Novel technique for monitoring micturition and sexual function in male rats using telemetry

We developed a novel technique to simultaneously monitor micturitions and erections in rats by using pressure monitoring within the corpus spongiosum of the penis (CSP). We present data validating this technique and report pressure waveform characteristics of micturition and erectile events during four different behavioral contexts in 10 awake, freely-moving male rats. Telemetric pressure transducers were implanted in the bulb of the CSP. CSP pressure was monitored while the animals were simultaneously recorded on video for determination of presence and volume (n = 7) of micturitions and while the animals underwent behavioral tests for determination of erections. Observed micturitions and CSP pressure waveforms characteristic of micturitions occurred simultaneously (r = 0.98) at a frequency of 32 +/- 4 micturitions per 24 h and with a volume of 0.95 +/- 0.12 ml/urination. Micturition duration recorded by CSP pressure and volume determined by urine weight were highly correlated (r = 0.82). We found that 100% of visually confirmed erectile events occurred simultaneously with CSP pressure waveforms characteristic of erections during ex copula reflex erection tests. During noncontact erection and mating tests more erections were identified by telemetry than by observation alone. Erections during mating tests had a different appearance than those seen in other contexts; they were shorter in duration (P < 0.05) and typically were characterized by a single suprasystolic CSP pressure peak, highlighting the context-specificity of erections. Quality of recordings remained stable in three of four rats we followed for 8 wk. We demonstrate that telemetric recording of CSP pressure provides a quantitative and qualitative assessment of penile erections and micturition in freely behaving rats.     

Erectile function and bulbospongiosus EMG activity in estrogen-maintained castrated rats vary with behavioral context.

Electromyographic (EMG) activity in the bulbospongiosus muscles (BS) was recorded to monitor potential castration-induced alterations in muscle activity during copulation and reflexive erections. EMG recordings were made from intact male rats and from castrated rats maintained from 7 to 50 days on estradiol benzoate (300 micrograms/day) or testosterone (200 micrograms/day). Despite a 40-50% postcastration reduction in the weight of the BS and accessory sexual glands in estrogen-treated rats, the pattern of EMG activity during copulation was similar across groups. In estradiol-treated males, the EMG burst frequency during mounts and burst duration during intromissions exceeded the parameters of intact males and of castrated males maintained on testosterone. Between intromissions, and following ejaculatory patterns, estrogen-treated males displayed spontaneous muscle bursts accompanied by visually confirmed erection of the glans penis, but these males quickly lost the capacity for reflexive erections. These data demonstrate that despite castration-induced atrophy of the penile muscles and, presumably, their spinal motor nuclei, the motor output to these muscles is maintained following androgen removal. The capacity for substantial penile erection is retained during copulation long after reflexive erections have diminished.     

Characterization of p-chloroamphetamine-induced penile erection and ejaculation in anesthetized rats

Methodological shortcomings present in elicitation of male sexual reflexes in anesthetized animals. The present study has demonstrated, however, that intraperitoneal (i.p.) injection of p-chloroamphetamine (PCA), an indirect serotonin (5-HT) agonist, elicited simultaneously both penile erection and ejaculation in anesthetized rats. PCA (2.5-10.0 mg/kg, i.p.) caused an intermittent cluster of genital responses consisting of penile erection, glans erections, and penile cups, which closely resembles the response observed during the ex copula tests in unanesthetized rats. Measurements of intracavernous penile pressure showed that rhythmic changes in penile pressure were produced by PCA, together with glans erections and penile cups. PCA also caused a frequent ejaculations and the weighing of ejaculate accumulated over 0.5 hr was increased in a bell-shaped pattern, and the maximum effect was observed at 5.0 mg/kg. Pretreatment with p-chlorophenylalanine, a serotonin (5-HT)-synthesis inhibitor, significantly inhibited the expression of PCA-induced penile erection and ejaculation, while acute spinal transection at thoracic level did not affect the sexual responses. These results indicate that PCA-induced penile erection and ejaculation in anesthetized rats are mainly produced by the release of 5-HT, which is limited to the lower spinal cord and/or the peripheral sites. Furthermore, the sexual responses can be easily and reliably elicited by administration of PCA, which may be useful for the study of the mechanisms underlying male sexual functions.     

Nitric oxide-dependent penile erection in mice lacking neuronal nitric oxide synthase.

