A model system consisting of two rat strains bred for nervous system excitability in response to electric shocks was used to study changes in the number density of neurons in hippocampal field CA3 at 24 h, two weeks, and two and six months after prolonged emotional-pain stress (PEPS). Neuron density in hippocampal field CA3 decreased after completion of PEPS. These changes arose at different time points in the different rat strains (one day for low-excitability rats, two months for high-excitability rats) and persisted to six months. Thus, this is the first demonstration that persistent differential effects of stress on the number density of neurons in hippocampal field CA3, which plays an important role in learning and memory processes, depend on genetically determined constitutive characteristics of the nervous system.

Stress during pregnancy affects the morphogenesis of embryonal brain, its structural and functional characteristics, and behavior of the progeny. Genetic mechanisms of this process remain unclear. Cytogenetic characteristics of neuroblasts were analyzed in 17-18-day embryos of rats selected by threshold excitability of the nervous system in health and after emotional painful stress during the third trimester of pregnancy. The strains differed by the effect of stress on proliferative activity and chromosome aberrations in cells of the future hippocampus depending on the strain-specific characteristics of the nervous system excitability. This effect is regarded as an important component of epigenetic regulation of neurogenesis and behavior.

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