Analgesic effects of chemical lumbar sympathectomy on refractory pain in the lower limbs / 南方医科大学学报

<p><b>OBJECTIVE</b>To evaluate the effect of chemical lumbar sympathectomy (CLS) on relieving refractory pain in the lower limbs.</p><p><b>METHODS</b>Twenty-four patients with refractory pain in the lower limbs underwent CLS under X-ray guidance, and 2 ml contrast agent was injected at 1/3 of the second L2 vertebrae (the L2 sympathetic ganglion). Lidocaine was then injected followed by injection of 7% phenol for performing CLS. The visual analog scale was used to assess the pain severity before and after CLS. The effect of CLS on relieving lower limb pain was compared with that of oral pain-relieving medication.</p><p><b>RESULTS</b>The lower limb pain was obviously relieved as shown by significantly decreased VAS scores in these patients after CLS. CLS exhibited a much more potent effect of pain relief in the lower limbs than the oral medication.</p><p><b>CONCLUSION</b>CLS produces significant analgesic effects to relieve refractory pain in the lower limbs.</p>

Botulinum toxin type A does not affect spontaneous discharge but blocks sympathetic-sensory coupling in chronically compressed rat dorsal root ganglion neurons / 南方医科大学学报

<p><b>OBJECTIVE</b>To study the effect of botulinum toxin type A (BTXA) on spontaneous discharge and sympathetic- sensory coupling in chronically compressed dorsal root ganglion (DRG) neurons in rats.</p><p><b>METHODS</b>In chronically compressed rat DRG, spontaneous activities of the single fibers from DRG neurons were recorded and their changes observed after BTAX application on the damaged DGR. Sympathetic modulation of the spontaneous discharge from the compressed DRG neurons was observed by electric stimulation of the lumbar sympathetic trunk, and the changes in this effect were evaluated after intravenous BTXA injection in the rats.</p><p><b>RESULTS</b>Active spontaneous discharges were recorded in the injured DRG neurons, and 47 injured DRG neurons responded to Ca2+-free artificial cerebrospinal fluid but not to BTXA treatment. Sixty-four percent of the neurons in the injured DRG responded to sympathetic stimulation, and this response was blocked by intravenously injection of BTXA.</p><p><b>CONCLUSION</b>BTXA does not affect spontaneous activities of injured DRG neurons, but blocks sympathetic-sensory coupling in these neurons.</p>

Inhibiting effect of vagal nerve stimulation to seizures in epileptic process of rats / 神经科学通报·英文版

<p><b>OBJECTIVE</b>Our previous work suggested that sensitivity of hippocampal neurons is changed in process of epileptic activities, and closely parallel to the dynamic characteristic of epileptic activity of the neurons. This study investigated the sensitivity of epileptic brain to vagal nerve stimulation (VNS) in epileptic process.</p><p><b>METHODS</b>Epileptic model was evoked by penicillin. Left vagal nerves were stimulated to inhibit the seizures induced by penicillin. The electrocorticography (ECoG) and electromyography (EMG) were recorded to analyze inhibiting effect of VNS in epileptic process.</p><p><b>RESULTS</b>It was found that VNS could inhibit the seizures caused by penicillin, and the inhibiting effect of VNS to seizures increased as the vagal nerve stimulating time prolonged. It was also found that the inhibiting effect of VNS to seizures decreased in epileptic process.</p><p><b>CONCLUSION</b>The results suggested that the sensitivity of epileptic brain to VNS was different in epileptic process. The inhibiting effect of VNS to seizure decreased as the development of seizures.</p>

The sensitivity of neurons with non-periodic activity to sympathetic stimulation in rat injured dorsal root ganglion / 神经科学通报·英文版

Objective The relationship between firing pattern and sensitivity of neurons was studied in chronically compressed dorsal root ganglion (DRG) neurons and the Hindmarsh-Rose (HR) neuronal model. Methods Spontaneous activities from single fibers of chronically compressed DRG neurons in rats were recorded, and divided into periodic and non-periodic firing patterns. The sensitivity of the two kinds of firing pattern neuron to sympathetic stimulation (SS) was compared. Result It was found that 27.3% of periodic firing neurons and 93.2% of non-periodic firing neurons responded to SS respectively (periodic vs non-periodic, P < 0.01). The responses to SS with different stimulation time were greater non-periodic firing neurons than periodic firing neurons (P < 0.01). The non-periodic firing neurons obviously responded to SS. After the firing pattern of these neurons transformed to periodic firing pattern, their responses to SS disappeared or decreased obviously. The HR neuronal model exhibited a significantly greater response to perturbation in non-periodic (chaotic) firing pattern than in periodic firing pattern. Conclusion The non-periodic firing neurons with deterministic chaos are more sensitive to external stimuli than the periodic firing neurons.

Spontaneous discharge modulation by acetylcholine in chronically compressed rat dorsal root ganglion neurons / 南方医科大学学报

<p><b>OBJECTIVE</b>To study the effects of acetylcholine (ACh) on spontaneous discharges of compressed rat dorsal root ganglion (DRG) neurons.</p><p><b>METHODS</b>In chronically compressed DRG model, the spontaneous discharge of a single fiber from the DRG neuron in response to ACh treatment was recorded.</p><p><b>RESULTS</b>Active spontaneous discharges were recorded in the injured DRG, and 77.9% of the injured DRG neurons responded to Ach treatment in the manner of simple excitation, or excitation followed by inhibition. The responses were enhanced with the increase of Ach concentration.</p><p><b>CONCLUSION</b>Injured DRG remains active in spontaneous discharges, which can be significantly influenced by ACh treatment.</p>

Different firing patterns induced by veratridine and aconitine in injured dorsal root ganglion neurons / 生理学报

Ectopic spontaneous activity originated from the injured dorsal root ganglion (DRG) neurons in rats was recorded through single dorsal root fiber. The firing patterns induced by veratridine and aconitine, inhibitors of inactivation gate of sodium channel operating on different binding sites, were compared. In the same neuron, veratridine (1.5 approximately 5.0 micromol/L) caused slow wave oscillations of interspike intervals (ISIs), while aconitine (10 approximately 200 micromol/L) caused tonic firing. Moreover, even if the background firing patterns were various and the reagent concentrations used were different, veratridine and aconitine still induced slow wave oscillations and tonic firing patterns, respectively. The results suggest that veratridine and aconitine induce different firing patterns in injured DRG neurons, which may relate to their inhibitory effects on different binding sites of the sodium channel.

