Ischiocavernosus Research Articles

Spring balance evaluation of the ischiocavernosus muscle.

We studied the voluntary contractile activity of the ischiocavernosus muscle (ICM) in 21 sexually potent and 97 erectile dysfunction (ED) subjects using a spring balance. A strap was placed around the coronal grove of the glans penis and tensioned with the spring balance. Subjects were asked and encouraged to contract the ICM against the spring balance. We evaluated the length of stroke, duration of contraction, and maximum contractile force. The length of stroke, duration of contraction, and maximum contractile force showed statistically significant differences between potent and ED subjects. Diagnosed psychogenic ED and arteriogenic ED showed higher contractile activity than cavernous ED and neurogenic ED. Our results corresponded to those of previous studies that have urged consideration of the role of the ICM during the process of erection in animal experiments and in human electrophysiological studies. The spring balance evaluation is a useful, inexpensive method for evaluating the ICM.

US identification of the anal sphincter complex and levator ani muscle in neonates: infracoccygeal approach.

To identify the anal sphincter complex and levator ani muscle at transperineal ultrasonography (US) with the infracoccygeal approach. Infracoccygeal US was performed with a 7-MHz linear-array transducer in 40 healthy neonates. The babies were placed in the supine position, and both legs were drawn up to the chest. The buttocks were accordingly lifted up. The approach site was just inferior to the coccyx and posterior to the anus. Scanning was performed to obtain transverse images of the anorectal area. The thickness of the anal sphincter complex and the puborectalis muscle were measured. Infracoccygeal US revealed the internal anal sphincter (IAS), the external anal sphincter (EAS), and the puborectalis muscle in all babies. The IAS and EAS were depicted as inner and outer hypoechoic ringlike structures, respectively. A round, hyperechoic space (intersphincteral space) was present between the hypoechoic IAS and EAS. The puborectalis muscle was identified as a U-shaped hypoechoic structure. The bulbocavernosus and ischiocavernous muscles were also identified. Mean thicknesses were as follows: IAS, 1.3 mm +/- 0.3 (SD) (range, 0.8-1.9 mm); EAS, 1.6 mm +/- 0.3 (range, 1.2-2.3 mm); and puborectalis muscle, 1.1 mm +/- 0.3 (range, 0.6-1.9 mm). Infracoccygeal transperineal US is an excellent diagnostic modality for demonstrating the anal sphincter complex and levator ani muscle in neonates.

Conservative treatment of erectile dysfunction. 3: Literature review.

This is the third of a three-part article addressing whether physiotherapy involving pelvic floor muscle exercises (PFMEs) is efficacious as a first-line treatment for erectile dysfunction (ED). The first part (Vol 9(11): 691-4) highlighted the prevalence of ED, associated risk factors, the anatomy of the penis and the physiology of erection. The second part (Vol 9(12): 755-62) concentrated on the published clinical trials investigating the treatment and prevention of ED. This part will critically analyse the literature. PFMEs using ischiocavernosus muscles (ICMs) and bulbocavernosus muscles (BCMs) seem to have merit as a treatment for ED due to mild or moderate venous leakage. Men suffering from ED due to other causes may also benefit. There is no strong evidence that electrical stimulation or electroacupuncture is effective or ineffective. No studies demonstrating preventive conservative treatments were found. There is evidence that the ICMs and BCMs increase penile rigidity in the tumescent penis, that pelvic floor muscle efficiency is higher in potent men than impotent men and that perineal muscle efficiency reduces with age in impotent men. There is limited evidence that pelvic floor exercises relieve ED due to venous leakage and are a realistic alternative to surgery. Randomized controlled trials are needed to explore the use of PFMEs as a first-line treatment for men with ED.

Perineal musculature and its innervation by spinal motoneurons in the male rabbit: effects of testosterone.

