Electrophysiological Observations During Body Cooling and Rewarming in Young Chickens

Abstract

The influence of body cooling and rewarming on the EEG, ERG, EMG and ECG was investigated in young chicks. The EEG was recorded from the surface of frontal bone corresponding to the Wulst (the accessory hyperstriatum). Typical slow waves of high amplitude gradually decreased in amplitude during cooling (below 30°C.). At 30°C., the EEG was characterized by a train of slow waves of low voltage intermingled with fast waves of low voltage. During recovery, the amplitude of the EEG increased. The ERG (b-wave) is a good indicator of survival in chicks. The amplitude of the b-wave was markedly reduced at 25°C.; the b-wave disappeared at 18°C. Reversible changes of the ERG were observed during recovery. A gradual lowering of body temperature evoked a series of large muscle potentials. Below 23°C., the EMG became silent. A sudden increase in amplitude of the EMG showed isoelectric or very small activity. At normal body temperature before cooling, interval between S waves was 126 ± 9 msec.; it gradually lengthened as body temperature was lowered. At 18°C., it reached a maximum of 1116 ± 228 msec. During the recovery phase, the interval between S waves gradually decreased. Judging from polygraphic recordings, a range in rectal temperature of 20 to 25°C. in young chick is adequate for hypothermic anesthesia.