| Peripheral nerve injury induced by mechanical trauma, ischemia, metabolic abnormality or local inflammation can lead to chronic pain symptoms, including hyperalgesia, allodynia, spontaneous pain and paraesthesia. The sciatic nerve and low back pain are often ascribed to chronic compression of the dorsal root ganglion (DRG) or its spinal root by herniated intervertebral disc, spur hyperplasia or stenosis of intervertebral foramen.. The receptive field, which is involved in this process, often has a pain sensitive area. In this case, the excitability of injured neurons within DRG, which is considered as the first stage of the sensory pathway, enhance abnormally, and that neurons become hyperexcitable. Experiments have documented a variety of changes occurring in injured hyperexcitable neurons, comprising of reduction of the spike rheobase, accommodation, initiation of spontaneous discharges, increase of peak sodium current and development of abnormal sympathetic sensitivity. Thus injured DRG neurons become the pacemaker of neuropatbic pain. So, alleviating neuropathic pain has focused on bow to suppress the hyperexcitability of these neurons. However, the essence of hyperexcitabiity and its molecular and channel mechanism are still not very clear, limiting the execution of the treatment for the chronic pain. The hyperexcitable specimens were studied in the neurons of chronically compressed DRG using intracellular recording in vivo. Through the systemic detection of hyperexcitability, we aim to elucidate the basic 4 electrophysio logical change and it抯 sodium channel mechanism. This will not only gain an insight into the essence of hyperexcitability but also help to make clear of the reason of why the pacemaker of chronic pain formed. So can supply a new therapy strategy for chronic pain. Results 1. Various firing patterns produced in injured DRG neurons According to the nonlinear dynamical features of the interspike interval (151) series, the firing pattern can be described as Periodic firing pattern, which was characterized by repeated appearance of 151 at regular interval, 25% of the total spontaneous discharge neurons fell into this category. <2> Nonperiodic firing pattern (35%), its scatter map of 151 series displayed a random-like distribution. <3>Bursting firing pattern (34%), which was characterized by bursts interrupted by silent periods. The ISIs of the action potential during the bursts were confined to a banding area. The intervals between bursts were often irregular. <4>Lnteger multiples firing pattern (6%), in which a basic ISI existed and other ISIs were concentrated at about integer multiples of the basic 151. 2. Subthreshold membrane potential oscillations (SMPOs) emerged from injured DRG neurons. A significantly higher presence (97/650, 14.90/o) of SMPOs was detected in the injured DRG neurons comparing to that of normal DRG A-type neurons (1/65, 1.5%). Three patterns of SMPOs were observed: regular, spindle-like and irregular. 3. The excitability of DRG neurons with SMPO enhanced evidently. The rheobase of neurons with SMPO in injured DRG was 0.9 ?0.lnA and that of neurons without SMPO was 2.2 ?0.4nA. They were lower, on average, than that of neurons in normal DRG (3.6 ?0.9nA). Accommodation was also used to qu...
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