bluuebunny/crossref_metadata_2025 huggingface dataset:
A potential role for spectrin during neurulation
Authors: Sadler T. W. , Burridge Keith , Yonker J.
Published: April 2021

An actin-myosin complex located in apical regions of the neurectoderm has been postulated to play a role in neurulation. Numerous studies have documented the presence of microfilaments in this area and confirmed their composition as actin. By necessity, if such a contractile system is to exert a force, these filaments must be anchored in some way to the cell membrane. In this study, the presence of the actin-binding protein, spectrin (fodrin), is demonstrated in the neurectoderm of neurulating mouse embryos using antispectrin antibodies and indirect immunofluorescent techniques. The patterns of spectrin localization correlate with the previously reported regions of increased numbers of microfilaments and also with the morphology of the neural folds. Thus, during the initial stages of cranial fold elevation, a process reportedly dependent on increased glycosaminoglycan synthesis, little spectrin is present in the neuroepithelial cells. Later as the folds begin to converge toward the midline, deposition of the protein, as demonstrated by the intensity of fluorescence, is increased in the apices of these cells, and is most prominent in regions of greatest bending in the neural folds. Caudal neural fold regions show a similar pattern of staining. Thus, the hypothesis that a cytoskeletal system assists in neurulation is supported by these results, which for the first time demonstrate the presence of a putative actin-membrane attachment protein in a morphogenetically active system.
The distribution of fibronectin, laminin and entactin in the neurulating rat embryo studied by indirect immunofluorescence
Authors: Tuckett Fiona , Morriss-Kay Gillian M.
Published: April 2021

This paper forms part of our study of the extracellular matrix and its role in the morphogenesis of the brain during the period of neurulation in the rat embryo. Using indirect immunofluorescence with polyclonal antibodies, we present here a descriptive study of the distribution of the matrix glycoproteins fibronectin, laminin and entactin.

The observed distribution of the fibronectin matrix implicates it in providing a structural element in several morphologically active sites; in addition our observations support the previously suggested involvement of fibronectin in the migration of neural crest cells. Entactin was present only in the basement membranes in conjunction with laminin which was not itself confined to these regions. Laminin was also identified within the mesenchymal extracellular matrix, and its general distribution confirms the previously documented role of laminin in maintaining epithelial structure and organization. No patterning in the distribution of these three glycoproteins could be correlated with the change in shape of the neural epithelium associated with either tube formation or neuromere morphogenesis.
Effect of alterations in follicular steroidogenesis on the nuclear and cytoplasmic maturation of ovine oocytes
Authors: Osborn J. C. , Moor R. M. , Crosby I. M.
Published: April 2021

The effects of inhibitors of follicular steroidogenesis on biochemical changes occurring in oocytes maturing in vitro were studied using radiolabelling and polyacrylamide gel electrophoresis. These effects were correlated with previously investigated developmental abnormalities induced by the same inhibitors.

The most severe effects were generated by inhibition of 17α-hydroxylase with the drug SU10603 which resulted in a greatly increased ratio of progesterone to testosterone and oestrogen. Such treatment halved the rate of meiotic maturation. Treated oocytes were analysed individually on SDS-PAGE gels and quantitative analysis showed that the drug had induced synthetic abnormalities even in those oocytes that resumed meiosis. This conclusion was confirmed by separation of oocyte proteins on two-dimensional gels. The effects of SU were reduced by delaying addition of the drug until 6 h after the beginning of maturation but were not alleviated by the addition of exogenous oestrogen to the culture medium. When oocytes from SU-treated follicles were transferred to inseminated, recipient ewes and recovered 24h later, two-dimensional electrophoresis again revealed abnormalities in their protein synthetic patterns.

Almost total abolition of steroid secretion by aminoglutethimide (AG) had much less effect on oocyte protein synthesis, although the proportion of oocytes maturing was reduced from 65 % to 46 %. The aromatase inhibitor, androstatriendione (AST) although eliminating follicular oestrogen secretion, had no effect on the rate of maturation and very little effect on protein synthesis. These results correlate well with the effects of steroid inhibitors on fertilization and early cleavage.
Size regulation in the mouse embryo: II. The development of half embryos
Authors: Rands G. F.
Published: April 2021

The study describes an analysis of the development of mouse embryos halved at the 2-cell stage by the destruction of one blastomere, in comparison with control embryos of parallel derivation, at 2·5–13·5 dayspostcoitum. The results showed that: (1) half embryos achieve size regulation some time between 7·5 and 10·5 days; (2) there is an indication that by 13·5 days half embryos may have again dropped back significantly in size relative to controls; (3) preregulation half embryos are slightly retarded developmentally, but this does not wholly account for their smaller size: morphogenesis is not size-dependent; (4) early postimplantation half embryos contain a significantly decreased proportion of inner cell mass derivatives and increased proportion of trophectoderm derivatives when compared with controls.

