Vaginal Distension Research Articles

Effect of vaginal distension on blood flow and hypoxia of urogenital organs of the female rat

Vaginal delivery of children causes traumatic injury to tissues of the pelvic floor and is correlated with stress urinary incontinence; however, the exact mechanism of organ and tissue injury leading to incontinence development is unknown. The purpose of this project was to test the hypothesis that vaginal distension results in decreased blood flow to, and hypoxia of, the urogenital organs responsible for continence, which would suggest an ischemic and/or reperfusion mechanism of injury. Thirteen female rats underwent vaginal distension for 1 h. Thirteen age-matched rats were sham-distended controls. Blood flow to the bladder, urethra, and vagina were determined using a microsphere technique. Hypoxia of these organs was determined by immunohistochemistry. Blood flow to all three organs was significantly decreased just before release of vaginal distension. Bladder blood flow decreased further immediately after release of vaginal distension and continued to be significantly decreased 15 min after the release. Blood flow to both the urethra and vagina tripled immediately after release, inducing a rapid return to normal values. Vaginal distension resulted in extensive smooth muscle hypoxia of the bladder, as well as extensive hypoxia of the vaginal epithelium and urethral hypoxia. Bladders from sham-distended rats demonstrated urothelial hypoxia as well as focal hypoxic areas of the detrusor muscle. We have clearly demonstrated that vaginal distension results in decreased blood flow to, and hypoxia of, the bladder, urethra, and vagina, supportive of hypoxic injury as a possible mechanism of injury leading to stress urinary incontinence.

Oviduct contractile response to vaginal distension: identification of vagino-tubal reflex

The effect of vaginal distension on the oviduct contractile activity during penile thrusting at coitus could not be traced in the literature. We investigated the hypothesis that vaginal distension effects oviduct contraction, which assists in ovum transport along the oviduct. Oviduct pressure was measured upon vaginal condom distension in 16 women (mean age 32.2+/-1.2 years) scheduled for abdominal hernia repair and oviduct ligation for sterilization. The test was repeated after individual anesthetization of the vagina and oviduct. Ten milliliters vaginal distension effected pressure elevation of the ampullary (AO) and isthmic (IO) parts of the oviduct (p<0.01, p<0.01 respectively) and a decrease in intramural oviduct (IMO; p<0.01). Twenty milliliters distension further increased the pressure in the AO and the IO (p<0.001, p<0.001) and decreased it in IMO (p<0.001). Vaginal distension with greater volumes produced an oviduct pressure response similar to that with 20 ml distension (p>0.05). Vaginal distension of anesthetized vagina or oviduct did not evoke the oviduct pressure response, but saline infusion did. Vaginal distension seems to produce oviduct motile activity as evidenced by oviduct pressure changes, which appear to assist in sperm-ovum transport and fertilization. These oviduct changes are suggested to occur reflexly through the "vagino-tubal reflex." Pathologic changes of the oviduct presumably interfere with this reflex action, a point that needs to be investigated.

Short-term functional and neuroregenerative response of the urethra to ovariectomy and vaginal distension in female rats

The objective of this study was to investigate the effects of ovariectomy (OVX) and vaginal distension (VD) on leak point pressure (LPP) and pudendal nerve regenerative response in the female rat. Twenty rats underwent OVX 3 days prior to either VD or sham distension. Seventeen rats did not receive OVX but underwent either VD or sham distension. Four days after distension, LPP testing was performed. In situ hybridization for beta(II) tubulin mRNA, an indicator of the neuroregenerative response, was performed on motoneurons of the pudendal nerve. In the non-OVX group, LPP was significantly decreased after VD. After OVX, the difference in LPP between VD and sham rats did not quite reach the level of statistical significance. There was a statistically significant interaction between the effects of OVX and VD on LPP. There was no significant difference in in situ hybridization results between any of the groups. No neuroregenerative response of motoneurons of the pudendal nerve was observed after either VD or OVX.

