bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ammonia, Urea and H+ Distribution and the Evolution of Ureotelism in Amphibians
Authors: Wood Chris M. , Munger R. S. , Toews D. P. 
Published: April 2021

ABSTRACT
In theory, the distribution of ammonia across cell membranes (Tammi/Tamme) between intracellular and extracellular fluids (ICF and ECF) may be determined by the transmembrane pH gradient (as in mammals), the transmembrane potential (as in teleost fish), or both, depending on the relative permeability of the membranes to NH3 and NH4+ (pNH3/pNH4+). The resting distributions of H+(via [14C]DMO), ammonia and urea between plasma and skeletal muscle, and the relative excretion rates of ammonia-N and urea-N, were measured in five amphibian species (Bufo marinus, Ambystoma tigrinum, Rana catesbeiana, Necturus maculosus and Xenopus laevis). Although ureai/ureae ratios were uniformly close to 1·0, Tammi/Tamme ratios correlated directly with the degree of ammoniotelism in each species, ranging from 9·1 (Bufo, 10% ammoniotelic) to 16·7 (Xenopus, 79% ammoniotelic). These values are intermediate between ratios of about 30 (low pNH3/pNH4+ ) in ammoniotelic teleost fish and about 3 (high pNH3/pNH4+) in ureotelic mammals. The results indicate that amphibians represent a transitional stage in which ammonia distribution is influenced by both the pHi—pHe gradient and the membrane potential, and that a reduction in cell membrane permeability to NH4+ (i.e. increased pNH3/pNH4+) was associated with the evolution of ureotelism. Hyperosmotic saline exposure increased urea excretion 10-fold in Xenopus, while ammonia excretion remained unchanged. Tammi/Tamme fell, but this response was attributable to an abolition of the pHi—pHe gradient, rather than a physiological change in the cell membrane pNH3/pNH4+.
Entrainment of the Swimmeret Rhythm of the Crayfish to Controlled Movements of Some of the Appendages
Authors: Deller Simon R. T. , Macmillan David L. 
Published: April 2021

ABSTRACT
A machine was used to impose controlled movements, closely resembling natural movements, on some of the swimmerets of crayfish with their ventral nerve cords cut between thorax and abdomen. The rhythm of the unrestrained swimmerets could be entrained to the imposed frequency. Full entrainment occurred most readily when three or four swimmerets were controlled and was uncommon with two. When one was controlled, only partial entrainment was seen. A small proportion of preparations could not be entrained irrespective of the number of swimmerets controlled. Entrainment of the neural rhythm also occurred when movement was imposed on one or more swimmerets attached to an otherwise isolated nerve cord.
This is the first demonstration that sensory input affects the periodicity of the swimmeret rhythm. In the light of this result, the hypothesis that swimmeret rhythm is largely controlled by a central pattern generator should be viewed with caution. It now appears that there is also an influential sensory component responsible for stabilizing and adjusting the timing of the swimmeret rhythm.
Effects of Nicotinic and Muscarinic Agents on an Identified Motoneurone and its Direct Afferent Inputs in Larval Manduca Sexta
Authors: Trimmer Barry A. , Weeks Janis C. 
Published: April 2021

