bluuebunny/crossref_metadata_2025 huggingface dataset:
The Influence of Body Mass on the Endurance to Restrained Submergence in the Pekin Duck
Authors: Hudson Dennis M. , Jones David R.
Published: April 2021

Pekin ducks, ranging in mass from 0·05 to 3·5 kg, were force-dived to determine the maximum tolerance to diving asphyxia. The size of the respiratory and blood oxygen storage compartments and oxygen utilization during the dive were also measured. By the end of a maximum dive, less than 4% of the original O2 store remained in the blood, whereas almost 25% remained in the respiratory system. In contrast, the level of arterial glucose did not change significantly during diving.

The relationship of a number of measured variables to body mass was analysed using linear regression analysis on log10-transformed variables to generate power equations of the form Y = aXb (Y, any variable; X, body mass; a, mass coefficient; b, mass exponent). The mass exponent was 1·19 for the total oxygen stores and 0·64 for maximum diving duration. Using measurements of brain and heart mass and literature estimates of the scaling of O2 consumption, it was also possible to predict a mass exponent aerobic metabolism by these organs during a maximum dive. Allometric cancellation of mass exponents for O2 availability and predicted utilization resulted in a residual mass exponent almost identical to the measured value for maximum dive duration. Thus it is possible to predict the relationship of maximum underwater endurance to body mass in Pekin ducks from a knowledge of the oxygen consumption by, and availability to, the central aerobic organs.
Localization and Stimulation of Chromatophore Motoneurones in the Brain of the Squid, Lolliguncula Brevis
Authors: Dubas Francoise , Hanlon Roger T. , Ferguson Graham P. , Pinsker Harold M.
Published: April 2021

The relatively simple chromatophore system of the squid, Lolliguncula brevis, was studied with combined behavioural, morphological and electrophysiological methods in order to understand how the chromatophore patterns in the skin are organized at the level of the posterior chromatophore lobes (PCL). There are nine simple chromatic components of patterning in L. brevis. Retrograde transport of horseradish-peroxidase from chromatophores in the mantle skin established that the chromatophore motoneurones are located in the PCL. Focal threshold stimulation of the PCL in perfused, semi-intact preparations showed that the motor fields of individual chromatophore motoneurones are compact, including 2-60 chromatophores, generally of the same colour. Adjacent motoneurones in the lobe do not necessarily have adjacent motor fields in the skin.
Two Types of Action Potentials in A Secretory Epithelium of A Clam Mantle
Authors: Beirão Paulo S. , Sorenson A. L.
Published: April 2021

The secretory epithelium that faces the shell of the clam Anomalocardia brasiliana is electrically excitable. It was found that two types of action potentials could be elicited by electrical stimulation. In mantles showing signs of being in the phase of shell secretion, cardiac-like action potentials were observed. They had an overshoot of 48·4 ±8·8mV (±S.D.), a rate of rise of 54·7 ±5·6 Vs−1 and three phases of repolarization of 9·3 ± 4·8, 1·44 ± 0·70 and 4·7 ± 1·1 Vs−1. Their duration averaged 38·4 ± 13·3 ms. Mantles of clams resorbing the shell had spike-like action potentials with an overshoot of 38·7 ± 5·5 mV, a rate of rise of 52·7 ± 16·8 Vs−1, and a single phase of repolarization of 12·4 ± 2·5 Vs−1. Their duration was 11·1 ± l’4ms. It is suggested that the presence of a plateau may be related to shell secretion. Significant differences were also found in the resting potentials: −54·8±5·4mV in cells of mantles with cardiac-like responses and −62·5 ±4·9 mV in cells of mantles with spikes. In both types of mantles the action potentials were propagated throughout the epithelium and both exhibited a refractory period. Lowered Ca or increased frequency of stimulation reduced the plateau of cardiac-like action potentials without any marked alteration in the resting potential, rate of rise, or overshoot. The action potential was elicited by outward (depolarizing) current across the basolateral membrane, and not by similarly-directed current across the apical membrane, so we conclude that the basolateral membrane is the excitable one.
The Contribution of Nasal Receptors to the Cardiac Response to Diving in Restrained and Unrestrained Redhead Ducks (Aythya Americana)
Authors: Furilla R. A. , Jones David R.
Published: April 2021

In restrained redhead ducks, forced submergence caused heart rate to fall from 100 ± 3 beats min−1 (mean± S.E.M., N = 12) to a stable underwater rate of 35 ± 4 beats min−1 (N = 12) within 5 s after submergence. Bradycardia was unaffected by breathing oxygen before a dive, but was virtually eliminated by local anaesthesia of the narial region. In contrast, in a dabbling duck (Anas platyrhynchos) bradycardia in short dives was eliminated by breathing oxygen before a dive. In unrestrained diving, on a man-made pond, heart rate in redheads diving voluntarily (y) was related to pre-dive heart rate (x) by the equation y = 76+0·29 ± 0·05× ± 17 (r2 = 0·71). Chasing, to induce submergence, had variable effects on this relationship. Local anaesthesia of the narial region inhibited voluntary diving but heart rates in chase-induced dives after nasal blockade were significantly higher, by 10–30%, than those obtained from untreated ducks in chase-induced dives. Breathing oxygen before voluntary dives had no apparent effect on heart rate after 2–5 s submergence. Voluntary head submersion by dabbling ducks caused no change in heart rate. We conclude that nasal receptors make only a minor contribution to cardiac responses in unrestrained dives, compared with forced dives, in diving ducks. Furthermore, these results show that little can be learned about cardiac responses in free diving ducks from studies of forced dives in dabblers or divers.
The Regulation of Haemocyanin Oxygen Affinity During Emersion of the Crayfish Austropotamobius Pallipes: I. An In Vitro Investigation of the Interactive Effects of Calcium and L-Lactate On Oxygen Affinity
Authors: Morris S. , Tyler-Jones R. , Taylor E. W.
Published: April 2021

