Kolk S M, Kramer B M R, Cornelisse L N, Scheenen W J J M, Jenks B G, Roubos E W
University of Nijmegen, Nijmegen Institute for Neurosciences and Institute of Cellular Signaling, Department of Cellular Animal Physiology, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands.
Comp Biochem Physiol B Biochem Mol Biol. 2002 May;132(1):257-68. doi: 10.1016/s1096-4959(01)00533-4.
Some amphibian brain-melanotrope cell systems are used to study how neuronal and (neuro)endocrine mechanisms convert environmental signals into physiological responses. Pituitary melanotropes release alpha-melanophore-stimulating hormone (alpha-MSH), which controls skin color in response to background light stimuli. Xenopus laevis suprachiasmatic neurons receive optic input and inhibit melanotrope activity by releasing neuropeptide Y (NPY), dopamine (DA) and gamma-aminobutyric acid (GABA) when animals are placed on a light background. Under this condition, they strengthen their synaptic contacts with the melanotropes and enhance their secretory machinery by upregulating exocytosis-related proteins (e.g. SNAP-25). The inhibitory transmitters converge on the adenylyl cyclase system, regulating Ca(2+) channel activity. Other messengers like thyrotropin-releasing hormone (TRH) and corticotropin-releasing hormone (CRH, from the magnocellular nucleus), noradrenalin (from the locus coeruleus), serotonin (from the raphe nucleus) and acetylcholine (from the melanotropes themselves) stimulate melanotrope activity. Ca(2+) enters the cell and the resulting Ca(2+) oscillations trigger alpha-MSH secretion. These intracellular Ca(2+) dynamics can be described by a mathematical model. The oscillations travel as a wave through the cytoplasm and enter the nucleus where they may induce the expression of genes involved in biosynthesis and processing (7B2, PC2) of pro-opiomelanocortin (POMC) and release (SNAP-25, munc18) of its end-products. We propose that various environmental factors (e.g. light and temperature) act via distinct brain centers in order to release various neuronal messengers that act on the melanotrope to control distinct subcellular events (e.g. hormone biosynthesis, processing and release) by specifically shaping the pattern of melanotrope Ca(2+) oscillations.
一些两栖动物的脑黑素细胞系统被用于研究神经元和（神经）内分泌机制如何将环境信号转化为生理反应。垂体黑素细胞释放α-黑素细胞刺激素（α-MSH），其根据背景光刺激控制皮肤颜色。当动物置于明亮背景下时，非洲爪蟾的视交叉上核神经元接收视觉输入并通过释放神经肽Y（NPY）、多巴胺（DA）和γ-氨基丁酸（GABA）来抑制黑素细胞活性。在这种情况下，它们加强与黑素细胞的突触联系，并通过上调与胞吐作用相关的蛋白质（如SNAP-25）来增强其分泌机制。抑制性递质汇聚到腺苷酸环化酶系统，调节Ca(2+)通道活性。其他信使，如促甲状腺激素释放激素（TRH）和促肾上腺皮质激素释放激素（CRH，来自大细胞神经核）、去甲肾上腺素（来自蓝斑核）、5-羟色胺（来自中缝核）和乙酰胆碱（来自黑素细胞自身）刺激黑素细胞活性。Ca(2+)进入细胞，由此产生的Ca(2+)振荡触发α-MSH分泌。这些细胞内Ca(2+)动态变化可用数学模型来描述。振荡以波的形式穿过细胞质并进入细胞核，在细胞核中它们可能诱导参与阿片-促黑素皮质素原（POMC）生物合成和加工（7B2、PC2）及其终产物释放（SNAP-25、munc18）的基因表达。我们提出，各种环境因素（如光照和温度）通过不同的脑中枢起作用，以释放各种作用于黑素细胞的神经信使，通过特异性塑造黑素细胞Ca(2+)振荡模式来控制不同的亚细胞事件（如激素生物合成、加工和释放）。
