Sensations evoked by thermal stimulation (temperature-related sensations) can be divided into two categories, "temperature sensation" and "thermal comfort." Although several studies have investigated regional differences in temperature sensation, less is known about the sensitivity differences in thermal comfort for the various body regions. In the present study, we examined regional differences in temperature-related sensations with special attention to thermal comfort. Healthy male subjects sitting in an environment of mild heat or cold were locally cooled or warmed with water-perfused stimulators. Areas stimulated were the face, chest, abdomen, and thigh. Temperature sensation and thermal comfort of the stimulated areas were reported by the subjects, as was whole body thermal comfort. During mild heat exposure, facial cooling was most comfortable and facial warming was most uncomfortable. On the other hand, during mild cold exposure, neither warming nor cooling of the face had a major effect. The chest and abdomen had characteristics opposite to those of the face. Local warming of the chest and abdomen did produce a strong comfort sensation during whole body cold exposure. The thermal comfort seen in this study suggests that if given the chance, humans would preferentially cool the head in the heat, and they would maintain the warmth of the trunk areas in the cold. The qualitative differences seen in thermal comfort for the various areas cannot be explained solely by the density or properties of the peripheral thermal receptors and thus must reflect processing mechanisms in the central nervous system.

The importance of low ambient temperature in the physiology of winter dormancy was studied in the brown bullhead (Ictalurus nebulosus) and the largemouth bass (Micropterus salmoides). The bullheads frequently entered a sleep-like state at low temperatures; the likelihood of being aroused from this state was inversely proportional to the ambient temperature. Spontaneous activity for both species was relatively constant from 17 to 7 degrees C; at lower temperatures activity decreased. The selected temperature was lowered in both species as a consequence of acclimation to 3 degrees C; if given the opportunity, fish of both species moved to temperatures above 25 degrees C within 1 day in spite of the consequent acid-base and metabolic imbalances. In bass, food intake was very low for acclimation temperatures of 8 degrees C and below; at higher temperatures the relationship between food intake and acclimation temperature required 4 wk to stabilize. Quiescent brown bullheads exhibited discontinuous breathing. Alteration of brain temperature with implanted thermodes indicated that the main locus of control of this breathing pattern is in the medulla; lesser influences emanate from the anterior hypothalamus and the midbrain. Metabolism was measured at a series of acclimation temperatures between 3 and 17 degrees C for both species. No evidence of a discontinuous function (metabolic shutdown) was seen for either species.

Subjects resting in a 39 degrees C environment were stimulated in different skin regions with a water cooled thermode. This local cooling produced decreases in sweating rate measured at the thigh and increases in magnitude estimates of the cold sensation. The are of cold stimulation varied from 111 cm2 to 384 cm2. Sensitivity coefficients of the changes in sweating rate and magnitude estimate were corrected for differences in size of the area of stimulation and change in skin temperature and were normalized to the responses of the chest. The normalized coefficients showed the following relative sensitivities for changes in sweat rate and magnitude estimate respectively: forehead 3.3, 2.2; back 1.2, 1.4; lower leg 1.1, 0.9; chest 1.0, 1.0; thigh 0.9, 1.0; abdomen 0.8, 0.8. Varying the area stimulated from 122 cm2 to 384 cm2 produced greater changes in the sweating response than in the magnitude estimate. Rate of skin cooling during the period of stimulation had more effect on the sweating response than on the magnitude estimate. We conclude that cooling different body regions produces generally equivalent changes in the sweat rate and sensation, with the forehead showing a much greater sensitivity per unit area and temperature decrease than other areas.

Redband trout (Oncorhynchus mykiss ssp.) in southeastern Oregon inhabit high-elevation streams that exhibit extreme variability in seasonal flow and diel water temperature. Given the strong influence and potential limitations exerted by temperature on fish physiology, we were interested in how acute temperature change and thermal history influenced the physiological capabilities and biochemical characteristics of these trout. To this end, we studied wild redband trout inhabiting two streams with different thermal profiles by measuring (1) critical swimming speed (U(crit)) and oxygen consumption in the field at 12 degrees and 24 degrees C; (2) biochemical indices of energy metabolism in the heart, axial white skeletal muscle, and blood; and (3) temperature preference in a laboratory thermal gradient. Further, we also examined genetic and morphological characteristics of fish from these two streams. At 12 degrees C, maximum metabolic rate (Mo2max) and metabolic power were greater in Little Blitzen redband trout as compared with those from Bridge Creek (by 37% and 32%, respectively). Conversely, Bridge Creek and Little Blitzen trout had similar values for Mo2max and metabolic power at 24 degrees C. The U(crit) of Little Blitzen trout was similar at the two temperatures (61+/-3 vs. 57+/-4 cm s(-1)). However, the U(crit) for Bridge Creek trout increased from 62+/-3 cm s(-1) to 75+/-3 cm s(-1) when water temperature was raised from 12 degrees to 24 degrees C, and the U(crit) value at 24 degrees C was significantly greater than for Little Blitzen fish. Cost of transport was lower for Bridge Creek trout at both 12 degrees and 24 degrees C, indicating that these trout swim more efficiently than those from the Little Blitzen. Possible explanations for the greater metabolic power of Little Blitzen redband trout at 12 degrees C include increased relative ventricular mass (27%) and an elevation in epaxial white muscle citrate synthase activity (by 72%). Bridge Creek trout had 50% higher lactate dehydrogenase activity in white muscle and presumably a greater potential for anaerobic metabolism. Both populations exhibited a preferred temperature of approximately 13 degrees C and identical mitochondrial haplotypes and p53 gene allele frequencies. However, Bridge Creek trout had a more robust body form, with a relatively larger head and a deeper body and caudal peduncle. In summary, despite the short distance ( approximately 10 km) and genotypic similarity between study streams, our results indicate that phenotypic reorganization of anatomical characteristics, swimming ability at environmentally pertinent temperatures and white axial muscle ATP-producing pathways occurs in redband trout.