bluuebunny/crossref_metadata_2025 huggingface dataset:
Metabolic Heat Dissipation and Internal Solute Levels of Artemia Embryos During Changes in Cell-Associated Water
Authors: Glasheen J. S. , Hand Steven C.
Published: April 2021

Embryos (cysts) of the brine shrimp Artemia enter a profound, yet reversible, state of metabolic arrest in response to cellular dehydration. We have monitored metabolic activity during this transition in embryos from the Great Salt Lake population by using microcalorimetric measurements of heat dissipation. Embryo hydration states can be precisely controlled by immersing cysts in solutions of varying ionic strength. When developing embryos were incubated in a 2·0 mol 1−2 NaCl solution, heat dissipation fell after 20 h to 1·13 mW g−2 dry mass, or 21 % of the value obtained when embryos were in control solutions of 0·25 mol 1−2. At higher ionic concentrations, heat dissipation declined to as low as 3 % of control values. Recovery from dehydration was rapid. Energy flow increased to 135 % of control values within 2h after returning cysts to the control medium.

These metabolic transitions were correlated with embryo hydration levels measured across the same dehydration series. Total cyst water ranged from 112 ± 2·6 g H2O 100 g−2 dry mass in 0·25 mol 1−2 NaCl to 46 ± 0·6gH2O 100 g−2 dry mass in 5·0 mol 1−2 NaCl. At the first point where heat dissipation was markedly suppressed (the 2·0 mol 1−2 incubation), cyst water content was 72·8±0·9gH2O 100g−2drymass. This water content is similar to the ‘critical’ hydration level required to suppress carbohydrate catabolism and respiration in San Francisco Bay Artemia embryos (Clegg, 1976a,b). However, hydration characteristics of the two populations differed in solutions of lower ionic concentration.

Total osmotic pressure in fully hydrated cysts was 1300 mosmolkg−2H2O. A comprehensive inventory of the internal osmolytes indicated that inorganic ions (Na+, K+, Cl-, Mg2−2-, Ca2+, Pi) accounted for 21 % of the osmotic activity and 1·48% of embryo dry mass. Organic solutes (trehalose, glycerol, ninhydrinpositive substances, and trimethylamine-N-oxide+betaine) contributed 60% of the osmotic pressure and 22% of the dry mass. Macromolecular components (protein, lipids, glycogen and DNA) were also quantified and formed the bulk of embryo mass. Taken together, 97·4% of the cyst dry mass was identified. At the cellular dehydration state promoting metabolic arrest, the concentrations of inorganic and organic osmolytes were 480–590 mmol kg−2H2O and 1200–1480 mmol kg−2 H2O, respectively. The influence of these osmolyte concentrations is considered in the context of macromolecular assembly and metabolic control.
Basic functional properties of the cardiac muscle of the common shrew (Sorex araneus) and some other small mammals
Authors: Vornanen M.
Published: April 2021

The resting heartbeat frequency of all the studied wild small mammals (body mass 3–20 g) was lower than that predicted by the allometric equation for a typical mammal. The heart rate of the laboratory mouse was a little higher than the expected value.

The ventricular mass of the small wild mammals was higher than predicted for their size, but that of the laboratory mouse was below the expected value. Thus, adequate cardiac output in the wild small mammals is achieved by compensating the low heartbeat frequency with greater stroke volume. The shrew species are notable exceptions, which, despite having a metabolic rate 2–3 times higher than the mammalian average, neither have exceptionally high heart rates nor larger hearts than other wild small mammals.

The adaptation of the shrew heart to high metabolic rate may reside in the shape of heart. The ventricular myocardium of shrews is characteristically long and narrow with a tapered apex, whereas other small mammals have rounder hearts.

The duration of the ventricular action potential was short and inversely proportional to the resting heart rate of the mammalian species. Caffeine (5 mmol l−1) strongly decreased the isometric contractile force of right ventricular strips in all the studied mammals. These findings suggest that in the small mammals intracellular stores are the main source of activating Ca2+, whereas transsarcolemmal Ca2+ movement may only serve the triggering function.
Cold tolerance mechanisms of the free-living stages of Trichostrongylus colubriformis (Nematoda)
Authors: Wharton D. A. , Allan G. S.
Published: April 2021

All free-living stages of the nematode parasite of sheep, Trichostrongylus colubriformis Giles, survived exposure to freezing temperatures in contact with water, with the exception of the first-stage juvenile (JI). The third-stage juvenile (J3) was the most resistant stage. The order of relative survival of the different stages was different from that of the lowest Fx (the temperature at which 50 % froze), suggesting that an ability to supercool was not the only determinant of survival. The F50 was shown to be a good measure of the degree of supercooling and to extend greatly the lower size limit of organisms that could be measured. The J3 uses a freeze-avoiding strategy by supercooling when in air or covered by liquid paraffin. In water it uses a mixture of freeze-avoiding and freeze-tolerant strategies, with a proportion of the population surviving freezing caused by exogenous ice nucleation. Removal of the J3 sheath results in a shift from freeze avoidance to freeze tolerance, with an overall reduction in survival. A major function of the sheath may be to reduce the probability of exogenous ice nucleation.
Serotonin differentially modulates two K+ currents in the Retzius cell of the leech
Authors: Acosta-Urquidi Juan , Sahley Christie L. , Kleinhaus Anna L.
Published: April 2021

The effects of 100 μmol I−1 serotonin (5-HT) were investigated on the Na+- and Ca2+-dependent action potential and distinct K+ currents in the Retzius (R) cells of the hirudinid leeches Macrobdella decora and Hirudo medicinalis by conventional current-clamp and two-microelectrode voltage-clamp techniques.

