Stankov B, Cimino M, Marini P, Lucini V, Fraschini F, Clementi F
Department of Pharmacology, University of Milan, Italy.
Neurosci Lett. 1993 Jun 25;156(1-2):131-4. doi: 10.1016/0304-3940(93)90456-u.
The existence and subunit identification of the nicotinic cholinergic receptors in the rat pineal gland were examined by autoradiography, using [3H]cytisine and [125I]alpha-bungarotoxin as labelled ligands. The experiments performed with radioactive cytisine did not reveal specific binding, while iodinated alpha-bungarotoxin disclosed moderate specific binding density, suggesting that the nicotinic cholinergic receptor in the rat pineal is structurally organized with the alpha 7 or alpha 8 subunits present, the only ones that bind alpha-bungarotoxin with high affinity. In vitro functional experiments using pineal explants demonstrated that the binding site may represent a readily accessible nicotinic cholinergic receptor. Nicotine, though having no effect per se on the synthesis and release of melatonin, significantly diminished, in a dose-dependent manner, the norepinephrine-stimulated melatonin accumulation. This effect could be blocked by coincubation with the cholinergic antagonist d-tubocurarine, suggesting that the nicotinic cholinergic receptor in the rat pineal could be involved in the functional regulation of the gland.
利用[3H]金雀花碱和[125I]α-银环蛇毒素作为标记配体，通过放射自显影法检测大鼠松果体中烟碱型胆碱能受体的存在及亚基鉴定。用放射性金雀花碱进行的实验未显示出特异性结合，而碘化α-银环蛇毒素则显示出中等程度的特异性结合密度，这表明大鼠松果体中的烟碱型胆碱能受体在结构上是由α7或α8亚基组成的，这是仅有的能与α-银环蛇毒素高亲和力结合的亚基。使用松果体组织块进行的体外功能实验表明，该结合位点可能代表一种易于接近的烟碱型胆碱能受体。尼古丁本身虽对褪黑素的合成和释放没有影响，但能以剂量依赖的方式显著降低去甲肾上腺素刺激的褪黑素积累。这种作用可通过与胆碱能拮抗剂d-筒箭毒碱共同孵育而被阻断，这表明大鼠松果体中的烟碱型胆碱能受体可能参与了该腺体的功能调节。
