction on voiding function is unknown. To investigate the effects of a reduction in cerebral blood flow on voiding function, the influence of chronic cerebral hypoperfusion (CH) on bladder activity was examined in rats.

MATERIALS AND METHODS

CH was induced in each of 11 female Sprague-Dawley rats by anastomosis between the right external jugular vein and the right common carotid artery with partial obstruction of the left common carotid artery. Twelve intact animals comprised a control group. Voided volume per micturition was assessed in a metabolic cage for 24 h on weeks 2, 4, and 8. Eight weeks after the operation, the rats were tested in a hippocampus-related learning paradigm, the Morris water maze. Bladder activity was monitored in 13 rats with continuous infusion cystometrography (CMG) at 2 weeks. After evaluation, the rats' brains were stained by perfusion with 2% 2,3,5-triphenyltetrazolium chloride (TTC).

RESULTS

Voided volume per micturition was significantly reduced and voiding frequency was significantly increased in CH rats 2 weeks after CH as compared to the control group (p < 0.05). Bladder capacity on CMG of CH rats was significantly reduced 14 days after CH as compared to the controls (p < 0.05). Although TTC staining of the CH rat brain did not show cerebral infarction, CH induced impairment of water maze learning.

CONCLUSIONS

These results indicate that mild forebrain ischemia without infarction results in the development of bladder hyperactivity and impairment of memory. Mild brain ischemia with aging may induce bladder overactivity in humans. Further studies of the nervous system related to bladder hyperactivity using this animal model may lead to pharmacological therapy or prevention of bladder overactivity in the aging individual with an unidentified origin of voiding dysfunction.

Acetylcholinesterase inhibitor acting on the brain improves detrusor overactivity caused by cerebral infarction in rats

PURPOSE

The functional contribution of the cholinergic pathway in the frontal cortex to micturition was evaluated following cerebral ischemia. Furthermore, it was examined whether reactivation of this regulatory system using acetylcholinesterase inhibitor could improve detrusor overactivity.

METHODS

Left middle cerebral artery occlusion (MCAO) was performed in female Sprague-Dawley rats. Choline acetyltransferase (ChAT) activities after MCAO were assayed to assess the damage to cholinergic neurons. ChAT activities in the bilateral cortex, hippocampus, and pons were calculated by measuring the conversion of 1-[14C] acetyl-coenzyme A to [14C] acetylcholine. Effects on cystometrography of i.v. or i.c.v. donepezil hydrochloride (DON), a centrally acting acetylcholinesterase inhibitor, were investigated in conscious sham-operated (SO) and cerebral infarcted (CI) rats. To investigate whether DON in the forebrain was affected, we decerebrated rats after CI or SO, and investigated the effects on cystometrography of i.v. DON.

RESULTS

Bladder capacity was markedly decreased after MCAO, and remained below half of the pre-occlusion capacity. The greatest increase in bladder capacity was attained at 1.2 x 10(-2) nM/kg of DON given i.v., with a change of 52.8% (P < 0.05). In cases of i.c.v. DON, the greatest increase in bladder capacity was at the dose of 6 x 10(-2) pmol with the change of 95.8% (P < 0.01). The activity of ChAT was decreased in the left cortex and hippocampus 24 h after MCAO (P < 0.05). In decerebrated rats, low dose of DON did not change micturition parameters.

CONCLUSIONS

These results suggest that by upregulation of the forebrain muscarinic inhibitory mechanism, acetylcholinesterase inhibitor improves detrusor overactivity by cerebral infarction.

Urodynamic effects of oxybutynin and tolterodine in conscious and anesthetized rats under different cystometrographic conditions

Background

Antimuscarinic agents are the most popular treatment for overactive bladder and their efficacy in man is well documented, producing decreased urinary frequency and an increase in bladder capacity. During cystometry in rats, however, the main effect reported after acute treatment with antimuscarinics is a decrease in peak micturition pressure together with little or no effect on bladder capacity. In the present experiments we studied the effects, in rats, of the two most widely used antimuscarinic drugs, namely oxybutynin and tolterodine, utilising several different cystometrographic conditions. The aim was to determine the experimental conditions required to reproduce the clinical pharmacological effects of antimuscarinic agents, as seen in humans, in particular their ability to increase bladder capacity.