In normal Na+-containing Ringer, 5-HT decreased the duration of the action potential prolonged by 5 mmol I−1 tetraethylammonium (TEA+) chloride. In Na+-free saline containing 25μmol I−1 TEA+ to block IK, 5-HT reduced the amplitude and duration of Ca2+ spikes evoked by intracellular current injection. Under voltage-clamp, 5-HT enhanced the peak amplitude of an early transient 4-aminopyridine (4-AP)-sensitive, voltage-dependent outward current, termed IA-A small but significant increase in the time constant of inactivation (τoff) of IA was also measured after exposure to 5-HT. 5-HT suppressed the peak and steady-state amplitudes of a delayed TEA+-sensitive, voltage-dependent outward current, termed IK.

These results demonstrate differential simultaneous modulation of distinct K+ currents in the Retzius cell of the leech by the endogenous transmitter serotonin. These cells contain and release 5-HT, and are believed to be multifunction neurons implicated in feeding and swimming. This modulation may change the excitable properties of the cell, leading to a negative feedback autoregulation of its transmitter output.
Separation of Hydrogen Ion Currents in Intact Molluscan Neurones
Authors: Mahaut-Smith M. P.
Published: April 2021

The amplitude and rate of activation of the voltage-dependent H+ pathway in intact Helix neurones were investigated using standard two-electrode voltage clamp techniques. Na+ and K+ currents were inhibited by a Na+-free, tetraethylammonium (TEA+) (low-Cl−) saline and by use of Cs+-filled electrodes. Ca2+ currents were abolished by holding the membrane at –15 to –10 mV. Depolarizing voltage pulses from these low potentials activated outward currents whose tail current reversal potential shifted with changes in intracellular and extracellular pH, but not with changes in external KC1; thus these remaining currents are carried by hydrogen ions. Furthermore, the amplitude of the voltage-dependent outward current increased as the outward gradient for H+ was increased and a rise in pHi shifted the activation towards negative potentials. At physiological pH levels, H+ currents were typically 60 nA at 30 mV (cell diameter 200–250 μm). H+ currents were rapidly activated; the time to half maximal current at 30 mV was less than 5 ms in the pHi range tested (7·4–0·9) (pHe 7·4). The H+ pathway will therefore be activated by individual action potentials and may play an important role in pH homeostasis during intense neural activity.
Strain, Muscle Length and Work Output in a Crab Muscle
Authors: Josephson Robert K. , Stokes Darrell R.
Published: April 2021

The relationships between muscle length, fractional change in length (strain) and work output during cyclic contraction were examined in scaphognathite levator muscle L2B of the green crab Carcinus maenas (L.). The muscle was subjected to sinusoidal strain at 2 Hz and to phasic stimulation in the strain cycle.

At an average length and stimulus phase which are optimum for net work output, the work from muscle L2B during shortening rises to a peak or a plateau with increasing strain. The failure of shortening work to increase continuously with strain is due, in part, to the greater shortening velocity associated with greater strain, and to the consequent reduction in muscle force during shortening at higher velocity. The work required to re-lengthen a muscle following contraction is a complex function of strain, with an initial peak followed by a work minimum and then a monotonic rise in work with further increase in strain. The early work minimum is a result of shortening inactivation which reduces muscle force and thus the work which must be done to re-lengthen the muscle. Because shortening work rises to a peak or plateau with increasing strain while lengthening work, for the most part, increases with strain, there is a sharp optimum strain (about 8 %) for net work output.

Muscle relaxation becomes slower with increasing muscle length. As muscle length is increased, fusion of tension from cycle to cycle becomes more pronounced and shortening inactivation becomes a more important determinant of optimum strain.
The Effect of Zinc on Calcium and Hydrogen Ion Currents in Intact Snail Neurones
Authors: Mahaut-Smith M. P.
Published: April 2021

The effects of external Zn2+ on Ca2+ and H+ currents in the soma of intact Helix neurones were investigated using standard two-electrode voltage-clamp procedures. Cells were exposed to a 0Na+, tetraethylammonium (TEA+) saline and clamped with Cs+-filled electrodes, which allows separation of voltagedependent H+ and Ca2+ currents using different holding potentials. Outward H+ currents, activated by depolarizations from holding potentials in the range −15 to −10 mV, were rapidly blocked by low concentrations of external Zn2+ with a Kd of approximately 16/zmoll-1. H+ current activation was also markedly slowed and the block was slow to reverse. Ca2+ currents, largely free from contamination by outward current, were activated by small depolarizations from a holding potential of −55 mV. Ca2+ currents were reduced by Zn2+, but the Kd for block was more than 80 times greater than for block of H+ currents. Thus, low concentrations of Zn2+ provide a method of selectively inhibiting H+ current in studies of Ca2+ current. This was demonstrated in cells which slowly acidified following exposure to 0Na+, TEA+ saline, leading to an increased outward H+ current. Washing with low concentrations of Zn2+ blocked the H+ current and uncovered the underlying Ca2+ current. The results also suggest that Zn2+ will be a useful tool in studies of the physiological role of the H+ pathway.
Influence of Pregnancy on Behavioral Thermoregulation in the Northern Pacific Rattlesnake Crotalus Viridis Oreganus
Authors: Gier Paul J. , Wallace Richard L. , Ingermann Rolf L.
Published: April 2021