A comparison is also made between the up-regulation of half embryos and the downregulation of aggregate embryos, and it is suggested that size regulation may occur by delaying a change in the normal growth rate.
Temporal and regional changes in DNA methylation in the embryonic, extraembryonic and germ cell lineages during mouse embryo development
Authors: Monk Marilyn , Boubelik Michael , Lehnert Sigrid
Published: April 2021

This paper shows stage- and tissue-specific global demethylation and remethylation occurring during embryonic development. The egg genome is strikingly undermethylated and the sperm genome relatively methylated. Following a loss of genomic methylation during preimplantation development, embryonic and extraembryonic lineages are progressively and independently methylated to different final extents. Methylation continues postgastrulation and hence could be a mechanism initiating, or confirming, differential programming in the definitive germ layers. It is proposed that much of the methylation observed in somatic tissues acts to stabilize and reinforce prior events that regulate the activity of specific genes, chromosome domains or the X chromosome (in females). Fetal germ cell DNA is markedly undermethylated and we favour the idea that the germ lineage is set aside before the occurrence of extensive methylation of DNA in fetal precursor cells.
Fate map for the 32-cell stage ofXenopus laevis
Authors: Dale L. , Slack J. M. W.
Published: April 2021

A complete fate map has been produced for the 32-cell stage of Xenopus laevis. Embryos with a regular cleavage pattern were selected and individual blasto-meres were injected with the lineage label fluorescein–dextran–amine (FDA). The spatial location of the clones was deduced from three-dimensional (3D) re-constructions of later stages and the volume of each tissue colonized by labelled cells in each tissue was measured.

The results from 107 cases were pooled to give a fate map which shows the fate of each blastomere in terms of tissue types, the composition of each tissue by blastomere, the location of each prospective region on the embryo and the fate of each blastomere in terms of spatial localization.

Morphogenetic movements up to stage 10 (early gastrula) were assessed by carrying out a number of orthotopic grafts at blastula and gastrula stages using donor embryos uniformly labelled with FDA.

Although there is a regular topographic projection from the 32-cell stage this varies a little between individuals because of variability of positions of cleavage planes and because of short-range cell mixing during gastrulation. The cell mixing means that the topographic projection fails for anteroposterior segments of the dorsal axial structures and it is not possible to include short segments of notochord or neural tube or individual somites on the pregastrulation fate map.
The ultrastructure of normal fetal and neonatal pig testis germ cells and the influence of fetal decapitation on the germ cell development
Authors: Van Vorstenbosch C. J. A. H. V. , Spek E. , Colenbrander B. , Wensing C. J. G.
Published: April 2021

The development of germ cells in the male pig was investigated ultrastructurally in normal and decapitated fetuses. The age ranged respectively from 30 days p.c. till one month after birth and from 52 days p.c. until birth. The ultrastructural organization of the germ cells changes dramatically between 30 days p.c. and 52 days p.c. which coincides with the formation of ‘true’ sex cords. From 52 days p.c. onwards the morphology is rather stable: cells show a ‘hydrated’ appearance and typical cell bridges. There is no obvious difference in the ultrastructure of germ cells in decapitated animals, their normal littermates and control animals. Therefore germ cell development in the pig is likely to be insensitive to gonadotropins during the fetal period. The development of pig germ cells follows closely the pattern described for several species. Quantitatively there is an increase in the ratio of germ cell/Sertoli cell per cross sectional diameter in the decapitated animals.
BDNF-GFP containing secretory granules are localized in the vicinity of synaptic junctions of cultured cortical neurons
Authors: Haubensak Wulf , Narz Frank , Heumann Rolf , Leβmann Volkmar
Published: April 2021

The protein family of mammalian neurotrophins, comprising nerve-growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 and -4/5 (NT-3, NT-4/5), supports the survival and the phenotype of neurons from the central as well as the peripheral nervous system (CNS, PNS). In addition, exogenous application of neurotrophins has recently been found to modulate synaptic transmission in the rodent CNS. However, to provide evidence for a role of neurotophins as endogenous fast acting modulators of synaptic transmission, the synaptic localization and secretion of neurotrophins needs to be shown.

We have now constructed a fusion protein consisting of N-terminal BDNF (the most abundant neurotrophin in the rodent hippocampus and neocortex) and C-terminal green fluorescent protein (GFP) to elucidate the cellular localization of BDNF in cortical neurons. Transient expression of BDNF-GFP in COS-7 cells revealed that the cellular localization in the trans-Golgi network (TGN), the processing of precursor proteins and the secretion of mature BDNF-GFP is indistinguishable from the properties of untagged BDNF.

Upon transient transfection of primary rat cortical neurons, BDNF-GFP was found in secretory granules of the regulated pathway of secretion, as indicated by colocalization with the secretory granule marker secretogranin II. BDNF-GFP vesicles were found in the neurites of transfected neurons with a pattern reminiscent of the localization of endogenous BDNF in untransfected cortical neurons. BDNF-GFP vesicles were found predominantly in the somatodendritic compartment of the neurons, whereas additional axonal localization was found less frequently. Immunocytochemical staining of synaptic terminals with synapsin I antibodies revealed that the density of BDNF-GFP vesicles is elevated in the vicinity of synaptic junctions, indicating that BDNF is localized appropriately to function as an acute modulator of synaptic transmission.

