Effects of the atypical neuroleptic clozapine on micturition parameters in anesthetized rats

The low dopamine hypothesis: A plausible mechanism underpinning residual urine, overactive bladder and nocturia (RON) syndrome in older patients

INTRODUCTION

Aging is associated with a combination of several lower urinary tract (LUT) signs and symptoms, including residual urine, overactive bladder and nocturia. One of the mechanisms of this LUT dysfunction that has not been discussed in dept so far is the role of dopamine (DA).

METHODS

In this narrative review, we explore the dopaminergic hypothesis in the development of this combination of LUT signs and symptoms in older adults.

RESULTS

DA is one of the neurotransmitters whose regulation and production is disrupted in aging. In synucleinopathies, altered DAergic activity is associated with the occurrence of LUTS and sleep disorders. Projections of DAergic neurons are involved in the regulation of sleep, diuresis, and bladder activity. The low dopamine hypothesis could explain the genesis of a set of LUT signs and symptoms commonly seen in this population, including elevated residual urine, Overactive bladder syndrome and Nocturia (discussed as the RON syndrome). This presentation is however also common in older patients without synucleinopathies or neurological disorders and therefore we hypothesise that altered DAergic activity because of pathological aging, and selective destruction of DAergic neurons, could underpin the presentation of this triad of LUT dysfunction in the older population.

CONCLUSION

The concept of RON syndrome helps to better understand this common phenotypic presentation in clinical practice, and therefore serves as a useful platform to diagnose and treat LUTS in older adults. Besides recognizing the synucleinopathy "red flag" symptoms, this set of multi-causal LUT signs and symptoms highlights the inevitable need for combination therapy, a challenge in older people with their comorbidities and concomitant medications.

The serotonin (5-hydroxytryptamine) 5-HT7 receptor is up-regulated in Onuf's nucleus in rats with chronic spinal cord injury

OBJECTIVES

To examine the effect of intrathecal (i.t.) serotonin (5-hydroxytryptamine) 5-HT₇ agonist administration on voiding function in the urethane-anesthetised rat, and the change in 5-HT₇ receptor (5-HT₇ R) expression in the lumbosacral cord Onuf's nucleus after spinal cord injury (SCI).

MATERIALS AND METHODS

In all, 32 female Sprague-Dawley (SD) rats were equally divided into a spinally intact (SI) group and SCI group (n = 16 each). At 8 weeks after transection, half of the rats underwent continuous cystometry under urethane anaesthesia, and the 5-HT₇ R-selective agonist LP44 was given (i.t.). The remaining rats were used for pseudorabies (PRV) retrograde tracing, immunofluorescence, and Western Blot.

RESULTS

LP44 administered i.t. had no effect in the SI rats. In SCI rats, LP44 (1-30 μg/kg) induced significant dose-dependent increases in micturition volume, voiding efficiency, number of high-frequency oscillations per micturition; and decreases in residual volume, bladder capacity, peak bladder pressure, threshold pressure and non-voiding contractions. The 5-HT₇ R antagonist, SB-269970 (10 μg/kg), partially reversed LP44-induced changes. Using PRV retrograde tracing and immunofluorescence, 5-HT₇ Rs were found in the L6-S1 spinal cord Onuf's nucleus in both SI and SCI rats, but the expression was significantly greater in the SCI rats. Western blot showed significantly more 5-HT₇ Rs in the ventral L6-S1 spinal cord in SCI rats.

CONCLUSION

A 5-HT₇ R agonist, given i.t., improved voiding efficiency in urethane-anesthetised SCI rats, and the 5-HT₇ R was significantly up-regulated in the lumbosacral cord Onuf's nucleus. If valid for humans, these findings suggest that the 5-HT₇ R could be a target for therapeutic interventions.

