In vitro autoradiography of serotonin 5‐HT2A2C receptor‐activated G protein: Guanosine‐5′‐(γ‐[35S]thio)triphosphate binding in rat brain

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Agonist activation of G protein-coupled receptors induces an increase in the binding of guanosine 5′-(γ-[35S]thio)triphosphate ([35S]GTPγS); this increase in binding has been used as a tool to investigate receptor interaction with the heterotrimer guanine nucleotide-binding regulatory protein (G protein). The present study uses agonist-stimulated [35S]GTPγS binding to characterize serotonin 5-HT2A/2C receptors in rat brain membrane fractions and demonstrate the anatomical localization of the receptors by in vitro autoradiography on slide-mounted sections. The stimulatory effect of the agonist [1-(2,5-dimethoxy-4-iodophenyl)]-2 aminopropane (DOI) is compared to that of serotonin (5-HT). Autoradiography revealed a similar localization of DOI- and 5-HT-stimulated binding of [35S]GTPγS in distinct areas of prefrontal and parietal cortex, consistent with previously reported 5-HT2A receptor distribution. Specific binding was demonstrated in the frontal and parietal cortex, medial prefrontal, and cingular and orbital-insular areas as well as in the hippocampal formation, septal areas, the nucleus accumbens, and the choroid plexus. MDL 100105, a specific 5-HT2A antagonist, and ketanserin, an antagonist of 5-HT2A/2C receptors, blocked DOI stimulation in all labeled areas, whereas 5-HT stimulation was only partially blocked (70–80%). A small but significant inhibition was observed with the specific antagonist of 5-HT2C/2B, SB 206553. This autoradiographic technique provides a useful tool for measuring in situ changes in specific receptor–Gq protein coupling in anatomically discrete brain regions, under physiological and pathological conditions. J. Neurosci. Res. 61:674–685, 2000. © 2000 Wiley-Liss, Inc.