An electrophysiological study of somatic and visceral convergence in the reflex control of the external sphincters

Sildenafil, a phosphodiesterase type 5 inhibitor, augments sphincter bursting and bladder afferent activity to enhance storage function and voiding efficiency in mice

Objectives

To investigate the influence of low‐dose sildenafil, a phosphodiesterase type 5 inhibitor (PDE5‐I), on the function of the mouse lower urinary tract (LUT).

Materials and Methods

Adult male mice were decerebrated and arterially perfused with a carbogenated Ringer's solution to establish the decerebrate arterially perfused mouse (DAPM). To allow distinction between central neural and peripheral actions of sildenafil, experiments were conducted in both the DAPM and in a ‘pithed’ DAPM, which has no functional brainstem or spinal cord. The action of systemic and intrathecal sildenafil on micturition was assessed in urethane‐anaesthetised mice.

Results

In the DAPM, systemic perfusion of sildenafil (30 pm) decreased the voiding threshold pressure [to a mean (sem) 84.7 (3.8)% of control] and increased bladder compliance [to a mean (sem) 140.2 (8.3)% of control, an effect replicated in the pithed DAPM]. Sildenafil was without effect on most voiding variables but significantly increased the number of bursts of the external urethral sphincter (EUS) per void in DAPM [to a mean (sem) 130.1 (6.9)% of control at 30 pm] and in urethane‐anaesthetised mice [to a mean (sem) 117.5 (5.8)% of control at 14 ng/kg]. Sildenafil (10 and 30 pm) increased pelvic afferent activity during both bladder filling and the isovolumetric phase [to a mean (sem) 205.4 (30.2)% of control at 30 pm]. Intrathecal application of sildenafil (5 μL of either 150 pm or 1.5 nm) did not alter cystometry and EUS‐electromyography variables in urethane‐anaesthetised mice.

Conclusions

Low‐dose sildenafil increases bladder compliance, increases pelvic nerve afferent activity, and augments the bursting activity of the EUS. We propose that the novel actions on afferent traffic and sphincter control may contribute to its beneficial actions to restore storage and voiding efficiency in LUT dysfunction.

Cough-Anal Reflex May Be the Expression of a Pre-Programmed Postural Action

When coughing, an involuntary contraction of the external anal sphincter occurs, in order to prevent unwanted leakages or sagging of the pelvis muscular wall. Literature originally described such cough-anal response as a reflex elicited by cough, therefore identifying a precise cause-effect relationship. However, recent studies report that the anal contraction actually precedes the rise in abdominal pressure during cough expiratory effort, so that the sphincter activity should be pre-programmed. In recent years, an important family of pre-programmed muscle activities has been well documented to precede voluntary movements: these anticipatory actions play a fundamental role in whole body and segmental postural control, hence they are referred to as anticipatory postural adjustments (APAs). On these basis, we searched in literature for similarities between APAs and the cough-anal response, observing that both follow the same predictive homeostatic principle, namely that anticipatory collateral actions are needed to prevent the unwanted mechanical consequences induced by the primary movement. We thus propose that the cough-anal response also belongs to the family of pre-programmed actions, as it may be interpreted as an APA acting on the abdominal-thoracic compartment; in other words, the cough-anal response may actually be an Anticipatory Sphincter Adjustment, the visceral counterpart of APAs.

Differences in neurotransmitter systems of ventrolateral periaqueductal gray between the micturition reflex and nociceptive regulation: An in vivo microdialysis study

OBJECTIVES

To elucidate the possible involvement of glutamate and serotonin (5-hydroxytryptamine) neurons in the ventrolateral midbrain periaqueductal gray during noxious stimulation.

METHODS

The study was carried out by evoking a noxious stimulation by acetic acid in an animal model of cystitis. Changes in glutamate and 5-hydroxytryptamine in the periaqueductal gray during the micturition reflex and acetic acid-induced cystitis were determined using in vivo microdialysis combined with cystometry in rats.

RESULTS

Extracellular glutamate levels slightly, but significantly, increased during the micturition reflex induced by saline infusion into the bladder. Intravesical infusion of acetic acid facilitated the micturition reflex characterized by increases in voiding pressure and decreases in the intercontraction interval. Glutamate levels were markedly increased by acetic acid, and this enhancement was sustained for at least 3 h. 5-Hydroxytryptamine levels, which were not altered during the micturition reflex, were increased after intravesical infusion of acetic acid.

CONCLUSION

The results suggest that periaqueductal gray glutamate and 5-hydroxytryptamine neurons differentially participate in the modulation of both nociception and the micturition reflex. Furthermore, periaqueductal gray 5-hydroxytryptamine levels appear to reflect the nociceptive stimuli.

Acupuncture at homotopic acupoints exerts dual effects on bladder motility in anesthetized rats

BACKGROUND

In Chinese medicine, dual effects on target organs are considered a primary characteristic of acupoint. Acupoints may be classified as heterotopic or homotopic in terms of spinal segmental innervation: homotopic acupoints contain afferent innervation in the same segment from which efferent fibers innervate target visceral organs, and heterotopic acupoints utilize different spinal segments to innervate target visceral organs than the segment receiving the afferent signal. It is well-known that dual effects of acupuncture on the bladder can be generated based on different states of the bladder, however, the dual effects of single acupoint stimulation and acupoint site-specificity (homotopic acupoints and heterotopic acupoints) on the bladder have yet to be investigated.

METHODS

Twenty Sprague-Dawley rats were anesthetized and the intravesical pressure was measured via a manometric balloon inserted into the bladder. The acupuncture needle was separately inserted to a depth of 4 mm at the acupoints RN1 (Huiyin), RN3 (Zhongji), BL28 (Pangguangshu), BL32 (Ciliao), RN2 (Qugu) or BL23 (Shenshu), and manually rotated right then left with a frequency of 2 Hz for 1 min. Following acupuncture stimulation, bladder pressure was recorded and compared against the pre-stimulation measurements.