1724: Alterations in EX Vivo BID Mechanical and Pharmacological Properties of the Urethra in a RAT Model of Birth Trauma Induced by Vaginal Distension

1724: Alterations in EX Vivo BID Mechanical and Pharmacological Properties of the Urethra in a RAT Model of Birth Trauma Induced by Vaginal Distension

Functional and Neuroanatomical Effects of Vaginal Distention and Pudendal Nerve Crush in the Female Rat

We tested the hypothesis that neuroanatomical degeneration near the external urethral sphincter (EUS) would parallel urinary dysfunction after vaginal distention or bilateral pudendal nerve crush in female rats. A total of 28 female rats underwent bilateral pudendal nerve crush or vaginal distention, or were unoperated controls. Two days later a catheter was implanted into the bladder dome and 2 days after that (4 days after injury) urethral leak point pressure testing was performed with the rat under urethane anesthesia. The pudendal nerve and urethra were then dissected and prepared for light and electron microscopy. Leak point pressure was significantly decreased 4 days after pudendal nerve crush and vaginal distention (29.3 +/- 3.4 and 31.0 +/- 2.5 cm H(2)O, respectively) compared with controls (44.3 +/- 3.4 cm H(2)O). The percentage of nerve fascicles with degeneration near the EUS was significantly greater in the nerve crush (13.1% +/- 1.7%) and vaginal distention (7.2% +/- 2.2%) groups than in the control group (0% +/- 0%). There were fewer nerve fascicles near the EUS in the ventral half of the urethral cross section than in the dorsal half in all 3 groups and the percent of fascicles with degeneration was greater in the ventral half than in the dorsal half in the 2 injury groups. These results suggest that the pudendal nerve is particularly vulnerable to injury during vaginal distention in this animal model. The 2 injury models may be useful for investigating the pathophysiology of stress urinary incontinence.

The influence of ovariectomy with or without estrogen replacement on responses of rat gracile nucleus neurons to stimulation of hindquarter skin and pelvic viscera

Responses of neurons in the gracile nucleus (NG) of female rats to tactile and visceral stimulation change across the estrous cycle [J. Neurosci. 20 (2000) 7722]. To investigate estrogen’s role in these changes, responses of NG neurons to tactile and visceral stimuli were examined in three groups: ovariectomized (OVX), OVX with estrogen replacement (OVX+E2), or sham OVX (tested in diestrus; shamOVX-D). The stimuli were: gentle brushing of hindquarter skin, pressure on the cervix, and distention of the uterus, vagina, or colon. After OVX, the magnitude of multi-unit responses to brushing the perineum, hip and tail, but not the foot and leg, were significantly reduced relative to shamOVX-D. OVX+E2 restored this magnitude to the same level as shamOVX-D, but not, as expected, to levels as large as previously observed in proestrus. After OVX, responses of single neurons to stimulation of the uterus, cervix, and colon were more likely to be excitatory (versus inhibitory) than they had been in cycling rats in proestrus (uterus, cervix) or diestrus (colon); OVX+E2 did not restore the inhibitory responses. In contrast, whereas all responses to vaginal distention after OVX were also excitatory, OVX+E2 in this case significantly restored the inhibitory responses. These findings provide further support for the conclusion that response characteristics of NG neurons are influenced by the rat’s hormonal milieu, but also indicate that the influences are not a simple reflection of estrogen levels. The findings further suggest that NG is a component of neural systems that contribute to both reproductive behaviors and vaginal nociception.

Estrous changes in vaginal nociception in a rat model of endometriosis

A rat model of endometriosis, in which pieces of uterine horn (versus fat in controls) are autotransplanted into the abdomen where they form cysts, reduces fecundity and produces vaginal hyperalgesia. The cysts gradually enlarge over a 2-month period postsurgically and then plateau. Cysts regress with low estrogen levels and reappear when they rise. Based on the hypothesis that the vaginal hyperalgesia depends upon the cysts, this study tested two predictions: that (1) the hyperalgesia would develop postsurgically in parallel with the cysts, and (2) the hyperalgesia would vary with estrous, being greatest when estrogen levels are high (proestrus) and least when low (estrus). In rats trained to escape vaginal distention, percentage escape responses to different distention volumes were measured across the rat's 4-day estrous cycle for 2.5 months before and up to 4 months after autotransplantation of uterus ( n = 9) or fat ( n = 6) in abdominal sites. Vaginal pressures were also measured. In rats with uterine but not fat autotransplants, escape percentages increased postsurgically over a 2-month period and then plateaued. The increase was greatest in proestrus and failed to occur in estrus. Vaginal pressures were unchanged in all groups. These results strongly support the hypothesis that the vaginal hyperalgesia depends upon the cysts. Because the cysts were located in sites remote from the vagina, the hyperalgesia involves viscero-visceral interactions and is likely centrally mediated, whereas the estrous modulation could involve hormonal actions either on the cysts or, more likely, on vaginal afferent fibers, and/or on central neurons.

