Zippel K C, Lillywhite H B, Mladinich C R
Department of Zoology, University of Florida, Gainesville 32611, USA.
J Morphol. 1998 Oct;238(1):39-51. doi: 10.1002/(SICI)1097-4687(199810)238:1<39::AID-JMOR3>3.0.CO;2-I.
Blood supplying the brain in vertebrates is carried primarily by the carotid vasculature. In most mammals, cerebral blood flow is supplemented by the vertebral arteries, which anastomose with the carotids at the base of the brain. In other tetrapods, cerebral blood is generally believed to be supplied exclusively by the carotid vasculature, and the vertebral arteries are usually described as disappearing into the dorsal musculature between the heart and head. There have been several reports of a vertebral artery connection with the cephalic vasculature in snakes. We measured regional blood flows using fluorescently labeled microspheres and demonstrated that the vertebral artery contributes a small but significant fraction of cerebral blood flow (approximately 13% of total) in the rat snake Elaphe obsoleta. Vascular casts of the anterior vessels revealed that the vertebral artery connection is indirect, through multiple anastomoses with the inferior spinal artery, which connects with the carotid vasculature near the base of the skull. Using digital subtraction angiography, fluoroscopy, and direct observations of flow in isolated vessels, we confirmed that blood in the inferior spinal artery flows craniad from a point anterior to the vertebral artery connections. Such collateral blood supply could potentially contribute to the maintenance of cerebral circulation during circumstances when craniad blood flow is compromised, e.g., during the gravitational stress of climbing.
脊椎动物中为大脑供血的主要是颈动脉系统。在大多数哺乳动物中，椎动脉会辅助供应脑血流，椎动脉在脑底部与颈动脉吻合。在其他四足动物中，一般认为脑血仅由颈动脉系统供应，椎动脉通常被描述为消失于心脏和头部之间的背部肌肉中。有几份报告称蛇的椎动脉与头部血管系统相连。我们使用荧光标记微球测量了局部血流，并证明在鼠蛇（Elaphe obsoleta）中，椎动脉对脑血流贡献了一小部分但显著的比例（约占总量的13%）。前部血管的血管铸型显示，椎动脉的连接是间接的，通过与脊髓下动脉的多次吻合，脊髓下动脉在颅骨底部附近与颈动脉系统相连。通过数字减影血管造影、荧光透视以及对孤立血管中血流的直接观察，我们证实脊髓下动脉中的血液从椎动脉连接点前方的一点向头侧流动。这种侧支血液供应在颅向血流受损的情况下，例如在攀爬的重力应激期间，可能有助于维持脑循环。