Striated muscles in the perineum, which include the ischiocavernosus (IC), bulbocavernosus (BC), and levator ani (LA), were identified in an attempt to understand motor regulation of penile erection in the male rabbit. The IC surrounded the corpus spongiosum of the penis whereas the BC attached to the dorsum of the penis at the midline. The LA encircled the rectum and attached to the base of the penis. This anatomy suggested that the IC plays the primary role in the erection in the rabbit, whereas the BC may cause flips of the erected penis. Spinal motoneurons that innervate the IC were identified by retrograde labeling by horseradish peroxidase (HRP). As in other mammals, spinal labels from the IC appeared ipsilaterally in the ventral horn that encompassed the sixth lumbar (L6) and the first sacral segments. HRP injections into the BC labeled a small number of cells bilaterally at the same spinal levels. Rabbits are peculiar in having the IC motoneurons scattered among other motoneurons, unlike the rat and other rodents that have their IC motoneurons aggregated to form a spinal nucleus. Castration caused significant decreases in both the wet weight of IC muscles and the size of IC motoneurons within 2 weeks. Testosterone supplement following castration maintained the IC muscle weight and the neuronal size. Neither castration nor testosterone supplement induced changes in the number of IC motoneurons.

Heterotopic endochondrial ossification with mixed tumor formation in C3(1)/Tag transgenic mice is associated with elevated TGF-beta1 and BMP-2 expression.

Transgenic mice which express the simian virus 40 large T-antigen (Tag) under the regulatory control of the hormone responsive rat C3(1) gene develop unusual lesions of heterotopic bone growth associated with mixed tumor formation arising from eccrine sweat glands found only in the foot pads of mice, ischiocavernosus muscle adjacent to bulbourethral glands and occasionally the salivary and mammary glands. These lesions are very similar to mixed tumors arising in several types of human cancers. Based upon electron microscopic examination and immunocytochemical analyses of cellular differentiation markers, the mixed proliferative lesions in this transgenic mouse model begin with the Tag-induced proliferation of epithelial and myoepithelial cells. The proliferation of these two types of cells results in hyperplasia and adenomatous transformation of the epithelial component, whereas the proliferating myoepithelial cells undergo metaplasia to form chondrocytes which deposit extracellular matrix, including collagen fibers. Cartilage develops focally between areas of epithelial proliferation and subsequently ossifies through a process of endochondrial bone formation. The metaplasia of myoepithelial cells to chondrocytes appears to require the inductive interaction of factors produced by the closely associated proliferating epithelial cells, including members of the TGF-beta superfamily. We demonstrate that TGF-beta1 protein accumulates in the extracellular matrix of the lesions, whereas RNA in situ hybridization reveals that BMP-2, another strong inducer of heterotopic bone formation, is overexpressed by the proliferating epithelial cells during the development of ectopic bone. The formation of sarcomatous tumors within the mixed tumors appears to be androgen-dependent and more frequent in mice lacking a normal allele of p53. This process of cartilage and bone induction may mimic epithelial-mesenchymal interactions which occur during embryonic bone formation. These transgenic mice may provide new insights into the processes of ectopic endochondrial bone formation associated with mixed tumor formation and serve as a useful model for human heterotopic bone disease.

5-Hydroxytryptamine 2C receptors on spinal neurons controlling penile erection in the rat

The localization of 5-hydroxytryptamine 2C receptors in the lumbosacral spinal cord of the rat was investigated using selective antibodies raised against the carboxyl-terminal part of the rat receptor. The distribution of immunoperoxidase labelling at the light microscope level revealed numerous labelled neurons in the gray matter, with a higher intensity in the sacral parasympathetic nucleus, the dorsal gray commissure and particularly the motoneurons of the ventral horn. Confocal microscope analysis showed that immunostaining was mainly intracellular (motoneurons), but could also be associated with the membrane of cell bodies and dendrites. Actually, electron microscope immunogold experiments demonstrated an exclusive staining of the cis-Golgi apparatus. Following pseudo-rabies virus transsynaptic retrograde labelling from the corpus cavernosum, labelled neurons were found in the sacral parasympathetic nucleus and the dorsal gray commissure of the L6–S1 segments. All virus-labelled neurons exhibited 5-hydroxytryptamine 2C receptor immunoreactivity. These results indicate that all parasympathetic preganglionic neurons and their related interneurons which contribute to the innervation of cavernosal tissue bear 5-hydroxytryptamine 2C receptors. In the sacral parasympathetic nucleus, most neurons which were retrogradely-labelled from the pelvic ganglion with Fast Blue also showed 5-hydroxytryptamine 2C receptor immunoreactivity. In the ventral horn, motoneurons retrogradely labelled from the ischiocavernosus muscle and the bulbospongiosus muscle, both of which are involved in erection and ejaculation, were also 5-hydroxytryptamine 2C receptor-immunopositive. The supraspinal serotoninergic control of erection at the lumbosacral level therefore appears to be strongly associated with the activation of 5-hydroxytryptamine 2C receptors, consistent with the proerectile properties of 5-hydroxytryptamine 2C agonists.

