Paul O. Chatfield

The effects of temperature on the spontaneous and induced electrical activity in the cerebral cortex of the golden hamster.

Abstract 1. 1. During hibernation the body temperature of the golden hamster may drop to 2.5°C. Arousal from hibernation is characterized by a gradual autogenous increase in body temperature to 37°C. Under anaesthesia the non-hibernating animal can be chilled to body temperatures which would be lethal to mammals which do not hibernate. 2. 2. Investigation of the electrocorticogram of the arousing hibernator revealed no conspicuous activity until the cortex reached 19–21°C. Slow, low voltage activity was the first to appear, to be replaced at higher temperatures by spontaneous burst activity and, at about 29°C., by very fast frequency low voltage discharges (fig. 1). Local strychninization did not produce convulsive activity until the temperature had reached levels at which spontaneous activity would normally have appeared (fig. 2). 3. 3. Though the cortex appeared quiescent early in arousal, peripheral movement could still be elicited at temperatures as low as 12°C. by electrical stimulation of motor areas and under anaesthesia (pentobarbital sodium) peripheral stimulation evoked a complex cortical response down to 9.1°C. (fig. 3). 4. 4. When the anaesthetised, non-hibernating hamster was artificially chilled, spontaneous electrical activity disappeared at 17°C. and reappeared at 19°C. (fig. 4). During progressive hypothermia the frequency of induced strychnine spikes gradually diminished until they disappeared at about 15°C. (fig. 5). 5. 5. It is concluded from this evidence that the bulbar reticular activating system is least resistant to cold because fast frequency, low voltage activity was the last to appear during arousal from hibernation. The intralaminar thalamo-cortical circuits must be second in order of resistance, since spontaneous burst activity appeared before the fast frequency discharges. Spino-bulbo-thalamo-cortical relay systems and the cortex itself are more resistant than either of the preceding since the cortex was electrically excitable at low temperatures and a complex evoked potential could be obtained at temperatures as low as 9.1°C. It has previously been shown that peripheral nerve is most resistant since conduction in vitro will occur down to 2°C. 6. 6. It is pointed out that the hibernating hamster, even though functionally decorticate, must retain the ability to function in other parts of the central nervous system, since the waking process is characterized by a coordinated, integrated series of events all designed to greatly increase the animals heat production and restore its body temperature to normal levels. The cold resisting structures would most certainly include peripheral nerves capable of activating the neuromuscular mechanisms, as well as ascending and descending (sensory and motor) systems associated with the heat regulating centers of the hypothalamus.

Subcortical electrical activity in the golden hamster during arousal from hibernation

1. 1. Results of a systematic electrical exploration of cerebral hemispheres and brain stem in golden hamsters (Mesocricetus auratus) arousing from hibernation are presented. 2. 2. Three types of subcortical electrical activity were recorded during the process of arousal, namely (a) transient, regular, initially 17/sec. activity, (b) fairly continuous waves, and (c) activity in bursts. 3. 3. The electrical activity recorded was confined to components of the limbic system and its presumed descending efferents. Olfactory bulbs, corpus striatum, thalamus, and anterior hypothalamus were conspicuously quiescent. 4. 4. These findings appear consistent with contemporary theories of the function of the limbic system and would serve to account for the apparent agitated state of the hamster immediately upon full arousal from hibernation. 5. 5. It is concluded that the process of arousal in the golden hamster is initiated when the limbic system is activated either directly or indirectly by afferent impulses from the periphery.