Biomedical subjects

V G Iyer

Publications and source records attributed to V G Iyer.

10 recordsLinked to original sources

PubMed2000

Agents which block potassium-chloride cotransport prevent sound-triggered seizures in post-ischemic audiogenic seizure-prone rats.

The purpose of this study was to determine whether the loop diuretics furosemide, bumetanide and ethacrynic acid, which block the KCC1 potassium-chloride transporter in the kidney loop of Henle and the KCC2 potassium-chloride transporter in neuronal membranes, would prevent sound-triggered seizures in post-ischemic audiogenic seizure-prone rats. The rats were infused with the test agent via tail vein shortly before being tested for seizure susceptibility by exposure to loud noise (an alarm bell) for 60 s. Sound exposures were repeated at intervals to determine the time course of the seizure suppression effect. All three loop diuretics suppressed sound-triggered seizures in post-ischemic rats tested 2 days to 4 weeks after the ischemic exposure. Furosemide 200 mg/kg had no effect in 4/4 rats made acutely audiogenic seizure-prone by infusion of bicuculline into the inferior colliculus, indicating that the effect was not due to general anti-seizure activity. Mannitol 2 g/kg had no effect in 6/6 post-ischemic rats, indicating that the effect was not due to diuresis or fluid shifts. These results are consistent with the hypothesis that the exposure to global ischemia caused an upregulation of the potassium-chloride transporter KCC2 in neurons which persisted for at least 4 weeks.

Acoustic Stimulation↗

PubMed1998

Palmaris brevis sign in ulnar neuropathy 1998.

A case of ulnar neuropathy, selectively affecting the deep branch and showing positive palmaris brevis sign, is reported. The palmaris brevis muscle was not only intact, but also showed excessive cocontraction with abductor digiti minimi. Palmaris brevis sign, when present, is useful in clinically localizing the site of the ulnar nerve lesion.

Accidental Falls↗

PubMed1998

Changes in brainstem auditory evoked response latency predict survival after CPR in a rat model of cardiac arrest and resuscitation.

Brainstem auditory evoked responses (BAER) are routinely used to monitor brainstem function in hospitalized comatose patients. We used a rat model of cardiac arrest and resuscitation to explore the possibility that the BAER, monitored during and immediately after cardiopulmonary resuscitation (CPR), could be used to determine whether the CPR was effective in restoring brainstem blood flow. Long-Evans rats were subjected to 7 min of cardiac arrest, induced by chest compression under Ketamine anesthesia sufficient to mechanically prevent the heart from pumping blood and were then resuscitated using a standard CPR protocol. During CPR, click stimuli were applied to one ear at 11/s and BAER averages recorded every 15 s. In three rats the BAER did not return after CPR; none of these rats respired spontaneously and all died. In 33 rats the BAER did return; within 15 min after the start of CPR BAER peak latencies decreased rapidly, increased again and then decreased. If the increase in the latency of the N2 peak was less than 0.3 ms, then the rat survived. If it was greater than 0.35 ms the rat died. This signal was used as a cue for intervention in three rats; two survived. Thus, in this preparation, the BAER provided a useful measure of CPR effectiveness, in time to permit successful intervention.

Animals↗

PubMed1998

Carbon dioxide narcosis-induced apnea in a rat model of cardiac arrest and resuscitation.

In the clinical literature there are reports of patients failing to breathe and becoming comatose when supplied with 100% oxygen for respiratory distress. This effect has been attributed to a loss of respiratory drive. Recent studies have established that this explanation is incorrect, but have left the phenomenon unexplained. We propose that the apnea and coma reported is due to carbon dioxide narcosis. We have reproduced this effect in an animal model and have documented PCO2 values in excess of 250 mmHg during the apneic period. Our results suggest that this level of PCO2 suppresses both brainstem auditory evoked potentials and spontaneous respiration. The high PCO2 is due to inadequate gas exchange, and is easily remedied by provision of adequate ventilation.

Animals↗

PubMed1997

Fos-like immunoreactivity in rat hippocampal neurons following transient global ischemia.

Immediate early genes are expressed following ischemia in many tissues including the brain. Using a chest compression global ischemia model that produced delayed neuronal degeneration in surviving rats, we examined the hippocampal Fos response to ischemia/reperfusion by immunohistochemistry and electron microscopy. Immunostained nuclei were seen in a few CA1 pyramidal cells 1-3 h after reperfusion while the entire dentate granular cell population was immunoreactive. By electron microscopy, subcellular Fos-like immunoreactive sites were found both in the cell nuclei and on segments of endoplasmic reticulum. These findings indicate that transient global ischemia differentially affects the early response genes in neurons of the hippocampal subfields and that such difference may be related to the adult neuroplasticity of the brain.

Animals↗

PubMed1995

Early, but not late, antiepileptic treatment reduces relapse of sound-induced seizures in the post-ischemic rat.

Global ischemia was used to induce a sensitivity to sound-triggered generalized seizures in 24 male Long-Evans rats. All showed a generalized seizure when exposed to a 108 dB bell for 1 min. They were assigned randomly to 3 groups of 8, and received 30 additional sound exposures. The early treatment group was injected with valproate (200 mg/kg i.p) 1 h prior to each of the first 10 sound exposures. The late treatment group received the same treatment during the second set of 10 sound exposures after 10 sound exposures without treatment. The third group was untreated. Both early and late treated groups had a significant reduction in seizure incidence during the treatment period, i.e. both groups showed seizure control. However, in the late group seizures returned promptly when valproate treatment was discontinued, while the early group showed a sustained reduction in seizure susceptibility. Since this outcome corresponds to seizure remission, the findings of this study favor early treatment.

Acoustic Stimulation↗

PubMed1993

Understanding nerve conduction and electromyographic studies.

Electromyography has become an integral part of evaluation of disorders of the peripheral nervous system. This article reviews the principles, methodology, indications, and pitfalls of nerve conduction velocity and needle electromyographic studies. Normal patterns are described, and the significance of abnormal patterns is discussed. The value of different electrophysiologic tests in the assessment of nerve trauma, in entrapment neuropathy, and during peripheral nerve surgery is also addressed.

Action Potentials↗

PubMed1989

Isolated injection injury to the posterior femoral cutaneous nerve.

The sciatic nerve is by far the most common nerve accidentally injured during intramuscular injection. Despite its close proximity to the sciatic nerve, however, injury to the posterior femoral cutaneous nerve is apparently quite rare. In this report, clinical features of a patient with isolated injection injury to the posterior femoral cutaneous nerve are described.

Humans↗

PubMed1988

Localized hypertrophic mononeuropathy involving the tibial nerve.

Localized hypertrophic neuropathy (LHN) is a disorder of unknown cause that presents with progressive, predominantly motor weakness in the distribution of a single nerve, with the histological appearance of the "onion bulb" formation. Because of its rarity, the condition is often ignored in the differential diagnosis of mononeuropathy. We report a case of LHN involving the posterior tibial nerve and review the literature.

Adult↗

PubMed1981

Ionic conductance and experimentally induced myotonia.

Experiments were conducted to study the effect of altering external potassium on in vitro induction of myotonia in rat diaphragm using 2,4-dichlorophenoxy acetate (2,4-D). An increase in external potassium inhibited, while a decrease enhanced, the myotonic response. However, in preparations which have undergone prior denervation, there was no myotonic response to 2,4-D, even when the external potassium was lowered. The experiments also support the existence of neural factors influencing the resting ionic conductance of the muscle membrane.

2,4-Dichlorophenoxyacetic Acid↗