Diss. Stockholm : Karol. inst.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1980. / Typescript. Vita. Description based on print version record. Includes bibliographical references (leaves 227-248).

The effects of tetrodotoxin (TTX) and other neurotropic drugs on anaerobic glycolysis, and on transport processes, of incubated cerebral cortex slices have been studied in an effort to understand more fully cerebral metabolic processes during anoxia, and the mode of action of certain neurotropic drugs. The general approach has been to study the action of various drugs on the rates of anaerobic glycolysis of incubated brain slices under a variety of conditions. The cation (Na⁺, K⁺) contents were also studied under these conditions and the changes in these contents were related to concomitant changes in cerebral metabolism. Experiments were also carried out on the cerebral transport of amino acids and glucose under a variety of incubation conditions. Measurement of the rates of anaerobic glycolysis in the presence of TTX showed that the drug, at low concentrations such as 2 μM, enhances the rate of anaerobic glycolysis of cerebral cortex slices two to three fold, the effects being greater in the absence of Ca⁺⁺. Such an effect of TTX is far greater than that obtained on the aerobic metabolism of the cerebral cortex slices. The anaerobic glycolysis of kidney medulla slices, 2-day old rat brain slices or of acetone powder extracts from brain are not affected by the drug, indicating that the effects of TTX on the anaerobic glycolysis are specific for mature cerebral tissue, and requires integrity of the brain cells for its action. TTX has little or no effect in increasing rate of anaerobic glycolysis when it is added 10 minutes, or later, after the onset of anoxia, or when high K⁺, protoveratrine, L-glutamate or NH₄⁺ are present in the incubation medium. Under these conditions, there is either an influx of Na⁺ into, or loss of K⁺ from, the incubated cerebral tissue. In the presence of TTX under anoxic conditions, a much slower decline in the K⁺ /Na⁺ ratio of the cerebral cortex slices is observed. These and other experiments lead to the conclusion that the effects of TTX on anaerobic glycolysis are due to its action at the brain cell membrane resulting in the prevention of the changes in brain cell permeabilities to Na⁺ and K⁺ brought about by the onset of anoxia. In the presence of TTX, the initial high rate of glycolysis tends to be maintained due to only a slow decline in the cellular K⁺/Na⁺ ratio. The effects of K⁺ and Na⁺ on the anaerobic glycolysis are thought to be mediated largely by changes in the pyruvate kinase activity, which is enhanced by K⁺ and diminished by Na⁺. TTX appears to affect the aerobic and anaerobic metabolism of brain in vitro in the same way as it affects the generation action potentials i.e. by diminishing the influx of Na⁺ and efflux of K⁺ . These results lead to the conclusion that action potentials are generated in the incubated cerebral tissue at the onset of anoxia. These are blocked by TTX which manifests its effect by a higher rate of anaerobic glycolysis. The effect of TTX on the Na⁺ and K⁺ contents may be greater in the neurons than in glial cells because the former are the site of action of TTX. Consequently, the changes in the neuronal K⁺/Na⁺ ratio brought about by TTX are probably much greater than those of the K⁺/ Na⁺ ratio found in the tissue as a whole. In addition to its effects on the Na⁺ and K⁺ fluxes, TTX also prevents the efflux of amino acids from the incubated cerebral cortex slices that occurs at the onset of anoxia. This effect of TTX is independent of the activity of the transport processes normally operating on the amino acid uptake into the brain. Local anesthetics, ouabain, amytal and reserpine also increase the rate of anaerobic glycolysis of cerebral cortex slices. Local anesthetics act in a manner similar to TTX, although much higher concentrations are required. The effects of ouabain in a Ca⁺⁺-free medium are much greater than in a Ca⁺⁺-containing medium. It is suggested that the increase in the rate of anaerobic glycolysis due to ouabain is possibly mediated by an increase in cell ATP concentration under anoxia, as a result of inhibition of Na⁺ , K⁺-ATPase. The actions of amytal and reserpine on the anaerobic glycolysis of cerebral cortex slices are possibly mediated by membrane cation changes, but further work is necessary to support this conclusion. / Medicine, Faculty of / Biochemistry and Molecular Biology, Department of / Graduate

