bluuebunny/crossref_metadata_2025 huggingface dataset:
Mevalonate reverses the developmental arrest of preimplantation mouse embryos by Compactin, an inhibitor of HMG Co A reductase
Authors: Surani M. Azim H. , Kimber Susan J. , Osborn Jeremy C.
Published: April 2021

Hydroxymethyl glutaryl Co A reductase (HMG Co A reductase) is the key regulatory enzyme in the conversion of acetate to mevalonate. Mevalonate is the precursor for sterol and non-sterol isoprenes involved in membrane biogenesis, DNA replication and protein glycosylation. The influence of two inhibitors of HMG Co A reductase, Compactin (or ML236B) and an oxygenated sterol, Diosgenin, were tested on preimplantation development of mouse embryos. Compactin arrested development at about the 32-cell stage, leaving the blastomeres decompacted. Ultrastructural examination of the embryos revealed reduced membrane apposition but no major effects on cell organelles. There was however a predominance of nuclei with highly condensed chromatin. Glycosylation of proteins also appeared to be inhibited as shown by reduced incorporation of sugar precursors but not that of amino acids. The influence of Compactin was judged to be highly specific since only 10μg/ml (0·08 mM) mevalonic acid abolished the effects of Compactin. Mevalonate in embryos may not be primarily utilized in the synthesis of sterols since a specific inhibitor of cholesterol synthesis, DL-4,4,10-β-trimethyl-trans-decal-3-β-ol had no detectable effect on development. The non-sterol isoprenes of mevalonate such as dolichol and isopentenyl adenine may play a more significant role during early development since the influence of Compactin resembled that previously described using tunicamycin, a specific inhibitor of dolichol mediated synthesis of N-glycosidically linked glycoproteins. Hence, lack of dolichol may partly be the cause of arrest of embryonic development by Compactin. Diosgenin caused embryonic arrest at about the 16-cell stage and the influence was not reversible by mevalonic acid. Cholesterol was able to rescue 50 % of the embryos but the effect of Diosgenin could be non-specific and probably caused by its entry into the plasma membrane.
A bootstrap model for the proximodistal pattern formation in vertebrate limbs
Authors: Meinhardt Hans
Published: April 2021

For the sequential determination of proximodistal structures during the outgrowth of vertebrate limbs, a ‘bootstrap’-mechanism is proposed: by increasing feedback of more dis-tally determined cells onto the production of a morphogen at the apical ectodermal ridge a successive increase of the morphogen concentration is achieved during outgrowth. The model accounts for the formation of a progress-zone at the limb tip, for the correct regeneration after truncation, for the presence and absence of proximodistal intercalation after certain graft experiments in amphibian limbs, for the tendency with which distal structures form in proximal position after certain experimental manipulations and for the intimate coupling of the anteroposterior and the proximodistal axes.
Regeneration of the eye margin in Periplaneta americana (Insecta, Blattodea)
Authors: Shelton P. M. J. , Pfannenstiel H.-D. , Wachmann E.
Published: April 2021

The regulative ability of the proliferative zone of the insect eye margin has been investigated in larval Periplaneta americana. After sections of the eye margin are removed the eye nevertheless recovers to form a normal shape. Using chimaeras of lavender and wild-type animals we were able to show that the margin can regenerate from the differentiated parts of the eye. When differentiated eye tissue is confronted with epidermis from the head capsule adjacent to the proliferative zone (the vertex), the regenerated margin always forms from the eye. There is no evidence that intervening levels can be intercalated between host and graft tissues when sections of the eye margin are moved to new circumferential levels. However, in that situation differences between tissues from non-adjacent circumferential positions lead to the rounding up of the graft and it fails to develop normally.
The retention of primary hypoblastic cells underneath the developing primitive streak allows for their prolonged inductive influence
Authors: Azar Yehudit , Eyal-Giladi Hefzibah
Published: April 2021

An experimental study was made of the distribution of the primary hypoblastic cells in the lower layer of the avian blastoderm throughout primitive streak formation and until stage 10 (Hamburger & Hamilton, 1951). The primary hypoblast of stage XIII (Eyal-Giladi & Kochav, 1976) chick blastoderms was exchanged for either an [H3]thymidine-labelled similar chick hypoblast, or a quail primary hypoblast. During the entire period of primitive streak formation, the lower layer proved to be a mosaic of labelled hypoblastic and non-labelled entodermal cells (chick cells of epiblastic origin). The persistance of hypoblastic cells underneath the developing primitive streak is regarded by us as a possible way to prolong the inductive influence of the hypoblast upon the forming streak.
Vascular endothelial growth factor induces VE-cadherin tyrosine phosphorylation in endothelial cells
Authors: Esser Sybille , Lampugnani Maria Grazia , Corada Monica , Dejana Elisabetta , Risau Werner
Published: April 2021

