Transient expression of somatostatin immunoreactivity in the developing olfactory-forebrain region of the chick.

在早期的鸡胚胎中，SST-ir细胞和纤维出现在嗅觉-前脑轴上，但这些SST-ir元素在孵化当天几乎消失(Murakami和Arai，1994)。SST-ir神经元的出现时间和分布与LHRH神经元相似，已有报道认为LHRH神经元起源于嗅觉胎盘，并迁移到前脑。SST和LHRH的双重染色结果表明，这两种类型的肽能神经元属于两种不同的细胞群。用荧光碳菁染料DiI标记胚胎2.5-3.5天(17-23期)鸡胚胎的胎盘上皮细胞。应用DiI后4-5天，标记的细胞在前脑内侧和视前隔区被识别。DII和SST双重染色显示，前脑内侧部分SST-ir细胞被DiI标记，提示SST-ir细胞起源于嗅觉胎盘，向内侧前脑迁移。此外，前脑内侧表面的一些LHRH神经元被发现伴随着一小部分从SST-IR嗅神经延伸出来的瞬时SST-ir纤维。这些瞬时的SST-ir纤维可能为LHRH神经元从鼻区向视前隔区域的迁移提供了结构性支持。需要进行电子显微镜或强制激光显微镜研究来阐明LHRH神经元的前导突起是否与瞬时的SST-ir纤维接触。

SST-ir cells and fibers appear in the olfactory-forebrain axis in early chick embryos but these SST-ir elements virtually disappear by the day of hatching (Murakami and Arai, 1994). The time of appearance and distribution of the SST-ir neural elements are similar to those of LHRH neurons which have been reported to originate in the olfactory placode and migrate into the forebrain. The results of double-staining for SST and LHRH indicate that these two types of peptidergic neurons belong to two different cell populations. The placodal epithelial cells of the embryonic day 2.5-3.5 (Stages 17-23) chick embryos were labeled with a fluorescent carbocyanine dye, DiI.Four to five days after DiI application, the labeled cells were recognized in the medial forebrain and in the septo-preoptic area. Double staining for DiI and SST in the brain showed that some of SST-ir cells in the medial forebrain were labeled with DiI.These results indicate that SST-ir cells originate in the olfactory placode and migrate into the medial forebrain. Moreover, a number of LHRH neurons in the medial forebrain surface are found to be accompanied by a small subset of transient SST-ir fibers extending from the SST-ir olfactory nerve. It is possibility that these transient SST-ir fibers provide structural support for the migration of LHRH neurons from the nasal region to the septo-preoptic area. Electron microscopic or conforcal laser microscopic study is needed to elucidate whether leading processes of LHRH neurons contact with a transient SST-ir fibers.