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Use of In Vivo Single-fiber Recording and Intact Dorsal Root Ganglion with Attached Sciatic Nerve to Examine the Mechanism of Conduction Failure

Single-fiber recording has been a classical and effective electrophysiological technique over the last few decades because of its specific application for ...

Fourth Military Medical University

Intrinsic resonant frequency properties of neurons in the brain provide a basis for different behavioral states and determine the responding modality (i.e. excitability) of different neurons. Previously, three types of excitability behaviors in rat Mesencephalic V neurons were found. To investigate the different resonant frequency and ionic current mechanisms underlying different resonances among three types of excitability, we performed whole-cell patch recordings and applied ZAP current on Mesencephalic V cells (N=70) in rat slices. The results show that: Class 2 neurons (30/30) have two resonances with U-shaped voltage dependence. One is a high frequency resonance (75.4 ± 2.11 Hz) significant at depolarized potentials (about -50 mV) and the other is a low frequency resonance (5.46 ± 0.31 Hz) significant at hyperpolarized potentials (about -70 mV). Voltage clamp experiments reveal two non-inactivating currents operating in the subthreshold voltage range: (1) 4-aminopyridine sensitive K(+) current, which activates at membrane potentials positive than -60 mV and was blocked by 4-AP (50 µM), was underlying the high frequency resonance of Class 2 neuron; (2) h-current, which activates negative than -60mV and was blocked by the hyperpolarization-activated cyclic nucleotide-gated channel blocker ZD7288 (10 µM), was underlying the low frequency resonance. Class 1 neurons do not show voltage-dependence resonant behaviors (10/10). Class 3 neurons (23/30) have two resonances, which are similar with Class 2 in both resonant frequency and currents. Our results provide clear evidence for the existence of multiple kinds of frequency resonances and how the relationship between the resonant frequency and the ionic current is based in Mesencephalic V neurons.

Resonance characteristic and its ionic basis of rat mesencephalic trigeminal neurons.

The dorsal striatum plays a key role in motor control and cognitive processes. Proper functioning of the striatum relies on the fine dynamic balance between the direct pathway projection medium spiny neurons (MSNs) that express D1 dopamine receptor (D1 MSNs) and indirect pathway projection MSNs that express D2 dopamine receptor (D2 MSNs). The inwardly rectifying K(+) channels (Kir), which express on both D1 and D2 MSNs, participate in the subthreshold dynamics including the membrane resonance and dendritic integration. However, it remains unclear whether dopamine differentially regulates Kir mediated subthreshold dynamics in two subtypes MSNs. Using transgenic mice that express either tdTomato in D1 MSNs or eGFP in D2 MSNs, we explored the Kir mediated subthreshold dynamics in D1 or D2 MSNs with whole cell patch clamp recording in acute brain slices. We found that D1 receptor agonist increased the Kir current while D2 receptor activation decreased the Kir conductance. The dopamine regulation of the Kir enhanced the resonant frequency and reduced the resonant impedance of D1 MSNs. The converse is ture for D2 MSNs. It also caused an opposing effect on dendritic integration between D1 and D2 MSNs, which can promote stability of the two pathways. The D1 receptor activation modulated Kir through cAMP-PKA signaling, whereas the D2 receptor modulated Kir through PLC-PKC signaling. Our findings demonstrated the differential dopaminergic regulation role of Kir, which mediates distinct subthreshold dynamics, and thus, contributes to the role of dopamine in fine tuning the balance of the striatal direct and indirect pathway activities.

Differential dopaminergic regulation of inwardly rectifying potassium channel mediated subthreshold dynamics in striatal medium spiny neurons.

Although conduction failure has been observed in nociceptive C-fibers, little is known regarding its significance or therapeutic potential. In a previous study, we demonstrated that C-fiber conduction failure, which is regarded as an intrinsic self-inhibition mechanism, was reduced in circumstances of painful diabetic neuropathy. In this study, we extend this finding in the complete Freund's adjuvant model of inflammatory pain and validate that the degree of conduction failure decreased and led to a greater amount of pain signals conveyed to the central nervous system. In complete Freund's adjuvant-injected animals, conduction failure occurred in a C-fiber-selective, activity-dependent manner and was associated with an increase in the rising slope of the C-fiber after-hyperpolarization potential. To target conduction failure in a therapeutic modality, we used ZD7288, an antagonist of hyperpolarization-activated, cyclic nucleotide-modulated channels which are activated by hyperpolarization and play a pivotal role in both inflammatory and neuropathic pain. ZD7288 promoted conduction failure by suppressing Ih as a mechanism to reduce the rising slope of the after-hyperpolarization potential. Moreover, perineuronal injection of ZD7288 inhibited abnormal mechanical allodynia and thermal hyperalgesia without affecting motor function or heart rate. Our data highlight the analgesic potential of local ZD7288 application and identify conduction failure as a novel target for analgesic therapeutic development.

