McMillian M K, Mullis S B, Wu G C, Hudson P M, Pennypacker K R, Hong J S
Laboratory of Molecular and Integrative Neurosciences, NIEHS, NIH, Research Triangle Park, NC 27709.
Brain Res. 1994 Sep 26;658(1-2):105-11. doi: 10.1016/s0006-8993(09)90015-4.
Regulation of tyrosine hydroxylase (TH) by second messenger pathway activators was examined in rat olfactory bulb cell cultures. The number of TH-immunoreactive neurons was increased 2-3-fold by 36 h treatments with forskolin (Fsk, 10(-6) M) or phorbol myristate acetate (PMA, 10(-7) M), but was not significantly increased by a depolarizing concentration of KCl (45 mM). In contrast, KCl increased media [Met5]enkephalin (ME) immunoreactivity 2-fold in these cultures, equivalent to stimulation with Fsk or PMA. The possibility was examined that ME or another opioid produced by the cultures selectively inhibited the TH response to KCl. Pretreatment with the opioid receptor antagonist naloxone (10(-6) M) greatly increased the number of TH-immunoreactive neurons observed in response to KCl treatment, but had no effect on basal or Fsk-stimulated TH immunostaining, nor on basal or stimulated ME release. The increase in TH-immunoreactivity observed with combined KCl plus naloxone treatment was prevented by pretreating the cultures with the calcium channel blocker nimodipine (10(-6) M), which had no effect on Fsk stimulation or basal TH immunostaining. These data suggest that endogenous opioids selectively inhibit KCl-stimulated Ca2+ entry and thus TH induction in olfactory bulb cell cultures. These cultures offer a simple model system for further study of TH regulation in dopaminergic neurons.
在大鼠嗅球细胞培养物中研究了第二信使途径激活剂对酪氨酸羟化酶（TH）的调节作用。用福斯可林（Fsk，10⁻⁶ M）或佛波酯（PMA，10⁻⁷ M）处理36小时后，TH免疫反应性神经元的数量增加了2 - 3倍，但在去极化浓度的氯化钾（45 mM）作用下，其数量没有显著增加。相反，氯化钾使这些培养物中的培养基[Met5]脑啡肽（ME）免疫反应性增加了2倍，这与Fsk或PMA刺激的效果相当。研究了培养物产生的ME或其他阿片类物质是否选择性抑制TH对氯化钾的反应。用阿片受体拮抗剂纳洛酮（10⁻⁶ M）预处理可显著增加氯化钾处理后观察到的TH免疫反应性神经元的数量，但对基础或Fsk刺激的TH免疫染色没有影响，对基础或刺激的ME释放也没有影响。用钙通道阻滞剂尼莫地平（10⁻⁶ M）预处理培养物可阻止氯化钾加纳洛酮联合处理时观察到的TH免疫反应性增加，而尼莫地平对Fsk刺激或基础TH免疫染色没有影响。这些数据表明，内源性阿片类物质选择性抑制氯化钾刺激的Ca²⁺内流，从而抑制嗅球细胞培养物中TH的诱导。这些培养物为进一步研究多巴胺能神经元中TH的调节提供了一个简单的模型系统。
