RESUMO
Spontaneous cord dorsum potentials (spontaneous CDPs) are produced by the activation of dorsal horn neurons distributed along the L4 to S1 spinal cord segments, in Rexed's laminae III-VI, in the same region in which there are interneurons rhythmically bursting during fictive scratching in cats. An interesting observation is that spontaneous CDPs are not rhythmically superimposed on the sinusoidal CDPs generated during fictive scratching episodes, thus suggesting that the interneurons producing both types of CDPs belong to different spinal circuits. In order to provide experimental data to support this hypothesis, we recorded unitary activity of neurons in the L6 spinal cord segment. We found that the neurons firing rhythmically during the sinusoidal CDPs associated with the extensor, flexor or intermediate phases of scratching were not synchronized with the spontaneous CDPs. Moreover, we found that the neurons firing during the spontaneous CDPs were not synchronized with the sinusoidal CDPs. These results suggest that the neurons involved in the occurrence of spontaneous CDPs are not part of the spinal cord central pattern generators (CPGs). This study will be relevant for understanding the relationships between the spinal cord neuronal populations firing spontaneously and the CPGs, in the intact and injured spinal cord.
Assuntos
Geradores de Padrão Central/fisiologia , Atividade Motora/fisiologia , Neurônios/fisiologia , Medula Espinal/fisiologia , Animais , Gatos , EletrofisiologiaRESUMO
GABA(A) receptors mediating tonic inhibitory currents are present in neurons from hippocampus, cerebellum, sensory cortex and thalamus. These receptors located at peri- and extra-synaptic sites are constituted mainly by α(4/6) and α(5) subunits which confer them high affinity for GABA and low desensitization. Immunohistochemical and in vitro hybridization studies have shown the expression of these subunits, while functional studies have reported the presence of GABAergic tonic currents in spinal dorsal horn neurons. However, the presence of this inhibitory current has not been documented in motoneurons. In addition, we previously reported that the monosynaptic reflex is facilitated by furosemide, an antagonist of the α(4/6) GABA(A) receptors, without affecting the dorsal root potential, which suggests the presence of a GABAergic tonic inhibitory current in motoneurons. The aim of this work was to investigate the presence of high affinity GABA(A) receptors in motoneurons. By intracellular recordings made with sharp electrodes and the whole-cell patch clamp recording technique we show here that the membrane input resistance and the monosynaptic excitatory post-synaptic potential (EPSPs) are significantly increased by bicuculline. Likewise, the depression of the EPSPs and the input membrane resistance normally induced by muscimol was partially reverted by 20 µM bicuculline and abolished when the concentration of the antagonist was raised to 100 µM. Last, bicuculline at low concentration did not affect the holding current as occur with the high concentration that block the tonic inhibitory GABAergic current. Together these results suggest that the excitability in motoneurons may be tonically inhibited by high affinity GABA(A) receptors.
Assuntos
Potenciais Pós-Sinápticos Excitadores/fisiologia , Neurônios Motores/metabolismo , Receptores de GABA-A/metabolismo , Medula Espinal/metabolismo , Animais , Estimulação Elétrica , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Agonistas de Receptores de GABA-A/farmacologia , Antagonistas de Receptores de GABA-A/farmacologia , Neurônios Motores/efeitos dos fármacos , Técnicas de Patch-Clamp , Receptores de GABA-A/efeitos dos fármacos , Medula Espinal/efeitos dos fármacos , TartarugasRESUMO
Penile reflexes (PRs) were monitored in chronic spinal cord-transected rats by identifying them visually, and at the same time they were recorded as the electromyographic activity of bulbospongiosus muscles. Intraperitoneal injection of the agonist muscarine (10 microg) produced a facilitation of PRs. A decrease in the latency, an increase in the number of clusters and often an increase in the duration of cups were found after muscarine. In addition, 66% (six out of nine) of the animals ejaculated after muscarine. These results suggest that cholinergic receptor stimulation may be involved in erectile and ejaculatory mechanisms mediated by the spinal cord.