Interendothelial junctions play an important role in the regulation of endothelial functions, such as vasculogenesis, angiogenesis, and vascular permeability. In this paper we show that vascular endothelial growth factor (VEGF), a potent inducer of new blood vessels and vascular permeability in vivo, stimulated the migration of endothelial cells after artificial monolayer wounding and induced an increase in paracellular permeability of human umbilical vein endothelial cells (HUVECs). Furthermore, VEGF increased phosphotyrosine labeling at cell-cell contacts. Biochemical analyses revealed a strong induction of VEGF-receptor-2 (flk-1/KDR) tyrosine-autophosphorylation by VEGF which was maximal after 5 minutes and was followed by receptor downregulation. 15 minutes to 1 hour after VEGF stimulation the endothelial adherens junction components VE-cadherin, β-catenin, plakoglobin, and p120 were maximally phosphorylated on tyrosine, while α-catenin was not modified. PECAM-1/CD31, another cell-cell junctional adhesive molecule, was tyrosine phosphorylated with similar kinetics in response to VEGF. In contrast, activation of VEGF-receptor-1 (Flt-1) by its specific ligand placenta growth factor (PlGF) had no effect on the tyrosine phosphorylation of cadherins and catenins. Despite the rapid and transient receptor activation and the subsequent tyrosine phosphorylation of adherens junction proteins the cadherin complex remained stable and associated with junctions. Our results demonstrate that the endothelial adherens junction is a downstream target of VEGFR-2 signaling and suggest that tyrosine phosphorylation of its components may be involved in the the loosening of cell-cell contacts in established vessels to modulate transendothelial permeability and to allow sprouting and cell migration during angiogenesis.
The nuclear import factor p10 regulates the functional size of the nuclear pore complex during oogenesis
Authors: Feldherr Carl , Akin Debra , Moore Mary Shannon
Published: April 2021

Previtellogenic, stage-1 Xenopus oocytes produce mainly 5S and tRNA, whereas vitellogenic oocytes, stages 2-6, synthesize predominantly 18S and 28S rRNA. Using nucleoplasmin-coated gold as a transport substrate, it was determined that the shift in synthesis from small to large RNAs during oogenesis is accompanied by an increase in both the rates of signal-mediated nuclear import and the functional size of nuclear pores. It was observed that, despite the reduction in transport capacity, gold still accumulated at the cytoplasmic surface of the pores in stage-1 oocytes. This suggested that transport in these cells is limited by translocation factors, rather than by cytoplasmic binding factors. Analysis of extracts prepared from stage-1 and vitellogenic oocytes revealed that the transport factor p10 is more abundant in stage-1 cells. Microinjection of purified p10 into stage-2 oocytes reduced the nuclear import of large gold particles to the level observed in stage-1 cells. It is concluded that p10 can modulate transport through the pores by regulating the functional size of the central transporter element.
Impaired mechanical stability, migration and contractile capacity in vimentin deficient fibroblasts
Authors: Eckes Beate , Dogic Dagmar , Colucci-Guyon Emma , Wang Ning , Maniotis Andrew , Ingber Donald , Merckling Alexandra , Langa Francina , Aumailley Monique , Delouvée Annie , Koteliansky Victor , Babinet Charles , Krieg Thomas
Published: April 2021

Loss of a vimentin network due to gene disruption created viable mice that did not differ overtly from wild-type littermates. Here, primary fibroblasts derived from vimentin-deficient (-/-) and wild-type (+/+) mouse embryos were cultured, and biological functions were studied in in vitro systems resembling stress situations. Stiffness of -/fibroblasts was reduced by 40% in comparison to wild-type cells. Vimentin-deficient cells also displayed reduced mechanical stability, motility and directional migration towards different chemo-attractive stimuli. Reorganization of collagen fibrils and contraction of collagen lattices were severely impaired. The spatial organization of focal contact proteins, as well as actin microfilament organization was disturbed. Thus, absence of a vimentin filament network does not impair basic cellular functions needed for growth in culture, but cells are mechanically less stable, and we propose that therefore they are impaired in all functions depending upon mechanical stability.
Distinct subcellular localization of calcium binding S100 proteins in human smooth muscle cells and their relocation in response to rises in intracellular calcium
Authors: Mandinova Anna , Atar Dan , Schäfer Beat W. , Spiess Martin , Aebi Ueli , Heizmann Claus W.
Published: April 2021

Changes in cytosolic Ca2+ concentration control a wide range of cellular responses, and intracellular Ca2+-binding proteins are the key molecules to transduce Ca2+ signaling via interactions with different types of target proteins. Among these, S100 Ca2+-binding proteins, characterized by a common structural motif, the EF-hand, have recently attracted major interest due to their cell- and tissue-specific expression pattern and involvement in various pathological processes. The aim of our study was to identify the subcellular localization of S100 proteins in vascular smooth muscle cell lines derived from human aorta and intestinal smooth muscles, and in primary cell cultures derived from arterial smooth muscle tissue under normal conditions and after stimulation of the intracellular Ca2+ concentration. Confocal laser scanning microscopy was used with a specially designed colocalization software. Distinct intracellular localization of S100 proteins was observed: S100A6 was present in the sarcoplasmic reticulum as well as in the cell nucleus. S100A1 and S100A4 were found predominantly in the cytosol where they were strongly associated with the sarcoplasmic reticulum and with actin stress fibers. In contrast, S100A2 was located primarily in the cell nucleus. Using a sedimentation assay and subsequent electron microscopy after negative staining, we demonstrated that S100A1 directly interacts with filamentous actin in a Ca2+-dependent manner. After thapsigargin (1 µM) induced increase of the intracellular Ca2+ concentration, specific vesicular structures in the sarcoplasmic reticulum region of the cell were formed with high S100 protein content. In conclusion, we demonstrated a distinct subcellular localization pattern of S100 proteins and their interaction with actin filaments and the sarcoplasmic reticulum in human smooth muscle cells. The specific translocation of S100 proteins after intracellular Ca2+ increase supports the hypothesis that S100 proteins exert several important functions in the regulation of Ca2+ homeostasis in smooth muscle cells.
Temperature and the Physiology of Intracellular and Extracellular Acid-Base Regulation in the Blue Crab Callinectes Sapid Us
Authors: Wood Chrism. , Cameron James N.
Published: April 2021

