mGluR and 2-AG regulation of synaptic activity. (A) In this scenario, the CB1R are present on glutamatergic terminals so increased 2-AG synthesis in response to mGluR receptor activation results in inhibition of glutamate release. As a result, the synaptic balance is shifted to reduced excitation and increased inhibition (A1). (B) In this scenario, the CB1R are present on GABA terminals and increased 2-AG synthesis results in inhibition of GABA release. As a result, the synaptic balance is shifted to greater excitation and reduced inhibition. 2-AG, 2-arachidonoylglycerol; CB1R, subtype 1 of the cannabinoid receptor; Glu, glutamate; mGluR, metabotropic glutamate receptor. Other abbreviations are in the legend to Figure 2.