Central serotonin1A receptors: Respective distributions of encoding mRNA, receptor protein and binding sites by in situ hybridization histochemistry, radioimmunohistochemistry and autoradiographic mapping in the rat brain

Abstract

The regional distribution of the mRNA encoding the 5-HT1A serotonin receptor (whose selective agonists are potential anxiolytic and antidepressant drugs) was investigated in rat brain sections by in situ hybridization histochemistry using two sets of [32P]labelled nucleoprobes, a riboprobe of 156 bases and oligoprobes of 30 bases corresponding to highly selective portions within the third intracellular loop and the N terminus domain of the amino acid sequence. These probes allowed the visualization of the 5-HT1A mRNA mainly in the limbic regions: dentate gyrus and area CA1 of the hippocampus, amygdala, entorhinal cortex, lateral septum and the dorsal raphe nucleus. These structures were also those which could be labelled by the specific 5-HT1A radioligand [125I]BH-8-MeO-N-PAT and antibodies raised against a synthetic 26 amino acid peptide whose sequence was taken from the most selective portion of the rat 5-HT1A receptor protein. These data suggest that the 5-HT1A receptors are not transported to a long distance from their site of synthesis, as it has been already reported for the somato-dendritic 5-HT1A autoreceptors in the dorsal raphe nucleus. Combined autoradiographic quantification of the 5-HT1A binding sites (labelled by a selective radioligand such as [125I]BH-8-MeO-N-PAT, the 5-HT1A receptor binding subunit (by radioimmunohistochemistry) and the 5-HT1A mRNA on adjacent brain sections should be a relevant approach for assessing the molecular mechanisms responsible for the functional alterations of these receptors under various pathological and pharmacological conditions.