ABSTRACT
The principal locomotory appendages of larval Manduca sexta, the prolegs, bear at their tips an array of mechanosensory hairs (the planta hairs). Each of the single sensory neurones associated with a planta hair sends an axon into the ganglion of the same segment where the afferent terminals make synaptic contact with interneurones and motoneurones. Electrical stimulation of a single afferent elicits a monosynaptic excitatory postsynaptic potential (EPSP) in PPR, one of the motoneurones controlling the prolegs. We have used this synapse to study the pharmacology of sensory transmission in M. sexta. The following observations were made.
The EPSP was reversibly inhibited in a dose-dependent fashion by the cholinergic antagonists d-tubocurarine, atropine and mecamylamine, indicating that the planta hair afferent neurones use acetylcholine (ACh) as a neurotransmitter. α-Bungarotoxin (αBGTX) also suppressed the EPSP but required concentrations above l×10−6moll-1. PPR depolarized in response to ionophoretic or bath application of cholinergic agonists, but compared to motoneurones of a non-nicotine-resistant insect such as the cockroach, PPR was relatively insensitive to nicotine. Application of N-methyl nicotinamide (NMN) to the nerve cord to inhibit putative alkaloid pumps in the central nervous system (CNS) only weakly potentiated PPR’s response to nicotine. This suggests that such pumps do not markedly contribute to PPR’s nicotine resistance. PPR’s responses to nicotinic agents showed several pharmacological differences from those reported for other insects, indicating that the nicotinic ACh receptors of M. sexta may be specifically adapted to accommodate a nicotine-rich diet. During the application of muscarinic agonists to isolated abdominal ganglia, the firing rate of motoneurones, as monitored in the ventral nerve, increased dramatically. PPR responded to muscarinic agents even during synaptic blockade, suggesting that muscarinic receptors may be present on PPR itself. The main effect of muscarine on PPR was to lower its spike threshold. Bath-applied muscarinic agents also affected the afferent-evoked EPSP in a manner consistent with the presence of another group of receptors that, when stimulated, act presynaptically to inhibit the release of ACh from the sensory terminals. These apparent pre- and postsynaptic actions of muscarinic agents are the first reported findings of muscarinic physiology in an identified insect neurone and its synaptic inputs.
Oxygen Transport and Acid-Base Balance in the Haemolymph of the Lobster, Homarus Gammarus, During Aerial Exposure and Resubmersion
Authors: Taylor E. W. , Whiteley N. M. 
Published: April 2021

ABSTRACT
Submerged lobsters at 15°C were normoxaemic ( at a of 6·53 kPa) and normocapnie (; [HCO3-] = 9·3mequivl-1 and pHa = 7·78). After 3h in air the haemolymph was markedly hypoxic and hypercapnic (; ; and pHa = 7·64). Disturbance after 3h in air caused a greater increase in to 1·28 kPa and a fourfold increase in lactate levels to 3·6 mmol l-1. The combined respiratory and metabolic acidosis reduced pHa to 7·39.
After 14 h in air, undisturbed lobsters remained hypoxic and hypercapnic (; ). Lactate levels had increased to 6·2mmoll-1. Despite this clear limit on respiratory gas exchange in air, oxygen transport by the haemolymph was restored. A rise in buffer base ([HCO3-] = 15·8mequivl-1) compensated for the potential respiratory and metabolic acidosis and pH was unchanged at 7·63. The combined effects of the increase in lactate (ΔlogP50/ Δlog[lactate] =–0·175) and calcium (ΔlogP50/Δlog[Ca2+] = — 0·20 at pH7·63) levels contributed to an increase in oxygen affinity of haemocyanin at constant pH. Consequently, mean increased from 0·2 to 0·38 mmol l-1 between 3h and 14 h in air.
Resubmergence after 14 h in air resulted in a transient alkalosis due to retention of bicarbonate; oxygen and CO2 were rapidly restored to submerged levels. The lobster possesses the appropriate respiratory adaptations for survival during the relatively long periods of exposure in air encountered during commercial shipment.
Circadian Change of Photosensiuivity in Paramecium Bursaria
Authors: Nakajima Kaname , Nakaoka Yasuo 
Published: April 2021

ABSTRACT
Circadian changes in behaviour and electrical properties of the membrane were investigated in Paramecium bursaria. Both photoaccumulation and swimming velocity were at a higher level during the day than at night. During the day, swimming velocity decreased as light intensity was increased and the cells almost stopped at the intensity at which they showed the maximum degree of photoaccumulation. When the intensity was increased further, the avoiding reaction was frequently observed. Step increases in the light intensity depolarized the membrane potential. The depolarization was larger in the night cells than in the day cells. The resting potential measured in the dark was about 4 mV more positive in the night cells than in the day cells. Membrane conductance was larger in the day than at night, which can explain the changes in the resting potential and also the photosensitive behaviour.
L-Glutamate Receptors on the Cell Body Membrane of an Identified Insect Motor Neurone
Authors: Wafford K. A. , Sattelle D. B. 
Published: April 2021