RESULTS

During the bladder's active state, manual acupuncture (MA) at RN1, RN3, BL28, BL32 or RN2 inhibited bladder motility (P < 0.01). In the static bladder, MA at RN1, RN3, BL28, BL32, RN2 or BL23 increased bladder motility (P < 0.01).

CONCLUSIONS

MA at homotopic acupoints may produce dual effects on bladder motility: inhibiting bladder motility when in an active state and enhancing bladder motility when in a static state.

Inhibition of micturition reflex by activation of somatic afferents in posterior femoral cutaneous nerve

This study determined if activation of somatic afferents in posterior femoral cutaneous nerve (PFCN) could modulate the micturition reflex recorded under isovolumetric conditions in α-chloralose anaesthetized cats. PFCN stimulation inhibited reflex bladder activity and significantly (P <0.05) increased bladder capacity during slow infusion of saline or 0.25% acetic acid (AA). The optimal frequency for PFCN stimulation-induced bladder inhibition was between 3 and 10 Hz, and a minimal stimulation intensity of half of the threshold for inducing anal twitching was required. Bilateral pudendal nerve transection eliminated PFCN stimulation-induced anal twitching but did not change the stimulation-induced bladder inhibition, excluding the involvement of pudendal afferent or efferent axons in PFCN afferent inhibition.Mechanical or electrical stimulation on the skin surface in the PFCN dermatome also inhibited bladder activity. Prolonged (2 × 30 min) PFCN stimulation induced a post-stimulation inhibition that persists for at least 2 h. This study revealed a new cutaneous-bladder reflex activated by PFCN afferents. Although the mechanisms and physiological functions of this cutaneous-bladder reflex need to be further studied, our data raise the possibility that stimulation of PFCN afferents might be useful clinically for the treatment of overactive bladder symptoms.

Neuroanatomy of the lower urinary tract

The lower urinary tract (LUT), which consists of the urinary bladder and its outlet, the urethra, is responsible for the storage and periodic elimination of bodily waste in the form of urine. The LUT is controlled by a complex set of peripheral autonomic and somatic nerves, which in turn are controlled through neural pathways in the spinal cord and brain. This influence of the central nervous system allows for the conscious control of the bladder, allowing the individual to choose an appropriate place to urinate. Defects in the CNS pathways that control the LUT can lead to incontinence, an embarrassing condition that affects over 200 million people worldwide. As a first step in understanding the neural control of the bladder, we will discuss the neuroanatomy of the LUT, focusing first on the peripheral neural pathways, including the sensory pathways that transmit information on bladder filling and the motoneurons that control LUT muscle contractility. We will also discuss the organization of the central pathways in the spinal cord and brainstem that are responsible for coordinating bladder activity, promoting continuous storage of urine except for a few short minutes per day when micturition takes place. To conclude, we will discuss current studies underway that aim to elucidate the higher areas of the brain that control the voluntary nature of micturition in higher organisms.

Neurophysiology of the lower urinary tract

The lower urinary tract (LUT) has two functions: (1) the storage of waste products in the form of urine and (2) the elimination of those wastes through micturition. The LUT operates in a simple "on-off" fashion, either storing urine or releasing it during voiding. While this activity may seem simple, micturition is controlled by a complex set of peripheral neurons that are, in turn, coordinated by cell groups in the spinal cord, brainstem, and brain. When this careful coordination is interrupted, the control of the bladder is lost, resulting in incontinence or retention of urine. The purpose of this chapter is to review how the neural systems coordinating the activity of the lower urinary tract form neural circuits that are responsible for either maintaining continence (the storage reflex) or inducing micturition (the voiding reflex). We will also discuss the brain centers that enable higher organisms to voluntarily choose the time and place for voiding. Finally, we will discuss how defects in the pathways controlling micturition can lead to urinary incontinence and which treatments may normalize LUT function.

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.

Functional coupling between motor and sensory nerves through contraction of sphincters in the pudendal area of the female cat

The question of whether skin receptors might help in the perception of muscle contraction and body movement has not been settled. The present study gives direct evidence of skin receptor firing in close coincidence with the contraction of the vaginal and anal sphincters. The distal stump of the sectioned motor pudendal nerve was stimulated. Single shocks induced a wavelike increase in the lumen pressure of the distal vagina and the anal canal, as well as constriction of the vaginal introitus and the anus. The constriction pulls on and moves the surrounding skin, which was initially detected visually. In the present experiments, a thin strain gauge that pressed on the skin surface detected its displacement. Single shocks to the motor nerve induced a wave of skin movement with maximal amplitude at 5 mm from the anus and propagated with decrement beyond 35 mm. The peripheral terminals of the sensory pudendal nerve and the posterior femoral nerve supply the skin that moves. Sensory axons from both nerves fired in response to both tactile stimulation and the skin movement produced by the constriction of the orifices (motor-sensory coupling). In cats with all nerves intact, a single shock to the sensory nerves induced reflex waves of skin movement and lumen pressure (sensory-motor coupling). Both couplings provide evidence for a feedforward action that might help to maintain the female posture during mating and to the perception of muscle contraction.

Anorectal stimulation causes increased colonic motor activity in subjects with spinal cord injury

BACKGROUND

Difficulty with evacuation (DWE) is a major problem after spinal cord injury (SCI). Stimulation of the anal canal and lower rectum, accomplished using a gloved finger (so-called digital rectal stimulation or DRS) is often used as an adjunct to laxatives and enemas to facilitate bowel evacuation. However, the basis for the efficacy of DRS is not known. This study assessed the effect of DRS on colonic motility.

METHODS

Six subjects with SCI were studied several hours after a bowel care session. Colonic motility was assessed using a manometric catheter (affixed endoscopically to the splenic flexure) at baseline, during DRS, and after DRS. In addition, evacuation of barium oatmeal paste (with the consistency of stool and introduced into the rectum and descending colon) was assessed simultaneously using fluoroscopic techniques.