Treatment of Erectile Dysfunction by an External Ischiocavernous Muscle Stimulator

Objective: The aim of the present study was to evaluate the therapeutic potency of an electrotherapy of striated ischiocavernous muscles in patients with erectile dysfunction. Patients and Methods: Transcutaneous electrostimulation of striated ischiocavernous muscles by self-adhesive penile or perineal skin electrodes was performed in 48 patients with erectile dysfunction. 6/48 patients (R) responded to intracavernous pharmacotherapy while 42/48 (NR) did not show significant penile rigidity even to intracavernous papaverine/phentolamine/PGE₁ triple drug medication. Results: Within the observation time of 3 months, 10/48 patients dropped out. 22/38 patients reported a penile rigidity for sufficient sexual intercourse whereby 3/22 NR required additional intracavernous pharmacotherapy. Penile rigidity could be objectivated by triple drug medicaton in 12/14 NR after ischiocavernous muscle stimulation (EIS) therapy. 5/6 R were treated successfully for premature erection loss. During EIS treatment neither discomfort nor complications could be observed. Conclusion: Transcutaneous electrostimulation of ischiocavernous muscles is a new, noninvasive therapy for the improvement of penile rigidity. The clinical results underline the importance of the striated ischiocavernous muscles for penile rigidity.

The mechanism of ejaculation: the glans-vasal and urethromuscular reflexes.

To assist in the understanding of the pathogenesis of the various ejaculatory disorders, 9 healthy male volunteers (mean age 30.4 +/- 4.8 years) were studied. The EMG response of the bulbocavernosus (BCM) and ischiocavernosus (ICM) muscles and the external urethral sphincter (EUS) to ejaculation induced by glans penis (GP) vibration was recorded. The test was repeated with individual anesthetization of the GP, BCM, ICM, and EUS. During ejaculation, the BCM, ICM, and EUS showed a significant increase in the motor unit action potentials. The contractions were rhythmic with a mean duration of the contractile episode of 0.8 s and the noncontractile episode of 0.72 s, and with a total muscle activity of 4.2 s. GP vibration after anesthetization of the GP produced no ejaculation or increased EMG activity of the BCM, ICM, and EUS, GP vibration after individual anesthetization of the BCM or the EUS produced semen emission but no ejection, and GP vibration after ICM anesthetization produced ejaculation (emission and ejection). The results suggest that the ejaculatory mechanism consists of two reflexes: the glans-vasal and urethromuscular. The former seems to bring the semen to the posterior urethra (the emission stage of ejaculation) and the urethromuscular reflex ejects it to the exterior (ejection stage of ejaculation). A dysfunction of these two reflexes would seem to induce ejaculatory disorders, a point that needs further study.

Androgen Receptor (AR) Immunoreactivity in Rat Pudendal Motoneurons: Implications for Accessory Proteins

Pudendal motoneurons in male rats are located in two sexually dimorphic motoneuronal pools: the spinal nucleus of the bulbocavernosus (SNB) and the dorsolateral nucleus (DLN). SNB motoneurons innervate sexually dimorphic muscles bulbocavernosus (BC) and levator ani (LA) and the sexually monomorphic external anal sphincter (EAS) muscle. DLN motoneurons innervate either the sexually dimorphic ischiocavernosus (IC) muscle or the sexually monomorphic external urethral sphincter (EUS) muscle. Previous observations indicate that the size of BC, LA, and IC motoneurons in males is sensitive to adult androgen manipulations, whereas the size of EAS and EUS motoneurons is not, raising the question of whether this difference in androgen sensitivity among pudendal motoneurons reflects a difference in androgen receptor (AR) expression. AR immunocytochemistry using the PG-21 antiserum was carried out on spinal cord tissue from normal adult male rats in which specific pudendal motoneuronal subpopulations were identified with retrograde markers. Over 90% of BC, LA, and IC motoneurons displayed AR immunoreactivity in their nuclei. Among motoneurons in the SNB, significantly fewer EAS motoneurons had AR-positive nuclei, which may contribute to the reported failure of EAS motoneurons to morphologically respond to changes in androgen levels. However, within the DLN, despite the fact that IC but not EUS motoneurons are reported to respond to androgen with an increase in soma size, IC and EUS motoneurons had the same proportion of AR-positive nuclei. These results indicate that androgen receptors, while necessary, are not sufficient to confer androgen sensitivity to cells.