ABSTRACT
Current-clamp experiments on an identified neurone have demonstrated the presence of L-glutamate receptors in the insect central nervous system. The cell body of the fast coxal depressor motor neurone (Df) in the metathoracic ganglion of the cockroach Periplaneta americana exhibits a hyperpolarizing response to L-glutamate, accompanied by an increase in membrane conductance. The response is dependent on both intracellular and extracellular chloride concentration, but is not affected by changes in potassium concentration. The hyperpolarization reverses at —82mV (the equilibrium potential for chloride), is mimicked by the action of L-aspartate, blocked by the antagonists picrotoxin and γ-D-glutamylglycine (γ-DGG) at high concentrations (l·0×10−4moll−1), and is enhanced by L-amino phosphonobutyrate (L-APB). The response is insensitive to glutamate diethyl ester (GDEE), cis-2,3-piperazine dicarboxylic acid (cir-2,3-PDA) and D-amino phosphonobutyrate (D-APB). The L-glutamate-activated increase in chloride conductance does not cross-desensitize with the y-aminobu-tyric acid (GABA) response on the same cell. It is less sensitive than the GABA response to block by picrotoxin. In addition, γ-DGG specifically blocks the L-glutamate receptor.
A depolarizing response is elicited by kainate and quisqualate; it is associated with an increase in conductance, and exhibits a much slower time course than the response to L-glutamate, indicating a different underlying mechanism. L-Cysteate produces a small depolarizing response of similar time course to that produced by L-glutamate. L-Homocysteate and N-methyl-D-aspartate (NMDA) are ineffective on the cell body membrane when applied at concentrations up to l·0×10−3moll−1. This first detailed description of the properties of L-glutamate receptors on an identified insect neurone reveals that they are not readily accommodated in the existing classification of receptor subtypes, based on vertebrate pharmacology.
The Tension in a Locust Flight Muscle at Varied Muscle Lengths
Authors: Malamud Jean G. 
Published: April 2021

ABSTRACT
Tension in a resting muscle increases when the muscle is stretched. If the stretch is maintained, the tension decays (stress relaxation). The time course of stress relaxation in the metathoracic second tergocoxal muscle (Tcx2) of the locust Schistocerca americana was found to be adequately described by a multiexponential function with four or more time constants. These constants were independent of strain, and the slowest had a value of more than 60 min. Tension continued to diminish even when stretch was maintained for 2—4h. Tension in a stretched, unstimulated muscle increased with increased length of stretch. Resting tension in the locust Tcx2 at the in vivo length was estimated to be IN cm-2 or less. At 10% strain, resting tension was about 2Ncm-2. The stiffness of the unstimulated locust muscle was similar to that of unstimulated frog muscles. The active tetanic tension was maximal (average = 32·4 Ncm-2) at slightly less than the in vivo muscle length. Tetanic tension was 50% or more of its maximum value over a range of 80–130% of the in vivo muscle length. The active twitch tension was maximal at slightly greater than the in vivo muscle length. The ratio twitch/tetanic force increased with muscle length. Twitch relaxation time increased with muscle length, but the time to peak for twitch force was nearly independent of muscle length in a stretched muscle.
Energy and Communication in Three Species of Hylid Frogs: Power Input, Power Output and Efficiency
Authors: Prestwich Kenneth N. , Brugger Kristin E. , Topping Mary 
Published: April 2021