These data suggest that BDNF-GFP will be a useful tool to investigate synaptic release of BDNF during physiological synaptic stimulation, and will thereby allow us to elucidate the participation of neurotrophin release in activity dependent synaptic plasticity.
The RNP protein, RNPS1, associates with specific isoforms of the P34CDC2 related PITSLRE protein kinase in vivo
Authors: Loyer Pascal , Trembley Janeen H. , Lahti Jill M. , Kidd Vincent J.
Published: April 2021

The PITSLRE protein kinases are members of the p34cdc2 superfamily, with >20 different isoforms expressed from two linked genes in humans. PITSLRE homologues have been identified in mouse, chicken, Drosophila, Xenopus, and possibly Plasmodium falciparum, suggesting that their function may be well conserved. A possible role for a caspase processed PITSLRE isoform has been suggested by studies of Fas- and TNF-induced cell death. However, the function of these kinases in proliferating cells is still unknown. Here we demonstrate that the 110 kDa PITSLRE isoforms (p110) are localized to both the nucleoplasm and nuclear speckles, and that these isoforms specifically interact in vitro and in vivo with the RNA-binding protein RNPS1. RNPS1 is also localized to nuclear speckles, and its over expression disrupts normal nuclear speckle organization by causing the aggregation of many nuclear speckles into ∼6 ‘mega’ speckles. This type of nuclear speckle aggregation closely resembles what occurs when cells are treated with several transcriptional inhibitors. These data indicate that the PITSLRE p110 isoforms interact with RNPS1 in vivo, and that these proteins may in turn influence some aspect of transcriptional and/or splicing regulation.
Role of fungal dynein in hyphal growth, microtubule organization, spindle pole body motility and nuclear migration
Authors: Inoue S. , Turgeon B. G. , Yoder O. C. , Aist J. R.
Published: April 2021

Cytoplasmic dynein is a microtubule-associated motor protein with several putative subcellular functions. Sequencing of the gene (DHC1) for cytoplasmic dynein heavy chain of the filamentous ascomycete, Nectria haematococca, revealed a 4,349-codon open reading frame (interrupted by two introns) with four highly conserved P-loop motifs, typical of cytoplasmic dynein heavy chains. The predicted amino acid sequence is 78.0% identical to the cytoplasmic dynein heavy chain of Neurospora crassa, 70.2% identical to that of Aspergillus nidulans and 24.8% identical to that of Saccharomyces cerevisiae. The genomic copy of DHC1 in N. haematococca wild-type strain T213 was disrupted by inserting a selectable marker into the central motor domain. Mutants grew at 33% of the wildtype rate, forming dense compact colonies composed of spiral and highly branched hyphae. Major cytological phenotypes included (1) absence of aster-like arrays of cytoplasmic microtubules focused at the spindle pole bodies of post-mitotic and interphase nuclei, (2) limited postmitotic nuclear migration, (3) lack of spindle pole body motility at interphase, (4) failure of spindle pole bodies to anchor interphase nuclei, (5) nonuniform distribution of interphase nuclei and (6) small or ephemeral Spitzenkörper at the apices of hyphal tip cells. Microtubule distribution in the apical region of tip cells of the mutant was essentially normal. The nonuniform distribution of nuclei in hyphae resulted primarily from a lack of both post-mitotic nuclear migration and anchoring of interphase nuclei by the spindle pole bodies. The results support the hypothesis that DHC1 is required for the motility and functions of spindle pole bodies, normal secretory vesicle transport to the hyphal apex and normal hyphal tip cell morphogenesis.
Localisation and interaction of the protein components of the yeast 2µ circle plasmid partitioning system suggest a mechanism for plasmid inheritance
Authors: Scott-Drew Suzanna , Murray James A. H.
Published: April 2021

Replicating plasmids are highly unstable in yeast, because they are retained in mother cells. The 2µ circle plasmid overcomes this maternal inheritance bias by using a partitioning system that involves the plasmid encoded proteins Rep1p and Rep2p, and the cis-acting locus STB. It is thus widely exploited as a cloning vehicle in yeast. However, little is known about the cellular or molecular mechanisms by which effective partitioning is achieved, and models of both free diffusion and plasmid localisation have been proposed. Here we show that Rep1p and Rep2p proteins interact to form homo- and hetero-complexes in vitro. In vivo, Rep1p and Rep2p are shown to be nuclear proteins, exhibiting sub-nuclear concentration in distinct foci. The number of foci appears constant regardless of plasmid copy number and cell ploidy level. Before cell division, the number of foci increases, and we observe approximately equal allocation of foci to mother and daughter cell nuclei. We show that whereas Rep2p expressed alone is found exclusively in the nucleus, Rep1p requires the presence of Rep2p for effective nuclear localisation. High levels of 2µ plasmid induce a multiple-budded elongated cell phenotype, which we show can be phenocopied by overexpression of both REP1 and REP2 together but not alone. Taken together, these results suggest that Rep1p and Rep2p interact in vivo, and occupy defined nuclear sites that are allocated to both mother and daughter nuclei during division. We propose a model for 2µm plasmid partitioning based on these results, involving the association of plasmid DNA with specific, segregated subnuclear sites.
Actin microfilaments control the MHC class II antigen presentation pathway in B cells
Authors: Barois Nicolas , Forquet Frédérique , Davoust Jean
Published: April 2021

