CGP 55845A: a potent antagonist of GABAB receptors in the CA1 region of rat hippocampus.

The new GABAB receptor antagonist CGP 55845A was tested on pre- and post-synaptic GABAB receptors in the hippocampus. CGP 55845A (1 microM) blocked (-)-baclofen (5-10 microM)-induced postsynaptic hyperpolarization and depression of evoked IPSPs and EPSPs. It also blocked three physiological consequences of GABAB receptor activation: the late IPSP, paired-pulse depression of IPSCs, and heterosynaptic depression of EPSPs. Therefore, CGP 55845A is an antagonist at pre- and post-synaptic GABAB receptors in the hippocampus and is approximately three orders of magnitude more potent than previously described GABAB receptor antagonists.