Mechanisms by which the serotonergic system inhibits micturition in rats

Delivery of the 5-HT2A Receptor Agonist, DOI, Enhances Activity of the Sphincter Muscle during the Micturition Reflex in Rats after Spinal Cord Injury

Simple Summary

Spinal cord injury often disrupts connections between the brain and spinal cord leading to a plethora of health complications, including bladder dysfunction. Spinal cord injured patients are left with symptoms such as a leaky bladder (the inability to hold their urine), frequent urinary tract infections, and potential kidney failure. However, previous studies have shown that manipulation of serotoninergic receptors can improve urinary performance following spinal cord injury. In the current study, we sought to explore how stimulation of a specific serotonergic receptor subtype can significantly enhance bladder function in spinal cord injured rats. To do so, we utilized spinal cord injured female rats that underwent various bladder performance evaluations combined with pharmacological intervention of a specific serotonergic subtype. Additionally, the primary site of action was investigated to determine effects elicited during various administration routes (e.g., directly into the cord, into the femoral vein, or into the skin). Stimulation of this receptor subtype, regardless of delivery route, improved activity of the external urethral sphincter and detrusor-sphincter coordination in spinal cord injured rats. Collectively, the results of these experiments have the potential to provide vital guidance for the development of therapeutic strategies to alleviate urinary dysfunction following spinal cord injury.

Abstract

Traumatic spinal cord injury (SCI) interrupts spinobulbospinal micturition reflex pathways and results in urinary dysfunction. Over time, an involuntary bladder reflex is established due to the reorganization of spinal circuitry. Previous studies show that manipulation of serotonin 2A (5-HT_2A) receptors affects recovered bladder function, but it remains unclear if this receptor regulates the activity of the external urethral sphincter (EUS) following SCI. To elucidate how central and peripheral serotonergic machinery acts on the lower urinary tract (LUT) system, we employed bladder cystometry and EUS electromyography recordings combined with intravenous or intrathecal pharmacological interventions of 5-HT_2A receptors in female SCI rats. Three to four weeks after a T10 spinal transection, systemic and central blockage of 5-HT_2A receptors with MDL only slightly influenced the micturition reflex. However, delivery of the 5-HT_2A receptor agonist, DOI, increased EUS tonic activity and elicited bursting during voiding. Additionally, subcutaneous administration of DOI verified the enhancement of continence and voiding capability during spontaneous micturition in metabolic cage assays. Although spinal 5HT_2A receptors may not be actively involved in the recovered micturition reflex, stimulating this receptor subtype enhances EUS function and the synergistic activity between the detrusor and sphincter to improve the micturition reflex in rats with SCI.

Psychopharmacological effects of riparin III from Aniba riparia (Nees) Mez. (Lauraceae) supported by metabolic approach and multivariate data analysis

Background

Currently there is a high prevalence of humor disorders such as anxiety and depression throughout the world, especially concerning advanced age patients. Aniba riparia (Nees) Mez. (Lauraceae), popular known as “louro”, can be found from the Amazon through Guianas until the Andes. Previous studies have already reported the isolation of alkamide-type alkaloids such as riparin III (O-methyl-N-2,6-dyhydroxy-benzoyl tyramine) which has demonstrated anxiolytic and antidepressant-like effects in high doses by intraperitoneal administration.

Methods

Experimental protocol was conducted in order to analyze the anxiolytic-like effect of riparin III at lower doses by intravenous administration to Wistar rats (Rattus norvegicus) (n = 5). The experimental approach was designed to last 15 days, divided in 3 distinct periods of five days: control, anxiogenic and treatment periods. The anxiolytic-like effect was evaluated by experimental behavior tests such as open field and elevated plus-maze test, combined with urine metabolic footprint analysis. The urine was collected daily and analyzed by ¹H NMR. Generated data were statistically treated by Principal Component Analysis in order to detect patterns among the distinct periods evaluated as well as biomarkers responsible for its distinction.

Results

It was observed on treatment group that cortisol, biomarker related to physiological stress was reduced, indicating anxiolytic-like effect of riparin III, probably through activation of 5-HT_2A receptors, which was corroborated by behavioral tests.

