Lutz P L, Nilsson G E
Department of Biological Sciences, Florida Atlantic University, Boca Raton 33149, USA.
J Exp Biol. 1997 Jan;200(Pt 2):411-9. doi: 10.1242/jeb.200.2.411.
Anoxia-tolerant turtles and carp (Carassius) exhibit contrasting strategies for anoxic brain survival. In the turtle brain, the energy consumption is deeply depressed to the extent of producing a comatose-like state. Brain metabolic depression is brought about by activating channel arrest to reduce ion flux and through the release of inhibitory gamma-aminobutyric acid (GABA) and the upregulation of GABAA receptors. Key glycolytic enzymes are down-regulated during prolonged anoxia. The result is a suppression of neurotransmission and a substantial depression in brain electrical activity. By contrast, Carassius remain active during anoxia, though at a reduced level. As in the turtle, there is an adenosine-mediated increase in brain blood flow but, in contrast to the turtle, this increase is sustained throughout the anoxic period. Key glycolytic enzymes are up-regulated and anaerobic glycolysis is enhanced. There is no evidence of channel arrest in Carassius brain. The probable result is that electrical activity in the brain is not suppressed but instead maintained at a level sufficient to regulate and control the locomotory and sensory activities of the anoxic carp. The key adaptations permitting the continued high level of glycolysis in Carassius are the production and excretion of ethanol as the glycolytic end-product, which avoids self-pollution by lactate produced during glycolysis that occurs in other vertebrates.
耐缺氧的乌龟和鲤鱼表现出不同的缺氧脑存活策略。在乌龟脑中，能量消耗大幅降低，达到产生类似昏迷状态的程度。脑代谢抑制是通过激活通道阻滞以减少离子通量、释放抑制性γ-氨基丁酸（GABA）以及上调GABAA受体来实现的。在长时间缺氧期间，关键糖酵解酶被下调。结果是神经传递受到抑制，脑电活动大幅降低。相比之下，鲤鱼在缺氧期间仍保持活跃，尽管活跃度有所降低。与乌龟一样，脑血流量会因腺苷介导而增加，但与乌龟不同的是，这种增加在整个缺氧期间持续存在。关键糖酵解酶被上调，无氧糖酵解增强。没有证据表明鲤鱼脑存在通道阻滞。可能的结果是，脑中的电活动不会受到抑制，而是维持在足以调节和控制缺氧鲤鱼运动和感觉活动的水平。允许鲤鱼持续进行高水平糖酵解的关键适应性变化是将乙醇作为糖酵解终产物进行产生和排泄，这避免了其他脊椎动物糖酵解过程中产生的乳酸造成的自我污染。
