Insect peripheral nerves: accessibility of neurohaemal regions to lanthanum.

During incubation in vivo, exogenously applied ionic lanthanum comes to surround the numerous neurosecretory terminals which are found lying within or immediately beneath the acellular neural lamella ensheathing the nerves from fifth instar and adult specimens of Rhodnius prolixus. The lanthanum does not penetrate beyond the cellular perineurium, which completely surrounds the non-neurosecretory axons in these nerves and constitutes a form of 'blood-brain barrier'. In some cases, however, lanthanum is found in the vicinity of a neurosecretory axon lying beneath the perineurium, where it can be assumed to have leaked in from the neurosecretory terminal lying free in the neural lamella. When nerves are incubated in calcium-free media, regions with an attenuated perineurium become 'leaky', in that lanthanum is found lying in those extracellular spaces between axons and glia which lie immediately below the thin part of the perineurial layer. Bathing solutions made slightly hyperosmotic to the haemolymph with sucrose have no apparent disruptive effects on the barrier. When the tissues are incubated in more hypertonic solutions, the perineurial barrier becomes 'leaky' throughout, and tracer pervades beyond its cells into all the intercellular spaced between glia and axons. The possible role of the zonulae occludentes in both the maintenance of the perineurial barrier and in the formation of interglial occlusions to local penetration of exogenous substances is considered.     

Ultrastructure of hatchling chaetognaths (Ferosagitta hispida): Epithelial arrangement of the mesoderm and its phylogenetic implications

The trunk and tail mesoderm of hatchling chaetognaths consists of a simple myoepithelium containing four stereotypically arranged cell types, each matching in position a specific adult tissue. The trunk mesoderm includes lateral cells, longitudinal muscle cells, dorsal and ventral medial cells, and peri-intestinal cells. These correspond, respectively, to the lateral fields, longitudinal body wall muscles, dorsal and ventral perimysial cells, and periintestinal muscles of adults. Because the developing intestine does not extend into the tail, tail cells equivalent in position to peri-intestinal cells in the trunk are designated mesenterial cells. Numerous small spaces situated among the apices of hatchling mesodermal cells have the same position relative to surrounding cells as both the coelomic cavities of early embryos and the adult body cavities. We infer that these spaces in hatchlings expand and coalesce to form the definitive adult body cavities, and that these spaces and the adult body cavities derive from the embryonic coeloms. Because hatchlings lack mesenchymal mesoderm, we infer that all adult mesodermal tissues develop by elaboration of the coelomic lining of hatchlings. Because hatchlings lack cells corresponding to the squamous peritoneocytes overlying the body wall muscles of adults, we conclude that peritoneocytes are specialized adult cells that are not equivalent to cells of the embryonic coelomic lining. Finally, hatchlings contain a complete trunk/tail septum. This observation contradicts reports that this septum forms several days after hatching. It also weakens arguments that chaetognaths are bimeric rather than trimeric. © 1994 Wiley-Liss, Inc.     

X-ray microanalysis with transmission electron microscopy determined presence and movement of tracer (lanthanum chloride) at blood-neuron barrier of Drosophila melanogaster (Diptera : Drosophilidae) larva

In studying the larval Drosophila (Diptera : Drosophilidae) blood-brain barrier, it was important to determine if even minute amounts of tracer ultimately seeped through the septate junctions between perineurial cells to reach the neuronal region. Concurrent TEM with X-ray microanalysis was undertaken to resolve that issue. Ultrathin sections of Drosophila nervous tissue in LR White embedment were exposed to ionic tracer (lanthanum chloride) and assayed for presence or absence of lanthanum extracellular to the perineurium and glia making up the nerve sheath. Tracer filled the distal interseptal lattice of pleated sheet-septate junctions, but was contained prior to reaching the proximal paracellular space. No detectable tracer passed through septate junctions to enter the glial-neuronal domain. Based on our present data and the research of others, septate junctions in immature Drosophila are multifunctional structures that enforce spatial relationships between cells, seal intercellular spaces, and control cell proliferation in the epithelia. Septate junctions in Drosophila with the (dlg) gene also exhibit protein homologies to the Z0–1 human tight junction component.     

