Amount of prenatal visual stimulation alters incubation times and postnatal preferences in leopard geckos (Eublepharis macularius).

The authors exposed gecko (Eublepharis macularius) embryos to patterned visual stimulation beginning at either 1 week or 2 weeks prior to hatching. Embryos exposed to the substantially augmented amount of prenatal visual stimulation hatched significantly earlier than the embryos either exposed to the moderately augmented prenatal visual stimulation or not exposed to any prenatal visual stimulation (p < .01). Hatchling mass was not affected. Embryos exposed to substantially augmented visual stimulation demonstrated a postnatal preference for patterned light in a simultaneous choice test at 24 hr of age (p < .01). Control embryos demonstrated a preference for normal light conditions (p < .01), whereas experimental embryos exposed to lesser amounts of prenatal visual stimulation did not show a preference for either stimulus. At 1 week of age, geckos in all conditions failed to exhibit a preference for either stimulus.

An allometric analysis of oxygen consumption rate and cardiovascular function in the cockroach, Blaberus discoidalis.

The interrelationship of metabolic rate and cardiovascular function has been well documented in vertebrates through allometric analyses. However, similar studies are lacking in insects. Unlike vertebrates, the cardiovascular system of insects does not play a significant role in oxygen transport. A comparison of the interrelationship in insects and vertebrates might provide insight into the nature of the connection between metabolic rate and the cardiovascular system. Oxygen consumption, heart rate and heart dimensions were measured in the nymphs of the cockroach Blaberus discoidalis over a mass range of 0.03-5 g. Oxygen consumption rate scaled with an exponent of 0.83. The relationship between heart rate and body mass scaled negatively, however, it did not appear to be linear. Using measurements of heart widths, abdominal length and heart rate, stroke volume and cardiac output were estimated. Cardiac output appeared to scale linearly with an exponent of 0.85, which was not significantly different from the exponent observed for the rate of oxygen consumption. Thus, the observed similarity between the exponents for oxygen consumption rate and cardiac output in vertebrates also appears to be present in insects.

The effect of changing the gaseous diffusion coefficient on the mass loss pattern of Hyalophora cecropia pupae.

The importance of gas phase diffusion in insect gas exchange remains unclear. The role of diffusion in gas exchange of developing Hyalophora cecropia pupae was examined by altering the gaseous diffusion coefficient in the breathing mixture. Gaseous diffusion coefficients were manipulated by substituting helium or sulfur hexafluoride for the nitrogen usually present in air. Sensitive mass loss recordings were employed to monitor gas exchange activity. Mass loss recordings showed a two-phase cycle, open and closed-flutter. Mass loss rates during the open and closed-flutter periods were not altered in proportion to the changes induced in the rate of diffusion. Open-phase duration was inversely and proportionally related to the diffusion coefficient. These results are consistent with changes in spiracle resistance or convective flow during the open period in response to a change in the diffusion coefficient. In addition, they indicate a significant gas phase diffusive resistance within the pupal tracheal system. This previously unreported gas phase resistance appears to be a major determinant of the duration of the open period and thus of overall water loss rates in these pupae.

Availability of water affects organ growth in prenatal and neonatal snapping turtles (Chelydra serpentina).

We manipulated the amount of water that was available to prenatal and neonatal snapping turtles (Chelydra serpentina) in order to assess the impact of water on growth by different organs in these animals. Three treatments were used: (1) turtles that completed their incubation on a wet substrate, (2) turtles that completed their incubation on a dry substrate, and (3) turtles that spent a few days in water after completing incubation on a dry substrate. Turtles hatching on a dry substrate (treatment 2) were smaller than animals in the other two treatments (which did not differ in size), so data for mass of different organs were adjusted by ANCOVA to remove effects of body size. Scaled masses of liver, stomach, lungs, kidneys, and small intestine did not differ between turtles emerging in wet environments and those hatching in dry environments, but hearts of turtles hatching in dry settings were substantially larger than those of animals hatching in wet ones. Thus, the mass of most organs in turtles developing in wet and dry environments scaled to body size, whereas the heart was hypertrophied in embryos developing in dry environments. Turtles that spent a few days in water after hatching from eggs in dry environments grew rapidly in size, and the increase in body size was accompanied by disproportionately rapid growth in the liver, stomach, lungs, kidneys, and small intestine. The heart did not increase in size during this period, despite the substantial increase in body mass over that at hatching. The enlarged heart of turtles hatching on dry substrates may have been caused by a circulatory hypovolemia late in incubation; the rapid growth of organs other than the heart when these animals were placed in water may reflect a release from constraints on growth once circulatory volume was restored.