Newly synthesised major histocompatibility complex class II molecules associate with invariant chains (Ii) to form nonameric complexes. These complexes are transported to endosomes, where proteolytic enzymes generate αβ class II dimers associated with nested Ii-derived peptides. These peptides are then exchanged with antigen peptide, and mature class II molecules reach the cell surface. The role of the actin cytoskeleton in the transport and maturation of class II molecules has not been studied. We show here that upon treatment with cytochalasin D (cyto D), the rate of Ii degradation is drastically reduced in B cells. Cyto D treatment also leads to a delayed appearance of stable forms of class II molecules, and a reduced presentation efficiency of antigen determinants requiring newly synthesised class II molecules. Under such conditions, we found that invariant chain fragments and class II molecules are accumulated in early and late endosomal compartments, whereas the leupeptin protease inhibitor induces their accumulation in lysosomal compartments. The addition of cyto D to leupeptin blocks the delivery of class II/invariant chain complexes to lysosomes, and further inhibits degradation of Ii. The dynamics of the actin cytoskeleton can therefore control the meeting point between newly synthesised class II molecules and lysosomal proteases, involved in Ii degradation and antigen peptide loading.
Nuclear import of protein kinase C occurs by a mechanism distinct from the mechanism used by proteins with a classical nuclear localization signal
Authors: Schmalz Dirk , Hucho Ferdinand , Buchner Klaus
Published: April 2021

Protein kinase C does not have any known nuclear localization signal but, nevertheless, is redistributed from the cytoplasm to the nucleus upon various stimuli. In NIH 3T3 fibroblasts stimulation with phorbol ester leads to a translocation of protein kinase C α to the plasma membrane and into the cell nucleus. We compared the mechanism of protein kinase C α’s transport into the nucleus with the transport mechanism of a protein with a classical nuclear localization signal at several steps. To this end, we comicroinjected fluorescently labeled bovine serum albumin to which a nuclear localization signal peptide was coupled, together with substances interfering with conventional nuclear protein import. Thereafter, the distribution of both the nuclear localization signal-bearing reporter protein and protein kinase C α was analyzed in the same cells. We can show that, in contrast to the nuclear localization signaldependent transport, the phorbol ester-induced transport of protein kinase C α is not affected by microinjection of antibodies against the nuclear import factor p97/importin/karyopherin β or microinjection of non-hydrolyzable GTP-analogs. This suggests that nuclear import of protein kinase C α is independent of p97/ importin/karyopherin β and independent of GTP. At the nuclear pore there are differences between the mechanisms too, since nuclear transport of protein kinase C α cannot be inhibited by wheat germ agglutinin or an antibody against nuclear pore complex proteins. Together these findings demonstrate that the nuclear import of protein kinase C α occurs by a mechanism distinct from the one used by classical nuclear localization signal-bearing proteins at several stages.
Three distinct steps in transport of vesicular stomatitis virus glycoprotein from the ER to the cell surface in vivo with differential sensitivities to GTPγS
Authors: Pepperkok Rainer , Lowe Martin , Burke Brian , Kreis Thomas E.
Published: April 2021

Microinjected GTPγS revealed three distinct steps in the exocytic transport of the temperature sensitive glycoprotein of vesicular stomatitis virus (ts-O45-G) from the ER to the cell surface in intact Vero cells. While COPII dependent export of ts-O45-G from the ER is blocked in cells injected with recombinant protein of a dominant mutant of SAR1a (SAR1a[H79G]) inhibited in GTP hydrolysis, neither injected GTPγS nor antibodies against β-COP (anti-EAGE) interfere with this transport step significantly. In contrast, transport to the Golgi complex is blocked by 5ø µM GTPγS, a dominant mutant of ARF1 (ARF1[Q71L]) inhibited in GTP hydrolysis, or microinjected anti-EAGE, but injected Sar1a[III9G]p has no effect. Microinjection of GTPγS or expression of ARF[Q71L] rapidly induces accumulation of COPI coated vesicular structures lacking ts-O45-G. Finally, transport of ts-O45-G from the trans -Golgi network (TGN) to the cell surface is inhibited only by high concentrations of GTPγS (500 µM). Interestingly, this step is only partially brefeldin A sensitive, and injected antibodies against β-COP and p200/myosin II, a TGN membrane associated protein, have no effect. These data provide first strong in vivo evidence for at least three distinct steps in the exocytic pathway of mammalian cells regulated by different sets of GTPases and coat proteins. COPII, but not COPI, is required for ER export of ts-O45-G. COPI plays a role in subsequent transport to the Golgi complex, and a so far unidentified GTPγS sensitive coat appears to be involved in transport from the TGN to the cell surface.
Radial F-actin arrays precede new hypha formation in Saprolegnia: implications for establishing polar growth and regulating tip morphogenesis
Authors: Bachewich Catherine , Heath; I. Brent
Published: April 2021

The roles of cortical F-actin in initiating and regulating polarized cell expansion in the form of hyphal tip morphogenesis were investigated by analyzing long term effects of F-actin disruption by latrunculin B in the oomycete Saprolegnia ferax, and detecting localized changes in the cortical F-actin organization preceding hyphal formation. Tubular hyphal morphology was dependent on proper F-actin organization, since latrunculin induced dose-dependent actin disruption and corresponding changes in hyphal morphology and wall deposition. With long incubation times (1 to 3 hours), abundant subapical expansion occurred, the polar form of which was increasingly lost with increasing actin disruption, culminating in diffuse subapical expansion. These extreme effects were accompanied by disorganized cytoplasm, and novel reorganization of microtubules, characterized by star-burst asters. Upon removing latrunculin, hyperbranching produced abundant polar branches with normal F-actin organization throughout the colony. The results are consistent with F-actin regulating polar vesicle delivery and controlling vesicle fusion at the plasma membrane, and suggest that F-actin participates in establishing polar growth. To test this idea further, we utilized the hyperbranching growth form of Saprolegnia. Early during the recovery time, prior to multiple branch formation, radial arrays of filamentous F-actin were observed in regions with no detectable surface protrusion. Their locations were consistent with those of the numerous branches that formed with longer recovery times. Similar radial arrays preceded germ tube formation in asexual spores. The arrays were important for initiating polar growth since the spores lost their ability to polarize when the F-actin was disrupted with latrunculin, and increased isometrically in size rather than producing germ tubes. Therefore, F-actin participates in initiating tip formation in addition to its previously demonstrated participation in maintenance of hyphal tip growth. The cortical location and radial organization of the arrays suggest that they recruit and stabilize membrane-bound and cytosolic factors required to build a new tip.
An Analysis of Branchial Ammonia Excretion in the Freshwater Rainbow Trout: Effects of Environmental Ph Change and Sodium Uptake Blockade
Authors: Wright P. A. , Wood C. M.
Published: April 2021

