Roles of metabotropic glutamate receptors on excitatory synaptic transmission in rat trigeminal caudal neurons

ABSTRACT

spinal trigeminal nucleus (medullary dorsal horn MDH) is implicated in the processing of nociceptive information in the orofacial region. Whole cell patch clamp recordings were carried out on MDH neurons in the brainstem slices of neonatal rats to investigate the roles of metabotropic glutamate receptors on excitatory synaptic transmission. In the presence of strychnine (1 microM) and bicuculline (20 microM), spontaneous inward currents at -70 mV were observed. Spontaneous excitatory postsynaptic currents (sEPSCs) were mediated by non-NMDA and NMDA receptors. The specific AMPA receptor antagonist GYKI 52466 (50 microM) completely blocked the non-NMDA mediated sEPSCs, indicating that they are mediated by an AMPA-preferring receptor. Group I, II metabotropic glutamate receptor (mGluR) agonist ACPD (20 microM) significantly decreased the average sEPSCs frequency. No significant effect on sEPSCs amplitude was observed. Frequency of miniature excitatory postsynaptic currents (mEPSCs) was significantly decreased by 20 microM ACPD, but amplitude of mEPSCs was not changed. The specific mGluR 2, 3 agonist DCG-IV (3 microM) reduced mEPSCs frequency, but did not change mEPSCs amplitude. There were no significant changes in the average sEPSCs frequency and amplitude. The mGluR 1, 5 agonist DHPG (100 microM) decreased sEPSCs and mEPSCs frequency, but had no effects on sEPSCs and mEPSCs amplitude. These data suggest that the activation of metabotropic glutamate receptors, via its presynaptic inhibition, can influence the excitatory synaptic transmission of MDH neurons.