Vasudeva G. Iyer

Administration of human chorionic gonadotropin affects sleep-wake phases and other associated behaviors in cycling female rats.

We investigated the possible effects of human chorionic gonadotropin (hCG) on sleep-wake phases and other associated behaviors controlled by the medial preoptic area, cerebral cortex and hippocampus. Chronic epidural electroencephalographic (EEG) and temporal muscle electromyographic (EMG) electrodes were placed in cycling female rats. After a week of recovery, rats were injected intraperitoneally at 3.00 pm on the day of proestrus with either saline or highly purified hCG or indomethacin or hCG plus indomethacin. Three hours after injection, EEG, EMG and behavioral activities were recorded for 3.5 h. The administration of hCG increased high and low amplitude sleep, resting phase and decreased active awake phase, walking, sniffing and chewing as compared to the controls. While the administration of indomethacin alone had no effect, coadministration inhibited hCG effects. Medial preoptic area, cerebral cortex and hippocampus contain immunostaining for LH/hCG receptors. The administration of hCG resulted in an increase of immunoreactive PGD2 and a decrease of PGE2 in median preoptic area, cerebral cortex and hippocampus as compared to the controls. In summary, hCG administration affects sleep-wake phases and other associated behaviors in rats which can collectively be described as decreased activity. These effects are probably mediated by increasing PGD2 and decreasing PGE2 in areas of brain which control these activities. The above findings may be relevant to pregnant women who experience decreased activity when hCG is present in the circulation and cerebrospinal fluid.

Audiogenic seizures following global ischemia induced by chest compression in Long-Evans rats

Transient global ischemia was used to produce a rat model of generalized tonic-clonic epilepsy. Controlled chest compression in ketamine-anesthesized Long-Evans rats produced transient global ischemia by mechanically preventing the heart from pumping blood. Circulation was restored by standard cardiopulmonary resuscitation techniques. With a temporal muscle (skull) temperature of 35 +/- 0.4 degrees C, 75% (76/102) of the rats survived 7 min of chest compression. Generalized seizures could be evoked in 78% (59/76) of the surviving rats by a 60 s exposure to a loud sound (bell, 110 dB) beginning 24 h after the ischemic episode. The seizure patterns seen resembled those described by Maresceaux (1987) for genetically seizure-prone Wistar rats. Susceptibility to sound-induced seizures declined with time, with wide variations in recovery rate between individuals; one rat showed a daily sound-induced seizure for over 5 months. Seizures were attenuated or blocked by treatment with carbamazepine or sodium valproate. This model is similar to the great vessel occlusion model used by Kawai et al. (1995), but is less invasive. We believe it will be useful in the evaluation of therapies for acquired generalized (grand mal) seizures.

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.

Fosphenytoin Reduces Hippocampal Neuronal Damage in Rat Following Transient Global Ischemia

Summary Fosphenytoin, a water-soluble disodium phosphate ester of phenytoin, is a phenytoin prodrug with similar anticonvulsant properties. In this study, we evaluated its neuroprotective properties in a cardiac arrest-induced global ischemia model. After 12 minute ischemia, Long-Evans hooded rats were resuscitated, given fosphenytoin (30 mg/kg, i.m.) or saline 5 minutes after the ischemic episode, and killed on day 7. Brains were removed, fixed, and vibratome sectioned to assess the numbers of normal appearing CAI pyramidal neurons and for immunohistological staining of glial fibrillary acidic protein (GFAP). After global ischemia, the number of hippocampal CA1 pyramidal neurons decreased significantly (from 14.33±1.73 to 2.19±0.16 per 100 μm2). Most hippocampal CA1 pyramidal neurons showed signs of injury and GFAP immunoreactivity of the region increased. With fosphenytoin treatment 5 min after ischemia, hippocampal CA1 pyramidal neurons remained at near control level (13.90±0.92), however, GFAP staining was not significantly changed. Our data, although indicating different neuronal and glial responses following fosphenytoin treatment, nevertheless, suggest that fosphenytoin is an effective neuroprotectant against ischemia-induced damage.

Cardiac arrest-induced global cerebral ischemia studied in vitro

The goal of the present study was to characterize the effects of chest compression-induced global cerebral ischemia on the hippocampal slice preparation. One of the characteristics of rats exposed to such cardiac arrest is a high susceptibility to sound-induced seizures. We tested audiogenic seizures as an in vivo indicator of ischemic cerebral damage and as a possible small animal model of epilepsy. The results of these tests were reported elsewhere. Long-Evans male rats (200-350 g) were subjected to 7 min of chest compression sufficient to stop the pumping action of the heart. The rats were then revived using cardiopulmonary resuscitation. Evaluation of cerebral damage following cardiac arrest and resuscitation was performed in vitro, by testing neuronal responses to electrical stimulation in hippocampal slices prepared from these animals. Sham control animals were used for comparisons. Twenty-one to 146 days after rats were chest-compressed, hippocampal slices were prepared. Sham control rats, anesthetized but not chest-compressed, were sacrificed one week later for preparation of slices. Rats in a second group exposed to 7-min chest compression, were sacrificed at different time intervals after their resuscitation (from 1 h to 7 days); hippocampal slices were prepared for electrophysiological analysis of neuronal damage. The results of these studies indicate that 3 weeks or longer after chest compression the evoked CA1 population spike amplitude in hippocampal slices was significantly attenuated; in 60% of these slices an epileptiform response was evoked. An increased proportion of slices prepared from rats 1 to 48 h after chest compression showed an augmentation in the amplitude of the evoked population spike; 72 h and up to 7 days after chest compression, an attenuation in the evoked CA1 population spike amplitude was observed, signaling delayed neuronal damage.

Experience with ketamine and sodium pentobarbital as anesthetics in a rat model of cardiac arrest and resuscitation

We review 7 years experience with the chest compression model of cardiac arrest and resuscitation, comparing two different anesthetics. Ketamine stimulates cardiac function and only mildly depresses respiration; of the two it provides easier resuscitation. However, ketamine severely depresses brain protein synthesis; in studies using this measure ketamine is unsuitable and another agent must be used. Sodium pentobarbital mildly depresses brain protein synthesis, but depresses both cardiac and respiratory function, making resuscitation more difficult. Use of alternate chest/abdominal pumping (Babbs resuscitation technique), with judicious use of intra-cardiac epinephrine (adrenaline), made resuscitation reliable under sodium pentobarbital as well.

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.

Average Evoked Potentials

In the decade of the 1980s, many clinical EEG laboratories have added average evoked potential studies to their routine procedures. Indeed, short-latency brain-stem auditory-evoked potentials, as well as short- and intermediate-latency cortical-evoked potentials, lately have proved to be valuable clinical tools for objectively testing afferent functions in patients with neurological and sensory disorders. This being the case, there is need for the EEG technician to become familiar with evoked-potential methods and to add a variety of new skills to his or her repertoire. At the same time, the person reading and interpreting the records will find it necessary to deal with concepts and techniques that are markedly different from those encountered in EEG interpretation.

Palmaris brevis sign in ulnar neuropathy

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.

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.