Cerebrovascular organization and dynamics in cephalopods
Abbott, N.J.; Miyan, J.A. (1995). Cerebrovascular organization and dynamics in cephalopods, in: Abbott, N.J. et al. (Ed.) Cephalopod neurobiology: neuroscience studies in squid, octopus and cuttlefish. pp. 459-476
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| Abstract |
It has proved extremely difficult to do electrophysiological recording from exposed preparations of cephalopod brain, with the result that our understanding of the cell physiology of the cephalopod CNS has lagged behind that of other vertebrate and invertebrate groups. Many of the problems can be traced to features of cerebrovascular dynamics in cephalopods. This chapter reviews the anatomy and physiology of the cerebral circulation in cephalopods, and its behaviour in experimental preparations. Cephalopods have a closed vasculature, and the arrangement of cerebral arteries, arterioles, capillaries and veins follows a similar pattern to that of vertebrates, with some differences at the electron microscopic level. 'Gliovascular' channels may act as routes for flow of interstitial fluid while 'lymphoid' channels return the fluid to the venous system. Careful measurements of vascularity in Sepia show that the microvessel density in the brain is similar to that of mammals, while in muscle it is generally lower. There is a good correlation between tissue vascularity and aerobic status as judged from the ratio of oxidative to glycolytic enzymes. The control of the cerebral circulation in cephalopods is poorly understood, but appears to be mainly neurogenic. In larger cephalopods, surgical exposure of the brain, and probing with electrodes, cause ischaemia, hypoxia, cell swelling and eventually cell death, by a combination of a drop in perfusion pressure, local vasoconstriction, and accumulation of toxic metabolites. Experimental strategies to overcome these problems and develop useful preparations for electrophysiology are outlined. |
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