Alpha 2-adrenoceptors not imidazole receptors mediate depression of a sacral spinal reflex in the cat

Stability of the acetic acid-induced bladder irritation model in alpha chloralose-anesthetized female cats

Time- and vehicle-related variability of bladder and urethral rhabdosphincter (URS) activity as well as cardiorespiratory and blood chemistry values were examined in the acetic acid-induced bladder irritation model in α-chloralose-anesthetized female cats. Additionally, bladder and urethra were evaluated histologically using Mason trichrome and toluidine blue staining. Urodynamic, cardiovascular and respiratory parameters were collected during intravesical saline infusion followed by acetic acid (0.5%) to irritate the bladder. One hour after starting acetic acid infusion, a protocol consisting of a cystometrogram, continuous infusion-induced rhythmic voiding contractions, and a 5 min "quiet period" (bladder emptied without infusion) was precisely repeated every 30 minutes. Administration of vehicle (saline i.v.) occurred 15 minutes after starting each of the first 7 cystometrograms and duloxetine (1mg/kg i.v.) after the 8(th). Acetic acid infusion into the bladder increased URS-EMG activity, bladder contraction frequency, and decreased contraction amplitude and capacity, compared to saline. Bladder activity and URS activity stabilized within 1 and 2 hours, respectively. Duloxetine administration significantly decreased bladder contraction frequency and increased URS-EMG activity to levels similar to previous reports. Cardiorespiratory parameters and blood gas levels remained consistent throughout the experiment. The epithelium of the bladder and urethra were greatly damaged and edema and infiltration of neutrophils in the lamina propria of urethra were observed. These data provide an ample evaluation of the health of the animals, stability of voiding function and appropriateness of the model for testing drugs designed to evaluate lower urinary tract as well as cardiovascular and respiratory systems function.

Neurophysiology and therapeutic receptor targets for stress urinary incontinence

Stress urinary incontinence is the most common type of urinary incontinence in women. Stress urinary incontinence involves involuntary leakage of urine in response to abdominal pressure caused by activities, such as sneezing and coughing. The condition affects millions of women worldwide, causing physical discomfort as well as social distress and even social isolation. This type of incontinence is often seen in women after middle age and it can be caused by impaired closure mechanisms of the urethra as a result of a weak pelvic floor or poorly supported urethral sphincter (urethral hypermobility) and/or a damaged urethral sphincter system (intrinsic sphincter deficiency). Until recently, stress urinary incontinence has been approached by clinicians as a purely anatomic problem as a result of urethral hypermobility requiring behavioral or surgical therapy. However, intrinsic sphincter deficiency has been reported to be more significantly associated with stress urinary incontinence than urethral hypermobility. Extensive basic and clinical research has enhanced our understanding of the complex neural circuitry regulating normal function of the lower urinary tract, as well as the pathophysiological mechanisms that might underlie the development of stress urinary incontinence and lead to the development of potential novel strategies for pharmacotherapy of stress urinary incontinence. Therapeutic targets include adrenergic and serotonergic receptors in the spinal cord, and adrenergic receptors at the urethral sphincter, which can enhance urethral reflex activity during stress conditions and increase baseline urethral pressure, respectively. This article therefore reviews the recent advances in stress urinary incontinence research and discusses the neurophysiology of urethral continence reflexes, the etiology of stress urinary incontinence and potential targets for pharmacotherapy of stress urinary incontinence.

Neural control of the female urethral and anal rhabdosphincters and pelvic floor muscles

The urethral rhabdosphincter and pelvic floor muscles are important in maintenance of urinary continence and in preventing descent of pelvic organs [i.e., pelvic organ prolapse (POP)]. Despite its clinical importance and complexity, a comprehensive review of neural control of the rhabdosphincter and pelvic floor muscles is lacking. The present review places historical and recent basic science findings on neural control into the context of functional anatomy of the pelvic muscles and their coordination with visceral function and correlates basic science findings with clinical findings when possible. This review briefly describes the striated muscles of the pelvis and then provides details on the peripheral innervation and, in particular, the contributions of the pudendal and levator ani nerves to the function of the various pelvic muscles. The locations and unique phenotypic characteristics of rhabdosphincter motor neurons located in Onuf's nucleus, and levator ani motor neurons located diffusely in the sacral ventral horn, are provided along with the locations and phenotypes of primary afferent neurons that convey sensory information from these muscles. Spinal and supraspinal pathways mediating excitatory and inhibitory inputs to the motor neurons are described; the relative contributions of the nerves to urethral function and their involvement in POP and incontinence are discussed. Finally, a detailed summary of the neurochemical anatomy of Onuf's nucleus and the pharmacological control of the rhabdosphincter are provided.

