bluuebunny/crossref_metadata_2025 huggingface dataset:
Perspectives on the Cell Biology of Glia
Authors: Nicholls John
Published: April 2021

From the vantage point of 1981, advances in our understanding of glial cells over the last 20 years seem at once significant, provocative and high in promise. It is sobering to remember that at that time speculation about their role included a spectrum of romantic possibilities, from blood-brain barrier to memory, from constituting the total extracellular space of the brain to playing a key role in learning, from being essential for the neuronal action potential to producing impulses themselves, from ferrying vital materials into and out of neurones to having no function at all other than support. Unfortunately, the ratio of speculation to sound experimental observations was so high that, apart from continuing contributions from anatomists, to be interested in glia was almost disreputable, somewhat akin to dabbling in parapsychology or memory transfer.
Mechanisms of Ionic Homeostasis in the Central Nervous System of An Insect
Authors: Treherne J. E. , Schofield P. K.
Published: April 2021

Extracellular ionic homeostasis in an insect central nervous system involves a peripheral intercellular diffusion barrier, an extracellular matrix and neuroglial cation transport.

The peripheral location of the barrier in the superficial neuroglia is confirmed by intracellular recording from glial cells identified by peroxidase injection. This barrier protects the underlying neurones from large changes in ionic composition of the blood-plasma, but renders them more susceptible to fluctuations in ion composition resulting from neuronal signalling within the very restricted extracellular system. Because of the peripheral intercellular barrier, sodium movements between the blood and the extracellular fluid are largely transcellular and are mediated by ion pumps on the perineurial and underlying glial membranes. It is suggested that the homeostatic role of the neuroglial ion pumps is augmented by an anion matrix which functions as an extracellular sodium reservoir. It is proposed that during depletion of extracellular sodium, this cation is released by the matrix to maintain the sodium activity in the fluid at the axon surfaces.
K+ Changes in the Extracellular Space of the Spinal Cord and Their Physiological Role
Authors: Syková Eva
Published: April 2021

K+ accumulates in the intercellular space as a result of neuronal activity. The changes in extracellular K+ concentration, Δ [K]e (estimated by K+-selective microelectrodes), depends on neuronal activity, on the density of discharging neurones and the removal of the accumulated K+ by diffusion, active transport and current flow through cells. In the mammalian as well as the amphibian spinal cord a single volley in a peripheral nerve increases [K]e by 0·2–0·5 mmol.1−1, while tetanic stimulation (100 Hz) by 7–8 m-mol.l−1, with a maximum in the lower dorsal horn. Increased [K]e was also found in lumbar segments when the somatosensory cortex of the cat and medulla of the frog were stimulated. In the frog spinal cord, the tactile stimulation of the hindlimb evoked Δ [K]e by about 0·1 mmol.1−1, nociceptive stimulation by 0· 2–1·0 mmol.1−1. Spontaneous Δ [K]e and dorsal root potentials (DRPs) were observed at various intervals after stimulation, associated with the decay phase of Δ [K]e.

It was shown that primary afferent depolarization (PAD) consists of two components: the ‘early’ component (mediated by GABA and depressed by picrotoxin or bicuculline) and the ‘late’ K+ component (potentiated by picrotoxin and bicuculline). Even when increased [K]e produces PAD, this does not mean that it also results in presynaptic inhibition. It was found that the Δ [K]e produced depolarization of motoneurones and neuroglia and there is every reason to believe that this also applies to the interneurones. Evidence is available that an increase of [K]e up to 6 mmol. 1−1 facilitates impulse transmission in the spinal cord while higher levels result in its inhibition.
Transfer of Habituation Shows an Interaction Between Neuronal Circuits of the Gill Withdrawal Reflex in Aplysia Californica
Authors: Goldberg Jeff , Lukowiak Ken
Published: April 2021

The gill withdrawal reflex (GWR) and its subsequent habituation can be evoked by tactile stimulation of the siphon or gill when the CNS is either intact or removed. It has been suggested that the neural circuits that mediate the GWR evoked at these two loci are parallel and independent. We provide three lines of evidence which show that these circuits interact and, therefore, comprise a single integrated system. Firtly, siphon and gill stimulation evoked similar excitatory responses in the central gill motor neurones. Secondly, the GWR habituated by repetitive stimulation at one locus was dishabituated by stimulation of the other locus. Thirdly, transfer of habituation occurred. Although the transfer was seen neurally at the level of central gill motor neurones, transfer of habituation also occurred after the CNS was removed. Therefore, the neuronal circuits mediating the reflexes evoked at the siphon and gill interact within both the CNS and PNS. The PNS is largely responsible for mediating this gill behaviour that is based on such interactions, while the CNS provides suppressive and facilitatory plasticity to these responses to enable Aplysia to better adapt to a changing environment.
Long-Term Submergence at 3 °C of the Turtle, Chrysemys Picta Bellii, in Normoxic and Severely Hypoxic Water
Authors: Ultsch Gordon R. , Jackson Donald C.
Published: April 2021

Survival and blood acid-base status were measured on freshwater turtles (Chrysemys picta bellii Gray) that were submerged at 3 °C in either aerated (high O2) or Na-equilibrated (low O2) water. Results from catheterized turtles, without access to air under these conditions, and from non-catheterized turtles which were either apnoeic (in high O2 and low O2 water) or in high O2 water with access to air, are compared.