BACKGROUND: Nitric oxide (NO) has been implicated as a mediator of penile erection, because the neuronal isoform of NO synthase (NOS) is localized to the penile innervation and NOS inhibitors selectively block erections. NO can also be formed by two other NOS isoforms derived from distinct genes, inducible NOS (iNOS) and endothelial NOS (eNOS). To clarify the source of NO in penile function, we have examined mice with targeted deletion of the nNOS gene (nNOS- mice). MATERIALS AND METHODS: Mating behavior, electrophysiologically induced penile erection, isolated erectile tissue isometric tension, and eNOS localization by immunohistochemistry and Western blot were performed on nNOS- mice and wild-type controls. RESULTS: Both intact animal penile erections and isolated erectile tissue function are maintained in nNOS mice, in agreement with demonstrated normal sexual behaviors, but is stereospecifically blocked by the NOS inhibitor, L-nitroarginine methyl ester (L-NAME). eNOS is abundantly present in endothelium of penile vasculature and sinusoidal endothelium within the corpora cavemosa, with levels that are significantly higher in nNOS- mice than in wild-type controls. CONCLUSIONS: eNOS mediates NO-dependent penile erection in nNOS- animals and normal penile erection. These data clarify the role of nitric oxide in penile erection and may have implications for therapeutic agents with selective effects on NOS isoforms.     

Tactile stimulation during artificial rearing influences adult function and morphology in a sexually dimorphic neuromuscular system

Maternal licking of rat pups affects the development of the spinal nucleus of the bulbocavernosus (SNB), a sexually dimorphic motor nucleus that controls penile reflexes involved with copulation. Maternal licking influences SNB motoneurons, with reductions in licking producing decreased SNB number, size, and dendritic length in adulthood. Reduced maternal licking also produces deficits in adult male copulatory behavior. In this experiment, we used an artificial rearing paradigm to assess the potential role of tactile stimulation in mediating the effects of maternal licking on the SNB neuromuscular system. During artificial rearing, pups were stroked with a paintbrush to mimic maternal licking, receiving low, medium, or high levels of daily stimulation. In adulthood, ex copula penile reflex behavior was tested and the morphology of SNB motoneurons assessed. SNB motoneurons were retrogradely labeled with cholera toxin-conjugated HRP and dendritic arbor was reconstructed in three dimensions. Animals that received low levels of stimulation showed deficits in penile reflexes relative to maternally reared controls, including a longer latency to erection, fewer cup erections, and fewer erection clusters. SNB dendritic morphology was also shaped by stimulation condition, with animals that received low or medium levels of stimulation showing an average 27% reduction in dendritic length. In addition, several reflex behaviors were significantly correlated with dendritic length, including latency to first erection, percent of cup erections, and number of erection clusters. These results suggest that tactile stimulation provided by maternal licking mediates some of the effects of maternal care on the development of male copulatory behavior.     

Androgen maintenance of erectile function in the rat penis.

Previous research has shown that the frequency and duration of penile erection is diminished after castration and that replacement with testosterone will restore the process. Using rats, the present study was designed to confirm that erection is androgen-dependent and to determine whether castration and androgen replacement affect the penile vascular smooth muscle responsiveness to vasoactive drugs. Blood pressure in the corpus cavernosum was measured directly during erections induced by electrical stimulation of the autonomic innervation of the penis. Maximal cavernosal pressure was markedly reduced after castration but was returned to normal levels if the castrated animals were treated with testosterone. Infusion of nitroglycerin (vasodilator) or phenylephrine (vasoconstrictor) resulted in a decline in cavernosal pressure in androgen-treated animals but not in castrated animals, even though the mean arterial blood pressure was strongly affected in all treatment groups by these drugs. When an inhibitor of nitric oxide synthesis was infused, cavernosal pressure was decreased in all groups, indicating that this substance is involved in penile erection. Taken together, these results show that androgens maintain the erectile process and may act specifically to support the responsiveness of the vascular smooth muscle to vasoactive drugs.     

