Pregnancy alters body-core temperature response to a simulated open field in rats

Fewell, James E., and Patricia A. Tang. Pregnancyalters body-core temperature response to a simulated open field in rats. J. Appl. Physiol. 82(4):1406-1410, 1997.Exposure of a rat to a novel environment (e.g.,a simulated open field) induces a transient increase in body-coretemperature, which is often called stress-induced hyperthermia.Although pregnancy is known to influence thermoregulatory control, itseffect on stress-induced hyperthermia is unknown. Therefore, 24 Sprague-Dawley rats (8 nonpregnant and 16 pregnant) were studied totest the hypothesis that pregnancy would alter the development ofstress-induced hyperthermia after exposure to a simulated open field.Body-core temperature index increased significantly after exposure to asimulated open field in nonpregnant and gestationday-10 rats but not in gestation day-15 andday-20 rats. Thus our data provideevidence that pregnancy influences the body-core temperature responseof rats exposed to a simulated open field in a gestation-dependentfashion. The functional consequences as well as the mechanisms involvedremain to be determined.

     

Individual constancy of local search strategies in the giant tropical ant,Paraponera clavata (Hymenoptera: Formicidae)

Paraponera clavata workers engage in a period of local search after encountering a small amount of artificial nectar. Giving-up times from local search are not distributed normally; there is a strong skew to longer times. There is no statistically significant relationship between the amount of time required to collect the food and the subsequent search time. Giving-up time in response to the first reward presented to an ant is positively correlated with that ant's response to a second such reward. However, giving-up times diminish when an ant is presented with a series of rewards. Local search is a function of individual strategies, which remain relatively constant in the short term.     

Effect of tracheostomy on lung development in fetal lambs

The effects of fetal tracheostomy on lung development in lambs have been investigated. Seven ewes, all with twin fetuses, were given a general anesthetic. One fetus in each set of twins was tracheostomized and the other fetus was sham operated (117-122 days gestation). The fetuses were delivered by cesarean section between 137 and 140 days gestation. Fetal tracheostomy decreased lung weight and volume, altered DNA concentration and the structural development of the acinus, and decreased lung distensibility. However, tissue and airway saturated phosphatidylcholine and lung stability during deflation were not significantly affected by fetal tracheostomy. It seems that tracheostomy in fetal lambs alters lung growth but does not affect the formation or release of surfactant. These data support the hypothesis that lung volume is actively maintained and lung growth promoted by the secretion of lung fluid against the resistance of the upper airway in fetal lambs.     

Influence of carotid-denervation on the arousal and cardiopulmonary responses to alveolar hypercapnia in lambs

Experiments were done on five lambs to determine if carotid-denervation influences the arousal and cardiopulmonary responses to alveolar hypercapnia during sleep. Each lamb was anaesthetized and instrumented for recordings of electrocorticogram, electro-oculogram, nuchal and diaphragm electromyograms and measurements of systemic arterial blood pressure and arterial haemoglobin oxygen saturation. The carotid chemoreceptors and baroreceptors were denervated, a tracheostomy was done and a fenestrated tracheostomy tube placed in the trachea so that the inspired gas mixture could be changed quickly. No sooner than three days after surgery, measurements were made in quiet sleep and active sleep during control periods when the animal was breathing room air and during experimental periods of alveolar hypercapnia when the lamb was breathing 10% carbon dioxide in air. Alveolar hypercapnia was terminated during an experimental period by changing the gas mixture back to room air once the animal aroused from sleep. If an animal did not arouse within 2 min, the gas mixture was changed back to room air. Arousal occurred during only 6 of 12 epochs in quiet sleep and during only 2 of 10 epochs in active sleep. These data provide evidence that the carotid chemoreceptors and/or carotid baroreceptors play a major role in causing arousal from sleep during alveolar hypercapnia in lambs.     

Influence of repeated exposure to rapidly developing hypoxaemia on the arousal and cardiopulmonary response to rapidly developing hypoxaemia in lambs

Experiments were done on four lambs to determine if repeated exposure to rapidly developing hypoxaemia influences the cardiopulmonary and arousal response from sleep. Each lamb was anaesthetized and instrumented for sleep staging and measurements of arterial haemoglobin oxygen saturation. No sooner than three days after surgery, measurements were made in quiet sleep and active sleep during control periods when the animal was breathing 21% oxygen and during experimental periods of rapidly developing hypoxaemia when the animal was breathing 5% oxygen for approximately 100 epochs of sleep. Arousal occurred from both sleep states during rapidly developing hypoxaemia but was delayed in active sleep compared to quiet sleep. The time to arousal and the decrease in arterial haemoglobin oxygen saturation were significantly increased with repeated exposure to rapidly developing hypoxaemia during both quiet sleep and active sleep. Thus, our data provide evidence that repeated exposure to rapidly developing hypoxaemia produces an arousal response decrement in lambs. Since it is possible that alterations in the arousal response to respiratory stimuli play a role in sudden infant death, studies to investigate the mechanism of the arousal response decrement following repeated exposure to rapidly developing hypoxaemia are warranted.     

Long-wavelength sensitive visual pigments of the guppy (<Emphasis Type="Italic">Poecilia reticulata</Emphasis>): six opsins expressed in a single individual

Background

The diversity of visual systems in fish has long been of interest for evolutionary biologists and neurophysiologists, and has recently begun to attract the attention of molecular evolutionary geneticists. Several recent studies on the copy number and genomic organization of visual pigment proteins, the opsins, have revealed an increased opsin diversity in fish relative to most vertebrates, brought about through recent instances of opsin duplication and divergence. However, for the subfamily of opsin genes that mediate vision at the long-wavelength end of the spectrum, the LWS opsins, it appears that most fishes possess only one or two loci, a value comparable to most other vertebrates. Here, we characterize the LWS opsins from cDNA of an individual guppy, Poecilia reticulata, a fish that is known exhibit variation in its long-wavelength sensitive visual system, mate preferences and colour patterns.

Results

We identified six LWS opsins expressed within a single individual. Phylogenetic analysis revealed that these opsins descend from duplication events both pre-dating and following the divergence of the guppy lineage from that of the bluefin killifish, Lucania goodei, the closest species for which comparable data exists. Numerous amino acid substitutions exist among these different LWS opsins, many at sites known to be important for visual pigment function, including spectral sensitivity and G-protein activation. Likelihood analyses using codon-based models of evolution reveal significant changes in selective constraint along two of the guppy LWS opsin lineages.

Conclusion

The guppy displays an unusually high number of LWS opsins compared to other fish, and to vertebrates in general. Observing both substitutions at functionally important sites and the persistence of lineages across species boundaries suggests that these opsins might have functionally different roles, especially with regard to G-protein activation. The reasons why are currently unknown, but may relate to aspects of the guppy's behavioural ecology, in which both male colour patterns and the female mate preferences for these colour patterns experience strong, highly variable selection pressures.