A theoretical unidirectional valve based on functional collapse of blood vessels in the penis

A model of a vessel exposed to external pressure was developed. Analytical derivation resulted in closed-form expressions describing pressure-flow relation in the vessel. These expressions describe a behavior of a unidirectional leaky valve. The vessel model was used to represent internal arteries and veins in the penis. Together with a compliant chamber representing the corpus cavernosum, the model demonstrates the valve action of the partially collapsed vessels during penile erection. This explains observations regarding arterial backflow during erectile contraction of the ischiocavernous muscles and demonstrates the differences in development of tumescence and rigidity.

Perineal nerve stimulation: role in penile erection.

The effect of perineal nerve stimulation on penile erection was studied in ten dogs. Through a paraanal incision, the nerve was exposed in the ischiorectal fossa and a bipolar electrode was applied to it. A radiofrequency receiver was implanted subcutaneously in the abdomen. Upon perineal nerve stimulation, the corporeal pressure and EMG activity of the bulbo- and ischiocavernosus muscles increased; penile erection occurred. With increased stimulus frequency up to 80 Hz, the pressure and muscles' response augmented while the latency and duration of response diminished. No further changes occurred above a frequency of 80 Hz (P > 0.05). Response was reproducible indefinitely after an off-time of double the time of the stimulation phase. Penile erection upon perineal nerve stimulation is suggested to be an effect of corporeal pressure elevation resulting from cavernosus muscles' contraction. In terms of force and speed of contraction, a stimulus frequency of 80 Hz evokes the most adequate cavernosus muscles' contraction.

Olfactory-Corporeal Reflex: Description of a New Reflex and Its Role in the Erectile Process

The dog approaches the bitch and smells the vulva. The relationship which seems to exist between a special smell in the bitch and sexual arousal in the male dog was investigated. 12 male dogs and 25 bitches were studied. The bitches were divided into five equal groups, each representing 1 of the 5 phases of the estrous cycle. A vaginal swab that soaked in the bitches' vaginal secretions was divided into two pieces: one was sent for estradiol and progesterone determination, and the other was smelt by the male dog. The responses of the intracorporeal pressure (IP) and the electromyographic activity of the bulbo- and ischiocavernosus (BC, IC) muscles of the male dog to the smelling of bitch's vaginal odor were assessed. The pressure response was also determined 10 min and 1 h after either the nasal mucosa or the corporeal tissue was anesthetized. Elevated IP was recorded in 12 of 12, 10 of 12 and 8 of 12 dogs smelling vaginal swabs of bitches in metestrus (p < 0.001), estrus (p < 0.001), and diestrus (p < 0.01), respectively. No pressure response occurred when the vaginal swab was smelt while the nasal mucosa or the corporeal tissue was anesthetized. The BC and IC muscles exhibited no response to smelling of the vaginal swab of bitches in any phase of the estrous cycle. The results were reproducible. The study showed that the IP increased with smelling of vaginal secretions containing high progesterone levels, whereas estradiol-17 beta did not effect IP elevations. The higher the progesterone level, the greater the IP. The increased IP is not due to BC and IC muscle contraction. It is postulated that a reflex relationship exists between IP elevation and olfactory stimulation. This reflex response was reproducible and was not evoked when the two arms of the reflex were anesthetized. We call this reflex 'olfactory-corporeal reflex'. This reflex seems to prime the male dog for sexual intercourse.

CNS cell groups involved in the control of the ischiocavernosus and bulbospongiosus muscles: a transneuronal tracing study using pseudorabies virus.

Transneuronal tracing techniques were used to identify spinal and brainstem neurons involved in the control of perineal muscles in the male rat. Two penile muscles, the bulbospongiosus and ischiocavernosus muscles, were injected with Bartha's strain of pseudorabies virus. After survival periods of 2, 4, and 5 days, the rats were killed and viral labeled neurons identified by immunohistochemistry. After a 2 day survival period, only pudendal motoneurons were labeled. More spinal and brainstem neurons were labeled at longer survival times. Putative spinal interneurons were found from T13 to S1. Large numbers of neurons were found in the lateral horn of the T13-L2 and L6-S1 segments which contain sympathetic and parasympathetic preganglionic neurons, respectively. However, retrograde labeling experiments verified that very few of the viral neurons were preganglionic neurons. Other labeled neurons were found in the intermediate cord, especially around the central canal. Relatively few labeled neurons were seen in the dorsal or ventral horn. In the brainstem, consistent labeling was seen in the ventrolateral medulla, raphe pallidus, and magnus, the A5 and locus ceruleus noradrenergic cell groups. Barrington's nucleus in the pontine tegmentum, the periaqueductal gray, and the paraventricular nucleus of the hypothalamus. The transneuronal labeling was consistent with what is currently known of the central nervous system (CNS) control of the perineal muscles.