Spasticity of the Pelvic Floor Mimicking an Obstructive Anomaly

Study Objective: Hematocolpos or hydrocolpos in menstruating women raises suspicion of a partial uterine or vaginal obstruction. The study objective is to report two unusual cases of a spastic pelvic floor leading to urine collecting in the vagina and mimicking an outflow obstruction.Design, Setting, Participants: The study took place at a tertiary care university's Reproductive Health Care Clinic for Women with Developmental Disabilities and involved two patients with spastic quadriplegic cerebral palsy and developmental disabilities who presented with irregular menses and abdominal pain and whose radiological evaluations were suspicious for an outflow obstruction. Medical records, including clinic visits, radiological findings, and surgical findings, were reviewed.Interventions: Both patients underwent ultrasound and MRI evaluation of their reproductive tracts that demonstrated fluid collections in the vagina. An examination under anesthesia was performed in one patient to rule out an obstruction. In the second patient, a pelvic examination under ultrasound observation revealed initial vaginal distension with urine, which resolved after placement of a speculum.Results: In both cases, the pseudo-obstruction was felt to be a urine-distended vagina due to a spastic pelvic floor.Conclusion: A spastic pelvic floor in an incontinent patient with spastic quadriplegia may result in urine accumulation in the vagina, mimicking an outflow tract obstruction. If the history, pelvic examination, and radiological images are inconsistent, performing an ultrasound-guided examination may assist with diagnosis.

Effects of vaginal distension on urethral anatomy and function.

To determine the effect of repeated and prolonged vaginal distension on the leak-point pressure (LPP) and urethral anatomy in the female rat, as prolonged vaginal distension has been clinically correlated with signs of stress urinary incontinence (SUI). Sixty female rats were placed into one of five groups; four groups underwent one of four vaginal distension protocols using a modified 10 F Foley catheter, i.e. prolonged (1 h), brief (0.5 h), intermittent (cycling inflated/deflated for 0.5 h) or sham distension. All animals had a suprapubic bladder catheter implanted 2 days after and were assessed urodynamically 4 days after vaginal distension. The fifth group of rats acted as controls and did not undergo vaginal distension, but did have a suprapubic bladder catheter placed and urodynamics assessed. To measure LPP the rats were anaesthetized with urethane, placed supine and the bladder filled with saline (5 mL/h) while bladder pressure was measured via the bladder catheter. LPPs were measured three times in each animal by manually increasing the abdominal pressure until leakage at the urethral meatus, when the external abdominal pressure was rapidly released. Peak bladder pressure was taken as the LPP and a mean value calculated for each animal. Immediately after measuring LPP the urethra was removed and processed routinely for histology (5 micro m sections, stained with haematoxylin/eosin and trichrome). The means (sem) were compared using a Kruskal-Wallis one-way anova on ranks, followed by a Dunn's test, with P < 0.05 indicating a significant difference. Both LPP and the external increase in abdominal pressure were significantly lower after prolonged distension, at 31.4 (1.7) and 19.8 (1.2) cmH2O, than in the sham group, at 41.1 (3.2) and 32.0 (4.7) cmH2O, respectively. There were no significant differences in LPP or in the increase in abdominal pressure between the brief, intermittent and sham groups. Qualitative histology showed that prolonged distension resulted in extensive disruption and marked thinning of urethral skeletal muscle fibres. Brief and intermittent distension showed mild and focal disruptions, respectively. As observed clinically, prolonged vaginal distension results in a lower LPP, greater anatomical injury and increased severity of SUI. These results suggest that ischaemia is important in the development of SUI after prolonged vaginal distension.

