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Warm-rearing does not modify facial cold input
J. therm. Biol. Vol. 8. p. 9. 1983 Printed in Great Britain. All rights reserved
0306-4565 83 010009-01S03.00 0 Copyright © 1983 Pergamon Press Lid
WARM-REARING DOES NOT MODIFY FACIAL C O L D I N P U T R. F. HELLON,1 N. J. DAWSON,2 A. A. YOUNG2 and J. G. HERINGTON2 1National Institute for Medical Research, London NW7. U.K. and 2Department of Physiology, Auckland University, New Zealand Abstract--1. Rats which develop from birth at 30°C cannot maintain their body temperatures when exposed to 10°C, but rats developing at 20°C can do so. Body insulation is the same in both groups. 2. Facial cold-receptor input to the trigeminal nucleus is unaffected by warm-rearing.
insulation from fat or fur had not been changed by warm-rearing. In the anaesthetized rats, microelectrode penetrations were made on a matrix pattern into the marginal layer of the ctn. In both control and warmreared rats the probability of detecting single or multi-unit activity driven by cold receptors was 0.3. Quantitative tests were made of the static responses of 13 neurons in control rats and 16 neurons in warmreared rats in the temperature range 15-40°C. There was no difference between the mean static responses of the two groups.
INTRODUCTION
THE REARINGof an animal from birth to maturity in a hot environment results in an inability of the mature animal to thermoregulate adequately during cold exposure. The phenomenon has been observed in rabbits (Cooper et al., 1980) and rats (Ferguson et al., 1981). Part of the deficiency might be explained by a failure of the afferent pathways from the skin cold receptors to develop normally, as happens in other sensory systems when their normal input is subdued during development. The hypothesis was tested in rats by recording from higher-order neurons in the caudal trigeminal nucleus (ctn) which receive a synaptic input from the facial cold receptors.
DISCUSSION
These findings have failed to confirm the hypothesis that deficient thermoregulation in warm-reared rats might be caused by a failure of thermal afferent pathways to develop normally. We have also been unable to demonstrate any change in the body insulation which might also have been modified by warm-rearing. The thermoregulatory deficient remains unexplained, but there are clearly many other mechanisms which could have failed to mature normally.
MATERIALS AND METHODS Pregnant rats gave birth in rooms kept at 20 or 30°C and their litters were maintained at these temperatures during development. Between 48 and 105 days after birth, the rats were either exposed under light restraint in an air stream at 10°C or anaesthetized with chloralose-urethane for microelectrode recordings in the superficial layers of the ctn.
REFERENCES
COOPER K. E.. FERGUSONA. V. & VEALE W. L. (1980) Modification of thermoregulatory responses in rabbits reared at elevated environmental temperatures. J. Physiol. 303, 165-172. FERGUSON A. V., VEALE W. L. ~¢. COOPER K. E. (1981) Evidence of environmental influence on the development of thermoregulation in the rat. Can, J. Physiol. Pharmac. 59, 91-95.
RESULTS
Ten control rats, reared at 20°C, showed some fall in body temperature on exposure for 3h at 10°C. Their mean fall was 1.4 + 0.3°C. However, 10 warmreared rats showed a fall of 3.8 + 0.7°C. At the end of 3 h each rat was killed with CO2 and the cold exposure continued. Cooling curves for the two groups of dead rats were identical, indicating body
Key Word Index--Rat: thermoregulation; insulation; cold receptors.
9 T.B. S- 1:2~-B
0306-4565 83 010009-01S03.00 0 Copyright © 1983 Pergamon Press Lid
WARM-REARING DOES NOT MODIFY FACIAL C O L D I N P U T R. F. HELLON,1 N. J. DAWSON,2 A. A. YOUNG2 and J. G. HERINGTON2 1National Institute for Medical Research, London NW7. U.K. and 2Department of Physiology, Auckland University, New Zealand Abstract--1. Rats which develop from birth at 30°C cannot maintain their body temperatures when exposed to 10°C, but rats developing at 20°C can do so. Body insulation is the same in both groups. 2. Facial cold-receptor input to the trigeminal nucleus is unaffected by warm-rearing.
insulation from fat or fur had not been changed by warm-rearing. In the anaesthetized rats, microelectrode penetrations were made on a matrix pattern into the marginal layer of the ctn. In both control and warmreared rats the probability of detecting single or multi-unit activity driven by cold receptors was 0.3. Quantitative tests were made of the static responses of 13 neurons in control rats and 16 neurons in warmreared rats in the temperature range 15-40°C. There was no difference between the mean static responses of the two groups.
INTRODUCTION
THE REARINGof an animal from birth to maturity in a hot environment results in an inability of the mature animal to thermoregulate adequately during cold exposure. The phenomenon has been observed in rabbits (Cooper et al., 1980) and rats (Ferguson et al., 1981). Part of the deficiency might be explained by a failure of the afferent pathways from the skin cold receptors to develop normally, as happens in other sensory systems when their normal input is subdued during development. The hypothesis was tested in rats by recording from higher-order neurons in the caudal trigeminal nucleus (ctn) which receive a synaptic input from the facial cold receptors.
DISCUSSION
These findings have failed to confirm the hypothesis that deficient thermoregulation in warm-reared rats might be caused by a failure of thermal afferent pathways to develop normally. We have also been unable to demonstrate any change in the body insulation which might also have been modified by warm-rearing. The thermoregulatory deficient remains unexplained, but there are clearly many other mechanisms which could have failed to mature normally.
MATERIALS AND METHODS Pregnant rats gave birth in rooms kept at 20 or 30°C and their litters were maintained at these temperatures during development. Between 48 and 105 days after birth, the rats were either exposed under light restraint in an air stream at 10°C or anaesthetized with chloralose-urethane for microelectrode recordings in the superficial layers of the ctn.
REFERENCES
COOPER K. E.. FERGUSONA. V. & VEALE W. L. (1980) Modification of thermoregulatory responses in rabbits reared at elevated environmental temperatures. J. Physiol. 303, 165-172. FERGUSON A. V., VEALE W. L. ~¢. COOPER K. E. (1981) Evidence of environmental influence on the development of thermoregulation in the rat. Can, J. Physiol. Pharmac. 59, 91-95.
RESULTS
Ten control rats, reared at 20°C, showed some fall in body temperature on exposure for 3h at 10°C. Their mean fall was 1.4 + 0.3°C. However, 10 warmreared rats showed a fall of 3.8 + 0.7°C. At the end of 3 h each rat was killed with CO2 and the cold exposure continued. Cooling curves for the two groups of dead rats were identical, indicating body
Key Word Index--Rat: thermoregulation; insulation; cold receptors.
9 T.B. S- 1:2~-B