Pépin J L, Lévy P, Garcin A, Feuerstein C, Savasta M
Inserm U 318, Department of Clinical and Biological Neurosciences, CHU de Grenoble, France.
Brain Res. 1996 Sep 9;733(1):1-8. doi: 10.1016/0006-8993(96)00250-8.
The nucleus tractus solitarius (NTS), the ventrolateral medulla (VLM), the dorsal motor vagus nucleus (DMnX) and the locus coeruleus (LC) are catecholaminergic brainstem areas involved in ventilatory and cardiovascular responses to hypoxia and tyrosine hydroxylation is the rate limiting step of cathecholamine biosynthesis in the central nervous system. The aim of this study was to evaluate the effects of long-term hypoxia on tyrosine hydroxylase (TH) content in these different areas using a quantitative autoradiographic technique. Two experimental groups of rats were studied: Group I (9 males, 8 females) was submitted to normobaric hypoxia (10% O2-90% N2) for 21 days and compared to 12 (6 males, 6 females) normoxic control rats (Group II). Coronal tissue sections from fresh-frozen rat brains, obtained along the caudo-rostral axis, were incubated in the presence of a TH monoclonal antibody, and the reaction was revealed by a 35S-labelled secondary antibody. TH levels were quantified in the NTS, VLM, DMnX and LC by measuring optical density on autoradiographic films using an automatic image analyser system. Regional antigen quantification was assessed by computer-assisted image analysis. Chronic hypoxia led to body weight decrease until day 5, haematocrit increase (65 +/- 2% vs. 44 +/- 2%, P < 0.01) and right ventricle hypertrophy (35 +/- 0.5% vs. 23 +/- 0.1% of the weight of the two ventricles, P < 0.01). TH protein contents expressed as percentage of controls were as follows. In males, in the rostral part of the NTS 132 +/- 9% (P < 0.02), in the caudal part of the NTS, 117 +/- 5% (P < 0.04). In female rats, the TH quantity reached a value of 124 +/- 4% (P < 0.01) in the rostral part and 126 +/- 6% (P < 0.01) in the caudal part of the NTS. In females, TH content was significantly increased in the VLM, 124 +/- 6%, P = 0.01, whereas in males there was only a non-significant trend to increase, 122 +/- 11%. In females, there was a significant increase in the DMnX, 127 +/- 9%, P = 0.05, whereas in males there was only a trend to increase, 120 +/- 5%. This study shows that long-term hypoxia induces a persistent increase in TH protein content both in the caudal and rostral part of the NTS, which are known to receive respectively chemo- and barosensory inputs, and in other catecholaminergic areas involved in baroreflex activity. Our data clearly demonstrate the implication of neurochemical mechanisms in the central relationship between chemo- and baroreflex which are responsible for changes in systemic arterial pressure and oxygen partial pressure as required for maintaining an adequate oxygen supply to the tissues.
孤束核（NTS）、延髓腹外侧区（VLM）、迷走神经背运动核（DMnX）和蓝斑（LC）是参与对缺氧产生通气和心血管反应的儿茶酚胺能脑干区域，而酪氨酸羟化是中枢神经系统中儿茶酚胺生物合成的限速步骤。本研究的目的是使用定量放射自显影技术评估长期缺氧对这些不同区域酪氨酸羟化酶（TH）含量的影响。研究了两组实验大鼠：第一组（9只雄性，8只雌性）在常压缺氧（10% O₂ - 90% N₂）条件下饲养21天，并与12只（6只雄性，6只雌性）常氧对照大鼠（第二组）进行比较。沿尾 - 嘴轴获取新鲜冷冻大鼠脑的冠状组织切片，在TH单克隆抗体存在下孵育，并用³⁵S标记的二抗显示反应。通过使用自动图像分析仪系统测量放射自显影片上的光密度，对NTS、VLM、DMnX和LC中的TH水平进行定量。通过计算机辅助图像分析评估区域抗原定量。慢性缺氧导致体重在第5天前下降、血细胞比容增加（65 ± 2% 对 44 ± 2%，P < 0.01）和右心室肥大（占两个心室重量的35 ± 0.5% 对 23 ± 0.1%，P < 0.01）。以对照百分比表示的TH蛋白含量如下。在雄性大鼠中，NTS嘴侧部分为132 ± 9%（P < 0.02），NTS尾侧部分为117 ± 5%（P < 0.04）。在雌性大鼠中，NTS嘴侧部分的TH量达到124 ± 4%（P < 0.01），尾侧部分为126 ± 6%（P < 0.01）。在雌性大鼠中，VLM中的TH含量显著增加，为124 ± 6%，P = 0.01，而在雄性大鼠中仅有不显著的增加趋势，为122 ± 11%。在雌性大鼠中，DMnX中有显著增加，为127 ± 9%，P = 0.05，而在雄性大鼠中仅有增加趋势，为120 ± 5%。本研究表明，长期缺氧会导致NTS的尾侧和嘴侧部分（分别已知接受化学和压力感受性输入）以及参与压力反射活动的其他儿茶酚胺能区域的TH蛋白含量持续增加。我们的数据清楚地证明了神经化学机制在化学反射和压力反射之间的中枢关系中的作用，这些反射负责根据维持组织充足氧气供应的需要改变体动脉压和氧分压。
