Effect of anoxia on the electroretinogram of three anoxia-tolerant vertebrates.
To survive anoxia, neural ATP levels have to be defended. Reducing electrical activity, which accounts for 50% or more of neural energy consumption, should be beneficial for anoxic survival. The retina is a hypoxia sensitive part of the central nervous system. Here, we quantify the in vivo retinal light response (electroretinogram; ERG) in three vertebrates that exhibit varying degrees of anoxia tolerance: freshwater turtle (Trachemys scripta), epaulette shark (Hemiscyllium ocellatum) and leopard frog (Rana pipiens). A virtually total suppression of ERG in anoxia, probably resulting in functional blindness, has previously been seen in the extremely anoxia-tolerant crucian carp (Carassius carassius). Surprisingly, the equally anoxia-tolerant turtle, which strongly depresses brain and whole-body metabolism during anoxia, exhibited a relatively modest anoxic reduction in ERG: the combined amplitude of turtle ERG waves was reduced by approximately 50% after 2 h. In contrast, the shark b-wave amplitude practically disappeared after 30 min of severe hypoxia, and the frog b-wave was decreased by approximately 75% after 40 min in anoxia. The specific A(1) adenosine receptor antagonist CPT significantly delayed the suppression of turtle ERG, while the hypoxic shark ERG was unaffected by the non-specific adenosine receptor antagonist aminophylline, suggesting adenosinergic involvement in turtle but not in shark.
Stensløkken
Kåre-Olav
KO
Surgical Division, Ullevål University Hospital, University of Oslo, NO-0407 Oslo, Norway.
Milton
Sarah L
SL
Lutz
Peter L
PL
Sundin
Lena
L
Renshaw
Gillian M C
GM
Stecyk
Jonathan A W
JA
Nilsson
Göran E
GE
D000241:Adenosine / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002347:Carps; D004596:Electroretinography / Q000379:methods*; D000860:Hypoxia; D015233:Models, Statistical; D009474:Neurons / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D011898:Ranidae; D012160:Retina / Q000378:metabolism; D012754:Sharks; D013045:Species Specificity; D014426:Turtles; D014714:Vertebrates
D000255:Adenosine Triphosphate; D000241:Adenosine; D010100:Oxygen