Runners adjust leg stiffness for their first step on a new running surface.

Human runners adjust the stiffness of their stance leg to accommodate surface stiffness during steady state running. This adjustment allows runners to maintain similar center of mass movement (e.g., ground contact time and stride frequency) regardless of surface stiffness. When runners encounter abrupt transitions in the running surface, they must either make a rapid adjustment or allow the change in the surface stiffness to disrupt their running mechanics. Our goal was to determine how quickly runners adjust leg stiffness when they encounter an abrupt but expected change in surface stiffness that they have encountered previously. Six human subjects ran at 3 m s(-1) on a rubber track with two types of rubber surfaces: a compliant "soft" surface (ksurf = 21.3 kN m(-1) and a non-compliant "hard" surface (ksurf = 533 kN m(-1). We found that runners completely adjusted leg stiffness for their first step on the new surface after the transition. For example, runners decreased leg stiffness by 29% between the last step on the soft surface and the first step on the hard surface (from 10.7 kN m(-1) to 7.6 kN m(-1), respectively). As a result, the vertical displacement of the center of mass during stance ( approximately 7 cm) did not change at the transition despite a reduction in surface compression from 6 cm to less than 0.25 cm. By rapidly adjusting leg stiffness, each runner made a smooth transition between surfaces so that the path of the center of mass was unaffected by the change in surface stiffness.     

Pharmacokinetics and tissue residues of Telazol in free-ranging polar bears

A pharmacokinetic and tissue residue study was conducted to assess the risks associated with human consumption of polar bears in arctic Canada that have been exposed to the immobilizing drug Telazol, a mixture of tiletamine hydrochloride and zolazepam hydrochloride. Twenty-two bears were remotely injected with about 10 mg/kg of Telazol. Following immobilization, serum samples were collected serially at regular intervals until the bears awakened. Sixteen of the bears were relocated and killed under permit by local hunters at various times from 0.5 to 11 days after dosing. Serum, kidney, muscle and adipose tissue samples were collected immediately after death. All samples were stored at -70 C until analysis by HPLC. The concentration-time data of tiletamine and zolazepam in serum during the immobilization period were fitted to curves by computer and the pharmacokinetic parameters assessed. In addition, the serum and tissue samples collected at the time of death were analyzed for both parent drugs, for one metabolite of tiletamine (CI-398), and for three metabolites of zolazepam (metabolites 1, 2 and 4). A one-compartment model with first-order absorption and elimination best fit the time-series data for the drugs in serum during the immobilization period. This model gave half-lives (mean +/- SE) for tiletamine and zolazepam of 1.8+/-0.2 h and 1.2+/-0.08 h, respectively, clearance values of 2.1+/-0.3 l x h(-1) x kg(-1) and 1.1+/-0.1 l x h(-1) x kg(-1), and volumes of distribution of 5.2+/-0.6 l/kg and 1.8+/-0.2 l/kg. The concentrations of both drugs and their metabolites declined rapidly to trace levels by 24 h post-dosing, although extremely low concentrations of some metabolites were encountered sporadically over the entire sampling period. In particular, zolazepam metabolite 2, remained detectable in fat and muscle tissue at the end of the study, 11 days after dosing. It was concluded that during immobilization, both tiletamine and zolazepam levels decline rapidly in a monoexponential fashion, and their pharmacokinetic parameters in polar bears are similar to those observed in other species. Tissue levels of the drugs and their metabolites declined sufficiently rapidly that individuals eating meat from exposed bears would be unlikely to experience pharmacological effects from the drugs. Nevertheless, slight exposure to the drugs and/or their metabolites might be possible for an indeterminate time after dosing.     

Efficient gene transfer to airway epithelium using recombinant Sendai virus

Clinical studies of gene therapy for cystic fibrosis (CF) suggest that the key problem is the efficiency of gene transfer to the airway epithelium. The availability of relevant vector receptors, the transient contact time between vector and epithelium, and the barrier function of airway mucus contribute significantly to this problem. We have recently developed recombinant Sendai virus (SeV) as a new gene transfer agent. Here we show that SeV produces efficient transfection throughout the respiratory tract of both mice and ferrets in vivo, as well as in freshly obtained human nasal epithelial cells in vitro. Gene transfer efficiency was several log orders greater than with cationic liposomes or adenovirus. Even very brief contact time was sufficient to produce this effect, and levels of expression were not significantly reduced by airway mucus. Our investigations suggest that SeV may provide a useful new vector for airway gene transfer.     

