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Photoperiod, temperature acclimation, and interscapular brown fat in Peromyscus leucopus
HIBERNATION-HYPOTHERMIA specimen (woodchuck) was monitored all winter while hibernating in a free environment. During changes in the winter air temperature, the heart rates showed a precise inverse and homeostatic relationship with air temperature during hibernation, unrelated to awakening from hibernation. Therefore, hibernation in the free environment with a changing air temperature must be a more variable process than in the constant-temperature coldroom. ‘Suported by the Arctic Institute of North -1merica under contract.ual arrangements with the Office of Naval Research. in the Eastern 40. Food Handling and Hibernation Chipmunk. WILLIAMSE. GRAVES(Department of Zoology, State University College of Forestry, Syracuse, New York).
Prehibernation patterns of food gathering were observed in 20 captive chipmunks for a lo-week period beginning in October. Animals were individually housed at 10°C and 2 hr of light per week. Food supplies were renewed twice weekly; after 1 day use and after 6 days use. Total food handled (hoarded, eaten, or wasted) was 1834 g per animal over the lo-week period with food handling being highest in October (82.5 g/day) and declining steadily to December (32.3 g/day) under the same light and temperature conditions. Body weights increased only 1.3 g/week over this same period. Weight increases ranged from 2-24% over initial weight and averaged 12.8%. Animals tended to handle the food available as soon as possible after renewal with one-half of their weekly gathering being done during the first day following renewal. Thirteen of the 20 chipmunks hibernated beginning 3 weeks after food renewal stopped in December for durations ranging from 1 to 12 weeks and with an average body temperature of 138°C. Three of the seven animals not hibernating died within 6 weeks after food renewal ceased and these had low food handling values. Hiberation did not occur in animals with low cache amounts. The animals which hibernated went through a pattern of declining food handling over the 10 weeks while no pattern existed in the seven nonhibernating individuals. Additional animals housed at 25°C and normal winter lighting conditions also had depressed body temperatures. 41. Physiological Evolution
and Behavioral of
Hibernation
in
Precursors to Bats. R. E.
HENSHAW (Pennsylvanian State University, University Park, Pennsylvania). It appears likely that capacity of bats for hibernation was evolved in the tropics and was refined
IV
303
as species invaded temperate regions. Out of 17 families of macrochiropt.era and microchiroptera only three familes of microchiroptera have cxtended their ranges into temperate regions. All of these species have been shown to hibernate to varying degrees in the natural habitat. Confamilial species which retain a wholly tropical distribution are tolerant of hypothermia. The microclimate of tropically distributed species is poorly known, but likely diurnal roosting sites are variously cooler than body temperature, usually well protected, and often totally dark-as in caves. Occasional reduction in food availability coupled with diurnal microclimate energy demand would convey selective advantage for occasional, then later priodic, torpidity with its concomitant reduction in energ) cost. Most bats have resting metabolic rates less than would be predicted for homeothermic mammals of like body weight according to the formula 3.8 body wt?‘. Evolution of echolocation to meet needs of nocturnal feeding and diurnal roosting may have potentiated natural selection for periodic torpor. All of the above observations are interpreted as presumptive evidence for initial evolution of hibernation in tropical homeothermic bats before they extended their ranges into temperate regions. 42. Photoperiod, Interscapular
Temperature Acclimation, and Brown Fat in Peromyscus
leucopus. G. R. LYNCH AND G. E. FOLK, JR. (Departments of Zoology and Physiology, University of Iowa, Iowa City, Iowa). Cold acclimation in small mammals involves an increase in the extent of nonshivering thermogenesis and an increase in the total weight of brown fat. Recently, photoperiod has been demonstrated to influence nonshivering thermogenesis (Lynch, F. R., Amer. Zool. 10, 308, 1970). Warm- and cold-acclimated Peromyscus leucopus under a 9:15 LD photoperiod exhibit a greater degree of nonshivering thermogenesis relative to their respective controls under a 16:8 LD photoperiod. Since cold-acclimated mammals differ from warm acclimated with respect to both nonshivering thermogenesis and brown fat, the photoperiodic influence on nonshivering thermogenesis might also stimulate hypertrophy of brown fat; thus. brown fat might influence nonshivering thermogenrsis. Sixty-four Peromyscus leucopus were reared at 26°C under a 16:s LD photoperiod to 8 months of age and separated into two groups of 32 mice. One group was treated under a short photoperiod (9:15 LD) for 12 weeks while the other remained under a long photoperiod (16:8 LD). The mice were then individually caged and separated into the following treatment groups: (1) warm accli-
