Regulation of catecholamine neurotransmitterlevels in the extracellular fluid by cyclic AMP

我们在单胺能神经元模型--嗜铬细胞瘤PC12细胞培养中发现，环磷酸腺苷(CAMP)抑制儿茶酚胺转运，增加细胞外多巴胺水平。本研究旨在阐明cAMP是否调节CNS和PNS的单胺转运和细胞外单胺类神经递质。采用脑微透析技术，观察cAMP对自由活动大鼠纹状体细胞外多巴胺水平的影响。用体外培养的PC12细胞研究这种cAMP对单胺转运的作用机制。向大鼠纹状体透析注入二丁酰cAMP(DBcAMP)可引起细胞外多巴胺水平的升高，这种作用在细胞外液中低浓度的Ca~(2+)和Gt~(2+)时可被检测到，而高K~(++)(50 MM)纹状体不能引起多巴胺的增加。比较dBcAMP与单胺转运抑制剂诺米芬辛和利血平对细胞外多巴胺的影响，也支持cAMP通过抑制纹状体多巴胺能神经元的胺转运来增加细胞外多巴胺的观点。我们还检测了dBcAMP对多巴胺代谢产物二羟基苯乙酸(DOPAC)水平的影响，并与单胺转运抑制剂进行了比较。DBcAMP表现出与利血平相似的作用，提示dBcAMP抑制了单胺通过分泌囊泡膜的转运。在PC12细胞中，我们证实cAMP抑制了儿茶酚胺的再摄取，并通过下调囊泡单胺转运而增加了细胞外的多巴胺。

We had found that cyclic AMP (cAMP) inhibited catecholamine transport and increased the extracellular dopamine level in pheochromocytoma PC12 cell culture, a model for monoaminergic neurons. An aim of the present study is to clarify whether cAMP regulates the monoamine transport and extracellular monoamine neurotransmitter in the CNS and PNS.With using a brain microdialysis technique, we examined cAMP effect on extracellular dopamine level in striatum regions of freely moving rat. Mechanisms of this cAMP action on the monoamine transport was also examined with PC12 cells in culture.Dialytic infusion of dibutyryl cAMP (dBcAMP) into rat striatum resulted in an increase in extracellular dopamine level and this dBcAMP effect was detectable under the low Ca^<2+> concentration in the extracellular fluid where the dopamine increase was not observed by the infusion of striatum with high K^+ (50mM). Comparison of the dBcAMP effect on extracellular dopamine with monoamine transport inhibiors, nomifensine and reserpine, also supported the idea that cAMP increases extracellular dopamine by inhibiting the amine transport in dopaminergic neurons in the striatum. Effect of dBcAMP on a level of dihydroxyphenylacetic acid (DOPAC), a dopamine-derived metabolite, was also examined and was compared with those of the monoamine transport inhibitors. dBcAMP showed an effect similar to that of reserpine, suggesting the inhibition of monoamine transport through secretory vesicular membrane by dBcAMP.With PC12 cells, we confirmed that cAMP inhibited catecholamine reuptake and increased extracellular dopamine by down-regulating the vesicular monoamine transport.