bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Desiccation, Water-Stress and Decapitation on Integumentary Water Loss in the Cockroach, Periplaneta Americana
Authors: Noble-Nesbitt John , Al-Shukur Marwan 
Published: April 2021

ABSTRACT
Cockroaches decapitated in a fully hydrated state at first lose water under desiccation much more rapidly than their intact counterparts. The rate of loss decreases with time of desiccation; this decrease is more marked in decapitated than in intact cockroaches.
The initial rate of water loss is lower and less variable in predesiccated cockroaches and continues to fall gradually during further desiccation. Decapitation of predesiccated cockroaches has little effect on the rate of water loss. Similarly, the rate of water loss is low with low variability in water-stressed cockroaches taken from dry culture conditions, and decapitation has no significant effect.
The lowering of the rate of water loss is not a simple response to lowering of the body water content, but is a two-stage, time-related physiological response of acclimatization to water-stress or desiccation. The initial phase of rapid response requires the presence of the head, whereas the subsequent gradual phase does not.
With the techniques used in this investigation, handling-related effects of the decapitation procedure are not significant.
The Effect of External Sodium and Calcium Concentrations on Sodium Fluxes by Salt-Depleted and Non-Depleted Minnows, Phoxinus Phoxinus (L.)
Authors: Frain W. J. 
Published: April 2021

ABSTRACT
The relationship between sodium influx and external sodium concentration in Phoxinus is complex and unusual. In non-depleted fish the relationship is approximately that given by the Michaelis–Menten equation of enzyme kinetics. However, the Km value (a measure of the affinity of the sodium uptake mechanism for sodium) is very high (3 mmol 1−1), indicating a low affinity of the uptake mechanism for sodium.
On sodium depletion, the relationship between sodium influx and external sodium concentration changes to produce a curve which has a stepped appearance, and is unusual in that the maximum influx is not increased above that in non-depleted fish. The overall Km alters very little; however, the Km for the lower part of the curve is very low (0·05 mmol 1−1).
A model is proposed to explain these results in the form of two sodium uptake mechanisms working in parallel across the gill. The second carrier is only active when the fish is sodium-depleted and kept in low external sodium concentrations.
Neither the external sodium concentration nor the external calcium concentration has any direct effect on sodium efflux. However, fish depleted in 1 mmol 1−1 calcium have a lower sodium efflux than fish depleted in distilled water.
Calcium appears to reduce the permeability of the gill to ions such as sodium. Since calcium has no effect on sodium influx, changes in gill permeability do not involve the sodium influx mechanism.
Synaptic Chloride Channels Generating Hyperpolarizing On-Responses in Monopolar Neurones of the Blowfly Visual System
Authors: Zettler F. , Straka H. 
Published: April 2021

ABSTRACT
The large monopolar neurones LI and L2 in the first optic ganglion of dipteran flies are postsynaptic to short-fibre photoreceptors (Trujillo-Cenòz, 1965; Boschek, 1971 ; Burkhardt & Braitenberg, 1976). Each neurone is contacted by six photoreceptor axons resulting in 1200 synaptic terminations (Nicol & Meinertzhagen, 1982). The photoreceptor response to light is a graded depolarization which, by synaptic transmission, is converted with considerable gain to a postsynaptic hyperpolarization (Järvilehto & Zettler, 1971). When presynaptic photoreceptors are stimulated with light of constant intensity, the postsynaptic potential (PSP) typically consists of a fast initial hyperpolarization (on-response) followed by a slower decay to a constant level about 100 ms after stimulus onset. Termination of the light stimulus results in an off-transient depolarization (the complete, normal PSP shape is shown in Fig. 1). All phases of the PSP are intensity-dependent. The present report is concerned with the hyperpolarizing on-response in the blowfly monopolar neurones.
Long-Distance Regulation of Regenerating Frog Axons
Authors: Kuffler Damien P. 
Published: April 2021

