Neuroprotective Effects of MK 801 and Hypothermia Used Alone and in Combination in Hypoxic-Ischemic Brain Injury in Neonatal Rats

Abstract

Although accumulating evidence suggests that increased extracellular glutamate concentrations may play an important role in hypoxic-ischemic brain injury, dopamine and other catecholamines also seem to be involved. The N-methyl-D-aspartate receptor antagonist MK 801 and moderate hypothermia (32-34 degrees C) are each known to be neuroprotective, but their combined effect on the release and metabolism of neurotransmitters is unknown. Seven-day-old pups (n: 150) underwent right common carotid artery ligation to induce hemispheric ischemia, and were later subjected to 120 minutes of hypoxia with 8% O2 and 92% N2O. Half the rats (Group I, n: 74) were subjected to normothermic conditions throughout the hypoxic period. Moderate hypothermia (30-32 degrees C) was induced in the other pups (Group II, n: 76) immediately after artery occlusion, and was maintained throughout the hypoxic period. Prior to inducing hypoxia, half of the rats in each group (Groups IA and IIA) received vehicle solution (0.9% NaCI) and the other rats (Groups IB and IIB) received MK 801 (0.5 mg/kg) subcutaneously at 45 and 120 minutes after occlusion. Intracerebral temperature was recorded every 15 minutes after occlusion. Infarct area (n: 40) was calculated after staining with 2% 2,3,5 triphenyltetrazolium chloride. Neuronal damage (n: 42) was assessed by quantifying CA1-CA3 neuronal loss at five hippocampal levels. The amount of damage to the monoamine system of the corpus striatum was determined based on the dopamine and 3,4 dihydroxyphenylacetic acid levels in the corpus striatum in both hemispheres (n: 46), as measured by high-pressure liquid chromatography and compared with normal control pups' values (n: 10). The normothermia/saline-treated pups had significantly larger infarct areas than the MK 801 only, hypothermia only, or MK 801/hypothermia combination groups. Neuropathological examination and striatal tissue monoamine data also confirmed marked neuronal damage in this group. Although MK 801 treatment alone resulted in significantly smaller infarct area and less tissue damage than was observed in the normothermia/saline-treated group, the moderate hypothermia and the MK 801/hypothermia combination treatment groups both exhibited better neuronal protection, especially in the corpus striatum. The rats that received combined treatment also had a significantly lower mortality rate.

Effects of citicoline used alone and in combination with mild hypothermia on apoptosis induced by focal cerebral ischemia in rats

“…24 Mild hypothermia (32-34°C) begun within 30 minutes of the onset of ischemia has a neuroprotective effect. 4,25,26 In our study, Bax and caspase-3 and caspase-9 proteins were highly expressed in hypothermia-treated animals compared to animals receiving citicoline or citicoline + hypothermia. Eberspacher et al showed that the application of postischemic hypothermia (34°C) for 1 hour had long-term anti-apoptotic effects in the rat brain via down-regulation of the proapoptotic protein Bax and up-regulation of the anti-apoptotic proteins Bcl-2 and Mdm-2; this effect persisted for as long as 28 days.…”

“…4 Although the neuroprotective effects of hypothermia and citicoline when used alone after experimental focal cerebral ischemia are well documented, our study demonstrates for the first time that mild hypothermia combined with citicoline has an additive effect in attenuating apoptosis in focal cerebral ischemia/reperfusion injury.…”

Combination of Systemic Hypothermia and N-acetylcysteine Attenuates Hypoxic-Ischemic Brain Injury in Neonatal Rats

“…Systemic hypothermia and a pan-caspase inhibitor, bocaspartyl-(OMe)-fluoromethyl-ketone (BAF), produced a strong protective effect against neuronal cell damage in the ipsilateral hippocampal CA1 region of the developing rat brain, along with a reduction in caspase-3 activity (15). The combination of MK-801 and hypothermia also protected animals against HI injury (16). These studies suggest that inhibiting some excitotoxic or inflammatory processes with combination therapy may have an agonistic effect on overall outcomes.…”

Hypothermia as an Alternative for the Management of Cerebral Ischemia

“…The increase in glutamate is related to the initiation of periinfarct depolarizations. Results using the N-methyl-D-aspartate receptor antagonist MK 801 and moderate hypothermia (32-34 ºC) have shown neuroprotective effects alone and in combination supporting these observations (Alkan et al, 2001). Several studies have shown that hypothermia decreased glutamate efflux by attenuating the initial rise of extracelluar K + and preventing Ca 2+ accumulation (reviewed in Yenari et al, 2008).…”