Somato-motor components of the pelvic and pudendal nerves of the female rat

Sustained activation of the triceps surae muscles produced by mechanical stimulation of the genital tract of the female cat

In decerebrate cats, controlled mechanical stimulation of the perivulvar skin, the vaginal wall or the cervix uteri induced visible hind limb extension. Pressing on the cervix uteri produced the greater response. To quantify these responses, the EMG activity and the tension developed by the normally inserted triceps surae muscles were recorded. The activity induced in these muscles by stimulation of the genital canal outlasted the stimulus by many seconds or a few minutes. These effects disappeared after spinalization at the T12 level. We propose that stimulation of the vaginal canal in the female cat may induce bistability of triceps surae motoneurones.

Mechanism of the reflex inhibition of micturition contractions of the urinary bladder elicited by acupuncture-like stimulation in anesthetized rats

The effects of acupuncture-like stimulation of various segmental areas on the rhythmic micturition contractions (RMCs) of the urinary bladder were examined in anesthetized rats. The urinary bladder was cannulated via the urethra and expanded by infusing saline until the urinary bladder produced micturition contractions rhythmically as a consequence of the rhythmic burst discharges of the vesical pelvic efferent nerves. An acupuncture needle, having a diameter of either 160 or 340 microns, was inserted to a depth of about 4-5 mm into the skin and underlying muscles at various segmental areas, rostrally from the face then caudally to the hindlimb. Once being inserted, the needle was twisted left and right with the fingers about once every second for 1 min. (1) Acupuncture-like stimulation applied to the perineal area inhibited both the RMCs and the rhythmic burst discharges of vesical pelvic efferent nerves without any significant changes in the hypogastric efferent nerve activity. By contrast, stimulation applied to the face, neck, forelimb, chest, abdomen, back, and hindlimb areas was ineffective. (2) After surgically separating the perineal skin from the underlying muscles with the main cutaneous nerve branches intact, stimulation of either the perineal skin or the perineal muscles inhibited the RMCs. Stimulation of the perineal muscles produced a stronger inhibition of the RMCs than that of the perineal skin. (3) Stimulation of the perineal area increased afferent nerve activity, either recorded from the pudendal nerve branches innervating the perineal skin or underlying muscles, or recorded from the pelvic nerve branches innervating the perineal muscles. (4) The stimulation-induced inhibition of the RMCs was abolished after surgically severing both pudendal and pelvic nerve branches that innervated the perineal skin and underlying muscles. (5) The present findings indicate that the inhibition of the RMCs following acupuncture-like stimulation of the perineal area is a reflex response characterized by segmental organization. The afferent arcs of the reflex are both pelvic and pudendal nerve branches innervating the perineal skin and underlying muscles, while the efferent arcs are pelvic nerve branches innervating the urinary bladder.

Expression of c-fos protein in lumbosacral spinal cord in response to vaginocervical stimulation in rats

The pattern of vaginocervical stimulation-evoked expression of the proto-oncogene c-fos in lumbar 5-sacral 1 segments of the spinal cord of ovariectomized adult rats was mapped using immunocytochemistry. A calibrated force of mechanostimulation was applied to the vaginal cervix of experimental animals and to the perineum of control animals while they were gently restrained. The number of cells expressing c-fos was significantly greater in the experimental than the control animals in laminae I, IV, V-VI and X. The implications of the present findings for elucidating the spinal pathways mediating the various behavioral, neuroendocrine and autonomic effects of vaginocervical stimulation (VS) are discussed.

