Irreversible impairment of inhibitory neurons and nitric oxide release in the neocortex produced by low temperature and hypoxia in vitro

Green tea polyphenol (−)-epigallocatechin gallate attenuates the neuronal NADPH-d/nNOS expression in the nodose ganglion of acute hypoxic rats

Recent studies have shown that (-)-epigallocatechin gallate (EGCG), one of the green tea polyphenols, has a potent antioxidant property. Nitric oxide (NO) plays an important role in the neuropathogenesis induced by brain ischemia/reperfusion and hypoxia. This study aimed to explore the potential neuroprotective effect of EGCG on the ganglionic neurons of the nodose ganglion (NG) in acute hypoxic rats. Thus, the young adult rats were pretreated with EGCG (10, 25, or 50 mg/kg, i.p.) 30 min before they were exposed to the altitude chamber at 10,000 m with the partial pressure of oxygen set at the level of 0.27 atm (pO2=43 Torr) for 4 h. All the animals examined were allowed to survive for 3, 7, and 14 successive days, respectively, except for those animals sacrificed immediately following hypoxic exposure. Nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry and neuronal nitric oxide synthase (nNOS) immunohistochemistry were carried out to detect the neuronal NADPH-d/nNOS expression in the NG. The present results show a significant increase in the expression of NADPH-d/nNOS reactivity in neurons of the NG at various time intervals following hypoxia. However, the hypoxia-induced increase in NADPH-d/nNOS expression was significantly depressed only in the hypoxic rats treated with high dosages of EGCG (25 or 50 mg/kg). These data suggest that EGCG may attenuate the oxidative stress following acute hypoxia.

Axotomy along with hypoxia enhances the neuronal NADPH-d/NOS expression in lower brain stem motor neurons of adult rats

This study was aimed to determine whether axotomy coupled with hypoxia would exert a more profound effect on injury-induced neuronal nitric oxide synthase (NOS) expression. In this connection, the vagus and the hypoglossal nerves of adult rats were transected unilaterally in the same animal, and half of the operated animals were subjected to hypoxia treatment. Both the neuronal NOS immunohistochemistry and the nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry were used to assess the neuronal NOS expression. The present results have shown that the number of NADPH-d/NOS-positive [NADPH-d/NOS(1)] neurons in the hypoglossal nucleus (HN) peaked at 14 days after axotomy, while that in dorsal motor nucleus of vagus (DMN) and nucleus ambiguus (NA) was progressively increased up to 60 days. The up-regulation of NADPH-d/NOS in HN and DMN was more pronounced in hypoxic than in normoxic animals, a feature that was not evident in the NA. Quantitative analysis showed that the number of surviving motoneurons in normoxic animals was significantly higher than those subjected to hypoxia at 14 days postaxotomy in HN and at all postaxotomy time points in DMN. The difference may be attributed to their different functional components. Since O2 deprivation leads to poor cellular function, the stronger expression of NADPH-d/NOS and the more drastic neuronal loss following nerve transection in the hypoxic animals compared with the controls suggest that hypoxia plays an important role in peripheral neuropathies in which NO is implicated.