Somatic innervation contributes to the release of bulbourethral gland secretion in male rats

BACKGROUND

In male rats, the bulbourethral glands (Bu-Gs) are the unique accessory sexual glands surrounded by striated musculature. However, until now the role of this musculature was unknown.

OBJECTIVES

(i) To characterize the Bu-Gs striated muscular layer in male rats and determine its innervation and response to genital stimulation. (ii) To reveal the role of the Bu-Gs striated musculature in the release of glandular secretion. (iii) To elucidate the effect of bilateral ablation of the Bu-Gs on copulatory behavior and seminal fluid characteristics.

MATERIALS AND METHODS

Adult Wistar male rats were allocated in three experiments: in Experiment 1, the Bu-Gs striated musculature, innervation and reflex activity were determined by gross anatomy and histological and electrophysiological techniques; electromyographic activity of the Bu-Gs striated musculature was evoked with genital stimulation. In Experiment 2, Bu-Gs were analyzed after copulatory behavior of intact or animals with unilateral transected motor branch of the sacral plexus (MBSP). In Experiment 3, copulatory behavior and spermatobioscopy of males with bilateral ablation of the Bu-Gs or sham surgery were analyzed.

RESULTS

The Bu-Gs striated fibers discharged in response to mechanostimulation of the prepuce, glans, and penile-urethra. Innervation of the Bu-Gs striated musculature originated from the MBSP; this nerve also innervates striated penile muscles. Unilateral transection of the MBSP significantly decreased the secretion from the ipsilateral Bu-G to the nerve transection. Bilateral ablation of Bu-Gs did not affect seminal plug formation but decreased semen viscosity.

DISCUSSION AND CONCLUSION

The Bu-Gs striated musculature contributes to expel glandular secretion during sexual intercourse. The somatic control of Bu-Gs secretion is additional to the reported autonomic innervation supplied by the cavernosus nerve, which may underlie the synthesis of secretion as well as contraction of Bu-Gs smooth muscle.

Copulation without seminal expulsion: the consequence of sexual satiation and the Coolidge effect

The studies of sexual satiety in male rats under the Coolidge effect indicate that males reassume copulation until ejaculation. Recently, it was demonstrated that sexually satiated males preserve the motor patterns of intromission and ejaculation, also penile erection, but not seminal expulsion. The first aim was to investigate if penile erections displayed by sexually satiated males dislodge the seminal plugs from the vagina and its effect on sperm transcervical transport. The second aim was to determine the recovery time of seminal expulsion after sexual satiety and its optimal ability to induce pregnancy. Results show that during the Coolidge effect males were able to dislodge the seminal plugs deposited by others (experiment 1A) disturbing the sperm transport (experiment 1B) then interfering with pregnancy (experiment 1C). After satiation, the ejaculate parameters recover slowly: it starts after 10 days with the seminal plug formation, and continues with an increase in sperm count in the uterus 15 days post-satiety (experiment 2). Sexually satiated males impregnated only 28% of the females during 15 days of cohabitation, whereas, satiated males that rested for 15 days impregnated 89% of the females (experiment 3). We concluded that males with successive ejaculations remain potential rivals, because they may disrupt the sperm transport of other males. The ejaculate features recovery after sexual satiety is gradual, begins with the secretions of the sex accessory glands and is followed by the sperm count. Full fertility recovery is reached after 15 days of sexual abstinence when males are able to impregnate most females.

Effects of genitofemoral nerve transection on copulatory behavior and fertility in male rats

Selective transection of peripheral nerves that innervate the pelvic region results in the alteration of some aspects of copulatory behavior, including seminal plug weight. Both branches of the genitofemoral nerve primarily innervate the cremaster muscle although the genital branch has a wide distribution in the cremasteric sac. Thermoregulation of spermatogenesis and the mechanical event of ejaculation largely depend on cremaster contractility. In this study, we analyzed the effects of bilateral transection of the genitofemoral nerve on male copulatory behavior and on fertility. Sexually experienced adult male rats were submitted to sexual behavior tests before and after surgical transection of the genitofemoral nerve. Tests were made four times before and on Days 9, 12, 15, 18 and 21 after surgery, and seminal plug weight was also analyzed. In addition, fertility was tested using two different approaches: by allowing the male to ejaculate once in an estrous female or keeping the male with three females during 15 days. Results showed that there were no differences in any of the copulatory parameters, including seminal plug weight. Regarding fertility, both procedures showed that the ability to induce pregnancy was significantly diminished in the neurectomized males tested at different times after surgery. These results support the notion that genitofemoral nerve regulation of fertility via contraction of the male cremaster muscle is an important factor in reproduction in rats.

The development of auditory callosal connections in normal and hypothyroid rats

Previous studies have shown that hypothyroidism modifies the development of callosal connections. In particular, adult hypothyroid rats have fewer callosally projecting neurons in layers II-III of the auditory cortex and more in layer V. This might be due to disturbance in the stabilization/elimination of juvenile callosal axons, or to abnormal neuronal migration during cortical histogenesis. To distinguish between these possibilities we have studied the distribution of callosally projecting auditory neurons at different postnatal ages using retrogradely transported tracers, and the cortical neurogenetic gradients using DNA labelling with 5-bromo-2'-deoxiuridine. In hypothyroid rats, injected at postnatal day 5 (P5) and killed at P18-20, most of the neurons retrogradely labelled from the contralateral hemisphere are distributed between layers IV and VI, as in older rats. In hypothyroid rats, many neurons are at locations inappropriate for their birthdate, including the subcortical white matter, resulting in more diffuse radial neurogenetic gradients. These results indicate that early induced hypothyroidism alters neuronal migration and prevents the establishment of callosal connections from cortical layers II-III.

Striated muscles and scent glands associated with the vaginal tract of the rabbit

BACKGROUND

Despite the importance of the rabbit (Oryctolagus cuniculus) in reproductive research, no comprehensive account of the anatomical organization of the female reproductive tract is presently available.

METHODS

Based on gross dissection and on the electrical stimulation of striated muscles in 10 domestic female rabbits, it was the aim of this study to help fill this gap by describing the origin, insertion, and general action of muscles associated with the vaginal tract and with associated scent glands.

RESULTS

Compared with the better-studied rat or cat, the long vaginal tract of the rabbit is characterized by a well-developed and complex musculature. The bulbospongiosus, ischiocavernosus, constrictor vestibuli, and constrictor vulvae muscles, poorly developed or absent in the female rat or cat, were particularly conspicuous. Scent glands, including the newly identified preputial glands, were also a distinctive feature.

CONCLUSION

These structures may represent specializations underlying the rapid copulation, rapid parturition, and well-developed chemical communication characteristic of the reproductive efficiency of the rabbit.

Participation of pelvic nerve branches in male rat copulatory behavior

The role of the pelvic nerve branches in the mediation of copulatory behavior was investigated. The somatomotor or the viscerocutaneous branch of the pelvic nerve was bilaterally sectioned in sexually experienced male rats. Somatomotor branch surgery had no detectable effect. Viscerocutaneous branch transection altered copulatory parameters that reflect impairments in penile erection and seminal plug emission. The altered behavioral parameters approached or reached presurgical and sham values 21 days after transection, indicating that the damage to erectile and ejaculatory function was transient. It is suggested that animals with viscerocutaneous branch transection recover copulatory efficiency through a compensatory plastic mechanism, possibly involving the hypogastric nerve.