Murphy J A, Deurveilher S, Semba K
Department of Anatomy and Neurobiology, Faculty of Medicine, Dalhousie University, Tupper Medical Building, Room 13MN, 5850 College Street, Halifax, Nova Scotia, Canada B3H 1X5.
Neuroscience. 2003;121(2):269-75. doi: 10.1016/s0306-4522(03)00461-5.
Although caffeine is a commonly used CNS stimulant, neuronal mechanisms underlying its stimulatory effect are not fully understood. Orexin (hypocretin)-containing neurons play a critical role in arousal and might be activated by acute administration of caffeine. We examined this possibility by using dual-immunostaining for orexin B and c-Fos protein as a marker for neuronal activation. Rats were administered intraperitoneally with 10, 30 or 75 mg/kg caffeine, or saline. As previously reported, caffeine increased locomotion at 10 and 30 mg/kg, but not at 75 mg/kg. The numbers of orexin-immunoreactive and non-orexin-immunoreactive neurons expressing c-Fos were analysed using three counting boxes within the orexin field in the posterior hypothalamus. Compared with saline, all doses of caffeine increased the number of cells immunoreactive for both orexin and c-Fos. The average magnitude of this increase across doses in orexin neurons differed amongst regions; c-Fos expression increased by 343% in the perifornical area and by 158% in the more medial, dorsomedial nucleus. In the lateral hypothalamic area, c-Fos expression increased by 226% at 10 and 30 mg/kg but no change was seen at 75 mg/kg. In contrast, caffeine significantly increased the number of non-orexin-immunoreactive neurons expressing c-Fos only in the dorsomedial nucleus. These results indicate that systemically administered caffeine preferentially activates orexin neurons over non-orexin neurons in the same field, and that this activation is most pronounced in the perifornical region where orexin neurons are most concentrated. The activation of orexin neurons might play a role in the behavioural activation by caffeine.
尽管咖啡因是一种常用的中枢神经系统兴奋剂，但其刺激作用背后的神经元机制尚未完全明确。含食欲素（下丘脑泌素）的神经元在觉醒中起关键作用，可能会被急性给予咖啡因激活。我们通过使用食欲素B和c-Fos蛋白的双重免疫染色作为神经元激活的标志物来研究这种可能性。给大鼠腹腔注射10、30或75mg/kg咖啡因或生理盐水。如先前报道，10mg/kg和30mg/kg的咖啡因可增加运动能力，但75mg/kg时则无此作用。使用下丘脑后部食欲素区域内的三个计数框分析表达c-Fos的食欲素免疫反应性和非食欲素免疫反应性神经元的数量。与生理盐水相比，所有剂量的咖啡因均增加了食欲素和c-Fos双免疫反应性细胞的数量。不同区域中食欲素神经元跨剂量的这种增加的平均幅度有所不同；穹窿周区的c-Fos表达增加了343%，更内侧的背内侧核增加了158%。在外侧下丘脑区域，10mg/kg和30mg/kg时c-Fos表达增加了226%，但75mg/kg时未见变化。相反，咖啡因仅在背内侧核显著增加了表达c-Fos的非食欲素免疫反应性神经元的数量。这些结果表明，全身给予咖啡因在同一区域内优先激活食欲素神经元而非非食欲素神经元，且这种激活在食欲素神经元最集中的穹窿周区域最为明显。食欲素神经元的激活可能在咖啡因引起的行为激活中起作用。