Results

Intravenous or oral administration of tolterodine or oxybutynin in conscious rats utilized 1 day after catheter implantation and with saline infusion at constant rate of 0.1 ml/min, gave a dose-dependent decrease of micturition pressure (MP) with no significant change in bladder volume capacity (BVC). When the saline infusion rate into the bladder was decreased to 0.025 ml/min, the effect of oral oxybutynin was similar to that obtained with the higher infusion rate. Also, experiments were performed in rats in which bladders were infused with suramin (3 and 10 μM) in order to block the non-adrenergic, non-cholinergic component of bladder contraction. Under these conditions, oral administration of oxybutynin significantly reduced MP (as observed previously), but again BVC was not significantly changed.

In conscious rats with bladders infused with diluted acetic acid, both tolterodine and oxybutynin administered at the same doses as in animals infused with saline, reduced MP, although the reduction appeared less marked, with no effect on BVC.

In conscious rats utilized 5 days after catheter implantation, a situation where inflammation due to surgery is reduced, the effect of tolterodine (i.v.) and oxybutynin (p.o.) on MP was smaller and similar, respectively, to that observed in rats utilized 1 day after catheter implantation, but the increase of BVC was not statistically significant.

In anesthetized rats, i.v. administration of oxybutynin again induced a significant decrease in MP, although it was of questionable relevance. Both BVC and threshold pressure were not significantly reduced. The number and amplitude of high frequency oscillations in MP were unmodified by treatment.

Finally, in conscious obstructed rats, intravenous oxybutynin did not modify frequency and amplitude of non-voiding contractions or bladder capacity and micturition volume.

Conclusion

Despite the different experimental conditions used, the only effect on cystometrographic parameters of oxybutynin and tolterodine in anesthetized and conscious rats was a decrease in MP, whereas BVC was hardly and non-significantly affected. Therefore, it is difficult to reproduce in rats the cystometrographic increase in BVC as observed in humans after chronic administration of antimuscarinic agents, whereas the acute effects seem more similar.

Effects of solifenacin succinate (YM905) on detrusor overactivity in conscious cerebral infarcted rats

Solifenacin succinate [YM905, (+)-(1S,3'R)-quinuclidin-3'-yl 1-phenyl-1,2,3,4-tetrahydroisoquinoline-2-carboxylate monosuccinate] is a novel muscarinic receptor antagonist. We examined the effects of solifenacin and two other muscarinic receptor antagonists, tolterodine and propiverine, on detrusor overactivity in cerebral infarcted rats. Evaluation was done under conscious conditions using cystometry 1 day after middle cerebral artery occlusion. The cerebral infarcted rats showed decreases in bladder capacity and voided volume and an increase in residual volume, but no change in micturition pressure. Solifenacin increased bladder capacity and voided volume at doses of 0.03 mg/kg i.v. or more. Tolterodine increased bladder capacity and voided volume at 0.03 and 0.1 mg/kg i.v., while propiverine increased bladder capacity and voided volume at 1 mg/kg i.v. and at 0.3 and 1 mg/kg i.v., respectively. In contrast, none of the three drugs affected residual volume or micturition pressure. These results suggest that solifenacin may improve detrusor overactivity without causing urinary retention and may be a promising drug in the treatment of patients with overactive bladder syndrome.

Urodynamics in a rat neurogenic bladder model with a unilateral electrolytic lesion of the basal forebrain

OBJECTIVE

To investigate the changes in bladder function in rats with an electrolytic lesion of the right basal forebrain (RBF) and to determine the effects of AH-9700, a novel sigma receptor ligand, on cystometry in RBF-lesioned rats.

MATERIALS AND METHODS

A lesion was made electrolytically in the RBF of male Wistar rats. At 7 or 8 days after the lesion or sham surgery, continuous cystometry was performed in awake rats. In addition, contractile responses to electrical field stimulation or carbachol were measured in isolated bladder strips, as were the forebrain contents of acetylcholine, monoamine neurotransmitters and their metabolites.

