Delbert L Kilgore

Effects of embryonic CO2 exposure on the adult ventilatory response in quail: does gender matter?

To test the hypothesis that the adult ventilatory response to CO2 can be modified by exposure to CO2 during development, we exposed Japanese quail (Coturnix japonica) from two populations to 2% CO2 throughout embryonic development. The ventilatory response to 6% CO2 was subsequently measured in control and CO2-exposed quail following a 6-9 week deacclimation period. In one population of quail, CO2-exposed female, but not male, quail had a reduced ventilatory response to 6% CO2 as adults (P<0.001). Although control and CO2-exposed quail had similar ventilation while breathing air, CO2-exposed females exhibited a 26% reduction in mean ventilation at 6% CO2, primarily due to a reduced tidal volume. In contrast, the identical incubation treatment had no effect on the ventilation of either gender in a second population of quail. It appears that developmental plasticity in the hypercapnic ventilatory response may generally be greater in females, although this conclusion may vary depending on genetic factors.

Temperature regulation in normothermic black-tailed prairie dogs, Cynomys ludovicianus

Abstract 1. 1. The relationship between body mass (g) and metabolism in the Family Sciuridae is described by the equation ml O 2 /hr = 3.9W 0.69 which is not statistically different from the standard mammalian relationship (3.8 W 0.73 ). 2. 2. Normothermic black-tailed prairie dogs have a narrow thermal neutral zone. Minimal .V O 2 was recorded at T A of 30.2°C ( .V O 2 = 2.6ml O 2 /g 0.73 .hr. T B = 38.1°C) and was 67% of that predicted based on body mass. 3. 3. A circadian cycle in T B exists with peak mid-day and low nocturnal values. 4. 4. Between T A of 20 and 30°C, T B rises yet .V O 2 decreases. Changes in conductance may account for hyperthermia during decreased heat output. Above thermal neutrality conductance increases sharply. 5. 5. Heat storage is discussed in terms of its contribution to water balance.

Ventilatory, cardiovascular and metabolic responses to hypoxia and hypercapnia in the armadillo

Armadillos have a low resting metabolic rate and high hemoglobin affinity for their size, a rigid carapace and a semi-fossorial life style. These characteristics could contribute to unusual respiratory responses to hypoxia and hypercapnia which were investigated in this study. Ventilatory and oxygen consumption responses of six adult unanesthetized armadillos to 15, 12, 10 and 8% O2 and 1.5, 3, 5 and 7% CO2 were measured by barometric plethysmography and flow-through respirometry. A significant increase in ventilation occurred in response to 10 and 8% O2 but a decline in oxygen consumption only occurred at 8% inspired O2. The convection requirement response has a threshold at a PaO2 of approximately = 28 Torr which corresponds to a Hb saturation of approximately 70%. Ventilation increased in response to 3% and higher levels of CO2, with no change in oxygen consumption. The magnitude of the ventilatory response to CO2 was similar to other semi-fossorial mammals and less than that of nonburrowing species. However, the pattern of the response was unique in being largely a frequency response with little change in tidal volume, contrary to the tidal volume dominated response to hypercapnia typical of mammals. This feature, not shared by another Xenarthran, the sloth, who lacks a carapace, is likely attributable to the low respiratory system compliance and increased airway resistance resulting from the rigid carapace and small lungs of armadillos and emphasizes the importance of respiratory mechanics in determining breathing pattern.

Brain temperature in the calliope hummingbird (Stellula calliope): a species lacking arete mirabile ophthalmicum

Summary1.Hypothalamic and colonic temperature were simultaneously measured in the calliope hummingbird (Stellula calliope). The vascular anatomy of the temporal region of these birds was also examined.2.At air temperatures below 36°C, calliope hummingbirds regulated their body temperature between 35.6 and 40.6°C. At higher air temperatures, colonic temperature increased.3.Brain temperature was lower than body temperature at high colonic temperatures (>39.5°C). The body-to-brain temperature difference in birds with high body temperatures averaged 0.73°C and remained relatively constant at all colonic temperatures above 39.5°C.4.At body temperatures below 39.5°C, brain temperature of calliope hummingbirds exceeded colonic temperature by an average of 1.38°C. The possible explanations for this observation are discussed.5.Calliope hummingbirds lack arete mirabile ophthalmicum, the countercurrent arterial-venous heat exchanger responsible for brain cooling in other birds.6.Brain cooling in calliope hummingbirds apparently depends on heat exchange between arterial blood flowing to the brain, and cool venous blood returning from evaporative and convective surfaces at sites other than therete mirabile ophthalmicum.

