RESUMO
The scrotum, representing the pouch surrounding the testes and their associated structures, plays a significant role in maintaining the gonad at a temperature lower than that of the body. Although thermoregulation of the testes has been ascribed as a main function of the scrotum, here we found that mechanical stimulation of the scrotum is important during mating to facilitate the appropriate expulsion of semen during ejaculation. Previously we showed that the scrotal skin area is innervated by two nerve branches, the proximal (Psb) and distal (Dsb) scrotal branches which supply the proximal or distal half of the scrotum, respectively. The sensory field of each nerve is testosterone-dependent. The decreased androgen levels following castration reduce the sensitive area to mechanical stimuli that can be restored following exogenous administration of the hormone. Here, we tested the effect of scrotal nerve transection on sexual parameters of experienced male rats. Data show that lesion of PSb or DSb alone or combined did not affect the execution of sexual behavior. However, these lesions significantly reduced the proportion of males that expelled semen during ejaculation, with that semen showing a reduced quantity of sperm. Thus, scrotal nerves are important in reproduction not for the appropriate display of sexual behavior, but for the expulsion of a normal quantity of semen and number of sperm during ejaculation. Our suggestion is that scrotal afferents trigger spinal reflexes to activate autonomic efferents supplying the male reproductive tract for the control of seminal emission.
Assuntos
Ejaculação/fisiologia , Escroto/inervação , Escroto/fisiologia , Sêmen/fisiologia , Animais , Sobrevivência Celular/fisiologia , Cor , Copulação/fisiologia , Denervação , Feminino , Masculino , Neurônios Aferentes/fisiologia , Ovariectomia , Ratos , Ratos Wistar , Sêmen/citologia , Contagem de Espermatozoides , Motilidade dos Espermatozoides/fisiologia , Espermatozoides/fisiologia , ViscosidadeRESUMO
The scrotal nerves in the rat were studied electrophysiologically to describe their topographic organization in the skin and in the dorsal roots, and to determine if the electrical properties of these afferents are under the influence of testosterone. There are 2 afferent nerve branches innervating this area, the proximal scrotal branch supplying the proximal half of the scrotum (PSb), and the distal scrotal branch supplying the distal half (DSb). Results showed that afferent axons from PSb enter the spinal cord through the L5 and L6 dorsal roots, and axons from DSb enter the cord through the L6 and S1 dorsal roots. Mechanical stimulation of the scrotal skin exposed 3 dermatome areas, the L5, L6, and S1, with L6 being the longest dermatome with intermingled terminals from PSb and DSb. Decreased levels of testosterone after castration increased the threshold to trigger the activity of scrotal afferents, and the exogenous administration of the hormone reverted it. This effect was similar in the dorsal penile nerve. The decrease in androgen levels produced a reduction in the skin sensory field to mechanical stimuli that was restored after the administration of the hormone. As the scrotal nerves are highly stimulated during copulation in parallel with the dorsal penile nerve, it is suggested that the sensory field of the scrotal skin could be closely related to the modifications in sexual behavior after testosterone manipulation.
Assuntos
Hormônios Esteroides Gonadais/farmacologia , Escroto/efeitos dos fármacos , Pele/inervação , Raízes Nervosas Espinhais/fisiologia , Testosterona/farmacologia , Animais , Castração/métodos , Relação Dose-Resposta à Radiação , Condutividade Elétrica , Estimulação Elétrica , Eletrofisiologia/métodos , Potenciais Evocados/efeitos dos fármacos , Potenciais Evocados/fisiologia , Masculino , Ratos , Ratos Wistar , Tempo de Reação , Escroto/inervação , Escroto/fisiologiaRESUMO
One of the hypotheses to explain the neural mechanisms underlying rhythmic behaviours suggests that the central nervous system has the intrinsic capacity to produce repetitive, rhythmic output to the muscles involved in the response by means of a neuronal circuit named central pattern generator (CPG). The occurrence of rhythmic motor patterns during ejaculatory behaviour in mammals, which includes the genital motor pattern, has been shown. A CPG might regulate the timing of the repetitive muscular responses that constitute the ejaculatory motor pattern. The objective of the present study was to evidence that a CPG at a spinal level is involved in the expression and pacing of the rhythmic motor pattern generated during ejaculation. To this purpose we used the genital reflex as a model system. Following the general principles for the study of rhythmic motor patterns, the data obtained in the present series of experiments document that: (1) a rhythmic muscular response, the genital motor pattern, is registered during the ejaculatory event (expulsion of the urethral contents); (2) this ejaculatory motor response has similar EMG characteristics in intact and in spinal urethane-anaesthetised male rats; (3) interruption of the afferent inflow (deafferentation) does not disrupt the expression of the ejaculatory motor train; (4) a change in the stimulation interval does not alter the intrinsic pacing of the ejaculatory-like response; and (5) fictive ejaculation can be induced by pharmacological means. Together, this evidence supports the notion that a CPG produces the rhythmic ejaculatory motor pattern registered during fictive ejaculation.