Meller E, Goldstein M, Bohmaker K
Millhauser Laboratories, Department of Psychiatry, New York University Medical Center, New York 10016.
Mol Pharmacol. 1990 Feb;37(2):231-7.
The irreversible receptor antagonist N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) was used to determine the relationship between receptor occupancy and response at central 5-hydroxytryptamine1A (5-HT1A) serotonin receptors mediating the inhibition of serotonin synthesis in rat cortex and hippocampus. Rats were treated with vehicle or EEDQ (2 or 6 mg/kg) and 24 hr later dose-response curves were constructed for inhibition of 5-hydroxytrytophan (5-HTP) accumulation (after decarboxylase inhibition with NSD-1015) by the selective 5-HT1A agonists 8-hydroxy-2(di-n-propylamino)tetralin (8-OH-DPAT) (0.01-3 mg/kg), buspirone (0.1-7.5 mg/kg), and ipsapirone (0.1-6.25 mg/kg) and the 5-HT1A agonist/antagonist BMY 7378 (0.015-5 mg/kg). In vehicle-pretreated rats, a similar maximal inhibition of 5-HT synthesis (range, 52-59%) was observed in both brain areas with 8-OH-DPAT, buspirone, and ipsapirone. These three agonists were also more potent in reducing 5-HTP accumulation in the cortex than in the hippocampus (ED50, 8-OH-DPAT, 14 and 30 microgram/kg; buspirone, 0.42 and 0.63 mg/kg; ipsapirone, 0.44 and 1.26 mg/kg, respectively). In the cortex, EEDQ treatment shifted the dose-response curves for 8-OH-DPAT, buspirone, and ipsapirone 8.6-, 2.0-, and 2.8-fold to the right, respectively. Corresponding rightward shifts in the hippocampus were smaller, 6.0-, 1.6-, and 2.1-fold, respectively. The EEDQ-induced shifts in the dose-response curves were accompanied by reductions in maximal response. In contrast, whereas the maximal inhibition of cortical 5-HTP accumulation by BMY 7378 (55%) was similar to that obtained with the agonists, maximal response in the hippocampus was much smaller (32%). Furthermore, in both brain regions EEDQ reduced the maximal response to BMY 7378 without shifting the dose-response curves. Analysis of the data by the double-reciprocal method of Furchgott, followed by calculation of fractional receptor occupancy for each dose of agonist, revealed a nonlinear relationship between receptor occupancy and response for 8-OH-DPAT, buspirone, and ipsapirone in both brain regions, demonstrating the presence of a large receptor reserve. For BMY 7378, in contrast, linear relationships were obtained. Because 5-HT1A receptor-mediated regulation of 5-HT synthesis appears to be mediated by somatodendritic autoreceptors on 5-HT neurons in the midbrain raphé nuclei, the results suggest that these autoreceptors possess a large receptor reserve for agonists. The relevance of these findings for the mechanism of action of nonbenzodiazepine anxiolytics is discussed.
不可逆受体拮抗剂N-乙氧羰基-2-乙氧基-1,2-二氢喹啉（EEDQ）被用于确定在大鼠皮层和海马中，介导5-羟色胺合成抑制的中枢5-羟色胺1A（5-HT1A）血清素受体处的受体占有率与反应之间的关系。给大鼠注射溶媒或EEDQ（2或6mg/kg），24小时后构建剂量反应曲线，以观察选择性5-HT1A激动剂8-羟基-2-（二正丙基氨基）四氢萘（8-OH-DPAT）（0.01 - 3mg/kg）、丁螺环酮（0.1 - 7.5mg/kg）、伊沙匹隆（0.1 - 6.25mg/kg）以及5-HT1A激动剂/拮抗剂BMY 7378（0.015 - 5mg/kg）对5-羟色氨酸（5-HTP）积累的抑制作用（在用NSD-1015抑制脱羧酶后）。在注射溶媒预处理的大鼠中，8-OH-DPAT、丁螺环酮和伊沙匹隆在两个脑区均观察到相似的最大5-羟色胺合成抑制率（范围为52 - 59%）。这三种激动剂在降低皮层中5-HTP积累方面也比在海马中更有效（8-OH-DPAT的半数有效剂量（ED50）分别为14和30μg/kg；丁螺环酮分别为0.42和0.63mg/kg；伊沙匹隆分别为0.44和1.26mg/kg）。在皮层中，EEDQ处理使8-OH-DPAT、丁螺环酮和伊沙匹隆的剂量反应曲线分别右移8.6倍、2.0倍和2.8倍。海马中相应的右移较小，分别为6.0倍、1.6倍和2.1倍。EEDQ诱导的剂量反应曲线右移伴随着最大反应的降低。相比之下，虽然BMY 7378对皮层5-HTP积累的最大抑制率（55%）与激动剂相似，但在海马中的最大反应要小得多（32%）。此外，在两个脑区中，EEDQ降低了对BMY 7378的最大反应，但未使剂量反应曲线移位。采用Furchgott双倒数法分析数据，随后计算每种激动剂剂量的受体占有率分数，结果显示在两个脑区中，8-OH-DPAT、丁螺环酮和伊沙匹隆的受体占有率与反应之间存在非线性关系，表明存在大量受体储备。相比之下，对于BMY 7378，则获得了线性关系。由于5-HT1A受体介导的5-羟色胺合成调节似乎是由中脑缝际核中5-羟色胺能神经元上的树突体自身受体介导的，结果表明这些自身受体对激动剂具有大量受体储备。讨论了这些发现与非苯二氮䓬类抗焦虑药作用机制的相关性。
