Mechanism of methionine-enkephalin modulation of glutamatergic transmission in the rat striatum.

The effect of methionine-enkephalin (Met-Enk) on responses of rat brain neostriatum neurones to microiontophoretic application of glutamate was studied in experiments with extracellular recording of spike activity. Met-Enk administered by microiontophoresis was shown to depress the glutamate-induced responses. In parallel experiments with synaptic membranes isolated from the striatum it was shown that Met-Enk reduces specific binding of glutamate. Analysis of binding curves suggests that the reduced [3H]glutamate binding in the rat striatum membranes was due to decreased binding sites, whereas binding affinity was not changed. The data obtained show that the depressive effect of Met-Enk may be due to the inhibitory influence of the peptide on glutamate binding to its postsynaptic receptors.