The haemolymph of the crayfish Austropotamobius pallipes exhibits a high affinity for oxygen (P50 = 2·7 Torr at pH 7·9 and 15°C) and a modest Bohr effect (φ =−0·455). The affinity of haemolymph dialysed against a crayfish Ringer was lower with a P50 value of 6·4 Torr at the same temperature and pH. The oxygen affinity of the dialysed haemolymph can be increased markedly by increased concentrations of L-lactate and to a greater extent by elevated concentrations of calcium ions.

In the dialysed preparation, the potentiating effects of L-lactate and Ca2+ on haemocyanin oxygen affinity were found to be interdependent. Elevating the concentration of one of these two ions reduced the effect of the other.

The increase in the oxygen affinity of the haemocyanin brought about by elevated Ca2+ and L-lactate was insufficient to account for the difference in affinity between dialysed and nondialysed haemolymph. The mutually agonistic effects of Ca2+ and L-lactate are described both empirically and graphically.
Two Coupling Mechanisms Which Determine the Coordination of Ipsilateral Legs in the Walking Crayfish
Authors: Cruse Holk , Müller Uwe
Published: April 2021

In a crayfish walking on a motor-driven belt at constant speed, the power stroke (stance phase) of an individual leg is experimentally prolonged for a short time; the ways the legs retain their normal coordination are then observed. The results are shown in a modified phase-response curve. Only ipsilateral coupling is considered in detail.

Two coordinating mechanisms are necessary and sufficient to describe the experimental results. (1) The forward-directed influence is only active when the controlling (posterior) leg performs a power stroke. If the controlled leg is in power stroke, this influence leads it to interrupt the power stroke and start a return stroke. If the leg is in return stroke, it is influenced to continue the return stroke, the duration of which is thereby prolonged. The speed of the return stroke is also decreased. (2) The backward-directed influence is active only during the last part of the power stroke and the first part of the return stroke of the controlling (forward) leg. If the controlled leg is in return stroke, it is influenced to interrupt the return stroke and start a power stroke. If it is at the end of its power stroke, it is influenced to continue this stroke.

For legs 3 and 4, each of which possesses both anterior and posterior neighbours, the influences exerted by these two coordinating mechanisms are assumed to be additive. A model calculation shows that the two mechanisms are sufficient to describe the behaviour observed. The results are compared with previous findings from the literature.
Intracellular Free Calcium Measured with Calcium-Selective Microelectrodes From Salivary Gland Cells of the Snail Planorbis Corneus
Authors: Barber Andrew
Published: April 2021

Double-barrelled Ca2+-selective microelectrodes have been used to make simultaneous measurements of the intracellular concentration of free Ca2+ ([Ca2+]i) and membrane potential (EM) from single salivary gland acinar cells of the pond snail Planorbis corneus. The mean [Ca2+]i recorded from nine cells in unstimulated glands was l·24×10−7moll−1 (S.D. ± 0·84×10−7moll−1), while the mean EM was −67·1 ±4·1 mV. The equilibrium potential for Ca2+ in these cells was calculated to be +132mV. Stimulating the glands with 10−4moll−1 acetylcholine (ACh) produced a simultaneous depolarization of EM and an increase in [Ca2+]i by 2·9×10−7moll−1 (S.D. ± 10× 10−7moll−1, N= 12), followed by a transient hyperpolarization of EM and the restoration of [Ca2+]i to its original level. ACh-induced increases in [Ca2+]i were abolished, or much reduced in size, after the removal of extracellular Ca2+, though the EM response to ACh was unaffected in Ca2+-free saline. This finding indicates that the application of ACh leads to an influx of Ca2+ from the medium bathing the glands. Li+ caused an increase in the size of the ACh-induced elevation in the Ca2+ signal and inhibited the recovery of [Ca2+]i following stimulation. The implications of this observation are discussed.
Ion Absorption by the Distal Tubules of Onychophoran Nephridia
Authors: Campiglia S. S. , Maddrell S. H. P.
Published: April 2021

The distal tubules of the 4th and 5th pairs of nephridia of Peripatus acacioi (Onychophora) absorb ions from the fluid passing through them. Since water follows this movement only to a limited extent, the fluid in the lumen becomes hypo-osmotic.

Absorption of ions stops when sodium is replaced by choline in the perfusion fluid and is much reduced by treatment with ouabain, particularly when this is applied to the basolateral faces of the cells. These results suggest that ion absorption may be driven by an Na/K exchange pump.

Cyclic AMP at 10−2moll−1 increases the rate of salt uptake by about four times; it seems likely from this that the tubules are hormonally controlled.
Chemical and Tactile Inputs to the Lymnaea Feeding System: Effects on Behaviour and Neural Circuitry
Authors: Kemenes G. , Elliott C. J. H. , Benjamin P. R.
Published: April 2021

Transfer of snails from distilled water to solutions of sucrose or maltose stimulated feeding behaviour. As the concentrations were increased from 10−5mol l−1 to 10−1mol l−1 the proportions of snails showing feeding movements and the median rate of feeding both increased until at 10−3 mol l−1 they reached a plateau. At higher concentrations (10−1 mol l−1), maltose, but not sucrose, reduced the proportion of feeding snails and median feeding rate to values occurring at 10−5 mol l−1. Increases in median feeding rate were due to an increase in the regularity of the feeding rhythm rather than increases in the maximum rates of feeding.