Incubation within appropriate thermal limits is important for the normal development of the reptilian embryo (Maderson & Bellairs, 1962; Fox et al. 1966; Osgood, 1978; Burger et al. 1987). Among the viviparous reptiles in which the optimum temperature for embryonic development differs from the temperature of optimum activity in the adult, one would predict a shift in thermoregulatory behavior of the pregnant female. We have examined the influence of pregnancy on the thermoregulatory behavior of the northern Pacific rattlesnake (Crotalus viridis oreganus) to test this prediction.
Mechanical Properties and Morphological Correlates of Fragile Skin in Gekkonid Lizards
Authors: Bauer Aaron M. , Russell Anthony P. , Shadwick Robert E.
Published: April 2021

The mechanical properties of gekkonid lizard skin are investigated for the first time. Although the skin of certain geckos, such as Gekko gecko, behaves in ‘typical’ vertebrate fashion, that of others, such as Ailuronyx seychellensis, exhibits unusual properties associated with identifiable morphological specializations. Light and scanning electron microscopy reveal that Ailuronyx dermis is functionally bilayered; the stratum compactum is divided into inner and outer layers by intervening loose connective tissue. The inner layer is strong and tough and does not differ significantly in its properties from that of Gekko gecko whole skin. The much thicker outer layer, however, is only 1/20 as strong and 1/50 as tough as the inner layer, and exhibits preformed zones of weakness. In nature, Ailuronyx parts with considerable portions of the outer components of the skin as an antipredator escape mechanism. Skin samples from 17 additional gecko species varied considerably in their strength, stiffness and toughness. None of the forms with tough skin employs regional integumentary loss as a predator escape strategy. Weak skin alone is not sufficient to permit regional integumentary loss, as the capability to lose the skin involves not only inherent properties of the tissue, but also features of the mechanical interaction of skin layers with one another and with the underlying body wall.
Computing motion in the primate’s visual system
Authors: Koch C. , Wang H. T. , Mathur B.
Published: April 2021

Computing motion on the basis of the time-varying image intensity is a difficult problem for both artificial and biological vision systems. We will show how one well-known gradient-based computer algorithm for estimating visual motion can be implemented within the primate’s visual system. This relaxation algorithm computes the optical flow field by minimizing a variational functional of a form commonly encountered in early vision, and is performed in two steps. In the first stage, local motion is computed, while in the second stage spatial integration occurs. Neurons in the second stage represent the optical flow field via a population-coding scheme, such that the vector sum of all neurons at each location codes for the direction and magnitude of the velocity at that location. The resulting network maps onto the magnocellular pathway of the primate visual system, in particular onto cells in the primary visual cortex (VI) as well as onto cells in the middle temporal area (MT). Our algorithm mimics a number of psychophysical phenomena and illusions (perception of coherent plaids, motion capture, motion coherence) as well as electrophysiological recordings. Thus, a single unifying principle ‘the final optical flow should be as smooth as possible’ (except at isolated motion discontinuities) explains a large number of phenomena and links single-cell behavior with perception and computational theory.
The evolution of complex sensory systems in mammals
Authors: Kaas J. H.
Published: April 2021

Much of the forebrain of many extant species of mammals appears to be sensory-perceptual in nature. Thus, much of the forebrain, especially the dorsal thalamus and neocortex, consists of nuclei and areas that are parts of complex systems that analyze sensory information and allow behavior to be guided by accurate inferences about the external world. Since mammals vary tremendously in brain size, they vary in the amount of tissue devoted to sensory processing. In addition, mammals vary in the sizes and numbers of processing nuclei and areas, and in how neurons and neuron groups (modules) are differentiated within such structures. Sensory-perceptual systems with more, larger and more differentiated parts may allow more stimulus parameters to be considered, experience to play a greater role, and speed calculations through increased parallel processing.

The evolution of species differences in brain size, the sizes of individual parts, and internal structure of these parts are potentially understandable within a theoretical framework of gradual modifications of developmental processes. In addition to changes in the generation and specialization of neurons, alterations in the developmental timing that modify internal and external influences on neuron activity patterns seem to have a major role in the construction and maintenance of organization in the nervous system. Because similar selection pressures may arise over and over again and the mechanisms for producing changes may be few, similar changes in the nervous system are likely to occur in independent lines of evolution.

It is uncertain how new cortical areas and nuclei evolve. Comparative studies suggest that: (1) all mammals have a few basic sensory areas and nuclei in common, (2) the number of areas and nuclei has increased independently in several lines of mammalian evolution, and (3) new areas have been added to the middle levels of cortical processing sequences. New areas and nuclei may have evolved as a result of sudden duplications and/or by the process of single areas or nuclei gradually differentiating into two or more areas or nuclei. The process of gradual differentiation may have involved the initial step of differentiating functionally distinct classes of cells that are mixed in a representation, followed by the local groupings of such cells into functionally distinct sets, and finally the fusion of cell groups of the same types to form separate representations.
The role of sensory adaptation in the retina
Authors: Laughlin S. B.
Published: April 2021

Adaptation, a change in response to a sustained stimulus, is a widespread property of sensory systems, occurring at many stages, from the most peripheral energy-gathering structures to neural networks. Adaptation is also implemented at many levels of biological organization, from the molecule to the organ. Despite adaptation’s diversity, it is fruitful to extract some unifying principles by considering well-characterized components of the insect visual system.

