MORPHOLOGICAL ALTERATIONS IN THE HIPPOCAMPUS FOLLOWING HYPOBARIC HYPOXIA

1 The morphological consequences of hypobaric hypoxia, exposure to red uced pressure atmospheres, were examined in the hippocampus of male Fi scher 344 rats. Severe chronic hypoxia can produce permanent neuronal damage with hippocampal structures being especially vulnerable. 2 Hipp ocampal morphology was studied using histological observations after a 4 day exposure to sea level, 5500 m, or 6400 m. Two groups tested at 6400 m were sacrificed at different intervals following exposure, 72 a nd 144 h, to examine the effect of post-exposure time on neuronal dama ge. 3 Histological damage was observed in rats' brains following expos ure to altitude, with cell degeneration and death increasing as altitu de increased. In addition, it was found that the longer the time follo wing exposure before sacrifice, the more noticeable the damage, sugges ting delayed neurotoxicity. Increases in the number of damaged cells f ollowing altitude were significant for the CA3 region of one 6400 m gr oup; however, other differences did not reach statistical significance . Rats exposed to altitude for 4 days ate less and lost significantly more weight than did animals at sea level. 4 It appears that 4 days of exposure to altitudes less than or equal to 6400 m does produce chang es in the CA3 subfield, but the damage is different than that seen wit h other models of non-transient ischemia.