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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.

Neurons in the region of the rostral nucleus paragigantocellularis (nPGi) mediate the inhibition of spinal sexual reflexes. Anatomical and pharmacological evidence is presented supporting a role for 5-hydroxytryptamine (5-HT) in this inhibition. Neurons in the rostral nPGi project to the ventral horn in the vicinity of the pudendal motoneurons. A significant number (78% ipsilateral) of these neurons contain 5-HT. Anterograde tracing with Phaseolus leucoagglutinin (PHA-L) confirmed the nPGi projection to pudendal motoneuron and interneuronal areas of the lumbar cord. 5-HT immunoreactive fibers and presumptive terminals surround the pudendal motoneurons. Urethral stimulation, in the anesthetized male rat, elicited penile erections, ejaculation and rhythmic contractions of the perineal muscles, we have used the term coitus reflex to describe this response. Intrathecal injection of 5-HT (4-50 micrograms) abolished the coitus reflex. Methysergide (1-10 mg/kg i.v.) prevented the 5-HT induced blockade of the coitus reflex. These data support the hypothesis that 5-HT is involved in the descending inhibition of spinal sexual reflexes.

Introduction Data concerning the physiology of desire, arousal, and orgasm in women are limited because of ethical constraints. Aim To gain knowledge of physiology of female sexual function through animal models. Methods To provide state-of-the-art knowledge concerning female sexual function in animal models, representing the opinions of seven experts from five countries developed in a consensus process over a 2-year period. Main Outcome Measure Expert opinion was based on the grading of evidence-based medical literature, widespread internal committee discussion, public presentation, and debate. Results Sexual desire may be considered as the presence of desire for, and fantasy about, sexual activity. Desire in animals can be inferred from certain appetitive behaviors that occur during copulation and from certain unconditioned copulatory measures. Proceptive behaviors are dependent in part on estrogen, progesterone, and drugs that bind to D1 dopamine receptors, adrenergic receptors, oxytocin receptors, opioid receptors, or gamma-amino butyric acid receptors. Peripheral arousal states are dependent on regulation of genital smooth muscle tone. Multiple neurotransmitters/mediators are involved including adrenergic, and nonadrenergic, noncholinergic agents such as vasoactive intestinal polypeptide, nitric oxide, neuropeptide Y, calcitonin gene-related peptide, and substance P. Sex steroid hormones, estrogens and androgens, are critical for structure and function of genital tissues including modulation of genital blood flow, lubrication, neurotransmitter function, smooth muscle contractility, mucification, and sex steroid receptor expression in genital tissues. Orgasm may be investigated by urethrogenital (UG) reflex, in which genital stimulation results in rhythmic contractions of striated perineal muscles and contractions of vagina, anus, and uterine smooth muscle. The UG reflex is generated by a multisegmental spinal pattern generator involving the coordination of sympathetic, parasympathetic, and somatic efferents innervating the genital organs. Serotonin and dopamine may modulate UG reflex activity. Conclusion More research is needed in animal models in the physiology of female sexual function.

Transneuronal tracing techniques were used to identify the putative spinal and brainstem neurons involved in continence and voiding in the female rat. Pseudorabies virus, Bartha's K strain, was injected into either the external urethral sphincter, the bladder base, or the bladder body. After 3-5 days, the rats were perfused with fixative, and virus-labelled cells were identified by using immunohistochemistry. External urethral sphincter (EUS) injections resulted in labelling of pudendal motoneurons in the dorsolateral nucleus of L6. Putative spinal interneurons were found in the medial cord from T13 to S1 and in the lateral gray of T13-L2 and L5-S1. After both bladder base and bladder body injections, the majority of pseudorabies virus-labelled cells were found in the lateral gray and medial cord of L6-S1. A number of those found in the intermediolateral cell column resembled the parasympathetic preganglionic neurons; the remaining neurons in the lateral and medial gray were presumed to be interneurons. Very few pseudorabies virus-labelled cells were found rostral to T10. In the brainstem, transneuronally labelled cells were found in the parapyramidal medullary reticular formation, Barrington's nucleus, raphe magnus, raphe pallidus, subcoeruleus pars alpha, locus coeruleus, the A5 noradrenergic cell group, and ventromedial periaqueductal gray after all injection sites. Pseudorabies virus-labelled cells were also seen in the forebrain following the longest survival times; areas consistently labelled included the lateral hypothalamus, the parvocellular region of the paraventricular nucleus, and the medial preoptic area. These studies indicate that there is a substantial overlap of central nervous system neurons that innervate the EUS and the bladder in the female.