Granger N A, Sturgis S L, Ebersohl R, Geng C, Sparks T C
Department of Cell Biology and Anatomy, University of North Carolina, Chapel Hill 27599, USA.
Arch Insect Biochem Physiol. 1996;32(3-4):449-66. doi: 10.1002/(SICI)1520-6327(1996)32:3/4<449::AID-ARCH17>3.0.CO;2-C.
The corpora allata (CA) of insects are innervated by axons of non-neurosecretory cerebral neurons, and of the various known neurotransmitters in the brain of the tobacco hornworm, Manduca sexta, only dopamine is detected in the CA by electrochemical detection HPLC. This neurotransmitter stimulates the biosynthetic activity of the CA in vitro for the first 2 days of the last larval stadium, but inhibits CA from day 3 through day 6, the beginning of the prepupal period. Stimulation of JH synthesis has previously been linked with an increase in the production of cyclic AMP (cAMP) in the CA, and dopamine stimulates the adenylyl cyclase system of CA from larvae early in the fifth stadium, while on day 6, its effect is inhibitory. These results suggest: (1) the existence in the CA of both D1- and D2-like dopamine receptors, which in vertebrates stimulate and inhibit, respectively, adenylyl cyclase; and (2) the developmental control of their expression. A potent D1 agonist, (+/-)-SKF 82958-HBr, did not stimulate JH biosynthesis by day 0 CA as expected, but appeared to inhibit it at a concentration of 10(-5)M. Thus the apparent D1-like receptor in Manduca CA may be pharmacologically distinct from vertebrate D1 receptors. The existence of D2-like receptors is supported by the finding that a vertebrate D2 receptor agonist, (+/-) PPHT-HCl, and an antagonist, eticlopride, have the predicted effects on JH acid biosynthesis and cAMP production by day 6 Manduca CA. However, the D1 agonist also significantly reduces JH acid biosynthesis and cAMP production, indicating that while the Manduca D2-like receptor is pharmacologically similar to the vertebrate D2, it shares some characteristics with D1 receptors. The developmental regulation of these receptors by ecdysteroids is suggested by the fact that when day 0 larvae are treated in vivo with exogenous ecdysone:20-hydroxyecdysone, the biosynthetic activity of the CA in vitro 24 h later is no longer stimulated by dopamine.
昆虫的咽侧体（CA）由非神经分泌性脑神经元的轴突支配，在烟草天蛾（Manduca sexta）大脑中已知的各种神经递质中，通过电化学检测高效液相色谱法仅在CA中检测到多巴胺。在最后一龄幼虫期的头两天，这种神经递质在体外刺激CA的生物合成活性，但在第3天至第6天（即预蛹期开始时）抑制CA。先前已将保幼激素（JH）合成的刺激与CA中环状AMP（cAMP）产量的增加联系起来，多巴胺在五龄幼虫早期刺激CA的腺苷酸环化酶系统，而在第6天，其作用是抑制性的。这些结果表明：（1）CA中存在D1样和D2样多巴胺受体，在脊椎动物中，它们分别刺激和抑制腺苷酸环化酶；（2）其表达的发育调控。一种有效的D1激动剂，（+/-）-SKF 82958-HBr，并未如预期那样在第0天刺激CA的JH生物合成，但在10^(-5)M浓度下似乎抑制了它。因此，烟草天蛾CA中明显的D1样受体在药理学上可能与脊椎动物的D1受体不同。脊椎动物D2受体激动剂（+/-）PPHT-HCl和拮抗剂依替必利对第6天烟草天蛾CA的JH酸生物合成和cAMP产生具有预测的作用，这一发现支持了D2样受体的存在。然而D1激动剂也显著降低JH酸生物合成和cAMP产生，这表明虽然烟草天蛾D2样受体在药理学上与脊椎动物D2相似，但它与D1受体具有一些共同特征。当用外源蜕皮激素：20-羟基蜕皮酮对第0天的幼虫进行体内处理时，24小时后体外CA的生物合成活性不再受多巴胺刺激，这一事实表明这些受体受蜕皮类固醇的发育调控。