Sugars and tactile stimuli were applied to putative sensory structures (interior of the buccal mass, lips and tentacles) in two types of semi-intact preparation whilst intracellular recordings were made from feeding motoneurones (1, 3, 4, 5 and 7 cells) and higher-order interneurones (Cerebral Giant Cells, CGCs, and the Slow Oscillator, SO). Both types of sensory stimuli applied to the lip–tentacle preparation produced strong activation of the CGCs but only long latency weak excitation of motoneurones with no clear initiation of synaptic inputs from central pattern generating (CPG) interneurones. In a more complex lip–tentacle–buccal mass preparation the evoked responses to sugars were comparable to those in the intact snail. Initiation of motoneuronal activity or increased frequency of activity was observed. This was due to increased CPG synaptic inputs as well as activation of a modulatory interneurone, the SO. Multiple sensory pathways from the periphery, present only in the lip–tentacle–buccal mass preparation, were necessary for sensory initiation of the feeding rhythm. The results support the hypothesis that multimodal sensory inputs are likely to be involved in the initiation or modulation of feeding in Lymnaea and act at several levels in the system.
The Role of Catecholamines in Erythrocyte pH Regulation and Oxygen Transport in Rainbow Trout (Salmo Gairdneri) During Exercise
Authors: Primmett D. R. N. , Randall D. J. , Mazeaud M. , Boutilier R. G.
Published: April 2021

Rainbow trout were subjected to burst swimming to exhaustion followed by 4 h aerobic swimming at 80% critical swimming velocity. Severe physiological disturbances, including a marked plasma acidosis caused by the burst swim, were corrected during the 4h of subsequent aerobic exercise. Erythrocytic pH and arterial oxygen content increased, even though plasma pH was reduced. We suggest that the increase in erythrocytic pH was caused by the action of elevated adrenaline and noradrenaline levels in the blood acting on β-adrenergic receptors on the trout red blood cell, causing the cell to swell and raising intracellular pH, offsetting any effect of a reduction of plasma pH on erythrocyte pH and haemoglobin-oxygen binding. Propranolol blocked the action of catecholamines on trout erythrocytes. We conclude that catecholamines play an important role in maintaining oxygen transport to aerobic muscles, following burst swimming and the associated acidotic conditions.
Sodium-Calcium Action Potential Associated With Contraction in the Heliozoan Actinocoryne Contractilis
Authors: Febvre-Chevalier Colette , Bilbaut André , Bone Quentin , Febvre Jean
Published: April 2021

The electrophysiology of the contractile protozoan Actinocoryne contractilis was studied with conventional intracellular recording techniques.

Resting membrane potential (−78 mV, S.D. = 8, A =18) was dependent upon external K+. Rapid action potentials (overshoot up to 50 mV) were evoked either by mechanical stimulation or by current injection. Graded membrane depolarizations induced by graded mechanical stimuli correspond to receptor potentials.

The receptor potential was mainly Na+-dependent; the action potential was also mainly Na+-dependent, but involved a minor Ca2+-dependence. The two components of the action potential could be separated in Ca2+-free solution containing EGTA (1 mmol l−1), in low-Na+ solutions or by the addition of Co2+. The repolarizing phase of the action potential was sensitive to TEA ions and to 4-aminopyridine (4-AP).

Action potentials were followed in 10–20 ms by a rapid all-or-none contraction of the axopods and stalk. Contraction was blocked in Ca2+-free solution containing EGTA and by Co2+, which suggests a requirement of external Ca2+ for this event. Contraction was also abolished by 4-AP.
Properties and Roles of the Three Subclasses of Histamine Receptors in Brain
Authors: Schwartz Jean-Charles , Arrang Jean-Michel , Garbarg Monique , Korner Marie
Published: April 2021

In brain, histamine (HA) is the transmitter of a neuronal system resembling other monoaminergic systems. It is also present in mast cells from which it may control vascular and inflammatory processes. Its various actions are mediated not only by the two well known H1 and H2-receptor subclasses but also by the recently discovered H1-receptors, with distinct localization and pharmacology. H1-receptors mediate a series of biochemical responses which have several features in common: they require intact cells to be observed and largely depend upon the availability of Ca2+.

H1 receptor-mediated responses include glycogenolysis, stimulation of cyclic GMP formation, potentiation of cyclic AMP formation. Recent studies indicate that H1-receptors are linked with phosphatidylinositol breakdown and generation of two intracellular signals which both contribute to the final response (e.g. in the cyclic AMP generation).

H2-receptors seem.to be directly linked with an adenylate cyclase and their stimulation results in enhanced electrophysiologically recorded responses to excitatory agents.

Finally whereas H1 and H2-receptors appear to be postsynaptically located, a novel subclass (H3) of HA receptors was recently revealed with a presynaptic localization. H3-receptors are autoreceptors mediating inhibition of HA release from and biosynthesis in histaminergic nerve terminals in the CNS.

