RESUMO
Vaginocervical stimulation (VS) releases multiple neurotransmitters into superfusates of the spinal cord; these can stimulate both nociceptive (e.g., glutamate, and glycine acting at the NMDA site), and antinociceptive (e.g., GABA, norepinephrine, 5-HT, and glycine acting at the strychnine-sensitive receptor) systems. Although the balance between these two opposing systems can determine the nature, magnitude, and duration of the response to VS, the characteristic prevailing response to VS is analgesia. We hypothesized that by counteracting the nociceptive component of this system, the magnitude and duration of the response to VS would be augmented. In the present study, the NMDA receptor antagonist AP5 [10 microg injected intrathecally (i.t.)] significantly increased the magnitude and duration of the analgesia (measured as tail flick latency to radiant heat) produced by VS (200 g force). At several time points the analgesic effect of AP5 combined with VS was greater than the sum of the effects of AP5 and VS separately, suggesting that they act synergistically. We propose that AP5 potentiates the analgesic effect of VS by two mechanisms: (a) antagonizing the putative pain-producing action of glutamate and glycine acting jointly at the NMDA receptor, and consequently, (b) permitting the unimpeded expression of the analgesic action of inhibitory neurotransmitters released by VS (e.g., glycine at the strychnine-sensitive receptor, and GABA).
Assuntos
2-Amino-5-fosfonovalerato/farmacologia , Analgésicos/farmacologia , Colo do Útero/fisiologia , Antagonistas de Aminoácidos Excitatórios/farmacologia , Receptores de N-Metil-D-Aspartato/antagonistas & inibidores , Vagina/fisiologia , 2-Amino-5-fosfonovalerato/administração & dosagem , Analgésicos/administração & dosagem , Animais , Feminino , Injeções Espinhais , Medição da Dor/efeitos dos fármacos , Estimulação Física , Ratos , Ratos Sprague-Dawley , Fatores de TempoRESUMO
To assess possible changes in nociception during copulation in estrous rats, electric shocks that were 20% suprathreshold for eliciting vocalization in response to tail shock (STS), were applied to the tail before the initiation of copulation and, thereafter, coincident with the onset of mounting bouts by the male (Experiment 1). Females vocalized significantly less during non-intromittive mounts (M; P < 0.001), intromissions (I; P < 0.001), and ejaculation (E; P < 0.01) than before the initiation of copulation. In order to assess the importance of vaginal stimulation (VS) by penile insertion during mating, in Experiment 2 30% STS were applied 300-400 ms after the initiation of mounting to ensure that the stimuli fell within the period of penile insertion occurring during I and E. M failed to significantly inhibit vocalizations to 30% STS. By contrast, both I and E markedly inhibited vocalizations in response to STS. This effect was transitory since subjects (Ss) vocalized to nearly all 30% STS when delivered 15 s after I or E. Copulatory analgesia (CA) was abolished by the bilateral transection of the pelvic and hypogastric nerves but not by the transection of the pudendal nerve (Experiment 3). The magnitude of CA was calibrated by determining the doses of morphine sulfate (MS) required to produce similar decrements in vocalization to STS. The analgesic effects of I and E were equivalent to more than 10 mg/kg and 15 mg/kg, respectively, of MS (Experiment 4). Pelvic-hypogastric neurectomy, but not pudendal neurectomy, also significantly reduced the effect of VS on facilitating lordosis, inducing immobilization and hind leg extension, and blocking the withdrawal reflex to foot pinch (Experiment 5).(ABSTRACT TRUNCATED AT 250 WORDS)
Assuntos
Analgesia , Copulação/fisiologia , Animais , Copulação/efeitos dos fármacos , Relação Dose-Resposta a Droga , Estimulação Elétrica , Feminino , Masculino , Morfina/farmacologia , Neurônios Aferentes/fisiologia , Ovariectomia , Limiar da Dor/efeitos dos fármacos , Limiar da Dor/fisiologia , Ratos , Ratos Wistar , Vagina/inervação , Vagina/fisiologia , Vocalização Animal/efeitos dos fármacos , Vocalização Animal/fisiologiaRESUMO
The present study describes several muscular reflexes produced by genital stimulation, the nerves that subserve them, and the visceral and postural effects induced by these reflexes. Electrical stimulation of the iliococcygeus (ic) and pubococcygeus (pc) (striated) muscles produced movement of the vaginal orifice and wall, membranous urethra, tail and pelvis. Electrical stimulation of the psoas major (pm) or iliacus (i) (striated) muscles produced movements of the lumbar vertebrae and extension of the ipsilateral hindlimb. Sensory mechanostimulation elicited responses of these muscles as follows: stimulation of the perineal skin, clitoral sheath or distal vagina produced reflex contraction of the ic and pc muscles. Stimulation of the cervix produced reflex contraction of the pm and i muscles and also blocked the above reflex contraction of the ic and pc muscles. Both the cervical stimulation-induced blockage of the ic and pc reflex response, and the cervical stimulation-induced activation of pm and i muscles was prevented by bilateral transection of the viscerocutaneous branch of the pelvic nerve. Based on the above observations, it is proposed that stimulation of the vaginal surface of the cervix resulting from penile intromission and/or seminal plug deposition during mating behavior in the rat may reflexively active pm and i, thereby contributing to the hindleg postural rigidity and lordotic dorsiflexion that are characteristic of the normal mating posture in female rats.
Assuntos
Músculos Abdominais/fisiologia , Genitália Feminina/fisiologia , Reflexo/fisiologia , Músculos Abdominais/inervação , Animais , Colo do Útero/fisiologia , Estimulação Elétrica , Feminino , Genitália Feminina/inervação , Contração Muscular/fisiologia , Estimulação Física , Ratos , Ratos EndogâmicosRESUMO
The efferent innervation of the pelvic and pudendal nerves was characterized in this study by identifying the muscles activated by electrical stimulation of the nerves distal to the point at which they bifurcate from the L6-S1 trunk. Pelvic nerve electrical stimulation produced EMG-monitored contraction of the ipsilateral ilio- and pubococcygeus muscles, which was abolished by cutting one ('muscular') branch of the bifurcated nerve. (This 'muscular' branch receives proprioceptive input activated by tail displacement, whereas the other, 'viscero-cutaneous' branch receives sensory innervation from the midline perineal region.) Pudendal nerve electrical stimulation produced contraction of the coccygeus, external anal sphincter, and ischiocavernosus muscles. Movements of the orifice and wall of the vagina were directly visualized during electrical stimulation of the two nerves. Intravaginal pressure measured by balloon was increased by pelvic nerve stimulation and decreased by pudendal nerve stimulation. Reflexive contraction of the ilio- en pubococcygeus muscles was produced by mechanostimulation of the perineum, clitoral sheath and distal vagina. This response was abolished by gentle cervical mechanostimulation. One implication of this finding is that passage of the fetuses through the cervix during parturition may relax the ilio- and pubococcygeus muscles, thereby facilitating delivery.
Assuntos
Genitália Feminina/inervação , Neurônios Motores/fisiologia , Neurônios Aferentes/fisiologia , Nervos Periféricos/fisiologia , Animais , Vias Eferentes/fisiologia , Estimulação Elétrica , Feminino , Genitália Feminina/fisiologia , Músculos/inervação , Ratos , Ratos EndogâmicosRESUMO
In the present study, the analgesia produced by vaginal stimulation (VS) in women was found to be dissociated from heart rate. The VS-produced analgesia was not accompanied by an acceleration of heart rate. Heart rate acceleration produced by exercise did not result in analgesia. The independence of VS-produced analgesia from this index of autonomic activity is consistent with recent findings in rats.