A major function of adaptation is to increase the amount of sensory information an organism uses. The amount of information available to an organism is ultimately defined by its environment and its size. The amount of information collected depends upon the ways in which an organism samples and transduces signals. The amount of information that is used is further limited by internal losses during transmission and processing. Adaptation can increase information capture and reduce internal losses by minimizing the effects of physical and biophysical constraints.

Optical adaptation mechanisms in compound eyes illustrate a common trade-off between energy (quantum catch) and acuity (sensitivity to changes in the distribution of energy). This trade-off can be carefully regulated to maximize the information gathered (i.e. the number of pictures an eye can reconstruct). Similar trade-offs can be performed neurally by area summation mechanisms.

Light adaptation in photoreceptors introduces the roles played by cellular constraints in limiting the available information. Adaptation mechanisms prevent saturation and, by trading gain for temporal acuity, increase the rate of information uptake. By minimizing the constraint of nonlinear summation (imposed by membrane conductance mechanisms) a cell’s sensitivity follows the Weber-Fechner law. Thus, a computationally advantageous transformation is generated in response to a cellular constraint.

The synaptic transfer of signals from photoreceptors to second-order neurones emphasizes that the cellular constraints of nonlinearity, noise and dynamic range limit the transmission of information from cell to cell. Synaptic amplification is increased to reduce the effects of noise but this resurrects the constraint of dynamic range. Adaptation mechanisms, both confined to single synapses and distributed in networks, remove spatially and temporally redundant signal components to help accommodate more information within a single cell. The net effect is a computationally advantageous removal of the background signal.

Again, the cellular constraints on information transfer have dictated a computationally advantageous operation.
Elevated Pericardial Pressure And Cardiac Output in the Leopard SharkTriakis SemifasciataDuring Exercise: The Role Of The Pericardioperitoneal Canal
Authors: Lai N. Chin , Graham Jeffrey B. , Lowell William R. , Shabetai Ralph
Published: April 2021

Changes in pericardial pressure, pericardial fluid volume, cardiac stroke volume and heart rate induced by swimming were monitored for Triakis semifasciata (Girard). Maximum pericardial pressure (Pmax, 0.07±0.03kPa) in resting sharks was typically above ambient, whereas minimum pressure (Pmin, –0.08±0.03 kPa) was slightly subambient. During swimming, both Pmax (0.23±0.03 kPa) and Pmin (–0.02±0.03kPa) became elevated, as did heart rate (51±2 to 55±2 beats min−1) and fractional cardiac stroke volume (0.49±0.03 to 0.65±0.04ml). After swimming, all variables fell, except fractional cardiac stroke volume. Estimates of total cardiac output from fractional cardiac stroke volume data during rest, exercise and recovery were 33.1, 56.2 and 60.4 ml kg−1 min−1, respectively. The occurrence of both elevated pericardial pressure and cardiac output during swimming argues against a primary role for pericardial-induced vis a fronte filling as the principal mechanism responsible for increasing cardiac output with exercise. Pericardial fluid loss via the pericardioperitoneal canal (PPC) occurs during swimming as a result of steady-state elevation of pericardial pressure, a series of transient high pericardial pressures, or both. Good general agreement seen for net pericardial fluid loss (0.6 ml kg−1) and the net increase in cardiac stroke volume (0.45 ml kg−1) during swimming establishes fluid displacement as a mechanism for increasing cardiac stroke volume and suggests that this is the primary function of the PPC.
The Auditory Behaviour of Flying Locusts
Authors: Robert Daniel
Published: April 2021

The auditory behaviour of tethered locusts flying in a wind tunnel was investigated under controlled acoustic conditions.

Reflection, attenuation and diffraction of ultrasound evoked by the locust’s physical presence caused pronounced distortions of the acoustic field. Interaural pressure variations were observed that account for directional hearing at high frequencies. Sound field measurements indicated only a minor influence of flight posture or wing position on the interaural pressure gradient. The locusts steered away from pulsed ultrasounds that simulated bat echolocation signals. The phonotactic response was measured as ruddering by the abdomen and hind legs, resulting in a yaw torque directed away from the sound source. Wingbeat frequency increased by 15% in response to ultrasonic stimulation. This behaviour is considered to be analogous to the bat avoidance behaviour of flying crickets. The avoidance response was observed for carrier frequencies higher than 10 kHz and for sound pressure levels (on average) higher than 45 dB SPL. Low-frequency stimuli (<10kHz) failed to elicit any phonotactic steering at any intensity used (up to 100dB SPL). Because of its relatively low threshold of reaction, this steering behaviour is thought to be part of an early-warning system adapted to the acoustic detection of echolocating predators. The avoidance response was suppressed when a 30 kHz (normally effective) tone was combined with a 5 kHz tone (which is ineffective alone). Two-tone suppression only occurred when the low-frequency component was 10–15 dB SPL higher than the high-frequency tone. The biological significance of two-tone suppression is discussed. The intensity-response characteristics, the frequency sensitivity and the two-tone suppression of the avoidance behaviour are discussed with respect to the auditory physiology of Locusta migratoria. The involvement of some identified auditory ascending interneurones in the avoidance behaviour is considered.
Warm-Up Rates and Body Temperatures in Bees: The Importance of Body Size, Thermal Regime and Phylogeny
Authors: Stone G. N. , Willmer P. G.
Published: April 2021