Conclusion

¹H NMR urine metabolic footprint combined with multivariate data analysis have demonstrated to be an important diagnostic tool to prove the anxiolytic-like effect of riparin III in a more efficient and pragmatic way.

The association between serum serotonin levels and overactive bladder: results from a community-based cross-sectional study in Japan

PURPOSE

To investigate the association between serum serotonin (5-HT) levels and overactive bladder (OAB) in a community-dwelling population.

METHODS

This cross-sectional study analyzed 1024 subjects who participated in the Iwaki Health Promotion Project in 2015 in Hirosaki, Japan. OAB was assessed using the Overactive Bladder Symptom Score (OABSS). OAB was defined as an occurrence of urinary urgency at least once a week and an OABSS of ≥ 3. We assessed serum 5-HT levels, laboratory data, and comorbidities of each participants. Participants' mental health status was evaluated using the Center for Epidemiologic Studies Depression (CES-D) scale. The association of serum 5-HT levels and OAB was analyzed by multivariable logistic regression analysis.

RESULTS

This study included 394 men and 630 women. Of those, 118 (44 male and 74 female) were OAB sufferers. There were significant group differences in age, history of cardiovascular disease, chronic kidney disease, hypertension, diabetes mellitus, and CES-D score. Participants' serum 5-HT levels in the OAB group were significantly lower than those in the non-OAB group (100 vs. 127 ng/mL, P < 0.001). Multivariable analysis showed that age (odds ratio [OR]; 1.06, 95% confidence interval [CI]; 1.04-1.08, P < 0.001) and log serum 5-HT level (OR; 0.25, 95% CI; 0.10-0.68, P = 0.006) were independently associated with OAB.

CONCLUSIONS

Lower serum 5-HT levels could independently be associated with the presence of OAB. Further study is necessary to elucidate a possible causal relationship between serum 5-HT levels and OAB.

Effect of 5-HT2A receptor antagonist ketanserin on micturition in male rats

OBJECTIVES

This study aimed to investigate the effects of ketanserin on micturition mediated via the 5-HT_2A receptor in the motoneuron nucleus of the Lumbosacral cord, as reflected in high frequency oscillations (HFOs) of intravesical pressure and the external urethral sphincter electromyogram (EUS-EMG) in anesthetized male rats. METHODS：: Male Sprague-Dawley rats were used. Cystometry and EUS-EMG were performed in all rats under urethane anesthesia to examine the variations after successive intrathecal (i.t.) administration of various doses of ketanserin into the lumbosacral cord. Immunofluorescence staining and Western blotting were made to observe the distribution of 5-HT2 A and -2C receptors in the lumbosacral cord motor neurons.

RESULTS

Compared to the controls, ketanserin-treated rats showed a declined trend of dose-dependent manner in the HFOs, in accordance with the variation of EUS-EMG, while decreased micturition volume, voiding efficiency, and increased post-void residual volume was only observed at the dose of 0.1 mg/kg. The effects of ketanserin on the HFO and EUS-EMG activity were partially or completely reversed by the 5-HT_2A/2C receptor agonist, DOI. Meanwhile, immunofluorescence staining and Western blot analysis showed that immunoreactivity of 5-HT_2A receptor was higher than that of 5-HT_2C, labeling in the lumbosacral cord motoneurons.

CONCLUSIONS

The intrathecally administrated 5-HT_2A receptor antagonist ketanserin can weaken the EUS bursting activity, decrease HFOs, and reduce voiding efficiency as dose dependently. The effects of ketanserin on micturition may be mainly mediated via the 5-HT_2A receptors in the motoneuron nucleus of the lumbosacral cord.

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.

Brain serotoninergic nervous system is involved in bombesin-induced frequent urination through brain 5-HT7 receptors in rats

BACKGROUND AND PURPOSE

Psychological stress exacerbates symptoms of urinary bladder dysfunction; however, the underlying brain mechanisms are unclear. We have demonstrated that centrally administered bombesin, a stress-related neuropeptide, facilitates the rat micturition reflex. Brain bombesin-like peptides modulate the serotoninergic nervous system activity under stress conditions; therefore, we examined whether brain 5-HT is involved in the bombesin-induced increased frequency of urination in urethane-anaesthetised male Sprague-Dawley rats.