RESULTS

The mean number (+/- SEM) of peristaltic waves per minute increased from 0 at baseline to 1.9 (+/- 0.5/min) during DRS and 1.5 (+/- 0.3/min) during the period immediately after cessation of DRS (P < 0.05). The mean amplitude (+/- SEM) of the peristaltic contractions was 43.4 (+/- 2.2) mmHg. The frequency of contractions, as well as amplitude of contractions, during or immediately after DRS was not significantly different. These manometric changes in response to DRS were accompanied by expulsion of barium oatmeal paste in every subject by the fifth DRS.

CONCLUSIONS

DRS causes left-sided colonic activity in subjects with SCI. At least in part, an anorectal colonic reflex that results in enhanced contractions of the descending colon and rectum may contribute to bowel evacuation in individuals with SCI.

Electromyography of pelvic floor muscles

Pelvic floor muscles (PFM) are intimately involved in function of lower urinary tract, the anorectum and sexual functions, therefore their neural control transcends the primarily important somatic innervation of striated muscle, as they are directly involved in "visceral activity". Neural control of pelvic organs is affected by a unique co-ordination of somatic and autonomic motor nervous systems. Visceral and somatic sensory fibres supply sensory information from pelvic organs; their input influences through central integrative mechanisms also pelvic floor muscle activity. Anatomically, somatic afferent and efferent nerves of the sacral cord segments, reflexly integrated at the spinal cord and brainstem level, conduct neural control of PFM. The inputs from several higher centres influence the complex reflex control and are decisive for voluntary control, and for socially adapted behaviour related to excretory functions.

Roles of glutamatergic and serotonergic mechanisms in reflex control of the external urethral sphincter in urethane-anesthetized female rats

This study was conducted to examine reflex mechanisms that mediate urinary bladder and external urethral sphincter (EUS) coordination in urethane-anesthetized female Sprague-Dawley rats. We investigated the properties of EUS reflexes elicited by electrical stimulation of pelvic nerve afferent axons (pelvic-EUS reflex). The changes in the reflexes induced by bladder distension and administration of agonists or antagonists for glutamatergic or serotonergic receptors were examined. The reflexes consisted of an early response (ER, 18- to 22-ms latency) and a late, long-duration (>100-ms latency) response (LR), which consisted of bursts of activity at 20- to 160-ms interburst intervals. In a few experiments, a reflex with an intermediate (40- to 70-ms) latency was also identified. With the bladder empty, the ER, but not the LR, was detected in the majority of experiments. The LR was markedly enhanced when the bladder was distended. The ER remained, but the LR was abolished, after spinal cord transection at T8-T9. The ER and LR were significantly decreased 75 and 35%, respectively, by the N-methyl-D-aspartate receptor antagonist MK-801 (0.3 mg/kg iv), but only decreased 18 and 14%, respectively, by the alpha-amino-5-methylisoxazole-4-propionate receptor antagonist LY-215490 (3 mg/kg iv). The serotonin (5-HT1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (1 mg/kg iv) enhanced spontaneous EUS activity and the pelvic-EUS reflex. WAY-100635 (0.1-1 mg/kg iv), a 5-HT1A antagonist, reversed the effect of 8-hydroxy-2-(di-n-propylamino)-tetralin and suppressed EUS activity and the pelvic-EUS reflex. These results indicate that glutamatergic and serotonergic mechanisms are important in the reflex pathways underlying bladder- sphincter coordination in rats.

Spinal mechanisms contributing to urethral striated sphincter control during continence and micturition: "how good things might go bad"

The external urethral sphincter motoneurons in the sacral ventral horn control the striated external urethral sphincter muscles that circle the urethra. Activity in these motoneurons and muscle normally contribute to continence but during micturition, when urine must pass through the urethra, the motoneurons and striated muscle must be silenced. Following injury to descending pathways in the spinal cord, the ability to inhibit sphincter activity is disrupted or lost, resulting in bladder-sphincter dyssynergia and functional obstruction of the urethra during voiding. This chapter will first review the various reflex pathways and neuronal properties that contribute to continence, and which must be modulated during micturition in the spinal intact animal. A discussion about how the dyssynergia seen with spinal cord injury may be produced will then be presented.

Reflexes evoked by electrical stimulation of afferent axons in the pudendal nerve under empty and distended bladder conditions in urethane-anesthetized rats

This study examined reflex mechanisms that mediate urinary bladder and external urethral sphincter (EUS) coordination in female Sprague-Dawley urethane-anesthetized rats under empty and distended bladder conditions. The bladder was distended either by a small balloon or a saline filled catheter inserted through the body of the bladder. Stimulation of the entire pudendal nerve elicited short latency (8-12 ms) responses in the EUS and short (3-8 ms) and long latency responses (16-20 ms) in contralateral pudendal nerve. The long latency pudendal-pudendal reflex was reduced by 36.7% in area during bladder distension with the balloon catheter. However, there was no significant change in the area of pudendal-EUS reflex during bladder distension. Peak amplitudes of both reflexes were reduced 32% by bladder distension. The effects of glutamatergic receptor antagonists on the reflexes were also examined. MK 801 (0.3-5mg/kg, i.v.), an N-methyl-d-aspartate glutamatergic receptor antagonist, markedly depressed the pudendal-pudendal reflex, but LY 215490 (3mg/kg, i.v.), an alpha-amino-5-methyl isoxazole-4-propionate antagonist, had a minimal inhibitory effect. Both glutamatergic receptor antagonists significantly suppressed the pudendal-EUS reflex. These results indicate that the EUS is innervated by multiple pathways and that glutamatergic excitatory transmission is important in the neural mechanisms underlying bladder-sphincter coordination in the rat.

