[³H]8‐Hydroxy‐2‐(Di‐n‐Propylamino)Tetralin Binding to Pre‐ and Postsynaptic 5‐Hydroxytryptamine Sites in Various Regions of the Rat Brain

Abstract

The specific binding of [3H]8-hydroxy-2-(di-n-propylamino)tetralin ([ 3H]8-OH-DPAT) to 5-hydroxytryptamine (5-HT)-related sites was investigated in several regions of the rat brain. Marked differences were observed in the characteristics of binding to membranes from hippocampus, striatum, and cerebral cortex. Hippocampal sites exhibited the highest affinity (KD approximately 2 nM) followed by the cerebral cortex (KD approximately 6 nM) and the striatum (KD approximately 10 nM). Ascorbic acid inhibited specific [3H]8-OH-DPAT binding in all three regions but millimolar concentrations of Ca2+, Mg2+, and Mn2+ enhanced specific binding to hippocampal membranes, whereas only Mn2+ increased it in the cerebral cortex and all three cations inhibited specific binding to striatal membranes. Guanine nucleotides (0.1 mM GDP, GTP) inhibited binding to hippocampal and cortical membranes only. As intracerebral 5,7-dihydroxytryptamine markedly decreased [3H]8-OH-DPAT binding sites in the striatum, but not in the hippocampus, the striatal sites appear to be on serotoninergic afferent fibers. In contrast, in the hippocampus the sites appear to be on postsynaptic 5-HT target cells, as local injection of kainic acid decreased their density. Both types of sites appear to be present in the cerebral cortex. The postsynaptic hippocampal [3H]8-OH-DPAT binding sites are probably identical to the 5-HT1A subsites, but the relationship between the presynaptic binding sites and the presynaptic autoreceptors controlling 5-HT release deserves further investigation.

Dependence of critical micelle concentration of a zwitterionic detergent on ionic strength: implications in receptor solubilization

“…After incubation for 30 miu, the contents were centrifuged at 100,000 X g for 1 h. The clear supernatant was carefully removed from the pellet, and either used immediately for binding assay or for PEG precipitation. PEG precipitation of the crude CHAPS extract was performed to remove NaC1 from the solubilized extract since the agonist binding of 5-HT]A receptor is inhibited by NaC1 [18]. This procedure is believed to remove the salt [19,20].…”

Actions of 5‐hydroxytryptamine and 5‐HT1A receptor ligands on rat dorso‐lateral septal neurones in vitro

“…In contrast, dissociation of the ligand was rapid and 85% of specifically bound [3H]-8-OH-DPAT dissociated within 10 min. Since the ionic conditions employed in the binding assays (50 mm Tris-HCl; Hall et al, 1985) were considerably different from those used in electrophysiology experiments, it cannot yet be excluded that the dissociation rate constant for 8-OH-DPAT (and the other synthetic ligands) is indeed very slow under conventional in vitro conditions.…”

“…Radioligand binding experiments with [3H]-8-OH-DPAT (Hall et al, 1985) showed that binding to hippocampal and striatal membranes reached equilibrium within 5-7 min, which might explain the slow onset of hyperpolarization. In contrast, dissociation of the ligand was rapid and 85% of specifically bound [3H]-8-OH-DPAT dissociated within 10 min.…”

Transcriptional regulation of the 5-HT1Areceptor: implications for mental illness

“…Aghajanian's group showed that autoregulation of firing was mediated by 5-HTreceptors on the 5-HT neurons [5][6][7]. Using the selective agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), Hamon's group identified the 5-HT 1A receptor as the major autoreceptor on the cell body and dendrites of 5-HT neurons of the raphe nuclei [8][9][10][11]. The 5-HT 1A autoreceptor was then shown to mediate 5-HT auto-inhibition [7,12].…”