Tyrrell S, Landis S C
Department of Neurosciences, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106.
J Neurosci. 1994 Sep;14(9):5708-21. doi: 10.1523/JNEUROSCI.14-09-05708.1994.
We compared the development of enkephalin (Enk) expression in normal rats and rats in which target contact was transiently disrupted with 6-hydroxydopamine (6-OHDA). During the first 3 postnatal weeks, there was a striking increase in Enk immunoreactivity (-IR) in superior cervical ganglia (SCG) assayed by radioimmunoassay (RIA). This increase was correlated with the appearance of Enk-IR in postganglionic neurons. In the caudal region of the SCG, the proportion of Enk-IR neurons and their immunoreactivity increased until one-third of the neurons possessed Enk-IR between postnatal days (P) 14 and 21. After P21, the number of Enk-IR neurons and their immunofluorescence decreased. By 6 weeks, only occasional neurons possessed moderate Enk-IR. The increases in Enk-IR were correlated with increased ganglionic proenkephalin A mRNA detected by in situ hybridization. The decrease in IR after P21 was not, however, paralleled by a comparable decrease in proenkephalin A mRNA. To determine whether interactions between SCG neurons and their target tissues influence Enk expression, we disrupted them by treating neonatal rats with a single dose of 6-OHDA at P0. This treatment transiently reduced sympathetic fiber density in the submandibular gland, one target of Enk-IR neurons, over 90%. Two weeks later, the fiber density in glands of treated animals was not different from control. Following 6-OHDA, the concentration of Enk-IR in SCG extracts and the number of Enk-IR neurons and their immunofluorescence intensity failed to increase. SCG from treated rats also contained fewer neurons with proenkephalin A mRNA. In contrast, the content of neuropeptide Y (NPY) and the proportion of NPY-IR neurons were not decreased by 6-OHDA treatment. Our results indicate that the developmental history of Enk expression differs from that of other neuropeptides in rat sympathetic ganglia, suggesting that distinct mechanisms regulate the expression of individual neuropeptides. Further, they provide evidence that target contact during a critical period is important for the induction of Enk.
我们比较了正常大鼠和经6-羟基多巴胺（6-OHDA）短暂破坏靶接触的大鼠中脑啡肽（Enk）表达的发育情况。在出生后的前三周，通过放射免疫分析（RIA）检测到，颈上神经节（SCG）中脑啡肽免疫反应性（-IR）显著增加。这种增加与节后神经元中脑啡肽-IR的出现相关。在SCG的尾部区域，脑啡肽-IR神经元的比例及其免疫反应性增加，直到出生后第（P）14至21天，三分之一的神经元具有脑啡肽-IR。P21之后，脑啡肽-IR神经元的数量及其免疫荧光减少。到6周时，只有偶尔的神经元具有中等程度的脑啡肽-IR。脑啡肽-IR的增加与原位杂交检测到的神经节前脑啡肽A mRNA增加相关。然而，P21后IR的减少并没有伴随着前脑啡肽A mRNA的相应减少。为了确定SCG神经元与其靶组织之间的相互作用是否影响脑啡肽表达，我们在P0时用单剂量的6-OHDA处理新生大鼠来破坏它们之间的相互作用。这种处理使脑啡肽-IR神经元的一个靶标——下颌下腺中的交感纤维密度暂时降低了90%以上。两周后，处理动物腺体中的纤维密度与对照组没有差异。给予6-OHDA后，SCG提取物中脑啡肽-IR的浓度、脑啡肽-IR神经元的数量及其免疫荧光强度均未增加。经处理大鼠的SCG中具有前脑啡肽A mRNA的神经元也较少。相比之下，神经肽Y（NPY）的含量和NPY-IR神经元的比例并未因6-OHDA处理而降低。我们的结果表明，大鼠交感神经节中脑啡肽表达的发育过程与其他神经肽不同，这表明不同的机制调节个体神经肽的表达。此外，它们提供了证据表明关键期的靶接触对脑啡肽的诱导很重要。