Characterization of a spinal, urine storage reflex, inhibitory center and its regulation by 5-HT1A receptors in female cats

Urine storage is facilitated by somatic (pudendal nerve) and sympathetic [hypogastric nerve (HgN)] reflexes to the urethral rhabdosphincter (URS) and urethral smooth muscle, respectively, initiated by primary afferent fibers in the pelvic nerve (PelN). Inhibition of storage reflexes is required for normal voiding. This study characterizes a urine storage reflex inhibitory network that can be activated by PelN afferent fibers concurrently with the reflexes themselves. Electrical stimulation of PelN produced evoked potentials recorded by URS EMG electrodes (10-ms latency) or HgN electrodes (60-ms latency) in chloralose-anesthetized cats. When a second (i.e., paired) pulse of the same stimulus intensity was applied to the PelN 50-500 ms after the first, the reflexes evoked by the second stimulus were inhibited. The inhibition was maximal at paired-pulse intervals of 50-100 ms and remained after acute spinal transection at T10, confirming that the inhibitory center is located in the spinal cord. The 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tertralin (8-OH-DPAT; 3-300 mug/kg iv) consistently reduced the paired-pulse inhibition from 20% to 60% of control in spinal-intact animals but had no effect in acute spinal animals (i.e., supraspinal site of action). N-{2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl}-N-2-pyridinylcyclohexanecarboxamide maleate (300 mug/kg iv) completely reversed 8-OH-DPAT's effects. The PelN-HgN reflex paired-pulse inhibition was not affected by 8-OH-DPAT. These results indicate the presence of a spinal, urine storage reflex, inhibitory center (SUSRIC) that is activated within 50 ms after activation of the reflexes themselves. SUSRIC is inhibited (disfacilitated) by supraspinal 5-HT(1A) receptors.

Neural control of the lower urinary tract: peripheral and spinal mechanisms

This review deals with individual components regulating the neural control of the urinary bladder. This article will focus on factors and processes involved in the two modes of operation of the bladder: storage and elimination. Topics included in this review include: (1) The urothelium and its roles in sensor and transducer functions including interactions with other cell types within the bladder wall ("sensory web"), (2) The location and properties of bladder afferents including factors involved in regulating afferent sensitization, (3) The neural control of the pelvic floor muscle and pharmacology of urethral and anal sphincters (focusing on monoamine pathways), (4) Efferent pathways to the urinary bladder, and (5) Abnormalities in bladder function including mechanisms underlying comorbid disorders associated with bladder pain syndrome and incontinence.

Duloxetine versus placebo for the treatment of women with stress predominant urinary incontinence in Taiwan: a double-blind, randomized, placebo-controlled trial

BACKGROUND

This manuscript compares the efficacy and safety of duloxetine with placebo in Taiwanese women with SUI.

METHODS

Taiwanese women with SUI were were randomly assigned to placebo (n = 61) or duloxetine 80 mg/day (n = 60) in this double-blind, 8-week, placebo-controlled study. Outcome variables included: incontinence episode frequency (IEF), Incontinence Quality of Life questionnaire (I-QOL) scores, and Patient Global Impression of Improvement rating (PGI-I).

RESULTS

Decrease in IEF was significantly greater in duloxetine-treated than placebo-treated women (69.98% vs 42.56%, P < .001). No treatment differences in I-QOL scores were significant. There were significant differences in PGI-I rating. Treatment-emergent adverse events (TEAEs) were experienced by more duloxetine-treated than placebo-treated women (80.0% vs 44.3%; P < .001). Discontinuations due to adverse events were significantly greater for duloxetine-treated than placebo-treated women (26.7% vs 6.6%; P = .003).

CONCLUSION

Data provide evidence for the safety and efficacy of duloxetine for the treatment for Taiwanese women with SUI.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT00475358.

