Time dependent loss of tissue GABA content and immunoreactivity in hippocampal slices

Immunohistochemical detection of GABA was used to evaluate changes of the GABA innervation in hippocampal slices maintained in vitro. In parallel experiments the amount of GABA, glutamate and aspartate was measured with high performance liquid chromatography. The results showed that while glutamate and aspartate levels remained fairly constant, GABAergic neurons suffered remarkable alterations. During 8 hours' incubation the GABA content of the tissue and the number of GABA containing neuronal cell bodies decreased by 79.7% and 84.6%, respectively. The qualitative features of the immunoreactivity of the neuropil did not change. In conclusion, while in hippocampal slices tissue glutamate and aspartate levels are only slightly affected by the in vitro maintenance, more than half of the tissue GABA content is lost during prolonged in vitro incubation. As a consequence of the GABA loss, the ratio of endogenous inhibitory and excitatory amino acid transmitters has been altered, which could influence the viability of adult hippocampal tissue in vitro conditions.