Brain-derived peptides inhibit synaptic transmission via presynaptic GABAB receptors in CA1 area of rat hippocampal slices.

GABAB receptors form the basis of a powerful and versatile inhibitory system in the mammalian brain. Presynaptic and postsynaptic actions of GABAB receptors have been described in various brain regions, including the hippocampus. We report here on a novel pharmacological agent, presumably a peptide, which inhibits synaptic transmission in the CA1 area of the rat hippocampus via GABAB receptors. The agent is a component of a nootropic drug, Cerebrolysin, obtained from pig's brain extract. In contrast to other, presently known agonists, such as baclofen or GABA, Cerebrolysin acts preferentially on presynaptic GABAB receptors and has no detectable postsynaptic inhibitory effects. Additional, postsynaptic depolarizing action of the drug resulting in increased excitability is pharmacologically distinct from the GABAB response and partially masked by the inhibition. The presynaptic GABAB agonist may add to clinical effects of Cerebrolysin in treatment of brain injuries. Moreover, it promises to be a useful experimental agent in further studies of many possible functional roles of GABAB receptors.