The hypothermic hamster brain: its water and electrolyte content and perfusion

Metabolism in the hamster brain during hibernation and arousal

Hibernation was induced in hamsters by placing them in a cold room for an extended period of time, after which the hibernating state was confirmed by marked reductions in heart rate, body temperature, and the respiratory rate. The animals were either frozen intact in liquid nitrogen, or aroused and then frozen when body temperature reached 8, 12, 16, 20, 24 or 32 degrees C. A metabolite profile, including glucose-related metabolites, high-energy phosphates, gamma-aminobutyric acid (GABA) and cyclic nucleotides, was determined for both the cerebral cortex and cerebellum. In general, the metabolite changes in the two regions elicited by hypothermia were alike, although some differences were evident. The brains of hibernators were biochemically characterized by (1) a high concentration of energy reserves including glycogen, glucose, adenosine triphosphate, and P-creatine, (2) significantly elevated levels of lactate and GABA, and (3) near depletion of cyclic guanosine monophosphate with only a moderate depression of cyclic adenosine monophosphate. During arousal, the metabolites were restored to near normal values and there was little or no indication that the brain energy metabolism was compromised by the arousal process. The study provides certain insights into the metabolic adaptation of the brain to prolonged periods of profound hypothermia in a hibernating species.

Comparative physiological and biochemical aspects of hypothermia as a model for hibernation

It is obvious that research is far from the last chapter in developing a model for natural hibernation. The relationships and comparative mechanisms for thermogenesis and survival in hibernation and experimental hypothermia are still unclear. Yet, two primary areas appear to be most promising, namely, the control of thermogenesis via the glucocorticoids and the specific role of the central nervous system (CNS) in survival of hypothermic subjects and arousal of hibernating subjects. Although there have been several approaches to understanding the role of the CNS in terms of circulation, integrity of the blood-brain barrier (BBB) system, and CNS sites of activity, it may appear that more questions have been raised than have been answered. However, a more optimistic view can also be taken. The development of a laboratory model, using experimental hypothermia for natural hibernation, is progressing. This view is justified in terms of results from the use of glucocorticoids in metabolic regulation of available carbohydrates, i.e., available glucose in hypothermia, and the continued promising parallel studies of physiological and biochemical integrity of areas of the CNS in hypothermic and hibernating subjects.