Estrogen replacement reverses ovariectomy-induced vaginal hyperalgesia in the rat

Objectives: The loss of ovarian function in women through aging or oophorectomy is often associated with the development of vaginal hyperalgesia that can be alleviated with estrogen replacement. This study examined if ovariectomy in rats would similarly give rise to vaginal hyperalgesia, and, if so, whether estrogen replacement would alleviate it. Methods: Female rats were trained to perform an operant response to escape vaginal distention delivered by inflating a balloon located in mid-vaginal canal. Percent escape responses to eight different volumes of distention measured in normally cycling rats were compared with measures made in the same rats following ovariectomy (OVX) or sham ovariectomy (shamOVX), and then, in the OVX group, estrogen replacement (OVX+E2). Pressures exerted by the eight volumes on the vaginal wall were also measured, thereby permitting assessment of vaginal tone. Results: Whereas overall escape response percentages after OVX, but not shamOVX, were significantly higher to the largest six distention volumes compared with responses during cycling, there were individual differences in the amount of hyperalgesia. Following OVX+E2, escape response percentages decreased in all but one rat. Vaginal tone after OVX, shamOVX or OVX+E2 did not differ from overall vaginal tone in cycling rats. Conclusions: Ovariectomy in rats evokes a variable amount of vaginal hyperalgesia that can be alleviated by estrogen replacement in most cases. Thus, the ovariectomized rat appears to provide a useful model for the study of mechanisms underlying the dyspareunia that is associated with loss of ovarian function in women.

Vaginal hyperalgesia in a rat model of endometriosis

This study examined whether a rat model of surgically-induced endometriosis that reduces fertility also evokes vaginal hyperalgesia along with changes in vaginal compliance. In nine rats trained to escape vaginal distention, percent escape responses to different volumes of vaginal distention were measured for 2.5 months before and after endometriosis or sham surgery. Vaginal pressures were also measured simultaneously to provide an estimate of vaginal compliance. Endometriosis (or sham) was induced by autotransplantation of small pieces of uterus (or fat) on mesenteric cascade arteries, abdomen, and ovary. Escape responses were significantly increased only in rats whose autotransplants had formed cysts. Vaginal pressures, however, remained unchanged. This vaginal hyperalgesia may involve a process of viscero-visceral referred hyperalgesia.

EFFECT OF VAGINAL DISTENTION ON VESICOURETHRAL FUNCTION WITH IDENTIFICATION OF THE VAGINO-VESICOURETHRAL REFLEX

To our knowledge the physiological mechanisms involved in sexual intercourse have not been completely explored. We hypothesized that vaginal distention induced by penile thrusting may affect the function of the bladder and urethra. To verify this supposition we assessed the effect of vaginal distention on vesical and urethral pressure. No relevant reports in the literature were identified. The response of vesical and urethral pressure to vaginal distention was recorded in 26 healthy women volunteers with a mean age plus or minus standard deviation of 36.7 +/- 9.8 years. A condom was introduced into the vagina and inflated with carbon dioxide in increments of 10 ml. up to 80 ml. Vesical and urethral pressure was measured by a 2-channel microtip catheter connected to a transducer. The vesicourethral pressure response to vaginal distention was also tested after individual anesthetization of the bladder, urethra and vagina. No vesicourethral pressure response was recorded with 10 and 20 ml. of vaginal distention. At 30 and up to 80 ml. of distention bladder pressure decreased and urethral pressure increased (p <0.05). There was no significant difference when the volume of vaginal distention was increased. Mean duration of the pressure response was 4.2 +/- 0.6 seconds. Pressure returned to normal after a latency period of 5.2 +/- 1.1 seconds, although the vagina was continuously distended. Vaginal distention during anesthetization of the bladder, urethra or vagina did not evoke a pressure response. The vesicourethral response to the inserted condom, which by inflation adopts the shape of the erect penis, seems to simulate the response of the vagina when it is distended by the erect penis during coitus. The constant vesicourethral pressure response to vaginal distention postulates a reflex relation, which we call the vagino-vesicourethral reflex. This reflex is apparently evoked during coitus, leading to momentary vesical dilatation and increased urethral sphincter activity, which most likely acts to prevent urinary leakage during coitus. Reflex disorders may explain urinary leakage during coitus in some neuropathic conditions.

The role of the levator ani muscle in evacuation, sexual performance and pelvic floor disorders.

