Cerebral energy metabolism in diving and non‐diving birds during hypoxia and apnoeic asphyxia.

Abstract

SUMMARY1. Cerebral energy metabolism during apnoeic asphyxia and steady-state hypoxia was compared in ducks and chickens; ducks tolerate apnoeic asphyxia 3-8 times longer than chickens.2. Fluctuations in the reduced form of respiratory chain nicotinamide adenine dinucleotide (NADH) were monitored from the left cerebral hemisphere by a noninvasive fluorometric technique and used as an indicator of mitochondrial hypoxia. NADH fluorescence was expressed in arbitrary units (a.u.) where 100 a.u. was defined as the fluorescence change from normoxia to anoxia. Electroencephalogram (e.e.g.) and surface P02 were recorded from the right hemisphere.3. After 1 min of asphyxia NADH fluorescence increased by 37 a.u. + 3-60 S.E. of mean (n = 54) in paralysed chickens and 8 a.u. + 1 41 (n = 55) in paralysed ducks. After 2 min the fluorescence increased by only 15 a.u. + 1P95 in ducks.4. Both species showed an isoelectric e.e.g. when fluorescence increased by approximately 35 a.u., indicating that anaerobic ATP production in ducks did not maintain brain function (e.e.g.) for a greater accumulation of respiratory chain NADH.5. At a given decrease in tissue P02 ducks and chickens showed the same level of NADH increase, indicating that both species are equally dependent on tissue P02 for the maintenance of redox state.6. We conclude that biochemical adjustments which enhance anaerobic ATP production and/or prolong oxidative phosphorylation during progressive hypoxia are not responsible for increased cerebral tolerance to apnoeic asphyxia in the duck.

Body temperature depression and peripheral heat loss accompany the metabolic and ventilatory responses to hypoxia in low and high altitude birds

“…Our findings suggest that this could also be the case in birds: vagotomy, which in birds eliminates afferent input from all arterial and pulmonary chemoreceptors, did not eliminate T b depression during hypoxia in ducks (Fig.·8A). Consistent with this hypothesis, metabolic O 2 limitation in the brain of ducks (Bryan and Jones, 1980) occurs at similar levels of hypoxia to that initiating T b depression in the present study. However, vagotomy did eliminate bill warming during hypoxia (Fig.·8B), so at least part of the hypoxic thermoregulatory response relies on information from peripheral chemoreceptors or thermoafferents carried by the vagus.…”

Alterations of local cerebral blood flow during hypoxic hypoxia; 14C-iodoantipyrine autoradiographic study.

“…with that of the white matter. These data may agree with other author's observations (1,11). During hypoxia, the pyramidal cell layer in the hippocampus, plexus choroideus and venous blood (cranial sinus) were unchanged in OD, while ODs in other cerebral regions were significantly decreased as Figs.…”

Effect of slaughter on the spontaneous and evoked activity of the brain

“…Unanaesthetised ducks are known to sustain spontaneous brain activity for 5 times longer than chickens when subjected to apnoeic asphyxia (Bryan and Jones, 1980). This difference, however, was not present following cardiac arrest or any of the exsanguination methods used in this study.…”