The physiological and pharmacological implications of three distinct receptor subclasses for HA will be discussed.
Messenger-Mediated Control of Potassium Channels in Secretory Cells
Authors: Petersen O. H. , Findlay I. , Suzuki K. , Dunne M. J.
Published: April 2021

In exocrine acinar cells (pancreas, salivary gland, lacrimal gland) stimulation with hormones or neurotransmitters evokes K+ loss due to opening of K+ channels in the plasma membrane whereas in the insulin-secreting pancreatic β-cells, stimulation with glucose or glyceraldehyde evokes membrane depolarization due to closure of K+ channels. By measuring directly the small K+ currents flowing through single channels, in electrically isolated patches of plasma membrane of intact cells, it can be shown that stimulants having no direct access to the small membrane area from which recording is made can influence the pattern of channel opening. In the case of hormonal activation of exocrine acinar cells, Ca2+ is the final messenger and the K+-selective channel involved in the response has a high unit conductance, is very voltage sensitive and can be blocked by external tetraethylammonium. In the case of the insulin-secreting cells, the K+ channel which is inhibited by metabolic stimulation is a voltage-insensitive, inward rectifier which can be blocked by quinine. In experiments on permeabilzed cells or cell-free excised, inside-out, membrane patches it can be shown that ATP evokes channel closure and ATP produced by glycolysis may therefore function as the internal messenger.
Inositol Lipid Metabolism and Signal Transduction in Clonal Pituitary Cells
Authors: Drummond Alan H.
Published: April 2021

A number of clonal cell lines derived from a rat pituitary tumour, collectively termed GH cells, have retained a range of differentiated cell functions, including their ability to secrete the hormones prolactin and growth hormone in response to stimuli such as thyrotropin-releasing hormone (TRH). The mechanisms underlying this release process involve, at least in part, an increase in cytosolic free calcium levels, and the cells have proved useful as a model system in studies of receptor-controlled calcium mobilization. The initial response of the cells to the addition of TRH now appears to be the interaction of the occupied TRH receptor with a GTP-binding protein. A sophisticated signalling system is then activated which initially involves the phosphodiesteratic hydrolysis of phosphatidylinositol 4,5-bisphosphate to 1,2-diacylglycerol and inositol 1,4,5-trisphosphate. Both of these products are important intracellular messengers, and their formation leads to a plethora of biochemical and electrical changes which culminate in. the biphasic release of hormone from the cell. The changes in cytosolic free calcium that occur following TRH addition follow a complex temporal pattern. Within 1 s, the concentration starts to increase from a resting level, in the range 100–150 nmol l−1, to a peak value of around 1 μmol l−1 which is attained within 6–8 s. This ‘spike’ of calcium is almost exclusively derived from intracellular stores, probably the endoplasmic reticulum, in response to the formation of inositol 1,4,5-trisphosphate. With high concentrations of the peptide, the cytosolic free calcium concentration declines promptly, due to the activation of a protein kinase C-mediated extrusion and/or sequestration process. This inhibitory phase is less marked at low agonist concentrations but, in all cases, is superseded by a second increase in free calcium, which is due to the stimulated influx of the cation through dihydropyridine-sensitive calcium channels. These biphasic changes in calcium, in concert with the activation of protein kinase C, appear sufficient to regulate prolactin secretion.
Ionic Signalling by Growth Factor Receptors
Authors: Moolenaar W. H. , Defize L. H. K. , Laat S. W. DE
Published: April 2021

The proliferation of cells in vivo and in culture is regulated by polypeptide growth factors, such as epidermal growth factor (EGF) and platelet-derived growth factor (PDGF). Growth factors initiate their action by binding to specific cell surface receptors. Receptor occupancy triggers a cascade of physiological changes in the target cell which ultimately lead to DNA synthesis and cell division. Immediate consequences of receptor activation include tyrosine-specific protein phosphorylations, a sustained increase in cytoplasmic pH (pH,) and a transient rise in free Ca2+. The rise in pH, has a permissive effect on DNA synthesis and is mediated by an otherwise quiescent Na+/H+ exchange mechanism in the plasma membrane, which is turned on by protein kinase C, the cellular receptor for phorbol esters. The rapid Ca2+ signal is due to either release from internal stores (PDGF) or net entry via a voltage-independent channel in the plasma membrane (EGF). Phorbol esters, acting via kinase C, inhibit the growth factor-induced Ca2+ signals without affecting resting Ca2+ levels.

Monoclonal antibodies against the human EGF receptor can act as partial agonists in that they activate the tyrosine-specific protein kinase without inducing any of the ionic signals. These antibodies fail to induce DNA synthesis when added to quiescent fibroblasts, indicating that the Ca2+ and pH, signals can be dissociated from tyrosine kinase activity and suggesting that these signals are indispensable for the stimulation of cell proliferation.
The Temperature and Humidity Relations of the Cockroach
Authors: Gunn Donald L. , Notley F. B.
Published: April 2021

The thermal death-points of three species of cockroaches in dry and in moist air have been determined for 1-day and 1-hour exposures. Moist air is more favourable than dry in the longer exposures, because in dry air death occurs from desiccation when the temperature itself is not fatal. Dry air is more favourable than moist in the shorter exposures, owing to the fact that the evaporation of water lowers the body temperature. Bearing in mind the thermotactic behaviour of these animals, these observations would seem to have little ecological importance
The Biological Basis of Sexual Behaviour in Amphibia
Authors: Shapiro H. A.
Published: April 2021