Assuntos
Ejaculação/efeitos dos fármacos , Disfunção Erétil/tratamento farmacológico , Muscarina/farmacologia , Agonistas Muscarínicos/farmacologia , Ereção Peniana/efeitos dos fármacos , Traumatismos da Medula Espinal/complicações , Animais , Ejaculação/fisiologia , Eletromiografia , Disfunção Erétil/etiologia , Disfunção Erétil/fisiopatologia , Masculino , Ereção Peniana/fisiologia , Ratos , Ratos Wistar , Receptores Muscarínicos/fisiologia , Reflexo/efeitos dos fármacos , Traumatismos da Medula Espinal/fisiopatologiaRESUMO
1, The mechanisms underlying the dorsal root potential (DRP) were studied in transverse slices of turtle spinal cord. DRPs were evoked by stimulating one filament in a dorsal root and were recorded from another such filament. 2. The DRP evoked at supramaximal stimulus intensity was reduced but not eliminated after blockade of GABAA receptors. The remaining component was eliminated by blocking NMDA and AMPA receptors. 3. The DRP was reduced but not eliminated after blockade of AMPA receptors. The early component of the remaining DRP was dependent on GABAA receptors and the residual component on NMDA receptors. 4. The DRP was reduced but not eliminated by TTX. GABAA, NMDA and AMPA receptors contributed to the generation of the TTX-insensitive DRP. The early component of the DRP in the presence of TTX depended on GABAA receptor activation, and the late component mainly on the activation of NMDA receptors. 5. Our results show that part of the DRP is generated by a TTX-resistant, probably non-spiking micro-circuit with separate components mediated by GABA and glutamate.
Assuntos
Potenciais Evocados/fisiologia , Rede Nervosa/efeitos dos fármacos , Medula Espinal/metabolismo , Raízes Nervosas Espinhais/metabolismo , Tetrodotoxina/farmacologia , 6-Ciano-7-nitroquinoxalina-2,3-diona/farmacologia , Animais , Bicuculina/farmacologia , Potenciais Evocados/efeitos dos fármacos , Antagonistas de Aminoácidos Excitatórios/farmacologia , Antagonistas GABAérgicos/farmacologia , Antagonistas de Receptores de GABA-A , Técnicas In Vitro , Rede Nervosa/citologia , Rede Nervosa/metabolismo , Tempo de Reação/efeitos dos fármacos , Receptores de AMPA/antagonistas & inibidores , Receptores de N-Metil-D-Aspartato/antagonistas & inibidores , Medula Espinal/citologia , Medula Espinal/efeitos dos fármacos , Raízes Nervosas Espinhais/citologia , Raízes Nervosas Espinhais/efeitos dos fármacos , TartarugasRESUMO
In decerebrate or spinal cats, sustained mechanical stimulation of the cervix uteri inhibited the flexor reflex elicited by electrical stimulation of the foot pad during the probing period (160 s). After probing, 3-15 min were required for reflex recovery. No additional inhibition was produced if probing was repeated before recovery, but instead the reflex was facilitated. When probing was applied 5-10 min after reflex recovery the reflex was again abolished. The recovery, however, occurred earlier and was followed by facilitation. Probing the cervix with single mechanical pulses inhibited transiently (140-200 ms) the short latency reflex components, but the components with longer latencies are unaffected or facilitated. Distension of the vaginal wall with a balloon also inhibited the flexor reflex, but a transient, mild facilitation appeared several seconds after the distension. In general, whenever the inhibition decreases, the facilitation predominates. Our findings suggest that cervical probing or vaginal distension triggers both a long-lasting inhibition and a concomitant facilitation in different intraspinal flexor reflex pathways.
Assuntos
Colo do Útero/fisiologia , Reflexo , Sinapses/fisiologia , Vias Aferentes/fisiologia , Animais , Gatos , Colo do Útero/inervação , Estado de Descerebração , Feminino , Músculo Liso/inervação , Músculo Liso/fisiologia , Estimulação Física , Medula Espinal/fisiologia , Fatores de Tempo , Vagina/fisiologiaRESUMO
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.