On the dispersal of leatherback turtle hatchlings from Mesoamerican nesting beaches

So little is known about the early life history of leatherback turtles (Dermochelys coriacea) from hatchling to adulthood that this period has been termed the 'lost years'. For critically endangered eastern Pacific leatherback populations, continued and rapid declines underscore the urgent need to develop conservation strategies across all life stages. We investigate leatherback hatchling dispersal from four Mesoamerican nesting beaches using passive tracer experiments within a regional ocean modelling system. The evolution of tracer distribution from each of the nesting beaches showed the strong influence of eddy transport and coastal currents. Modelled hatchlings from Playa Grande, Costa Rica, were most likely to be entrained and transported offshore by large-scale eddies coincident with the peak leatherback nesting and hatchling emergence period. These eddies potentially serve as 'hatchling highways', providing a means of rapid offshore transport away from predation and a productive refuge within which newly hatched turtles can develop. We hypothesize that the most important leatherback nesting beach remaining in the eastern Pacific (Playa Grande) has been evolutionarily selected as an optimal nesting site owing to favourable ocean currents that enhance hatchling survival.     

Can the insect nervous system synthesize ecdysteroids?

The term "neurosteroid" refers to both classic and unique steroid molecules that are synthesized from cholesterol (C) by the central and peripheral nervous systems of higher vertebrates. Therein, they accumulate and modulate nervous activity by a variety of mechanisms other than the classic steroid receptor-mediated modulation of genomic activity, although such may also be involved. Since the insect nervous system expresses ecdysteroid receptors and responds both directly and developmentally to ecdysteroids, the possibility of ecdysteroidogenesis in the pupal and adult central and peripheral nervous system of Manduca sexta and the nervous system of Drosophila melanogaster larvae was investigated. The endogenous concentrations of the critical, dietary-derived delta 5,7-sterols ergosterol and 7-dehydrocholesterol (7dC) remained 10 to 20-fold higher in the Manduca pupal and adult nervous tissues than was found in the larval hemolymph at the cessation of feeding. In addition, it was determined that the Manduca pupal nervous system, but not that of the adult, could synthesize 3H/14C-7dC or 3H-7-dehydro-25-hydroxycholesterol (3H-7d25C) from 3H/14C-cholesterol (3H/14C-C) or the polar sterol substrate 3H-25-hydroxycholesterol (3H-25C), respectively. However, none of the nervous system samples from the two species and the several stages analyzed, a small window of neural development in these insects, were capable of incorporating any of the above tracer precursor sterols into a radiolabelled ecdysteroid, i.e. less than 0.0005%. Thus, the absence of neurosteroidogenesis by the insect nervous system stands in sharp contrast to previously described nervous system steroid hormone biosynthesis by the mammalian nervous system.     

Opening of blood-brain barrier in Triturus cristatus carnifex by hyperosmolar mannitol solutions

The permeability of the newt cerebral capillaries to lanthanum ion has been studied after perfusion with mannitol solutions of increasing molarity. In the control specimens lanthanum deposits were limited to the luminal side of the capillaries and tracer did not spread to the pericapillary spaces due to the tight junctions. Treatment with hypertonic solutions of mannitol (0.25M, 0.5M, 1M) caused opening of the blood brain barrier with a progressive increase in lanthanum between the endothelial cell edges, in the basal lamina and in the extracellular spaces of the nervous parenchyma in relation to the molarity of the mannitol solution. The spread of lanthanum is probably due to opening of the tight junctions between the endothelial cells, since pinocytotic vesicles labelled with tracer were not evident.     

The penetration of ionic lanthanum into the central nervous system of the tick, Amblyomma variegatum

ABSTRACT. The ultrastructure of the tick central nervous system resembles that of insects except that the perineurial layer of specialized glial cells is less well developed in the tick. In particular, the cells are not connected by tight or septate junctions. Probably as a consequence, ionic lanthanum penetrates the entire central nervous system of the tick, whereas it fails to penetrate the perineurium of insects. These observations suggest that ticks lack the 'blood—brain barrier' which protects the insect nervous system.     

The use of lead as an ionic tracer for investigating routes of passive fluid transfer

Several inorganic ions, including lead, barium, silver, and thallium, have been tested as possible tracers for demonstrating fluid-accessible channels in functional epithelia at the ultrastructural level. The most useful of the ionic tracers examined was the lead (plumbous) ion, administered for short time intervals (less than 2 min) and "captured" with phosphate used as the buffer in the fixative. Passive fluid and ion-accessible channels of rat parotid salivary gland have been examined with this method. At short tracer infusion times (0.5-1.0 min), localization of the tracer was primarily extracellular, although intracellular deposits were observed in the following sites: smooth membrane-delimited endocytic vesicles of both epithelial and connective tissue cells, inner Golgi cisternae, and occasional cisternae of rough endoplastic reticulum. The lead tracer readily penetrated tight junctions between parotid acinar cells but rarely passed through the tight junctions between intercalated duct cells and did not penetrate junctions of striated duct cells. Fat cells observed in the stroma of this gland were the only cells that exhibited lead tracer in the cytosol, suggesting that the plasmalemma of this cell type is more permeable to exogenous ions than the plasmalemma of other cell types present in this gland.     

