LIGHT AND ELECTRON-MICROSCOPIC LOCALIZATION OF ALPHA SUBUNITS OF GTP-BINDING PROTEINS, GO AND GI, IN THE CEREBRAL-CORTEX AND HIPPOCAMPUS OF RAT-BRAIN

Antibodies that recognize a 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.