Short-term treatments (3 h) designed to change the relative NH3 and NH4+ (ΔNH4+) gradients and sodium transport (JNa) across the gills were employed to analyse the normal mechanism(s) of branchial ammonia excretion in trout acclimated to fresh water of pH ≃8·0. Control occurred in the absence of, or against, an apparent gradient, while ΔNH4+ was positive. Severe acid exposure (pH = 4·06) raised and ΔNH4+, abolished , and reduced by 28%, while moderate acidity (pH = 6·64), which also elevated had no significant influence on and . Severe alkaline exposure (pH = 9·4) raised ΔNH4+, reduced to a very negative value, and decreased and by equ1molar amounts, representing 55% and 80% of control levels respectively. Moderate alkalinity (pH = 8·69) had similar effects on and , but reduced and by only ∼25%. The sodium transport inhibitor amiloride (10−4moll −1 in the external water, pH ≃8·0) had very similar effects to pH = 4·06 on both and , but did not alter or . The results discount the quantitative importance of NH4+ diffusion and favour a flexible combination of NH3 diffusion and Na+/NH4+ exchange as the major mechanisms of , with the latter dominating under the particular control conditions of the present study.
Insect Cardioactive Peptides: I. Distribution and Molecular Characteristics of two Cardioacceleratory Peptides in the Tobacco Hawkmoth, Manduca Sexta
Authors: Tublitz Nathan J. , Truman James W.
Published: April 2021

Using an in vitro heart bioassay, the pharmacological and biochemical properties of two cardioactive peptides derived from neural tissues of the moth, Manduca sexta, were analysed.

Gel filtration of ventral nerve cords (VNC) from pharate adults identified two cardioacceleratory peptides (CAP1 and CAP2) with apparent molecular weights of 1000 and 500 Da, respectively. Both CAPs were localized to the abdominal perivisceral organs, the major neurohaemal release sites in the insect VNC. Pulse application of CAP1 or CAP2 on the in vitro Manduca heart produced a dose-dependent increase in rate but had no effect on beat amplitude. The threshold dose for the action of each peptide on the isolated heart bioassay was less than 0·05 abdominal nerve cord equivalents.

Both CAPs were present in the pharate adult VNC of several other Lepidopteran species. Neither CAP1 nor CAP2 was detected in the prepupal VNC of Manduca sexta.
Effects of Body Temperature on Respiration, Blood Gases and Acid-Base Status in the Turtle Chrysemys Picta Bellii
Authors: Glass M. L. , Boutilier R. G. , Heisler N.
Published: April 2021

Freshwater turtles (Chrysemys picta bellii Gray) were acclimated to temperatures of 5, 10, 20 and 30°C for at least 12 days, and pulmonary ventilation, oxygen uptake and arterial pH, and were determined in completely unrestrained specimens. Oxygen uptake increased overproportionately (6·7-fold) as compared to pulmonary ventilation (, 4·4-fold) when the temperature increased from 10 to 30°C. The observed rise in arterial from 13 (5 °C) to 32 mmHg (30°C) was the result of a decrease in , whereas an increase of arterial from 12Torr at 5°C to about 60Torr at 20 and 30°C mainly resulted from the effects of intracardiac blood shunting combined with temperature-dependent shifts of the oxygen dissociation curve. Arterial pH fell with rising temperature significantly less (ΔpH/Δt = −0·010U/°C) than required for constant relative alkalinity and for constant dissociation of imidazole. The changes of cerebrospinal fluid pH with temperature, calculated from the mean arterial values, were even smaller [ΔpH/Δtcsf = −0·008). It is concluded that the observed temperature dependence of the acid-base status is not in agreement with the alphastat hypothesis.
Unilateral Ciliary Reversal and Motor Responses During Prey Capture by the Ctenophore Pleurobrachia
Authors: Tamm Sidney L. , Moss Anthony G.
Published: April 2021

High-speed cinematography of feeding Pleurobrachia revealed a stereotyped sequence of ciliary motor responses underlying the feeding behaviour of this ctenophore. Prey capture by a tentacle first elicited high frequency beating in all comb rows, propelling the animal forward at a rapid speed for several seconds. This was followed by a brief period of inactivity on some or all comb rows. Then comb rows adjacent to the catching tentacle beat in the reverse direction, causing the ctenophore to spin rapidly toward this side and sweeping the prey-catching tentacle to the opened mouth, which bent towards it. After engulfing the prey, the animal slowly swam forward to re-set the relaxed tentacles as à fishing net. The patterns, timing, onset and coordination of these ciliary responses particularly the unilateral reversal of comb rows on the catching side, are analysed with respect to possible conducting pathways mediating this behaviour.
The Effects of Temperature Acclimation on the Resting Membrane of Skeletal Muscle Fibres from Green Sunfish
Authors: Klein M. G. , Prosser C. L.
Published: April 2021