ABSTRACT
Following a nerve crush, damaged frog motor axons regenerate to reinnervate their denervated muscle fibre targets. The axons do this by growing down their old nerve tubes to their former synaptic sites. It is the naked basal lamina of the nerve tube that appears to direct the regenerating axons by providing a substratum over which the axons will preferentially grow. Another possible mechanism for directing the regenerating axons to the end-plates is the release of molecular signals by the cells of the nerve tube or by the denervated muscle fibres. This paper provides evidence that chemical signals do direct the regeneration process. Such signals, released several millimetres from a growing nerve tip, cause it to change direction and bend towards the source. Both the cells of the nerve tube and the denervated muscle fibres release diffusible substances and thereby establish a gradient that affects the regenerating axons.
Tissue Culture Observations Relevant to the Study of Axon-Schwann Cell Interactions During Peripheral Nerve Development and Repair
Authors: Bunge Richard P. 
Published: April 2021

ABSTRACT
During peripheral nerve development the Schwann cell population is expanded so that adequate numbers are available for ensheathment of both nonmyelinated and myelinated nerve fibres. As ensheathment of these fibres progresses each axon-Schwann cell unit becomes surrounded by a basal lamina, providing a unique microtubular framework within the peripheral nerve trunk. Tissue culture studies of pure populations of neurones and Schwann cells cultured separately and in combination indicate that a surface component on the axon provides a mitogenic signal to Schwann cells requiring cell-cell contact. Biochemical, electron microscopic and immunocytochemical analyses of these cultures indicate that Schwann cells in contact with axons are able to generate a basal lamina (containing type IV collagen, laminin and heparan sulphate proteoglycan) and fibrous collagen, without the aid of other cells, and that axonal contact is required for deposition of the basal lamina. The role of Schwann cells and the extracellular matrix they synthesize and organize, as well as the role of the other known products of the Schwann cells in the process of peripheral nerve regeneration, are discussed. It is suggested that the large numbers and advantageous position of the Schwann cells, as well as their ability to provide their own surfaces, a basal lamina and multiple secretory products, may account for their extraordinary ability to foster nerve fibre regeneration.
The Nerve Dependence of Amphibian Limb Regeneration
Authors: Brockes Jeremy P. 
Published: April 2021

ABSTRACT
The regeneration of limbs in urodele amphibians is a context where the developing and regenerating peripheral nervous system interacts with the mechanisms of epimorphic regeneration. After amputation of a limb, there arise at the amputation plane the blastemal cells which are the progenitor cells of the regenerate. These cells divide rapidly and subsequently differentiate to give rise to the internal tissues (cartilage, muscle and connective tissue) of the regenerate. Division of the blastemal cells requires the presence of nerve axons at the amputation plane, at least during the initial stages of regeneration. This requirement can be circumvented by allowing a limb to develop in the absence of a nerve supply (the ‘aneurogenic limb’), but the underlying mechanisms have been unclear. We have derived a monoclonal antibody called 22/18 that has provided new information about these issues. It is specific for blastemal cells versus normal tissue in the limb, specific for regeneration versus development, and specific for blastemal cells that arise after amputation in the presence of the nervous system versus its absence (in either development or the aneurogenic limb). The antibody reactivity appears to mark a cell transition involved in the imposition of nerve-dependent growth control.
Structural Changes In Intercostal Motoneurones Following Axotomy
Authors: Sears T. A. 
Published: April 2021

ABSTRACT
Motoneurone disease (MND or amyotrophic lateral sclerosis) is a paralysing disease of unknown cause involving progressive, widespread muscle atrophy due to degeneration of spinal and other motoneurones and an accompanying loss of Betz cells in the motor cortex. A current hypothesis attributes the disease to the loss of a muscle-derived neurotrophic factor acting in concert with the normal age-related deterioration and loss of motoneurones. The roots of this hypothesis are traced through research based mainly on the developing neuromuscular system, and in particular on the age-related processes of natural motoneurone death during embryogenesis: the neonatal reduction of polyneuronal innervation and the age dependent variations in motor nerve terminal sprouting in response to partial denervation. A consideration of the disease process itself in association with the review of earlier work provide the background for the present work which reexamines ultrastructurally the chromatolytic and later responses to axotomy and the muscle-dependent factors responsible for the reformation of the Nissl bodies.
Regulation Of Blood Oxygen Transport and Red Cell pHi After Exhaustive Activity in Rainbow Trout (Salmo Gairdneri) and Starry Flounder (Platichthys Stellatus)
Authors: Milligan C. Louise , Wood Chris m. 
Published: April 2021