Response of bladder, urethral and intracavernous pressure to ventral lumbosacral root stimulation in Sprague-Dawley and Wistar rats

Six Sprague-Dawley and six Wistar rats were used for electrostimulation of the L5 to S2 ventral roots. Landmarks for identification of the roots were developed; bladder, urethral and intracavernous pressures were recorded; and tail and leg movements were checked. Urethral sphincter contraction was elicited by stimulation of the L5-L6 ventral roots, while bladder contraction and penile erection were mediated by the L6-S1 ventral roots. The best sphincteric response and intracavernous pressure rise were obtained by stimulation of the L6 ventral root, and the highest bladder pressures by stimulation of the S1 ventral root. Stimulation of the S1-S2 ventral roots provoked ipsilateral tail movement; of L6, tail movement, hindleg muscle twitch, and slight toe spread; and of L5, hindleg stretch and plantar flexion. No significant differences were found between the two strains of rats, although a higher bladder pressure was recorded during stimulation of the L6 ventral root in Sprague-Dawley rats, which might be explained by a small caudal shift of the sacral parasympathetic nucleus in the Wistar strain.

Copulatory analgesia in male rats ensues from arousal, motor activity, and genital stimulation: blockage by manipulation and restraint

The effect of copulation on the vocalization threshold to tail shock (VTTS) was assessed in freely-moving, sexually experienced, Wistar male rats. Mean VTTS during the first copulation was 40% above the baseline values and slightly decreased during the first postejaculatory interval (PEI; 28% above baseline). VTTS mean values further increased during the second copulatory series (93% above baseline and 63% during the PEI). Testing at the same intervals in noncopulating rats did not induce analgesia. VTTS values also increased after the display of either one ejaculation (E), five intromissions (I), or five mounts (M), the analgesia persisting for at least 20 min. Analgesia following M was smaller and shorter than that observed after either I or E. Analgesia developed gradually during copulation since VTTS values after five I were significantly higher than those after one I. The incidence of vocalizations to suprathreshold shocks (STS, 20% above the VTTS) occurring during various phases of copulation was also studied to determine the onset and short-term fluctuations of copulatory analgesia. The proportion of STS inducing vocalizations decreased from 91% (mean of individual proportions) before copulation, to 24% during copulation, and to 25% during the PEI. A maximal reduction in the proportion of vocalizations to STS was found during the last third of copulation. Nearly all vocalizations to STS during copulation occurred when subjects were quiescent, while few or no vocalizations occurred when rats were engaged in sexual activity, i.e., during M, I, or penile grooming. In contrast to the above-mentioned data, no significant analgesia was observed using the tail-flick latency test (TFL) following either E, five I, or five M.(ABSTRACT TRUNCATED AT 250 WORDS)

Visceral and postural reflexes evoked by genital stimulation in urethane-anesthetized female rats

The present study describes several muscular reflexes produced by genital stimulation, the nerves that subserve them, and the visceral and postural effects induced by these reflexes. Electrical stimulation of the iliococcygeus (ic) and pubococcygeus (pc) (striated) muscles produced movement of the vaginal orifice and wall, membranous urethra, tail and pelvis. Electrical stimulation of the psoas major (pm) or iliacus (i) (striated) muscles produced movements of the lumbar vertebrae and extension of the ipsilateral hindlimb. Sensory mechanostimulation elicited responses of these muscles as follows: stimulation of the perineal skin, clitoral sheath or distal vagina produced reflex contraction of the ic and pc muscles. Stimulation of the cervix produced reflex contraction of the pm and i muscles and also blocked the above reflex contraction of the ic and pc muscles. Both the cervical stimulation-induced blockage of the ic and pc reflex response, and the cervical stimulation-induced activation of pm and i muscles was prevented by bilateral transection of the viscerocutaneous branch of the pelvic nerve. Based on the above observations, it is proposed that stimulation of the vaginal surface of the cervix resulting from penile intromission and/or seminal plug deposition during mating behavior in the rat may reflexively active pm and i, thereby contributing to the hindleg postural rigidity and lordotic dorsiflexion that are characteristic of the normal mating posture in female rats.

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.