This paper reviews the role of the levator ani muscle (LAM) in evacuation, sexual performance and pelvic floor disorders. The LAM fixes the vesical neck, anorectal junction and vaginal fornices to the side wall of the pelvis by means of the suspensory sling and hiatal ligament. On contraction it shares in the mechanism of evacuation (urination, defecation). During the sexual act vaginal distension by the erect penis evokes the vaginolevator and vaginopuborectalis reflexes, with a resulting LAM contraction. The LAM also contracts upon stimulation of the clitoris or cervix uteri, an action mediated through clitoromotor and cervicomotor reflexes. LAM contraction leads to upper vagina ballooning, which acts as receptacle for semen collection, to uterine elevation and straightening and to elongation and narrowing of the vagina. These actions enhance the sexual response and prepare the uterus and vagina for the reproductive process. During ejaculation LAM contraction facilitates semen ejection. Levator subluxation and sagging leads to levator dysfunction syndrome, which may present as pudendal canal syndrome.

Estrous Changes in Responses of Rat Gracile Nucleus Neurons to Stimulation of Skin and Pelvic Viscera

Multi- and single-unit recording was performed in the gracile nucleus in urethane-anesthetized rats to examine estrous variations in responses of its neurons to brushing the hindquarters and mechanical stimulation of the uterus, vaginal canal, cervix, and colon. Six rats each were studied in each of the four estrous stages: proestrus (P), estrus (E), metestrus (M), and diestrus (D). The magnitude of multi-unit responses to gentle brushing of the perineum, hip, and tail, but not the foot and leg, was significantly greater during proestrus than during other stages. Of 70 single units responsive to brush, 56 (80%) responded to stimulation of at least one viscus. Although this percentage did not change with estrous stage, the direction and latency of some responses did. Pressure on the cervix evoked significantly more inhibitory (vs excitatory) responses in P than in E and M, and the response latency was significantly longer in D and P than in E and M. The direction of response to vaginal distention did not change with estrous stage, but response latency was significantly longer in D than in P and E. Uterine distention evoked significantly more inhibitory responses in D than in P, with no estrous changes in latency. Responses to colon distention did not change. These variations in both magnitude of response to tactile stimulation and characteristics of response to stimulation of reproductive organs, but not the colon, correlate with changes in mating behaviors of the female rat, suggesting that the gracile nucleus is a component of neural systems that control reproductive behaviors.

Estrous variations in behavioral responses to vaginal and uterine distention in the rat

Response properties of peripheral afferent fibers supplying the vagina and uterus of the rat vary with estrous stage (Robbins A, Berkley KJ, Sato Y. Estrous cycle variation of afferent fibers supplying reproductive organs in the female rat. Brain Res 1992;596:353–356), suggesting that behavioral sensitivity to vaginal and uterine stimulation might similarly vary. To test this hypothesis, detection and escape responses of 12 rats to different volumes of distention of the vaginal canal or uterine horn (six rats each) were compared during each of the four estrous stages, proestrus (P), estrus (E), metestrus (M), and diestrus (D), using previously-published behavioral techniques (Berkley KJ, Wood E, Scofield SL, Little M. Behavioral responses to uterine or vaginal distention in the rat. Pain 1995;61:121–131). Estrous variations in vaginal or uterine tone (pressure-volume functions) were also measured in the same rats. Vaginal canal: escape response percentages increased significantly as vaginal distention volume increased, but neither escape nor detection responses varied with estrous stage. Vaginal tone, however, was greater in P and E than in M and D, with the greatest tone in E and the least in D. When escape responses to different pressures were analyzed, it was found that escape response percentages to the same vaginal pressure were lower during P and E than during M and D. One outcome of these estrous influences would be that a vaginal stimulus of a given volume (such as an erect penis) would exert higher pressures during P and E (i.e. the penis would be held within the vaginal canal more firmly) than during M and D, but would be less likely during P and E to provoke escape responses. This modification of nociceptive sensitivity has obvious reproductive advantages, because P and E constitute the rat's fertile period. Uterine horn: escape response percentages increased significantly as uterine distention volume increased only during M and D, with no differences between them. Detection responses also occurred only during M and D. Similarly, uterine tone was significantly greater in M and D than in P and E, with the greatest tone occurring during M and the least during P. Although these changes in uterine tone were opposite to those of the vaginal canal, escape response percentages to the same uterine pressures were, in a manner similar to vaginal pressures, lower during P and E than during M and D. The functional significance of these variations for the uterus is unclear, but does suggest that, under pathophysiological conditions, stimulation of the uterine horn, as well as the vaginal canal, would be more likely to provoke escape behaviors in M and D than in P and E. A similar increased sensitivity in rats during M and D to noxious stimulation of other pelvic organs has been observed by others. This situation resembles that in women, for whom many visceral pain conditions are exacerbated during a comparable part of their ovarian cycle, i.e. perimenstrually.