Conductive properties of muscle fibres from green sunfish (Lepomis cyanellus) acclimated to different temperatures were examined. The relative membrane permeability to chloride and potassium ions, PCI/PK, measured at acclimation temperature, was approximately 7·0 after acclimation at 25 °C and 1·3 after acclimation at 7°C. This difference was due to a six-fold reduction in the membrane chloride conductance upon acclimation to 7 °C as compared to 25 °C-acclimated fibres. Mean (±S.E.M.) values of the chloride conductance were 554 + 68μS cm−2 in warm-acclimated sunfish, and 75 ± 9μ.Scm−2 in cold-acclimated sunfish. Membrane capacitance also differed significantly between the two acclimation groups.

When the temperature was varied acutely, the magnitude of the chloride conductance exhibited a maximum Q10 of only 1·9, compared with a Q10 of 3·0 associated with acclimation. Upon transferring 25 °C-acclimated sunfish to holding tanks at 7 °C, the total membrane resistance exhibited a sigmoidal increase over about 14 days, and a steady membrane capacitance was achieved in about 10 days. For 7°C-acclimated sunfish, transferred to 25 °C, resistance showed a sigmoidal decrease over 10 days and capacitance was steady after 8 days. The results indicate that thermal acclimation of the muscle membrane involves cellular regulatory processes which underlie significant changes in the electrical properties of the fibre.
Swimming In The Pteropod Mollusc, Clione Limacina: I. Behaviour and Morphology*
Authors: Satterlie Richard A. , Labarbera Michael , Spencer Andrew N.
Published: April 2021

In the pteropod mollusc Clione limacina (Phipps), swimming is accomplished through alternate dorsal and ventral flexions of a pair of strongly muscularized wing-like parapodia (wings). Wing musculature is arranged in seven muscle groups. The two outermost dorsal and ventral groups produce the bending movements of swimming. The three inner muscle groups include longitudinal and transverse wing retractors and dorso-ventral muscles. The overall muscle arrangement is similar to that of the generalized mollusc foot.

During hovering locomotion the wings pronate on downstroke and supinate on upstroke to produce a maximal angle of attack of 42° for both phases. Wing tips nearly touch or overlap in the saggital plane at the extreme of each half-cycle. High speed movie analysis of hovering swimming indicates that upstroke and downstroke are nearly symmetrical. It is suggested that wings produce lift in both wing phases.

We estimate from wing dimensions and velocity measurements that the Reynolds number of the wings is approximately 200. A novel lift-generating mechanism, similar to the ‘clap-and-fling’ of insects, may be utilized by the Clione wing to generate lift throughout the wing cycle despite the reversal of wing movement in each half-stroke.
Identification of Neurones Containing Cardio-Acceleratory Peptides (Caps) in the Ventral Nerve Cord of the Tobacco Hawkmoth, Manduca Sexta
Authors: Tublitz Nathan J. , Truman James W.
Published: April 2021

The abdominal ganglion neurosecretory cells responsible for the synthesis and release of two insect neurohormones, cardioacceleratory peptides 1 and 2 (CAP1 and CAP2), from the perivisceral organs (PVOs) have been identified in the tobacco hawkmoth, Manduca sexta. Previous work established the existence of two groups of abdominal ganglion cell bodies with axons projecting to the PVO: four laterally-situated pairs and five pairs lying on the midline (Taghert & Truman, 1982b). Micro dissection and bioassay of various parts of an abdominal ganglion revealed that CAP activity was greatest in the medial portion of the ganglion, the portion containing the 10 midline neurones. Six of the 10 midline neurosecretory cells, the new midline bilateral (MB) cells, appeared to differentiate post-embryonically, commencing differentiation late in the last larval instar and reaching maturity midway through adult development. The development of the new MB cells was mirrored by the accumulation of CAP activity in the abdominal nerve cord. Not present in measurable amounts in larvae, CAP activity was first detectable a few days after pupation and reached maximal levels midway through adult development. CAP-like bioactivity was collected from the PVO in response to antidromic stimulation of the nerve containing the new MB axons. No CAP-like bioactivity was detected in those preparations in which the new MB axons were severed or in which other nerves were stimulated. Intracellular stimulation of a new MB neurone evoked the release from the PVO of measurable levels of CAP bioactivity. It was shown that this stimulation-evoked, cardioacceleratory activity was sensitive to protease treatment, and was released only from the cell that was stimulated. On the basis of these experiments, it was concluded that the CAPs are synthesized and secreted from the new MB cells.
Short Communication Urea Efflux From the Squalus Acanthias Pup: the Effect of Stress
Authors: Evans David H. , Kormanik Gregg A.
Published: April 2021

