Delayed transient ischemic attacks kill some CA1 neurons previously salvaged with postischemic hypothermia: neuroprotection undone

Neuroprotective effects of the AMPA antagonist PNQX in oxygen-glucose deprivation in mouse hippocampal slice cultures and global cerebral ischemia in gerbils

PNQX (9-methyl-amino-6-nitro-hexahydro-benzo(F)quinoxalinedione) is a selective AMPA antagonist with demonstrated neuroprotective effects in focal ischemia in rats. Here we report corresponding effects in mouse hippocampal slice cultures subjected to oxygen and glucose deprivation (OGD) and in transient global cerebral ischemia in gerbils. For in vitro studies, hippocampal slice cultures derived from 7-day-old mice and grown for 14 days, were submersed in oxygen-glucose deprived medium for 30 min and exposed to PNQX for 24 h, starting together with OGD, immediately after OGD, or 2 h after OGD. For comparison, other cultures were exposed to the NMDA antagonist MK-801 using the same protocol. Both PNQX and MK-801 displayed significant neuroprotective effects in all hippocampal subfields when present during and after OGD. When added just after OGD, only PNQX retained some neuroprotective effect. When added 2 h after OGD neither PNQX nor MK-801 had an effect. Transient global cerebral ischemia was induced in Mongolian gerbils by occlusion of both common carotid arteries for 4.5 min, with PNQX (10 mg/kg) being injected i.p. 30, 60 and 90 min after the insult. Subsequent analysis of brain sections stained for the neurodegeneration marker Fluoro-Jade B and immunostained for the astroglial marker glial fibrillary acidic protein revealed a significant PNQX-induced decrease in neuronal cell death and astroglial activation. We conclude that, PNQX provided neuroprotection against both global cerebral ischemia in gerbils in vivo and oxygen-glucose deprivation in mouse hippocampal slice cultures.

Combined use of a cytoprotectant and rehabilitation therapy after severe intracerebral hemorrhage in rats

After moderate intracerebral hemorrhage (ICH), both hypothermia (HYPO) and constraint-induced movement therapy (CIMT) improve recovery and reduce the volume of brain injury. We tested the hypothesis that more severe ICH requires both cytoprotection and rehabilitation to significantly improve recovery. Rats were subjected to a unilateral striatal ICH via collagenase infusion. Rats remained normothermic or were subjected to mild HYPO ( approximately 2 days) starting 12 h later. Fourteen days after ICH, half of the rats received CIMT (7 days of restraint of the less affected limb plus daily exercises); the remainder were untreated. Walking, limb use and skilled reaching were assessed up to 60 days, at which time animals were euthanized and the volume of tissue lost was determined. The HYPO treatment alone did not improve outcome, whereas CIMT alone provided significant benefit on the limb use asymmetry test. In the staircase test, the greatest benefit was achieved with the combination of HYPO and CIMT treatments. The volume of tissue lost after ICH was similar among groups arguing against cytoprotection as a mechanism of functional recovery. Finally, these findings suggest that, at least under the present circumstances (e.g., severe striatal ICH), CIMT provides superior benefit to HYPO and that combination therapy will sometimes further improve recovery.

Perinatal asphyxia, hyperthermia and hyperferremia as factors inducing behavioural disturbances in adulthood: A rat model