Chronic spinal cord injury causes upregulation of serotonin (5-HT)2A and 5-HT2C receptors in lumbosacral cord motoneurons

OBJECTIVES

To investigate whether the voiding dysfunction caused by spinal cord injury (SCI) in rats can be improved by i.v. administration of the serotonin (5-HT)_2A/2C receptor agonist 2,5-dimethoxy-4-iodophenyl-2-aminopropanehydrochloride (DOI), and to discuss whether the mechanism can be ascribed to 5-HT_2A and 5-HT _2C receptor upregulation in lumbosacral cord motoneurons.

MATERIALS AND METHODS

Female Sprague-Dawley rats were divided into two groups (SCI group vs normal control [NC] group). Under urethane anaesthesia, cystometry was performed to examine the variation in urodynamic variables before and after successive intrathecal (i.t.) administration of various doses of DOI into the lumbosacral cord. Changes in 5-HT_2A and -_2C receptors in the lumbosacral cord were also investigated using immunohistochemical staining and Western blot analysis.

RESULTS

Compared with NC rats, the SCI rats had higher bladder capacity and post-void residual urine volume, and lower voiding efficiency. After SCI, DOI improved voiding efficiency, probably via external urethral sphincter (EUS) activity. Immunohistochemical staining and Western blot analysis showed that 5-HT_2A and -_2C receptors were upregulated in lumbosacral cord motoneurons.

CONCLUSION

In rats with SCI, DOI can improve voiding efficiency; this may be attributable to 5-HT_2A and -_2C receptor upregulation in lumbosacral cord motoneurons controlling EUS activity.

Characterization of bladder and external urethral activity in mice with or without spinal cord injury--a comparison study with rats

To clarify the lower urinary tract function in mice, we compared bladder and urethral activity between rats and mice with or without spinal cord injury (SCI). Female Sprague-Dawley rats and C57BL/6N mice were divided into five groups:1) spinal intact (SI) rats,2) SI mice,3) pudendal nerve transection (PNT) SI mice,4) spinal cord injury (SCI) rats, and 5) SCI mice. Continuous cystometry (CMG) and external urethral sphincter (EUS)-electromyogram (EMG) analyses were conducted under an awake, restrained condition. During voiding bladder contractions, SI animals exhibited EUS bursting with alternating active and silent periods, which, in rats but not mice, coincided with small-amplitude intravesical pressure oscillations in CMG recordings. In SI mice with bursting-like EUS activity, the duration of active periods was significantly shorter by 46% (32 ± 5 ms) compared with SI rats (59 ± 9 ms). In PNT-SI mice, there were no significant differences in any of cystometric parameters compared with SI mice. In SCI rats, fluid elimination from the urethra and the EUS bursting occurred during small-amplitude intravesical pressure oscillations. However, SCI mice did not exhibit clear EUS bursting activity or intravesical pressure oscillations but rather exhibited intermittent voiding with slow large-amplitude reductions in intravesical pressure, which occurred during periods of reduced EUS activity. These results indicate that EUS pumping activity is essential for generating efficient voiding in rats with or without spinal cord injury. However, EUS bursting activity is not required for efficient voiding in SI mice and does not reemerge in SCI mice in which inefficient voiding occurs during periods of reduced tonic EUS activity.

The effect of the 5-HT7 serotonin receptor agonist, LP44, on micturition in rats with chronic spinal cord injury

AIMS

To better understand the effects of the selective 5-HT7 receptor agonist 4-[2-(Methylthio)phenyl]-N-(1,2,3,4-tetrahydro-1-naphthalenyl)-1-piperazinehexanamide hydrochloride (LP44) on micturition in spinal cord injury (SCI) rats.

METHODS

Female Sprague-Dawley rats weighing 200-275 g were used. SCI was produced in 8 of the 16 rats by transection at the T10 level; cystometric study occurred 8-12 weeks post-transection. Intravesical pressure was monitored in urethane-anesthetized animals via a transvesical catheter. The selective 5-HT7 antagonist (R)-3-[2-[2-(4-Methylpiperidin-1-yl)ethyl]pyrrolidine-1-sulfonyl] phenol hydrochloride (SB-269970) was administered after each LP44 dose-response curve (all drugs were administered intravenously, i.v).