ABSTRACT
In vitro, exogenous adrenaline reduced the Bohr and Root shifts caused by elevated , and depressed plasma pH in rainbow trout blood, but not in starry flounder blood. In vivo immediately after exercise, plasma adrenaline (Ad) and noradrenaline (NAd) increased about 12-fold in rainbow trout. Associated with this catecholamine mobilization was a significant haemoconcentration, red blood cell (RBC) swelling and a reduction in RBC [NTP]; the latter was larger than that explained by cell swelling alone, indicating metabolic degradation of nucleoside triphosphate (NTP). RBC intracellular pH (pHi) fell only slightly after exercise (0·07 units) at 0h, but was restored by 0·5 h in the face of a large plasma acidosis (0·4 units). [O2]/[Hb] fell significantly, but this decline may have been due in part to the significant reduction in . The reduction in [O2]/[Hb] was less than predicted from in vitro O2-dissociation curves at low (0·5 nmol 1−1) catecholamine levels, but similar to that predicted at high (90 nmol 1−1) catecholamine levels. In flounder, resting Ad and NAd levels were about 10 times those in trout and did not change significantly after exercise. As a consequence, there was no reduction in RBC [NTP], and RBC pH, fell significantly (0·10 units) after exercise in the face of a large plasma acidosis (0·4 units) and remained depressed until 4h, although RBC swelling did occur. These factors in addition to the increased , may have contributed to the reduction in arterial [O2]/[Hb], in the face of a constant . However, [O2]/[Hb] was restored to resting levels prior to the correction of RBC pHi and . This, in conjunction with the observation that catecholamines did not affect the in vitro blood-O2 dissociation curve, suggests that additional factors may be involved in regulating O2 transport after exercise in flounder.
Ion Exchange Mechanisms on the Erythrocyte Membrane of the Aquatic Salamander, Amphiuma Tridactylum
Authors: Tufts B. L. , Nikinmaa M. , Steffensen J. F. , Randall D. J. 
Published: April 2021

ABSTRACT
The effects of different pharmacological agents and incubation media on the intracellular pH and water content of Amphiuma erythrocytes were investigated in vitro.
Adrenaline had no significant effect on the intracellular pH or cell water content. D1DS caused an intracellular alkahnization that could be abolished by amiloride, ouabain or removal of sodium from the incubation medium. In addition, amiloride and DIDS both caused a decrease in cell water content. The data indicate that sodium/proton and chloride/bicarbonate exchangers are present on the membrane of Amphiuma erythrocytes and these exchangers are active under steady-state conditions.
The Distribution of Branchial Carbonic Anhydrase and the Effects of Gill and Erythrocyte Carbonic Anhydrase Inhibition in the Channel Catfish Ictalurus Punctatus
Authors: Henry Raymond P. , Smatresk Neal J. , Cameron James N. 
Published: April 2021