Therapeutic receptor targets for lower urinary tract dysfunction

The functions of the lower urinary tract, to store and periodically release urine, are dependent on the activity of smooth and striated muscles in the bladder, urethra, and external urethral sphincter. During urine storage, the outlet is closed, and the bladder smooth muscle is quiescent. When bladder volume reaches the micturition threshold, activation of a micturition center in the dorsolateral pons (the pontine micturition center) induces a bladder contraction and a reciprocal relaxation of the urethra, leading to bladder emptying. During voiding, sacral parasympathetic (pelvic) nerves provide an excitatory input (cholinergic and purinergic) to the bladder and inhibitory input (nitrergic) to the urethra. These peripheral systems are integrated by excitatory and inhibitory regulation at the levels of the spinal cord and the brain. Injury or diseases of the nervous system, as well as drugs and disorders of the peripheral organs, can produce lower urinary tract dysfunction. In the overactive bladder (OAB) condition, therapeutic targets for facilitation of urine storage can be found at the levels of the urothelium, detrusor muscles, autonomic and afferent pathways, spinal cord, and brain. There is increasing evidence showing that the urothelium has specialized sensory and signaling properties including: (1) expression of nicotinic, muscarinic, tachykinin, adrenergic, bradykinin, and transient receptor potential (TRP) receptors, (2) close physical association with afferent nerves, and (3) ability to release chemical molecules such as adenosine triphosphate (ATP), acetylcholine, and nitric oxide. Increased expression and/or sensitivity of these urothelial-sensory molecules that lead to afferent sensitization have been documented as possible pathogenesis of OAB. Targeting afferent pathways and/or bladder smooth muscles by modulating activity of ligand receptors (e.g., neurokinin, ATP, or beta3-adrenergic receptors) and ion channels (e.g., TRPV1 or K) could be effective to suppress OAB. In the stress urinary incontinence condition, pharmacotherapies targeting the neurally mediated urethral continence reflex during stress conditions such as sneezing or coughing could be effective for increasing the outlet resistance. Therapeutic targets include adrenergic and serotonergic receptors in the spinal cord as well as adrenergic receptors at the urethral sphincter, which can enhance urethral reflex activity during stress conditions and increase baseline urethral pressure, respectively.

Placebo-controlled study of the effects of atomoxetine on bladder control in children with nocturnal enuresis

INTRODUCTION

Nocturnal enuresis is a condition in which children at least 5 years of age are incontinent of urine at night. Atomoxetine, a potent inhibitor of the presynaptic norepinephrine transporter, is used to treat attention-deficit/hyperactivity disorder (ADHD). This study tested the hypothesis that atomoxetine will provide significant therapeutic benefit for nocturnal enuresis in patients with the diagnosis of nocturnal enuresis.

METHODS

Atomoxetine's efficacy for improving nocturnal enuresis was studied in 87 pediatric subjects using an outpatient, multicenter, randomized, double-blind, parallel, placebo-controlled study. Efficacy was determined by measuring the mean number of dry nights per week using an intent-to-treat analysis of the primary outcome measure, the Dry Night Log-Parent Report (DNL-PR), a daily parent diary.

RESULTS

Baseline and end point DNL-PR data were available from 42 atomoxetine-treated and 41 placebo-treated subjects. Atomoxetine increased the average number of dry nights per week by 1.47 compared with .60 for placebo (F = 7.06; df = (1, 75); p = 0.01). Fifteen atomoxetine-treated subjects (35.7%) had an increase of at least 2 dry nights per week compared with only 6 (14.6%) placebo-treated subjects (Fisher's exact test; p = 0.042). There were no significant differences in adverse events between the groups.

CONCLUSIONS

Compared with placebo, atomoxetine treatment was associated with a significant increase in dry nights in children with nocturnal enuresis.

Duloxetine vs placebo in the treatment of stress urinary incontinence: a four-continent randomized clinical trial

OBJECTIVES

To further assess, in a phase 3 study, treatment with duloxetine for women with stress urinary incontinence (SUI) in other geographical regions, including Argentina, Australia, Brazil, Finland, Poland, South Africa and Spain, as previous trials in North America and Europe provided evidence for the safety and efficacy of duloxetine as a pharmacological treatment for SUI in women.

