[Intermittent hypobaric hypoxia during development--morphologic changes in the neocortex and hippocampus]

Infant rats, together with their mother, were exposed to the simulated altitude of 7,000 m for 8 hours per day since birth to the age of 18 days. Animals were studied the 25th day, 7 days after the last exposure to hypoxia. The experimental and control animals were killed the 25th day by the transaortic perfusion with 4% buffered neutral formaldehyde under ether anaesthesia. Brains were processed for classical neurohistological analysis (Nissl staining). 1. Cortical area in the AP plane 3 mm posterior to bregma were subjected to quantification and "laminar analysis" of the neuron count. 2. Hilus of the dentate gyrus between the AP plane 2.5 mm and 4 mm posterior to bregma were subjected to quantification of the neurons. The findings were as follows: a) The cytoarchitectonics of the brain in animals exposed to hypoxia was not severely damaged. b) The thickness of neocortex is in the experimental animals lower than that in the controls. c) The "laminar analysis" of neocortex showed a relative increase of neuronal density in layers I., II., V. and VI. of the cortex. d) The quantification of the neuron count showed a decrease in hilus of the dentate gyrus. These results demonstrate that the intermittent hypobaric hypoxia has a profound effect on morphological maturation of central nervous system in infant rats.