The 14C-DMO/3H-inulin method for pHi was critically assessed in intact Callinectes and found to be reliable provided adequate equilibration time and significant radiolabel excretion were taken into account. An unusually high ‘mean whole body pHi’ (7·54 at 20°C compared with a pHa of 7·80) was due to a highly alkaline fluid compartment (pHi = 8·23) in the carapace. At 20°C the pHi of the heart was 7·35 and skeletal muscle pHi was 7·30, and there were small but consistent differences in the pHi of different muscle types. The change in pHa with temperature was −0·0151 u°C−1 between 10 and 30 °C, slightly less than the slope for the neutral pH of water (ΔpN/ΔT ≃ −0·0175 u °C−1). With data corrected to constant , this was associated with a change in [HCO3−]a between 10 and 20°C ( −0·13 mequiv l−1 °C−1, constant ) and a change in between 20 and 30 °C ( + 0-13 Torr °C−1, constant [HCO3−]a). The disturbing effect of relatively small changes on this pattern was demonstrated. ApHi/AT slopes for all tissues except carapace were not significantly different from pHa/AT but generally lower than ΔpN/ΔT. The slope for the. carapace was very flat and greatly influenced the ‘mean whole body pHi’ slope ( −0·0062u°C−1). In haemolymph in vitro at constant , ‘passive’ Δ [HCO3−]/ ΔT (−0·17mequivl −1°C−’ ) was comparable to that in vivo between 10 and 20 °C, independent of absolute , and directly related to total protein concentration. Haemolymph non-bicarbonate buffer value (μ) was similarly related to protein, but increased with temperature. Crabs subjected to an acute 20→10 °C shift showed initial overshoots of pHa and pHi associated with undershoot of , all of which were corrected over 24 h as [HCO3−]a rose. During this period there was a significant net uptake of acidic equivalents (base output) from the environment. The relevance of ‘passive’ Δ [HCO3−]/ ΔT in an open system to the observed in vivo effects is discussed.
Temperature Coupling and ‘Trade-Off’ Phenomena in the Acoustic Communication System of the Cricket, Gryllus Bimaculatus de Geer (GRYLLIDAE)
Authors: Doherty John A.
Published: April 2021

The effects of ambient temperature on stridulation (calling song) in males, and phonotaxis in females, were studied in the chirping cricket, Gryllus bimaculatus. In the male, temperature had the greatest effect on the syllable and chirp repetition rates. Both increased linearly with increasing temperature between 15 and 24°C; there was no effect of temperature on these temporal properties at higher temperatures (24-33°C). Syllable duration, number of syllables per chirp and dominant frequency remained relatively unaffected by changes in temperature. Stridulation and phonotaxis were temperature coupled because the female at 15, 22 and 30°C responded best to synthetic songs with syllable and chirp repetition rates that matched these temporal properties of the male’s calling song at the same temperature. The phonotactic behaviour of the female indicates that certain combinations of temporal properties in the male’s calling Song improve the female’s response at different temperatures, suggesting the presence of ‘trade-off’ phenomena in phonotaxis and pattern recognition in G. bimaculatus.
Physiology of the Femoral Chordotonal Organ in the Stick Insect, Cuniculina Impigra
Authors: Hofmann T. , Koch U. T. , Bässler U.
Published: April 2021

The femoral chordotonal organ of the stick insect Cuniculina impigra Redtenbacher (Phasmida) can be stimulated precisely by moving the receptor apodeme. Single sensory units in the sensory nerve are recorded using glass microelectrodes. The units are classified according to their sensitivity to (a) position, (b) position and velocity and (c) velocity. Nearly all transitional forms exist between the position and velocity receptors. Both elongation- and relaxation-sensitive receptors exist, and also units which are bi-directionally sensitive. Many position receptors have their maximum frequency at one of the extreme joint positions, but others have their maximum frequency near the middle position of the joint. Some velocity-sensitive units respond with equal sensitivity over the whole operating range of the joint, whereas other velocity receptors respond only in a part of the operating range, thus providing further evidence of range-fractionation.
Leg Thrust Important in Flight Take-Off in the Pigeon
Authors: Heppner Frank H. , Anderson John G. T.
Published: April 2021

Measurements of the force generated by the legs of rock doves Columba livia during vertical and near-vertical take-off showed that the birds were able to develop an upward directed force of from 1·3 to 2·3 times their body weight. This force resulted in an instantaneous acceleration of 15·63 m s−2 at maximum thrust. Motion pictures taken during the take-off showed that as the birds’ feet left the experimental perch, their wings were in the overhead clap position. We suggest that the vertical take-off in birds is accomplished in three stages; leg thrust, clap-and-fling and steady-state flight.
The Effects Of Behaviourally Relevant Temperatures On Mechanosensory Neurones Of The Grasshopper, Schistocerca Americana
Authors: Miles Carol I.
Published: April 2021