PATIENTS AND METHODS

The study included 458 women aged 27-79 years enrolled in a double-blind, placebo-controlled trial. The patients with predominantly SUI were identified using a validated clinical algorithm. They were randomly assigned to receive placebo (231) or duloxetine 40 mg twice daily (227) for 12 weeks. The primary outcome variables included the incontinence episode frequency (IEF) and the Incontinence Quality of Life (I-QOL) questionnaire. Van Elteren's test was used to analyse the percentage changes in IEF where the stratification variable was weekly baseline IEF (IEF < 14 and > or = 14). Analysis of covariance was used to analyse I-QOL scores.

RESULTS

The mean baseline IEF was 18.4/week; 55% of patients had a baseline IEF of > or = 14. There was a significantly greater median decrease in IEF with duloxetine with placebo (54% vs 40%, P = 0.05), with comparable significant improvements in quality of life (I-QOL score increases of 10.3 vs 6.4, P = 0.007). The improvements with duloxetine were associated with significantly greater increases in voiding intervals than with placebo (20.4 vs 8.5 min, P < 0.001). The placebo response was 10.7% and 12.5% higher than those reported in two European and North American phase 3 trials. This may have been related to more patients being naïve for incontinence management in the current trial. Discontinuation rates for adverse events were 1.7% for placebo and 17.2% for duloxetine (P < 0.001), with nausea being the most common reason for discontinuation (3.1%); it was the most common adverse event with duloxetine, but was mild or moderate in most (81%), did not worsen in any patient and resolved within 7 days in 60% and within 1 month in 86% of continuing patients; 88% of women who experienced nausea while taking duloxetine completed the trial.

CONCLUSIONS

These results show improvements in incontinence and quality of life with duloxetine 40 mg twice daily for 12 weeks that are in keeping with those reported in two other recently completed phase 3 trials in Europe and North America.

Duloxetine versus placebo in the treatment of European and Canadian women with stress urinary incontinence

OBJECTIVE

To assess the efficacy and safety of duloxetine in women with stress urinary incontinence.

DESIGN

Randomised double-blind, placebo-controlled clinical trial.

SETTING

Fort-six centres in seven European countries and Canada.

POPULATION

Four hundred and ninety-four women aged 24-83 years identified as having predominant symptoms of stress urinary incontinence using a clinical algorithm that was 100% predictive of urodynamic stress urinary incontinence in a subgroup of 34 women.

METHODS

The case definition included a predominant symptom of stress urinary incontinence with a weekly incontinence episode frequency > or =7, the absence of predominant symptoms of urge incontinence, normal diurnal and nocturnal frequencies, a bladder capacity > or =400 mL and both a positive cough stress test and positive stress pad test. Subjects completed two urinary diaries prior to randomisation and three diaries during the active treatment phase of the study, each completed during the week prior to monthly visits. Subjects also completed quality of life questionnaires at each visit. Safety was assessed by the evaluation of treatment-emergent adverse events, discontinuation of treatment because of adverse events, serious adverse events, vital sign measurements, electrocardiograms (ECG) and clinical laboratory tests.

INTERVENTION

After a two-week placebo lead-in, women received placebo or duloxetine 40 mg BD for 12 weeks.

MAIN OUTCOME MEASURES

The percentage decrease in incontinence episode frequency and the change in the Incontinence Quality of Life (I-QOL) questionnaire total score were prespecified as co-primary outcome variables in the protocol.

RESULTS

Incontinence episode frequency decreased significantly with duloxetine compared with placebo (median decrease of 50%vs 29%; P= 0.002) with comparable improvements in the more severely incontinent subgroup (those experiencing at least 14 incontinence episodes per week at baseline; 56%vs 27% decreases; P < 0.001). The primary analysis of I-QOL scores did not reveal a significant difference between treatment groups, due primarily to the carrying forward of low scores from patients who discontinued treatment very early due to duloxetine-associated adverse events. The increase in I-QOL scores was significantly greater for duloxetine than for placebo at each of the three postrandomisation visits after 4, 8, and 12 weeks of treatment. Discontinuation rates for adverse events were higher for duloxetine (22%vs 5%; P < 0.001) with nausea being the most common reason for discontinuation (5.3%). Nausea tended to be mild to moderate, not progressive, and transient.

