Light and electron microscopic localization of α subunits of GTP-binding proteins, G₀ and G₁, in the cerebral cortex and hippocampus of rat brain

Antibodies that recognize α subunits of G_o, G_i2 and G_i3 were used to evaluate their association with synaptic junctions. G_o, but not G_i, was concentrated within perikaryal and dendritic cytoplasm of a small population of bipolar neurons. All three G-proteins were associated with the intracellular surface of dendritic, axonal and astrocytic plasma membranes and postsynaptic densities (PSDs). However, association with PSDs was more prevalent for the two G_i's than for G_o while the association with terminals forming putatively excitatory synapses was more prevalent for G_o and G_i3 than for G_i2. Thus, neuromodulators may modulate the release of excitatory transmitters via activation of presynaptic G_i3 and G_o and also regulate the opening of Ca²⁺ and/or K⁺ channels via activation of G_i's and G_o at PSDs.