RESUMEN
We compared the responsiveness of a neural firing pacemaker in different dynamic states during the process of period-adding bifurcation to excitatory and inhibitory electrical field stimulus. In the region far from the bifurcation point, with the increase of the intensity of excitatory stimulus, the firing rate increased in an approximately linear manner and no firing pattern transition was observed. While in the region near the bifurcation point, the firing rate increased markedly higher accompanied with the transition of firing pattern when the intensity of excitatory stimulus remained the same. The stimulus-response of the region near the bifurcation point shifted upward significantly compared to that of the region far from the bifurcation point. Inhibitory stimulus with the same intensity, however, decreased the firing rate slightly without the transition of firing pattern in the region near the bifurcation point. These results suggest that the responsiveness in the region near the bifurcation point is more sensitive than that in the region far from the bifurcation point, which we named "critical sensitivity", and this has directional selectivity.
Asunto(s)
Potenciales de Acción/fisiología , Relojes Biológicos/fisiología , Neuronas/fisiología , Potenciales de Acción/efectos de la radiación , Animales , Relojes Biológicos/efectos de los fármacos , Calcio/metabolismo , Quelantes/farmacología , Relación Dosis-Respuesta a Droga , Relación Dosis-Respuesta en la Radiación , Ácido Egtácico/farmacología , Estimulación Eléctrica/métodos , Femenino , Masculino , Inhibición Neural/efectos de los fármacos , Inhibición Neural/fisiología , Inhibición Neural/efectos de la radiación , Neuronas/efectos de los fármacos , Neuronas/efectos de la radiación , Dinámicas no Lineales , Ratas , Ratas Sprague-Dawley , Neuropatía Ciática/fisiopatologíaRESUMEN
A specific bursting, parabolic bursting induced by veratridine, has been observed in rat injured sciatic nerve. With the help of Plant model, the biophysical mechanism for such a phenomenon is revealed from the viewpoint of nonlinear dynamical theory. The slow sodium influx educed by veratridine and the calcium-dependent potassium outflux are regarded as the two slow variables, which are responsible for the parabolic bursting. Furthermore, the roles that veratridine plays in the emergence of the parabolic bursting, namely inhibiting the inactivation of sodium channels and eliciting the slow sodium influx, are clarified.
Asunto(s)
Nervio Ciático/efectos de los fármacos , Veratridina/farmacología , Animales , Femenino , Masculino , Potenciales de la Membrana/efectos de los fármacos , Modelos Neurológicos , Ratas , Ratas Sprague-Dawley , Nervio Ciático/lesiones , Nervio Ciático/fisiopatología , Factores de TiempoRESUMEN
Firing patterns of injured nerve fibers were recorded using the single-fiber firing recording technique. Under the same background firing pattern, three types of bursting were induced separately by EGTA, veratridine or high [Ca(2+)](o) in the same type of nerve fibers. The results suggest that different firing patterns are related to different stimuli, which means that each firing pattern carries corresponding neural information.
Asunto(s)
Potenciales de Acción , Fibras Nerviosas/efectos de los fármacos , Veratridina/farmacología , Animales , Calcio/farmacología , Ácido Egtácico/farmacología , Fibras Nerviosas/patología , RatasRESUMEN
Veratridine, a blocker of inactive gate of sodium channel, was used to perfuse L5 dorsal root ganglion (DRG) topically. Afferent activities of type A single fiber from these DRGs were recorded. It was found that after a 10-min bath of veratridine (1.8-3 micromol/L), some of the primary silent DRG neurons were triggered by touch or pressure on the receptive fields or by electrical stimulation of the sciatic nerve to produce high-frequency firing, which was termed triggered oscillation presenting a U-type of interspike intervals (ISI) or other types of oscillations. The longer the intervals between stimulating pulses, the more stimulating pulses were needed to trigger the oscillation. The oscillation, triggered by electric stimuli with different duration or patterns, had no significant difference in their patterns. The duration of the inhibitory period after a triggered oscillation was generally 30-90 s. It was also observed that this kind of triggered oscillation was induced by afferent pulses of the same neurons. These results suggest that triggered oscillation, which may contribute to the fit of triggered pain, can be produced in primary sensory neurons after application of veratridine.