Sensitivity Of Non-periodic Activity in Neurons

Neurons respond to external stimuli. But, different neurons may have various responses to the same stimuli. This is very important to neural function. The sensitivity of neurons is related to neurons?receptors, ion channels, signal transduction messengers, genes, neurotrophy and so on. The relationship between sensitivity and non-linear dynamic characteristic of neurons is unknown. The spike trains generated in neurons have many firing patterns. In fact, most neural firing patterns are variable and are usually considered to be 搉oise~~. With the development of chaos theory, it became clear that the non-periodic discharges contain deterministic chaos that has special importance in brain function. The extreme sensitivity to initial conditions is a basic feature of the chaos system, and a small change of system parameters can cause great change of the chaos system. The sensitivity of chaos may influence the responsiveness of neurons with chaotic activities. In this research, we used single fibre recoding in vivo, extracelluar recording in vitro and in vivo, ECoG and EMG recording technique, studied the relationship between sensitivity and non-linear dynamic characteristic of activity from the chronically compressed dorsal root ganglion (DRG) model, hippocampal neurons, Hindmarsh-Rose (HR) neuron model and epileptic model. 7 Results 1. Non-periodic firing injured DRG neurons were more sensitive to stimulis than periodic firing neurons. Spontaneous activities of single fibers from the injured DRG neurons in rats were recorded. According to the dynamics of interspike interval (151), the injured DRG neurons can be divided into periodic firing neurons (ISIs were equal) and non-periodic firing neurons (ISIs were irregular). The sensitivities of the two kinds of firing patterns neurons to extraneous norepinephrine (NE), tetraethylammoniurn (TEA), Ca2~ and sympathetic stimulation were compared. it was found that the incidences of responses among non-periodic firing neurons were higher than that among periodic firing neurons. The response thresholds of non-peridic firing neurons were lower than that of periodic firing neurons. The curve of dose-response relationship of non-periodic neurons shifted toward the left significantly compared to that of the periodic firing neurons. 2. In the same DRG neurons, the neuron exhibited greater responses in non- periodic firing pattern than that in periodic firing pattern. In the process of responses of bursting firing neurons, the non-periodic component of the bursting activity exhibited greater responses to stimulis than periodic component did. 3. The unstable period orbits were found in bursting firing series, and this indicated the deterministic chaos contained within bursting firing series. 4. Non-periodic firing hippocampal CAl neurons were more sensitive to stimulis than periodic firing neurons. The spontaneous activity of hippocampal CAl neuron was recorded from hippocampa.1 brain slide. The sensitivity of non-periodic and periodic firing neurons to Glu and GABA was compared. It was found that the responses of non-periodic firing neurons to Glu and GABA with different concentration were greater than that of periodic neurons. 5. The HR neuronal model exhibited a signif...