Introduction. Calretinin (CR) is a protein, which is present in GABAergic neurons and belongs to the calcium-binding proteins family. It may reduce the excitotoxicity phenomenon through its Ca²⁺ buffering properties. This phenomenon is due to the increase of calcium ions levels caused by the excess of glutamate — the main excitatory neurotransmitter. The aim of the study was to investigate alterations of calretinin-immunoreactivity in neurons of hippocampal CA1 region and dentate gyrus with hilus in 10 day-old rats treated with monosodium glutamate (MSG).

Material and methods. Ten 7 day-old Wistar rats were used. The MSG-group consisted of 5 MSG-treated rats at a dose of 4 g/kg b.w. for 3 consecutive days and the second group consisted of 5 control animals. After euthanasia the brains containing hippocampus were dissected and embedded in paraffin blocks. The immunohi­stochemical peroxidase-antiperoxydase reaction was performed on tissue sections. The morphometric analyses of CR-immunopositive neurons: density, percentage ratio to the density of all cells and an assessment of digital immunostaining intensity were performed.

Results. The distribution of the CR-immunoreactive neurons in the hippocampus was irregular. In the MSG-group there were single cells, which were more intensely stained than in control animals. Some of cells contained processes of different length. The density of CR-immunopositive cells and their percentage ratio to the density of all cells did not change significantly after MSG treatment. However, there was a statistically significant increase in the staining intensity of CR-immunopositive cells.

Conclusions. The obtained results indicate that CR-positive cells in P7–P10 rats are only slightly affected by MSG in CA1 region and dentate gyrus with hilus of the hippocampus.