Inactivation of 5-HT1A receptors in hippocampal and cortical homogenates

5-HT1A receptor function can be assessed in rat hippocampal and cortical membrane preparations as agonist-stimulated [S-35]GTP gamma S binding. Membranes were preincubated in vitro with N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ). R(+)-8-hydroxy-2-(di-n-propylamino)tetralin [R(+)-8-OH-DPAT]-stimulated [S-35]GTP gamma S binding and [H-3]8-OH-DPAT binding assays were used to assess 5-HT1A receptor function and density, respectively. EEDQ decreased both R(+)-8-OH-DPAT-stimulated [S-35]GTP gamma S and [H-3]8-OH-DPAT binding in hippocampal and cortical membranes. The E-max but not the EC50 of R(+)-8-OH-DPAT to stimulate [S-35]GTP gamma S binding was decreased by EEDQ in both preparations. Additionally, the IC50 for EEDQ to reduce R(+)-8-OH-DPAT-stimulated [S-35]GTP gamma S and [H-3]8-OH-DPAT binding was the same for both brain regions in both assays. In contrast to EEDQ alone, agonist-stimulated [S-35]GTP gamma S binding was not reduced in hippocampal membranes preincubated with EEDQ and the 5-HT1A receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-cyclohexanecarboxamide maleate (WAY 100,635), suggesting that EEDQ acts directly on the receptor. Due to parallel reductions in receptor density and maximal functional response, it is concluded that there is little or no reserve for 5-HT1A receptor coupling to G alpha in these preparations. In addition, the sensitivity of hippocampal and cortical 5-HT1A receptors to inactivation by EEDQ in vitro is the same. (C) 2000 Elsevier Science B.V. All rights reserved.