CNS cell groups involved in the control of the ischiocavernosus and bulbospongiosus muscles: A transneuronal tracing study using pseudorabies virus

CNS cell groups involved in the control of the ischiocavernosus and bulbospongiosus muscles: A transneuronal tracing study using pseudorabies virus

The Hemodynamic Influence of the Ischiocavernosus Muscles on Erectile Function

Purpose Special attention has been focused on the contribution of the ischiocavernosus muscles to intracorporeal pressure during erection. Materials and Methods Length of the ischiocavernosus muscles and corpora cavernosa was studied in 30 cadavers. Results A biomechanical model for calculating interference of the ischiocavernosus muscles in rigidity during the initial phase of penile erection is proposed. Conclusions We found that, among other things, intracorporeal pressure can be influenced by the ischiocavernosus muscles during erection.

Corpus spongiosum penis pressure and perineal muscle activity during reflexive erections in the rat.

This experiment represents the first simultaneous analysis of corpus spongiosum of the penis (CSP) pressure and perineal muscle activity during reflex-induced penile erections in the awake rat and provides new data on the coordination of muscular and vascular events in erection physiology. Nine male Sprague-Dawley rats were implanted with pressure transducers under pentobarbital anesthesia (60 mg/kg) for use in a new technique of chronic erection recording involving simultaneous CSP pressure monitoring and electromyography (EMG) of the ischiocavernosus (IC) and bulbospongiosus (BS) muscles. The association of these physiological measurements with visually scored ex copula erectile events was investigated. Reflexive erectile events were systematically associated with an increase in baseline CSP pressure. Glans erections were associated with dramatic suprasystolic CSP pressure peaks concurrent with BS muscle bursts. Indeed, measures of CSP pressure and BS EMG activity were found to vary significantly with the intensity of glans erection. Flips of the penile body, however, involved small CSP pressure increases and IC bursts. These data demonstrate for the first time that both CSP pressures and perineal muscle activity vary significantly with the intensity of penile erection.

Motoneurons innervating guinea pig perineal muscles are sexually dimorphic in size but not number

Sexual differentiation occurs prenatally in guinea pigs but extends into the postnatal period in rats. Steroids affect the development of two motoneuron nuclei of the rat lumbar spinal cord that innervate sexually dimorphic perineal muscles. The spinal nucleus of the bulbocavernosus (SNB) innervates the bulbocavernosus (BC) and levator ani (LA) muscles while the dorsolateral nucleus (DLN) innervates the ischiocavernosus (IC). In male rats, perinatal testosterone prevents degeneration of these muscles and results in a sex difference in both motoneuron size and number in adulthood. For comparative purposes, we examined the guinea pig motoneurons innervating these muscles, as well as those innervating the retractor penis (RP) and retractor clitoris (RC), muscles that have no counterpart in rats. Injections of horseradish peroxidase localized the BC LA and IC motoneurons of guinea pigs to discrete columns in spinal levels L6 and S1, with the BC LA motoneurons occupying a more medial position. The RP RC motoneurons were found in L5. Motoneuronal soma area was larger in males in all examined motor pools, as was nuclear area of BC LA and IC motoneurons. Although raw counts suggested a sex difference in cell number in the motor columns containing BC LA and IC motoneurons, either of two different correction procedures for split nuclei error eliminated the sex difference in cell number, emphasizing the importance of such corrections when comparing neurons of different size.

Response of the urethral and intracorporeal pressures to cavernosus muscle stimulation: role of the muscles in erection and ejaculation.

