Biomedical subjects

S Verma-Ahuja

Publications and source records attributed to S Verma-Ahuja.

5 recordsLinked to original sources

PubMed2004

Intraoperative human vagus nerve compound action potentials.

OBJECTIVE: Although electrical stimulation of vagus nerve is used widely for treatment of epilepsy the electrophysiological properties of human vagus nerve are not well characterized. Our objective was to measure compound action potentials of human vagus nerve fiber groups intraoperatively by stimulation using a commercially available generator and electrode system (Neurocybernetic Prosthesis System, NCP). MATERIAL AND METHODS: During NCP implantation we recorded compound action potentials evoked by stimulating the left vagus nerve through the NCP bipolar lead. Current intensities were varied from 0.25 to 3.0 mA. RESULTS: Vagus nerve compound action potential components conducting in the A, Adelta, and C velocity ranges could be elicited using either the NCP pulse generator or by a standard evoked potential instrument. A fiber potentials were recordable in all nerves, and were activated by very low stimulus currents. Adelta and C fibers were less reliably elicited, with C fibers requiring the highest currents. CONCLUSIONS: Three clearly identified fiber populations can be identified using therapeutic electrical stimulation of the human vagus. Intraoperative measurements of NCP-induced action potentials may potentially provide a marker for therapeutic stimulation and better insight into mechanisms of vagus nerve stimulation (VNS) efficacy.

Action Potentials↗

PubMed2000

Delayed effects of pyridostigmine and exercise training on acetylcholinesterase and muscle tension in mouse lower extremity.

In this study, the interactive effects of pyridostigmine, a pretreatment drug against nerve agents, and exercise training on muscle tension were investigated in the mouse lower extremity anterior muscular compartment by dorsiflexion of the foot with stimulation of the peroneal nerve. Acetylcholinesterase (AChE), lipid peroxidation (in terms of the end-product malondialdehyde, MDA) and creatine phosphokinase (CPK) activity in the muscle were correlated with muscle tension. Male NIH Swiss mice were divided into four groups and treated as follows: (1) sedentary control; (2) pyridostigmine (1.2 mg/kg orally) daily for the 5th and 6th weeks; (3) exercise training for 10 weeks; and (4) pyridostigmine plus exercise training for 10 weeks. Experiments on muscle tension were conducted 4 weeks after the last dose of pyridostigmine or saline and 24 h after exercise. The muscle tension was measured in right and left legs using a tension transduction device connected to a polygraph. After muscle tension recording, mice were killed, blood and triceps muscle were isolated, and plasma CPK and muscle AChE activities, and MDA were determined. There was a significant increase in the muscle tension (P<0.05) in the group treated with pyridostigmine plus exercise as compared to the control and exercise groups. The pyridostigmine plus exercise group also showed a significant reduction in AChE activity (P<0.01) and enhanced MDA (P<0.05) in the triceps muscle. These results suggest that subchronic dosages of pyridostigmine and interaction with exercise training result in the delayed effects of reduction in muscle AChE activity and enhanced muscle tension.

Acetylcholinesterase↗

PubMed1998

Evidence of increased excitability in GEPR hippocampus preceding development of seizure susceptibility.

The genetically epilepsy-prone rat (GEPR) provides a valuable model to study the mechanism of neonatal seizure susceptibility because seizure predisposition in GEPRs is determined by factors present from birth. We have previously shown that reduced afterhyperpolarization (AHP), reduced spike frequency adaptation and increased excitation with repetitive stimulation are present in the adult GEPRs. To investigate whether these abnormalities are present at birth or appear at the time when GEPRs show seizure susceptibility and to elucidate whether these abnormalities were a consequence of seizure experience (the adult rats previously tested were induced to seize in three tests), we studied the membrane and synaptic properties of CA3 hippocampal neurons in preseizing offspring of GEPR-9s (seizure naive GEPRs). Electrophysiological recordings were done in the in vitro brain slice preparation during three different stages of early postnatal development (postnatal day (P) 7-10, P12-15 and P18-28) in GEPRs and compared to age matched control Sprague-Dawley (SD) rats. Reduction in AHP amplitude and duration and reduced inhibitory post synaptic potentials (IPSPs) were observed in the CA3 region in all the three stages tested. Reduction in spike frequency adaptation in 40% of CA3 neurons and reduction in fast AHP occurred in the 3rd and 4th weeks of postnatal development in GEPRs. Therefore, our results suggest that reduced synaptic inhibition and increased membrane excitability in the CA3 circuitry are present from early postnatal development and may represent few of the general cortical features that might eventually contribute to development of enhanced seizure susceptibility in developing GEPRs.

Action Potentials↗

PubMed1995

Evidence for decreased calcium dependent potassium conductance in hippocampal CA3 neurons of genetically epilepsy-prone rats.

The genetically epilepsy-prone rat (GEPR) has become an important model to study genetic predisposition to epilepsy involving not only the brainstem but also forebrain structures. Previous work in CA1 hippocampal cells showed a reduction in spike frequency adaptation and only subtle changes in slow afterhyperpolarization (AHP). As important differences exist in calcium dependent potentials in the CA1 and CA3 hippocampal cells, we compared the membrane properties of hippocampal CA3 cells in GEPRs and Sprague-Dawley (SD) rats. There was no significant difference in the resting membrane potential, input resistance, charging time constant or rheobase between GEPRs and SD rat neurons. The action potential amplitude and the width at half maximal amplitude did not differ. A marked reduction in spike frequency adaptation accompanied by a very significant reduction in AHP was seen in the GEPR rats. Since calcium dependent potassium conductance produces both spike frequency adaptation and AHP, our results suggest that this conductance is reduced in the GEPR CA3 neurons.

Animals↗

PubMed1994

Hippocampal CA1 neuronal properties in genetically epilepsy-prone rats: evidence for increased excitation.

The genetically epilepsy prone rats (GEPRs) are abnormally susceptible to seizures with a variety of treatments and can be used as a model to study generalized seizure predisposition involving the brainstem and forebrain structures. We investigated the basic membrane and synaptic properties of hippocampal CA1 cells in Sprague-Dawley (SD) rats and GEPRs. Several differences in cellular properties were observed in the GEPRs. These include an increase in membrane input resistance and reduced spike frequency adaptation in the majority of GEPR cells. A decrease in the amount of current required to elicit a 5-mV EPSP was observed in the GEPR. A marked increase in excitability with paired pulse stimulation was also observed in GEPRs both in extracellular population spikes and intracellular EPSPs. Applying bicuculline, a GABAA antagonist, markedly increased paired pulse facilitation of the population spike in SD rats but in GEPRs produced only a minimal effect on facilitation. This difference suggests reduced GABAA-mediated inhibition in GEPR hippocampus with paired pulse stimulation. Several factors could interact or act independently to produce these effects because the epileptic phenotype in GEPRs is regulated by multiple genes.

Acoustic Stimulation↗