Alertness was studied in adult male Wistar rats after neonatal critical anoxia applied under three different thermal conditions: (i) at physiological neonatal body temperature of 33 degrees C, (ii) at body temperature elevated to 37 degrees C, and (iii) at body temperature elevated to 39 degrees C (both during anoxia and for 2 h postanoxia). To elucidate the effect of iron-dependent postanoxic oxidative damage to the brain, half of the group (iii) was injected with deferoxamine, a chelator of iron. Postanoxic behavioural disturbances were recorded in open-field, elevated plus-maze, and sudden silence tests when the rats reached the age of 4 month. Moreover, spontaneous motor activity of the rats was recorded radiotelemetrically in their home-cages. Both open-field stress-induced and spontaneous motor activity were reduced in rats subjected to neonatal anoxia under hyperthermic conditions. In contrast, these rats were hyperactive in the plus-maze test. Both the plus-maze and sudden silence tests revealed that these rats show reduced alertness to external stimuli signalling potential dangers. The behavioural disturbances were prevented by the body temperature of 33 degrees C and by postanoxic administration of deferoxamine. These data support the conclusion that permanent postanoxic behavioural disturbances are due to iron-dependent oxidative damage to the brain, which can be prevented by the reduced neonatal body temperature.

Immediate constraint-induced movement therapy causes local hyperthermia that exacerbates cerebral cortical injury in rats

Constraint-induced movement therapy (CIMT), which involves restraint of the nonimpaired arm coupled with physiotherapy for the impaired arm, lessens impairment and disability in stroke patients. Surprisingly, immediate ipsilateral forelimb immobilization exacerbates brain injury in rats. We tested whether immediate ipsilateral restraint for 7 days aggravates injury after a devascularization lesion in rats. Furthermore, we hypothesized that ipsilateral restraint aggravates injury by causing hyperthermia. In experiment 1, each rat received two lesions, one in the motor cortex and one in the visual cortex. Ipsilateral restraint increased only the motor cortex lesion. In additional rats, no differences in core temperature occurred after ipsilateral or contralateral restraint. Thus, ipsilateral restraint does not aggravate injury by a systemic side effect. In experiment 2, we hypothesized that ipsilateral restraint causes hyperthermia in the region surrounding the initial cortical lesion. Brain temperature, measured via telemetry, was significantly higher (approximately 1 degrees C for 24 h) with ipsilateral restraint. A third experiment similarly found that ipsilateral restraint aggravates injury and causes local cortical hyperthermia and that contralateral restraint with externally induced mild hyperthermia aggravates injury. In conclusion, immediate ipsilateral restraint aggravates injury apparently by localized events that include hyperthermia. Caution must be exercised in applying early CIMT to humans, as hyperthermia is detrimental.

Post-ischemic diazepam does not reduce hippocampal CA1 injury and does not improve hypothermic neuroprotection after forebrain ischemia in gerbils

The hippocampal CA1 sector is especially vulnerable to brief forebrain ischemia. Excitotoxicity is widely thought to contribute to this cell death. Accordingly, drugs that presumably counteract excitotoxicity, such as GABAergic agonists, have been repeatedly tested and found to reduce CA1 cell loss. Post-ischemic diazepam reduces CA1 injury. However, diazepam also causes hypothermia, which by itself is neuroprotective. Most studies fail to adequately control for this confound. In this study, we tested whether diazepam reduces injury in temperature controlled gerbils subjected to brief forebrain ischemia. Furthermore, we tested whether diazepam augments hypothermic neuroprotection. All gerbils were implanted with a core temperature telemetry probe and a cannula for the subsequent insertion of a thermocouple probe to measure ischemic brain temperature. Subsequently, they were given a 5-min normothermic ischemic insult. In Experiment 1, two groups of gerbils were given 10 mg/kg doses of diazepam (i.p.) at both 30 and 90 min post-ischemia. Temperature was maintained in one group by heating lamps. Another group was administered saline. Diazepam reduced cell death at 7 days post-ischemia when the drug-induced hypothermia was permitted, but not when it was prevented. In Experiment 2, four groups of ischemic gerbils were treated starting at 12 h post-ischemia with prolonged hypothermia, diazepam and the combination or saline treatment. Hypothermia, but not diazepam, provided partial neuroprotection and diazepam did not augment hypothermic neuroprotection. Thus, neuroprotection with diazepam is solely due to hypothermia. These data do not support the clinical use of diazepam as a neuroprotectant after global ischemia.