Oxygen availability is critical for survival for most organisms. The nematode, C. elegans, has been useful for studying genetic regulation of anoxia tolerance due to the oxygen deprivation response mechanisms shared with other metazoans. Studies examining long-term anoxia (72h, LTA) tolerance have only been conducted at adult day 1. To investigate the effect of aging on anoxia tolerance wild-type and mutant strains were exposed to LTA between adult day 1 and day 9. Wild-type isolates and daf-16(mu86) (FOXO transcription factor regulated by insulin-signaling) and aak-2(gt33) (catalytic subunit of AMP-activated protein kinase) strains were anoxia sensitive at day 1 and displayed increased LTA tolerance with aging correlated with reproductive senescence followed by a decline in survivorhsip through day 9. The daf-2(e1370) (insulin receptor homologue of C. elegans), glp-1(e2141) (a lin-12/Notch receptor) and fog-2(q71) (required for spermatogenesis) strains were LTA-tolerant through day 5. I conclude that aging influences LTA-tolerance in a strain- and age-dependent manner. In addition to being LTA-tolerant the daf-2(e1370) and glp-1(e2141) strains have a longevity phenotype that is suppressed by loss of kri-1 or daf-12. While loss of kri-1 did not suppress the LTA-tolerant phenotype of glp-1(e2141) at day 1 the portion of impaired survivors increased at day 3 and by day 5 tolerance was suppressed. Similarly, when exposed to 4 days of anoxia the glp-1(e2141);daf-12(rh41rh611) double mutant had a reduced survivor rate at all ages analyzed compared to glp-1(e2141) controls. To better understand formation of an anoxia-tolerant physiology I exposed adults to one or more 24h bouts. Recurrent bouts increased LTA tolerance in wild-type hermaphrodites in a dose-dependent manner. Bout-treated daf-16(mu86) animals had increased survival rate compared to controls yet maximum survival remained below age-matched wild-type. Anoxia bouts decreased LTA-tolerance in aak-2(gt33) mutants, indicating the requirement for ATP regulation in establishing an LTA-tolerant phenotype. These data support the idea that anoxia tolerance is multi-factorial and influenced by environment, metabolism, food, reproduction, sex phenotype and likely additional factors.

Mammalian neurons are anoxia-sensitive and rapidly undergo excitotoxic cell death when deprived of oxygen, mediated largely by calcium entry through N-methyl-D-aspartate receptors (NMDARs). This does not occur in neurons of the anoxia-tolerant western painted turtle, where a decrease in NMDAR currents is observed with anoxia. This decrease is dependent on a modest increase in cytosolic [Ca2+] during anoxia. The aim of this study was to determine if activation of the mitochondrial permeability transition pore (mPTP) decreases NMDAR currents through release of mitochondrial Ca2+. The data indicate that mPTP opening is sufficient to cause a decrease in NMDAR currents during normoxia and the anoxia-mediated rise in cytosolic [Ca2+] and depolarization of the mitochondrial membrane potential is due to opening of the mPTP. Furthermore, since a mitochondrial uncoupler releases additional calcium during anoxia we speculate that the mitochondrial membrane potential decreases in a regulated fashion to a new set-point.

Mammalian neurons are anoxia-sensitive and rapidly undergo excitotoxic cell death when deprived of oxygen, mediated largely by calcium entry through N-methyl-D-aspartate receptors (NMDARs). This does not occur in neurons of the anoxia-tolerant western painted turtle, where a decrease in NMDAR currents is observed with anoxia. This decrease is dependent on a modest increase in cytosolic [Ca2+] during anoxia. The aim of this study was to determine if activation of the mitochondrial permeability transition pore (mPTP) decreases NMDAR currents through release of mitochondrial Ca2+. The data indicate that mPTP opening is sufficient to cause a decrease in NMDAR currents during normoxia and the anoxia-mediated rise in cytosolic [Ca2+] and depolarization of the mitochondrial membrane potential is due to opening of the mPTP. Furthermore, since a mitochondrial uncoupler releases additional calcium during anoxia we speculate that the mitochondrial membrane potential decreases in a regulated fashion to a new set-point.

Thesis (Ph. D.)--Case Western Reserve University, 2009. / [School of Medicine] Department of Biomedical Engineering. Includes bibliographical references.

Thesis (M.S.)--Case Western Reserve University, 2008. / [School of Medicine] Department of Biochemistry. Includes bibliographical references.

Thesis (M.S.)--University of Michigan, Ann Arbor, 1965. / Typescript (photocopy). Includes bibliographical references (leave 40). Also issued in print.

Thesis (M.S.)--University of Michigan, Ann Arbor, 1967. / Typescript (photocopy). Includes bibliographical references (leaves 25-31). Also issued in print.