Rat hippocampal neurons maintain their own GABAergic synaptic transmission in culture.

The whole-cell patch-clamp technique was used to record monosynaptic inhibitory postsynaptic currents (IPSCs) from pairs of hippocampal neurons cultured for 2-3 weeks. The application of fresh physiological solution for 2-3 min reversibly reduced the amplitude of evoked GABAergic IPSCs to 72.5% of control value. The amplitude and frequency of spontaneous IPSCs decreased too. The depression of evoked IPSCs was significantly smaller or absent if conditioned solution was applied (physiological solution which had been previously in contact with neurons for 30 min). Currents evoked by exogenously applied GABA were unaffected by fresh solution. These results suggest that hippocampal neurons release some endogenous substance(s), by which they up regulate presynaptically their own inhibitory synaptic transmission.