Grasshopper mechanosensory hair neurones respond to displacement of their associated hairs in a temperature sensitive manner: comparable increases in the number of spikes per stimulus result from increases in temperature with constant stimulus strengths and from increasing stimulus strengths at constant temperature. It is therefore not obvious that neurones in the CNS which receive inputs from mechanosensory hairs would be able to distinguish between these two parameters. The temperatures which populations of mechanosensory hairs on the thorax, head and tarsus experienced were measured in freely moving animals. Animals in thermally heterogeneous environments spent 90% of the accounted time in locations where thoracic temperatures of 32-44 °C were maintained (the behaviourally ‘preferred’ range). Head temperatures covered a wider range, and tarsal temperatures the widest. Different populations of mechanosensory hair neurones exhibited different sensitivities to temperature. Thoracic hair neurones were significantly more temperature sensitive than one of the two populations of head hairs studied, and tarsal hairs exhibited a pronounced temperature compensation in the behaviourally ‘preferred’ range. Wind sensitive head hairs, however, showed exceptionally high temperature sensitivities. There is a negative correlation between the temperature sensitivity of a population of mechanosensory hair neurones and the temperature variability to which those neurones are normally exposed. Implications of this correlation for the central interpretation of mechanosensory input are considered.
Spectral Sensitivity and Photo-Behaviour of the Water Mite Genus Unionicola
Authors: Dimock Ronald V. , Davids Cornelis
Published: April 2021

Behavioural response spectra for phototaxis by four European species of water mites that are differently associated with freshwater mussels were determined. The wavelength for maximal stimulation of positive phototaxis and the corresponding energy threshold, were: 560nm and 3·6 × 10−7μW cm−2 for the free-living species Unionicola aculeata, 560 nm and 2·1 × 10−6μWcm−2 for the commensal U. bonzi, 600nm and 3·3 × 10−6μWcm−2 for the obligate symbiont U. ypsilophora, and 600 nm and 1·3 × 10−5μWcm−2 for the parasitic species U. intermedia. Sensitivity of these water mites to yellow-orange light is consistent with the spectral transmission of their native stream, the water of which readily absorbs wavelengths shorter than 500 nm.

U. intermedia exhibited wavelength-dependent phototaxis, with maximal positive phototaxis occurring in response to 600 nm light and negative phototaxis occurring at 440 nm. This differential photo-behaviour was not attributable to intensity effects. However, the positive phototaxis of this species to 600 nm light became negative when the mite was exposed to the chemical influence of its molluscan host. The spectral sensitivities of this acarine genus suggest the presence of at least two visual pigments within the taxon.
Short Communication Mechanoreceptors in the Fins of the Cuttlefish, Sepia Officinalis
Authors: Kier William M. , Messenger John B. , Miyan Jaleel A.
Published: April 2021

Little is known about mechanoreceptors in cephalopods. The anatomical data are fragmentary; Graziadei (1964) described multipolar nerve cells in the arms of Octopus and the lips of Sepia and similar structures have been described in the mantle of Octopus (Sereni & Young, 1932) and Eledone (Alexandrowicz, 1960). While there is good physiological evidence for the existence of mechanoreceptors in the mantle of Octopus (Gray, 1960; Wilson, 1960; Boyle, 1976), mechanoreception in the mantle and fins of decapods has not been investigated. Here we present physiological evidence that there are receptors along the entire length of the cuttlefish fin that respond to mechanical stimuli. We also identify unusual structures in the fin whose distribution is consistent with their being these receptors.
Fields of View of the Eyes Of Primitive Jumping Spiders
Authors: Land M. F.
Published: April 2021

Most spiders have eight simple eyes, of which one forward-pointing pair (the principal eyes) has a different structure from the other three pairs (the secondary eyes). The principal eyes are often movable, whereas the secondary eyes are fixed. In most jumping spiders (Salticidae) two of the secondary eyes, the postero-median pair, are so reduced that they seem to be vestigial, and their fields of view overlap those of the other secondary eyes (the antero-and postero-laterals) (Homann, 1928; Land, 1969a; Eakin & Brandenburger, 1971). However, in certain supposedly primitive Salticid sub-families the postero-median eyes are comparable in size with the other secondary eyes, and would appear to play a more equal part in the function of the secondary eye system, which is the detection of movement (Land, 1972). The origins of the Salticidae are something of a mystery, and it is therefore of considerable interest to see whether the fields of view of the eyes of these primitive sub-families give any clue that might indicate to which of the other spider families the Salticidae might be linked. The form of the fields of view appears to be a conservative feature in spider evolution (Land, 1985), just as does the layout of the eyes themselves. The anatomy and ultrastructure of these eyes have been described before (Blest, 1983, 1984, 1985; Blest & Sigmund, 1984) and the systematic position of the sub-family considered here, the Spartaeinae, is discussed by Wanless (1984).
Jamming Avoidance in the Electric Fish Eigenmannia: Harmonic Analysis of Sexually Dimorphic Waves
Authors: Kramer Bernd
Published: April 2021