Heart rate during development in the turtle embryo: effect of temperature.

Growth and development can occur over a wide range of physical conditions in reptiles. Cardiovascular function must be critical to this ability. However, information on cardiovascular function in developing reptiles is lacking. Previous work indicated that in reptiles the effects of temperature on growth and metabolism are largely restricted to early development. This study examined whether the previously observed effects of temperature and different perinatal patterns of metabolism observed in amniotic vertebrates are correlated with cardiovascular function. Embryonic and hatchling carcass mass, heart mass and heart rate (HR) were compared for snapping turtle eggs (Chelydra serpentina) incubated at 24 degrees and 29 degrees C. Incubation time was shorter at 29 degrees C (56.2 days) than at 24 degrees C (71.1 days). Carcass and heart growth showed a sigmoidal pattern at both temperatures. However, cardiac growth showed a relative decrease as incubation proceeded. Incubation temperature significantly affected the HR pattern during development. The HR of embryos incubated at 24 degrees C was constant for most of incubation (51.8 +/- 4.8 min-1). A small decrease was observed just prior to and a large decrease immediately following hatching (posthatch, 22.3 +/- 4.1 min-1). At 29 degrees C embryonic HR was greater than at 24 degrees C early in development (72.3 +/- 3 min-1). The HR steadily decreased to values equivalent to those at 24 degrees C. The HRs of 24 degrees C and 29 degrees C hatchlings were not different. Cardiac output (estimated as the product of heart mass and HR) increased rapidly during early development and then slowed dramatically at both temperatures. These data are consistent with the suggestion that temperature exerts its effects primarily early in development. Furthermore, the changes in cardiovascular function are correlated with metabolic changes in hatching vertebrates.

Ventilatory and hematopoietic responses to chronic hypoxia in two rat strains.

Hilltop (H) and Madison (M) strains of Sprague-Dawley rats exhibit strikingly different susceptibilities to the effects of chronic altitude exposure. The H rats develop greater polycythemia, hypoxemia, and pulmonary hypertension. We studied ventilation, pulmonary gas exchange, tissue oxygenation, and hematologic adaptations in the two rat strains during a 50-day exposure to a simulated altitude (HA) of 5,500 m (18,000 ft). There were no strain differences among the variables we studied under sea level (SL) conditions. Within the first 14 days of hypoxic exposure, the only significant strain differences were that erythropoietin (EPO) rose much higher and erythroid activity was greater in the H rats, even though arterial Po2 and PCo2 (Pao2 and PaCo2, respectively), renal venous PO2 (Prvo2), and ventilation (VE) were equivalent in the two strains during this time. By day 14 at HA, the H rats had significantly higher erythroid activity, hematocrit (Hct), and EPO levels, significantly lower PaO2 and PrvO2, but equivalent VE and PaCO2. These changes persisted for the remainder of the exposure, except that the Hct continued to rise and the increase was greater in H rats. Despite the greater O2-carrying capacity of H rats in the later stages of hypoxic exposure, PaO2 and PrvO2 were significantly lower in H rats. There were no strain differences at either SL or HA in ventilatory responses to hypercapnia or hypoxia, in blood O2 affinity or 2,3-diphosphoglycerate, in extrarenal production of EPO, or in EPO clearance. We conclude that early in the hypoxic exposure the H rats produce more EPO at apparently equivalent levels of hypoxia, and this is the first step in the pathogenesis of the maladaptation to HA manifest by H rats. We find no consistent evidence that differences in VE contribute to the variable susceptibility to hypoxia in the two rat strains.

Regional variations in human toxics exposure in the USA: an analysis based on the National Human Adipose Tissue Survey.

Regional human exposure was evaluated by examining human tissue chemical concentrations. National Human Adipose Tissue Survey data for 54 toxic substances [pesticides, polychlorinated biphenyls (PCBs), semivolatiles, volatiles, and polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs)], were sorted by United States census divisions. Regional differences in human toxics exposure were found. Based on the data analyzed, it appears that individuals residing in the South Atlantic, East South Central, West South Central, and East North Central regions may be exposed to greater amounts of toxic substances than those of other regions of the country. Higher concentrations of organochlorine pesticides, PCBs, and PCDDs in older individuals indicate that these toxics bioaccumulate in human adipose tissue.

Relationship between blood-oxygen affinity and blood volume.