Electrophysiological responses of neurones in the rat nucleus tractus solitarius to oxytocin-releasing stimuli

Neurones in the nucleus tractus solitarius (NTS) of the rat are, at least partially, responsible for mediating the excitatory effects of systemic cholecystokinin (CCK) injection and parturition on oxytocin release. Utilising in vivo electrophysiological recordings in urethane-anaesthetised rats we examined the effects of systemic CCK injection and vaginal distension (VD) on NTS neuronal activity. Approximately 25% of neurones were excited by CCK injection and a population of neurones (24%) responded specifically to VD, but only one neurone responded to both oxytocin-releasing stimuli. NTS neurones that projected to the hypothalamus also responded in a specific manner to either CCK or VD. It is known that the excitatory effects of CCK and VD on oxytocin release are mediated by separate peripheral pathways and the results from this study suggest that separation of these two inputs persists at the level of the NTS.

Antinociceptive effects of morphine and U-50,488h on vaginal distension in the anaesthetized rat

The antinociceptive activity of the k- and μ-opioid receptor agonists, (±)-U-50,488H and morphine, was examined in a vaginal distension model in anaesthetized female rats. Vaginal distension induced a reproducible cardiovascular response (CVR) which was inhibited in a dose related manner by morphine ( 0.03 − 1.0 mg kg i.v., ED 50 = 0.16 mg kg ) and (±)-U-50,488H ( 0.08−1.6 mg kg i.v., ED 50 = 0.49 mg kg ). Morphine (0.3 μg/rat) administered i.c.v. inhibited the CVR by 81.6 ± 7.9% whereas (±)-U-50,488H (30–300 μg/rat) was inactive by this route. A low dose of naloxone (30 μg kg i.v.) blocked the effect of morphine but not that of (±)-U- 50, 488H. The k-opioid antagonist, nor-binaltorphimine (10 mg kg s.c.) abolished the response to (±)-U-50,488H but not that of morphine. This demonstrates that both central and peripheral μ-opioid receptors may be involved in morphine-induced antinociception whereas the k-opioid agonist, (±)-U-50,488H, blocks vaginal nociception by acting on peripheral k-opioid receptors.

Study of the uterine response to vaginal distension: the 'vagino-uterine reflex'.

To study the effect of vaginal distension on the uterus, the uterine pressure was measured in 20 healthy female volunteers (mean age 34.3 +/- 7.8 years; 7 nulli-, 13 multiparous) by means of a manometric tube perfused by a pneumohydraulic system. Vaginal distension was induced by a 12 F condom-ended catheter. The condom was inflated in increments of 10 ml of air. The test was repeated after anesthetizing the vagina and uterus, respectively. The uterine pressure increased upon vaginal distension; it showed more rise as the distension increased (p < 0.01). The response was momentary and the pressure returned to basal values although vaginal distension continued. It disappeared upon sustained or successive inflations of 5-7 times and was restored after a resting period of 3-5 min. There was no uterine pressure response when the vagina or uterus were anesthetized and it returned when the anesthetic effect had worn off. No significant difference was found in the pressure response between nulli- and multiparous women (p > 0.05). The aforementioned results were reproducible when repeated in the same woman with no significant difference (p > 0.05). The inflated condom looks like the erect penis, and the uterine response to the inflated condom seems to simulate that of the erect penis distending the vagina during coitus. The constant rise of uterine pressure to vaginal distension postulates a reflex relation which we call 'vagino-uterine' reflex. Uterine contractions during coitus are suggested to have a 'suction-pumping' action on the semen deposited in the vaginal fornices.

Spinothalamic and spinohypothalamic tract neurons in the sacral spinal cord of rats. II. Responses to cutaneous and visceral stimuli.