The complete disappearance of all sexual activity in Xenopus laevis, male or female, is observed under laboratory conditions. A technique is described whereby the mating reflex (coupling) can be established in the laboratory during the pond breeding season as well as midway between breeding seasons, by means of injections of human pregnancy urine extracts, or by acid extracts of the anterior lobe of the pituitary gland of sheep and goats. The mating reflex has been induced in 101 different pairs of toads with pregnancy urine extracts and in 39 different pairs of toads with anterior pituitary extracts. The reflex induced by anterior pituitary extracts in no way differs from that produced by pregnancy urine extracts. The possibility that the extract acts through the intermediation of the gonads is considered. The mating reflex is described, and attention is drawn to the passive role of the female, while the male is stimulated to activity. It is suggested that a stimulus from the female reflexly activates the male to clasping activity. Fertilised ova from coupling pairs have been reared successfully to an advanced tadpole stage (4-5 months). Tadpoles can be reared also midway between breeding seasons. The injected extract, acting possibly through the intermediation of the gonads, may be suggested to inhibit the clasping reflex inhibitory centre in the brain described by Steinach and others. The mating reflex appears to be independent of the pituitary mechanism associated with chromatic response in Xenopus laevis. The larger doses (500 mg. fresh tissue) of anterior pituitary extract required to produce in summer a response of the same magnitude as that produced by smaller doses (192 mg. fresh tissue) in winter cannot be attributed to a diminished sensitivity of the ovaries. Control extracts of male urine and of sheep and goat brains repeatedly gave negative results.
A Failure of Induction in Normal Development
Authors: Waddington C. H.
Published: April 2021

The just formed side-plate mesoderm from the gastrula in the medium-sized yolk-plug stage can induce the formation of an extra neural plate when implanted into the blastocoel of a young gastrula. The dorsal lip of a young gastrula, substituted for the side-plate mesoderm mentioned in (1), evocates a neural plate. The failure of evocation by the side-plate mesoderm in normal development can only be explained by supposing both that the evocating capacity of the sideplate mesoderm is lower than that of the dorsal lip and that the lateral ectoderm does not react to an evocating stimulus as easily as does the young gastrula ectoderm. The weakness of the evocating capacity of the side-plate mesoderm might be due either to its intrinsic nature or to an active suppression by the rest of the mesoderm. The evidence suggests that both factors may be involved, but it can be shown that the latter factor by itself is not sufficient to explain the facts. Isolated gastrula ectoderm retains its competence to be evocated to neural tissue at least until the age of an open neural plate embryo. Thus the normal loss of competence by the lateral ectoderm is not due to an inherent process. Nor is it caused solely by a continued connection with the neural plate. It cannot be due merely to the presence of side-plate mesoderm; but it may be due to an influence proceeding from side-plate mesoderm which is part of a mesoderm field, or it may be dependent on a preparation of the ectoderm by reason of its connection with the neural plate, or, more probably, by an inherent process, so that by the stage at which the side-plate mesoderm forms, the ectoderm has become such that it reacts with side-plate mesoderm with rapid loss of competence.
Studies in Animal Locomotion
Authors: Gray J.
Published: April 2021

It is well known that certain aquatic vertebrates (notably dolphins and some of the larger teleostean fishes) are able to travel at surprisingly high speeds. The movements performed by such animals during rectilinear locomotion are all of the same type, for the hind end of the body vibrates rhythmically in a plane at right-angles to the axis of locomotion; the plane of vibration of the dolphin is dorso-ventral, whereas that of a fish is transverse to the long axis of the body. In all cases the orientation of the hind end of the body and of the caudal fin, in particular, is such that during both phases of each vibration the leading surface (relative to the direction of the vibration) is inclined at an angle to its own direction of motion through the water and is directed obliquely backwards relative to the head of the animal (Gray, 1933). The anatomical arrangements of the propulsive muscles of a dolphin appear to be simpler than those of a fish, since the locomotory movements are produced by four bands of musculature connected to the base of the caudal fin by strong tendons ; on the ventral side of the vertebral column the two muscle bands extend forward to the region of the diaphragm, whereas the two dorsal bands extend over the whole back of the animal. The weight of the dorsal musculature is approximately twice that of the ventral muscles. The tail is deflected upwards by the contraction of the dorsal muscles and downwards by contraction of the ventral muscles. Reciprocity thus exists between the dorsal and ventral muscle groups, whereas, in a fish, reciprocity of this type is restricted to the right and left musculature of individual segments. Apart from these anatomical differences the propulsive mechanisms of a fish and of a dolphin appear to be of essentially the same type.
The Further Effects of Irradiation on the Oestrous Cycle of the Ferret
Authors: Marshall F. H. A. , Bowden F. P.
Published: April 2021

In our previous paper (1934) it was shown that the recurrence of oestrus in the female ferret is greatly accelerated by irradiation with light, and is retarded by darkness, thus confirming and extending the observations of Bissonette (1932). It was also shown that heat rays and the near infra-red (λ7500Å.) were inactive. The active radiation extended throughout the spectrum from the red (λ 6500 Å.) to the ultra-violet (λ3650Å.). Further, the animals irradiated with ultra-violet light remained on heat far longer than any of the others, although the irradiation had been for a long time discontinued. Of the two ferrets which are recorded as having been still on heat on August 1, 1933, one (No. 2) remained in a state of full oestrus until August 28, but the vulval swelling did not finally disappear until October 2, while the second ferret (No. 14) began to go off heat on September 11, but was not completely anoestrus until November 14.
A Note on the Mechanism of Salt and Water Balance in the Heterotrichous Ciliate, Spirostomum Ambiguum
Authors: Picken L. E. R.
Published: April 2021