In vivo two-photon imaging reveals a role of arc in enhancing orientation specificity in visual cortex

Cortical representations of visual information are modified by an animal's visual experience. To investigate the mechanisms in mice, we replaced the coding part of the neural activity-regulated immediate early gene Arc with a GFP gene and repeatedly monitored visual experience-induced GFP expression in adult primary visual cortex by in vivo two-photon microscopy. In Arc-positive GFP heterozygous mice, the pattern of GFP-positive cells exhibited orientation specificity. Daily presentations of the same stimulus led to the reactivation of a progressively smaller population with greater reactivation reliability. This adaptation process was not affected by the lack of Arc in GFP homozygous mice. However, the number of GFP-positive cells with low orientation specificity was greater, and the average spike tuning curve was broader in the adult homozygous compared to heterozygous or wild-type mice. These results suggest a physiological function of Arc in enhancing the overall orientation specificity of visual cortical neurons during the post-eye-opening life of an animal.     

Developmental changes in the embryo, pronymph, and first molt of the scorpion Centruroides vittatus (scorpiones: buthidae)

For the first time the scanning electron microscope was used to compare developmental changes in scorpion embryos and the first and second stadia. In the buthid species of this study, Centruroides vittatus, and all other scorpions, the newborn climb up on their mother's back and remain there without feeding for several days. At this location, they undergo their first molt and in a few days they disperse, fully capable of foraging in the terrestrial environment. The results here support earlier suggestions that the first stadium (pronymph) is a continuation and extension of embryological development. The first molt results in a nymph with exoskeletal features much like those in the adult. In the first molt the metasoma becomes relatively longer, and the sting (aculeus) becomes sharp and functional. The metasomal segments are modified for dorsal flexion and sting use. The embryos and the pronymphs have spiracles that open into an invagination near the posterior margin of flap-like abdominal plates in segments 4-7 of the ventral mesosoma. The second instars have spiracles that lead to book lungs farther anterior in sternites. Tubular legs with cylindrical segments in embryos and pronymphs become more sculptured and oval in the transverse plane. Each leg in the pronymph has a blunt, cup-shaped tip while distal claws (ungues, dactyl) are present in the second instar and subsequent stages. There are some sharp bristles and primordial sensilla in the pronymphs, but the second stadium has adult-like surface features: rows of knobs or granulations (carinae), serrations on the inner surfaces of cheliceral and pedipalpal claws, filtering hairs at the mouthparts, peg sensilla on the pectines, and mechano- and chemoreceptor sensilla on the body and appendages. Scorpion embryos and pronymphs have some structures like fossil scorpions thought to have been aquatic. There is a gradual development of features that appear to be terrestrial adaptations. Evidence is provided for the formation of the sternum from third and fourth leg coxal primordia and possibly from the first abdominal segment. This study is the first to provide evidence for a forward shift of the gonopore along with other structures in the anterior abdomen.     

Electron microscopic and histochemical characterization of intra-arterial cushions of the rat and porcine uterine vascular bed

Scanning and transmission electron microscopic studies, together with histochemical investigations, were conducted on rat and porcine intra-arterial cushions from the uterine vascular bed. In the rat, the fine structure of these cushions closely resembled that previously described in the rat kidney. The cushions were composed of modified smooth muscle, circularly disposed in an incomplete, raised band surrounding the entrance to arterial branches. These muscle cells projected as attenuated processes throughout the loosely organized, PAS-positive stroma, and established close contact with thin endothelial extensions projecting from the base of the surface endothelial cells. Scanning electron microscopic observations of furrows on the endothelial surface gave rise to the suggestion that such contacts might mediate muscular control of endothelial surface topology. In similar cushions from the pig uterine artery, the smooth muscle of the cushions was much more compactly organized, and was disposed radially, rather than circumferentially, within the cushion structure. The enzyme histochemical profile of porcine cushions did not differ appreciably from that of normal vascular smooth muscle and endothelium, suggesting the maintenance of a metabolic similarity with adjacent tissues. These studies clarify the fine-structural basis for recently reported contraction and relaxation of uterine artery cushions during ischemia and perfusion of the rat uterine vascular bed, and thus, for their functional role in the regulation of uterine vascular flow.     

Continuous measurement of changes in intracellular calcium concentration in mouse splenic T cells attached to a glass substrate

Mitogen- and isoproterenol-induced changes of [Ca²⁺]_i in T cells attached to a glass substrate were examined. Murine (C57BL/6) splenic T cells were attached to coverslips or 35-mm dishes (MatTek) precoated with Cell Tak® (3.5 µg/cm²). The cells were then loaded with fluorescent dye (2 µg/ml of fura2-AM or fluo3-AM) and changes in [Ca²⁺]_i in a population of cells (using a spectrofluorometer) or in single cells (using a confocal microscope) were measured during continuous superfusion. Population measurements of [Ca²⁺]_i demonstrated that concanavalin A (Con A, 2 or 5 µg/ml) caused an increase in [Ca²⁺]_i that rose to a peak and then declined to a steady state. The concentration-response relationship (0.05–5 µg/ml) had an EC₅₀ of 0.3 µg/ml. Isoproterenol decreased the Con A-induced elevation of steady state [Ca²⁺]_i. In single cell studies, the increase in [Ca²⁺]_i in response to Con A typically occurred in about 50% of the cells in a microscope field, and the delay before activation varied among cells. Taken together, these data demonstrate that Cell Tak® can be used to attach T cells to glass coverslips and will be useful for the study of signaling mechanisms in T cells.     