1. A goal of this study was to determine whether neurons in the sacral spinal cord that project to the diencephalon are involved in the processing and transmission of sensory information that arises in the perineum and pelvis. Therefore, 58 neurons in segments L6-S2 were activated antidromically with currents < or = 30 microA from points in the contralateral diencephalon in rats that were anesthetized with urethan. 2. Responses to mechanical stimuli applied to the cutaneous receptive fields of these neurons were used to classify them as low-threshold (LT), wide dynamic range (WDR) or high-threshold (HT) neurons. Twenty-two neurons (38%) responded preferentially to brushing (LT neurons). Eighteen neurons (31%) responded to brushing but responded with higher firing frequencies to noxious mechanical stimuli (WDR neurons). Eighteen neurons (31%) responded only to noxious intensities of mechanical stimulation (HT neurons). LT neurons were recorded predominantly in nucleus proprius of the dorsal horn. Nociceptive neurons (WDR and HT) were recorded throughout the dorsal horn. 3. Cutaneous receptive fields were mapped for 56 neurons. Forty-five (80%) had receptive fields that included at least two of the following regions ipsilaterally: the rump, perineum, or tail. Eleven neurons (20%) had receptive fields that were restricted to one of these areas or to the ipsilateral hind limb. Thirty-eight neurons (68%) had cutaneous receptive fields that also included regions of the contralateral tail or perineum. On the perineum, receptive fields usually encompassed perianal and perivaginal areas including the clitoral sheath. There were no statistically significant differences in the locations or sizes of receptive fields for LT neurons compared with nociceptive (WDR and HT) neurons. 4. Thirty-seven LT, WDR, and HT neurons were tested for their responsiveness to heat stimuli. Five (14%) responded to increasing intensities of heat with graded increases in their firing frequencies. Thirty-two LT, WDR, and HT neurons also were tested with cold stimuli. None responded with graded increases in their firing frequencies to increasingly colder stimuli. There were no statistically significant differences among the responses of LT, WDR, and HT neurons to either heat or cold stimuli. 5. Forty LT, WDR, and HT neurons were tested for their responsiveness to visceral stimuli by distending a balloon placed into the rectum and colon with a series of increasing pressures. Seventeen (43%) exhibited graded increases in their firing frequencies in response to increasing pressures of colorectal distention (CrD). None of the responsive neurons responded reproducibly to CrD at an intensity of 20 mmHg, and all responded at intensities of > or = 80 mmHg. More than 90% responded abruptly at stimulus onset, responded continuously throughout the stimulus period, and stopped responding immediately after termination of the stimulus. 6. Thirty-one neurons were tested for their responsiveness to distention of a balloon placed inside the vagina. Eleven (35%) exhibited graded increases in their firing frequencies in response to increasing pressures of vaginal distention (VaD). The thresholds and temporal profiles of the responses to VaD were similar to those for CrD. Twenty-nine neurons were tested with both CrD and VaD. Thirteen (45%) were excited by both stimuli, four (14%) responded to CrD but not VaD, and one (3%) was excited by VaD but not CrD. Neurons excited by CrD, VaD, or both were recorded throughout the dorsal horn. 7. As a population, WDR neurons, but not LT or HT neurons, encoded increasing pressures of CrD and VaD with graded increases in their firing frequencies. The responses of WDR neurons to CrD differed significantly from those of either LT or HT neurons. Regression analyses of the stimulus-response functions of responsive WDR neurons to CrD and VaD were described by power functions with exponents of 1.6 and 2.4, respectively.(ABSTRACT TRUNCATED)

Vagino-levator reflex: description of a reflex and its role in sexual performance

A new reflex, termed the ‘vagino-levator reflex’, was studied in 17 healthy women (mean age 36.6 years). The vagina was distended with up to 300 ml air in a condom tied to a catheter, and the levator ani response was determined by means of needle electrode introduced into the muscle. The test was repeated after anesthetizing the vagina and the levator muscle, respectively. The levator EMG activity rose when the vagina was distended; the amplitude and duration of activity increased in parallel with vaginal distension. The levator response did not occur after successive repetition of vaginal distension due probably to levator muscle fatigue; nor did it occur after anesthetizing the vagina or the levator muscle. The mean latency of the reflex was 39.5 ms. The vagino-levator reflex seems to play a role in the sexual act. Levator contraction upon penile thrusting leads to genital responses that could facilitate sexual performance. These responses comprise widening of the vaginal introitus, vaginal elongation and ballooning of the upper vagina as well as uterine elevation. Vagino-levator reflex dysfunction may result in disorders of sexual act.