Spike firing allometry in avian intrapulmonary chemoreceptors: matching neural code to body size

SUMMARY Biological rates in small animals are usually higher than those in large animals, yet the maximal rate of action potential (spike) generation in sensory neurons encoding rate functions is similar in all animals, due to the conserved genetics of voltage-gated ion channels. Therefore, sensory signals that vary at rates approaching maximal spike generation rate, as might occur in animals of diminished body size, may require specialized spike coding to convey this information. To test whether spike coding scales allometrically in sensory neurons monitoring signals that change frequency with body size, we recorded action potentials from 70 avian intrapulmonary chemoreceptors (IPC), respiratory neurons that detect lung CO2 changes during breathing, in five different avian species ranging in size from body mass Mb = 0.045 kg (lovebirds) to 5.23 kg (geese). Since breathing frequency scales approximately to Mb–1/4 (higher in small birds, lower in large birds), we reasoned that IPC discharge frequencies may also scale to maintain spike information transmission within each breath. We found that phasic action potential discharge pattern, as quantified by the peak discharge rate and the magnitude of spike frequency adaptation, scaled between Mb–0.22 and Mb–0.26, like breathing rate (P<0.05). Previously published values of peak discharge rate in IPC also fit this allometric relationship. We suggest that mass-dependent scaling of neural coding may be necessary for preserving information transmission with decreasing body size.

How stiff is the armadillo? A comparison with the allometrics of mammalian respiratory mechanics

Static respiratory mechanics were examined in the armadillo (Dasypus novemcinctus) and compared with allometric relationships newly derived for adult mammals from values in the literature. Normalised by body weight, chest wall compliance (Cw) in the armadillo is lower than predicted. Lung compliance (Cl) is also low in the armadillo, however it is appropriately matched to the resting lung volume (Vr) (ie. Cl/Vr infinity Mass0.0) and the ratio of Cw/Cl is appropriate for the size of the animal. Respiratory system resistance is high in the armadillo, presumably because of smaller airways associated with the small lung. The power of breathing in the armadillo is comparatively high, mainly due to the high resistive forces. Indeed, the oxidative cost of breathing is approximately double that of a mammal with similar Vr. Hypoxia or hypercapnia are known to invoke an attenuated ventilatory response in the armadillo and one that relies more on changes in frequency rather than volume. While such a breathing pattern helps to reduce the power of breathing it also compromises the degree of hyperventilation achieved.

Temperature regulation and basal metabolic rate in the spotted skunk, Spilogale putorius

1. Metabolic rate, body temperature, and evaporative water loss of six spotted skunks were measured at air temperatures between 8 and 40 degrees C. 2. The mean metabolic rate of spotted skunks at thermoneutral air temperatures was 30.5% below that predicted by body mass. 3. Thermal conductance, body temperature, and rates of evaporative water loss were like those of similar sized mammals. 4. The non-elongate body form, omnivorous diet, and low level of activity of spotted skunks distinguish them from other mustelids and may account for their lower-than-expected basal metabolism.

Blood characteristics, tracheal volume and heart mass of burrowing owls (Athene cunicularia) and bobwhite (Colinus virginianus)

1. Measurements of certain hematological and morphological characteristics were made in burrowing owls and bobwhite in search of features that could be associated with the previously described ventilatory adaptations of the burrowing owl to hypoxia and hypercarbia. 2. Values for burrowing owls and bobwhite, respectively, were: P50 = 44.9, 46.0 torr; Hct = 36.6, 38.8 vol%, Hb = 12, 12.3 (g/100 ml); RBC = 2.72 X 10(6), 3.02 X 10(6); log P50/pH = -0.412, -0.485; delta log PCO2/delta pH = -1.39, -1.585. 3. The owls had greater heart weights and smaller tracheal volumes than the bobwhite or the predicted value. 4. No hematological characteristics of the burrowing bird distinguish it from the non-burrowing bird.

Ventilatory and metabolic responses of a bat,Phyllostomus discolor, to hypoxia and CO2: implications for the allometry of respiratory control

AbstractThe ventilatory and metabolic responses of lesser spear-nosed bats to hypoxia and hypercapnia were measured to determine whether these corresponded to preliminary allometries and a positive relationship between hypoxic ventilatory threshold andP50. Ventilatory responses of lesser spear-nosed bats to 3, 5 and 7% CO2 differed significantly from ventilation on air and each other. The magnitude of their ventilatory response to CO2 is consistent with the prediction of a smaller ventilatory response to hypercapnia in small compared to large mammals [