Frank E. South

Central regulation of temperature in hibernation and normothermia.

Abstract Normothermic hibernators respond proportionally to both peripheral and brain temperature changes like other mammals. Their quantitative responsiveness to peripheral and brain temperature inputs are consistent with body-size relationships seen in other vertebrates. The basic temperature regulatory mechanisms seen in seasonal hibernators are not altered with season although certain response parameters, such as vasomotion, are not obvious in prehibernating marmots. During hibernation, hibernators respond to peripheral- and core-temperature manipulation in a manner which is consistent with the contention that temperature is regulated in a similar but less precise manner to that seen during normothermia.

Calcium and magnesium levels in tissues and serum of hibernating and cold-acclimated hamsters

Abstract Calcium and magnesium levels were examined in serum, heart, skeletal muscle, and bone of hibernating, cold-acclimated, and room-temperature control hamsters. Relative to the controls, Ca levels in hibernating hamsters increased significantly in the serum, heart, and skeletal muscle while Mg levels increased in the serum but decreased in the heart and skeletal muscle, and did not change in the bone. In comparing hibernators to cold-acclimated animals, Ca was higher in heart tissue while Mg was lower in heart and muscle and higher in the serum. These results support the hypothesis that calcium might accumulate in muscle tissue (especially the heart) during hibernation where it might serve to enhance the contractile process.

A mathematical biothermal model of the california sea lion

Abstract The thermal behavior of the California sea lion is modeled by a set of seventeen simultaneous partial differential equations. Numerical solution of these equations yields temperature profiles in the sea lion that closely reproduce experimental data obtained with the animals at rest in air. The model predicts that exercise is necessary to maintain body temperature while immersed in very cold water (0°C) but that very efficient heat conservation occurs during diving because of bradycardia, limited circulation, and absence of respiration.

Air temperature and direct partitional calorimetry of the California sea lion (Zalophus Californianus)

Abstract The objective of these experiments was to study the partitional heat exchange of the California sea lion as affected by air temperature (Ta) through the use of direct and indirect calorimetry. o 1. Throughout the temperature range of 10°–25°C the total heat production remained quite constant. Radiant loss fell from 58% at 10° to 40% at 28°C Ta. Conduction-convection accounted for 35% at 15° and 20°C Ta but declined to 15% at 28°C. Evaporative loss was 21% at 10°C Ta, fell to 14% at 15°C and rose to account for over 50% of the exchange at 28°C. 2. At 25°C Ta, hyperpyrexia was usually apparent although an accompanying increase in heat production (O2 consumption) was not. It is hypothesized that a metabolic depression and/or a temporary heat sequestration might account for the observation. Oxygen consumption increased and effective heat loss diminished at a Ta of 28°C. 3. An abrupt rise in recorded Tb accompanied by postural adjustments followed removal of the animals from the higher Tas, indicating the occurrence of a circulatory sequestration of heat. It is postulated that a temporary storage of blood in the splanchnic circulation might account for this observation.

Thermoregulatory responses of a hibernator to hypothalamic and ambient temperatures

Abstract Local cooling or heating of the hypothalamus of yellow bellied marmots elicited appropriate thermoregulatory responses to maintain body temperature. Increases in EMG, heart rate, and oxygen consumption were observed during hypothalamic cooling. Conversely, hypothalamic heating generally decreased thermogenic parameters toward minimal levels. Normothermic marmots retained thermoregulatory heat production throughout the year although loss of vasomotor regulation seemed to occur as they prepared for hibernation. The relationship between manipulated changes in hypothalamic temperature and induced changes in oxygen consumption was linear. This proportional relationship at one air temperature (15 °C) was parallel and displaced to the right of that relationship obtained at a lower air temperature (10 °C). These results are consistent with the hypothesis that hypothalamic regulation of body temperature in normothermic marmots is similar to that of nonhibernating mammals, although vasomotor regulation may differ.

Hypothermia and behavioural thermoregulation by the hamster (Mesocricetus auratus)

Abstract Behavioural thermoregulatory temperature preference was investigated prior to and following both mild (approximately 10 °C) and deep (0 °C for 1 hr) hypothermia. Temperature preference of adult male hamsters ( Mesocricetus auratus ) was assessed with apparatus specifically designed and constructed for that purpose. Each of the ten sets of apparatus consisted of five individual boxes arranged as a pentagon around a central arena. The temperatures of the boxes were controlled so that a subject could select environmental temperatures of 1 °, 6 °, 12 °, 18 ° or 26 °C. Activity was continuously monitored on an event recorder which was controlled by photocells at the entry ways of each box. Box temperature was monitored with recording thermocouples. All animals lived in the apparatus from 4 to 35 days before the initial hypothermia. Eight hours prior to hypothermia the mean time spent per hour in the 26 °C box was 5·38 min, with the remaining 6·2 min per hr being divided approximately equally between the other four boxes. Upon regaining normal body temperature following hypothermia the animals were returned to the chambers. Immediately after being returned, the hamsters exhibited a preference for the 6 °, 12 ° and 18 °C environments. The duration of this post-hypothermic temperature preference was significantly longer following mild hypothermia than that following deep hypothermia. Following this ‘down-shift’ all animals returned to the 26 °C box where they stayed for an average of 56·6 min per hr over a period of at least 8 hr. Consistent with the impaired thermoregulatory stability and the labile body temperature generally observed following hypothermia, one might expect these animals preferentially to select the warmest environmental temperature (26 °C). However, the post-hypothermic, transient, ‘down-shift’ to the lower environmental temperatures might suggest that as a result of some physiological readjustment (vasomotor activity, metabolism, hypothalamic ‘set’) during this period that the thermocomfort ‘set’ of these hamsters has also been temporarily altered.

TEMPERATURE PREFERENCE IN GOLDEN HAMSTERS

Abstract The preference of pre- and post-hibernative hamsters for relatively cool (8 °C) or relatively warm (19 °C or 24 °C) environmental temperatures was tested in a T-maze using the method of forced choice to equate number of visits to, and total time spent in, each environment. The findings of the experiment were (1) pre-hibernative hamsters show a marked preference for an 8 °C environment to either a 19 ° or 24 °C environment, and (2) following arousal there occurs a shift in preference on the part of the hamsters to a 24 °C environment over one of 8 °C. The significance of these results is discussed in terms of possible purposive thermoregulatory behaviours.

Influence of hypothermia on renal function of the marmot, Marmota flaviventris.

Abstract Eight male and seven female Marmota flaviventris were subjected to experimentally induced hypothermia. Glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were reduced and filtration fraction (FF) was increased. Urine flow was unchanged by males but increased almost 2-fold by females. The fractional excretion of water ( V C I ) and glucose excretion increased, while sodium and chloride excretion remained unchanged. Hypothermia decreased renal function and active transport mechanisms as demonstrated by decreased GFR, decreased ERPF, increased glucose excretion, and diminished creatinine to inulin clearance ratios. However, the degree of depression of transport processes was not as great and recovery after rewarming was more rapid than reported for animals incapable of undergoing natural hibernation.

A new thermode perfusion system for local temperature manipulation.

Abstract A thermode perfusion system incorporating a miniature heater was used to alter the local temperature in the brain of the marmot and of the cat. In the marmot, local temperature has been changed or clamped over a range of 35–39°C at the rate of 0.4°C/W. In the cat, local temperature has been increased by 1.5°C and decreased by 2°C at the rate of 0.15°C/W.