Abstract—The suprachiasmatic nucleus (SCN) regulates the functioning of the body in accordance with circadian rhythms thanks to the pacemaker neurons present in it and afferents modulating these neurons. One of the afferents is represented by nerve fibers containing only the first enzyme for the synthesis of catecholamines, tyrosine hydroxylase (TH). In ontogeny, the concentration of these fibers (amount per unit volume of tissue) reaches a maximum on the 10th postnatal day (P10), and then gradually decreases. The aim of this work was to verify our assumption that, in TH-containing fibers in SCN of rats, L-DOPA is synthesized from L-tyrosine as the final secretory product, and the efficiency of this synthesis is higher in the early postnatal period than in adults. The synthesis of L-DOPA was evaluated by an increase in the total content of L-DOPA in SCN and in the incubation medium after a two-hour incubation of SCN in a medium with or without L‑tyrosine. We found that the addition of L-tyrosine to the incubation medium led to a multifold increase in the total L-DOPA content in SCN and in the medium, which is evidence of the synthesis of L-DOPA as a final product in TH-containing fibers. A comparative analysis of the synthesis of L-DOPA in SCN at P10 and P60 showed that the synthesis rate (a ratio between the total content of L-DOPA in SCN and in the incubation medium to the incubation time) at P60 exceeds the synthesis rate at P10, while the efficiency of L‑DOPA synthesis (a ratio between the rate of L-DOPA synthesis and the total protein content in SCN) is higher at P10. Thus, we obtained evidence of L-DOPA synthesis in TH-containing SCN nerve fibers, and the efficiency of this synthesis in rats in the early postnatal period is higher than in adult animals.

中文翻译：

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大鼠单上裂性核中含单酶酪氨酸羟化酶的神经纤维合成L-二羟基苯丙氨酸的过程

摘要-由于存在起搏器神经元并调节这些神经元的传入，因此视交叉上核（SCN）根据昼夜节律调节身体的功能。其中一个传入神经的神经纤维仅包含用于合成儿茶酚胺的第一种酶酪氨酸羟化酶（TH）。在个体发育中，这些纤维的浓度（每单位组织体积的含量）在产后第10天（P10）达到最大值，然后逐渐降低。这项工作的目的是验证我们的假设，即在大鼠SCN中含TH的纤维中，L-DOPA由L-酪氨酸作为最终分泌产物合成，并且这种合成的效率在出生后早期较高。比成年人 在SCN和含或不含L-酪氨酸的培养基中孵育2小时后，通过SCN和孵育培养基中L-DOPA总含量的增加来评估L-DOPA的合成。我们发现向培养培养基中添加L-酪氨酸导致SCN和培养基中总L-DOPA含量成倍增加，这证明了L-DOPA作为含TH的最终产物的合成纤维。对P10和P60的SCN中L-DOPA合成的比较分析显示，P60的合成速率（SCN和培养液中L-DOPA的总含量与培养时间的比）超过了合成速率在P10时，L‑DOPA合成效率（L-DOPA合成速率与SCN中总蛋白含量之比）在P10时较高。从而，