Commande nerveuse peripherique de l’erection

Local mechanisms causing penile erection and detumescence result from variation in tone of vascular and trabecular smooth muscles and in a lesser part of striated muscles around the crura penis. All these events are neurally mediated. We reviewed human and animal data concerning the functional peripheral neuroanatorny of erection. General organization of peripheral nervous system is recalled. Somatic efferents of the pudendal nerve, originating in the sacral spinal cord, innervate the striated musculature of the perineum. Somatic afferents of the penis are conveyed by the dorsal penile nerve, a branch of the pudendal nerve. Afferent terminations project into the spinal cord, their role is discussed. Parasympathetic pathways are involved in the reflexogenic erections. Sympathetic pathways destinated to the erectile structures are more complex. They are issued from thoracolumbar spinal cord and travel through the hypogastric nerve or the lumbosacral sympathetic chain. Sympathetic fibers originating in the sacral sympathetic chain are present in both pelvic and pudendal nerves. Inhibitory role on the erection of the sympathetic nervous system is well-known, it could be also responsible for psychogenic erections. Parasympathetic and sympathetic fibees are mixed in the pelvic plexus and the cavernous nerves which are described. Relations between the four sets of peripheral nerves (somatic efferents, penile afferents, thoracolumbar sympathetic sacral parasympathetic and sympathetic) are discussed.     

Nonpharmacologic treatment of erectile dysfunction

Nonpharmacologic treatment for erectile dysfunction (ED) includes sex therapy, the use of vacuum erection devices, penile prosthesis implantation, and penile vascular surgery. Sex therapy is indicated for psychogenic ED and is at times a useful adjunct for other treatments in men with mixed psychogenic and organic ED. Vacuum erection devices produce usable erections in over 90% of patients; however, patient and partner acceptability is an issue. Three-piece inflatable penile prostheses create flaccidity and an erection that comes close to that which occurs naturally. Penile vascular surgery has shown greatest efficacy in young men with vasculogenic ED resulting from pelvic or perineal trauma.     

Spinal control of erection by glutamate in rats

The lumbosacral spinal network controlling penile erection is activated by information from peripheral and supraspinal origins. We tested the hypothesis that glutamate, released by sensory afferents from the genitals, activates this proerectile network. In anesthetized intact and T8 spinalized (i.e., freed from supraspinal inhibition) male rats, the parameters of electrical stimulation of the dorsal penile nerve (DPN) that elicited intracavernous pressure (ICP) rises were determined. In T8 spinalized rats, DPN stimulations were applied in the presence of d(-)-2-amino-5-phosphonopentanoic acid (d-AP5), a competitive NMDA receptor antagonist, or of 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulphonamide (NBQX), an AMPA-kainate receptor antagonist, injected intrathecally at the lumbosacral level. Both antagonists, alone or in combination, dose dependently decreased the ICP rise and increased its latency. In conscious rats, reflexive erections were depressed by d-AP5 and NBQX, as revealed by an increased latency of the first erection and by decreases of the number of rats displaying erections, of the number of erection clusters and of the number of erections per cluster. In anesthetized ats, the combined administration of the glutamatergic agonists NMDA and AMPA elicited ICP rises in the absence of DPN stimulation. In contrast, both agonists moderately decreased the ICP rise elicited by DPN stimulation but did not affect its latency. These results support our hypothesis that glutamate, released on stimulation of the genitals and acting at AMPA and NMDA receptors, is a potent reactivator of the spinal proerectile network.     

Etude de l’erection chez le rat: un nouveau modele physiologique

Penile erection is a muscular and vascular event mediated by the autonomic nervous system. The neurophysiology of erection remains poorly understood and controversial, requiring a suitable model for in-vitro studies of erectile function. Such a model, based in the rat whose penile innervation is very similar to man, is described here. The first study using this model considers the influence of systemic blodd pressure (BP) on penile erection. In 33 anaesthetized rats the pelvic and cavernosal nerves were identified and dissected. Supra maximal electrical stimulation was delivered over 1 minute by a train of 1 ms pulses onto the pelvic nerve (10 V, 15 Hz) or the cavernosal nerve (6 V, 10 Hz). Systemic blood pressure and intracavernosal pressure (ICP) were monitored and stored on a computer. As in previous animal models (dog, monkey), four phases of the cavernosal response to neural electrical stimulation were observed: latency, tumescence, full erection, and détumescence. In all rats electrical stimulation of either the pelvic or cavernosal nerves significantly increased intracavernosal pressure. Complete erectile response (rigidity and unfolding of the penis) was only seen with intracavernosal pressures > 95 mm Hg. Intracavernosal pressure increased proportionally with blood preessure during the full erection phase according to the equation ICP=0.94 BP ? 31 mm Hg (r=0.94 BP ? 31 mm Hg (r=0.94) for electrical stimulation of the cavernosal nerve, or the alternative aquation ICP=0.76 BP ? 21 mm Hg (r=0.73) for electrical stimulation of the pelvic nerve. The rat is a readily available model for the study of erection and present obvious advantages over existing models such as the dog, cat and monkey. Cavernosal repsonse to neural stimulation was closely related to arterial blood pressure and the two linear equations presented above should be considered further in studies modifying autonomic neurotransmission as well as in relation to the effects of pharmacological compounds with vasomotor actions on erectile function.     

