PRESYNAPTIC CALCIUM CURRENT MODULATION BY A METABOTROPIC GLUTAMATE-RECEPTOR

Metabotropic glutamate receptors (mGluRs) regulate transmitter release at mammalian central synapses. However, because oi the difficulty of recording from mammalian presynaptic terminals, the mechanism underlyi ng mGluR-mediated presynaptic inhibition is not known. Here, simultane ous recordings from a giant presynaptic terminal, the calyx of Held, a nd its postsynaptic target in the medial nucleus of the trapezoid body were obtained in rat brainstem slices. Agonists of mGluRs suppressed a high voltage-activated P/Q-type calcium conductance in the presynapt ic terminal, thereby inhibiting transmitter release at this glutamater gic synapse. Because several forms of presynaptic modulation and plast icity are mediated by mGluRs, this identification of a target ion chan nel is a first step toward elucidation of their molecular mechanism.