Role of Endogenous Glutaminergic Systems in Mammalian Pineal Gland : A novel inhibitory systems for melatonin synthesis.

哺乳动物松果体细胞合成和分泌褪黑素，这是一种影响昼夜节律和季节性繁殖等生理功能的疏水激素。除了褪黑素外，还发现松果体细胞通过胞外机制分泌L-谷氨酸：松果体细胞在微囊泡中积累L-谷氨酸，并通过钙离子调节的胞吐作用分泌它。我们之前的研究表明，该系统对褪黑素的合成起负调控机制。在本课题中，我们对内源性谷氨酸能系统进行了详细的研究，得到以下结果：(1)代谢型谷氨酸受体3型(MGluR3)通过抑制性G蛋白介导的信号级联参与该系统。(2)乙酰胆碱通过烟碱型乙酰胆碱受体在大鼠松果体细胞中触发谷氨酸的胞吐。(3)MVS含有一些突触小泡标志蛋白，如SV2B，证实MVS与神经元突触小泡相对应。(4)松果体细胞中含有高浓度的D-天冬氨酸，它也可能是抑制性递质。(5)AMPA型iGluR的一个亚型GluR1主要在松果体细胞中表达和功能。

Mammalian pinealocytes synthesize and secrete melatonin, a hydrophobic hormone that affects many physiological functions such as circadian rhythm and seasonal reproduction.Besides melatonin, pinealocytes have been found to secrete L-glutamate by exocytic mechanism : pinealocytes accumulate L-glutamate in microvesicles (MVs) and secrete it through Ca2+ regulated exocytosis.Previously we showed that this system functions as a negative regulatatory mechanism for melatonin synthesis.In this project, we characterized in somje details on the endogenous glutaminergic systems and obtained following results.(1) Metabotropic glutamate receptor type 3 (mGluR3) is involved in the systems through an inhibitory G proteins-mediated signaling cascade.(2) Acetylcholine triggers glutamate exocytosis via nicotinic acetylcholine receptor in rat pinealocytes.(3) MVs contain some synaptic vesicle marker proteins such as SV2B, confirming MVs as counterparts of neuronal synaptic vesicles.(4) Pinealocytes contain high concentration of D-aspartate, which may also function as an inhibitory transmitters.(5) GluR1, an isoform of AMPA-type iGluRs, is predominantly expressed and functions in pinealocytes.