ABSTRACT
Carbonic anhydrase (CA) activity was assayed in lysed erythrocytes and in branchial cytoplasm, mitochondria and microsomes of the channel catfish, Ictalurus punctatus. Branchial CA activity was highest in the cytoplasmic fraction, but activity was very low in mitochondria and microsomes. Erythrocyte CA activity was over four-fold greater than that in the gills.
Intact animals were injected with the CA inhibitors acetazolamide and benzolamide. Slow, intra-arterial injection of both inhibitors elicited transient side effects of apnoea, bradycardia and hypoxaemia. Acetazolamide and benzolamide induced a mixed but primarily respiratory acidosis. The onset and the time course of the acidosis were correlated with the inhibition of erythrocyte CA; acetazolamide acted faster because it is more freely diffusible than benzolamide. The acid-base disturbance in the blood reached its maximum after 2 h ; compensation was delayed until 24 h, when CA inhibition began to disappear.
We conclude from these results that there is very little, if any, membrane-associated CA in the gill, and that the branchial enzyme is not quantitatively important in directly converting plasma HCO3− to CO2 for excretion. Rather, CO2 excretion is accomplished via the traditional chloride shift, followed by intracellular dehydration of HCO3− by erythrocyte CA. These results also suggest that branchial cytoplasmic CA inhibition might impair ion transport processes that are used to compensate blood acid-base disturbances and thus delay compensation of the respiratory acidosis.
Octopaminergic Modulation of Flight Muscle in the Locust
Authors: Whim Matthew D. , Evans Peter D. 
Published: April 2021

ABSTRACT
The modulatory actions of octopamine on neurally induced twitch tension in the dorsal longitudinal flight muscles of the locust are described. Octopamine increases the amplitude of twitch tension, the rate of twitch contraction and the rate of twitch relaxation in this fast twitch muscle. The specificity of the receptors mediating these octopamine responses is also described. Evidence is presented to suggest that the dorsal unpaired median neurone to the locust dorsal longitudinal flight muscles (DUMDL) is an octopaminergic neurone whose activation mimics the application of exogenous octopamine to the muscle. The effects of both DUMDL and octopamine on the dorsal longitudinal muscle depend upon the frequency of stimulation of motor neurone input to the muscle. The results are discussed in terms of the behavioural significance of the release of octopamine during the first few minutes of locust flight. It is suggested that such a release is likely to be an important modulatory factor influencing the kinetics of contraction of the dorsal longitudinal muscles, resulting in an increase in the force generated by each muscle contraction together with an energy-saving adaptation due to a reduced overlap in the duration of twitches in antagonistic muscles.
Homing of Magnetized and Demagnetized Pigeons
Authors: Walcott Charles , Gould James L. , Lednor Anthony J. 
Published: April 2021

ABSTRACT
Homing pigeons appear to use the earth’s magnetic field as a compass and perhaps as part of their position-finding system or ‘map’. The sensory system they use to detect magnetic fields is unknown, but two current possibilities are some mode of response by the pineal organ or by the visual system, or it may be based on the magnetite crystals found in their heads. Three series of experiments to test the involvement of magnetite are reported here. The alignment of the permanent magnetic domains in the birds heads was altered by (a) demagnetizing the birds, (b) magnetizing them with a strong magnetic field and (c) exposing the birds to a strong magnetic gradient. None of these treatments had a marked effect on the pigeon’s orientation or homing under sunny skies, but a few results obtained under overcast skies suggest that demagnetizing the birds may have increased the scatter of their vanishing bearings. Perhaps pigeons use one magnetic sensor for their magnetic compass and another for some component of the map.
Mechanics of Jet Propulsion in the Hydromedusan Jellyfish, Polyorchis Penicillatus:II. Energetics of the Jet Cycle
Authors: Demont M. Edwin , Gosline John M. 
Published: April 2021

ABSTRACT
The mechanical energy generated by the contraction of the subumbrellar swimming muscles to power the jet cycle in the hydromedusan jellyfish Polyorchis penicillatus (Eschscholtz, 1829) was measured. This energy was experimentally partitioned into three components during the contraction. The sum of these components was taken to be the mechanical energy generated by the muscles during the jet cycle and was between 8·9×10−5 and 1·4×10−4J per contraction. Energy from one of these components is stored as strain energy in the mesoglea and powers the refilling phase. The mesoglea can clearly act as an effective elastic structure to antagonize the contraction of the swimming muscles completely, and it may be designed to function at some optimum. The mechanical significance of elastic energy storage systems in jet-propelled animals is discussed, and this significance is clearly displayed in Polyorchis. The unusually long-duration action potential of the swimming muscles may be an important component of the swimming mechanism, allowing the muscles to store energy in an elastic structure at the end of the contraction phase when little hydrodynamic thrust is developed. It is suggested that the action potential of vertebrate cardiac muscle may have a similar mechanical function.
Hmechanics of Jet Propulsion in the Hydromedusan Jellyfish, Polyorchis Penicillatus: III. A Natural Resonating Bell; the Presence and Importance of a Resonant Phenomenon in the Locomotor Structure
Authors: Demont M. Edwin , Gosline John M. 
Published: April 2021

