Metabotropic glutamate receptors inhibit GABA release in rat histamine neurons

The modulation of GABAergic transmission by metabotropic glutamate (mGlu) receptors was examined in histaminergic neurons using a conventional whole-cell patch clamp technique. DHPG, a selective group I mGlu receptor agonist, had no effect on GABAergic inhibitory postsynaptic currents (IPSCs). However, DCG-IV (1 μМ) and L-AP4 (1 μМ), selective group II or III mGlu receptor agonists, respectively, decreased the amplitude of GABAergic IPSCs and simultaneously increased the paired-pulse ratio. The inhibitory effect of DCG-IV was completely blocked by 200 nM LY341495, a group II and III mGlu receptor antagonist, and the inhibitory effect of L-AP4 was completely blocked by 10 μМ LY341495. These results suggest that multiple mGlu receptors are involved in regulating the excitability of histaminergic neurons.