Relative dependence of different outputs of the Saccharomyces cerevisiae pheromone response pathway on the MAP kinase Fus3p

Fus3p and Kss1p act at the end of a conserved signaling cascade that mediates numerous cellular responses for mating. To determine the role of Fus3p in different outputs, we isolated and characterized a series of partial-function fus3 point mutants for their ability to phosphorylate a substrate (Ste7p), activate Ste12p, undergo G1 arrest, form shmoos, select partners, mate, and recover. All the mutations lie in residues that are conserved among MAP kinases and are predicted to affect either enzyme activity or binding to Ste7p or substrates. The data argue that Fus3p regulates the various outputs assayed through the phosphorylation of multiple substrates. Different levels of Fus3p function are required for individual outputs, with the most function required for shmoo formation, the terminal output. The ability of Fus3p to promote shmoo formation strongly correlates with its ability to promote G1 arrest, suggesting that the two events are coupled. Fus3p promotes recovery through a mechanism that is distinct from its ability to promote G1 arrest and may involve a mechanism that does not require kinase activity. Moreover, catalytically inactive Fus3p inhibits the ability of active Fus3p to activate Ste12p and hastens recovery without blocking G1 arrest or shmoo formation. These results raise the possibility that in the absence of sustained activation of Fus3p, catalytically inactive Fus3p blocks further differentiation by restoring mitotic growth. Finally, suppression analysis argues that Kss1p contributes to the overall pheromone response in a wild-type strain, but that Fus3p is the critical kinase for all of the outputs tested.     

Regulation of air and blood flow through the booklungs of the desert scorpion, Paruroctonus mesaensis

Injections of dye, latex and India ink were used to reveal the path of hemolymph circulation through the scorpion booklungs. Fine, branched arteries carry blood directly to muscle and other organs. The blood returns through venous channels to the ventral mesosoma where it passes laterally through the booklungs and into the pneumocardial veins just beneath the pleural cuticle. Blood flows dorsally through these veins to the pericardial sinus and heart. The scorpion has four pairs of booklungs located in the anterior segments of the ventral mesosoma. Each booklung has a spiracle which opens into an atrium enclosed by cuticular membrane. Air passes from the atrium into the booklung lamellae. Agitation of the animal or application of CO(2) causes retraction of the anterior and posterior atrial membrane. This expands the atrial chamber and allows gas exchange in the booklung lamellae. The posterior atrial membrane has a specialized region which forms a springy valve. This normally closes the spiracle unless pulled open by contraction of the attached poststigmaticus muscle. The pectens and receptors within the atrium may mediate the responses to CO(2). Slender hypocardial ligaments containing muscle fibers extend from the heart (dorsal mesosoma) to the booklungs in the ventral mesosoma. Heart movements thus cause dorso-ventral movement of the booklungs. The significance of these movements is as yet unclear. They may increase ventilation, help force blood to the heart and/or agitate the blood and booklung lamellae and thereby aid gas exchange. Passage of blood through the booklungs is regulated by dorsal and ventral muscles attached to the atrium at the lateral edge of the booklung. Contraction of the ventral atrial muscle closes the excurrent channel for passage of blood from the booklung into the pneumocardial vein. Electrical stimulation of the segmentai nerves from the subesophageal and first three abdominal ganglia causes spiracle opening and contraction of muscles attached to the atrial membrane. A previous study showed that these same segmental nerves also modulate heart activity. They thus provide a major pathway for regulation of the respiratory and circulatory systems.     

The role of pore structures in the selective permeability of antennal sensilla of the desert burrowing cockroach, Arenivaga sp

To obtain information about the chemical composition of pore structures in antennal sensilla, the antennae were exposed to lipid solvents, or they were prepared to show negative-contrast images in electron micrographs. A heavy-metal tracer, lanthanum nitrate, was also used to indicate the permeability of the receptors to water. The grooves of the large grooved peg open into tubular cavities containing electronopaque material, through which stimulatory molecules must pass to reach the sensory dendrites at the center of the sensillum. The material in these cavities was removed by chloroform or acetone, suggesting a lipid composition. Lanthanum penetrated this receptor only after it had been exposed to acetone or chloroform. Strands at pores of the thin-walled pegs were also removed by the lipid solvents, and the water-soluble tracer failed to penetrate these receptors unless they had been previously exposed to chloroform or acetone. The pore structures appear to be hydrophobic, allowing entry of lipid-soluble substances, while preventing passage of water. The differential action of the solvents on the various types of sensilla suggests that receptor discrimination among different classes of chemical stimuli may be partially determined by the chemical properties of structures at the sensillar pores.