Although considerable attention has been paid to the kinetics of water balance in the Protozoa, e.g., Adolph (1926), and more recently Kitching (1934) and Kamada (1935), comparatively little is known of the instantaneous distribution of salt, water and colloidal substances in the body of a protozoon, and nothing is known of the magnitude of the hydrostatic pressure within the animal and its possible importance in the process of excretion. The experiments described here were made in order to obtain direct information on the total osmotic concentration of the body fluid, the maximum value for the colloid osmotic pressure of the cell contents, and the hydrostatic pressure within the organism.
Some Reactions of the Ammocoete
Authors: Francis Eric T. B. , Horton Frances M.
Published: April 2021

Experiments are described which show that the threshold value for the light energy, which will initiate swimming movements in the ammocoete, is in the region of 3 foot-candles. The part of the spectrum which is most active is in the green-blue region (0.55μ-0.4μ). Ammocoetes are very strongly thigmotactic, the most sensitive region being the sides of the trunk. Ammocoetes between 40 and 70 mm. long are not rheotactic. The relation of these responses to one another and their relative importance to the ammocoete in its natural environment are discussed.
Modulation of crayfish retinal sensitivity by 5-hydroxytryptamine
Authors: Aréchiga Hugo , Bañuelos Enrique , Frixione Eugenio , Picones Arturo , Rodríguez-Sosa Leonardo
Published: April 2021

The responsiveness of crayfish retinal photoreceptors to light was enhanced by exposure to 5-hydroxytryptamine (5-HT), either following injection into whole animals or following topical application to isolated eyestalks or retinas. The effect was measured as an increment in the amplitude of the receptor potential, and was dose-dependent in the range 10−6–10−3mol l−1 (injected as a 0.1 μl dose in intact animals). It was more pronounced at low levels of illumination and was reversibly blocked by methysergide.

The enhancement was a consequence of a dual effect: (a) retraction of the proximal pigment granules within the photoreceptors, with a corresponding increase in the light-admittance function of the retina; and (b) a direct effect, facilitating a membrane conductance increase which mediated the generation of the receptor potential. A set of axons in the lamina ganglionaris with a 5-HT-like immunoreactivity was found in the vicinity of the photoreceptor axons. 5-HT antagonists were capable of blocking the physiological retraction of pigment granules in photoreceptors at night, suggesting that 5-HT acts as a modulator during the nocturnal phase of the circadian cycle in the crayfish retina.
Non-voltage-gated calcium channels in snail heart ventricle cells
Authors: Brezden B. L. , Gardner D. R.
Published: April 2021

Two recently identified channel types in Lymnaea stagnalis heart muscle cells were shown to conduct Na+ in the absence of extracellular Ca2+. They did not appear to be ‘voltage-gated’ as they were not activated by voltage. Also, they remained active over a wide range of membrane potentials. However, they were weakly ‘voltage-sensitive’ as their activity usually tended to increase with depolarization. The weak voltage-sensitivity and similarity to other non-voltage-gated Ca2+ channels suggested that one or both of these channels may be receptor-operated Ca2+ channels. One of the two channels had a slope conductance of 15 pS. The other appeared to have at least two subconductance states with slope conductances of 50 and 72 pS. Both these conductance states had very similar open dwell-time constants and identical reversal potentials. The open dwell-time constants of both conductance states were not affected by voltage, suggesting that the channels’ weak voltage-sensitivity was mediated by one of the closed states. With divalent cations in the patch pipette, non-voltage-gated Ba2+ and Ca2+ currents were also detected. The Ba2+ conductance (12 pS) was similar to the Ca2+ conductance (11 pS).
Ultrastructure of Aerobic Muscle in Antarctic Fishes may Contribute to Maintenance Of Diffusive Fluxes
Authors: Londraville Richard L. , Sidell Bruce D.
Published: April 2021

Quantitative ultrastructural analyses were performed on red (oxidative) and white (glycolytic) skeletal muscles from two species of antarctic fish to identify features of subcellular structure that may be related to muscle metabolism at cold body temperature. Trematomus newnesi (Boulenger) is an active pelagic species and Notothenia gibberifrons (Lönnberg) is a sluggish bottom-dweller. White fibres of both species are poorly vascularized [capillary density, NA(c,f), for T. newnesi is 73.9±11.3 mm−2; for N. gibberifrons is 76.0±14.1 −2], and have low percentages of cell volume occupied by mitochondria [volume density, Vv(mit,f), for T. newnesi is 0.014±0.005; for N. gibberifrons is 0.006±0.003]. Ultrastructure of oxidative fibres in both species resembles that of cold-acclimated temperate-zone fishes. Mitochondrial volume densities of red fibres reflect differences in ecotype between species [Vv(mit,f) for T. newnesi is 0.348±0.012; for N. gibberifrons is 0.249± 0.007], The less clustered array of mitochondria in oxidative fibres of T. newnesi compared with N. gibberifrons may support an equivalent flux of aqueous metabolites between mitochondrial and cytoplasmic compartments, despite a greater mean intracellular diffusion distance (τh) between these compartments in T. newnesi than in N. gibberifrons (τh=1.05±0.07μm and 0.77±0.06μm, respectively). Although Vv(mit,f) is higher in red fibres of the active species, capillary supply is less extensive [capillary length density, Jv(c,f), for T. newnesi is 481.3±49.0mmmm−3; N. gibberifrons is 696.3±33.7 mm mm’− 3] and the maximal diffusion-distance for oxygen is greater in T. newnesi than in N. gibberifrons (Krogh’s radius, N=26.3±1.64μm and 21.5±0.51 μm, respectively). A mismatch appears to exist between oxygen supply [Jv(c,f)] and oxygen demand [Vv(mit,f)] in T. newnesi red fibres in view of published data for other fishes. The twofold higher volume density of lipid [Vv(lip,f)] in T. newnesi compared with N. gibberifrons may resolve this paradox [Vv(lip,f) is 0.026±0.002 and 0.012±0.004, respectively]. Because oxygen is at least four times more soluble in lipid than in aqueous cytoplasm, lipid may enhance oxygen flux through oxidative muscle and play a role similar to myoglobin in these myoglobin-poor fishes.
Comparative Study of Chill-Coma Temperatures and Muscle Potentials in Insect Flight Muscles
Authors: Goller Franz , Esch Harald
Published: April 2021