Neonatal capsaicin treatment attenuates sensory-induced analgesia and nociception

Neonatal capsaicin treatment (50 mg/kg SC in two-day-old rats) increased thermal pain thresholds in both sexes when measured at different ages, decreased the responsiveness of adult females to specific noxious stimulation, and differentially decreased the magnitude of vaginocervical stimulation (VS)-produced analgesia in nociceptive tests. When adult, "capsaicin" females (n = 37) were significantly greater than controls (n = 24) in vocalization threshold (VT) to electrical tail shock (55.4%) and in paw lick (PL) latency to a hot plate (75.9%). In contrast, neither tail flick (TF) latency nor the leg withdrawal reflex (LWR) to mechanical pressure of the ipsilateral hind paw was affected by neonatal capsaicin. In response to VS, the controls showed a significant increase in thermal (TF, 279%; PL, 411%), mechanical pressure (LWR, 100%) and electrical (VT, 86.8%) pain thresholds. The "capsaicin" females response to VS was significantly less than controls in TF (26.1%), PL (26.0%), and LWR (54.1%) measures, and surprisingly, during VS their VT was significantly decreased below baseline levels 12.2% +/- 4.3. These results suggest that neonatal capsaicin treatment differentially attenuates the analgesia-producing component of VS, while sparing a nociception-inducing component of this stimulus. That is, after neonatal capsaicin treatment, the ability of VS to produce analgesia is reduced; moreover, VS lowers the VT, suggesting that it actually becomes a noxious stimulus in and of itself.

Differential roles of hypogastric and pelvic nerves in the analgesic and motoric effects of vaginocervical stimulation in rats

Bilateral transection of the pelvic and/or hypogastric nerves, which convey afferent activity from the reproductive tract, was performed to ascertain the role of these nerves in the analgesic and motoric effects of vaginocervical mechanostimulation (VS) in rats. Two indices of analgesia were used: tail flick latency to radiant heat (TFL) and vocalization threshold to electrical shock of the tail (Voc-T). Nerve cuts were performed at least one week prior to behavioral testing. Bilateral transection of both the pelvic and hypogastric nerves eliminated the analgesic effects of VS on the TFL and Voc-T tests. Bilateral transection of only the pelvic nerves reduced the number of rats showing maximal VS-induced elevation in TFL, without altering the effect of VS on Voc-T. By contrast, bilateral transection of only the hypogastric nerves attenuated the Voc-T-elevating effect of VS, without reducing the effect of VS on elevating TFL. The effects of VS on producing immobility, hindlimb extension and blockage of hindlimb withdrawal to foot pinch were eliminated by combined bilateral pelvic and hypogastric neurectomy. However, bilateral transection of either nerve alone did not significantly alter the efficacy of VS in producing these effects. These findings indicate that the pelvic and hypogastric nerves contribute to the immobility- and extensor-inducing, and flexor-inhibiting effects of VS, and differentially mediate the analgesia-producing effects of VS.

Projections of the paraventricular nucleus of the hypothalamus to the sexually dimorphic lumbosacral region of the spinal cord

Lumbar regions L5-L6 of the spinal cord of the male rat contain the sexually dimorphic motor nuclei, the spinal nucleus of the bulbocavernosus (SNB) and the dorsolateral nucleus (DLN), which innervate perineal muscles, the bulbocavernosus and the ischiocavernosus, respectively. This neuromuscular system controls penile reflexes which are essential to male reproductive success. Oxytocin has been shown to induce penile reflexes and the site of action for these effects is the PVN. Since PVN is known to project to cervical and thoracic levels of spinal cord, the present study examined projections of the PVN to the L5-L6 region of the spinal cord. WGA-HRP was injected into the region of L5-L6, aimed at the SNB and DLN and their dendritic extents, in intact male, castrated male and female rats. WGA-HRP-labelled cells bodies were found in the parvocellular subnuclei of PVN, as well as regions of the lateral hypothalamus and the dorsal area of the hypothalamus. These results demonstrate that the PVN projects to lumbar levels of the spinal cord that are sexually dimorphic and androgen-dependent. This suggests that PVN may modulate the activity of these motoneurons.