EXPERIMENTAL APPROACH

Evaluation of intercontraction intervals (ICI) and maximal voiding pressure (MVP) during cystometrograms were started 1 h before i.c.v. administration of bombesin or i.c.v. pretreatment with the 5-HT receptor antagonists.

KEY RESULTS

Bombesin (0.03 nmol per animal, i.c.v.) significantly reduced ICI without affecting MVP. The bombesin-induced response was significantly suppressed by acute depletion of brain 5-HT, which was induced by pretreatment with p-chlorophenylalanine, a 5-HT synthesis inhibitor. Bombesin at a lower dose (0.01 nmol per animal, i.c.v.) showed no significant effect on ICI, while it significantly reduced ICI in the presence of WAY-100635 (5-HT_1A receptor antagonist, 0.1 or 0.3 μg per animal, i.c.v.), which can block the negative feedback control of 5-HT release. Bombesin (0.03 nmol per animal)-induced ICI reduction was significantly attenuated by SB269970 (5-HT₇ receptor antagonist, 0.1 or 0.3 μg per animal, i.c.v.) but not by ritanserin (5-HT₂ receptor antagonist, 0.3 or 1 μg per animal, i.c.v.).

CONCLUSIONS AND IMPLICATIONS

The brain serotoninergic nervous system is involved in the facilitation of the rat micturition reflex induced by bombesin-like peptides at least in part through brain 5-HT₇ receptors.

Serotonergic regulation of distention-induced ATP release from the urothelium

Serotonin [5-hydroxytryptamine (5-HT)] is involved in both motor and sensory functions in hollow organs, especially in the gastrointestinal tract. However, the involvement of 5-HT in visceral sensation of the urinary bladder remains unknown. Because distention-induced ATP release from the urothelium plays an essential role in visceral sensation of the urinary bladder, we investigated the regulation of urothelial ATP release by the 5-HT signaling system. RT-PCR and immunohistochemical analyses of the urothelium revealed specific expression of 5-HT_1D and 5-HT₄ receptors. The addition of 5-HT did not affect urothelial ATP release without bladder distention, but it significantly reduced distention-induced ATP release by physiological pressure during urine storage (5 cmH₂O). The inhibitory effect of 5-HT on distention-elicited ATP release was blocked by preincubation with the 5-HT_1B/1D antagonist GR-127935 but not by the 5-HT₄ antagonist SB-204070. mRNA encoding tryptophan hydroxylase 1 was detected in the urinary bladder by nested RT-PCR amplification, and l-tryptophan or the selective serotonin reuptake inhibitor citalopram also inhibited ATP release, indicating that 5-HT is endogenously synthesized and released in the urinary bladder. The addition of GR-127935 significantly enhanced the distention-elicited ATP release 40 min after distention, whereas SB-204070 reduced the amount of ATP release 20 min after distention. These data suggest that 5-HT₄ facilitates the distention-induced ATP release at an earlier stage, whereas 5-HT_1D inhibits ATP release at a later stage. The net inhibitory effect of 5-HT indicates that the action of 5-HT on the urothelium is mediated predominantly by 5-HT_1D.

Regulatory Effects of 5-Hydroxytryptamine Receptors on Voiding Function

A growing body of evidence suggests that 5-hydroxytryptamine (5-HT; serotonin) has both physiological and pathological functions in the lower urinary tract. A wide variety of 5-HT receptor subtypes are variably expressed in different organs, both peripheral and central. On urinary bladder smooth muscle, 5-HT1A, 5-HT2, 5-HT3, and 5-HT7 subtypes could function as postjunctional receptors. Postjunctional 5-HT2 receptors induce detrusor contraction of the bladder body. 5-HT1A is suggested to have a similar effect to 5-HT2, while 5-HT3 might suppress detrusor contraction evoked by direct muscle stimulation. Postjunctional 5-HT7 is reported to induce relaxation of the bladder neck, which might be required for efficient voiding. 5-HT1A, 5-HT2A, 5-HT2C, 5-HT3, 5-HT4, and 5-HT7 subtypes also could act as prejunctional receptors in autonomic excitatory nerve terminals. 5-HT2A, 5-HT2C, 5-HT3, 5-HT4, and 5-HT7 subtypes facilitate the neurogenic contraction of the detrusor by enhancing cholinergic or purinergic transmission, whereas 5-HT1A receptors might inhibit the release of acetylcholine in the detrusor. Furthermore, 5-HT1D could be involved in the suppression of ATP release from the urothelium, aiding visceral sensation of the urinary bladder. In the central pathways controlling the micturition reflex, 5-HT1A, 5-HT2A, and 5-HT7 are involved in regulation of bladder and urethral sphincter activities. Their functions, especially that of 5-HT1A, vary in a species- and site (spinal or supraspinal)- dependent manner. In addition to urinary bladder, 5-HT could be involved in prostate contraction and cell proliferation. Evidence indicates that 5-HT receptor subtypes may be novel therapeutic targets for lower urinary tract symptoms.

