Morphological Features of the Ventral Segment of the Hippocampus in Rats on Aging with Reference to the Expression of Inducible and Endothelial NO Synthases

Structural changes in hippocampal fields CA1 and CA3 of the ventral part of the hippocampus were studied in 12- and 24-month-old rats (n = 20). Paraffin sections of brains were stained by the Nissl method and the proportion of shrunken neurons with cytoplasmic hyperchromatosis was determined, along with changes in the expression levels of inducible and endothelial NO synthase (iNOS, eNOS). Older rats (24 months) showed more severe signs of neuron damage in the pyramidal layer of hippocampal field CA3. An increase in the proportion of shrunken neurons with cytoplasmic hyperchromatosis was seen, with a decrease in the relative density of neurons, accompanied by pericellular edema, and cytoplasmic vacuolization. An increase in iNOS expression in neurons in the pyramidal layer of field CA3 occurred, with decreases in eNOS expression in fields CA1 and CA3 both in neurons and in vascular endotheliocytes of the microcirculatory bed, as compared with levels in 12-month-old animals.