5-HT1A receptors couple to different Go/Gi proteins in order to mediate a wide range of physiological actions. While activation of post-synaptic 5-HT1A receptors is mainly related to inhibition of adenylyl cyclase activity, functionality of autoreceptors located in raphe nuclei has been classically ascribed to modifications of the activity of potassium and calcium channels. In order to evaluate the possible existence of agonist-directed trafficking for 5-HT1A autoreceptors in the rat dorsal raphe nucleus, we studied their activation by two agonists with a different profile of efficacy [(+)8-OH-DPAT and buspirone], addressing simultaneously the identification of the specific Gα subtypes ([35S]GTPγS labelling and immunoprecipitation) involved and the subsequent changes in cAMP formation. A significant increase (32%, p<0.05) in (+)8-OH-DPAT-induced [35S]GTPγS labelling of immunoprecipitates was obtained with anti-Gαi3 antibodies but not with anti-Gαo, anti-Gαi1, anti-Gαi2, anti-Gαz or anti-Gαs antibodies. In contrast, in the presence of buspirone, significant [35S]GTPγS labelling of immunoprecipitates was obtained with anti-Gαi3 (50%, p<0.01), anti-Gαo (32%, p<0.01) and anti-Gαi2 (29%, p<0.05) antibodies, without any labelling with anti-Gαi1, anti-Gαz or anti-Gαs. The selective 5-HT1A antagonist WAY 100635 blocked the labelling induced by both agonists. Furthermore, (+)8-OH-DPAT failed to modify forskolin-stimulated cAMP accumulation, while buspirone induced a dose-dependent, WAY 100635-sensitive, inhibition of this response (Imax 30.8±4.9, pIC50 5.95±0.46). These results demonstrate the existence of an agonist-dependency pattern of G-protein coupling and transduction for 5-HT1A autoreceptors in native brain tissue. These data also open new perspectives for the understanding of the differential profiles of agonist efficacy in pre- vs. post-synaptic 5-HT1A receptor-associated responses.This research was supported by Ministry of Science, SAF04–00941, SAF07-61862, Fundación Alicia Koplowitz, Fundación de Investigación Médica Mutua Madrileña, Instituto de Salud Carlos III and University of Cantabria-FAES research contract.Peer reviewe