Spinal cord neural organization controlling the urinary bladder and striated sphincter

The storage and elimination of urine requires the coordination of activity between the autonomic nervous system (thoracolumbar sympathetic and sacral parasympathetic divisions) controlling the urinary bladder and urethra and the lumbosacral somatic motoneurons innervating the striated sphincter and pelvic floor muscles. These three efferent systems involved in the control of lower urinary tract function receive segmental sensory information from various visceral organs and the perineum, as well as inputs from supraspinal regions. Ascending and descending connections between the various spinal segments levels and supraspinal regions provide the reflex substrates participating in normal bladder continence and micturition reflexes. Many of the actions of descending and segmental reflexes are mediated by excitatory and inhibitory sacral spinal interneurons located within the region of the parasympathetic preganglionic autonomic neurons and the sphincter ventral horn motoneurons. This review will: (1) discuss the basic organization and spinal elements of the reflex pathways subserving continence and micturition; (2) describe features of the identified sacral interneuronal circuitry contributing to the control of the bladder and sphincter function; and (3) discuss how changes in the control of these reflex pathways and neurons may contribute to abnormal patterns of bladder and sphincter function commonly observed following spinal cord injury.

Bulbocavernosus muscle responses after suprapubic stimulation: analysis and measurement of suprapubic bulbocavernosus reflex latency

Our objective was to describe pelvic floor responses with measurement of reflex latency after suprapubic mechanical stimulation. Twenty-one patients without neurological disease were studied. They were 14 women and seven men. The mean age was 51 (SD = 14.2). Motor responses were recorded with a needle electrode inserted in the left bulbocavernosus muscle. Stimulation was delivered with an electromechanical hammer, tapping directly on the suprapubic area. A polyphasic muscular response was always easily elicited in all patients. The man latency was 67.5 milliseconds (SD = 14.7). The reproducibility between the first and second mechanical responses was good with no statistical difference (r=0.966;P = 0.0001). In three patients who underwent cystometry, no rise in detrusor pressure was observed during mechanical stimulation of the suprapubic area. Our study clearly demonstrates a suprapubic bulbocavernosus reflex (SBR). Tapping the suprapubic area is a strong stimulus, reflexively mediated, used in the management of neurogenic bladder to determine a bladder contraction. However, the reflex consisting of pelvic floor muscle contraction after suprapubic stimulation was not specifically studied in humans. Many arguments can be put forth for a polysynaptic reflex (polyphasic response, habituation and short latency of the reflex, mean latency in the habitual values of R2 responses after electrical stimulation of the dorsal nerve of the penis). We hypothesize that the true stimulus is the stimulation of the bladder wall tensoreceptors, the integration level of the SBR is the sacral segments and the efferent limb the pudendal nerve, and afferent pathways could be conducted by pelvic nerve fibers. Competition between a preponderant (or exaggerated) SBR and a bladder contraction after suprapubic tapping may constitute an equivalent of detrusor-sphincter dyssynergia in some suprasacral bladders.

[Suprapubic reflex. Electrophysiological study in normal patients]

INTRODUCTION

In spinal cord injuries patients, tapping the suprapubic aera is a strong stimulus to ellicit detrusor contraction and can be used in the management of neurogenic bladder. This stimulation also determines a perineal muscles contraction. This striated response was mentionned in animal studies but never specifically analysed in men especially in normal subjects.

AIMS OF THE STUDY

Our objective was to describe pelvic floor responses with measurement of reflex latency following suprapubic mechanical stimulation.

METHODS

21 patients without neurological disease were studied. They were 14 women and 7 men. Mean age was 51 (SD=14,2). Motor responses were recorded with a needle electrode inserted in the left bulbocavernosus muscle. Stimulation was delivered with an electromechanical hammer, tapping directly on the suprapubic aera.

RESULTS

A polyphasic muscular response was always and easily elicited in all patients. Mean latency was 67,5 ms. (SD = 14,7). The reproducibility between the first and second mechanical responses was good with no statistical difference (r=0,966; p=0,0001).

DISCUSSION

Our study clearly demonstrates a suprapubic bulbocavernosus reflex (SBR). Many arguments can be retained for a polysynaptic reflex (polyphasic response, habituation and short latency of the reflex, mean latency in the habitual values of R2 responses following electrical stimulation of the dorsal nerve of the penis). We hypothetize that: the true stimulus is the stimulation of the bladder wall tenso-receptors; integration level of the SBR is the sacral segments and the efferent limb the pudendal nerve; afferent pathways could be vehicled by pelvic nerve fibers.

CONCLUSION

Competition between a preponderant (or exaggerated) SBR and a bladder contraction following suprapubic tapping, may constitute a real functional outlet obstruction giving incomplete or complete retention in some suprasacral bladders. In normal subjects, SBR can be considered as a continence reflex with increase of perineal tone following the stimulation of the bladder wall tenso-receptors during stress.

Sacral spinal interneurones and the control of urinary bladder and urethral striated sphincter muscle function

Normally, during bladder filling (continence) and expulsion (micturition) there is a reciprocity between the pattern of activity in the urinary bladder sacral parasympathetic efferents and the somatic motoneurones innervating the striated external urethral sphincter muscle. The co-ordination of this pattern of reciprocal activity appears to be determined by excitatory and inhibitory actions of a variety of segmental afferents and descending systems with sacral spinal actions. These actions may in part be mediated through lower lumbar and sacral excitatory and inhibitory spinal interneurones. Over the past 30 years, both neuroanatomical and electrophysiological approaches have been used to reveal an ever-increasing richness in the neuronal network in the lower spinal cord related to the bladder and striated external urethral sphincter muscle. The purpose of this review is to present an overview of the identified excitatory and inhibitory spinal interneurones hypothesized to be involved in the central networks controlling the sacral bladder parasympathetic preganglionic neurones and striated urethral sphincter motoneurones during continence and micturition.

Clinical value of ipsi- and contralateral sacral reflex latency measurement: a normative data study in man

The latency of the bulbocavernosus reflex (BCR) evoked by electrical stimulation of the penis provides a measure of the conduction velocity over the sacral reflex arc at the S2-4 level but does not allow evaluation of the side affected since it results from the simultaneous excitation of both dorsal nerves of the penis (DNP) at the penile root. To evaluate the reliability of the side-to-side BCR latency measurement, this study compared the reflex characteristics of the response elicited by both DNP stimulation and unilateral DNP block. After a unilateral selective DNP anesthesic block, we found that the early response of the contralateral BCR is strictly ipsilateral with no differences in terms of latency, morphology, and reflex threshold from controls. This result may indicate that the side-to-side BCR latency measurement allows a comparative study of the respective right and left sacral reflex arcs in men. We found a mean inter-latency difference of 1.8 +/- 0.4 millisecond of the early BCR response after simultaneous recording of the right and left sides in 10 normal men. We established that an inter-latency difference >3 milliseconds may be indicative of a significant alteration in the conduction over the sacral reflex arc.