A novel intrinsic analgesic mechanism: the enhancement of the conduction failure along polymodal nociceptive C-fibers.

To explore the combined effects of environmental radio-frequency (RF) field and X-ray, mouse spermatocyte-derived (GC-1) cells were exposed to 1950 MHz RF field at specific absorption rate (SAR) of 3 W/kg for 24 h combined with or without X-ray irradiation at 6 Gy. After treatment, the cell proliferation level was determined by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) Assay and 5-Bromo-2-deoxy Uridine (BrdU) enzyme linked immunosorbent (ELISA) Assay. The apoptosis level was detected by annexin V flow cytometry assay, transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) Assay and Caspase-3 Activity Assay. It was found that the proliferation and apoptosis level did not change in GC-1 cells after RF exposure alone. However, compared with the X-ray group, the proliferation level significantly decreased and the apoptotic rate significantly increased in the RF+X-ray group. Moreover, a significant decrease in Bcl-2 protein expression and increase in Bax protein expression were observed. The findings suggested that RF exposure at SAR of 3 W/kg did not affect apoptosis and proliferation in GC-1 cells by itself, but that it did enhance the effects of X-ray induced proliferation inhibition and apoptosis, in which B-cell lymphoma-2 (Bcl-2) and Bcl-2 associated X protein (Bax) might be involved.

Enhancement of X-ray Induced Apoptosis by Mobile Phone-Like Radio-Frequency Electromagnetic Fields in Mouse Spermatocyte-Derived Cells.

The olfactory circuitry in mice involves a well-characterized, vertical receptor type-specific organization, but the localized inhibitory effect from granule cells on action potentials that propagate laterally in secondary dendrites of mitral cell remains open to debate. To understand the functional dynamics of the lateral (horizontal) circuits, we analyzed odor-induced signaling using transgenic mice expressing a genetically encoded Ca indicator specifically in mitral/tufted and some juxtaglomerular cells. Optical imaging of the dorsal olfactory bulb (dOB) revealed specific patterns of glomerular activation in response to odor presentation or direct electric stimulation of the olfactory nerve (ON). Application of a mixture of ionotropic and metabotropic glutamate receptor antagonists onto the exposed dOB completely abolished the responses to direct stimulation of the ON as well as discrete odor-evoked glomerular responses patterns, while a spatially more widespread response component increased and expanded into previously nonresponsive regions. To test whether the widespread odor response component represented signal propagation along mitral cell secondary dendrites, an NMDA receptor antagonist alone was applied to the dOB and was found to also increase and expand odor-evoked response patterns. Finally, with dOB excitatory synaptic transmission completely blocked, application of 1 mM muscimol (a GABA receptor agonist) to a circumscribed volume in the deep external plexiform layer (EPL) induced an odor non-responsive area. These results indicate that odor stimulation can activate olfactory reciprocal synapses and control lateral interactions among olfactory glomerular modules along a wide range of mitral cell secondary dendrites by modulating the inhibitory effect from granule cells.

Blocking of Dendrodendritic Inhibition Unleashes Widely Spread Lateral Propagation of Odor-evoked Activity in the Mouse Olfactory Bulb.

Transcranial direct current stimulation (tDCS) is a noninvasive neural control technology that has become a research hotspot. To facilitate further research of tDCS, the biosafety of 500 μA cathodal tDCS, a controversial parameter in rats was evaluated.

Junling Xing

Department of Neurobiology,
School of Basic Medicine,
Department of Radiation Biology,
Faculty of Preventive Medicine,
Department of Neurobiology, School of Basic Medicine,
Department of Radiation Biology, Faculty of Preventive Medicine

Fourth Military Medical University

Use of In Vivo Single-fiber Recording and Intact Dorsal Root Ganglion with Attached Sciatic Nerve to Examine the Mechanism of Conduction Failure