RESULTS

RBF-lesioned rats showed a remarkable increase in voiding frequency, with a decrease in voiding threshold pressure but no change in voiding pressure, compared with sham-operated rats. However, contractile responses in bladder strips isolated from RBF-lesioned rats were no different from those in strips isolated from sham-operated rats. In RBF-lesioned rats, the contents of acetylcholine, dopamine, 4-dihidroxyphenylacetic acid and homovanillic acid were significantly decreased in the right forebrain. AH-9700 dose-dependently decreased the voiding frequency and increased the threshold pressure in RBF-lesioned rats. Anti-muscarinic agents (oxybutynin and propiverine) also decreased the voiding frequency, but their effects were less potent than that of AH-9700.

CONCLUSIONS

The RBF-lesioned rat may be a useful model for the neurogenic bladder of supraspinal origin. Moreover, AH-9700 effectively improves bladder dysfunction in this model.

Overactive bladder--experimental aspects

Supra-pontine lesions resulting from neurological disorders such as vascular disease, Parkinson's disease, or Alzheimer type senile dementia lead to an increase in bladder activity. This is due in part to the removal at the cortical inhibitory control of the micturition center in the brain stem - i.e. the pontine micturition center (PMC) - and in part to facilitation of excitatory control. These inhibitory or excitatory controls consist of several neurotransmitter systems, including glutamate, dopamine, gamma-aminobutyric acid (GABA), and acetylcholine. Bladder overactivity caused by cerebral infarction is mediated by upregulation of N-methyl-D-aspartate (NMDA) glutamatergic and D2 dopaminergic excitatory mechanisms, and by downregulation of NMDA glutamatergic and Ml muscarinic inhibitory mechanisms in the brain. Bladder overactivity associated with Parkinson's disease is reportedly induced by a loss of input to the D1 dopaminergic receptor. Furthermore, bladder overactivity caused by Alzheimer type dementia is thought to be mediated by downregulation of M1 muscarinic inhibitory mechanisms. Development of bladder overactivity following cerebral infarction is mediated by activation of the NMDA receptor and accompanied by an increase in c-fos, zif268 and COX-2 mRNA expression in the dorsal pontine tegmentum.

Functional role of central muscarinic receptors for micturition in normal conscious rats

PURPOSE

Antimuscarinic agents, which are used in to treat urgency and urge incontinence, have well-known effects on peripheral muscarinic receptors. However, some currently used drugs may have effects on muscarinic receptors in the brain and/or spinal cord involved in voiding control. We tested if muscarinic receptors within the central nervous system mediate a tonic excitatory influence on voiding in rats and if these receptors can be differently influenced by antimuscarinic drugs.

MATERIALS AND METHODS

The effects on cystometrography of intracerebroventricular atropine, oxybutynin, tolterodine and darifenacin were investigated in normal conscious rats.

RESULTS

Atropine (0.2 to 2 nmol.) dose dependently affected urodynamic parameters. At 2 nmol. in 6 rats the drug decreased voiding pressure (p <0.01), and increased bladder capacity (p <0.001), voided volume (p <0.05) and post-void residual volume (p <0.05). In 6 rats oxybutynin (6 to 40 nmol.) given at a dose of 6 nmol. caused no change in cystometric parameters, while at 20 nmol. the drug decreased voiding pressure (p <0.01). Tolterodine (2 to 20 nmol.) dose dependently changed urodynamic parameters, while at 20 nmol. in 6 rats the drug decreased voiding pressure (p <0.01) and increased bladder capacity (p <0.05) and voided volume (p <0.05). Darifenacin given at a dose of 20 nmol. in 6 rats caused no change in cystometric parameters.

CONCLUSIONS

Muscarinic receptor mechanisms in the central nervous system mediate a tonic excitatory influence on voiding in rats, while nonsubtype selective antimuscarinic drugs may have an inhibitory effect on these mechanisms.