We assess the importance of body mass and the minimum ambient temperature at which foraging occurs in determining the warm-up rates and thoracic temperatures in flight at an air temperature of 22 °C of 55 species of bee (Hymenoptera: Apoidea) from six families adapted to a variety of thermal environments. To control for the effects of taxonomic differences in the relationships between these variables, we use multiple regression incorporated in the phylogenetic regression method developed by Grafen (1989). The prediction made by May (1976) that for very small heterotherms warmup rate will correlate positively with body mass is confirmed when the effects of phylogeny and the thermal environment to which the bee is adapted have been controlled for. The relationship between warm-up rate and body mass within the Apoidea is thus not an extension to lower body masses of the relationship found for heterothermic vertebrates. Having controlled for the effects of body mass in our analyses, we demonstrate that bees able to fly at lower ambient temperatures have higher thoracic temperatures and warm-up rates than bees adapted to warmer environments. There is some suggestion that kleptoparasitic bees, being freed from the need to forage in order to provision cells, have lower warm-up rates than provisioning species. The significance of these relationships in the ecology of bees is discussed in relation to studies of body temperatures and warm-up rates in bees and other insects.
Monoclonal Antibodies Detecting Regulatory Polypeptides of the Insect Neuronal Acetylcholine Receptor
Authors: Benke D. , Stahmer I. , Breer H.
Published: April 2021

Monoclonal antibodies affecting the ligand binding of the neuronal acetylcholine receptor were prepared. A clone was detected which produced antibodies that increased [125I]-α-bungarotoxin binding, but decreased [3H]acetylcholine binding. Western blot analysis established that these antibodies did not recognize the receptor protein, but labelled a 20×103Mr polypeptide. This putative regulatory polypeptide was purified and was found to inhibit [125I]-αr-bungarotoxin binding to pretreated neuronal membranes.
Cerebral Interneurones Controlling Feeding Motor Output In The SnailLymnaea Stagnalis
Authors: McCrohan Catherine R. , Kyriakides Michael A.
Published: April 2021

The cerebral ventral 1 (CV1) interneurones of Lymnaea occurred as a population of at least three in each ganglion, all with similar morphologies. Steady depolarization of a CV1 cell led to initiation and maintenance of rhythmic feeding motor output from the buccal ganglia. CV1 interneurones produced facilitating excitatory postsynaptic potentials in N1 interneurones of the buccal central pattern generator for feeding. Connections with N2 interneurones were not found. The CV1 population could be separated into two subgroups. CVla received strong synaptic feedback in phase with the buccal rhythm, leading to strong bursting during generation of feeding motor output. CVlb received only weak feedback, and often fired continuously when depolarized. Unitary inhibitory postsynaptic potentials were characteristic of all CV1 neurones, but were only visible in CVlb when it was depolarized. These inputs are thought to arise indirectly from the buccal central pattern generator. The CV1 population is probably homologous with similar neurones in other gastropod species.
Diurnal Variation in Membrane Lipid Composition of Sonoran Desert Teleosts
Authors: Carey Cynthia , Hazel Jeffrey R.
Published: April 2021

Phospholipid molecular species and headgroup compositions were determined for sarcoplasmic reticular and microsomal membranes in two species of Sonoran desert cyprinid fish (Agosia chrysogaster Girard and Notropis lutrensis Girard) trapped in an isolated pool of a desert stream. Fish populations were sampled in the cool of the morning (water temperature 21–21·9°C for Agosia and 22–26°C for Notropis) and 7–11 h later in the heat of the afternoon (water temperature 34·2°C) to determine whether membrane lipid composition varied with sampling time and thermal exposure. The composition of sarcoplasmic reticular membranes did not vary significantly through the day. In contrast, the molecular species composition of muscle microsomes (a mixture of endoplasmic reticulum and plasma membranes) changed markedly from the cool of the morning to the heat of the afternoon in both species. Adjustments were particularly striking in phosphate dylcholine (PC). For example, in Agosia, the ratio of saturated-to-unsaturated species of PC, the unsaturation index (the average number of double bonds per molecular species) and the proportion of diunsaturated molecular species decreased from 7·48 to 0·77, from 1·36 to 0·35 and from 7·23% to 2·46%, respectively, between the morning and afternoon samples. Similar, but less dramatic, changes were noted for phosphatidylethanolamine (PE) in both species, and for phosphatidylinositol (PI) in Notropis. In addition, microsomal membranes of Agosia exhibited a significant reduction in the proportion of PE (from 12·1 to 2·7 %) and a corresponding increase in the proportion of PC between the morning and afternoon samples. These patterns of change in membrane lipid composition are in a direction consistent with thermal compensation of membrane function and suggest that rapid adjustments in the lipid composition of biological membranes may stabilize membrane structure against substantial diurnal fluctuations in temperature.
A Novel Gaba Receptor in the Heart of a Primitive Arthropod,Limulus Polyphemus
Authors: Benson Jack A.
Published: April 2021

