Nonlinear Dynamics In Interspike Intervals Of An Experimental Neural Pacemaker

Nervous system transforms the information corning from the environment (inside and outside) by way of the sensory devices (including receptor, channel, sensory organ), and then transmit, integrate, memorize these information, and make the corresponding effector to react. The neuron is the basic function unit of nervous system, and one of its primary ability is deal with and transmits the biological electrical signal. In carrying out these functions, two kinds of basic forms are adopted, one is the local potential, another is the action potential. The action potential is " all or none " and stereotyped electricity signal. The action potential can propagate over long distance without weakening, and makes the neuron realize the long distance transmission of neural information. The neural information should be encoded in interspike intervals (ISIs) series of action potential trains (including firing frequency and temporal pattern), considering that every pulse of the action potential trains propagating on the nerve is identical. The action potential trains often show various kinds of temporal patterns, and part of them are irregular. How are these rich and colorful rhythms given rise to? Is theinherent contact existed between the different patterns? What are the functional meanings of these temporal patterns in action potential trains? These problems have caused the concern of more and more neurophysiologists.Many experiments found that the nerve membrane at injured area has been accumulated a large number of ion channels after the nerve injury, includes sodium channel, potassium channel and calcium channel etc, and formed ectopic pacemaker, and the spontaneous afferent discharges were given rise to. The further research indicates that sodium, potassium and calcium current all participated in spontaneous discharge. What is worth attention is that rhythms of spontaneous discharge of nerve is very various, the period rhythm can transformed to each other via period-adding bifurcation. The experimental neural pacemaker become a good biological model for exploring the dynamical mechanism of firing pattern because of its merits: easy to functioning for drugs and the electric field stimulus, easy to long time recording with contrasting and having similar electrical physiology characters with normal neurons. Combining with the nonlinear dynamics theory, deeper mechanism underlying different firing patterns as well as the inherent contact between the various patterns can be elucidated.In this study, Bennett and Xie's model of injured nerve was employed. The interspike intervals were recorded and analyzed by nonlinear dynamics methods.The main results as follows:1. According to the nonlinear dynamical features of the ISI series, the firing patterns of the neural pacemaker can be described as periodic rhythm, bursting rhythm and chaotic rhythm. These different discharge rhythms can be transformed mutually when drugs or electrical field stimulus were operated atthe pacemaker.2. When [Ca2+]0is decreased by perfusing the pacemaker with Ca2*-free Kreb's solution, the rhythm transitions from period one to period two, chaos, period three, chaos even to period four are observed. The increase of [Ca2+]0 turns period two to period one, and to quiescency. Similar phenomena of bifurcation as that of Ca^-free Kreb's solution are observed in the ISI series when the increase of [K^o and TEA (a kind of K+ channel bloker) is added into the perfusing solution.3. The EGTA can induce the bistable bursting; The veratridine can bring out the parabola bursting; The increase of [Ca2+]0 can lead to the third kind of bursting.4. Accompanying ISIs bifurcation, the firing frequency showed the corresponding nonlinear change. When the pacemaker was perfused with Ca2+-free Kreb's solution (containing 10 mMol EGTA), a successive change of the firing rate going with ISIs bifurcation was observed. The result displayed that at the bifurcation points, corresponding firing rate changed dramatically by contrast with that of...