RESUMO

Axons from receptors in the cat vaginal wall run in the sensory pudendal nerve (SPN), and brief (<10 s) vaginal probing (VP) in the decerebrate cat produces a long-lasting (>1 min) contraction of the triceps surae (TS) muscles. The aim of the present project was to find out whether brief SPN stimulation also produces sustained TS response and, eventually, to study the mechanisms involved in it. Decerebrate female cats were used. In some cats, TS electromyography (EMG) and tension response were recorded; stimulation of left SPN with single or repetitive trains of shocks produced a bilateral TS response that outlasted the stimulus >1 min as VP did. In paralyzed cats (pancuronium; Panc), intracellular recordings were made from hind limb motoneurons (MNs). SPN stimulation produced a depolarization 1 min) electroneurographic (ENG) postdischarge in a small filament of the medial gastrocnemius (MG) nerve; the MG EMG postdischarge was also recorded. Large spikes (LS) and small spikes (SS) were distinguished in the ENG. During the postdischarge, LS frequency and the integrated EMG activity correlated well (r > 0.9); no correlation was found between SS and EMG. After Panc injection, LS postdischarge was absent but the SS postdischarge remained. LS followed by EMG potential were also evoked by brief TS stretch (reflex LS); single shocks to SPN only elicited SS that were not followed by EMG potential. It is concluded that alpha axons and gamma axons produced LS and SS, respectively, and that SPN activates gamma axons. It is proposed that, in the nonparalyzed cats, the stimulation of SPN with trains of shocks might cause an increase in the afferent inflow from muscle spindles to alpha MNs through the sustained firing of gamma MNs. The increased excitatory inflow would depolarize alpha MNs and allow bistable MN firing; Panc would decrease this inflow by blocking transmission to the spindle fibers.

Assuntos

Membro Posterior/inervação , Neurônios Motores/fisiologia , Pelve/inervação , Potenciais de Ação/efeitos dos fármacos , Animais , Gatos , Estado de Descerebração , Estimulação Elétrica , Eletromiografia , Eletrofisiologia , Feminino , Neurônios Motores gama/fisiologia , Contração Muscular/fisiologia , Músculo Esquelético/fisiologia , Fenômenos Fisiológicos do Sistema Nervoso , Fármacos Neuromusculares não Despolarizantes/farmacologia , Pancurônio/farmacologia , Paralisia/induzido quimicamente , Paralisia/fisiopatologia

RESUMO

In decerebrate cats, controlled mechanical stimulation of the perivulvar skin, the vaginal wall or the cervix uteri induced visible hind limb extension. Pressing on the cervix uteri produced the greater response. To quantify these responses, the EMG activity and the tension developed by the normally inserted triceps surae muscles were recorded. The activity induced in these muscles by stimulation of the genital canal outlasted the stimulus by many seconds or a few minutes. These effects disappeared after spinalization at the T12 level. We propose that stimulation of the vaginal canal in the female cat may induce bistability of triceps surae motoneurones.

Assuntos

Colo do Útero/fisiologia , Músculos/fisiologia , Fenômenos Fisiológicos da Pele , Vagina/fisiologia , Vulva/fisiologia , Animais , Gatos , Colo do Útero/inervação , Copulação/fisiologia , Estado de Descerebração , Eletromiografia/instrumentação , Eletromiografia/métodos , Potenciais Evocados , Feminino , Músculo Liso/inervação , Músculo Liso/fisiologia , Estimulação Física , Pele/inervação , Vagina/inervação , Vulva/inervação