Oxidative stress and antioxidant capacity of a terrestrially hibernating hatchling turtle

Hatchlings of the painted turtle, Chrysemys picta, hibernate terrestrially and can survive subfreezing temperatures by supercooling or by tolerating the freezing of their tissues. Whether supercooled or frozen, an ischemic hypoxia develops because tissue perfusion is limited by low temperature and/or freezing. Oxidative stress can occur if hatchlings lack sufficient antioxidant defenses to minimize or prevent damage by reactive oxygen species. We examined the antioxidant capacity and indices of oxidative damage in hatchling C. picta following survivable, 48 h bouts of supercooling (−6°C), freezing (−2.5°C), or hypoxia (4°C). Samples of plasma, brain, and liver were collected after a 24 h period of recovery (4°C) and assayed for Trolox-equivalent antioxidant capacity (TEAC), thiobarbituric acid reactive substances (TBARS), and carbonyl proteins. Antioxidant capacity did not vary among treatments in any of the tissues studied. We found a significant increase in TBARS in plasma, but not in the brain or liver, of frozen/thawed hatchlings as compared to untreated controls. No changes were found in the concentration of TBARS or carbonyl proteins in supercooled or hypoxia-exposed hatchlings. Our results suggest that hatchling C. picta have a well-developed antioxidant defense system that minimizes oxidative damage during hibernation.     

Age‐dependent,negative heterozygosity–fitness correlations and local effects in an endangered Caribbean reptile,Iguana delicatissima

Inbreeding depression can have alarming impacts on threatened species with small population sizes. Assessing inbreeding has therefore become an important focus of conservation research. In this study, heterozygosity–fitness correlations (HFCs) were measured by genotyping 7 loci in 83 adult and 184 hatchling Lesser Antillean Iguanas, Iguana delicatissima, at a communal nesting site in Dominica to assess the role of inbreeding depression on hatchling fitness and recruitment to the adult population in this endangered species. We found insignificant correlations between multilocus heterozygosity and multiple fitness proxies in hatchlings and adults. Further, multilocus heterozygosity did not differ significantly between hatchlings and adults, which suggests that the survivorship of homozygous hatchlings does not differ markedly from that of their heterozygous counterparts. However, genotypes at two individual loci were correlated with hatching date, a finding consistent with the linkage between specific marker loci and segregating deleterious recessive alleles. These results provide only modest evidence that inbreeding depression influences the population dynamics of I. delicatissima on Dominica.     

The Use of Lanthanum Chloride as a Marker for Intercellular Junctions in Rat Exocrine Pancreas

A simple technique of perfusion and immersion of tissue in fixative containing lanthanum chloride as an extracellular tracer is described. In addition to functioning as a tracer, the lanthanum chloride appears to enhance electron staining. In rat exocrine pancreas, intercellular spaces between exocrine and centroductular cells were outlined clearly by electron dense material and, at cellular interfaces, spot desmosomes, gap junctions, and tight junctions were demonstrated. The technique proved simple and effective and should prove useful in studies of epithelial and other tissues.     

The variance of incubation temperatures does not affect the phenotype of hatchlings in a colubrid snake, Xenochrophis piscator

It has been documented in some reptiles that fluctuating incubation temperatures influence hatchling traits differently than constant temperatures even when the means are the same between treatments; yet whether the observed effects result from the thermal variance, temperature extremes or both is largely unknown. We incubated eggs of the checkered keelback snake Xenochrophis piscator under one fluctuating (Ft) and three constant (24, 27 and 30 °C) temperatures to examine whether the variance of incubation temperatures plays an important role in influencing the phenotype of hatchlings. The thermal conditions under which eggs were incubated affected a number of hatchling traits (wet mass, SVL, tail length, carcass dry mass, fatbody dry mass and residual yolk dry mass) but not hatching success and the sex ratio of hatchlings. Body sizes were larger in hatchlings from incubation temperatures of 24 and 27 °C compared with the other two treatments. Hatchlings from the four treatments could be divided into two groups: one included hatchlings from the 24 and 27 °C treatments, and the other included hatchlings from the 30 °C and Ft treatments. In the Ft treatment, the thermal variance was not a significant predictor of all examined hatchling traits, and incubation length was not correlated with the thermal variance when holding the thermal mean constant. The results of this study show that the mean rather than the variance of incubation temperatures affects the phenotype of hatchlings.     

