Study on the possibility for drug utilization of peptidergic neurotransmitter using knockout mouse

PACAP与血管活性肠多肽（vasoactive intestinal polypeptide， VIP）的氨基酸序列同源性高达68%，可调节中枢和外周神经系统的多种生理功能。目前已克隆出3个编码PACAP/VIP受体亚型的基因，它们与PACAP具有较高的亲和力，但每种亚型的生理意义尚未完全表征。为了阐明PACAP信号系统的作用，我们在胚胎干细胞中使用基因靶向来破坏PACAP受体基因的外显子2，并对突变小鼠和野生型小鼠进行了表征。突变小鼠脑内PACAP-27结合和cAMP生成减少[^<125>]。然而，这些突变的老鼠是可以存活和繁殖的，并且在形态上、组织学上和电生理学上与它们的野生型同类没有区别。在野生型小鼠和大鼠交感神经系统中均可见到PACAP受体和PACAP的共表达。在交感神经元中，PACAP在转录水平上刺激PACAP受体和PACAP mrna的表达。研究了小鼠胰岛素瘤细胞产生PACAP的机制。综上所述，这些结果表明，PACAP作为自分泌或旁分泌调节因子，有助于交感肾上腺系统的持续激活，并且PACAP通过自分泌机制调节葡萄糖刺激的β细胞胰岛素分泌。然而，完整的PACAP受体并不是正常小鼠发育或生存的先决条件。

PACAP has an amino acid sequence identity of 68% with vasoactive intestinal polypeptide (VIP) and regulates a wide range of physiological functions in the central and peripheral nervous systems. Three genes encoding PACAP/VIP receptor subtypes, which bind PACAP with a high affinity, have been cloned, but the physiological significance of each subtype has not been completely characterized. To elucidate the role of the PACAP signaling system, we have used gene targeting in embryonic stem cells to disrupt exon 2 of the PACAP receptor gene, and characterized the mutant mice as well as wildtype mice.1. The mutant mice had reduced [^<125>I]PACAP-27 binding and cAMP production in their brains.2. The mutant mice, however, were viable and fertile, and morphologically, histologically and electrophysiologically indistinguishable from their wild-type counterparts.3. Coexpression of PACAP receptor and PACAP was seen in the sympathetic nervous system of the wild-type mice and rats.4. In the sympathetic neurons, PACAP stimulates the expression of PACAP receptor and PACAP mRNAs at a transcriptional level.5. The mechanism of the PACAP production was studied in mouse insulinoma cells.In conclusion, these results suggest that PACAP acts as a autocrine or paracrine regulatory factor and contributes to sustained activation of the sympathoadrenal system, and that PACAP regulates glucose-stimulated insulin secretion from beta cells by an autocrine mechanism. However, the intact PACAP receptor is not a prerequisite for normal mouse development of for survival.