Muscle potentials in insect flight muscles decrease in amplitude and increase in duration with decreasing temperature. Amplitudes fall to zero at distinct temperatures, which are characteristic for different species. Chill-coma temperature is thus defined here as the critical temperature below which flight muscles cannot be activated. Chill-coma temperatures were 2°C in the species of butterflies measured and −2 to 0°C in the moths. In the species of Hymenoptera, Coleoptera and Diptera measured, chill-coma temperatures ranged from 3 to 14°C. The rate of decline of muscle potential amplitudes with decreasing temperature was different for different species. Rates were smaller over most of the temperature range for species that warm up from low environmental temperatures to reach thoracic temperatures necessary for flight. Amplitudes decreased faster at higher thoracic temperatures in species that start shivering only at higher ambient temperatures. Temperature has a similar effect on durations of muscle potentials in different species. Between 25 and 15°C, durations increased by 100% in all species. The results suggest that cold-adaptation is not strongly related to chill-coma temperature but is strongly related to the rate of decline of muscle potential amplitudes.
Rates of energy processing by blowflies: the uses for a joule vary with food quality and quantity
Authors: Hainsworth F. R. , Fisher G. , Precup E.
Published: April 2021

Data on the variation of crop volumes with time for blowflies (Phormia regina Meigen) fed various volumes and concentrations of fructose or sucrose (from Gelperin, 1966, and Edgecomb et al. 1987) were used to characterize energy processing rates to test the assumption of food energy additivity of optimal foraging theories. Six regression models (linear, square root, cube root, hyperbolic, inverse cube root and exponential) were compared for data from Edgecomb et al. (1987) with measurements of crop volumes from 10 min to 5 h after blowflies were fed 9.7 or 14.5 μl of 0.25moll−1 sucrose. Only the hyperbolic regression could be discriminated as statistically different, and the linear model was selected as most parsimonious for examining rates of energy processing. About the same volume bypassed the crop for flies fed 9.7 or 14.5μ. Volume rates of crop emptying (from Gelperin, 1966) did not change at intermediate concentrations but decreased from lowest and to highest concentrations. Energy processing patterns indicate that long-term storage rates increase with meal size and at intermediate concentrations and decrease (3.0moll−1 fructose) or remain constant (2.0moll−1 sucrose) at high concentrations, so the uses for a unit of energy are not additive across concentrations and meal sizes. Animals that process energy in this way should attempt to maximize meal size and include high-energy foods in their diet out of proportion to the amount of energy gained for the time spent foraging.
Dual motor output interneurons in the abdominal ganglia of the crayfish Procambarus clarkii: synaptic activation of motor outputs in both the swimmeret and abdominal positioning systems by single interneurons
Authors: Murchison D. , Larimer J. L.
Published: April 2021

Many behavior patterns of the crayfish involve the positioning of the abdomen by the tonic motor system. Movements and positionings of the swimmerets are coordinated with these abdominal movements. Evidence from extracellular analyses suggested that single interneurons of the abdominal nerve cord could produce motor outputs in both the swimmeret and the abdominal positioning systems. Our intracellular investigation has revealed that many single cells can evoke outputs in both motor systems. Interneurons which produced fictive extension or flexion of the abdomen or inhibition of abdominal movement were also able to modulate a variety of swimmeret behavior including cyclic beating and excitation or inhibition of episodic outputs. Although interneurons were discovered that evoked each of the possible classes of dual-output combinations, those that evoked combinations frequently observed in the freely behaving animal were more common than those that evoked infrequently observed combinations.

Evidence also indicated that abdominal positioning inhibitors are present in greater numbers than previously suspected and that many are closely associated with the swimmeret circuitry. Interneurons with the ability to start and stop swimmeret cyclic outputs with current injections of opposite polarity are proposed to be higher-order cells, and some are shown to have the properties of trigger neurons. It is proposed that most dual-output cells are presynaptic to single-output cells and that groups of related dual-output cells may function together as command elements.
Fast-Start Performance of Rainbow TroutSalmo Gairdneriand Northern PikeEsox Lucius
Authors: Harper David G. , Blake Robert W.
Published: April 2021

The escape performances of rainbow trout Salmo gairdneri (Richardson) and northern pike Esox lucius (Linnaeus) (mean lengths 0·32 m and 0·38 m, respectively) were measured with subcutaneously implanted accelerometers. Acceleration-time plots reveal two types of fast-starts for trout and three for pike. Simultaneous high-speed ciné films demonstrate a kinematic basis for these differences. Trout performing C-shaped fast-starts produce a unimodal acceleration-time plot (type I) while during S-shaped fast-starts a bimodal accelerationtime plot (type II) results. Pike also exhibit similar type I and II fast-starts, but also execute a second S-shaped fast-start that does not involve a net change of direction. This is characterized by a trimodal acceleration-time plot (type III).

