Photoperiodicity and the thermoregulatory response to noradrenaline in the pigeon

Function of melatonin in thermoregulatory processes

Accumulated information shows that, besides its role in the timing of seasonal reproduction, melatonin also plays an important role in seasonal thermoregulatory adjustments of animals including torpor and hibernation. Furthermore, melatonin has a crucial role in circadian thermoregulatory adjustments of body temperature (Tb). Melatonin appears to send signals to the preoptic area of anterior hypothalamus (PoAH) where it adjusts the set point of Tb consistent with the metabolic rate of the animal. This new function for melatonin as a transducer mediating information about energy balance has been suggested in this review. Melatonin also adjusts the activity of the biological clock in vertebrates.

Effect of photoperiod and melatonin on cold resistance, thermoregulation and shivering/nonshivering thermogenesis in Japanese quail

The effect of photoperiod and melatonin treatment on cold resistance and thermogenesis of quails was studied. The birds were acclimated for 8 weeks to short day (8L:16D) or long day (16L:8D) conditions, and 8 of 16 quails in each group were implanted with melatonin capsules. One group of quails was maintained outside in an aviary during winter. Oxygen consumption (VO2), body temperature (Tb, recorded with temperature transmitters) and shivering (integrated pectoral EMG) were recorded continuously, and samples of heart rate and breathing rate were picked up when ambient temperature was decreased stepwise from 27 down to -75 degrees C. Heat production maximum (HPmax), cold limit, lower critical temperature, basal metabolic rate (BMR) and thermal conductance were determined. The results show that short day, cold and melatonin treatment improved cold resistance and thermal insulation of quails when compared with quails acclimated to long day conditions. An increase in HPmax was induced only by melatonin treatment. The results suggest that the acclimatization of quails is under control of the pineal gland. The linear increase of shivering intensity with VO2 at moderate cold load shows that shivering is the primary source for thermoregulatory heat production in the quail. At Ta's below -40 degrees C shivering remained constant although VO2, heart rate and breathing rate continued to increase with increasing cold load. This could indicate the existence of a nonshivering thermogenesis in birds. Unlike to mammals, this non-shivering thermogenesis in birds would serve as secondary source of heat supporting shivering thermogenesis in severe cold.

Photoperiod-induced changes in temperature-metabolism curve, shivering threshold and body temperature in the pigeon

A short photophase combined with cold-acclimation changed the shivering threshold of the pigeon from 21 to 14 degrees C. The change of critical temperature was also found in the temperature-metabolism curve. A long photophase both alone and combined with warm-acclimation induced a reduction of body temperature to a lower level (about 2 degrees C) at all ambient temperature, ranging from 5 to 40 degrees C.

Changes in body temperature after administration of adrenergic and serotonergic agents and related drugs including antidepressants

This survey, the third in a series, presents extensive tabulations of literature, primarily since 1965, on thermoregulatory effects of adrenergic and serotonergic agonists and their antagonists including ergot alkaloids, amphetamines, tryptamines, monoamine oxidase inhibitors, tricyclic and other antidepressants, a variety of other agents which alter presynaptic aminergic mechanisms including reserpine, 6-hydroxydopamine, p-chlorophenylalanine, alpha-methyltyrosines, cocaine, guanethidine and bretylium. The information listed includes the species used, route of administration and dose of drug, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions, such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary drug.