Naloxone does not alter the "regulated" decrease in core temperature during hypoxemia in guinea pigs

In newborns andadults of a number of species, exposure to acute hypoxemia produces a"regulated" decrease in core temperature, the mechanism of whichis unknown. The present experiments were carried out in chronicallyinstrumented newborn (5-10 days of age;n = 59) and older (25-30 days ofage; n = 61) guinea pigs to test thehypothesis that the endogenous opioids mediate this regulated decreasein core temperature. During an experiment, core temperature, oxygenconsumption, and selected ambient temperature were measured in athermocline (linear temperature gradient of 10-40°C) during acontrol period of normoxemia, an experimental period of normoxemia orhypoxemia (inspired oxygen fraction 0.10), and during a recovery periodof normoxemia following an intraperitoneal injection of naloxonehydrochloride (a nonspecific opioid antagonist; 1, 2, or 4 mg/kg) orvehicle. Naloxone did not significantly alter basal core temperature orthe core temperature response to acute hypoxemia in newborn or olderguinea pigs. Naloxone did, however, decrease basal oxygen consumptionin newborn and older guinea pigs and altered the thermoregulatoryeffector mechanism used to decrease core temperature during hypoxemiain the newborn guinea pigs. Our data do not support the hypothesis thatthe endogenous opioids mediate the regulated decrease in coretemperature that occurs in newborn and older guinea pigs duringexposure to acute hypoxemia.

     

Small molecule modulators of endogenous and co-chaperone-stimulated Hsp70 ATPase activity

The molecular chaperone and cytoprotective activities of the Hsp70 and Hsp40 chaperones represent therapeutic targets for human diseases such as cancer and those that arise from defects in protein folding; however, very few Hsp70 and no Hsp40 modulators have been described. Using an assay for ATP hydrolysis, we identified and screened small molecules with structural similarity to 15-deoxyspergualin and NSC 630668-R/1 for their effects on endogenous and Hsp40-stimulated Hsp70 ATPase activity. Several of these compounds modulated Hsp70 ATPase activity, consistent with the action of NSC 630668-R/1 observed previously (Fewell, S. W., Day, B. W., and Brodsky, J. L. (2001) J. Biol. Chem. 276, 910-914). In contrast, three compounds inhibited the ability of Hsp40 to stimulate Hsp70 ATPase activity but did not affect the endogenous activity of Hsp70. Two of these agents also compromised the Hsp70/Hsp40-mediated post-translational translocation of a secreted pre-protein in vitro. Together, these data indicate the potential for continued screening of small molecule Hsp70 effectors and that specific modulators of Hsp70-Hsp40 interaction can be obtained, potentially for future therapeutic use.     

Environmental physiology of the invasion of the Americas by Africanized honeybees

The expansion of Africanized honeybees (AHB) through the Americashas been one of the most spectacular and best-studied invasionsby a biotype. African and European honeybees (EHB) hybridize,but with time, tropical and subtropical American environmentshave become dominated by AHB that exhibit only 20–35%genetic contribution from western European bees, and a predominanceof African behavioral and physiological traits. EHB persistin temperate environments. Clines between AHB and EHB existin ecotones of South and Central America, and are forming inNorth America. What individual-level genetic, behavioral andphysiological traits determine the relative success of the AHBas an invader in the neotropics, and of the EHB in temperateareas? Preference for pollen versus nectar may be an importanttrait mediating these ecological trade-offs, as preference forpollen enhances nutrient intake and brood production for theAHB in the tropics, while a relative preference for nectar enhanceshoney stores and winter survival for EHB. AHB exhibit morphological(higher thorax-to-body mass ratios) and physiological (higherthorax-specific metabolic rates) traits that may improve flightcapacity, dispersal, mating success and foraging intake. Enhancedwinter longevity, linked with higher hemolymph vitellogeninlevels, may be a key factor improving winter survival of EHB.Data from South America and distributions of AHB in the southwesternUnited States suggest that AHB–EHB hybrids will extend200 km north of regions with a January maximal temperaturesof 15–16°C. The formation of biotypic clines betweenAHB and EHB represents a unique opportunity to examine mechanismsresponsible for the range limit of invaders.     

Threshold levels of maternal nicotine impairing protective responses of newborn rats to intermittent hypoxia.

