Pittaluga A, Vaccari D, Raiteri M
Istituto di Farmacologia e Tossicologia, Università degli Studi di Genova, Italy.
J Pharmacol Exp Ther. 1997 Oct;283(1):82-90.
Some putative cognition enhancers (oxiracetam, aniracetam and D-cycloserine) were previously shown to prevent the kynurenic acid antagonism of the N-methyl-D-aspartate (NMDA)-evoked norepinephrine (NE) release in rat hippocampal slices. This functional in vitro assay was further characterized in the present work. D-Serine, a glutamate coagonist at the NMDA receptor glycine site, concentration-dependently (EC50 approximately 0.1 microM) prevented the kynurenate (100 microM) block of the NMDA (100 microM)-evoked [3H]NE release. L-Serine was ineffective up to 10 microM. The gamma-aminobutyric acidB (GABA[B]) receptor antagonist CGP 36742, reported to improve cognitive performance, potently prevented the kynurenate antagonism. The activity of CGP 36742 (1 microM) appeared to be unaffected by 10 microM (-)-baclofen, a GABA(B) receptor agonist; furthermore, CGP 52432, a GABA(B) antagonist more potent than CGP 36742, but reportedly devoid of nootropic properties, was inactive in the "kynurenate test." The novel putative cognition enhancer CR2249, but not its enantiomer CR2361, also potently prevented the kynurenate antagonism. In contrast, linopirdine, nicotine and tacrine were inactive. In rat hippocampal synaptosomes glycine and D-cycloserine enhanced the NMDA-evoked [3H]NE release, whereas oxiracetam and CR2249 did not. These four compounds were all similarly effective in preventing kynurenate antagonism, both in slices and in synaptosomes. The NMDA potentiation caused by glycine (0.1-100 microM) was not affected by 100 microM oxiracetam, which suggested that drugs active in the "kynurenate test" may bind to sites different from the glycine site of the NMDA receptor. To conclude, the "kynurenate test" is an in vitro assay useful in the identification and characterization of putative cognition enhancers acting via NMDA receptors.
一些假定的认知增强剂（奥拉西坦、阿尼西坦和D-环丝氨酸）先前已被证明可防止犬尿氨酸对大鼠海马切片中N-甲基-D-天冬氨酸（NMDA）诱发的去甲肾上腺素（NE）释放的拮抗作用。在本研究中对这种体外功能测定进行了进一步的特性研究。D-丝氨酸是NMDA受体甘氨酸位点的谷氨酸协同激动剂，其浓度依赖性地（EC50约为0.1微摩尔）可防止犬尿酸盐（100微摩尔）对NMDA（100微摩尔）诱发的[3H]NE释放的阻断作用。L-丝氨酸在高达10微摩尔时无效。据报道可改善认知能力的γ-氨基丁酸B（GABA[B]）受体拮抗剂CGP 36742可有效防止犬尿酸盐的拮抗作用。CGP 36742（1微摩尔）的活性似乎不受10微摩尔（-）-巴氯芬（一种GABA[B]受体激动剂）的影响；此外，CGP 52432是一种比CGP 36742更有效的GABA（B）拮抗剂，但据报道没有促智特性，在“犬尿酸盐试验”中无活性。新型假定的认知增强剂CR2249，而非其对映体CR2361，也能有效防止犬尿酸盐的拮抗作用。相比之下，里诺吡啶、尼古丁和他克林无活性。在大鼠海马突触体中，甘氨酸和D-环丝氨酸可增强NMDA诱发的[3H]NE释放，而奥拉西坦和CR2249则不能。这四种化合物在防止切片和突触体中的犬尿酸盐拮抗作用方面都同样有效。甘氨酸（0.1 - 100微摩尔）引起的NMDA增强作用不受100微摩尔奥拉西坦的影响，这表明在“犬尿酸盐试验”中有活性的药物可能与NMDA受体的甘氨酸位点不同的位点结合。总之，“犬尿酸盐试验”是一种体外测定方法，有助于鉴定和表征通过NMDA受体起作用的假定认知增强剂。