The extremely high concentration of urea found in elasmobranch blood (approx. 400 mmol 1–1) is secondary to nearly complete reabsorption (90–95%) of this solute in the renal tubules (Forster, 1967), and a branchial urea permeability which is approximately 1% that of the toad bladder (<10 × 10–8cm s–1, Payan, Goldstein & Forster, 1973). Evans, Oikari, Kormanik & Mansberger (1982) have recently shown that the premature spiny dogfish (Squalus acanthias) pup is capable of osmoregulation in sea water, despite an initial reduction in plasma urea concentration (13% in 3 days). This fall could have been secondary to a reduced synthetic rate, or caused by an increased efflux across surfaces such as the gills, renal and/or rectal gland epithelia, or yolk sac. The present study was therefore undertaken to measure the rate of urea efflux from intact spiny dogfish pups, and to determine the effect of stress on that efflux. Stress was induced by the experimentally common procedure of handling, MS-222 anaesthesia, and weighing.
Angiotensin II Can Initiate Contact-Rehydration in Terrestial Slugs
Authors: Makra Martha E. , Prior David J.
Published: April 2021

Moist-skinned terrestrial animals such as snails and slugs are highly susceptible to desiccation. It has been shown that active slugs can lose up to 35% of their initial body weight (%IBW) within 2-3 h (Dainton, 1954; Prior, Hume, Varga & Hess, 1983). They can, however, rapidly recover from dehydration by integumental absorption of water while in contact with a moist substrate (Burton, 1966; Prior, 1982, 1984). This process of contact-rehydration involves an increase in the epithelial paracellular permeability of the foot and is mediated by a well regulated behavioural sequence (Prior, 1982, 1984; Prior & Uglem, 1984). Contact-rehydration is initiated when slugs have been dehydrated to the threshold level of 60–70% IBW. They move onto a moist surface and assume a characteristic flattened posture while water is absorbed through the foot. They remain in this posture until enough water has been absorbed to achieve their rehydration set-point (93·6 ± 12·2% IBW for Limax maximus;Prior, 1984). Once rehydrated, the slugs move off the moist surface and come to rest on a dry surface, thus terminating the behaviour.
A Rotating Respirometer to Monitor Voluntary Activity and Associated Exchange of Respiratory Gases in the Land Hermit Crab (Coenobita Compressus)
Authors: Wheatly Michèle G. , McMahon Brian R. , Burggren Warren W. , Pinder Alan W.
Published: April 2021

A rotating respirometer was designed which enabled respiratory gas exchange in the land hermit crab Coenobita compressas to be correlated with voluntary submaximal sustained pedestrian activity. In the laboratory, crabs remained spontaneously active for up to 150 min, maintaining velocities of 0·6 cm s−1. Comparable activity patterns were observed in the field. Quiescent O2 uptake increased logarithmically as a function of load rating of the adopted molluscan shell. Steady-state and were measured after 30 min of spontaneous activity and both increased linearly with velocity. There was good correspondence between Y-intercept values and those measured in inactive crabs. At the mean locomotory speed, and were increased 3·4-fold and 2·6-fold respectively above settled rates. Minimum and gross energetic cost of transport were estimated and compared with values in the literature. and returned to settled levels within the first hour of recovery. The activity profile and concomitant changes in gas exchange are discussed in the context of acquisition of the shell-dwelling habit.
Effects of Low Ambient Calcium Levels on Whole-Body Ca2+ Flux Rates and Internal Calcium Pools in the Freshwater Cichlid Teleost,Oreochromis Mossambicus
Authors: Flik Gert , Fenwick James C. , Kolar Zvonimir , Mayer-Gostan Nicole , Bonga Sjoerd E. Wendelaar
Published: April 2021

Calcium fluxes and internal calcium pools were measured in fed, rapidly growing, male tilapia, Oreochromis mossambicus, acclimated to 0·8 mmol l−1 (FW) and 0-2 mmol l−1 (LFW) Ca2+. Plasma calcium levels were slightly and significantly higher in the LFW tilapia, but muscle calcium concentrations were independent of ambient Ca2+. At the time of the experiments, the LFW fish were growing and accumulated calcium, although the calcium content of their hard tissues was reduced. The LFW fish had higher Ca2+ influx and efflux rates than the FW fish. The increase in the influx of Ca2+ in LFW fish was, however, substantially greater than the increase in the efflux of Ca2+, giving these fish a more than four-fold increase in net Ca2+ influx from the water: for a 20-g tilapia net uptake rates of Ca2+ from the water were 390 and 1620 nmol Ca2+ h−1 for FW-and LFW-adapted fish, respectively. These values were calculated to represent at least 69 % of the total calcium accumulated by these growing fish. This indicates that even in low-calcium water, tilapia absorb a significant amount of their calcium requirement directly from the water.

The pool of readily exchangeable calcium in the bone of FW fish was estimated to be about 7 % of the total hard tissue calcium. In the fish acclimated to LFW, this percentage increased to about 15 % as total hard tissue mineralization decreased. This may indicate that tilapia can increase the mobility of their h
A Biological Feedback Control System with Electronic Input: the Artificially Closed Femur-Tibia Control System of Stick Insects
Authors: Weiland G. , Bässler U. , Brunner M.
Published: April 2021

An experimental arrangement was constructed which is based on the open-loop femurtibia control system of two stick insect species (Carausius morosus and Cuniculina impigra). It could be artificially closed in the following way: the position of the tibia was measured by an optical device and this value was used to drive a penmotor which moved the receptor apodeme of the femoral chordotonal organ in the same way as in intact animals. This arrangement allows direct comparison of the behaviour of the open-loop and the closed-loop system as well as introducing an additional delay.

