Changes in the length and width of the postsynaptic density, the width of the intersynaptic density and the synaptic cleft in the cerebral cortex synapses of rats exposed to prolonged aerogenic hypoxia during early ontogenesis. An electron microscopic morphometric study.

Infant rats, together with the female, were exposed daily from birth to the age of 17 days (except for the 6th, 7th, 13th and 14th day) to a simulated attitude of 7,000 m. On the 18th day, 20 hours after the last exposure to hypoxia, the animals were perfused. In each of 118 synapses from the two control animals and 162 synapses from the two experimental animals (type I synapses, second cortical layer of the somatosensory cortex, impregnated with phosphotungstic acid), we measured A) the maximal thickness of the postsynaptic density and B) the minimal thickness of the postsynaptic density, C) estimated the thickness of the postsynaptic density and measured D) the distance between the pre- and the postsynaptic density, E) the thickness of the intersynaptic density and F) the length of the postsynaptic dense projection. In the experimental animals we found value A) to be 25% lower, value B) 28% lower, value C) 30% lower, value D) 5% lower, value E) 2.5% lower and value F) 17% higher than in the controls. The differences are statistically significant (evaluated by a t-test). It was found that, under our experimental hypobaric conditions, the maturation of synapses is retarded or modified.