Objective - to study the morphometric parameters and serine racemase expression in the hippocampus of rats exposed to repeated gravitational overloads in caudo-cranial direction (-9 Gz). Material and methods. 12 months-old rats were exposed to a force of 9G for 5 min twice daily with an interval of 12 h for 28 days - group 2 (exposure to gravitation, n=10). Rats not affected by hypergravitation formed group 1 (control, n=10). Morphometric methods were used to calculate an average size of the cell nuclei and perikarya of pyramidal neurons, the proportion of neurons with the signs of damage, the relative areas of pyramidal neuron perikarya and neuropil. Immunohistochemically the level of serine racemase expression was studied in all the hippocampal areas. Results. The signs of cerebral microcirculatory disorders were detected such as spongiosis, capillary wall thickening, erythrocyte diapedesis. In all the zones of the hippocampus significant increase in number of pyramidal neurons with the signs of injury was observed. The atrophic changes were demonstrated by the decrease in the average and relative areas of pyramidal neuron perikarya in all the hippocampal areas. Immunohistochemical study has shown the increase in serine racemase expression in CA1, as well as translocation of immunoreactive material into the processes of pyramidal neurons. In CA3 and CA4, a tendency to decreased expression of serine racemase was found. Conclusions. Following a long-term exposure of rats to gravitational overloads in caudo-cranial direction, all the hippocampal areas demonstrated the signs of damage combined with an enhanced expression and accumulation serine racemase in the dendrites of pyramidal neurons of the CA1 area, which may indicate the participation of excitotoxicity in the mechanisms of secondary damage in this area.