The Carausius system has a phase reserve of only 30° –50° and the factor of feedback control approaches 1 between 1 and 2 Hz. This agrees with the observation that an additional delay of 70–200 ms produces long-lasting oscillations of 1–2 Hz. The Cuniculina system has a larger phase reserve and consequently a delay of 200 ms produced no oscillations. All experiments show that extrapolation from the open-loop system to the closed-loop system is valid, despite the non-linear characteristics of the loop. Consequences for servo-mechanisms during walking and rocking movements are discussed.
Distance and Size Discrimination in a Water Stick Insect, Ranatra Linearis (Heteroptera)
Authors: Cloarec Ann
Published: April 2021

The role of vision in distance, position and size discrimination in prey capture has been investigated in normal adult water stick insects (Ranatra linearis L. : Heteroptera) and in ones with one eye covered.

Both monocular and intact Ranatra were able to discriminate between two targets subtending the same angle but presented at different distances. They usually chose the target nearer to their foreleg claws. Although monocular subjects undershot more often than controls, they could still estimate distance correctly.

When presented with two different-sized targets at the same distance, both monocular and intact subjects usually preferred the larger target within a 1°–10° range, even though monocular animals chose the larger object less consistently. They were able to distinguish between two targets differing in size by only 1 °.

Asymmetrical presentations of two identical targets stressed the importance of the central position. Intact animals always preferred the target nearer their midline.

These data also revealed the unexpected ability of Ranatra to strike accurately at two targets or prey items simultaneously. When two identical targets were presented simultaneously and symmetrically, aims were directed at both targets, and one was grasped by each raptorial foreleg, thus indicating an absence of confusion.
The Physiology of Wandering Behaviour in Manduca Sexta: IV. Hormonal Induction of Wandering Behaviour from the Isolated Nervous System
Authors: Dominick Oliver S. , Truman James W.
Published: April 2021

Prior to exposure to ecdysteroids, the isolated central nervous system (CNS) of the fifth instar Manduca sexta larvae exhibited infrequent motor bursts over a 24-h period of extracellular recording from segmental motor nerves. In contrast, the CNS isolated from wandering larvae was characterized by persistent, frequent spontaneous motor bursts throughout the 24-h incubation. The motor bursts generated by the isolated CNS of wandering larvae were similar to those observed in deafferented segments of partially dissected wandering larvae during locomotion. In both cases bursts in the deafferented ganglia were synchronous and had a lower frequency than in intact animals. Removal of the brain from a CNS isolated prior to ecdysteroid exposure resulted in the appearance of spontaneous bursts, which were abolished by removing the suboesophageal ganglion (SEG). By contrast, when the brain was removed from the isolated CNS of wandering larvae, spontaneous bursts ceased. These results parallel the behavioural effects of the same lesions in intact larvae of the respective stages. The CNS isolated from larvae prior to ecdysteroid exposure initiated sustained frequent bursting after an average latency of 15 h following incubation in haemolymph taken from larvae during the interval of ecdysteroid secretion. Incubations of the CNS with 1μgml−1 20-hydroxyecdysone (20-HE) resulted in the onset of the same pattern of sustained motor activity. In a CNS isolated prior to ecdysone release, it was necessary and sufficient to expose the brain to 20-HE in order to induce the state of persistent motor bursts characteristic of wandering. We conclude that the spontaneous persistent motor bursts observed in the isolated CNS of wandering larvae are directly related to the sustained locomotion seen during the wandering behaviour. 20-HE acts directly on the CNS, specifically the brain, to induce this state of neural activity.
Energy Cost of Contraction in Fast and Slow Muscle Fibres Isolated from an Elasmobranch and an Antarctic Teleost Fish
Authors: Altringham J. D. , Johnston I. A.
Published: April 2021

Single fast and small bundles of slow fibres were isolated from the muscles of an elasmobranch (dogfish, Scyliorhinus canicula) and an Antarctic teleost (Notothenia neglecta). A third fibre type present in the dogfish (superficial fibre) was also isolated. Fibres were chemically skinned with a non-ionic detergent. Tension generation and ATPase activity were measured during isometric activations. ATPase activity was estimated by measuring the release of ADP into the experimental solutions using high performance liquid chromatography. In the dogfish fibre types, both tension and ATPase activity increased in the order superficial < slow < fast, even after corrections were made for differences in myofibrillar density. The economy of isometric contraction (tension/ATPase activity) was 50–60% higher in the slow and superficial fibres than in the fast. In the Antarctic species, both tension and ATPase activity of the fast fibres were higher than those of the slow fibres, and the slow fibres were 30% more economical than fast fibres. After correction for differences in myofibrillar density, tensions were very similar. The results are discussed with reference to the energy supply, recruitment pattern and function of the various fibre types.
Evidence Against Hormonal Control of Integumentary Water Loss in Periplaneta Americana
Authors: Machin J. , O’donnell M. J. , Kestler P.
Published: April 2021

The effect of decapitation on water loss from adult male cockroaches was studied in order to re-examine the possibility of hormonal modulation of integumental permeability. We found no effect of decapitation on the permeability or water content in measurements made on the pronotum. Although overall weight losses of the decapitated animals always exceeded those of intact animals, loss rates and their rate of decline depended on the apparent severity of handling. There was a small but significant difference between the controls and all decapitated and sham-operated animals, and this difference persisted for at least 96 h. We attribute these results principally to the differential effects of cuticle damage, though increased respiratory water loss may also be a factor. Our results draw attention to the complex practical problems involved in obtaining accurate, representative cuticle permeabilities for Periplaneta, and form a basis for questioning the notion of inhibition of cuticular water loss by hormones from the head.