IN-VITRO AUTORADIOGRAPHIC LOCALIZATION OF 5-HT1A RECEPTOR-ACTIVATED G-PROTEINS IN THE RAT-BRAIN

Serotonin 5-HT1A receptors belong to the superfamily of G-protein-coup led receptors, Receptor activation of G-proteins can be determined by agonist-stimulated [S-35]GTP gamma S binding in the presence of excess GDP, and in vitro autoradiographic adaptation of this technique allow s visualization of receptor-activated G-proteins in tissue sections. T he present study was performed to examine 5-HT1A receptor activation o f G-proteins using 8-OH-DPAT-stimulated [S-35]GTP gamma S binding in m embranes and brain sections. In hippocampal membranes, 8-OH-DPAT stimu lated [S-35]GTP gamma S binding by twofold, with an ED50 value of 25 n M. 5-HT1 antagonists, but not 5-HT2 antagonists, increased the ED50 of 8-OH-DPAT in a manner consistent with competitive antagonists, Scatch ard analysis of [S-35]GTP gamma S binding showed that 8-OH-DPAT induce d the formation of high affinity [S-35]GTP gamma S binding sites with a K-D for GTP gamma S of 3.2 nM. [S-35]GTP gamma S autoradiography, pe rformed in brain sections with the 5-HT1A agonist 8-OH-DPAT, revealed high levels of 5-HT1A-stimulated [S-35]GTP gamma S binding in the hipp ocampus, lateral septum, prelimbic cortex, entorhinal cortex, and dors al raphe nucleus, 5-HT1A-stimulated [S-35]GTP gamma S binding in secti ons was blocked by the addition of the 5-HT1 antagonist methiothepin. These results show that the use of agonist-stimulated [S-35]GTP gamma S autoradiography for the 5-HT1A receptor system should provide new in formation regarding signal transduction in specific brain regions. (C) 1997 Elsevier Science Inc.