Katz D M, Erb M J
Department of Medicine, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106.
Dev Biol. 1990 Feb;137(2):233-42. doi: 10.1016/0012-1606(90)90250-m.
The regulation of transmitter phenotype in primary sensory neurons remains poorly understood. However, recent studies of catecholaminergic (CA) sensory neurons suggest that expression of this particular phenotype may be related to innervation of specific peripheral tissues. In the glossopharyngeal petrosal ganglion (PG) of adult rats, for example, the vast majority of CA sensory neurons innervate a single target, the carotid body. The present study was undertaken, therefore, to begin investigating factors that underlie CA differentiation in sensory neurons, using the rat PG as a model system. Immunocytochemical, biochemical, and morphometric methods were used to investigate the normal time course of CA development in the PG in vivo, employing tyrosine hydroxylase (TH) as a phenotypic marker. These studies revealed two temporally distinct waves of TH expression during embryogenesis. TH immunoreactivity was initially detectable on Embryonic Day (E) 11.5; the number of stained cells increased markedly by E12.5 and then fell off sharply to near 0 by E15.5. Simultaneous immunostaining for TH and neurofilament proteins revealed a high proportion of double-labeled perikarya on E12.5, indicating that the transiently TH-positive cells are neurons. A second, sustained phase of TH expression began on E16.5, and by Postnatal Day 1 adult numbers of TH-containing ganglion cells were present. Western blot analysis demonstrated that TH levels per cell rose 3.5-fold in the perinatal period, indicating that maturation of this particular catecholaminergic trait in PG sensory neurons is highly regulated around birth. Morphometric techniques were used to define the relationship between neurons that transiently exhibit TH immunoreactivity early in gangliogenesis and those that maintain enzyme expression in the mature PG. These studies revealed separate and distinct growth curves for the early and late TH cells, respectively, demonstrating that the appearance, disappearance, and reappearance of immunoreactive cells reflects the differentiation of two separate populations of PG neurons. Moreover, these data indicate that TH expression in the population of CA cells that persists in the mature PG begins around E16.5. This is after peripheral target innervation has begun, raising the possibility that neuron-target interactions regulate biochemical differentiation of these CA sensory neurons.
初级感觉神经元中递质表型的调控仍知之甚少。然而，最近对儿茶酚胺能（CA）感觉神经元的研究表明，这种特定表型的表达可能与特定外周组织的神经支配有关。例如，在成年大鼠的舌咽神经岩神经节（PG）中，绝大多数CA感觉神经元支配单一靶点——颈动脉体。因此，本研究以大鼠PG为模型系统，开始研究感觉神经元中CA分化的潜在因素。采用免疫细胞化学、生物化学和形态计量学方法，以酪氨酸羟化酶（TH）作为表型标记，研究PG中CA发育的正常时间进程。这些研究揭示了胚胎发育过程中TH表达的两个时间上不同的阶段。TH免疫反应性最初在胚胎第（E）11.5天可检测到；到E12.5天时，染色细胞数量显著增加，然后在E15.5天时急剧下降至接近0。对TH和神经丝蛋白的同时免疫染色显示，在E12.5天时，有很大比例的双核周体，表明短暂TH阳性细胞是神经元。TH表达的第二个持续阶段始于E16.5天，到出生后第1天，出现了成年数量的含TH的神经节细胞。蛋白质印迹分析表明，围产期每个细胞的TH水平上升了3.5倍，表明PG感觉神经元中这种特定儿茶酚胺能特性的成熟在出生前后受到高度调控。形态计量学技术用于确定在神经节发生早期短暂表现出TH免疫反应性的神经元与在成熟PG中维持酶表达的神经元之间的关系。这些研究分别揭示了早期和晚期TH细胞各自独立且不同的生长曲线，表明免疫反应性细胞的出现、消失和再次出现反映了PG神经元两个不同群体的分化。此外，这些数据表明，在成熟PG中持续存在的CA细胞群体中，TH表达始于E16.5天。这是在外周靶点神经支配开始之后，这增加了神经元 - 靶点相互作用调节这些CA感觉神经元生化分化的可能性。