RESULTS

Compared to controls, SCI rats had a higher bladder capacity and residual volume, and a lower voiding efficiency. In SCI rats, LP44 (0.003-0.3 mg/kg, i.v) induced significant dose-dependent increases in micturition volume, significant dose-dependent decreases in residual volume, resulting in significant increases in voiding efficiency. CMG measurements showed a dose-dependent increase of the high-frequency oscillation (HFO) activity, including the number of small oscillation per voiding. This was correlated with the improved voiding efficiency. SB-269970 (0.1 mg/kg, i.v) partially or completely reversed all LP44-induced changes.

CONCLUSIONS

HFOs seems to be correlated with external urethral sphincter (EUS) bursting activity during voiding. Both the bladder voiding efficiency and the periodic EUS activity were decreased in SCI rats. 5-HT7 receptor agonist can enhance HFO activity, thereby improving voiding efficiency. Whether or not these results may have implications for the future treatment of voiding dysfunction in SCI patients remains to be studied.

A 2-year prospective follow-up study of lower urinary tract symptoms in patients treated with clozapine

Urinary incontinence and enuresis are well-known side effects of clozapine. However, clinical experience has shown that patients also suffer from diverse lower urinary tract symptoms (LUTS). The natural course of clozapine-related LUTS is unclear. Thus, a longitudinal follow-up study is needed. A total of 101 subjects who were taking clozapine initially participated. Their LUTS were evaluated using the International Prostate Symptom Score (IPSS), other questionnaires, and a medical records review. After 2 years, 87 of the original subjects could be contacted, and the status of their LUTS was re-evaluated. The average IPSS total was 7.4 +/- 5.9 at the initial evaluation. Although only 11 subjects (10.9%) reported actual incontinence, 42 subjects (41.6%) were found to have clinically significant LUTS (IPSS total score > or =8). No influencing factors could be found among the demographic and clinical variables. At the follow-up, the average IPSS total (7.9 +/- 6.0) and the percentage of subjects with clinically significant LUTS (43.7%) had both increased, although the change was not statistically significant. The prevalence of LUTS in clozapine-medicated patients was higher than in the general population of the same age. However, the prevalence of incontinence was only a quarter of that of LUTS. If clinicians focus only on incontinence, distress from LUTS will not receive appropriate attention. Furthermore, contrary to literature observations, clozapine-related LUTS did not remit easily but rather persisted even into the long-term maintenance phase. More concern should be directed at these troublesome and often neglected side effects.

Dopaminergic mechanisms controlling urethral function in rats

AIMS

To investigate the role of dopamine receptor subtypes in the control of urethral activity.

METHODS

Simultaneous recordings of intravesical and urethral perfusion pressure (UPP) were performed in rats under urethane anesthesia. Changes in coordinated activity of the bladder and urethral sphincter were examined following intravenous (i.v.), intrathecal (i.t.), or intracerebroventricular (i.c.v.) administration of dopamine D1- and D2-like receptor agonists (SKF38393 and quinpirole, respectively) and antagonists (SCH23390 and remoxipride, respectively).

RESULTS

Quinpirole (0.03, 0.1, and 0.3 mg/kg i.v.) dose-dependently decreased baseline urethral pressure to 45.33 +/- 5.8, 33.7 +/- 3.3 (P < 0.05, n = 6), and 27.7 +/- 3.3 cm H(2)O (P < 0.05, n = 5) from the control value (46.0 +/- 4.0 cm H(2)O), respectively. i.c.v. injection of quinpirole (1 microg) decreased baseline urethral pressure to 33.6 +/- 5.0 cm H(2)O (P < 0.05, n = 4) from the control value (51.4 +/- 4.9 cm H(2)O) in contrast to the insignificant effects of i.t. administration of the drug (3 microg). The decrement of baseline pressure induced by quinpirole (0.1 mg/kg i.v.) was suppressed by alpha-bungarotoxin (BGT), a neuromuscular blocking agent. SCH23390 (1 and 3 mg/kg, i.v.) dose-dependently decreased the frequency of high frequency oscillation (HFO) of the urethral sphincter. SKF38393 or remoxipride did not have significant effects on any parameters of bladder and urethral activity.