Neurogenic bowel dysfunction after spinal cord injury: clinical evaluation and rehabilitative management

Neurogenic bowel dysfunction (NBD) is one of many impairments that result from spinal cord injury (SCI). The experience of persons with SCI reveals that the risk and occurrence of fecal incontinence and difficulty with evacuation are particularly significant life-limiting problems. This review relates the anatomy and physiology of colon function to the specific pathophysiology that detracts from the quality of life of persons after SCI. There are two patterns of NBD after SCI: the upper motor neuron bowel, which results from a spinal cord lesion above the sacral level, and the lower motor neuron bowel, which results from a lesion to the sacral spinal cord, roots, or peripheral nerve innervation of the colon. Rehabilitation evaluation consists of a comprehensive history and examination to define impairments, disabilities, and handicaps pertinent to NBD. Rehabilitation goals include continence of stool, simple willful independent defecation, and prevention of gastrointestinal complications. Intervention consists of derivation and implementation of an individualized person-centered bowel program, which may include diet, oral/rectal medications, equipment, and scheduling of bowel care. Bowel care is a procedure devised to initiate defecation and accomplish fecal evacuation. Digital-rectal stimulation is a technique utilized during bowel care to open the anal sphincter and facilitate reflex peristalsis. Recent advances in rehabilitation practices, equipment, pharmacology, and surgery have offered patients new bowel program alternatives. Interdisciplinary development of solutions for problems of NBD are evolving rapidly.

The nitric oxide synthase inhibitor L-NAME reduces inhibitory components of somato-vesical parasympathetic reflexes in the rat

Reflex discharges of pelvic postganglionic parasympathetic efferent fibers on the bladder surface induced by afferent volleys in the hindlimb nerve have been recorded in anesthetized rats, and the effects of the nitric oxide synthase inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME) on the reflex discharges have been investigated. Single electrical stimulation of the tibial nerve at intensities supramaximal for excitation of A- and C-afferents evoked a reflex discharge in the postganglionic parasympathetic efferents with four distinct components, i.e., two inhibitory components with latencies of 49 and 203 ms, respectively, and two excitatory components with latencies of 126 and 308 ms, respectively. These reflexes could be observed when the bladder was expanded, but not markedly when the bladder was empty. Intravenous administration of L-NAME resulted in (a) a reduction in the level of resting discharge, (b) a reduction in the size of the first inhibitory component, (c) the disappearance of the second inhibitory component and (d) the exaggeration of the late excitatory component. Intracisternal injection of L-NAME caused changes similar to those observed following intravenous injection. The results suggest that inhibitory components of the somato-pelvic parasympathetic reflex are mediated by pathways that utilize nitric oxide as a neurotransmitter or neuromodulator at the level of the brainstem.

Axotomy transiently down-regulates androgen receptors in motoneurons of the spinal nucleus of the bulbocavernosus

Testosterone is an important trophic factor for motoneurons in the spinal nucleus of the bulbocavernosus (SNB), and SNB motoneurons are more responsive to testosterone than are other motoneurons. Axonal injury during early postnatal life prevents the normal development of steroid-sensitivity by adult SNB motoneurons. Axonal injury also causes changes in the expression by motoneurons of a wide range of proteins, including the up-regulation of trophic factor receptors. We have used a polyclonal antibody (PG-21; G.S. Prins) to study the expression of androgen receptors in SNB motoneurons after axonal injury. PG-21 labeled motoneuronal nuclei in the lower lumbar spinal cord of rats in a pattern that matched autoradiographic reports of androgen accumulation in this region of the nervous system. A population of numerous, small cells located dorsal to the central canal also showed evidence of androgen receptor expression. Cutting the axons of SNB motoneurons in adulthood or in development caused a decrease in androgen receptor immunoreactivity in SNB motoneurons. This is the first report that a trophic factor receptor in motoneurons is down-regulated after axonal injury, and is interesting in light of reports that testosterone treatment can facilitate motoneuronal regeneration after nerve cut. Androgen receptor levels subsequently returned to normal, regardless of the age at axotomy, providing no evidence for a lasting effect of developmental axotomy on androgen receptor levels in SNB motoneurons. Thus, axotomy-induced down-regulation of androgen receptors does not underlie the inability of SNB motoneurons to respond to androgen treatment several months after pudendal nerve cut in development.

Long-lasting facilitation and depression of periurethral skeletal muscle following acupuncture-like stimulation in anesthetized rats

The effects of acupuncture-like stimulation on the tone of the partially filled bladder and on the periurethral electromyogram (EMG) were examined in urethane-anesthetized rats. Acupuncture-like stimuli were usually applied to the skin and underlying muscles (or other structures), either separately or together, for a period of 1 min; the effects were studied in spinal cord intact and in spinalized animals. Maps have been constructed showing the effects of acupuncture-like stimulation at different sites on the body surface and of similar stimulation applied to individual muscles, the urethra and the testis. When acupuncture-like stimuli were applied to the skin and underlying structures, in the rostral half of the body and the hindpaw, testis or urethra, these stimuli usually induced excitation of periurethral EMG activity. Depression of EMG activity was seen predominantly during stimulation of structures close to the urethra, but not opposed to it. When acupuncture-like stimuli were applied only to structure beneath the skin, depression of EMG activity usually occurred. Acupuncture-like stimulation of the bulbocavernosus, which partly overlies the proximal urethra produced depression of EMG activity in 50% of trials, but the incidence of similar effects from the more distant pubococcygeus, or the dorsal or ventral sacrococcygeal muscles was about 90-100%. Acupuncture-like stimulation for 1 min could produce either excitation or depression of periurethral EMG activity lasting about 5 or 6 min, depending on the site of insertion and rotation of the acupuncture needles. Excitation of short duration (less than 3 min) was consistently observed from areas of the body distant to the bladder, i.e. the nose, forepaw, forelimb, chest, abdominal wall and hindpaw. Longer lasting excitation of EMG activity was often seen from the penile urethra, perineal area and hindlimb. Depression of EMG activity with a duration of more than 3 min was consistently seen from the muscles at the base of the tail (sacrococcygeus) and perineal area (pubococcygeus and bulbocavernosus). The bladder was partially filled in these experiments, so that micturition contractions were never seen; acupuncture-like stimulation of the perineal area induced some increase in bladder tone in 40% of trials. In spinalized animals, the pattern of activity induced by acupuncture-like stimulation was similar to that seen in spinal cord intact animals and the durations of the effects were not significantly different in these two groups. The distribution of sites from which acupuncture-like stimuli can influence the activity of the lower urinary tract is discussed.

