bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role of sensory adaptation in the retina
Authors: Laughlin S. B. 
Published: April 2021

ABSTRACT
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

ABSTRACTChanges 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

ABSTRACTThe 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 (&lt;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

ABSTRACTWe 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

ABSTRACT
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

ABSTRACTThe 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

ABSTRACTPhospholipid 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

ABSTRACTThe 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 &gt; ZAPA&gt;GABA≈TACA&gt;isoguvacine&gt;THIP&gt;3-aminopropane sulphonic acid&gt; 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

ABSTRACTMuscle 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

ABSTRACTRainbow 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

ABSTRACTBuoyancy 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

ABSTRACT
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

ABSTRACTAmong 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.