The intermediate circulation in the nonsinusal spleen of the cat, studied by scanning electron microscopy of microcorrosion casts

Scanning electron microscopy of microcorrosion casts was used to visualize circulatory pathways of the intermediate circulation in nonsinusal spleen of cat. The marginal sinus (MS) around lymphatic nodules is a distinct vascular space which fills preferentially before the filling of the marginal zone (MZ) and surrounding red pulp occurs. The MS, which has a plentiful vascular supply, does not usually enclose the nodule completely. From the MS, flow occurs radially outwards into the MZ. Corrosion casts and histological sections both showed that a diversity of forms of the MZ exists: The thickness of MZ and the arrangement of its reticulum vary among nodules and between different areas of the same nodule, from a complete absence to a region of up to 50 microns in width. No direct arteriovenous connections were found (in contrast to dog spleen: Schmidt et al., '83b). Aside from capillary endings in the MS and MZ, all arterial capillaries terminate in the reticular spaces of the red pulp, i.e., the circulation appears to be entirely "open." From each capillary termination a great variety of flow pathways through the reticular meshwork to the pulp venules is available; some of these routes are quite long but others may involve distances as short as 15-25 microns. Evidence of flow into ellipsoid sheaths was abundant in casts from dilated spleens, but scarce in contracted spleens. In contrast to the extensive system of interconnected venous sinuses in dog spleen, the pulp venules found in cat spleen are nonanastomosing, shorter, and much smaller in caliber, and all receive flow freely from the reticular meshwork via open ends and fenestrations in their walls.     

Effects of pH and flow rate on the release of 'bound' red cells from the splenic pulp.

On perfusion of isolated, denervated spleens with Ringer solution, immature and abnormal red cells are released into the venous outflow much more slowly than normal mature cells, being delayed through adherence to fine structures of the red pulp (Am. J. Physiol. 231, 1665-1671 (1976)). Evidence suggested that the rate at which such cells are released from the 'bound' state might depend on local pH and fluid shear rate within the pulp. Therefore, the rate of washout for this slow component of red cells, from cat spleens, was measured as a function of pH and flow rate of the perfusate. The volume of solution (V 1/2) for 50% washout of 'bound' cells decreased as pH was lowered from 7.8 to 6.6, especially (from 97 to 18 ml/g) between 7.4 and 6.6. The percentage total red cell outflow thus represented rose from 0.06 to 0.5 as pH fell from 7.8 to 6.6. At a high perfusion rate (14-16 ml/min) the V 1/2 value was only one-half that prevailing at a lower rate (4-6 ml/min), and the percentage flow of 'bound' red cells was more than three times greater. Both acidic pH and augmented blood flow thus assist release of adherent red cells from the splenic pulp.     

The diet of Herring Gulls (Larus argentatus) during winter and early spring on the lower Great Lakes

In the Great Lakes, the Herring Gull (Larus argentatus) is a prominent member of the aquatic bird community, and has been used to monitor spatial and temporal trends in contaminant levels. To understand more fully contaminant loading outside the breeding season, we analysed the contents of 1298 freshly regurgitated pellets and 179 fresh faeces, collected in March and early April 1978–83, and between late December and late February 1990–91, from the vicinity of breeding colonies in Lakes Ontario and Erie, the Niagara River, Detroit River, and south-eastern parts of Lake Huron. Most adult Herring Gulls from the Great Lakes population winter in these areas, but there is no published account of their food habits other than during the breeding season. Most pellets from colonies close to large urban centres contained remains of garbage, as well as various fish species. Small mammals, notably Deer Mice (Peromyscus maniculatus) dominated the early spring diet at Lake Huron colonies near agricultural areas. At all other sites fish predominated in pellets and faeces, but garbage items were also recorded regularly. The species of fish consumed varied regionally, probably reflecting local availability. In Lake Ontario, Rainbow Smelt (Osmerus mordax) and Alewife (Alosa pseudoharengus) occurred most frequently in samples, whereas Freshwater Drum (Aplodinotus grunniens) was the main fish prey in Lake Erie and the Detroit River. Dietary differences were apparent between years, within seasons, and amongst areas. While these may have reflected some real differences in food availability, interpretation of these results was confounded by various biases inherent in the sampling of pellets and faeces to determine diet in such an opportunistic species. Therefore, it would be unwise to draw rigid conclusions as to regional or seasonal differences in the diets of piscivorous birds, based upon analyses of diet from only a small sample of sites or years. Herring Gulls appear to feed mainly on fish and garbage in winter and early spring on the lower Great Lakes (much as during the breeding season), but any locally abundant food source is probably exploited opportunistically.     