A biomechanical model of Peyronie's disease

Peyronie's disease is a pathological condition of the penis which is characterized by localized ossification of the tunica albuginea. A common symptom of the chronic stage is penile deformity during erection, which is frequently associated with pain and erectile dysfunction. A two-dimensional biomechanical model of the penis was applied to study the development of Peyronie’s disease by simulating the mechanical stress distribution which would result from the interaction of the ossified tunical tissue with other penile soft tissues. The model was solved by using commercial finite element software for a characteristic erectile pressure. The results demonstrate that Peyronie’s plaques may induce intensified stresses around the penile nerves and blood vessels, up to double those in the normal penis. These elevated stresses may cause a painful sensation of neural origin or ischemia in regions of compressed vascular tissue. Severe penile deformities have been shown to develop if Peyronie’s plaques develop only around one of the corpora cavernosa due to the non-homogeneous resistance of the tunica to expansion during erection. The present model can be clinically applied as an aid in the planning process of reconstructive surgery or insertion of a prosthesis.     

Erection après échec d’implants pénines

Satisfactory erection was obtained in a 50-year-old patient after explantation of a penile implant by the combined use of intracavernous injection of alprostadil and vacuum. Other cases have been reported in the literature, in which erections have been obtained with one of these two methods in this particularly difficult setting.     

Neural control of erection

Activation of sacral parasympathetic pathways elicits penile erection through the release of vasorelaxant neurotransmitters that increase blood flow to the penis and relax the penile erectile tissue. Sympathetic pathways are antierectile. The pudendal pathway, responsible for the contraction of the perineal striated muscles, enhances an already present erection. All pathways originate in the spinal cord, but at various levels and areas. The convergence of information from peripheral and supra-spinal origins onto spinal neurones is very likely activating more specifically the spinal pro-erectile network. Peripheral information is the afferent limb of reflexive erections, impinges onto spinal interneurones and is able to activate or regulate the activity of sympathetic, parasympathetic and somatic nuclei. Supra-spinal information impinges onto either the same or a different spinal network. Premotor neurones located in supra-spinal structures, that project directly onto spinal sympathetic, parasympathetic or pudendal motoneurones, are present in the medulla, pons and diencephalon. Several of these premotor neurones may in turn be activated by sensory information from the genitals. Descending pathways release a variety of aminergic and peptidergic neurotransmitters in the vicinity of spinal neurones, thereby exerting complex effects on the spinal pro-erectile network. Brainstem and hypothalamic nuclei (among the latter, the paraventricular nucleus and the medial preoptic area) may not reach directly the spinal pro-erectile network. They are prone to regulate penile erection in more integrated and coordinated responses of the body, as those occurring during sexual behaviour. The pro-erectile central and spinal effects of neuropeptides such as oxytocin, melanocortins and endorphins have only recently been analyzed. Such compounds may represent therapeutic strategies to treat erectile dysfunction through a central site of action.     

DA-8159 has erectile potentials much longer than the plasma half-life in a conscious rabbit model