ABSTRACT
Rates of oxygen consumption for calling, rest and locomotion were measured for three species of treefrogs from the south-east United States: Hyla cinerea (Schneider), H. gratiosa LeConte and H. squirella Bosc. Anaerobic metabolism was slight during calling but large during forced hopping in H. squirella. It is assumed that calling in all three species is primarily aerobic. For all species, oxygen consumption during calling rivalled or exceeded that for locomotion in a closed chamber. Calling apparently is at least as costly as closed-chamber locomotion, if anaerobic contributions to hopping are ignored. The mass-specific costs of producing calls are similar in most species of hylids whose calling energetics have been studied. As in other species of hylids, abdominal trunk muscle masses in male H. squirella and H. gratiosa were large - approximately 10% of the total body mass. Complete sound fields (with measures of variation) were mapped for each species. Each species is an essentially omnidirectional radiator with only a slight flattening of the field behind the head. Efficiencies of sound production (acoustic power/metabolic power) were calculated for each species and compared with values from other frogs, insects and loudspeakers. Efficiencies in hylids vary between 0-8 and 4-9%. Factors that contribute to determining the efficiency of sound production are reviewed. Small animals such as frogs and insects must either use low-efficiency radiators or use high-frequency sounds that do not propagate over great distances. It is possible that low-efficiency transducers maximize the area over which an animal is heard per unit of energy expended.
Processing of Sensory Input From the Femoral Chordotonal Organ by Spiking Interneurones of Stick Insects
Authors: Büschges Ansgar 
Published: April 2021

ABSTRACT
The femoral chordotonal organ (ChO) of the right middle leg of the inactive stick insect Carausius morosus was stimulated by applying movements having a ramp-like time course, while recordings were made from local and interganglionic interneurones in the anterior ventral median part of the ganglion. Position, velocity and acceleration of the movements were varied independently and the interneurones were categorized on the basis of their responses to the changes in these parameters. Position-sensitivity was always accompanied by responses to velocity and/or acceleration. Velocity-sensitive responses were excitatory or inhibitory and were produced by elongation or relaxation, or by both. In some cases, velocity-sensitive neurones were also affected by position and acceleration. Acceleration responses were always excitatory and were often found in neurones that showed no effects of velocity or position. It is inferred that sensory input from different receptors in the ChO is processed by single interneurones. No interneurone in the recording region was found to be directly involved in the resistance reflex of the extensor tibiae motoneurones, elicited by stimulation of the ChO.
H+-Dependent Contraction of the Tritonextracted Tentacle of the Dinoflagellate Noctiluca Miliaris
Authors: Oami Kazunori , Naitoh Yutaka 
Published: April 2021

ABSTRACT
The intracellular conditions required for contraction in the food-gathering tentacle of a marine dinoflagellate Noctiluca miliaris were examined in the isolated tentacle, treated with Triton X-100. The tentacle flexed to its full extent when the pH of the reactivation medium was lowered to 4·0, and extended when it was raised again to its original value. Adenosine triphosphate (ATP) was not needed for the pH-dependent flexion–extension. The flexion was also produced by Ca2+, but in a concentration range more than a thousand times higher than the effective H+ concentration range for producing the flexion. It is concluded that movement of the tentacle in a live specimen of Noctiluca is controlled by membrane potential-regulated cytoplasmic pH.
Rate of Water Admission Through the Madreporite of a Starfish
Authors: Ferguson John C. 
Published: April 2021

ABSTRACT
Time course studies employing the fluorescent, high molecular weight tracer, fluorescein isothiocyanate dextran, confirm that there is a steady entry of sea water through the madreporite of the starfish, Echinaster graminicola, even under constant environmental conditions. This entry serves to supply replacement fluid to both the water vascular system and the perivisceral coelom, with more going to the latter than the former (10·67 vs 6·35 μl h−1 for a 7·25 g animal). Since nearly 2·4 days may be required for an animal to take up 1 ml of sea water through the madreporite, the rate of entry is too low to be easily seen in direct observation, or to have immediate physiological consequences if prevented. Nevertheless, the rate is probably sufficient to make a substantial contribution to fluid volume regulation, functioning along with osmolyte transport and other processes that have been emphasized in recent literature.
Characterization of single non-inactivating potassium channels in primary neuronal cultures of Drosophila
Authors: Yamamoto Daisuke , Suzuki Nobuyuki 
Published: April 2021