The hypothesis was tested that total blood volume (TBV) is correlated with hemoglobin oxygen affinity. Intraspecifically Hb-O2 affinity was manipulated in rats using NaOCN. Interspecifically the hypothesis was evaluated using data gathered from the literature. Both intra- and interspecifically TBV increased with increasing hemoglobin oxygen affinity (delta TBV/delta P50 = -1.18). Intraspecifically decreases in P50 were associated with an increase in red blood cell mass and hematocrit. Interspecifically plasma volume had an inverse relationship with Hb-O2 affinity (delta TBV/delta P50 = -1.10) and hematocrit showed no changes. These data suggest that an increased blood volume may be part of the mechanism explaining the inverse correlation between P50 and hypoxic tolerance.

Cardiorespiratory responses of the woodchuck and porcupine to CO2 and hypoxia.

The burrow-dwelling woodchuck (Marmota monax) (mean body wt. = 4.45 +/- 1 kg) was compared to a similar-sized (5.87 +/- 1.5 kg) but arboreal rodent, the porcupine (Erithrizon dorsatum), in terms of its ventilatory and heart rate responses to hypoxia and hypercapnia, and its blood characteristics. VT, f, T1 and TE were measured by whole-body plethysmography in four awake individuals of each species. The woodchuck has a longer TE/TTOT (0.76 +/- 0.03) than the porcupine (0.61 +/- 0.03). The woodchuck had a higher threshold and significantly smaller slope to its CO2 ventilatory response compared to the porcupine, but showed no difference in its hypoxic ventilatory response. The woodchuck P50 of 27.8 was hardly different from the porcupine value of 30.7, but the Bohr factor, -0.72, was greater than the porcupine's, -0.413. The woodchuck breathing air has PaCO2 = 48 (+/- 2) torr, PaO2 = 72 (+/- 6), pHa = 7.357 (+/- 0.01); the porcupine blood gases are PaCO2 = 34.6 (+/- 2.8), PaO2 = 94.9 (+/- 5), pHa = 7.419 (+/- 0.03), suggesting a difference in PaCO2/pH set points. The woodchuck exhibited no reduction in heart rate with hypoxia, nor did it have the low normoxic heart rate observed in other burrowing mammals.

The hypoxic ventilatory response of rats with increased blood oxygen affinity.

Experimental work has established an interspecific relationship between the threshold for the hypoxic ventilatory response and the 'knee' of the Hb-O2 dissociation curve. However, whether this relationship exists intraspecifically remains unclear. To examine the problem further rats were treated with sodium cyanate (NaOCN) to lower P50 and their hypoxic ventilatory response was measured. NaOCN treated rats had a lower PaO2 and higher Hct than control rats. There was no difference between the control and lowered P50 condition in the ventilatory response to hypoxia when % delta VI was plotted against PaO2. The results are consistent with PaO2 sensing chemoreceptors.

Effect of carbonic anhydrase inhibition on blood acid-base balance in the chicken embryo.

The role of carbonic anhydrase in chicken embryo blood acid-base balance was examined using the carbonic anhydrase inhibitor acetazolamide during the second half of incubation. Day 13, 16, and 17 embryos of treated eggs had significant increases in blood PCO2 and decreases in blood pH when compared with controls.

Effect of perinatal hypercapnia on the adult ventilatory response to carbon dioxide.

Burrowing mammals show a reduced ventilatory response to CO2 and CO2 retention. We examined whether this reduced responsiveness could be due to modification of chemoreceptors by persistent hypercapnia during development. Mice and rats were exposed to 6.0% CO2 throughout gestation and/or weaning and then removed to normocapnic air for a minimum of 6 weeks. Mouse gas pocket O2 and CO2 tensions and hematocrits were analyzed and compared with normocapnically raised controls. The ventilatory and blood gas and pH response to CO2 were compared in chronically cannulated test and control rats. Hematocrits and gas pocket CO2 and O2 tensions of mice and rat ventilatory and arterial blood CO2 and O2 tensions and pH responses were not different in test and control groups. There appears to be little or no developmental affect of CO2 suggesting that the reduced CO2 response seen in burrowers is genetically determined.

Ventilation and CSF ions during hypocapnic HCl and HNO3 acidosis in conscious rabbits.