The use of lanthanum chloride as a marker for intercellular junctions in rat exocrine pancreas

A simple technique of perfusion and immersion of tissue in fixative containing lanthanum chloride as an extracellular tracer is described. In addition to functioning as a tracer, the lanthanum chloride appears to enhance electron staining. In rat exocrine pancreas, intercellular spaces between exocrine and centroductular cells were outlined clearly be electron dense material and, at cellular interfaces, spot desmosomes, gap junctions, and tight junctions were demonstrated. The technique proved simple and effective and should prove useful in studies of epithelial and other tissues.     

Permeability of the haemolymph-neural interface in the terrestrial snail Megalobulimus abbreviatus (Gastropoda, Pulmonata): an ultrastructural approach

The aim of this study was to investigate the ultrastructure of the interface zone between the nervous tissue and the connective vascular sheath that surround the central ganglia of the terrestrial snail of Megalobulimus abbreviatus and test its permeability using lanthanum as an electron dense tracer. To this purpose, ganglia from a group of snails were fixed by immersion in a 2% colloidal lanthanum solution, and a second group of animals was injected in the foot with either a 2%, 10% or 20% lanthanum nitrate solution and then sacrificed 2 or 24 h after injection. Ganglia from both groups were processed for transmission electron microscopy. The vascular endothelium, connective tissue and basal lamina of variable thickness that ensheathe the nervous tissue and glial cells of the nervous tissue constitute the interface zone between the haemolymph and the neurones. The injected lanthanum reached the connective tissue of the perineural capsule; however, it did not permeate into the nervous tissue because the basal lamina interposed between both tissues interrupted this passage. Moreover, the ganglia fixed with colloidal lanthanum showed electron dense precipitates between the glial processes in the area adjacent to the basal lamina. It can be concluded from these findings that, of the different components of the haemolymph-neuronal interface, only the basal lamina, between the perineural capsule and the nervous tissue, limits the traffic of substances to and from the central nervous system of this snail.     

Compass Orientation During Dispersal of Freshwater Hatchling Snapping Turtles (Chelydra serpentina) and Blanding's Turtles (Emydoidea blandingii)

Freshwater turtle hatchlings primarily use visual cues for orientation while dispersing from nests; however, hatchlings rapidly develop a relationship between a sun or geomagnetic compass and a dispersal target that allows them to maintain an established direction of movement when target habitats are not visible. We examined dispersal patterns of hatchling snapping turtles (Chelydra serpentina) and Blanding's turtles (Emydoidea blandingii) dispersing in large arenas in a mowed field and in dense corn. The dispersal of three categories of hatchlings were examined: (1) naïve individuals (no previous dispersal experience), (2) arena‐experienced (limited dispersal experience in arenas in natural habitat), and (3) natural‐experienced hatchling Blanding's turtles (captured after extensive experience dispersing W in natural habitats toward wetlands). Experienced hatchlings were assigned to treatments consisting of having a magnet or a non‐magnetic aluminum sham or nothing glued to their anterior carapace before release in the corn arena. Dispersal patterns of naïve hatchlings of both species were strongly directional in the field arena with visible target horizons and primarily random in the corn arena where typical target horizons were blocked. When released in corn, dispersal patterns were similar for arena‐experienced hatchlings with magnets or shams attached and differed from their prior dispersal headings in the field arena as naïve hatchlings. Natural‐experienced hatchling Blanding's turtles with and without magnets were able to accurately maintain their prior headings to the WNW while dispersing in the field or corn arenas (i.e., the presence of a magnet did not disrupt their ability to maintain their prior heading). Based on the assumption that no other type of compass exists in hatchlings, we conclude that they were not using a geomagnetic compass, but by default were using sun compass orientation to maintain dispersal headings in dense corn where no typical target habitats were visible.     

Sex Ratio and Sexual Size Dimorphism in a Toad-headed Lizard,Phrynocephalus guinanensis

Phrynocephalus guinanensis has sexual dimorphism in abdominal coloration, but its ontogenetic development of sexual size dimorphism(SSD) is unknown. Using mark-recapture data during four days each year from August from 2014 to 2016, we investigated the development of sex ratios, SSD, sex-specific survivorship and growth rates in a population of P. guinanensis. Our results indicated that the sex ratio of males to females was 1:2.8. Males had a lower survival rate(6%) than females(14%) across the age range from hatchling to adult, which supported the discovered female-biased sex ratio potentially associated with the low survival rate of males between hatchlings and juveniles. Male-biased SSD in tail length and head width existed in adults rather than in hatchling or juvenile lizards. The growth rates in body dimensions were undistinguishable between the sexes during the age from hatchling to juvenile, but the growth rate in head length from juvenile to adult was significantly larger in males than females. Average growth rate of all morphological measurements from hatchling to juvenile were larger compared with corresponding measurements from juvenile to adult, but only being significant in tail length, head width, abdomen length in females and snout-vent length in males. We provided a case study to strengthen our understanding of the important life history traits on how a viviparous lizard population can survive and develop their morphology in cold climates.     

