| Nervous system receives and transforms the information involving the change in internal and external environment through sensory receptor. The signal of receptor is transferred alone fiber into dorsal root ganglia (DRG), and then integrated in DRG The soma in DRG then transfers the train of action potential into central nervous system. In this transmission procedure, the soma in DRG responses to the afferent train of action potential, and then integrated them. So, the responsiveness of DRG neuron to input plays an important role in the mechanism of coding rule of the primary sensory neuron. In chronically compressed DRG, injured neurons exhibit hyperexcitability, and some of them generate a new type of bursting rhythm. The characteristics of this rhythm are as follows(1) the first spike in a burst emerged from amplitude-increasing damped SMPO; (2) the discharge terminated by an amplitude-decreasing damped SMPO; (3) spike frequency may not decline at burst termination. The mechanism underlying this bursting is not clear. Investigation of this mechanism will benefit the understanding of the change in electrophysiological states and coding rule of injured DRG neurons. This is also important for realizing of generating mechanism of hyperexcitability.The nonlinear dynamics methods were used to study the coding ruleof cold receptor, and some mathematical models were established to simulate the coding characters in stable temperature. But, under the condition of dynamic change in temperature, the coupling between the firing pattern and the dynamics of temperature is known little. The dynamic characteristics of irregular firing of cold receptor is not clear.In the present study, the classification of the novel bursting pattern in injured DRG neurons is identified and the nonlinear mechanism of the type of bursting is discussed; Based on the established the experimental model of rat tail nerve's cold receptor, the coupling between the firing rhythm and the dynamics of temperature was investigated. By using the extraction of unstable periodic orbits, the nonlinear characters of irregular firing of cold receptor were also analyzed. These investigation will benefit establishing a more reasonable dynamic model of cold receptor, and understanding the dynamic responsiveness of cold receptor.Method1. The classification of the novel burst firing recorded from injuredDRG1.1 CriterionThe first step of classification is to identify the deterministic dynamics of burst firing. Next, according to the bifurcation mechanism, we can determine the exact topological type of bursting by using the geometry of membrane potential oscillations. Since the burst firing is similar to elliptic bursting, the topological criterion is as follows: (1) the first spike of the burst emerges from amplitude-increasing damped subthreshold membrane potential oscillation (SMPO); (2) The amplitude of spikes is full-amplitude and intraburst frequency is relatively constant.1.2 Identification of deterministic dynamics in burst firingOur basic assumption is that there exists a significant deterministic component within the seemingly noisy bursting discharge of neurons. If this is true, there is a correlation between the occurrence of a burst and the next one. The identification of hierarchy of unstable periodic orbits(UPOs) can be used to characterize the system's deterministic dynamics.A burst is considered as an event, and the ISI series were processed to extract bursting events and the interevent interval (IEI) series were used for analysis. The bursting event is defined as the longest sequences of spikes with all interspike intervals(ISIs) less than or equal to a certain discriminating threshold which was selected for each record.The IEI sequence is embedded into a delay embedded state space with embedding dimension d=3 and time lag r=l by creating the set of delay vectors. We employed a transformation utilizing the local dynamics of the system such that the transformed data are concentrated about distinct UPOs. However, in a real experi...
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