CONCLUSIONS

These results indicate that activation of D2-like dopamine receptors at a supraspinal site can suppress activity of the striated muscle urethral sphincter. Thus, decreased urethral resistance induced by D2 dopamine receptor activation might aggravate urge incontinence symptoms often seen in patients with Parkinson's disease (PD).

Central effects of clozapine in regulating micturition in anesthetized rats

BACKGROUND

We previously showed that systemic administration of the atypical neuroleptic clozapine in the rat altered a number of urodynamic variables and inhibited the external urethral sphincter. Since clozapine acts at several receptor types both at the periphery and the central nervous system, the site of action remained uncertain. Therefore, the purpose of this study was to determine the effects of central administration of clozapine on the bladder and the external urethral sphincter during cystometry and to examine differences in spinal versus supraspinal administration. We extended our observations by delivering clozapine centrally in anesthetized rats instrumented with either an intrathecal (L6-S1 spinal segment) or an intracerebroventricular (lateral ventricle) catheter.

RESULTS

Clozapine decreased micturition volume and increased residual volume possibly by acting at a supraspinal site. Expulsion time and amplitude of the high frequency oscillations were reduced by clozapine possibly by acting at a spinal site. Bladder capacity was increased after central clozapine but probably due to a peripheral effect. Clozapine acting at spinal and supraspinal sites increased pressure threshold. Contraction time and peak pressure were not affected by clozapine. The EMG from the external urethral sphincter was also reduced following clozapine centrally and suggests a spinal and a supraspinal site of action.

CONCLUSIONS

The results from the present study suggest that spinal and supraspinal central sites mediate clozapine's action in inhibiting expulsion parameters and the external urethral sphincter of the rat. Therefore, the reduction in the voiding efficiency observed after clozapine appears to be mediated by spinal and supraspinal sites.

Effects of two atypical neuroleptics, olanzapine and risperidone, on the function of the urinary bladder and the external urethral sphincter in anesthetized rats

BACKGROUND

A previous report showed that the atypical neuroleptic clozapine resulted in marked changes in urodynamic parameters and greatly inhibited the activity of the external urethral sphincter in anesthetized rats. Such findings may help explain the high incidence of urinary disturbances reported during clozapine therapy. In an effort to extend our observations to other atypical neuroleptic agents, the present study investigated the effects of two newer atypical antipsychotics, olanzapine and risperidone, on the bladder and external urethral sphincter during cystometry in anesthetized rats.

RESULTS

At a dose of 0.1 mg/kg (i.v.), olanzapine decreased the micturition volume and increased the residual volume. In addition, olanzapine decreased the expulsion time and the amplitude of the high frequency oscillations observed during the expulsion phase. Larger doses (1 mg/kg) had a greater effect. Olanzapine also reduced the activity recorded from the external urethral sphincter, and the bursting observed during the expulsion phase was abolished by 1.0 mg/kg. Risperidone had similar effects although the maximal effects were smaller than those observed with olanzapine. The amplitude of bladder contractions elicited by electrical stimulation of the pelvic nerve was reduced by olanzapine but not risperidone suggesting a possible anti-muscarinic peripheral effect of olanzapine.

CONCLUSIONS

Olanzapine and risperidone significantly altered several voiding parameters and decreased the activity of the external urethral sphincter in the anesthetized rat. We propose that these effects are due to the central action of these drugs and not to peripheral effects. These findings may explain some of the clinical reports of urinary incontinence with risperidone and may predict similar occurrences with olanzapine therapy.

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.