Periodic and spontaneous Ca(2+) spikes are observed in neurons during development of the central nervous system, and spontaneous changes in intracellular Ca(2+) concentration in neurons play important roles in the development of neural circuits. To clarify the roles of metabotropic glutamate receptors (mGluRs) in the regulation of spontaneous Ca(2+) spikes, we investigated the effects of selective and nonselective mGluRs ligands on primary cultures of rat cortical neurons. Cultured cortical neurons expressed all eight mGluR subtypes on reverse transcription-PCR. The mGluR2 and mGluR3 agonists LY379268, LY354740, and (2R,4R)-APDC increased the amplitude but decreased the frequency of spontaneous Ca(2+) spikes in cultured cortical neurons. The effects of these mGluR2 and mGluR3 agonists were completely inhibited by the presence of a potent mGluR2 and mGluR3 antagonist, LY341495, and by pretreatment with pertussis toxin. No significant effect was observed with either activation or inhibition of mGluR1, mGluR4, mGluR5, mGluR6, mGluR7, and mGluR8 on the spontaneous Ca(2+) spikes in cultured cortical neurons. These findings indicate that, among mGluRs, the group II mGluR subtypes mGluR2 and mGluR3 play principal roles in modulation of spontaneous Ca(2+) spikes.