Evidence That Acetylcholine Mediates Increased Cerebral Blood Flow Velocity in Crucian Carp through a Nitric Oxide—Dependent Mechanism

Abstract

Summary: Nitric oxide (NO)-dependent regulation of brain blood flow has not been proven to exist in fish or other ectothermic vertebrates. Using epi-illumination mi croscopy on the brain surface (optic lobes) of crucian carp (Carassius carassius), we show that superfusing the brain with acetylcholine (ACh) induces an increase in ce rebral blood flow velocity that can be completely blocked by the NO synthase inhibitors NG-nitro-L-arginine meth ylester (L-NAME) and NG-nitro-L-arginine. Also, sodium nitroprusside, which decomposes to liberate NO, causes an increase in cerebral blood flow velocity. By contrast,In the mammalian brain, acetylcholine (ACh) causes vasodilation of cerebral arteries, both when it is administered exogenously and when it is re leased from parasympathetic fibers innervating ce rebral arteries and arterioles (Morita-Tsuzuki et aI., 1993). The vasodilatory action of ACh is mediated by an endothelium-derived relaxing factor (EDRF), which is now generally accepted to be identical with nitric oxide (NO) or a closely related molecule (re viewed by Faraci, 1993). Nevertheless, a role for NO in stimulating tissue blood flow by vasodilation in ectothermic vertebrates has not been demon strated. In fact, after having failed to find NO dependent mechanisms in trout vasoregulation, Ol son and Villa (1991) suggested that EDRF-like va sodilator mechanisms are not present in trout vessels.Received March 28,1994; final revision received July 7,1994; accepted August 2, 1994.Address correspondence and reprint requests to Dr. P. Hylland at Vertebrate Physiology and Behaviour Unit, Dept. of Limnology, Uppsala University, Norbyvagen 20, S-752-36 Upp sala, Sweden, Abbreviations used: ACh, acelytcholine; EDRF, endothelium derived relaxing factor; L-NA, NG-nitro-L-arginine; L-NAME, W-nitro-L-arginine methylester; NOS, NO synthase; SNP, so dium nitroprusside, 519L-NAME does not block the increase in blood flow ve locity caused by anoxia. The results suggest that NO is an endogenous vasqdilator in crucian carp brain that medi ates the effects of ACh. Because teleost fish deviated from other vertebrates 400 million years ago, these results suggest that NO-dependent brain blood flow regulation was an early event in vertebrate evolution. Key Words:Adenosine-Aminophylline-Anoxia-Carassius caras sius-Hypoxia-Endothelium-derived relaxing factor NG-Nitro-L-arginine methylester-Sodium nitroprusside.

Nitric oxide control of the dorsal aorta and the intestinal vein of the Australian short-finned eel Anguilla australis

“…The present study, however, demonstrates that SNP mediated a dilation in both the dorsal aorta and intestinal vein that could be blocked by ODQ, suggesting that NO stimulates the production of cGMP via a soluble GC. This observation is consistent with a number of previous studies that have shown that the vascular smooth muscle of teleost fish contains a NO receptor that mediates vasodilation Olson and Villa, 1991;Hylland and Nilsson, 1995;Kågström and Holmgren, 1996;McGeer and Eddy, 1996;Mustafa et al, 1997;Miller and Vanhoutte, 2000). In contrast to these studies, Pellegrino et al (2002) reported a vasoconstrictive effect of NO in the branchial circulation of A. anguilla using the NO donors, SNP and SIN-1, at a range of concentrations.…”

Role of Nitric Oxide in the Elevation of Cerebral Blood Flow Induced by Acetylcholine and Anoxia in the Turtle

“…Similar results have been obtained in crucian carp (Hylland and Nilsson, 1995). How ever, in mammals, NOS inhibitors often produce a lowering of basal CBF (Fernandez et aI., 1993;Macrae et aI., 1993), indicating a NO tonus, al though the absence of an effect of NOS inhibitors per se has also been reported in CBF studies on mammals (Faraci and Heistad, 1992).…”

“…The search for NO mediated mechanisms in a variety of tissues has been greatly facilitated by the recent development of potent inhibitors of NOS, such as N G -nitro-L arginine methyl ester (L-NAME) (Rees et aI., 1990). However, very little is known about the role of NO in the regulation of brain blood flow in non mammalian vertebrates, one exception being a re cent study showing that ACh superfusion elevates brain blood flow velocity in crucian carp through a NO-dependent mechanism (Hylland and Nilsson, 1995).…”

Dramatic increase of nitrite levels in hearts of anoxia-exposed crucian carp supporting a role in cardioprotection

“…However, the NOS1 variant is found in perivascular nerves in fish, meaning that NO produced by NOS can control the vasculature also in fish, despite the lack of Nos3 (36,56). Indeed, several studies have shown that endogenous NO produces vasodilation in fish (30,34,52).…”