Long-term potentiation by activation of group I metabotropic glutamate receptors at excitatory synapses in the spinal trigeminal subnucleus oralis

In this study, I examined if activation of group I metabotropic glutamate receptors (mGluRs; mGluR1 and 5) induces long-term potentiation (LTP) at excitatory synapses in the ascending pathway from the spinal trigeminal subnuclei caudalis (Vc) to oralis (Vo), in which group I mGluRs are strongly expressed. As a result, the activation of group I mGluRs produced an initial short-lasting depression and subsequently a delayed type of long-term potentiation (LTP) of excitatory synaptic transmission. Analyses of paired pulse ratio and coefficient of variation indicated that the initial short-lasting depression was induced presynaptically, whereas LTP was expressed postsynaptically. In addition, the short-lasting depression and LTP were mostly mediated by mGluR1, and only partially by mGluR5 and the N-methyl-d-aspartate receptor. Thus, this study suggests that group I mGluRs play an important role in the expression of LTP in the Vc-to-Vo pathway.