| Time series of discharge in neurons, that is, interspike interval (IS I) series of action potential is considered to contain plenty of sensory information. However, there is little understanding of basic type and generating mechanism of this time coding because of the complexity of ISI series. The frequency and pattern of discharge of dorsal root ganglion (DRG), which is considered as the forst stage of the sensory pathway, play an important role in determining the property and intensity of sensory. It is evidenced that ectopic spontaneous activities in injured DRG are the signal source of spontaneous pain and hyperalgesia. Latest research also find that the type of this discharge series is related to the distribution of sodium channel and its activity change. However, the role of inactivation gate of sodium channel is not clear. In present study, single fibre recording in vivo from dorsal root on chronically compressed DRG model was used. We analyzed the characters of ISI series of oscillation firing of type A neurons induced by veratridine, an inhibitor of inactivation gate of sodium channel. So we can establish a basis for understanding the relationship between the inactivation gate of sodium channel and the firing pattern, so as to explore the relationship between the firing pattern and pain.Results1. Injured DRG neurons have many firing patterns. According to the nonlinear dynamical features of ISI series, the firing pattern can be described as: (1) Periodic firing pattern, which was characterized by repeated appearance of ISI at regular interval. (2) Bursting firing pattern, which was characterized by bursting interrupted by silent periods. ISIs of the action potential during the bursts were confined to a banding area. The intervals between bursts were often irregular. (3) Irregular firing pattern, its scatter map of ISI series displayed a random-like distribution. (4) Integer multiple firing pattern, in which a basic ISI existed and other ISIs were concentrated at about integer multiples of the basic ISI.2. hi some of the neurons with spontaneous activities, veratridine can transform ISI series to oscillation type. This ISI series oscillation has following characters: (1) long term cycle duration, whose duration of most oscillations ranged from 3 0-120ms, so we called it slow wave oscillation; (2) large amplitude of oscillation, the minimum ISI is about 2ms while the maximum is beyond 40ms, which suggested that the firing frequency vary from several tens to hundred Hz; (3) abrupt turn always occurs during the continuous change in ISI, this turn is called inflexion temporarily.3. According to the shape of ISI scatter map, ISI slow wave oscillation can be divided into 5 basic types: V, reversal H, integer multiple, diffusive and compound patterns. V pattern (53.9%), its ISIs varied continuously from big to small, then from small to big and form a gently inflexion in the trough. Reversal n pattern (25. 6%), its downtrend and uptrend were steep and its ISIs had two significant inflexion hi the trough. Integer multiple pattern (7.7%), its ISIs showed clear layered structure. There existed a basic ISI and other ISIs were concentrated at about integer multiples of the basic ISI. Diffusive pattern (6.4%), its ISIs changed irregularly and displayed a random-like and diffusive distribution. Compound pattern (6.4%), its scatter map of ISI series displayedtwo or more oscillation patterns.4. After the bath in 1.8-3 U mol/L veratridine, touch or pressure on the L5 receptive fields could trigger some primary silent DRG neurons to produce high-frequency firing, termed triggered oscillation, whose interspike intervals (ISI) showed U-type or other types of oscillations. Triggered oscillation was recorded in 39 neurons out of 481 neurons. The latency of this oscillation was 5-47ms. Its duration was 7-80s. The minimum of ISI in oscillation trough was 2-20ms, that is, the firing frequency was 50-500Hz.5. Stimulating sciatic nerve can induce triggered oscillation on some silen...
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