Marks M J, Smith K W, Collins A C
Institute for Behavioral Genetics, University of Colorado, Boulder, Colorado 80409-0447, USA.
J Pharmacol Exp Ther. 1998 Apr;285(1):377-86.
The binding of [3H]epibatidine, an alkaloid isolated from the skin of an Ecuadorean tree frog, was measured both in brain regions dissected from mouse brain and in tissue sections. Binding to each of 12 brain areas was saturable, but apparently monophasic; no indication of multiple binding sites was obtained. However, inhibition of epibatidine binding by nicotine, acetylcholine, methylcarbachol and cytisine in olfactory bulbs revealed a biphasic pattern consistent with the presence of two sites differentially sensitive to inhibition by these nicotinic agonists. Cytisine displayed the greatest difference in inhibitory potency between the two apparent sites. Subsequent analysis of the inhibition of epibatidine binding by cytisine in membranes prepared from 12 brain areas also suggested the presence of two sites in each brain region. The estimated potency of cytisine at each site was similar in each brain region. However, the proportion of [3H]epibatidine binding sites that were more sensitive to inhibition by cytisine and those sites less sensitive to inhibition by this agonist varied markedly among the brain regions. Quantitative autoradiographic analyses of mouse brain revealed pattern of [3H]epibatidine binding sites less sensitive to inhibition by cytisine that differed markedly from the pattern obtained with [3H]nicotine. Among brain regions demonstrating substantial sites less sensitive to cytisine inhibition were the accessory olfactory nucleus, medial habenula, interpeduncular nucleus, fasciculus retroflexus, superior colliculus, inferior colliculus and the pineal gland. The results indicate that epibatidine binds to at least two distinct nicotinic sites in mouse brain that may represent different nicotinic receptor subtypes, one of which appears to be identical to that measured by the binding of other agonists such as nicotine or cytisine.
从厄瓜多尔树蛙皮肤中分离出的一种生物碱[3H]埃皮巴蒂啶的结合情况，在从小鼠脑部分离出的脑区以及组织切片中均有测定。与12个脑区中的每一个的结合都是可饱和的，但显然是单相的；未获得多个结合位点的迹象。然而，在嗅球中，尼古丁、乙酰胆碱、甲基卡巴胆碱和金雀花碱对埃皮巴蒂啶结合的抑制显示出一种双相模式，这与存在两个对这些烟碱激动剂抑制作用敏感性不同的位点一致。金雀花碱在两个明显位点之间的抑制效力差异最大。随后对金雀花碱在从12个脑区制备的膜中对埃皮巴蒂啶结合的抑制作用进行分析，也表明每个脑区都存在两个位点。在每个脑区中，金雀花碱在每个位点的估计效力相似。然而，对金雀花碱抑制作用更敏感的[3H]埃皮巴蒂啶结合位点与对该激动剂抑制作用不太敏感的位点的比例在不同脑区之间有显著差异。对小鼠脑的定量放射自显影分析显示，对金雀花碱抑制作用不太敏感的[3H]埃皮巴蒂啶结合位点模式与用[3H]尼古丁获得的模式明显不同。在对金雀花碱抑制作用不太敏感的大量位点的脑区中，有副嗅核、内侧缰核、脚间核、后屈束、上丘、下丘和松果体。结果表明，埃皮巴蒂啶在小鼠脑中与至少两个不同的烟碱位点结合，这可能代表不同的烟碱受体亚型，其中之一似乎与通过尼古丁或金雀花碱等其他激动剂结合所测量的相同。