The role of the bulbocavernosus (BC) and ischiocavernosus (IC) muscles in erection and ejaculation was studied. The response of the urethral and intracorporeal pressure to cavernosus muscle stimulation was evaluated in 18 male volunteers (mean age, 36.6 years). A two-channel microtip catheter was placed in the prostatic and bulbous urethra. Muscle stimulation was done by two needle electrodes inserted into the BC and IC muscles. BC muscle stimulation caused an increase in the pressure of the bulbous urethra (P < 0.001) and corpus spongiosum (P < 0.01) and an insignificant change in the prostatic and pendulous urethral and corpus cavernosal pressures (difference not significant). IC muscle stimulation effected an increase in the corpus cavernosal pressure (P < 0.001) without changing the urethral pressure (difference not significant). The BC muscle contracts rhythmically at orgasm and this might help to eject the semen from the posterior to the anterior urethra. It is apparent that the muscle has minimal or no role in erection. IC muscle may have a role in erection by increasing the intracavernosal pressure. It seems that it has no role in ejaculation. BC may be considered the "muscle of ejaculation," and IC the "muscle of erection."

Motoneurons dorsolateral to the central canal innervate perineal muscles in the mongolian gerbil

The Mongolian gerbil provides a model in which sexually dimorphic areas in the hypothalamus are correlated with sociosexual behaviors such as scent marking and male copulatory behavior. To extend this model, investigations were conducted to determine whether sexually dimorphic areas existed in the spinal cord that could be relevant to male sexual behavior. The focus of these investigations was the perineal muscles associated with the penis. Therefore, this research identified the spinal motoneurons that innervate the bulbocavernosus, levator ani, anal sphincter, and ischiocavernosus muscles of Mongolian gerbils. The motoneuron pool that innervates the bulbocavernosus, levator ani, and anal sphincter was designated the spinal nucleus of the bulbocavernosus (SNB), as for other species of rodents. The motoneuron pool innervating the ischiocavernosus was identified as the dorsolateral nucleus, again, to be consistent with the designation for other rodents. The motoneurons of the gerbil SNB were distributed dorsolateral to the central canal in the lumbosacral transition zone of the spinal column. These motoneurons are located in the region classically defined as area X of the spinal cord. The number of SNB motoneurons was sexually dimorphic, with male gerbils having about five times as many SNB motoneurons as do female gerbils. The size of SNB motoneurons was also sexually dimorphic. The SNB motoneurons of males were 1.5 times larger than the SNB motoneurons of females. The effects of adult castration on the male SNB were also studied. After castration, the size, but not the number, of SNB motoneurons in males was significantly decreased. This decrease was prevented by testosterone treatment. The percentage of calcitonin gene-related peptide (CGRP)-immunoreactive SNB motoneurons was also affected by adult castration. The percentage of CGRP-immunoreactive motoneurons was significantly decreased after adult castration. Again, this decrease was reversed by testosterone treatment. These findings suggest that the SNB of gerbils is sexually dimorphic and is sensitive to circulating levels of gonadal steroids. The unique placement of the SNB motoneurons suggests that an alternative laminar organizational scheme may be necessary for Mongolian gerbil.

Differences in the connectivity of rat pudendal motor nuclei as revealed by retrograde transneuronal transport of wheat germ agglutinin.

Bilateral coordinated activation of pudendal motoneurons is an essential component of penile reflexes in male rats. However, little is known about the intraspinal organization of these reflexes. In the present study, retrograde transneuronal transport of wheat germ agglutinin (WGA) was used to examine the organization of spinal motoneurons and putative interneurons mediating penile reflexes in adult male rats. Injection of WGA into the ventral bulbospongiosus muscle resulted in direct retrograde labeling of motoneurons in the ipsilateral dorsomedial (DM) nucleus and transneuronal labeling of ipsilateral and contralateral DM motoneurons. Motoneurons in the ipsilateral and contralateral dorsolateral (DL) nuclei were not labeled. WGA-labeled putative interneurons were observed bilaterally, primarily in the ventromedial spinal gray matter extending dorsally to the central canal and the dorsal gray commissure. The number of transneuronally labeled putative interneurons increased with longer survival times. Injection of WGA into the ischiocavernosus muscle resulted in direct retrograde labeling of motoneurons in the medial subdivision of the ipsilateral DL nucleus. However, no WGA labeling was detected in motoneurons in the lateral subdivision of the ipsilateral DL nucleus, the contralateral DL nucleus, or the DM nuclei at any of the survival times studied (1-7 days). Only a small number of transneuronally labeled putative interneurons was observed in the ventrolateral gray matter at longer survival times (3-7 days). Thus, marked differences were observed between the DM and DL nuclei with respect to the transneuronal transport of WGA. These results are discussed with respect to the organization of the spinal circuits that mediate pudendal motor reflexes.