Fig. 4

Hippocampal Ntyr immunoreactivity in normoxic and hypobaric hypoxic rats pretreated with normal saline or melatonin, and sacrificed at 0 h, 1 and 3 days of reoxygenation. Light photomicrographs (a) show that majority of pyramidal cells in the CA1 region of normoxic rats are weak Ntyr immunoreactive (A, B, arrows) but significantly increased in immunoreactivity following hypoxic exposure for 0 h (C), 1 (E) and 3 (G) days. Melatonin pretreatment appreciably decreases Ntyr immunoreactivity boosted at 0 h (D), 1 (F) and 3 (H) days after hypoxic exposure. Ntyr(+) neurons are magnified in each representative figure and shown in the inserts. Scale bar 50 μm for all figures, insert 100 μm. Quantitative results are shown the mean optical density of Ntyr(+) neurons (b) and the level of total Ntyr protein (c) quantified by immunoblots in the hippocampus of rats treated with hypoxia alone (black column) and melatonin pretreated (white column) and sacrificed at 0 h, 1 and 3 days of reoxygenation. The staining intensity and the levels of total protein of Ntyr in the hippocamus are drastically increased in the rats sacrificed at 0 h, 1 and 3 days after hypoxic insult. The enhanced intensity of Ntyr stain and protein levels are markedly reduced in rats treated with hypoxia and pretreated melatonin as compared with those of hypoxic along. Controls (set as 100 %, indicated by dashed line) are the staining intensity (b) or protein levels (c) of saline or melatonin treatment under normoxic condition rats. Loading control is the levels of β-actin. *P < 0.05 (Student’s t test) when compared with values (expressed as mean ± SEM) of rats merely treated with hypoxia at the same survival time point