ABSTRACT
The bell of the hydromedusan jellyfish Polyorchis penicillatus (Eschscholtz, 1829) was modelled as a harmonically forced, damped oscillator. The robustness of the model was tested and verified by comparing estimates of the work done during the contraction phase predicted by the model with analogous values measured in completely independent experiments. Data suggest that the animals swim at a frequency that is at or near the resonant frequency of the locomotor apparatus. The implications of this phenomenon for the mechanics and phvsiology of the system are discussed. If the swimming muscles force the bell at its resonant frequency, as opposed to a single contraction at the same rate of deformation, the amplitude of the oscillation will be increased by about 40%, and the energetic requirement for the cycle will be reduced by about 24–37 % of the total cost of the cycle. The advantages of forcing the structure at its resonant frequency seem quite remarkable.
Autonomic Influences on Heart Rate and Blood Pressure in the Toad, Bufo Marinus, At Rest and During Exercise
Authors: Wahlqvist Inger , Campbell Graeme 
Published: April 2021

ABSTRACT
Blood pressure (PA) and heart rate (HR) were measured in the conscious, resting toad, Bufo marinus. Treatment with bretylium (an adrenergic neurone blocking agent), alone or in combination with phentolamine and propranolol (adrenoceptor antagonists) did not alter PA or HR significantly. Atropine caused a small but significant increase in HR but had no effect on PA. The experiments indicate a cholinergic cardio-inhibitory tone but give no evidence for an adrenergic pressor tone at rest.
Treadmill exercise caused a rapid increase in PA and HR which was sustained throughout the exercise period. This response was partly psychogenic. The concentration of plasma catecholamines increased during exercise and was high enough to affect organs that were included in an extracorporeal blood circuit with the exercising animal. Bretylium treatment revealed an initial hypotension, presumably due to work hyperaemia, followed by a hypertension which was reduced compared to controls. The tachycardia was delayed but HR eventually reached control levels. Additional treatment with phentolamine and propranolol did not further affect the PA response, but significantly reduced the tachycardia reached during exercise.
It is concluded that the cardiovascular responses to exercise involve adrenergic nerve fibres causing hypertension and an initial rapid tachycardia. Circulating catecholamines seem to be the major cause of the sustained tachycardia.
Systems That Control the Burrowing Behaviour of A Sea Anemone
Authors: Pickens Peter E. 
Published: April 2021

ABSTRACT
The sand-dwelling sea anemone, Phyllactis concinnata, buries itself by attaching sand grains to the lower column as this is bent under the anemone by a travelling peristaltic wave. Some of the sand is then released as the column expands laterally. Once buried, the anemone increases in length over a period of several hours until the pedal disc finally attaches to a buried shell. Burrowing is controlled by bursts of pulses generated by the through-conducting nerve net. These pulses produce column shortening and peristalsis. Regular intervals between pulses and between bursts suggest that pacemakers are driving the nerve net. Pulse patterns are modified after sand has surrounded the column and when the pedal disc touches hard substratum. A second conducting system (the SS2) can, under specific experimental conditions, respond to mechanical and chemical stimuli and inhibit nerve net discharge, but its function during burrowing is not known, even though it produces a distinctive pattern of pulses. After the column has been buried, an anemone may contract spontaneously and rapidly. Two other types of behaviour, pharynx eversion and antiperistaltic behaviour (crawling), usually precede burrowing and each is associated with its own characteristic pattern of pulses.