In conscious rabbits with preimplanted arterial, central venous, and cisterna magna catheters, we infused HNO3 or HCl to lower and maintain arterial PCO2, pH, and plasma HCO-3 at the same mean values in both groups over 9 h. The hypothesis was that greater entry into cerebrospinal fluid (CSF) of the strong anion NO-3 vs. Cl- would result in a greater decrease in CSF [HCO-3] in the HNO3 vs. the HCl experiment, even though the acid-base stress as measured by arterial PCO2 and plasma [HCO-3] was the same. The results did not support the hypothesis. With HCl acidosis, delta CSF [HCO-3] was equal to delta CSF [Cl-]. With HNO3 acidosis, delta CSF [HCO-3] was equal to delta CSF [NO-3] + delta CSF [Cl-], as both CSF Cl- and HCO-3 decreased with NO-3 entry into CSF. The change in CSF [HCO-3] appeared tightly linked to the PCO2 or the plasma [HCO-3], it did not depend on the type of acid used. The ionic mechanisms that determine the CSF [HCO-3] in metabolic acidosis appear able to utilize changes in the strong anions NO-3 and Cl- to bring about CSF acid-base regulation. The change in alveolar ventilation per unit CO2 production as reflected by the arterial PCO2 was the same in both groups, although the expired minute ventilation and respiratory frequency responses were diminished in the HNO3 vs. the HCl groups. In both groups with acidosis, tidal volume increased, whereas respiratory frequency decreased.

Effects of hypoxia on lung volume in the garter snake.

Ventilation and lung volume were measured in unanesthetized garter snakes using a headout body plethysmograph. The breathing cycle consisted of expiration, inspiration and a prolonged post-inspiratory breath-holding period, which lasted until the onset of the next expiration. Hypoxia induced increases in VT and in the volume at which the breath was held between cycles. Hypercapnia usually elicited hyperpnea after an initial, transient inhibition of breathing movements, but was accompanied by little or no increase in breath-holding lung volume. Snakes with T-tube tracheostomies failed to maintain the normal positive intrapulmonary pressure during the breath-holding period and failed to increase breath-holding lung volume in hypoxia, despite increased inspiratory excursions. These studies demonstrate a pronounced increase in lung volume during hypoxia and indicate that this response requires an intact upper airway. These findings in a reptile may be related in evolutionary terms to the increase in lung volume and post-inspiratory laryngeal narrowing that occur in mammals during hypoxia.

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.

Respiratory properties of blood from embryos of highland vs. lowland geese.

Respiratory properties of whole blood during development were studied in embryos of the bar-headed and Canada geese. In both species, affinity of the blood for O2 [expressed as O2 half-saturation pressure (P50)] increased with development, to a low and stable value. The low and stable P50 at pH 7.4 for the bar-headed goose, 20.1 +/- 0.3 Torr, is significantly lower than that for the Canada goose, 26.9 +/- 0.8 Torr. The data suggest a higher Bohr effect for the bar-headed goose. Hill's coefficients, buffering capacity, red cell 2,3-diphosphoglycerate, and blood hemoglobin concentrations are similar in both species. We suggest that the affinity of the whole blood for O2 is an important genetically based adaptation to ensure a high O2 content in the blood in the face of reductions in ambient PO2 associated with nesting at high altitudes. The higher Bohr effect may ensure high tissue PO2 in the presence of the high-affinity hemoglobin.

Water loss and survival in embryos of the domestic chicken.

In this report we show that the amount of water lost during incubation is an important determinant of hatchability in embryos of the domestic chicken. However, when the loss of water is restricted to the first half versus the second half of the total incubation period, it is the loss of water during the first half that affects hatching success. We propose that regulating the permeability of the egg shell may be important in preventing excessive drying of the inner shell membrane during early development along with limiting the total amount of water lost from the embryo during incubation.

Oxygen permeability of the shell and membranes of chicken eggs during development.

Oxygen permeability (KO2) was measured through the shell and shell membranes of chicken eggs throughout incubation. Shell KO2 was constant at 1.90 x 10(-6) cm3 O2 STP . sec-1 . cm-2 . Torr-1. Outer shell membrane KO2 was constant at 1.78 x 10(-6) cm3 O2 STP . sec-1 . cm-2 . Torr-1. Inner membrane KO2 increased from 0.11 x 10(-6) cm3 O2 STP . sec-1 . cm-2. Torr-1 to 1.56 x 10(-6) cm3 O2 STP . sec-1 . cm-2 . Torr-1. Calculations of KO2 from oxygen uptake rates and air cell PO2's were in close agreement with direct measurement of KO2. Resistance to oxygen flux was partitioned at each level. The outer membrane added 6% to the resistance of the shell. The inner membrane initially accounted for 88% of the shell/membrane complex resistance, but fell to 12% of the resistance by the end of incubation. The hypothesis is discussed that the increased permeability of the inner membrane is related to the evaporation of water from the membrane surface. The possibility is rejected that the shell membranes may be potential sites for respiratory adaptation to incubation at altitude.