THE EFFECTS OF ANOXIA UPON ENERGY SOURCES AND SELECTED METABOLIC INTERMEDIATES IN THE BRAINS OF FISH, FROG AND TURTLE¹

Abstract

Abstract— The levels of the main cerebral energy reserves, ATP, P‐creatine, glycogen and glucose, and of several glycolytic intermediates and lactate, were measured in the brains of fish (Carassius auratus), turtle (Pseudemys scripta elegans) and frog (Rana pipiens). The levels of glycogen in these brains were 2‐9 times higher than those reported for mammals. In frog, cerebral glycogen levels were 35 per cent higher during the winter than in spring. The P‐creatine: ATP ratios were 3 instead of the more usual (mammalian) value of 1. The levels of other intermediates were similar to those found in mammalian brain. When anoxia was produced by decapitation, changes in the various substances measured were similar to those in mammalian brain, but were much slower. The initial rate at which high‐energy phosphate was used could be calculated from these changes. Values of 1.1 m‐equiv./kg/min for fish and frog and of 0.46 m‐equiv./kg/min for turtle were found, which are 1/20 and 1/50, respectively, of the rate in mouse brain. The rate of disappearance of high‐energy phosphate reserves followed first‐order kinetics for 4 hr in turtle and for at least an hour in the other species. Changes in metabolites as the experiment progressed were interpreted to indicate a progressively falling intracellular pH, prolonged inhibition of phosphofructokinase, and a long period of hexokinase inhibition.

Glycogen dynamics of crucian carp (Carassius carassius) in prolonged anoxia

“…Although the importance of glycogen as anaerobic energy substrate is well documented, mobilization of glycogen stores from different tissues under anoxia is still poorly elucidated. Unanswered questions include the following: (1) are glycogen stores of various tissues simultaneously mobilized or is there a certain order of recruitment between tissues [it has been suggested that glycogen stores of brain and heart are used at the onset of anoxia to win time for the second phase of the anoxic defense mechanism (Merrick and Meyer 1954;McDougal et al 1968)]? (2) Is glycogen gradually degraded according to the energy demands of the anoxic body or is it released in one or several bouts during anoxia?…”

Effects of sciatic nerve transection on glucose uptake in the presence and absence of lactate in the frog dorsal root ganglia and spinal cord

“…Other aspects include the simplicity of the amphibian central nervous system and the economic advantage of using these animals. In addition, the metabolic changes are much slower in frog brain than those found in the mammalian brain (McDougal et al, 1968). Thus, frog nervous tissue offers a unique model to examine the relationship between SNT and glucose metabolism.…”

“…Many of these alterations share similarities with those observed in mammals (Partata et al, 2002;Guedes et al, 2004a, b). As glucose has been considered the major energy substrate for the frog brain (McDougal et al, 1968), glucose transporters (Glut) types 1 and 3 are found in the nervous tissue of these animals (Rigon et al, 2013) and they accumulate lactic acid under some conditions (Warren and Jackson, 2005 14 C-3-OMG) was used to demonstrate the steady-state tissue/medium glucose distribution ratio under these conditions. All these parameters were also analysed in the lumbosacral spinal cord, where most of the afferent fibres of the sciatic nerve enter and the motor neurons of this nerve are located (Penicnak and Dunlap, 1962;Sutherland and Nunnemacher, 1974).…”

Effect of Sciatic Nerve Transection on acetylcholinesterase activity in spinal cord and skeletal muscles of the bullfrog Lithobates catesbeianus

“…However, while SNT induced a rapid initial decrease in AChE activity in rat skeletal muscles (Guth et al, 1964), such reduction occurred later and more slowly in bullfrog tissues. We suggest that such difference may be related to the nervous system's slower metabolic rate in frogs than in mammals (McDougal Junior et al, 1968). Nevertheless, this difference does not preclude the use of frogs as an experimental model to study the effect of SNT on cholinergic synapses.…”