Intraspecific and interspecific comparisons of distance, time, mean and maximum velocity, and mean and maximum acceleration rate indicate that fast-start performance is significantly higher for pike than for trout, for all performance parameters. This indicates that performance is related to body form. Overall mean maximum acceleration rates for pike were 120.2±20.0ms−2 and 59.7±8.3ms−2 for trout.

Performance values directly measured from the accelerometers exceed those previously reported. Maximum acceleration rates for single events reach 97.8ms−2 and 244.9ms−2 for trout and pike, respectively. Maximum final velocities of 7.06 ms−2 (18.95 Ls−1) were observed for pike and 4.19 ms−2 (13.09 Ls−1) for trout, where L is body length; overall mean maximum velocities were 2.77 m s−2 for trout and 3.97 m s−2 for pike.
Bicarbonate Transport Systems in the Intestine of the Seawater EEL
Authors: Ando Masaaki , Subramanyam M. V.
Published: April 2021

Utilizing a pH-stat method, the rates of mucosal and serosal alkalinization were measured separately in the seawater eel intestine. These two rates were dependent on contralateral HCO3− concentration and were inhibited by contralateral application of DIDS, an inhibitor of HCO3− transport, indicating that the mucosal and serosal alkalinization are due to HCO3− secretion and absorption, respectively. The mucosal alkalinization was enhanced after inhibiting Na+/K+/Cl− cotransport by treatment with bumetanide, furosemide or Ba2+, with a latent period of more than 10 min, suggesting that HCO3− absorption from mucosa to serosa depends on Na+/K+/Cl− cotransport. The serosal alkalinization caused by HCO3− absorption was completely abolished after mucosal application of bumetanide. After pretreatment with bumetanide, mucosal omission of Cl− halved the enhanced rate of mucosal alkalinization, and Na+ omission had no effect on it; this indicates that the exit of HCO3− into the lumen depends on luminal Cl−, i.e. on the existence of the usual C1−/HCO3− exchange on the brushborder membrane. When serosal Na+ was removed under the same conditions, mucosal alkalinization was reduced, indicating that HCO3− entry from the serosal fluid depends on Na+. Serosal omission of Cl− did not reduce mucosal alkalinization. In addition, serosal alkalinization was enhanced by serosal removal of Na+ but not of Cl−. These results suggest that there is a Na+/HCO3− cotransport on the basolateral membrane. A possible model for HCO3− transport systems in the seawater eel intestine is proposed, and a possible role for these transport systems is discussed in relation to Na+, Cl− and water transport.
Reflexes, fictive respiration and cell division in the brain and spinal cord of the newborn opossum, Monodelphis domestica, isolated and maintained in vitro
Authors: Nicholls J. G. , Stewart R. R. , Erulkar S. D. , Saunders N. R.
Published: April 2021

The entire central nervous system (CNS) was isolated from 1-to 4-day-old newborn South American opossums (Monodelphis domestica). At this stage the CNS has only an embryonic forebrain (two-layered) and no cerebellum and corresponds to a 14-day rat embryo. Its eyes, ears and hind-limbs are only at an early stage of formation. The isolated CNS preparations continue to develop and to produce electrical signals for up to 4 days in oxygenated Krebs’ fluid at 23 °C. The longitudinal axis of the CNS showed markedly different stages of development. More neuroblast cells were present in the proliferative zone in lumbosacral than in cervical or thoracic regions of the cord. The progeny of dividing cells were labelled in isolated preparations by applying bromodeoxyuridine (BrdU) to the bathing solution for 2h. Stained precursor cells were observed in CNS that had been left in Krebs’ fluid for 4 days before applying BrdU and also in CNS that had been exposed to BrdU shortly after dissection and then left for 4 days. Compound action potentials were evoked from the isolated CNS by stimulation with extracellular electrodes. Compound action potentials increased in amplitude with stronger stimulation and showed discrete peaks of conduction velocity. All electrical activity was eliminated reversibly by 0.1μmol l−1 tetrodo-toxin applied to the bathing solution. Block and recovery occurred with a halftime of approximately 5 min. High concentrations of magnesium (20 mmol l−1) reversibly blocked slower components of the volley. Reflexes in cervical and thoracic segments of the spinal cord continued to function in isolated preparations. Stimulation of a dorsal root evoked bursts of impulses in the appropriate ventral root. Spontaneous and evoked activity in ventral roots was eliminated reversibly by 20 mmol l−1 magnesium. In thoracic segments, spontaneous rhythmical bursts of action potentials were recorded. Burst activity was correlated with respiratory movements of the ribs in semi-intact preparations in which a few ribs and muscles were left attached to the isolated CNS. At raised temperatures of 28°C compared to 23°C both spontaneous and evoked electrical activity were reversibly reduced. Together these results show that the isolated CNS of the newborn opossum survives well in culture. The preparation offers advantages for pharmacological and physiological studies of spinal reflexes, for analysis of the mechanisms underlying rhythmical respiratory activity and for following the time course of CNS development in vitro.