HIBERNATION-HYPOTHERMIA
304
mated (26°C) under a long photoperiod; (2) warm acclimated under a short photoperiod; (3) cold acclimated (SC) for 8 days under a long photoperiod; (4) cold acclimated for 8 days under a short photoperiod. Each treatment group consisted of 16 mice with approximately equal numbers of males and females. All mice were then sacrificed and interscapular brown fat excised and dried. These data were subjected to analysis of variance to assess the significance of differences in brown fat per gram body weight due to differences in photoperiod, temperature acclimation, sex, and interactions among these factors. Comparison of weighted group means indicates that: (1) the effect of sex differences on interscapular brown fat weight is not significant (t = 1.58, cZf = 56); (2) short photoperiod treatment stimulates an increase (19%) in interscapular brown fat when compared with long photoperiod (t = 2.58) ; and (3) eight days of cold acclimation effected a greater increase (44%) in weight when compared with warm-acclimated mice (t = 5.30). However, photoperiod effects on mean weight of brown fat are large in warm-acclimated but slight in coldacclimated animals. This photoperiodic effect differs from that described for nonshivering thermogenesis where a larger difference exists between the two photoperiods with cold acclimation than with warm acclimation. In conclusion, although Peromyscus leucopus under short photoperiod show both increased nonshivering thermogenesis and interscapular brown fat, the photoperiodic effect on these two differ. Thus, the data are insufficient to establish a photoperiodically cued increase in brown adipose tissue as an explanation of photoperiod influence on nonshivering thermogenesis. 43. Loss of Weight Ground
Squirrels
Cycles Kept
in
Thirteen-Lined
in Constant
N. MROSOVSKY (Departments ology and Psychology, University ronto, Toronto, Canada). tions.
Condi-
of Zoof To-
Thirteen-lined ground squirrels, Citellus tridecemlineatus, were kept for l-3 years on a 12-hr light-dark schedule. Initially room temperatures were set at 11.5 ? 1.75 and 4 f 3°C. More than half the animals did not show prehibernatory weight gains during their second season in captivity; in some weight remained level for over 18 months. These animals hibernated poorly if at all. When temperatures were raised to over 24”C, nearly all animals gained weight. When the rooms were cooled again, most animals hibernated. These observations suggest that endogenous control is not so well developed in thirteen-lined as in golden-mant.led ground squirrels, and that warm temperatures in the summer are an important ex-
IV
ternal controlling factor. (A full account of this work will appear in J. Interdiscipl. Cycle Res., 1971.) 44. Seasonal Variations in the Physiology
and Bioof the European Hedgehog (Erinaceus europaeus) : An Introductory Note. chemistry
J. B. SENTURIA AND B. W. JOHANSSON (Department of Biology, The Cleveland State University, Cleveland, Ohio, and Heart Laboratory, Department of Medicine, General Hospital, Malmij, Sweden). This work represents an attempt at an interdisciplinary approach to the question of hibernation. The study was completed in 1 year of data collection and 2 years of data analysis. It involved 11 principal investigators (B. Eklund, B. G. Johansson, B. W. Johansson, S. 0. Olsson, C. Owman, M. Pandolfi, J. B. Senturia, W. von Studnits, T. Soderquist, J. Thorell, and B. Akesson) and numerous technical personnel. Three species were used in the study; the European hedgehog (Erinaceus europaeus), a hibernator, the guinea pig (Cavia procellus), a nonhibernator, and man (Homo sapiens). The study was conducted at Malmo, Sweden. Samples were taken at four seasonal periods. Each sample generally consisted of six males and six females of each species in the following pattern: Season I (fall period) 3 of the 12 hedgehogs are just beginning to enter hiberation (October 25-November 14). Season II (winter period) all hedgehogs are hibernating (January l&January 31). Season III (spring period) 8 of the 10 hedgehogs have completed their final arousal from hibernation (March 19-April 9). Season IV (summer period) all hedgehogs are active (June IO-June 26). The following data were obtained: body, weight, superficial abdominal temperature, electrocardiogram, and organ weights. Samples of blood were taken for determination of glood gasses, ions, glucose, hemoglobin, urea creatinine, total protein, LDH, GOT, GPT, total fat, triglycerides, free fatty acids, cholesterol, and lipoprotein electrophoresis.