Influence of Social Factors on Seasonal Variations in Plasma Testosterone Levels of Microcebus murinus

Blue tail coloration in hatchling skinks (Eumeces fasciatus and E. laticeps) appears to be an antipredatory adaptation that distracts attention away from the body to the tail. The tail itself serves as a decoy that may be autotomized as a final defense against capture. The effectiveness of intact tails in deflecting attacks from the body was 50% against scarlet kingsnakes in the experimental conditions used. Brightness rather than hue presumably accounts for the higher attack frequency on blue than black tails in this study, but the blue color may have evolved in response to avian predation. Repeated predation without ill effects by several predators allows rejection of the hypothesis that the blue tail is aposematic for the predators tested. The hypothesis that blue tails provide stimuli inhibiting aggression or predation by adult male conspecifics is untenable for E. laticeps because adult males readily eat intact hatchlings. Although this study provides no statistical evidence that blue tail coloration inhibits attack by female E. laticeps on hatchlings, the trend of predation rates on blue- and black-tailed hatchlings is in the direction predicted for inhibition.     

Cyclic nucleotide-stimulable protein kinases in the central nervous sytem of Manduca sexta.

Cyclic nucleotide-stimulable protein kinase (EC 1.7.1.37) has been studied in crude extracts from the central nervous system of the tobacco hornworm Manduca sexta (Lepidoptera: Sphingidae). The insect kinase was fulfhydryl-sensitive and required Mg-2+ for optimal activity. Polyacrylamide gel electrophoresis of supernatants demonstrated the presence of multiple kinases in the larval nerve cord. At low concentrations, cyclic AMP was a much more potent activator of soluble and particulate activities than was cyclic GMP. The specific activity of coluble kinase and the magnitude of its activations by cyclic AMP were greater in the adult than in the larval central nervous system. The exogenous protein substrate specificity of the insect enzyme was similar to that of rat brain kinase with the sole exception that protamine was more readily phosphorylated than histone by nerve cord kinase. It was observed that cyclic AMP lowered the Km of Manduca sexta kinase for ATP, a phenomenon which is apparently nervous tissue=specific in mammals. An effective inhibitor of cyclic AMP-dependent protein kinase was prepared from the larval central nervous system.     

Thermal control of hatchling emergence patterns in marine turtles

The emergence patterns of green turtle (Chelonia mydas) hatchlings on two beaches on Ascension Island, South Atlantic were monitored and related to thermal patterns in the sand at 10, 20, 30 and 40 cm depth. A total of 6001 hatchlings were recorded emerging on Long Beach, and 3171 emerged on North East Bay during the study period. No significant difference was observed in the temporal pattern of hatchling emergence among nights, or between the two beaches. Hatchling emergence predominantly occurred at night with over 93% of hatchlings emerging during the hours of darkness. Almost all hatchlings emerging in daylight suffer predation by the Ascension frigatebird (Fregata aquila). Counts of frigatebirds both above the study beaches and offshore were highest just after sunrise, with a smaller peak prior to sunset, when frigatebirds were found to predate hatchlings emerging, crawling down the beach or detected in inshore waters. The likely thermal cues controlling hatchling emergence were investigated (temperature at different depths, thermal gradients in the sand and temperature change). The most plausible thermal factor appears to be the change of temperature at superficial sand depths, with hatchling emergence inhibited when subsurface sand temperatures were increasing. This simple mechanism is likely to ensure predominantly nocturnal hatchling emergence regardless of sand albedo, seasonality or latitude as long as night is relatively cooler than day.     

Electron microscopic research on the capillary permeability of the primary portal plexus in rats in the prenatal period

Permeability of portal capillaries to intravascularly injected ionic lanthanum, ferritin and horse-radish peroxidase has been examined in rats on the 18th fetal day, and on days 1 and 9 of postnatal life. For several minutes, tracer molecules pass through the capillary wall and reach the median eminence. In the case of immature capillaries, the materials pass freely through the endothelial cells, and to a lesser extent are transferred via occasional plasmalemmal vesicles and fenestrae. As the maturation of capillaries proceeds their permeability via plasmalemmal vesicles and fenestrae increases considerably due to a gradual rise in the number of these structures. The plasmalemma of differentiated endothelial cells becomes impermeable to all the tracers. Only ionic lanthanum appears to penetrate through transendothelial channels and intercellular junctions between adjacent endothelial cells.