The isolated, intact heart of the marine arachnid Limulus polyphemus continues to beat in vitro for many hours. Application of γ-aminobutyric acid (GABA) decreased the heart beat frequency with a threshold of 3×10−7moll−1 and an EC50 of 2·0±0·6×10−5moll−1 (mean±S.D., N = 8). At 10−4moll−1 and above the heart beat was completely and reversibly inhibited. The agonist potency profile of the Limulus heart chronotropic GABA receptor was very similar to that of the vertebrate GABAA receptor: muscimol > ZAPA>GABA≈TACA>isoguvacine>THIP>3-aminopropane sulphonic acid> imidazole-4-acetic acid ≈β-guanidino proprionic acid ≈5-aminovalerate. In contrast, the antagonist profile differed dramatically: bicuculline, pitrazepin and SR 95103, as well as the channel blocker picrotoxin, were without effect at concentrations up to 10−4moll−1. The benzodiazepines clorazepate, flunitrazepam, flurazepam and diazepam, as well as the barbiturate sodium pentobarbital, were without effect on the GABA response, suggesting that the Limulus heart GABA receptor is not complexed with the benzodiazepine and barbiturate modulatory subunits that characterize vertebrate GABAA receptor. The GABAB ligands baclofen, phaclophen and kojic amine were inactive on the heart. However, 3-aminopropyl-phosphonous acid (CGA147 823), a potent and highly selective GABAB agonist, was the most active of the compounds tested. It inhibited the heart beat with a threshold of about 3 nmol l−1, an EC50, of 4.0±2·7×10−7moll−1, and produced total inhibition of the heart at 10−imoll−1. CGA 147 823 was inactive on the locust thoracic somal GABA receptors. cis-4-aminocrotonic acid (CACA), the ligand defining a proposed GAB Ac-type receptor, was inactive on the heart. The GABA-induced inhibition of the heart beat was enhanced by pretreatment with the GABA uptake inhibitor nipecotic acid but not with sodium valproate or β-alanine. The Limulus heart chronotropic GABA receptor appears to be of a hitherto undescribed type that differs in pharmacology from the vertebrate GABAA and GABAB receptors as well as from the well-defined GABA receptors on the somata of locust neurones and the muscle fibres of insects and the nematode Ascaris.
The Mechanics of the Medial Gastrocnemius Muscle in the Freely Hopping Wallaby (Thylogale Billardierii)
Authors: Griffiths R. I.
Published: April 2021

Muscle force, electromyogram and length were monitored in the medial head of the gastrocnemius (MG) muscle in freely hopping wallabies (Thylogale billardierii Desmarest).

During take-off hops from rest, MG muscle developed force with an isometric contraction. For constant-speed hops, force was produced in MG muscle during rapid stretch. The muscle resisted this stretch with a constant impedance that was independent of hopping speed. The rate of stretch of the muscle during high-speed hopping was as high as 1ms−1 (5–6 muscle lengths per second) at the onset of stretch and slowed to no stretch at the peak of force. Since the mechanical impedance was constant while the stretch velocity changed, there was no significant viscosity present in the muscle.

The tendon stretched by 3·2% at 7kmh−1 hopping and by 4·4% at 18kmh−1 hopping. Elastic energy storage in the tendons increased with hopping speed but the percentage of total work done by elastic recoil of the whole muscle did not increase at higher hopping speeds.

The significance of the muscle stretch is in producing high forces rapidly and, in addition, there is considerable energy storage in the tendons.
The Role ofβ-Adrenoreceptors in the Recovery From Exhaustive Exercise of Freshwater-Adapted Rainbow Trout
Authors: McDonald D. G. , Tang Y. , Boutilier R. G.
Published: April 2021

Rainbow trout, fitted with arterial catheters, were exercised to exhaustion by manual chasing and then injected with either saline (controls), the /8-agonist isoproterenol or the β-antagonist propranolol. Blood acid-base status, branchial unidirectional and net fluxes of Na+ and CP, and net fluxes of ammonia and acidic equivalents were monitored over the subsequent 4 h of recovery. These same parameters were also monitored in normoxic, resting fish following isoproterenol injection and in exercised fish following acute post-exercise elevation of external NaCl concentration. In addition to confirming an important role for β-adrenoreceptors in the regulation of branchial gas exchange and red cell oxygenation and acid-base status, we find a significant β-adrenergic involvement in the flux of lactic acid from muscle and in across the gills. Both isoproterenol infusion (into nonexercised fish) and exhaustive exercise were found to cause net acid excretion. The post-exercise was further augmented by elevating [NaCl] but was not affected, in this instance, either by β-stimulation or blockade, indicating that was not entirely regulated by a β-adrenergic mechanism. On the basis of a detailed analysis of unidirectional Na+ and Cl− fluxes, we conclude that the increase in following exercise arose mainly from increased Na+/H+(NH4+) exchange and that the upper limit on was set by the supply of external counterions and by the increase in branchial ionic permeability that invariably accompanies exhaustive exercise.
A Hydromechanical Estimate of the Power Requirements of Diving and Surface Swimming in Lesser Scaup (Aythya Affinis)
Authors: Stephenson R. , Lovvorn J. R. , Heieis M. R. A. , Jones D. R. , Blake R. W.
Published: April 2021

Buoyancy and body drag were measured in lesser scaup (Aythya affinis) and the data were used to estimate average power output during diving and surface swimming. Buoyant force (mean±s.D.) of fully submerged ducks was 2.89±0.17N (body mass 0.623 ±0.089kg; body volume 918±88cm3; N=11). Buoyancy was decreased by 6.2 % by artificial compression of the feathers during full immersion, but was reduced by 42 % when the ducks were allowed to breathe during head-out immersion. Therefore, voluntary compression of the plumage by the duck appears to have relatively small effects on buoyancy and hence dive costs, whereas alteration of respiratory volume (e.g. by pre-dive expiration) could substantially alter buoyancy and power requirements.

