Mapping of serotonin 5-HT4 receptor mRNA and ligand binding sites in the post-mortem human brain

Abstract

The anatomical localization of 5-HT(4) receptor mRNA and 5-HT(4) receptor protein was examined in sections of post-mortem human brain by in situ hybridization histochemistry and radioligand receptor autoradiography. In the in situ hybridization study, the highest levels of 5-HT(4) receptor mRNA were found in caudate nucleus, putamen, nucleus accumbens, and in the hippocampal formation. No 5-HT(4) receptor mRNA was detected in globus pallidus and substantia nigra. For receptor autoradiography, two new and highly selective radioligands were compared: [(3)H]prucalopride, which preferentially labels the G-protein coupled fraction of receptors, and [(3)H]R116712, which labels the entire receptor population at subnanomolar concentrations. [(3)H]Prucalopride and [(3)H]R116712 binding was performed on human brain hemisphere sections. The highest densities for both radioligands were found in the basal ganglia (caudate nucleus, putamen, nucleus accumbens, globus pallidus, substantia nigra). Moderate to low densities were detected in the hippocampal formation and in the cortical mantle. Mismatches between 5-HT(4) receptor mRNA and binding sites in the globus pallidus and the substantia nigra suggested that the binding sites may be localized on axonal projections originating from the striatum. To compare densities of binding sites, concentration binding curves with [(3)H]prucalopride, [(3)H]R116712 and [(3)H]GR113808 were performed on membranes from homogenates of several human brain regions. Comparison of B(max)-values obtained with [(3)H]prucalopride and [(3)H]R116712 indicated that the G-protein coupled fraction of 5-HT(4) receptors in the substantia nigra was exceptionally high (54%) in comparison with percentages (16-27%) found in the frontal cortex, the striatum and the hippocampus. Such a high percentage (40%) of [(3)H]prucalopride vs. [(3)H]R116712 binding was also observed in the substantia nigra in the receptor autoradiography experiments. The [(3)H]prucalopride binding was GppNHp-sensitive, whereas [(3)H]R116712 and [(3)H]GR113808 was not. These data indicate that in the substantia nigra 5-HT(4) receptors are more strongly coupled to their signal transduction pathway than in other brain regions.

A High-ResolutionIn VivoAtlas of the Human Brain's Serotonin System

“…We compared our in vivo imaging atlases with meticulous autoradiography studies of the relevant 5-HT targets in postmortem human brain slices (Bonaventure et al, 2000;Varnäs et al, 2004). The postmortem brains in Varnäs et al (2004) and Bonaventure et al (2000) were retrieved from individuals older than those included in our study, with a respective mean age of 58 and 55 versus 26 years in our cohort.…”

A High-Resolution In Vivo Atlas of the Human Brain's Serotonin System

“…The atlas was generated using a subset of the Center for Integrated Molecular and Brain Imaging's (Cimbi's) extensive database , including 210 healthy volunteers aged between 18 and 45 years. Regional PET binding values were compared with corresponding postmortem autoradiography data (Bonaventure et al, 2000;Varnäs et al, 2004), allowing us to validate our results and convert binding values into densities (Bmax). Furthermore, regional densities were compared with mRNA levels from the Allen Human Brain Atlas (Hawrylycz et al, 2012;French and Paus, 2015) to confirm previous findings and to gain novel insights into the localization of the receptor/transporter protein versus its expression.…”

Age and sex effects on 5-HT4 receptors in the human brain: A [11C]SB207145 PET study

“…Experimental studies have suggested several beneficial effects from central 5-HT 4 receptor agonism: better cognitive performance (King et al, 2008), fast treatment response in depression (Lucas et al, 2007), modulation of acetylcholine release (Matsumoto et al, 2001), and beneficial effects on the accumulation of b-amyloid have been shown (Cho and Hu, 2007). No sex or age effects on the 5-HT 4 receptor density have been described in the human postmortem studies (Bonaventure et al, 2000;Reynolds et al, 1995;Varnas et al, 2003). In an earlier PET study with [ 11 C]SB207145 in a smaller younger cohort, we found that 5-HT 4 receptor binding declined with age, and a post hoc analysis suggested that women have lower binding in the hippocampus than men (Marner et al, 2010).…”