The present report shows an intraspecific, sexually dimorphic variation in harmonic content and waveform, as well as intensity, of the Electric Organ Discharges (EODs) in the green knife fish, Eigenmannia (Figs 2, 11). There is a close correlation between harmonic content of the EODs and waveform (as defined by the ratio of intervals between zero-crossings in the two half-waves of one EOD cycle; Fig. 3). The aim of the following experiments was to determine whether the fish are sensitive to differences in stimulus waveform or harmonic content. Stimulation with electric fields of various waveforms but equal peak-to-peak amplitudes at frequencies close to the fish’s frequency elicited the Jamming Avoidance Response (JAR) which is an EOD frequency change increasing the frequency difference (Watanabe & Takeda, 1963). The strength of JARs to distorted square wave and sawtooth stimuli was 25% smaller than that elicited by sine wave stimuli (Fig. 6). Undistorted square waves elicited stronger responses than sine waves, while undistorted sawtooth waves were the least effective (Table 1). The differences in response strength were proportional to differences in the intensity of the fundamental frequency or first harmonic, fi, of the stimulus waveforms. Subharmonic stimuli of nine artificial or synthesized natural waveforms at frequencies near one-half or one-third of the EOD resting frequency elicited responses only when a strong higher harmonic, or overtone, of the stimulus was close to the EOD fundamental frequency (Fig. 7). Stimuli of different waveforms, but identical spectral amplitudes, elicited similar responses not significantly different from each other, at stimulus frequencies near one-half (Table 3) and near the EOD resting frequency (Fig. 10). Eigenmannta’s JARs to synthesized male EODs at frequencies close to the fish’s frequency were weaker than those to female EODs of equal peak-to-peak amplitude. The weaker response was proportional to the weaker intensity of the first harmonic of the male EOD (Fig. 12). A stimulus frequency near one-half of the EOD baseline frequency evoked opposite results, as the second harmonic, f2, of the male EOD was relatively four times stronger than that of the female EOD (Table 4). Eigenmannia responded to jamming signals as if it performed a limited spectral amplitude (Fourier) analysis, determining the intensity of that stimulus harmonic (at least up to the third) enclosed within a narrow frequency band centred on its own EOD fundamental frequency. The assessment of that harmonic was independent of stimulus waveform, peak-to-peak amplitude, or power, demonstrating linear filtering of the stimulus wave. Because of Eigenmannia’s sensitivity to the harmonic content of the stimulus wave, as also demonstrated in subharmonic experiments, the natural variation of EODs in harmonic content may serve in species and mate recognition.
Locomotion of Hermit Crabs (Coenobita Compressus) on Beach and Treadmill
Authors: Herreid Clyde F. , Full Robert J.
Published: April 2021

Coenobita compressus (H. Milne Edwards) walk forward on six legs using an alternating tripod gait similar to that of insects. The first walking leg provides the driving force for locomotion aided secondarily by the second walking leg, while the chelipeds act largely as supports. The left appendages are longer and heavier than the right, and they extend further laterally from the midline during their stride, thus compensating for the asymmetry of the crab which has a dextrally coiled shell and an abdomen displaced to the right. The abdomen is normally carried off the ground, but it is dragged when the shell is large.

Bilateral leg autotomy alters gait patterns; usually a diagonal quadrupedal gait was adopted. Walking was poor in crabs without chelae (L1 and R1) because of problems of balance. Crabs without their first walking legs (L2 and R2) were the most accomplished amputee walkers. Crabs lacking legs L3 and R3 showed the most gait diversity.

Velocity of travel is a function of crab size and the substrate walked upon. Large crabs travel faster than small ones on the beach by increasing their stride length rather than stepping frequency. Studies on a miniature treadmill showed individual crabs change velocity by changing both stepping frequency and stride length.

Snail shells of the genus Nerita are carried; they are the lightest shells on the beach. Shell mass for an individual may vary three-fold, but usually the masses of the shell and crab are similar. Crabs running with and without shells have the same step frequency and stride length.
Responsiveness of the Parotid Salivary Gland of Red Kangaroos (Macropus Rufus) to Mineralocorticoids
Authors: Beal A. M.
Published: April 2021

During both acute and chronic mineralocorticoid administration, parotid saliva was obtained by acetylcholine stimulation at rates of 1·0–1·5 ml min−1 from anaesthetized red kangaroos. The Na/K ratio of saliva from chronically Na-replete kangaroos was virtually unaltered by ipsilateral intracarotid infusion of aldosterone at rates of 8, 40 or 80μgh−1 for 4h, the ratio falling from 20·1 ± 1·09 to 17·5 ± 0·53 (t6 = 2·07; NS) at 80μgh−1. Kangaroos given intramuscular injection of the mineralocorticoid, deoxycorticosterone (DOCA), at rates of 0· 25 or 0· 30mgkg−1 12h−1 showed a progressive fall in salivary Na/K ratio from 19· 1 ±0· 47 to 1· 76 ± 0· 41 (t5 = 27· 4; P<0· 001) over the 21-day period of injection. The DOCA treatment caused hypertrophy of the ducts, particularly the intralobular ducts of the parotid gland. Aldosterone acetate given intramuscularly at 0· 03 mg kg−1 12h−1 for 10 days also reduced the Na/K ratio of the saliva. As soon as the salivary Na/K ratio had returned to replete values, some 3– 4 days after cessation of the DOCA injections, the kangaroos were given a 5-h infusion of aldosterone. Intracarotid infusion of aldosterone at 8 μgh−1 produced a near maximal fall in salivary Na/K ratio after 3 h of infusion, and increasing the infusion to 80μgh−1 had little additional effect. The minimum Na/K ratio obtained at this time was 5· 7 ± 1· 04 (t5 = 14· 21 ; P< 0· 001), which was equivalent to the ratio obtained at 3– 6 days of DOCA injection. Significant regression of the intralobular ducts occurred during the 3 days following cessation of DOCA administration; 24 days after the end of DOCA treatment duct development was approaching that of Na-replete, untreated kangaroos.