ABSTRACT
Permeability and gating properties of single, non-inactivating, K+ channel currents in cultured Drosophila neurons were studied using the gigaohm-seal patch-clamp technique. The non-inactivating K+ currents were activated by depolarizing the membrane to −30 mV or to more positive potentials. The slope conductance of the channel was estimated to be 17·6 ± 3·70 pS when the cytoplasmic side of the inside-out membrane patch was perfused with solutions containing 145 mmol l−1 K+. The single-channel conductance was temperaturesensitive, with a Q10 of 1-44 between 10 and 20°C. Single-channel currents could be recorded when the cytoplasmic K+ was replaced with NH4+, Rb+ or Na+, but not with Cs+. The conductance ratio of the channel for these cations was: K+(l) &gt; NH4+(0·53) &gt; Rb+(0·47) &gt; Na+(0·44). Tetraethylammonium (TEA+) ions applied at a concentration of 10 mmol l−1 to the cytoplasmic side of the membrane increased the frequency of ‘blank’ traces which contained no channel openings during repetitive depolarization. In addition, single-channel amplitude was reduced by about 20%. The open-time distribution was fitted by a single exponential function, whereas the closed-time distribution required a three-exponential fit. Permeability and gating properties of single, non-inactivating K+ channel currents in neurons of eag, a mutant which has defects in the delayed rectifier K+ channel, were indistinguishable from those recorded from wild-type neurons.
Critical Swimming Speeds of Yellow Perch Perca Flavescens: Comparison of Populations from a Naturally Acidic Lake and a Circumneutral Lake in Acid and Neutral Water
Authors: Nelson Jay A. 
Published: April 2021

ABSTRACT
The objectives of this study were to determine if environmental acidity reduces swimming performance in the acid-tolerant yellow perch (Perca flavescens) and to use swimming performance as an indicator of fitness in testing whether fish from naturally acidic environments perform better in acidic water. Perch from a naturally acidic lake (pH 4·4) or a nearby circumneutral lake were swum after either 5–7 months of laboratory acclimation to simulated soft, natural waters or after more than 2 years of acclimation to hard, circumneutral water. The performance test was a critical swimming speed (Ucrit) determination, with 5cms-1 velocity increments at 30 min intervals. Low environmental pH (4·0) produced significant decreases in average swimming performance in each of three experimental series. Acid decreased performance in most but not all fish. The two perch populations had similar mean Ucrit values when swimming in acid water. Pre-acclimation to hard water significantly increased swimming performance. Gravid females acclimated to acid water had very low critical swimming speeds in acid water, whereas Ucrit changed little in acid water when oogenesis occurred in neutral water.
Role of the Telencephalon in the Synchronization of Locomotor and Respiratory Frequencies During Walking in Canada Geese
Authors: Funk Gregory D. , Milsom William , Sholomenko Gerald N. , Steeves John D. 
Published: April 2021

ABSTRACT
To elucidate the importance of telencephalic structures and the effects of metabolic rate in the production of locomotor-respiratory coupling, we examined the relationship between locomotor and ventilatory patterns in: (1) intact trained geese, and (2) brainstem-stimulated (medullary reticular formation) decerebrate geese, that were walking on a treadmill. The decerebrate geese, however, were not completely self supporting. Thus, while the two groups walked with similar stride frequencies (fs), they did so at two different work rates.
While at rest, tidal volume (VT), breathing frequency (fv) and minute ventilation were very similar in the two groups. increased 120% during walking in the intact geese, primarily as a result of increases in fv, while both VT and fv increased to produce a smaller 40 % increase in in the decerebrate birds. Although the magnitude of the increase in was three times greater in the intact geese, the relationships between and oxygen uptake and and CO2 output were similar in the two groups.
Significant coupling between locomotor and respiratory patterns was found in both intact (28·3%) and decerebrate birds (28·9%), suggesting that the telencephalon is not essential for the coupling of locomotor and respiratory rhythms during walking in geese. In addition, the incidence of locomotor-respiratory synchrony was virtually identical in the two groups in spite of a threefold difference in metabolic work rate.