[Show abstract][Hide abstract] ABSTRACT: Noise can play a constructive role in the detection of weak signals in various kinds of peripheral receptors and neurons. What the mechanism underlying the effect of noise is remains unclear. Here, the perforated patch-clamp technique was used on isolated cells from chronic compression of the dorsal root ganglion (DRG) model. Our data provided new insight indicating that, under conditions without external signals, noise can enhance subthreshold oscillations, which was observed in a certain type of neurons with high-frequency (20-100 Hz) intrinsic resonance from injured DRG neurons. The occurrence of subthreshold oscillation considerably decreased the threshold potential for generating repetitive firing. The above effects of noise can be abolished by blocking the persistent sodium current (I(Na, P)). Utilizing a mathematical neuron model we further simulated the effect of noise on subthreshold oscillation and firing, and also found that noise can enhance the electrical activity through autonomous stochastic resonance. Accordingly, we propose a new concept of the effects of noise on neural intrinsic activity, which suggests that noise may be an important factor for modulating the excitability of neurons and generation of chronic pain signals.
[Show abstract][Hide abstract] ABSTRACT: Recent experimental and theoretical data indicate that the functional capabilities of axons with specialized structures are much more diverse than traditionally thought. However, few observations were concerned with the main axons without arborization. In the present study, electrical stimulation of the saphenous nerve at different frequencies (2, 5, 10, 20 Hz) was used to test the role of activity-dependent effects on the pattern of action potentials that propagate along individual unmyelinated fibers (C fibers) within the trunk of the saphenous nerve in rabbits. Three basic types of C fiber responses to repetitive stimulation were observed: type-1 fibers showed an entrained response without conduction failure; type-2 fibers discharged with intermittent conduction failures; while only sporadic conduction failures happened in type 3. The failure modality in type-2 and type-3 fibers is closely related to the conductive distance as well as the frequency and duration of stimuli which lead to a critical level of conduction velocity slowing. A novel fluctuation in interspike intervals was always observed immediately before the occurrence of the failures, implying that the fluctuation of conduction velocity is correlated with imminent failures. Both the 4-aminopyridine-sensitive potassium current and hyperpolarization-activated cation current were recognized to be involved in the regulation of conduction failure patterns. The results confirmed, at least in part, the existence of conduction failures in the main axon of C fibers, suggesting that axonal operations may also be determinants for adaptation phenomenon and information processing in peripheral nervous system.
[Show abstract][Hide abstract] ABSTRACT: Objective
To investigate the different suppressive effect of lidocaine on persistent Na+ current and transient Na+ current in injured or uninjured dorsal root ganglion neurons.Methods
Totally 23 SD rats were randomly divided into 2 groups; control group (n = 10) and chronically compressed DRG (dorsal root ganglion) group (CCD group, n = 13). Rats were anesthetized and DRG was isolated. Single DRG neuron was isolated by enzymatic disassociation method. Persistent Na+ current (INaP) and transient Na+ current (INaT) were elicited in voltage clamp mode.ResultsThe presence of INaP was testified in most DRG neurons (38/46 neurons in CCD group and 31/39 neurons in control group, P>0.05). However, the current density of INaP in CCD group (4.6 ± 0.6 pA/pF, n = 38 neurons) was greater than that in control group (2.5 ± 0.4 pA/pF, n = 31 neurons) (P<0.05). The characteristics of INaP was observed and found that INaP could be blocked by 0.2 μmol/L tetrodotoxin easily. Furthermore, the does-effect relationship of Iidocaine on INaP and INaT were also examined. INaP and INaT were suppressed by different concentrations of lidocaine, the range for INaP was 5-20 μmol/L and for INaT was 0.05-2 mmol/L.ConclusionINaP and INaT were suppressed by different concentrations of lidocaine. INaP was suppressed by very low concentration of lidocaine (5-20 μmol/L). However, INaT could only be blocked by high concentration of lidocaine (0.05-2 mmol/L).
Journal of Medical Colleges of PLA 12/2007; 22(6):325–328. DOI:10.1016/S1000-1948(08)60012-X