CONCLUSIONS

The findings support duloxetine as a potential treatment for women with stress urinary incontinence.

Duloxetine versus placebo for the treatment of North American women with stress urinary incontinence

PURPOSE

Duloxetine, a selective serotonin and norepinephrine reuptake inhibitor, increases rhabdosphincter contractility via the stimulation of pudendal motor neuron alpha-1 adrenergic and 5-hydroxytryptamine-2 receptors. In this first phase 3 study we assessed the efficacy and safety of duloxetine in women with stress urinary incontinence (SUI).

MATERIALS AND METHODS

A total of 683 North American women 22 to 84 years old were enrolled in this double-blind, placebo controlled study. The case definition included a predominant symptom of SUI with a weekly incontinence episode frequency (IEF) of 7 or greater, the absence of predominant symptoms of urge incontinence, normal diurnal and nocturnal frequency, a bladder capacity of 400 ml or greater, and a positive cough stress test and stress pad test. After a 2-week placebo lead-in period subjects were randomly assigned to receive placebo (339) or 80 mg duloxetine daily (344) as 40 mg twice daily for 12 weeks. Primary outcome variables included IEF and an incontinence quality of life questionnaire. Van Elteren's test was used to analyze percent changes in IEF with a stratification variable of weekly baseline IEF (less than 14 and 14 or greater). ANCOVA was used to analyze incontinence quality of life scores.

RESULTS

Mean baseline IEF was 18 weekly and 436 subjects (64%) had a baseline IEF of 14 or greater. There was a significant decrease in IEF with duloxetine compared with placebo (50% vs 27%, p <0.001) with comparably significant improvements in quality of life (11.0 vs 6.8, p <0.001). Of subjects on duloxetine 51% had a 50% to 100% decrease in IEF compared with 34% of those on placebo (p <0.001). These improvements with duloxetine were associated with a significant increases in the voiding interval compared with placebo (20 vs 2 minutes, p <0.001) and they were observed across the spectrum of incontinence severity. The discontinuation rate for adverse events was 4% for placebo and 24% for duloxetine (p <0.001) with nausea the most common reason for discontinuation (6.4%). Nausea, which was also the most common side effect, tended to be mild to moderate and transient, usually resolving after 1 week to 1 month. Of the 78 women who experienced treatment emergent nausea while taking duloxetine 58 (74%) completed the trial.

CONCLUSIONS

These phase 3 data are consistent with phase 2 data and they provide further evidence for the safety and efficacy of duloxetine as a pharmacological agent for the treatment of women with SUI.

Duloxetine versus placebo in the treatment of stress urinary incontinence

OBJECTIVE

The purpose of this study was to assess the efficacy and safety of duloxetine, a selective inhibitor of serotonin and norepinephrine reuptake, in the treatment of stress urinary incontinence.

STUDY DESIGN

A double-blind, randomized, placebo-controlled study was conducted in 553 women aged 18 to 65 years with a predominant symptom of stress urinary incontinence. Subjects were randomized to placebo (n = 138 women) or duloxetine at one of three doses (20 mg/d, n = 138 women; 40 mg/d, n = 137 women; or 80 mg/d, n = 140 women). Outcome variables that were assessed after 12 weeks of treatment included incontinence episode frequency recorded in a real-time diary and answers provided to the Patient Global Impression of Improvement scale and the Incontinence Quality of Life questionnaire.

RESULTS

Duloxetine was associated with significant and dose-dependent decreases in incontinence episode frequency that paralleled improvements that were observed in the Patient Global Impression of Improvement scale and the Incontinence Quality of Life questionnaire. The median incontinence episode frequency decrease with the use of the pooled diary analysis with placebo was 41% compared with 54% for duloxetine 20 mg per day (P =.06), 59% for duloxetine 40 mg per day (P =.002), and 64% for duloxetine 80 mg per day (P <.001). One half of the subjects at the 80 mg per day dose had a > or = 64% reduction in incontinence episode frequency (P <.001 vs placebo); 67% had > or = 50% reduction (P =.001 vs placebo). These improvements were observed despite significant concurrent dose-dependent increases in the average voiding interval in the duloxetine groups compared with the placebo group. Similar statistically significant improvements were demonstrated in a subgroup of 163 subjects who had more severe stress urinary incontinence (> or = 14 incontinence episode frequency per week; 49%-64% reduction in incontinence episode frequency in the duloxetine groups compared with 30% in the placebo group). Discontinuation rates for adverse events were 5% for placebo and 9%, 12%, and 15% for duloxetine 20, 40, and 80 mg per day, respectively (P =.04). Nausea was the most common symptom that led to discontinuation. None of the adverse events that were reported were considered to be clinically severe.