Surface and subsurface body drag (DSUR and DSUB. respectively, in newtons) of frozen duck carcasses increased with velocity (U, ms−1) as follows:

Work required to overcome body drag is greater for a lesser scaup during diving than during surface swimming at average velocities normally attained during these activities (less than 0.7 ms−1). However, the drag force curves merge at 0.8–1.0ms−1.

It is calculated that the average power output during diving ranges from 1.003 to 1.695 W and that in ducks at least 95 % of the work done during a dive is required to overcome buoyancy. Comparison of these biomechanical estimates with aerobic metabolic power input data reported by Woakes and Butler (1983) indicates that, for freely diving ducks, aerobic efficiency (ηa=average power output/total aerobic power input) is 0.088–0.149 and net aerobic efficiency [ηnet=average power output/(total aerobic power input minus resting aerobic power input)] is 0.124–0.209. These values are significantly greater than those during surface swimming at the same velocities (ηa=0.004–0.037, ηnet=0.039–0.063).
Antennal Reflexes in the Desert Locust Schistocerca Gregaria
Authors: Saager Frank , Gewecke Michael
Published: April 2021

The control of horizontal motion of the locust antenna was studied by behavioural and electrophysiological investigations. Deflection of the flagellum and the pedicel induced by air currents or a needle were used as mechanical stimuli. The forces at this needle during imposed movements were measured with a semiconductor force transducer. The antennal movements were recorded with a capacitative movement transducer, and myograms were recorded simultaneously from the lateral and median scape muscle.

Each scape muscle is innervated by at least three excitatory motoneurones. Reflex movements of the scape-pedicel joint are triggered by several sense organs of the locust, e.g. antennal sensilla. Touching a flagellum of a resting locust normally evokes either an avoidance reflex, which removes the antenna from the stimulus source, or reflex chains, during which the antenna oscillates against the stimulus source. Air-current stimuli induce synchronous phasic-tonic responses in both scape muscles and a stereotyped movement of the antenna (flight-start reaction). This reaction occurs synchronously with the onset of flight muscle activity, and is the beginning of the antennal-positioning reaction that leads to the antennal flight posture. This posture is held constant during steady flight within a range of ±1°. Sudden deflections of the antenna of a flying locust by air-current modulations or by a solid object cause phasic-tonic responses similar to those during the start of flight. Force measurements indicate these responses to be resistance reflexes. Experiments in which one antennal joint was immobilized at a time show the following. (1) Stimulation of only the sensilla of the pedicel flagellum joint triggers transient avoidance reflexes in resting locusts and sustained resistance reflexes in flying ones. (2) Stimulation of the sensilla of the scape pedicel joint alone causes avoidance and resistance reflexes in resting locusts, and resistance reflexes in flying ones.
Short Communication Long-Term Anoxia inArtemiaCysts
Authors: Clegg James S. , Jackson Susan A.
Published: April 2021

Among the many adaptations associated with the rigorous life history of the brine shrimp, Artemia, is the striking resistance of the encysted embryo (cyst) to oxygen lack (anoxia). Dutrieu and Chrestia-Blanchine (1966) reported that these cysts could be incubated in sea water under anoxic conditions for over 5 months without a decrease in viability. Subsequent work showed that anoxic cysts did not carry out a conventional lactate-producing metabolism and that the breakdown of trehalose, a disaccharide required for the energy metabolism of aerobic cysts, was not detected over an g-h period of anoxia (Ewing and Clegg, 1969). Comprehensive studies of the nucleotide pool by Stocco et al. (1972) suggested that utilization of the unusual guanine nucleotide diguanosine tetraphosphate (Gp4G) might provide the free energy presumably required to support the maintenance of anoxic cysts. Most recently, Hand and Gnaiger (1988) used calorimetric methods to show that anoxic energy metabolism, as reflected by heat production, was reduced to less than 2 % of aerobic values during short-term anoxia (10 h). Those authors also calculated that the utilization of Gp4G could account for only about 2 % of anoxic heat production and suggested that the very slow catabolism of trehalose might be a more likely explanation for their results. We examined that suggestion by measuring the concentrations of trehalose and other carbohydrates in cysts incubated under anoxic conditions for 3 months (Clegg and Jackson, 1989). We found no measurable change in trehalose and glycerol content under these conditions, but did observe a statistically significant decrease in the glycogen content of anoxic cysts. In the present paper we report comparable data from additional studies on anoxic cysts incubated for 3 and 6 months, and we measure the free amino acid pool, cyst dry mass and hydration.
Analysis of Mechanisms of Spiking in Normally ‘Non-Spiking’ Motoneurone Somata in Crayfish
Authors: Czternasty Gerard , Kado Raymond T. , Bruner Jan
Published: April 2021