The results demonstrate that the parotid glands of kangaroos from a sodium-rich environment are almost unable to respond to acute fluctuations in endogenous aldosterone levels; that chronically high levels of mineralocorticoids cause hypertrophy of the sodium-transporting ducts of the parotid gland, which results in an increasing ability to reduce the Na/K ratio of the saliva; and that responsiveness to mineralocorticoids declines rapidly in the absence of high mineralocorticoid levels due to regression of the ducts.
Respiration Beneath Desert Sand: Carbon Dioxide Diffusion and Respiratory Patterns in A Tenebrionid Beetle
Authors: Louw G. N. , Nicolson S. W. , Seely M. K.
Published: April 2021

The massive dune sea of the southern Namib Desert is approximately 800 km in length and some 140 km wide. These dunes are among the highest in the world and, in spite of very sparse vegetation cover, they support a surprising variety of reptiles and arthropods (Koch, 1961 ; Louw & Seely, 1982). A feature of the arthropod fauna is the high species diversity of flightless tenebrionid beetles. These beetles do not construct burrows, but swim through the sand as if it were a fluid medium. For a description of the physical properties of dune sand see Lancaster (1981). Among the tenebrionids, Onymacris unguicularis is of special interest because it engages in fogbasking on the crests of the dunes when intermittent condensing fog occurs in the desert (Hamilton & Seely, 1976). This beetle occurs almost exclusively on the high slip-faces of the dunes, where it feeds on wind-blown plant detritus. To escape extremely high surface temperatures during midday and very low temperatures at night, O. unguicularis submerges beneath the sand to a depth of 5–10 cm for as much as 18 h per day (Seely, Mitchell & Louw, 1985). The present study assesses the respiratory consequences of such submergence by measuring the diffusion rate of carbon dioxide through a 5-crn layer of sand and the respiratory patterns, carbon dioxide production, and oxygen consumption of the beetles.
The Physiology of Wandering Behaviour in Manduca Sexta: III. Organization of Wandering Behaviour in the Larval Nervous System
Authors: Dominick Oliver S. , Truman James W.
Published: April 2021

The locomotor patterns typical of wandering behaviour were studied electro-myographically in abdominal segments of freely moving larvae of Manduca sexta. Crawling locomotion consisted of stereotyped, anteriorly-directed, peristaltic waves of intersegmental muscle contraction. During burrowing the intersegmental muscles of all abdominal segments contracted simultaneously for several consecutive cycles and then performed a single bout of the crawling pattern. Sensory inputs determined which motor patterns were used and how they were modified. Local sensory inputs could modify patterns in the specific segments affected. The neural circuitry that was required to generate the peristaltic and bracing patterns was repeated among the thoracic and abdominal ganglia, and normally was activated by the suboesophageal ganglion (SEG) and brain. In the absence of connections with the SEG and brain the segmental motor pattern generators could be activated by strong sensory stimuli. When the thoracic and abdominal segments lacked connections with the SEG, spontaneous movements were infrequent prior to wandering, but increased markedly at wandering or following 20-hydroxyecdysone (20-HE) infusion. Prior to wandering the SEG drives spontaneous locomotion in debrained larvae, but this function disappears in wandering larvae, or following 20-HE infusion. Prior to wandering the brain exerted a net inhibitory influence on locomotion. Removal of the medial region of the brain abolished this inhibition, resulting in strong, continuous locomotion which was driven by the lateral region of the brain. This lateral excitatory function of the brain was not altered by 20-HE infusion prior to wandering, nor did it change with the appearance of wandering behaviour. We conclude that the locomotor patterns used during wandering are produced by pattern generators in the segmental ganglia and are modified by sensory information. The circuitry responsible for activating these motor pattern generators is associated with the SEG, and is under the control of the brain. The brain exerts a net inhibitory influence prior to wandering, which becomes excitatory during wandering. Ecdysteroids appear to alter locomotor function by acting at various levels including the segmental ganglia, the SEG and the brain. A model is advanced describing this effect.
Motion of Magnetotactic Microorganisms
Authors: S. Esquivel Darci Motta , De Barros Henrique G. P. Lins
Published: April 2021

Magnetic moments for different magnetotactic microorganisms are obtained by electron microscopic analyses and studies of cell motion by optical microscopy. The results are analysed in terms of a model due to C. Bean. The considerations presented suggest that magnetotaxis is an efficient mechanism for orientation only if the time for reorientation is smaller than the mean time of environmental perturbations.
Function of the Epithelial Channel Cells of the Body Wall of A Terrestrial Slug, Ariolimax Columbianus
Authors: Martin A. W. , Deyrup-Olsen I.
Published: April 2021

The body wall of the land slug Ariolimax columbianus Gould (Arionidae) secretes fluid in response to mechanical stimulation. This fluid is a product of specialized channel cells, with addition of mucus. Channel cell function can be explained in terms of ultrafiltration of blood components into the central channel, and modification of this ultrafiltrate, prior to extrusion from the body surface, by cellular transport of univalent ions but without change in osmotic pressure. Sodium and chloride ions are conserved, and potassium and bicarbonate ions are transferred out into the channel cell product. Agents known to affect epithelial transports and ion processing in a variety of animals - ouabain, amiloride, furosemide, SITS and acetazolamide - depress the function of the slug channel cells.
Effect of Experimental Ventilation of the Skin On Cutaneous Gas Exchange in the Bullfrog
Authors: Burggren Warren W. , Feder Martin E.
Published: April 2021

