Components of the neural circuitry of the vaginocavernosus reflex in rabbits

Abstract

In mammals the mechanisms underlying female sexual and reproductive biology are poorly understood. Little attention has been paid to striated muscles and their neural regulation. The aim of the present study was to describe the components of the vaginocavernosus reflex in adult rabbits. It was found that mechanical stimulation of the glans of the clitoris and the perineal vagina induced electromyographic (EMG) responses in bulbocavernosus (Bcm) and ischiocavernosus (Icm) muscles. Unilateral and bilateral nerve transection indicated that the clitoral nerve is the main afferent path of the reflex and that it recruits ipsilateral and contralateral perineal motoneurons. Injection of horseradish peroxides-wheat germ agglutinin (HRP-WGA) into the Bcm and Icm labeled spinal motoneurons scattered in L7 and S1 segments. According to the results of this study and previous work, the elements of the vaginocavernosus reflex may be described as follows. Mechanical receptors are located in the glans clitoris and in the wall of the perineal vagina. The main afferent pathway is the clitoral nerve. It activates ipsilateral and contralateral Bcm and Icm motoneurons in lumbosacral segments. Axons of efferent neurons travel through the clitoral and ischiocavernosus nerves, and the effectors are the Bcm and Icm perineal muscles. Identification of neural components of the vaginocavernosus reflex in rabbits will allow the use of this animal as a model to assess the physiological characteristics of the perineal motoneurons as well as the contribution of the Bcm and Icm in female urogenital functions.

The Role of Pelvic and Perineal Muscles in Reproductive and Excretory Functions

“…Furthermore, mechanical stimulation, by passing a small balloon filled with saline into different regions of the vagina, differentially activated these muscles. Stimulation causes electromyographic activity of the Ism and the Bsm (Cruz et al, 2002;2010A) and the Pcm (Cruz et al, 2010B). Such findings are similar to those described in women as the vaginocavernosus and the vaginolevator reflexes (Shafik, 1993(Shafik, , 1995.…”

“…Vaginal stimulation causes the reflex activity of the Bsm and the Ism (Shafik, 1993;Cruz et al, 2002;Cruz et al, 2010a), which is called the vaginocervical reflex that participates in the erection of the clitoris (Shafik, 1993). Furthermore, the distension of the vagina by the fetal head during delivery causes the contraction of perineal muscles, which has been suggested to support the head during its descent and prevent vaginal and perineal tears (Shafik, 1993;Cruz et al, 2002;Shafik et al, 2007;Cruz et al 2010a).…”

“…Furthermore, the distension of the vagina by the fetal head during delivery causes the contraction of perineal muscles, which has been suggested to support the head during its descent and prevent vaginal and perineal tears (Shafik, 1993;Cruz et al, 2002;Shafik et al, 2007;Cruz et al 2010a). …”

Neural pathways of somatic and visceral reflexes of the external urethral sphincter in female rats

“…The present study shows that in female rats EUS reflex activity is also activated by cutaneous, genital, anal, and rectal mechanoreceptors, with the DNC and CN as the main afferent pathways and the MBLSP as the efferent pathway. These somato‐somato and viscera‐somatic reflexes seems not to be specific for rats because in both rabbits and women, electrical or mechanical stimulation of the clitoris and vagina activates perineal muscles such as the bulbocavernosus, ischiocavernosus, and the EUS, and its reflex latency has been considered of clinical significance for determining sacral motor neuron impairment (Bilkey et al, 1983; Shafik, 1993; Cruz et al, 2010).…”

Striated Perineal Muscles: Location of Somatic and Autonomic Neurons Projecting to the Male Pig Ischiocavernous Muscle. Neurochemical Features of the Sympathetic Subset

“…The primary role of the muscle is to enhance the elongation of the penis or clitoris, by compressing the veins that carry blood away from the corpora cavernosa and inducing cavernous tissue turgidity and tumescence (generation of suprasystolic cavernosal pressures). Moreover, the ICM seems to partecipate not only in reproductive processes, but also in urinary and fecal continence (Shafik et al, a,b; 2008; Zempoalteca et al, 2008; Cruz et al, ; Juàrez et al, ), through a reflex mechanism. Given this involvement in penile erection and continence, it has been extensively studied in different mammals, such as rat, rabbit, carnivores and primates, to define its neuroanatomical (Breedlove and Arnold, ; Schrøder, ; Ueyama et al, ; Roppolo et al, ; Katagiri et al, ; Mc Kenna and Nadelhaft, ; Holstege and Tan, ; Yucel and Baskin, ; Zempoalteca et al, ), electrophysiological (Shafik et al, a,b; 2008) and functional (Juàrez and Cruz, ) properties.…”