The soma membrane of the abdominal giant motor neurone (MoG) of the crayfish was studied by use of current injection and by measurements of total and local membrane current under voltage-clamp. Depolarization of the soma from the recorded resting potential (about −70 mV) did not produce a regenerative potential. Sodium and calcium currents were observed under voltage-clamp. It was shown that the sodium spike cannot develop at the usual resting potential since sodium channels are already partially inactivated; the spike can appear after the removal of inactivation by a hyperpolarizing prepulse. It was also shown that an early outward current prevents the Ca2+ regenerative potential; the potential can appear after inactivation of this outward current by a depolarizing prepulse.
Mechanics of six-legged runners
Authors: Full R. J. , Tu M. S.
Published: April 2021

Six-legged pedestrians, cockroaches, use a running gait during locomotion. The gait was defined by measuring ground reaction forces and mechanical energy fluctuations of the center of mass in Blaberus discoidalis (Serville) as they travelled over a miniature force platform. These six-legged animals produce horizontal and vertical ground-reaction patterns of force similar to those found in two-, four-and eight-legged runners. Lateral forces were less than half the vertical force fluctuations. At speeds between 0.08 and 0.66 ms−1, horizontal kinetic and gravitational potential energy changes were in phase. This pattern of energy fluctuation characterizes the bouncing gaits used by other animals that run. Blaberus discoidalis attained a maximum sustainable stride frequency of 13 Hz at 0.35 ms-1, the same speed and frequency predicted for a mammal of the same mass. Despite differences in body form, the mass-specific energy used to move the center of mass a given distance (0.9 J kg−1 m−1) was the same for cockroaches, ghost crabs, mammals and birds. Similarities in force production, stride frequency and mechanical energy production during locomotion suggest that there may be common design constraints in terrestrial locomotion which scale with body mass and are relatively independent of body form, leg number and skeletal type.
Observations on the Compound Eyes of the Deep-Sea Ostracod Macrocypridina Castanea
Authors: Land M. F. , Nilsson D.-E.
Published: April 2021

Macrocypridina lives at depths of 800 m, where residual daylight is very weak. It has a pair of mobile apposition compound eyes with large lenses, wide rhabdoms and high acceptance angles, all of which contribute to a calculated sensitivity comparable with the superposition eyes of deep-water decapod crustaceans. The axes of the 27 ommatidia in each eye are not uniformly distributed in space, with a modest acute zone in the anteroventral region. Here the interommatidial angles are about 6°, compared with 20° at the rear of the eye.

The eyes make two kinds of spontaneous movements: large slow rotations of up to 50° around a transverse axis, and a superimposed 2 Hz tremor with an amplitude of 5 °.
Response Characteristics of Four Wide-Field Motion-Sensitive Descending Interneurones IN Apis Melufera
Authors: Ibbotson Michael R. , Goodman Lesley J.
Published: April 2021

The anatomical projections and directional tuning of four descending interneurones sensitive to wide-field motion over the compound eyes are described. The cells are slow to adapt, resistant to habituation and their responses are dependent on the contrast frequency of the periodic patterns used as stimuli. Two of the cells (DNIV2 and DNIV4) are maximally stimulated by movement around the longitudinal axis of the bee (simulated roll), one (DNII2) by movement around the horizontal axis (simulated pitch) and one (DNVI1) by movement around the vertical axis (simulated yaw). The cells are binocular, their directional response being shaped by the interaction of the inputs from each eye. The cells which respond predominantly to roll (DNIV2 and DNIV4) have their arborizations restricted to the ipsilateral side of the brain and thoracic ganglia, i.e. the side which contains the cell soma. The cell responding to pitch (DNII2) has its arborizations distributed bilaterally, invading similar regions of the neuropile in both sides of the brain and thoracic ganglia. The cell which responds to yaw (DNVI1) has its major dendritic field in the ipsilateral side of the brain and descends into the thoracic ganglia in the contralateral side. The majority of its arborizations in the thoracic ganglia are confined to the contralateral neuropile.
Force Maintenance with Reduced Ability to Shorten Actively in Barnacle Striated Muscle
Authors: Iwamoto H. , Muraoka A. , Goto A. , Sugi H.
Published: April 2021

Fibres from adductor scutorum muscle of a barnacle Tetraclita squamosa were made to contract isometrically by electrical stimulation, and the change in the ability to shorten actively during the mechanical responses was examined by suddenly allowing the fibres to shorten under a very small load (<3 % of the force immediately before shortening) at various times after the onset of stimulation. The shortening velocity (Vsl) was nearly constant during stimulation. After the cessation of stimulation, shortening velocity decreased steeply while isometric force decayed slowly, indicating that isometric force was maintained with reduced ability to shorten actively. Similar results were obtained when the maximum rate of force redevelopment following a quick release was measured at various times during the mechanical response to electrical stimulation. In these fibres, but not in fibres from frog skeletal muscle, a quick restretch following a quick release could restore the force to a level similar to that observed without a quick release. These results, together with those above, indicated a reduced cross-bridge cycling rate during the relaxation phase of mechanical responses of barnacle fibres to electrical stimulation. During electrical stimulation, Vsl showed less dependence on [Ca2+]o than was shown by isometric force. These results are discussed in connection with the mechanism of force maintenance with reduced cross-bridge cycling rate.