| Noise, as sound, is unwanted and disgusted. It disturbs other sounds. In electronic system and information science, noise is all random and unexpected disturbances, which can cover up the true signal. People try to eliminate it in order to get enough signals. But the view about noise has been greatly changing since R.Benzi firstly proposed the conception of 'stochastic resonance' in 1980's. Then scientists proved the of existence of stochastic resonance (SR) in a wide range of physical and chemical fields in a few years. In nonlinear system, a certain level noise can enhance the detection of weak regular signal (subthreshold signal). The ratio of signal to noise (SNR) reaches to the maximum under an optimize strength of noise, and SNR is decreased while strong noise overwhelms signal. This is SR. Nervous system is nonlinear system, and is fulfilled with background noise. In the beginning of 1990's, Longtin, Bulsara and Moss, three physical scientists, came up with a novel idea-SR may be involved in the exciting behaviors of neurons. In the followed decade, SR in nervous system was paid lots of attentions and became one of the hottest subjects. There were large amounts of data about SR in nervous system. It is proed that there are various SR innervous system on different levels, including aperiod, Internal and automatic SR. Without the input of period stimulation, noise can enhance the coherence degree of output signals of neurons with membrane potential oscillation; this is autonomous SR(ASR). Until now ASR was testified only in model neurons, but actually model cell is too simple to identify to true neuron. Our study's aim is to investigate automatic SR in single neuron and noise' effect on the excitability of single neuron.Our laboratory accumulated lots of work about dorsal root ganglia's excitability for years. The data show that part of dorsal root ganglia (DRG) neurons discharged bursts and had subthreshold membrane potential oscillation (SMPO) following the injury. The proportion of neurons with SMPO in injured DRG is higher than those in normal DRG, the neurons with SMPO usually have a high excitability. DRG neurons are primary sensory neurons and are in a state full of both internal and external noise. Noise may affect the excitability of injured DRG neurons by the mechanism of ASR. In this study, we recorded neurons' excitability under pulse and ramp current with perforated patch-clamp in freshly isolated injured DRG neurons. Noise was generated by computer and attached to patch-clamp amplifier. The results are as follows:The first part: neurons was classified by neurons' responses to various stimulations; including the characteristics of firing frequency, SMPO, FAP rebound spike and the number of spikes.1. 36/40 large cells (d>40 m) and 11/105 medium cells (d=30-40 m) are type I. They show no SMPO, and seldom discharge except FAP (first action potential, AP initiated in the very beginning of pulse current stimulation).2. 4/40 large cells and 40/105 medium cells are type II. Underexcitatory stimulation, they exhibit regular and spindle SMPO, and discharge spike bursts. The number of spike is many, and the frequency is relatively stable. Cells show FAP under excitatory pulse and rebound AP under inhibitory pulse.3. 50/105 medium cells and 12/65 small cells (d<30um) are type III. Under excitatory stimulation, they exhibit damp or spindle SMPO, and discharge spike burst. Spike and SMPO occur only on the middle part of ramp and the beginning of pulse, and the frequency is relatively stable. Cells exhibit FAP under excitatory pulse and rebound AP under inhibitory pulse.4. 4/105 medium cells and 53/65 small cells are type IV. Under excitatory stimulation, they show irregular SMPO, and discharge non-bursting spikes. The frequency of spikes is sensitive to and dependent on membrane potential. Cells don't exhibit FAP under excitatory pulse and rebound AP under inhibitory pulse.The second part: investigating the effect of noise on the excitability of different...
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