Mechanism of Glutamate-induced [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> Increase in Substantia Gelatinosa Neurons of Juvenile Rats

Mechanism of Glutamate-induced [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> Increase in Substantia Gelatinosa Neurons of Juvenile Rats

The glutamate receptors (GluRs) are key receptors for modulatory synaptic events in the central nervous system. It has been reported that glutamate increases the intracellular Ca<SUP>2&#8290;</SUP> concentration ([Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB>) and induces cytotoxicity. In the present study, we investigated whether the glutamate-induced [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> increase was associated with the activation of ionotropic (iGluR) and metabotropic GluRs (mGluR) in substantia gelatinosa neurons, using spinal cord slice of juvenile rats (10∼21 day). [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> was measured using conventional imaging techniques, which was combined with whole-cell patch clamp recording by incorporating fura-2 in the patch pipette. At physiological concentration of extracellular Ca<SUP>2&#8290;</SUP>, the inward current and [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> increase were induced by membrane depolarization and application of glutamate. Dose-response relationship with glutamate was observed in both Ca<SUP>2&#8290;</SUP> signal and inward current. The glutamate-induced [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> increase at holding potential of &#8291;70 mV was blocked by CNQX, an AMPA receptor blocker, but not by AP-5, a NMDA receptor blocker. The glutamate-induced [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> increase in Ca<SUP>2&#8290;</SUP> free condition was not affected by iGluR blockers. A selective mGluR (group I) agonist, RS-3,5-dihydroxyphenylglycine (DHPG), induced [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> increase at holding potential of &#8291;70 mV in SG neurons. These findings suggest that the glutamate-induced [Ca<SUP>2&#8290;</SUP>]<SUB>i</SUB> increase is associated with AMPA-sensitive iGluR and group I mGluR in SG neurons of rats.