Regional Differences in the Coupling of 5-Hydroxytryptamine-1A Receptors to G Proteins in the Rat Brain

Abstract

Numerous data showed that 5-hydroxytryptamine-1A (5-HT 1A ) receptors couple to G␣ o /␣ i proteins for signal transduction. However, the ␣ subunit isoforms really involved in 5-HT 1A receptor coupling in brain remain to be identified. Moreover, regional differences in the functional characteristics of brain 5-HT 1A receptors have been evidenced repeatedly. Because such differences could be due to variations in G proteins interacting with the same receptor, relevant approaches were used for identifying ␣ subunits physically coupled to 5-HT 1A receptors in different regions of the rat brain. Using immunoaffinity chromatography coupled to Western blot detection, 5-HT 1A receptors were found to interact equally with G␣ o and G␣ i3 in the cerebral cortex, mainly with G␣ o and weakly with G␣ i3 in the hippocampus and exclusively with G␣ i3 in the anterior raphe area. In the hypothalamus, 5-HT 1A receptors seemed to be coupled to the latter two G proteins plus G␣ i1 and G␣ z . Complementary experiments based on an antibody capture technique coupled to both classic radioactivity and scintillation proximity assay detections showed that hippocampal 5-HT 1A receptor stimulation induced 5Ј-O-(3-[35 S]thio)triphosphate binding to immunoprecipitates with G␣ i3 and G␣ o antisera. In the anterior raphe, such 5-HT 1A receptor-mediated effect was obtained with G␣ i3 antiserum only. These results demonstrated the existence of regional differences in the coupling of 5-HT 1A receptors to G proteins in the rat brain. In the anterior raphe, 5-HT 1A receptors seem to interact specifically with G␣ i3 , whereas in the hippocampus, they are mainly coupled to G␣ o proteins. Such a disparity in G-protein coupling might explain regional differences in adaptive regulations of brain 5-HT 1A receptors.Because of its involvement in various psychiatric pathologies, such as affective disorders, the 5-HT 1A type of serotonin (5-hydroxytryptamine, 5-HT) receptors is a subject of great interest. 5-HT 1A receptor stimulation has been shown to activate different signaling pathways sensitive to pertussis toxin through G␣ i /G␣ o proteins (Raymond et al., 1993). Inhibition of adenylyl cyclase (AC) activity mediated by 5-HT 1A receptors has been evidenced in most brain regions as a result of G␣ i protein activation (De Vivo and Maayani, 1986;Hamon, 1997). In addition, in the hippocampus, 5-HT 1A receptors have been shown to mediate G-protein-gated inwardly rectifying K ϩ current (GIRK) through a direct interaction of the ionic channel with the ␤␥ subunits of the G␣ o isoform (Andrade and Nicoll, 1987;Oleskevich, 1995).The development of heterologous recombinant systems expressing the 5-HT 1A receptor, such as COS-7, HeLa, Chinese hamster ovary, Sf9, GH4C1, LLC-PK1, and NIH-3T3 transfected cells, has provided relevant models to study the receptor coupling with different G-protein subtypes and to identify

Effects of the antidepressant fluoxetine on the subcellular localization of 5-HT 1A receptors and SERT

“…The fact that it was partial (30 -40%) suggests the existence of a functional and a non-functional pool of autoreceptors on the plasma membrane of DRN neurons. In hippocampus, there was no internalization, in keeping with the notion that 5-HT 1A heteroreceptors do not desensitize [27,48,53], probably due to G-protein interactions different from those in DRN [54] or different type and level of expression of regulatory proteins (e.g. kinases, arrestins).…”

Single Exposure to a Serotonin 1A Receptor Agonist, (+)8-Hydroxy-2-(di-n-propylamino)-tetralin, Produces a Prolonged Heterologous Desensitization of Serotonin 2A Receptors in Neuroendocrine Neurons in Vivo

“…Alternative explanations include the following: 1) systemic (Ϫ)DOI injection may also activate 5-HT 2A receptors in other nuclei that are involved in ACTH release, such as the amygdala (Beaulieu et al, 1986;Feldman et al, 1998), which could mask the effects occurring in hypothalamic CRF neurons; and 2) 5-HT 1A receptor-associated signaling pathways in oxytocincontaining cells in the PVN could be different from those found in CRF-containing cells. This hypothesis is supported by studies demonstrating that 5-HT 1A receptors are coupled to different G-proteins within different brain areas (Lin et al, 2002;La Cour et al, 2006).…”

Cellular profile of the dorsal raphe lateral wing sub-region: Relationship to the lateral dorsal tegmental nucleus

“…Stimulation of the 5HT 1A receptor suppresses cell firing via Gi/o G-protein signaling, which inhibits cyclic-AMP (cAMP) in heteroreceptor configurations but not in raphe autoreceptors (Clarke et al, 1996). A difference in the expression of specific Gi/o subunit subtypes in different brain regions is believed to be responsible for this functional distinction (Mannoury la Cour et al, 2006). In addition to cAMP modulation, activation of the 5HT 1A receptor opens potassium (K + ) channels (specifically G-protein coupled inwardly rectifying potassium (GIRK) channels), and modifies calcium (Ca 2+ ) channel conductance and likely triggers other downstream effects (Penington and Kelly, 1990; Polter and Li, 2010; Valdizan et al, 2009).…”

“…Activation of this receptor via 5HT or agonist administration ultimately results in hyperpolarization of the neuron and a dose-dependent decrease in cell firing (Martin et al, 1999). However, the different G-protein subunit subtypes associated with anatomical distribution of 5HT 1A receptors (auto- versus heteroreceptors) may result in different time courses of inhibitory action (Mannoury la Cour et al, 2006; Polter and Li, 2010; Valdizan et al, 2009). Thus, it is reasonable to predict that following activation by 5HT, 5HT 1A receptors expressed on LDT NOS neurons (heteroreceptors) may differ in sensitivity and mechanistic action compared to those on DRN cells (autoreceptors).…”