CONCLUSION

This trial provides evidence for the efficacy and safety of duloxetine as a pharmacologic agent for the treatment of stress urinary incontinence.

The antinociceptive effect of the mu-opioid fentanyl is reduced in the presence of the alpha(2)-adrenergic antagonist idazoxan in inflammation

Interactions between alpha(2)-adrenergic and mu-opioid systems play an important role in the modulation of hyperalgesic states. The antinociceptive effects of alpha(2)-adrenergic agonists and mu-opioids are potentiated when co-administered; however, attempts to induce cross reversal of the antinociceptive effects of alpha(2)-adrenergic and mu-opioid systems have produced contradictory results. We have studied the possible endogenous tonic control of the alpha(2)-adrenergic systems in the modulation of pain in inflammation, and the interactions between the two antinociceptive systems in rat spinal cord nociceptive reflexes activated by both natural and electrical stimulation. The facilitatory actions of the alpha(2)-adrenergic antagonist idazoxan were compared in control rats and in animals with carrageenan-induced paw inflammation. The antinociceptive effect of the mu-opioid fentanyl was tested alone and in the presence of idazoxan. In agreement with some previous observations, idazoxan i.v. produced no change in responses to natural and electrical stimulation in normal animals. In animals with inflammation, idazoxan only induced facilitation of responses evoked by noxious thermal stimulation but not by mechanical or electrical stimulation. Fentanyl reduced the responses to either stimuli with lower potency in the presence of idazoxan, but only in animals with inflammation. Its dose-response curve was shifted to the right between 1.8- and 3. 5-fold depending on the stimulus used. It is concluded that the increase of thermal responses by idazoxan in animals with inflammation is probably due to changes in the peripheral blood flow. Nevertheless, since an interaction with mu-opioids is clear in inflammation, endogenous alpha(2)-adrenergic systems play an important role in the modulation of the effectiveness of opioids during inflammation.

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.

Spinal 5-HT2 receptor-mediated facilitation of pudendal nerve reflexes in the anaesthetized cat

1. 5-Hydroxytryptamine (5-HT) is intimately associated with central sympathetic and somatic control of the lower urinary tract. The sympathetic and somatic innervation of the lower urinary tract is conveyed through efferent axons of the hypogastric and pudendal nerves, respectively. 2. The present study examined the effects of 2,5-dimethoxy-4-iodophenylisopropylamine (DOI), a 5-HT2 receptor subtype-selective agonist, on evoked potentials recorded from the central ends of the hypogastric and pudendal nerves in response to electrical stimulation of afferent fibres in the pelvic and pudendal nerves, respectively. Various spinalization paradigms were employed to localize the site of action. All cats were pretreated with xylamidine (1 mg kg-1), a peripherally-restricted 5-HT2 receptor antagonist. 3. In acute spinal cats, DOI (0.01-3 mg kg-1, i.v.) reliably produced dose-dependent increases in the pudendal nerve reflex (to 228 +/- 31% of control). These increases were reversed by the 5-HT2 receptor-selective antagonist, LY53857 (0.3-3 mg kg-1, i.v.). On the other hand, in spinally-intact cats, DOI produced no significant changes in the pudendal reflex. However, within minutes of spinalization of DOI-pretreated cats, a marked increase (to 221 +/- 16% of control) in the pudendal reflex was observed which could be reversed by LY53857. No significant effects were observed on hypogastric reflexes in either acute spinal or spinally-intact cats following DOI administration. No effects were seen in either spinally-intact or acute spinal animals when LY53857 was administered as the initial drug. 4. These results indicate that activation of spinal 5-HT2 receptors facilitates pudendal reflexes. In spinally-intact cats, it is hypothesized that DOI activates supraspinal pathways that mediate inhibition of the pudendal reflexes and counteracts the facilitatory effects of spinal 5-HT2 receptor activation.