Akt and its downstream targets play key roles in mediating dormancy in land snails

Estivation, a state of aerobic dormancy, facilitates survival during adverse environmental conditions and is characterized at the molecular level by regulatory protein phosphorylation. The Akt (protein kinase B) signaling pathway regulates diverse responses in cells and the present study analyzes its role in the estivating desert snail Otala lactea. Kinetic analysis (maximal velocity, substrate affinities) determined that Akt was activated in tissues of estivating snails and Western blotting and in vitro incubations promoting changes to Akt phosphorylation state both confirmed that higher amounts of active (phosphorylated Ser473) Akt were present during estivation. Akt protein stability was also enhanced during estivation as assessed from urea denaturation studies. Multiple downstream targets of Akt were differentially regulated during estivation. Estivating animals showed elevated levels of phosphorylated FOXO3a (Ser253) and BAD (Ser136), no change in mTOR (Ser2481 and Ser2448), and reduced amounts of phosphorylated glycogen synthase kinase-3 (GSK-3) beta subunit (Ser9). Kinetic analysis of GSK-3 showed 1.5-1.7 fold higher activities in estivating snails coupled with increased GSK-3 substrate affinities in hepatopancreas. The data suggest an active role for Akt signaling during estivation emphasizing anti-apoptotic actions but uncoupling growth/proliferation actions to help achieve life extension on a limited energy budget.     

Excitation–Contraction Coupling: Acute exposure to extracellular BTP2 does not inhibit Ca2+ release during EC coupling in intact skeletal muscle fibers

The inhibitor of store-operated Ca²⁺ entry (SOCE) BTP2 was reported to inhibit ryanodine receptor Ca²⁺ leak and electrically evoked Ca²⁺ release from the sarcoplasmic reticulum when introduced into mechanically skinned muscle fibers. However, it is unclear how effects of intracellular application of a highly lipophilic drug like BTP2 on Ca²⁺ release during excitation–contraction (EC) coupling compare with extracellular exposure in intact muscle fibers. Here, we address this question by quantifying the effect of short- and long-term exposure to 10 and 20 µM BTP2 on the magnitude and kinetics of electrically evoked Ca²⁺ release in intact mouse flexor digitorum brevis muscle fibers. Our results demonstrate that neither the magnitude nor the kinetics of electrically evoked Ca²⁺ release evoked during repetitive electrical stimulation were altered by brief exposure (2 min) to either BTP2 concentration. However, BTP2 did reduce the magnitude of electrically evoked Ca²⁺ release in intact fibers when applied extracellularly for a prolonged period of time (30 min at 10 µM or 10 min at 20 µM), consistent with slow diffusion of the lipophilic drug across the plasma membrane. Together, these results indicate that the time course and impact of BTP2 on Ca²⁺ release during EC coupling in skeletal muscle depends strongly on whether the drug is applied intracellularly or extracellularly. Further, these results demonstrate that electrically evoked Ca²⁺ release in intact muscle fibers is unaltered by extracellular application of 10 µM BTP2 for <25 min, validating this use to assess the role of SOCE in the absence of an effect on EC coupling.     

Origins and implications of apid bees (Hymentopera: Apidae) in French Polynesia

Island plant–pollinator networks are typically simpler than their continental counterparts and this can make them less resilient to disturbance from exotic species. French Polynesia has a very low diversity of bees, but their status as either native or introduced species has been largely speculative. We combine previous studies with new DNA sequence data to show that 11 bee species have now been recorded for French Polynesia. Haplotype variation at the ‘barcode’ region of the mitochondrial gene cytochrome c oxidase subunit I (COI) for four of these species, Ceratina dentipes Freise, Xylocopa sonorina Smith, Braunsapis puangensis (Cockerell) and Amegilla pulchra (Smith), indicates that they all represent very recent introductions. Apis mellifera Linnaeus was a purposefully introduced species, and four megachilid species probably arrived due to human‐aided dispersal through maritime activities in the Pacific. The two remaining bee species, an unidentified partial specimen of a halictid bee and the colletid bee Hylaeus (P.) tuamotuensis Michener, are collectively known from only four specimens collected in the 1930s and their provenance is uncertain. French Polynesia therefore comprises a region where recently introduced bee species greatly overwhelm any possible native bee fauna. These introductions are likely to have major ecosystem impacts, including disruptions of existing plant–pollinator networks and facilitating the spread of weedy plant species, as well as positive impacts for agriculture. Future biosecurity initiatives need to consider these potential impacts and the likely routes of dispersal to effectively control any further unintended introductions.     

Microcirculation in mouse spleen (nonsinusal) studied by means of corrosion casts

Corrosion casts of mouse spleen, examined by scanning electron microscopy, enabled vascular pathways of the arterial, intermediate, and venous circulations to be traced over considerable distances. The arterial tree is surrounded by white pulp immediately upon entering at the hilus, and relatively few arterioles extend into red pulp. A profusion of capillaries is present in both periarterial lymphatic sheaths and lymphatic nodules, arranged as bifurcating systems (rather than anastomosing networks) terminating in the marginal sinus (MS) and marginal zone (MZ). The MS, which is situated between white pulp and MZ, consists of a discontinuous layer of flattened anastomosing spaces which are up to six times as large as those in rat spleen. Extensive filling of the entire MZ took place before appreciable filling of surrounding red pulp occurred. Capillary terminations in red pulp are always continuous with reticular meshwork, i.e., no evidence for a “closed” circulation was found. Casts of the venous origins support the classification “pulp venules” rather than “venous sinuses” and show major morphological differences from the richly anastomosing system of sinuses in rat. In the subcapsular region of mouse spleen large anastomosing veins ramify over the surface, with reticular meshwork occupying extensive areas between adjacent veins. For in vivo microscopy this arrangement offers advantages over that found in rat spleen (accompanying paper), where almost the entire surface is densely covered with venous sinuses.