Visually guided patch-clamp recording of spinal dorsal horn neuron's postsynaptic current evoked by primary afferent fiber / 生理学报

The authors describe here the procedures for using the gelatin half-embedding method to obtain thin spinal cord slices with attached dorsal roots and performing visually guided whole-cell patch-clamp recording of postsynaptic currents evoked by primary afferent fibers in rat spinal dorsal horn. A segment of spinal cord with attached dorsal roots was prepared and half-embedded in an agar block with 20% (w/v) gelatin. Thin spinal cord slices with attached dorsal roots were obtained with a vibratome and whole-cell patch-clamp configuration was established under the infrared observation. At the holding potential of -70 mV, spontaneous excitatory postsynaptic currents (EPSCs) and dorsal root stimulation-evoked EPSCs were recorded as inward currents. According to the conduction velocity of afferent fibers and stimulus threshold, evoked EPSCs that are mediated by A-like or C-like fibers were distinguished. At the holding potential of 0 mV, spontaneous inhibitory postsynaptic currents (IPSCs) and dorsal root stimulation-evoked IPSCs were recorded as outward currents. Using 5 micromol/L strychnine or 20 micromol/L bicuculline, GABAergic or glycinergic evoked IPSCs could be isolated. Using visual patch-clamp method synaptic transmission can be accurately assessed by measuring postsynaptic currents of the dorsal horn neurons. More importantly, with the aid of infrared observation, the incidence of failure to establish a clamp configuration can be greatly reduced and it becomes easier to make recordings from the neurons in deep dorsal horn laminae. Thus, the present research approach an effective approach to study the modulation of primary afferent synaptic transmission.

Effect of bradykinin on the sodium channel current in dorsal root ganglion neuron / 中国应用生理学杂志

<p><b>AIM</b>To investigate the effects of bradykinin on voltage-dependent sodium channel currents in rat dorsal root ganglion neurons (DRG).</p><p><b>METHODS</b>Whole-cell patch clamp technique was used to determine sodium channel current.</p><p><b>RESULTS</b>Bradykinin at 0.01 - 10.0 micromol/L dose dependently increased the frequency of repetitive firing of DRG. Bradykinin at 0.01 - 10.0 micromol/L dose dependently enhanced the TTX-R sodium current, and had no effect on TTX-S sodium current.</p><p><b>CONCLUSION</b>Mechanism underlying the inflammation induced by bradykinin is related to the TTX-R sodium channel.</p>

The role of vagal innervation in the variability of heart beat / 生理学报

To determine the role of vagi in heart rate variability, conscious rabbits were employed and electrocardiogram was recorded under conditions of bilateral vagi intact, unilateral vagotomy, and bilateral vagotomy. The variability of RR intervals (RRI) was analyzed using power spectrum and approximate entropy (ApEn). The results showed that the values of high frequency power (HF) component, low frequency power (LF) component and ApEn in animals with bilateral vagi intact were the highest, but the LF/HF ratio was the lowest; unilateral vagotomy decreased ApEn, right vagotomy increased LF/HF ratio but left vagotomy did not; the LF/HF ratio increased while ApEn decreased significantly in animals with bilateral vagotomy. It is suggested that the variability of RRI is mainly regulated by the vagi and the role of right vagi is more important than that of the left. When measuring heart rate variability, the results obtained with conventional method are consistent with those with nonlinear method.

Triggered oscillations in type A dorsal root ganglion neurons induced by veratridine / 生理学报

Veratridine, a blocker of inactive gate of sodium channel, was used to perfuse L5 dorsal root ganglion (DRG) topically. Afferent activities of type A single fiber from these DRGs were recorded. It was found that after a 10-min bath of veratridine (1.8-3 micromol/L), some of the primary silent DRG neurons were triggered by touch or pressure on the receptive fields or by electrical stimulation of the sciatic nerve to produce high-frequency firing, which was termed triggered oscillation presenting a U-type of interspike intervals (ISI) or other types of oscillations. The longer the intervals between stimulating pulses, the more stimulating pulses were needed to trigger the oscillation. The oscillation, triggered by electric stimuli with different duration or patterns, had no significant difference in their patterns. The duration of the inhibitory period after a triggered oscillation was generally 30-90 s. It was also observed that this kind of triggered oscillation was induced by afferent pulses of the same neurons. These results suggest that triggered oscillation, which may contribute to the fit of triggered pain, can be produced in primary sensory neurons after application of veratridine.

Three types of induced bursting rhythm in rat injured nerves / 生理学报

Firing patterns of injured nerve fibers were recorded using the single-fiber firing recording technique. Under the same background firing pattern, three types of bursting were induced separately by EGTA, veratridine or high [Ca(2+)](o) in the same type of nerve fibers. The results suggest that different firing patterns are related to different stimuli, which means that each firing pattern carries corresponding neural information.