DA-8159 is a pyrazolopyrimidinone derivative which is a potent and selective phosphodiesterase type 5 inhibitor. The efficacy of oral DA-8159 has been demonstrated in conscious and spinalized rabbits by its enhancement of nitric oxide-induced erections. The aim of this study was to investigate the time dependency of this efficacy on its plasma concentration in rabbits. DA-8159 was given orally to normal rabbits at a dose of 10 or 30 mg/kg in order to determine its pharmacokinetic parameters. After then, to investigate the relationship between penile erectile activity and plasma half-life, a dose of 10 mg/kg DA-8159 was administered and the erectile response was examined in a time-course manner by measuring the length of the uncovered penile mucosa after the intravenous administration of sodium nitroprusside, which was administered 1, 3, 6, 8, 24 hours after administering DA-8159. DA-8159 was absorbed rapidly with a Tmax of 0.6 hours in 30 mg/kg and 1.0 hour in the 10 mg/kg group, and T1/2 of 1.23 hours in 30 mg/kg and 1.17 hours in 10 mg/kg, respectively. DA-8159 was not detected in the blood plasma 3 hours (10 mg/kg) or 6 hours (30 mg/kg) after administration. In an erection test, DA-8159 alone (10 mg/kg) induced a penile erection for approximately 2 hours but there was no significant erection thereafter. Although the DA-8159-induced penile erection disappeared, an intravenous injection of sodium nitroprusside significantly induced a penile erection for 6 hours, when the plasma drug concentration was below the detection limit and a no longer visible erection was noted. These results demonstrate that DA-8159 is absorbed and rapidly cleared in rabbits. In addition, it can enhance a sodium nitroprusside-induced penile erection even after 6 hours, which is approximately five times longer than the plasma half-life in the rabbits. These results suggest that DA-8159 may have an erectile potential for much longer than its measured half-life.     

Proerectile effects of apomorphine in mice

Dopaminergic pathways play a key role in the central control of sexual behavior. Stimulation of central dopaminergic receptors elicits penile erection in a variety of species and has been proposed as a treatment option for erectile dysfunction in humans. The present study investigated the proerectile effects of apomorphine in mice. In this species, subcutaneous injection of apomorphine (range: 0.11-110 microg/kg sc) elicited three different behavioral responses: erection, erection-like responses and genital grooming. Proerectile effects of apomorphine were dose-dependent. More than 50% of mice displayed erections after administration of 1.1-11 microg/kg of apomorphine sc. Proerectile effects of apomorphine were blocked by haloperidol, a central D2 antagonist, but not by domperidone, a peripherally active dopaminergic antagonist. We conclude that apomorphine elicits erection in mice. This effect is dose-dependent and due to activation of central D2 dopaminergic receptors. The mouse model may be useful for pharmacological approaches designed to provide a better understanding of the central mechanisms of penile erection and sexual behavior.     

Antagonism of Rho-kinase stimulates rat penile erection via a nitric oxide-independent pathway

Relaxation of the smooth muscle cells in the cavernosal arterioles and sinuses results in increased blood flow into the penis, raising corpus cavernosum pressure to culminate in penile erection. Nitric oxide, released from non-adrenergic/non-cholinergic nerves, is considered the principle stimulator of cavernosal smooth muscle relaxation, however, the inhibition of vasoconstrictors (that is, norepinephrine and endothelin-1, refs. 5-9) cannot be ignored as a potential regulator of penile erection. The calcium-sensitizing rho-A/Rho-kinase pathway may play a synergistic role in cavernosal vasoconstriction to maintain penile flaccidity. Rho-kinase is known to inhibit myosin light chain phosphatase, and to directly phosphorylate myosin light-chain (in solution), altogether resulting in a net increase in activated myosin and the promotion of cellular contraction. Although Rho-kinase protein and mRNA have been detected in cavernosal tissue, the role of Rho-kinase in the regulation of cavernosal tone is unknown. Using pharmacologic antagonism (Y-27632, ref. 13, 18), we examined the role of Rho-kinase in cavernosal tone, based on the hypothesis that antagonism of Rho-kinase results in increased corpus cavernosum pressure, initiating the erectile response independently of nitric oxide. Our finding, that Rho-kinase antagonism stimulates rat penile erection independently of nitric oxide, introduces a potential alternate avenue for the treatment of erectile dysfunction.     

Resultats preliminaires d’injections intracaverneuses d’un donneur d’oxyde d’azote (NO), la linsidomine,dans le traitement de l’impuissance