FUNDING

Grants-in-Aid for Scientific Research (C) (KAKENHI 23590707, 24590722, and 26460694) from the Japan Society for the Promotion of Science.

Spinal mechanism of micturition reflex inhibition by naftopidil in rats

AIM

We investigated the spinal mechanism through which naftopidil inhibits the micturition reflex by comparing the effects of noradrenaline and naftopidil in rats.

METHODS

The following were investigated: the influence of oral naftopidil on plasma monoamine and amino acid levels, the distribution of oral 14C-naftopidil, the effects of intravenous (IV) or intrathecal (IT) injection of noradrenaline or naftopidil on isovolumetric bladder contractions, amino acid levels in the lumbosacral spinal cord after IT noradrenaline or naftopidil, and the effects of IT naftopidil and strychnine and/or bicuculline on isovolumetric bladder contractions.

KEY FINDINGS

Oral naftopidil decreased the plasma adrenaline level, while it increased the serotonin and glycine levels. After oral administration, 14C-naftopidil was detected in the spinal cord and cerebrum, as well as in plasma and the prostate gland. When the bladder volume was below the threshold for isovolumetric reflex contractions, IV (0.1mg) or IT (0.1μg) noradrenaline evoked bladder contractions, but IV (1mg) or IT (0.01-1μg) naftopidil did not. When the bladder volume was above the threshold for isovolumetric reflex contractions, IV or IT noradrenaline transiently abolished bladder contractions. IT noradrenaline decreased the levels of glycine and gamma-aminobutyric acid (GABA) in the lumbosacral cord, while IT naftopidil increased the GABA level. IT strychnine and/or bicuculline blocked the inhibitory effect of IT naftopidil on bladder contractions.

SIGNIFICANCE

Naftopidil inhibits the micturition reflex by blocking α1 receptors, as well as by the activation of serotonergic, glycinergic, and GABAergic neurons in the central nervous system.

Acupuncture of the sacral vertebrae suppresses bladder activity and bladder activity-related neurons in the brainstem micturition center

Acupuncture of the sacral vertebrae has therapeutic effects in patients with overactive bladders. The mechanism of these effects, however, remains unclear. The present study, using urethane-anesthetized rats, investigated the effects of acupuncture stimulation of the sacral vertebrae on bladder activity and bladder activity-related neurons in and around Barrington's nucleus. In 95 of 147 trials (64.6%), acupuncture stimulation of the sacral vertebrae for 1 min suppressed bladder contraction for 27-2347s. Acupuncture-induced suppression of bladder contraction was blocked by intraperitoneal injection of bicuculline (Bic). Acupuncture stimulation strongly affected bladder activity-related neurons, including those which fired only prior to the start of contraction (Type E1), those whose firing was maintained during contraction (Type E2), and those whose firing was strongly suppressed during contraction (Type I). All Type E1 neurons and most (93.8%) Type E2 neurons decreased firing when bladder activity was suppressed by acupuncture stimulation. Four of 14 (28.6%) Type I neurons exhibited an excitatory response while 3 of 14 (21.4%) exhibited an inhibitory response. These findings suggest that acupuncture stimulation of the sacral vertebrae suppresses bladder contraction and changes the firing properties of bladder activity-related neurons in and around Barrington's nucleus, and that these changes are mediated by GABAergic systems.