The significance of skin ventilation to cutaneous gas exchange in vertebrates has seldom been recognized. Unlike the lungs and gills, the skin lacks a dedicated ventilatory pump, and most analyses have implicitly or explicitly ignored skin ventilation because the skin is in contact with an ‘infinite pool’ (Piiper & Scheid, 1977) of respiratory medium. For example, models of gas exchangers consider amphibian skin to have an infinite ventilatory conductance (e.g. Piiper & Scheid, 1977) and in experimental studies the respiratory medium is often stirred thoroughly (e.g. Gottlieb & Jackson, 1976; Burggren & Moalli, 1984), which may eliminate any impact of ventilatory inadequacy upon cutaneous gas exchange. Indeed, as discussed by Piiper (1982) and Feder & Burggren (1985), most previous analyses have not accounted for ‘stratification’ or ‘diffusion boundary layers’ about the skin, which theoretically may limit cutaneous gas exchange, especially in still water. Skin ventilation may be important in dissipating such boundary layers, and several skinbreathing vertebrates have particular behaviour patterns that might serve this function (reviewed by Feder & Burggren, 1985). However, there is no direct experimental evidence that the movement of respiratory medium across the skin can affect cutaneous gas exchange.
Muscarinic Response In Rat Lacrimal Glands
Authors: Marty A. , Evans M. G. , Tan Y. P. , Trautmann A.
Published: April 2021

A large variety of responses has been uncovered by recent investigations of conductance changes elicited by muscarinic agonists. In exocrine glands, the permeability to K+, Cl− and Na+ ions is increased, and internal Ca2+ serves as a second messenger. Patch-clamp analysis of the secreting cells has revealed three types of Ca2+-dependent channels, which are respectively selective for K+, for Cl−, and for monovalent cations. The channels differ in their sensitivity to the internal Ca2+ concentration, Ca,. K+-selective channels are partially activated at rest, with Ca, approx. 10 nmol I−1; Cl−-selective channels are activated between 100 nmol l−1 and 1 μmoll−1; activation of cationic channels requires micromolar Ca, levels.

Cell-attached recordings, performed either on isolated cells or on cell clusters, show an activation of all three channel types upon application of acetylcholine. In whole-cell recordings, mostly K+-and Cl−-selective channels are activated. The cell currents display slow oscillations linked to variations of Ca,. Whole-cell currents rise after a delay of approx. 1 s, and decay with a time constant of approx. 0·7 s upon removal of acetylcholine. They do not depend on extracellular Ca2+.

The recent demonstration that Ca2+-dependent currents can also be obtained when dialysing the cells with inositoltrisphosphate or with GTPγS, a non-hydrolysable analogue of guanosine triphosphate, opens promising leads to an analysis of intracellular events regulated by acetylcholine.
Allosteric Effects of Mg2+ on the Gating of Ca2+-Activated K+ Channels From Mammalian Skeletal Muscle
Authors: Golowasch Jorge , Kirkwood Alfred , Miller Christopher
Published: April 2021

Ca2+-activated K+ channels from rat muscle transverse tubule membranes were inserted into planar phospholipid bilayers, and the activation of these channels by Ca2+ was studied. On the cytoplasmic side of the channel, calcium ions (in the range 10–100μmol l−1) increase the opening probability of the channel in a graded way. This ‘activation curve’ is sigmoid, with an average Hill coefficient of about 2. Magnesium ions, in the range 1–10 mmol l−1, increase the apparent affinity of the channel for Ca2+ and greatly enhance the sigmoidicity of the Ca2+ activation curve. In the presence of 10 mmol l−1 Mg2+, the Hill coefficient for Ca2+ activation is about 4·5. This effect depends upon Mg2+ concentration but not upon applied voltage. Mg2+ is effective only when added to the cytoplasmic side of the channel. The results argue that this high-conductance, Ca2+-activated K+ channel contains at least six Ca2+-binding sites involved in the activation process.
The Activity of the Horizontal Semicircular Canal of the Dogfish, Scyllium Canicula
Authors: Löwenstein Otto , Sand A.
Published: April 2021

Oscillographic records from the horizontal ampulla of the dogfish show: (a) A spontaneous discharge of impulses when the fish is stationary in the normal position. (b) An increased discharge during ipsilateral rotation. (c) A diminution of the spontaneous discharge during contralateral rotation. (d) A prolonged after-discharge on stopping contralateral rotation. The threshold for the responses is an angular acceleration of the order of 11° per sec2. This mechanism provides a means of signalling to the centre equal and opposite phases of a biphasic physical change. The two opposite ampullae work antagonistically, and the reflex responses of the normal fish depend upon the balance of the afferent discharges from the left and right labyrinths.
Short Communication: Distribution of Ion Channels in the Membrane of the DinoflagellateNoctiluca Miliaris
Authors: Oami Kazunori , Naitoh Yutaka , Sibaoka Takao
Published: April 2021

Noctiluca miliaris, a marine dinoflagellate, exhibits spontaneous flexion of its tentacle. The movement of the tentacle is always accompanied by perturbations of membrane potential, termed the ‘tentacle regulating potentials’ (TRPs) (Eckert and Sibaoka, 1967). Though the waveform of the TRPs is liable to variation, it consists of four successive basic components: (1) a Na+-dependent depolarizing (positive) spike, (2) a depolarizing plateau potential, (3) a Cl−-dependent hyperpolarizing (negative) spike, and (4) a long-lasting hyperpolarization (Eckert and Sibaoka, 1967; Oami et al. 1988). A slow flexion of the tentacle is seen during the plateau, and the flexion is suddenly accelerated when the negative spike occurs. The tentacle then extends during the long-lasting hyperpolarization. There is no correlation between the positive spike and the tentacular movement (Hisada, 1957; Oami et al. 1988).
Muscle Recruitment During Terrestrial Locomotion: How Speed and Temperature Affect Fibre Type Use in a Lizard
Authors: Jayne Bruce C. , Bennett Albert F. , Lauder George V.
Published: April 2021