Recent experimental studies showed an important role of endothelium derived relaxing factor (EDRF) for cavernous smooth muscle relaxation. Since nitric oxide (NO) seems to account for the biological actions of EDRF, a study was done to examine a possible role of the NO-donor SIN-1 in the treatment of erectile dysfunction. To determine the therapeutic range, 0.1, 0.2, 0.5 and 1 mg SIN-1 were injected intracavernously in 2 patients with erectile dysfunction each. Then, 40 patients were injected 1 mg SIN-1 including 4 patients that had prolonged erections to minimal doses of papaverine-phentolamine and 4 patients that did not respond with a full erection to other pharmacologic agents. Intracavernous injection of SIN-1 induced a dose dependent erectile response by increasing the arterial inflow and relaxing cavernous smooth muscle. To 1 mg SIN-1, 19 patients had a full, 14 an almost full and 7 a moderate erection. There were no systemic or local side effects. In the patients with prolonged erections to papaverine-phentolamine, the mean duration of a full erection to SIN-1 was 68 minutes. Compared to a papaverine (15 mg/ml)-phentolamine (0.5 mg/ml) mixture, the erectile response to SIN-1 was superior in 8, comparable in 29 and inferior in 3 patients. Our preliminary data suggest a possible role of SIN-1 for the treatment of erectile dysfunction. The absence of prolonged erections by its spontaneous intracavernous decomposition, a maximal smooth muscle relaxation by a receptor independant action and its low cost indicate its potential to become a standard drug for intracavernous pharmacotherapy.     

The Ferrier lecture, 1986. The actions of parasympathetic and sympathetic nerves in human micturition, erection and seminal emission, and their restoration in paraplegic patients by implanted electrical stimulators

Implants that stimulate the S2, S3 and S4 anterior roots improve micturition, defaecation and penile erection in many patients with spinal-cord injuries. The posterior rhizotomy that is commonly done at the same time usually cures their urinary incontinence, and may greatly improve bladder compliance. Implants that stimulate the hypogastric plexus allow semen to be obtained easily from some men with spinal injuries who cannot ejaculate, and may allow an implant-driven erection. A little new knowledge about the neurophysiology of the pelvic organs has come from studying the performance of these implants.     

Ca2+-activated Cl- channels in corpus cavernosum smooth muscle: a novel mechanism for control of penile erection.

Little is known of the excitatory mechanisms that contribute to the tonic contraction of the corpus cavernosum smooth muscle in the flaccid state. We used patch-clamp electrophysiology to investigate a previously unidentified inward current in freshly isolated rat and human corporal myocytes. Phenylephrine (PE) contracted cells and activated whole cell currents. Outward current was identified as large-conductance Ca(2+)-activated K(+) current. The inward current elicited by PE was dependent on the Cl(-) gradient and was inhibited by niflumic acid, indicative of a Ca(2+)-activated Cl(-) (Cl(Ca)) current. Furthermore, spontaneous transient outward and inward currents (STOCs and STICs, respectively) were identified in both rat and human corporal myocytes and derived from large-conductance Ca(2+)-activated K(+) and Cl(Ca) channel activity. STICs and STOCs were inhibited by PE and A-23187, and combined 8-bromoadenosine cAMP and 8-bromoadenosine cGMP decreased their frequency. When studied in vivo, chloride channel blockers transiently increased intracavernosal pressure and prolonged nerve-evoked erections. This report reveals for the first time Cl(Ca) current in rat and human corpus cavernosum smooth muscle cells and demonstrates its key functional role in the regulation of penile erection.     

The vasculature of the rat penis: a scanning electron microscopic and histologic study.

As a basis for understanding the mechanism of erection in an animal model frequently used in research in reproductive biology, the angioarchitecture of the penis of the rat has been described using scanning electron microscopy. Study of the penile vasculature of the rat indicates that the corpora cavernosa penis and the corpus spongiosum are independent erectile tissues, each with its own arterial and venous vessels. The large vascular spaces and abundant smooth muscle of the penile crura are compatible with its role in regulating blood flow to more distal penile tissues. Helicine arteries of the crura, but not the parent deep penile artery or arteries elsewhere, have muscular cushions in their walls. The venous drainage of the penile crura is via subtunical veins which are thought to be compressed during erection to elevate pressure within the penis. Large, paired cavernous veins drain the shaft of the penis. A unique method for inhibiting blood flow from the penis is indicated by the division of the cavernous veins into smaller channels prior to joining the subtunical venous plexus. Erectile tissue in the bifid origins of the corpus spongiosum has abundant cavernous muscle, while in the remainder of the corpus spongiosum little smooth muscle lines the cavernous spaces. The cavernous spaces on either side of the urethra coalesce to form vessels, each of which communicates with cavernous spaces in the glans. In addition, a bypass of the glans is effected by communication of these vessels directly with the deep dorsal vein. The apparent absence of muscular pads in vessels of the spongiosum, the relative paucity of cavernous smooth muscle, and the ample venous drainage provided by the deep dorsal vein may account for the lack of a venous occlusive mechanism similar to that of the corpora cavernosa penis.