Figure 2.

Functional crosstalk between GABA_B and mGlu1a receptors in cortical neurons and in transfected HEK293 cells. (A) Activation of GABA_B receptor alone by Baclofen 100 μM (filled squares) and mGlu1a by DHPG in the presence (open circles) or in the absence (filled circles) of baclofen (100 μM), in cortical neurons. (B, C) Potentiation of the glutamate response by co-activation of the GABA_B receptors in HEK293 cells. In (B), Ca²⁺ responses mediated by various concentrations of glutamate (circles) and GABA (triangles) in cells expressing both mGlu1a and GABA_B receptors. Glutamate responses were measured in the absence (filled circles) and in the presence (open circles) of 50 μM GABA. The GABA-mediated responses were measured in the absence (filled triangles) and in the presence (open triangles) of 100 μM glutamate. (C) Glutamate responses, as in (B), in cells expressing either a low (triangles) or a high (circles) density of mGlu1a. (D, E) The GABA_B effect needs Gi/o protein activation. (D) Same as in (C) in cells co-expressing the WT (circles) or a G protein activation-deficient (L686P represented by triangles) GABA_B receptor and mGlu1a receptor. (E) Same as in (C), in cells expressing GABA_B and mGlu1a receptors, treated OVN with PTX (squares) or not (circles). The Gαo protein was co-expressed in all of these experiments. Data are means±s.e.m. of triplicate determinations from a representative experiment reproduced at least three times.