The effects of baclofen and two GABAB-receptor antagonists on long-term potentiation

The aim of the present study was to investigate whether activation or inhibition of GABAB receptors in hippocampal slices of rats has an impact on the synaptic plasticity in the CA1 area. Long-term potentiation (LTP) was induced by tetanic stimulation of the Schaffer collateral/commissural fiber tract and the responses of CA1 pyramidal neurons were recorded extracellularly. The increase in population spike amplitude after tetanic stimulation was taken as a measure of LTP. The selective GABAB receptor blockers phaclofen (1 mM) and CGP 35,348 (100 microM) facilitated the induction of LTP. Although baclofen (1 microM) reduced the population spike amplitude, it did not affect LTP. If, however, the stimulation voltage was increased to compensate for the baclofen-induced decline in population spike amplitude, LTP was facilitated. Under these conditions the induction of LTP was accompanied by the appearance of additional population spikes. In conclusion, GABAB receptors appear to exert a modulatory action on LTP.