Tissue samples were t,aken for determining catecholamine concentration and enzymes of catecholamine metabolism. Samples of tissues were also examined to determine act,irity of some of the enzymes of carbohydrate metabolism, glycogen, fatty acid concentrations in brown and white fat, and the tissue plasma activator of fibrinolysis. It is hoped that this type of multidisciplinary approach using the same organisms from the same local area will lead to results which can be compared easily between laboratories.
Prehibernation patterns of food gathering were observed in 20 captive chipmunks for a lo-week period beginning in October. Animals were individually housed at 10°C and 2 hr of light per week. Food supplies were renewed twice weekly; after 1 day use and after 6 days use. Total food handled (hoarded, eaten, or wasted) was 1834 g per animal over the lo-week period with food handling being highest in October (82.5 g/day) and declining steadily to December (32.3 g/day) under the same light and temperature conditions. Body weights increased only 1.3 g/week over this same period. Weight increases ranged from 2-24% over initial weight and averaged 12.8%. Animals tended to handle the food available as soon as possible after renewal with one-half of their weekly gathering being done during the first day following renewal. Thirteen of the 20 chipmunks hibernated beginning 3 weeks after food renewal stopped in December for durations ranging from 1 to 12 weeks and with an average body temperature of 138°C. Three of the seven animals not hibernating died within 6 weeks after food renewal ceased and these had low food handling values. Hiberation did not occur in animals with low cache amounts. The animals which hibernated went through a pattern of declining food handling over the 10 weeks while no pattern existed in the seven nonhibernating individuals. Additional animals housed at 25°C and normal winter lighting conditions also had depressed body temperatures. 41. Physiological Evolution
and Behavioral of
Hibernation
in
Precursors to Bats. R. E.
HENSHAW (Pennsylvanian State University, University Park, Pennsylvania). It appears likely that capacity of bats for hibernation was evolved in the tropics and was refined
IV
303
as species invaded temperate regions. Out of 17 families of macrochiropt.era and microchiroptera only three familes of microchiroptera have cxtended their ranges into temperate regions. All of these species have been shown to hibernate to varying degrees in the natural habitat. Confamilial species which retain a wholly tropical distribution are tolerant of hypothermia. The microclimate of tropically distributed species is poorly known, but likely diurnal roosting sites are variously cooler than body temperature, usually well protected, and often totally dark-as in caves. Occasional reduction in food availability coupled with diurnal microclimate energy demand would convey selective advantage for occasional, then later priodic, torpidity with its concomitant reduction in energ) cost. Most bats have resting metabolic rates less than would be predicted for homeothermic mammals of like body weight according to the formula 3.8 body wt?‘. Evolution of echolocation to meet needs of nocturnal feeding and diurnal roosting may have potentiated natural selection for periodic torpor. All of the above observations are interpreted as presumptive evidence for initial evolution of hibernation in tropical homeothermic bats before they extended their ranges into temperate regions. 42. Photoperiod, Interscapular
Temperature Acclimation, and Brown Fat in Peromyscus
leucopus. G. R. LYNCH AND G. E. FOLK, JR. (Departments of Zoology and Physiology, University of Iowa, Iowa City, Iowa). Cold acclimation in small mammals involves an increase in the extent of nonshivering thermogenesis and an increase in the total weight of brown fat. Recently, photoperiod has been demonstrated to influence nonshivering thermogenesis (Lynch, F. R., Amer. Zool. 10, 308, 1970). Warm- and cold-acclimated Peromyscus leucopus under a 9:15 LD photoperiod exhibit a greater degree of nonshivering thermogenesis relative to their respective controls under a 16:8 LD photoperiod. Since cold-acclimated mammals differ from warm acclimated with respect to both nonshivering thermogenesis and brown fat, the photoperiodic influence on nonshivering thermogenesis might also stimulate hypertrophy of brown fat; thus. brown fat might influence nonshivering thermogenrsis. Sixty-four Peromyscus leucopus were reared at 26°C under a 16:s LD photoperiod to 8 months of age and separated into two groups of 32 mice. One group was treated under a short photoperiod (9:15 LD) for 12 weeks while the other remained under a long photoperiod (16:8 LD). The mice were then individually caged and separated into the following treatment groups: (1) warm accli-
HIBERNATION-HYPOTHERMIA
304