Experiments were carried out to determine the threshold level of maternal nicotine that impairs protective responses of rat pups to hypoxia. From days 6 or 7 of gestation, pregnant rats received either vehicle or nicotine (1.50, 3.00, or 6.00 mg of nicotine tartrate. kg body wt(-1).day(-1)) or vehicle continuously via a subcutaneous osmotic minipump. On postnatal days 5 or 6, pups were exposed to a single period of hypoxia produced by breathing an anoxic gas mixture (97% N(2) or 3% CO(2)) and their time to last gasp was determined, or they were exposed to intermittent hypoxia and their ability to autoresuscitate from hypoxic-induced primary apnea was determined. Perinatal exposure to nicotine did not alter the time to last gasp or the total number of gasps when the pups were exposed to a single period of hypoxia. The number of successful autoresuscitations on repeated exposure to hypoxia was, however, decreased in pups whose dams had received either 3.00 or 6.00 mg of nicotine tartrate/kg body wt; these dosage regimens produced maternal serum nicotine concentrations of 19 +/- 6 and 35 +/- 8 ng/ml, respectively. Thus our experiments define the threshold level of maternal nicotine that significantly impairs protective responses of 5- to 6-day-old rat pups to intermittent hypoxia such as may occur in human infants during episodes of prolonged sleep apnea or positional asphyxia.     

Duplicate <Emphasis Type="Italic">dmbx1</Emphasis>genes regulate progenitor cell cycle and differentiation during zebrafish midbrain and retinal development

Background  

The Dmbx1 gene is important for the development of the midbrain and hindbrain, and mouse gene targeting experiments reveal that this gene is required for mediating postnatal and adult feeding behaviours. A single Dmbx1 gene exists in terrestrial vertebrate genomes, while teleost genomes have at least two paralogs. We compared the loss of function of the zebrafish dmbx1a and dmbx1b genes in order to gain insight into the molecular mechanism by which dmbx1 regulates neurogenesis, and to begin to understand why these duplicate genes have been retained in the zebrafish genome.     

Combined monte carlo and molecular dynamics simulation of fully hydrated dioleyl and palmitoyl-oleyl phosphatidylcholine lipid bilayers

We have applied a new equilibration procedure for the atomic level simulation of a hydrated lipid bilayer to hydrated bilayers of dioleyl-phosphatidylcholine (DOPC) and palmitoyl-oleyl phosphatidylcholine (POPC). The procedure consists of alternating molecular dynamics trajectory calculations in a constant surface tension and temperature ensemble with configurational bias Monte Carlo moves to different regions of the configuration space of the bilayer in a constant volume and temperature ensemble. The procedure is applied to bilayers of 128 molecules of POPC with 4628 water molecules, and 128 molecules of DOPC with 4825 water molecules. Progress toward equilibration is almost three times as fast in central processing unit (CPU) time compared with a purely molecular dynamics (MD) simulation. Equilibration is complete, as judged by the lack of energy drift in 200-ps runs of continuous MD. After the equilibrium state was reached, as determined by agreement between the simulation volume per lipid molecule with experiment, continuous MD was run in an ensemble in which the lateral area was restrained to fluctuate about a mean value and a pressure of 1 atm applied normal to the bilayer surface. Three separate continuous MD runs, 200 ps in duration each, separated by 10,000 CBMC steps, were carried out for each system. Properties of the systems were calculated and averaged over the three separate runs. Results of the simulations are presented and compared with experimental data and with other recent simulations of POPC and DOPC. Analysis of the hydration environment in the headgroups supports a mechanism by which unsaturation contributes to reduced transition temperatures. In this view, the relatively horizontal orientation of the unsaturated bond increases the area per lipid, resulting in increased water penetration between the headgroups. As a result the headgroup-headgroup interactions are attenuated and shielded, and this contributes to the lowered transition temperature.     

Abnormal cardiac structure and function in mice expressing nonphosphorylatable cardiac regulatory myosin light chain 2.

A role for myosin phosphorylation in modulating normal cardiac function has long been suspected, and we hypothesized that changing the phosphorylation status of a cardiac myosin light chain might alter cardiac function in the whole animal. To test this directly, transgenic mice were created in which three potentially phosphorylatable serines in the ventricular isoform of the regulatory myosin light chain were mutated to alanines. Lines were obtained in which replacement of the endogenous species in the ventricle with the nonphosphorylatable, transgenically encoded protein was essentially complete. The mice show a spectrum of cardiovascular changes. As previously observed in skeletal muscle, Ca(2+) sensitivity of force development was dependent upon the phosphorylation status of the regulatory light chain. Structural abnormalities were detected by both gross histology and transmission electron microscopic analyses. Mature animals showed both atrial hypertrophy and dilatation. Echocardiographic analysis revealed that as a result of chamber enlargement, severe tricuspid valve insufficiency resulted in a detectable regurgitation jet. We conclude that regulated phosphorylation of the regulatory myosin light chains appears to play an important role in maintaining normal cardiac function over the lifetime of the animal.