Synchronized electromyography and cinematography were used to study the activity of the red and white regions of the iliofibularis muscle in savannah monitor lizards, Varanus exanthematicus (Bosc), during locomotion. Analysis of variance on results from four individuals moving at speeds of up to 1.5 km h−1 at two body temperatures (25 and 35 °C) revealed that all kinematic variables were significantly affected by speed but none was affected by temperature. Hence, patterns of limb movement at any speed were similar at both temperatures. However, this similarity resulted from differences in muscle activity. Analysis of variance on electromyographic variables for activity in the red and white regions showed widespread significant effects of both temperature and speed. The red region was active at all speeds, and it displayed regular bursts of activity which usually occurred when the foot was above the ground, the femur was being abducted and the knee flexed. Variables measuring the intensity of red region activity generally increased with speed until a maximum was attained and no further change occurred with additional increases in speed. The speed at which maximum red activity was attained at 25 °C was less than that at 35 °C. For equal locomotor speeds, amplitudes of electromyograms (EMGs) from the red region at 25 °C were greater than those at 35°C. In contrast to the red region, the white region was active only above some threshold speed, and activity was often rather irregular compared to that of the red region. At 25°C the threshold speed for recruitment of the white region (0.9kmh−1) was less than that at 35°C (1.3kmh−1). The relationship between locomotor speed and activity per minute for the red region was very similar to the relationship between speed and rate of oxygen consumption described in previous studies of lizards, and the threshold speed for recruitment of the white region was also similar to the maximal aerobic speed previously reported for this species. Hence, lizards increase speed and compensate for lower temperature by increasing intensity of activity within the red region and recruiting fibres in the white region. We suggest that compensation for muscle function at decreased body temperature may involve recruitment of greater numbers of motor units.
Nitrite and Red Cell Function in Carp: Control Factors for Nitrite Entry, Membrane Potassium Ion Permeation, Oxygen Affinity and Methaemoglobin Formation
Authors: Jensen Frank B.
Published: April 2021

Red cell function was studied in carp by a combination of in vivo and in vitro experiments with nitrite as the perturbing agent. In vivo accumulation of nitrite caused a marked increase in the red cell methaemoglobin content, and reduced the mean cellular volume. The oxygen affinity of unoxidized haemoglobin was strongly decreased, partly as result of the elevated concentration of cellular nucleoside triphosphates and haemoglobin associated with red cell shrinkage. Red cell pH was unchanged compared to controls, but reduced when referred to constant extracellular pH and O2 saturation. The mean cellular K+ content decreased, reflecting a K+ loss from the red cells during their shrinkage. This K+ loss contributed significantly to the large plasma hyperkalaemia during nitrite exposure. In vitro experiments revealed that nitrite influx into deoxygenated red cells was much larger than into oxygenated red cells. Nitrite permeation of the red cell membrane was not inhibited by DIDS and did not change extracellular pH. Methaemoglobin (MetHb) formation was more pronounced in deoxygenated blood than in oxygenated blood, but quasi-steady states were reached, reflecting a balance between nitrite-induced MetHb formation and the action of MetHb reductase. Red cells incubated in the oxygenated state released K+, whereas a net K+ uptake occurred in deoxygenated cells. Nitrite did not change the K+ loss from oxygenated cells, but shifted the K+ uptake in deoxygenated cells to a pronounced K+ release by the time high MetHb levels were reached. Both types of red cell K+ release were inhibited by DIDS and appeared to occur via a route involving Band 3. The data are consistent with the hypothesis that a significant DIDS-sensitive K+ efflux from the red cells occurs whenever a large fraction of the haemoglobin molecules assumes an R-like quaternary structure.
Decreased Sprint Speed as A Cost of Reproduction in the LizardSceloporus Occidentals:Variation Among Populations
Authors: Sinervo Barry , Hedges Richard , Adolph Stephen C.
Published: April 2021

Decreased mobility of gravid females is thought to be an important cost of reproduction in lizards. We measured sprint speeds of female western fence lizards (Sceloporus occidentalis Baird and Girard) before and after they had oviposited. Females from two California populations were about 20% slower when gravid, females from an Oregon population were about 30% slower, and females from a Washington population were about 45 % slower, compared to their speeds after recovering from reproduction. The decrease in sprint speed persisted for several weeks after oviposition, suggesting that reproduction impairs sprint performance by affecting body condition in addition to the burdening effect of eggs.

Oregon and Washington females carried more mass (both somatic and clutch mass) per unit body length than California females. On the shorter bodies of Oregon and Washington lizards, eggs may interfere with the mechanics of running, in addition to their effect on the total mass of the female. In addition, gravid females from Washington had significantly higher reproductive investment (mass of clutch relative to the mass of the female after oviposition) than Oregon and California populations. Greater reproductive investment by Washington females increases, the burden carried per unit of body length; we suggest this further impairs sprint performance.

Decrements in sprint speed were not significantly correlated with level of reproductive investment (per unit body mass) among females within any of the study populations. However, the burden carried per unit body length was correlated with the sprint speed decrement among gravid females from Oregon. Comparisons within and among populations suggest that differences in morphology among northern and southern populations interact with reproductive investment to produce interpopulation differences in sprint performance for gravid females.