The influence of afferent inputs from skin and viscera on the activity of the bladder and the skeletal muscle surrounding the urethra in the rat

(1) Somato-visceral and viscero-visceral reflex interactions have been studied in the bladder branches of the pelvic nerve and in the electromyographic (EMG) activity of the periurethral skeletal muscles of the anesthetized rat, and by observations of changes in bladder motility. (2) Slow distensions of the bladder caused some elevation of intravesical pressure, and culminated in a micturition contraction. Periurethral EMG activity increased gradually during the bladder distension, and showed an oscillatory marked increase during the bladder contraction. There was a small increase in pelvic nerve efferent activity during slow distension, and there was a substantial increase before, or at the start, of a micturition contraction. (3) Oscillatory bursting activity occurred in recordings of the EMG activity from periurethral skeletal muscle during the rising phase of micturition contraction; this was particularly so during the most rapid rise in intravesical pressure, and periods of electrical silence lasting 80-270 ms alternated with bursts of activity in the periurethral EMG. (4) In the present experiments, the switching mechanism activated by pelvic afferent signals related to intravesical pressure reversed the behavior of a number of reflex pathways. When the bladder pressure was low, nociceptive pinching of the perineal skin usually caused bladder contraction and a rise in pelvic nerve efferent activity and in periurethral EMG activity. When the bladder was full, micturition contractions were present and reduced in size and frequency by pinching of the perineal skin. The pelvic nerve efferent activity was correspondingly reduced, while the EMG activity increased during and following the nociceptive stimulus. Cooling the scrotal skin with ice also decreased the frequency of bladder contractions. (5) When the bladder pressure was low, distension of the anus and colon increased periurethral EMG activity, but did not affect bladder tone. However, when the bladder was full, these stimuli reduced the size and frequency of bladder contractions, associated with a reduction in the pelvic nerve efferent activity. There was usually a simultaneous reduction in the EMG activity in periurethral muscles. Similar results were obtained during distension of the seminal vesicles or vagina, or following injection of 20-60 microliters of saline into the lumen of the vas deferens. Reversal of the responses at extremes of intravesical pressure was observed in every case. (6) Following spinal transection at the upper cervical or thoracic level, micturition contractions were absent at high bladder volumes. However the effects described when the neuraxis was intact and the bladder pressure was low were still observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Activity patterns of pubococcygeal muscles in nulliparous continent women

Simultaneous electromyographic (EMG) recordings from the left and right pubococcygeal muscles were obtained in 10 continent nulliparous women (aged 22-32 years) via wire electrodes inserted percutaneously. During relaxation, sustained motor unit firing was obtained in 14 and no EMG activity in 4 of the 20 recorded muscle sites. During voluntary squeeze, stopping urine in midstream and coughing there was always bilateral recruitment of motor units that was gradual in the recording sites with ongoing EMG activity and brisk in the sites without EMG activity; the 2 different patterns of activity were called "tonic" and "phasic" respectively. Voluntary squeeze led to activation of motor units sustained for 26 to 647 s (median 193.9) with the bladder empty and 25 to 600 s (median 198.4) with a full bladder. A marked decrease in ongoing tonic motor unit activity was seen during the attempt to urinate. Bladder filling caused an increase in tonic activity in 7 females bilaterally and in 1 unilaterally, whereas there was no change in 3 women. During the Valsalva manoeuvre, simultaneous motor unit recruitment was seen in all subjects bilaterally with the bladder empty and in all but one with the bladder full: in the latter case the motor unit recruitment with an empty bladder changed into simultaneous bilateral inhibition of firing of motor units with a full bladder (both in the supine and erect position); this pattern changed to bilateral recruitment of motor units again after bladder emptying. It is important to be familiar with the normal patterns of activity of the pubococcygeal muscles in continent nulliparous women since the denervation injury caused by childbirth might not only weaken these muscles but also influence their behaviour.

Androgenic modulation of the activity of lumbar neurons involved in the rat bulbocavernosus reflex

The bulbocavernosus (BC) reflex, produced in the BC motor nerve in response to electrical stimulation of the contralateral pudendal sensory nerve, was investigated in intact, castrated, and testosterone-treated castrated male rats under urethane anesthesia. No significant group differences in the reflex latency, sensory or motor conduction velocity, or central delay were observed. A conditioning pulse to the pudendal sensory nerve caused suppression of the averaged antidromic field potential recorded in the contralateral spinal nucleus of the bulbocavernosus (SNB) after stimulation of the SNB axons in the BC motor nerve. The suppression occurred at 6- to 35-ms intervals between shocks to pudendal sensory nerve and BC motor nerve, and was markedly smaller in castrated males than in the other two groups. In contrast, a conditioning pulse to the contralateral BC motor nerve had no effect on the SNB antidromic field potential. These results indicate that androgen modulates the efficacy of synaptic transmission onto SNB motoneurons or other neurons involved in the BC reflex.

