Quantitative autoradiographic characterisation of the binding of [ super(3)H]WAY-100635, a selective 5-HT sub(1A) receptor antagonist

• Published in: Brain research Vol. 673; no. 2; pp. 217 - 225
• Main Author: Khawaja, X
• Format: Journal Article
• Language: English
• Published: 01.01.1995
• ISSN: 0006-8993

The binding characteristics of [ super(3)H]WAY-100635 ([O-methyl super(3)H]-N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2 pyridinyl)cyclohexane carboxamide trihydrochloride), a potent and selective 5-HT sub(1A) antagonist radioligand, were examined in the rat brain using in vitro quantitative receptor autoradiography. The regional distribution of specific [ super(3)H]WAY-100635 binding sites was heterogenous and demonstrated a strong correlation with that of [ super(3)H]8-OH-DPAT binding. The highest concentrations of [ super(3)H]WAY-100635-labelled sites were found in the lateral septal areas, dorsal raphe n., entorhinal cortex and the hippocampal formation (CA1, CA3 and dentate gyrus). Scatchard transformation of saturation isotherms revealed saturable [ super(3)H]WAY-100635 binding sites of high-affinity: in the hippocampal formation, K sub(d) was similar to 1 nM and B sub(max) ranged between 187 and 243 fmol/mg tissue wet weight, in the entorhinal cortex, K sub(d) = 0.44 nM and B sub(max) = 194 fmol/mg tissue wet weight, and in the rostral portion of the dorsal raphe n., K sub(d) = 0.52 nM and B sub(max) = 157 fmol/mg tissue wet weight. The affinity of [ super(3)H]WAY-100635 for the 5-HT sub(1A) binding site tended to be higher in the dorsal raphe n. and entorhinal cortex compared with that of the hippocampal formation. In contrast, the binding affinity of [ super(3)H]8-OH-DPAT in the hippocampal formation was between 1.1 and 2.3 nM and the B sub(max) was 137 to 183 fmoles/mg tissue wet weight; in the entorhinal cortex, K sub(d) = 3.2 nM and B sub(max) = 141 fmoles/mg tissue wet weight, and in the rostral portion of the dorsal raphe n., K sub(d) = 3.4 nM and B sub(max) = 163 fmol/mg tissue wet weight. Our findings support the use of [ super(3)H]WAY-100635 as a novel antagonist radioligand for studying the binding characteristics of the 5-HT sub(1A) receptor by quantitative receptor autoradiography.