Activation of 5HT1B receptors inhibits glycinergic synaptic inputs to mammalian motoneurons during postnatal development.

We investigated whether 5-HT(1B) receptor-mediated inhibition of evoked glycinergic inhibitory postsynaptic currents (eIPSCs) in hypoglossal motoneurons (HMs) changed postnatally. In HMs from postnatal days 2-3 (P2-3, neonate) and P10-11 (juvenile) rats bath application of 5-HT (10 microM) caused a not significantly different large reduction in eIPSC amplitude to 35.0+/-22.5% (mean+/-S.D.) and 35.4+/-10.6% of control; respectively. The dose-response relationship for the 5-HT(1B) receptor agonist, CP-93,129, revealed that the mean agonist concentration at half-maximal inhibition (IC(50)) was similar, 1.6 and 2.0 nM, respectively. Additionally, strong antibody labeling of 5-HT(1B) receptors in the hypoglossal motor nucleus was observed in neonates, juveniles and adults. These results demonstrate that over the postnatal period studied, 5-HT(1B) receptor-mediated inhibition of glycinergic eIPSCs is not age dependent.