Pelvic floor muscles response to graded rectal distension and cutaneous stimulation

The responses of the external ani sphincter (EAS) and the levator ani (LA) muscles to graded rectal distension and to cutaneous and genital stimulation were examined in 25 cats of either sex. The animals were anesthetized with sodium pentobarbital (30 mg/kg, intraperitoneal) and then tested in two positions: with hindlimbs extended and with hindlimbs flexed simulating the straining position. Graded rectal distension was performed at two speeds: 1 and 10 sec. Basal levels of activity in the EAS were higher in the straining than in the extended position (P less than 0.005). The EAS responded to rapid rectal distension with inhibition of its activity. When changed to the straining position significant increases in muscular activity were observed after 35 cc of balloon insufflation (P less than 0.005). In the same muscle, slow distension produced an initial decrease in activity followed by significant increases after insufflation of 40 cc in the extended position and of 30 cc in the straining position. Basal activity in the LA was similar in both positions tested. The main effects of rectal distension in this muscle were increases in activity, significant only after high volumes of air inflation in the straining position (P less than 0.0001). Cutaneous stimulation disclosed a receptive field that was widespread for the EAS, extending over lumbosacral dermatomes (L3-S2), but greatly restricted for the LA. Responses to vaginal and cervical stimulation were more reliably obtained from the LA (P less than 0.001). These differences indicate that the EAS and LA muscles of the cat correspond with distinct, although related neural circuits.

[Physiology of fecal continence and defecation]

Defaecation is a complex function that requires interactions between the somatic and autonomic nervous systems. Moreover, social living standards lead to self-control of continence involving supraspinal nervous structures. After a brief description of the anatomy of the hind gut, the various reflex mechanisms underlying faecal continence and defaecation are exposed; the specificities of the nervous control of the smooth and striated muscles brought into play in these events are detailed. Then the main useful investigations allowing to localize the nervous structures at the origin of the anorectal disorders are reviewed.

Effects of visceral distension on the activities of neurones receiving cutaneous inputs in the rat lumbar dorsal horn; comparison with effects of remote noxious somatic stimuli

(1) Unitary extracellular recordings were made from 92 lumbar dorsal horn neurones in urethane-anaesthetised rats. These neurones were classed as 'noxious-only' (4), 'non-noxious-only' (33) or 'convergent' (55) by their responses to stimulation of their cutaneous receptive fields on the ipsilateral hindpaw. (2) Distension of abdominal viscera (colon, urinary bladder) depressed the activities of the vast majority (93%) of the convergent neurones but of only one other cell (a non-noxious-only neurone). Similarly, noxious stimulation of widespread somatic structures depressed activity in all but one of the convergent neurones but in only 3 other cells (one non-noxious- and two noxious-only neurones). One or other of these procedures also excited 3 cells--one convergent neurone responding to distension of the colon, another to stimulation of widespread somatic structures and one non-noxious-only neurone being excited by stimulation on the contralateral hindpaw. (3) The inhibitory effects of the noxious somatic stimuli were very like those described previously and termed 'diffuse noxious inhibitory controls' (DNIC) and it seems likely that the effects of the visceral stimuli were also manifestations of DNIC, particularly in view of their similar, nearly total, specificity to convergent neurones. There were however, some small differences in the extent and temporal evolution of the inhibitory effects of the visceral and of the somatic stimuli--the visceral stimuli generally producing weaker inhibitions with slower rates of onset and recovery. It is proposed that these differences may have reflected different amounts and patterns of activity in the relevant primary afferent fibres rather than being due to different central neural mechanisms. (4) These results and the likely explanation that the effects of the visceral stimuli were mediated by a diffuse mechanism should be taken into account when interpreting the results of other studies in which inhibitory effects are produced by visceral stimulation.

Midbrain stimulation inhibits the micturition, defecation and rhythmic straining reflexes elicited by activation of sacral vesical and rectal afferents in the dog

Inhibition of the micturition, defecation and rhythmic straining reflexes by midbrain stimulation was compared with the inhibition of the jaw-opening reflex caused by tooth pulp stimulation in decerebrate dogs. All of the reflexes were inhibited by stimulation of the dorsal and ventral periaqueductal gray, dorsal raphe nucleus and central tegmental field with similar threshold intensities. After a hemisection of the spinal cord at the C2 segment, the midbrain stimulation still suppressed the micturition reflex as well as field potential changes which were evoked by stimulation of the pelvic nerve and recorded from the lateral funiculus just caudal to the hemisection, but did not influence the discharges of the vesical branch of the pelvic nerve which were elicited by stimulation of the lateral funiculus just rostral to the hemisection. The results suggest that stimulation of the neural elements in the 4 midbrain areas depresses the ascending activities from vesical and colorectal afferents of the pelvic nerve at the spinal level, and consequently inhibits the pelvic nerve reflexes. Systemic methysergide suppressed midbrain inhibition of the jaw-opening reflex, but did not affect the midbrain inhibition of the pelvic nerve reflexes. Systemic naloxone did not influence midbrain inhibition of the pelvic nerve reflexes or the jaw-opening reflex, but enhanced the micturition and rhythmic straining reflexes. Possible roles of the midbrain inhibition of the pelvic nerve reflexes are discussed.

Neurobiological aspects of the pelvic floor muscles involved in defecation

Neurobiological aspects of the organization of pelvic floor musculature are reviewed. Evolutionary considerations on the origin of these muscles indicate that they develop with specific attachments and function, i.e., do not derive from preexisting muscles such as the ones from the tail. Anatomically, pelvic floor muscles can be divided into 1) true sphincters and related muscles and 2) muscles which flank the visceral outlets. While in quadrupedal mammals the EAS behaves as a fast twitch muscle, in man this muscle has slow twitch characteristics. Like some epaxial muscles the EAS has a strong connectivity with its surrounding skin. In further analogy with some epaxial muscle the EAS, although endowed with muscle spindles, is devoid of the phasic, monosynaptic component of the stretch reflex. Onuf's nucleus which innervates pelvic floor muscles receives an important group of suprasegmental afferents including, probably, direct corticospinal fibers. Pelvic floor muscles play a fundamental role in signaling arrival of feces to the perineum. While sphincteric activity is important for continence, other mechanisms such as the anorectal angle and anal cushions are also of relevance. Although emphasis has been put on motor factors, fecal incontinence can also result from impairments in sensory mechanisms of the anorectal system. In diseases like amyotrophic lateral sclerosis, Werdnig Hoffman's and others there is selective sparing of neuropathology in Onuf's nucleus. In contrast, the nucleus is affected in some autonomic visceromotor neuronal disorders, e.g., Shy Drager syndrome, Fabry's disease. It has been suggested that Onuf's nucleus occupies an intermediate position between visceral and somatic nuclei.

