Pre and postsynaptic effects of metabotropic glutamate receptor activation on neonatal rat hypoglossal motoneurons.

Activation of metabotropic glutamate receptors by (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (t-ACPD) produced pre- and postsynaptic effects on hypoglossal motoneurons (HMs) patch clamped in thin slices from neonatal rat brainstem. t-ACPD depolarized HMs (with parallel increase in R(in)), induced membrane oscillations, and depressed glutamatergic transmission. However, t-ACPD neither changed the discharge pattern of HMs induced by current pulses nor modulated the spike afterhyperpolarization. The only apparent alteration in firing was the delayed onset of the second spike in a train. The present results provide new evidence that activation of metabotropic glutamate receptors could influence HM excitability by changing the cell responsiveness to synaptic inputs rather than via obvious alterations in the spike firing properties.