mated (26°C) under a long photoperiod; (2) warm acclimated under a short photoperiod; (3) cold acclimated (SC) for 8 days under a long photoperiod; (4) cold acclimated for 8 days under a short photoperiod. Each treatment group consisted of 16 mice with approximately equal numbers of males and females. All mice were then sacrificed and interscapular brown fat excised and dried. These data were subjected to analysis of variance to assess the significance of differences in brown fat per gram body weight due to differences in photoperiod, temperature acclimation, sex, and interactions among these factors. Comparison of weighted group means indicates that: (1) the effect of sex differences on interscapular brown fat weight is not significant (t = 1.58, cZf = 56); (2) short photoperiod treatment stimulates an increase (19%) in interscapular brown fat when compared with long photoperiod (t = 2.58) ; and (3) eight days of cold acclimation effected a greater increase (44%) in weight when compared with warm-acclimated mice (t = 5.30). However, photoperiod effects on mean weight of brown fat are large in warm-acclimated but slight in coldacclimated animals. This photoperiodic effect differs from that described for nonshivering thermogenesis where a larger difference exists between the two photoperiods with cold acclimation than with warm acclimation. In conclusion, although Peromyscus leucopus under short photoperiod show both increased nonshivering thermogenesis and interscapular brown fat, the photoperiodic effect on these two differ. Thus, the data are insufficient to establish a photoperiodically cued increase in brown adipose tissue as an explanation of photoperiod influence on nonshivering thermogenesis. 43. Loss of Weight Ground
Squirrels
Cycles Kept
in
Thirteen-Lined
in Constant
N. MROSOVSKY (Departments ology and Psychology, University ronto, Toronto, Canada). tions.
Condi-
of Zoof To-
Thirteen-lined ground squirrels, Citellus tridecemlineatus, were kept for l-3 years on a 12-hr light-dark schedule. Initially room temperatures were set at 11.5 ? 1.75 and 4 f 3°C. More than half the animals did not show prehibernatory weight gains during their second season in captivity; in some weight remained level for over 18 months. These animals hibernated poorly if at all. When temperatures were raised to over 24”C, nearly all animals gained weight. When the rooms were cooled again, most animals hibernated. These observations suggest that endogenous control is not so well developed in thirteen-lined as in golden-mant.led ground squirrels, and that warm temperatures in the summer are an important ex-
IV
ternal controlling factor. (A full account of this work will appear in J. Interdiscipl. Cycle Res., 1971.) 44. Seasonal Variations in the Physiology
and Bioof the European Hedgehog (Erinaceus europaeus) : An Introductory Note. chemistry
J. B. SENTURIA AND B. W. JOHANSSON (Department of Biology, The Cleveland State University, Cleveland, Ohio, and Heart Laboratory, Department of Medicine, General Hospital, Malmij, Sweden). This work represents an attempt at an interdisciplinary approach to the question of hibernation. The study was completed in 1 year of data collection and 2 years of data analysis. It involved 11 principal investigators (B. Eklund, B. G. Johansson, B. W. Johansson, S. 0. Olsson, C. Owman, M. Pandolfi, J. B. Senturia, W. von Studnits, T. Soderquist, J. Thorell, and B. Akesson) and numerous technical personnel. Three species were used in the study; the European hedgehog (Erinaceus europaeus), a hibernator, the guinea pig (Cavia procellus), a nonhibernator, and man (Homo sapiens). The study was conducted at Malmo, Sweden. Samples were taken at four seasonal periods. Each sample generally consisted of six males and six females of each species in the following pattern: Season I (fall period) 3 of the 12 hedgehogs are just beginning to enter hiberation (October 25-November 14). Season II (winter period) all hedgehogs are hibernating (January l&January 31). Season III (spring period) 8 of the 10 hedgehogs have completed their final arousal from hibernation (March 19-April 9). Season IV (summer period) all hedgehogs are active (June IO-June 26). The following data were obtained: body, weight, superficial abdominal temperature, electrocardiogram, and organ weights. Samples of blood were taken for determination of glood gasses, ions, glucose, hemoglobin, urea creatinine, total protein, LDH, GOT, GPT, total fat, triglycerides, free fatty acids, cholesterol, and lipoprotein electrophoresis.
Tissue samples were t,aken for determining catecholamine concentration and enzymes of catecholamine metabolism. Samples of tissues were also examined to determine act,irity of some of the enzymes of carbohydrate metabolism, glycogen, fatty acid concentrations in brown and white fat, and the tissue plasma activator of fibrinolysis. It is hoped that this type of multidisciplinary approach using the same organisms from the same local area will lead to results which can be compared easily between laboratories.