Examination of the descending pathway to the external anal sphincter and pelvic floor muscles by transcranial cortical stimulation

In 26 neurologically normal patients and 9 healthy volunteers EMG responses after transcranial cortical stimulation (TCCS) were recorded from the external anal sphincter (EAS), the anterior tibial muscle (TA), the bulbocavernosus muscle (BC) and the rectus abdominis muscle (RA). Electrical TCCS was used in 29 subjects and magnetic TCCS in 6 subjects. Response patterns in the different muscles in relation to the strength of the stimulus were analyzed. It was found that the response patterns related to the strength of stimulation differed totally between the TA and the EAS. When the stimulus strength was increased stepwise, a response with a latency of 31.9 +/- 2.5 msec was first recorded in the TA, followed at higher strength by a secondary response with a latency of approximately 100 msec. In contrast, a response with a latency of 105.5 +/- 23.9 msec was first recorded in the EAS. The latency of this response gradually shortened with increasing stimulus strength until a response with a constant latency of 36.1 +/- 6.1 was obtained. In some subjects the response pattern in the BC was similar to that in the TA, and in others it was similar to that in the EAS. Responses in the TA, RA and EAS were all facilitated during voluntary contraction of the EAS. Both responses in the TA and in the EAS were facilitated by voluntary contraction of the TA. During voluntary contraction of the TA an inhibitory period was always recorded, while in the EAS no inhibitory periods were observed during either contraction or relaxation. The hypothesis that the fastest cortico-motoneuronal pathway to the EAS is polysynaptic is proposed.

The pudendo-pudendal reflex in male and female rats

The pudendo-pudendal reflex (bulbocavernosus reflex) was studied in male and female rats. Electrical stimulation of pudendal nerve afferents induced reflex volleys in ipsi- and contralateral pudendal nerves. The early components of the reflex were unaffected by acute spinal transection. The reflex was shown to be polysynaptic and bilaterally organized. No qualitative differences were noted between males and females, but a significantly longer central delay was observed in female rats, compared to males.

Quantitative synaptology of feline motoneurones to external anal sphincter muscle

Motoneurones innervating the cat external anal sphincter muscle were labelled retrogradely following intramuscular injections with horseradish peroxidase (HRP). Labelled motoneurones were examined by correlative light and electron microscopy (LM and EM) with special regard to a qualitative and morphometric analysis of the axon terminals resident on the neuronal membrane. By LM, labelled motoneurones were (1) ipsilateral to the injections; (2) all in S1-S2; (3) found only in the superior dorsomedial region of Onuf's nucleus; and (4) exhibited a broad spectrum of diameters (25-72 micron, mean 47.4 +/- 11.3 micron). By EM, axon terminals on the neuronal membrane when classified according to size, vesicle shape, and synaptic complex ultrastructure conformed to the S-, F-, T-, M-, and C-type terminals previously described for cat lumbosacral motoneurones. C-terminals confirmed these sphincteric motoneurones to be skeletomotor. Pooled data from midnuclear sections through 15 random labelled motoneurones (20-64-micron diameter) revealed that S- and F-type terminals predominated, with numerically few M and C types. Notwithstanding their low frequency (0.3/100 micron membrane) C-terminals contributed 1% of the mean areal coverage by terminals, which implies a potentially larger synaptic influence relative to other terminal types. Linear relationships occurred between terminal frequency (or cover) and motoneurone diameter. While motoneurones greater than 40 micron in diameter exhibited all five terminal types, labelled motoneurones less than or equal to 30 micron generally possessed only S-, F-, and occasional T-type terminals, and in this respect resembled gamma motoneurones.

Discharge patterns of pudendal efferent fibres innervating the external anal sphincter of the cat

Segmental somatic reflexes to pudendal motor axons which innervate the skeletal muscle of the external anal sphincter were studied in cats with an intact spinal cord and in acutely spinalized cats (T13-L2 spinal cord transection level) during electrical stimulation of afferent fibres in the pudendal nerve, during distension of the anal canal and reproductive organs, and during tactile (light touch and pressure) and nociceptive stimuli (pinch) applied to the mucosa of the anal canal, anal-perianal skin region, and the skin surrounding reproductive organs. Forty single pudendal motor axons recorded from nerve filaments in the pudendal nerve branch to the external anal sphincter which responded reflexly to electrical stimulation of afferent fibres in the contralateral pudendal nerve were studied. Only one motor axon was spontaneously active. 70% of these motor axons were also activated by distension of the anal canal and reproductive organs and by mechanical stimulation of the skin. 61% of motor axons which were activated by distension of the anal canal were also activated by mechanical stimulation of the mucosa of the anal canal, anal-perianal skin region. 29% of motor axons were activated by convergent afferent inputs (during distension and mechanical stimulation) from both reproductive organs and from the external anal sphincter region. Motor axons exhibited bursts of action potentials during reflexes initiated during distension of the anal canal and vagina. Motor axons exhibited phasic discharges of action potentials during reflexes initiated by tactile or nociceptive stimuli applied to the mucosa of the anal canal, anal-perianal skin region and the skin surrounding reproductive organs. The peak firing frequencies of action potentials during mechanical stimulation of the skin ranged from 8 to 35 Hz. The average firing frequencies of action potentials during continuous distension of the anal canal ranged from 4 to 16 Hz.