Section of Pharmacology and Toxicology, Department of Experimental Medicine, University of Genoa, Genoa, Italy.
Neurochem Int. 2011 Oct;59(5):729-38. doi: 10.1016/j.neuint.2011.06.022. Epub 2011 Jul 5.
In the present study, using an in vivo approach (a microdialysis technique associated to HPLC with fluorimetric detection) and in vitro purified hippocampal synaptosomes in superfusion, we investigated the glycinergic transmission in the hippocampus, focusing on the nicotinic control of glycine (GLY) release. The acute administration of nicotine in vivo was able to evoke endogenous GLY release in the rat hippocampus. The specific nicotinic agonists PHA-543613 hydrochloride (PHA543613) selective for the α7 nicotinic receptor subtype administered in vivo also elicited GLY release in a similar extent, while the α4β2 agonist 5-IA85380 dihydrochloride (5IA85380) was less effective. Nicotine elicited GLY overflow also from hippocampal synaptosomes in vitro. This overflow was Ca(2+)-dependent and inhibited by methyllycaconitine (MLA), but was not modified by dihydro-beta-erythroidine (DHβE, 1 μM). Choline(Ch)-evoked GLY overflow was Ca(2+) dependent, unaltered in presence of DHβE and blocked by methyllycaconitine (MLA). Additionally, 5IA85380 elicited a GLY overflow, which in turn was Ca(2+) dependent, was significantly inhibited by DHβE but was unaffected by MLA. The GLY overflow produced by these nicotinic agonists quantitatively resembles that evoked by 9 mM KCl. The effects of a high concentration of 5IA85380 (1mM), in the presence of 2 μM DHβE, on the release of GLY was also studied comparatively to that on glutamate and aspartate release. The nicotinic agonist 5IA85380 tested at high concentration (1mM) was able to produce a stimulatory effect of endogenous release of the three amino acids, even in the presence of 2 μM DHβE, indicating the existence of a DHβE resistant, α4β2 nAChR subtype with a functional role in the modulation of GLY, ASP, and GLU release. Our results show that in the rat hippocampus the release of GLY is, at least in part, of neuronal origin and is modulated by the activation of both α7 and α4β2 (low and high affinity) nAChR subtypes.
在本研究中，我们采用体内（微透析技术结合 HPLC 荧光检测）和体外纯化的海马突触体灌流方法，研究了海马中的甘氨酸能传递，重点关注烟碱型乙酰胆碱受体（nAChR）对甘氨酸（GLY）释放的调控。体内给予烟碱急性处理能够诱发大鼠海马内源性 GLY 释放。体内给予α7 型 nAChR 选择性激动剂 PHA-543613 盐酸盐（PHA543613）也能以相似的程度诱发 GLY 释放，而α4β2 型激动剂 5-IA85380 二盐酸盐（5IA85380）的效果则较差。烟碱也能诱发体外海马突触体的 GLY 外溢。这种外溢是 Ca(2+)依赖性的，可被甲基牛扁亭碱（MLA）抑制，但不受二氢-β-石蒜碱（DHβE，1 μM）影响。Ch 诱发的 GLY 外溢也是 Ca(2+)依赖性的，在存在 DHβE 的情况下没有改变，并被 MLA 阻断。此外，5IA85380 诱发的 GLY 外溢也是 Ca(2+)依赖性的，可被 DHβE 显著抑制，但不受 MLA 影响。这些烟碱激动剂引起的 GLY 外溢在数量上与 9 mM KCl 诱发的外溢相似。还比较了高浓度 5IA85380（1mM）在存在 2 μM DHβE 时对 GLY 释放的影响与对谷氨酸和天冬氨酸释放的影响。在高浓度（1mM）下测试的烟碱激动剂 5IA85380 能够产生三种氨基酸内源性释放的刺激作用，即使在存在 2 μM DHβE 的情况下也是如此，这表明存在一种对 DHβE 有抗性的、具有功能作用的α4β2 nAChR 亚型，能够调节 GLY、ASP 和 GLU 的释放。我们的结果表明，在大鼠海马中，GLY 的释放至少部分是神经元起源的，并受α7 和α4β2（低亲和性和高亲和性）nAChR 亚型的激活调节。