Under the most adverse conditions (catheterized, submerged, low O2), survival duration was 126 ± 14 (X ± s.E.) days, and 2 of the 10 turtles so treated were still alive after 177 days, although their condition was poor. Apnoeic, high O2 turtles generally survived longer and were in better condition despite a skin fungus condition that selectively affected these animals. Six of ten non-catheterized high O2 turtles were still alive after 189 days without breathing.

All apnoeic turtles developed an acidosis which, except for a transient hypercapnia in low O2 turtles, was a metabolic acidosis attributable to elevated lactic acid. Acidosis was most severe in low O2 turtles in which peak plasma lactates exceeded 200 mm. High O2 turtles, as judged by higher blood and lower lactate concentrations, were able to extract dissolved O2 from the water and support a significant portion of their metabolic requirements by aerobic metabolism. Our data indicate that wintering turtles can remain alive for up to 6 months, even while totally anoxic and severely acidotic, but that the acid-base state and probably the recovery potential are significantly improved if dissolved O2 is available for extra-pulmonary uptake.
Neural Lesions Can Cause Dendritic Sprouting of an Undamaged Adult Insect Motoneurone
Authors: Pitman Robert M. , Rand Kathryn A.
Published: April 2021

The effect of nerve lesions upon the dendritic branching of the metathoracic ‘fast’ coxal depressor motoneurone in the adult cockroach, Peri-planeta americana has been studied by intracellular cobalt injection. Dendrites may sprout after several nerve trunks entering the metathoracic ganglion are lesioned. Direct surgical damage to the neurone is not a pre-requisite for sprouting. New sprouts may extend into regions of the ganglion or into nerve trunks which the neurone would not normally occupy. The developing sprouts appear to grow preferentially within regions containing degenerating nerve fibres. The nerve sprouts frequently have varicosities along their length and at their ends.
Sensory and Motor Neurones Responsible for the Local Bending Response In Leeches
Authors: Kristan William B.
Published: April 2021

Intracellular recordings were made from identified mechanosensory neurones (T and P cells) and longitudinal muscle motor neurones of leeches Hirudo medicinalis and Macrobdella decora while the skin was electrically stimulated to produce local bending responses. The stimulus intensity required to produce local bending was found to activate the mechanosensory neurones at physiological firing rates. For a given stimulation frequency, intracellular activation of the mechanosensory neurones produced the same local bending response as did skin stimulation. Hyperpolarization sufficient to block the propagation of the afferent impulses into the central nervous system eliminated the local bending response to skin stimulation. Stimulating identified longitudinal muscle motor neurones at frequencies observed during the local bending response produced body wall movements similar to those seen in local bending. Hyperpolarization of the motor neurones to block impulse initiation abolished local bending. Mechanosensory neurone to longitudinal muscle motor neurone connexions were demonstrated to be effective and reliable, but polysynaptic for all but the previously documented monosynaptic connexions from mechanosensory neurones onto the L motor neurone (Nicholls & Purves, 1970). It is concluded that the previously identified mechanosensory and motor neurones are exclusively responsible for the local bending response.
Transient Rhythms in the Swimming Activity ofSarsia Tubulosa(Hydrozoa)
Authors: Leonard Janet L.
Published: April 2021

Maximum entropy spectral analysis (MESA) was used to assess the contribution of endogenous rhythms to the timing of swim bouts in a hydro-zoan jellyfish, Sarsia tubulosa M. Sars. The results show that the high degree of variability in Sarsia swimming activity is due largely to the number of rhythms which may contribute to the behaviour and to the transient nature of these rhythms. I conclude that the ability to ‘choose’ among behavioural rhythms may be a widespread behavioural mechanism in cnidarians and I suggest that, in Sarsia, these transient behavioural rhythms may originate in activity of the marginal pacemaker system.
The Influence of Experimental Anaemia On Blood Acid-Base Regulation In Vivo and In Vitro in the Starry Flounder (Platichthys Stellatus) and the Rainbow Trout (Salmo Gairdneri)
Authors: Wood Chris M. , McDonald D. G. , McMahon B. R.
Published: April 2021

Severe experimental anaemia caused a rise in and an associated fall in pH (respiratory acidosis) in arterial and venous blood of both flounder and trout in vivo. In some trout, but not in flounder, there was also a rise in blood lactate, indicating metabolic acidosis. In vitro, blood buffer capacities declined with haematocrit, a factor which contributed to the extent of the acidoses in vivo. However, haematocrit did not influence the pK1 of the plasma system or the actual measurement of blood pH. The Donnan ratio for varied linearly with pH over the range 7·0–7·6, indicating a passive distribution of across the trout erythrocyte. The present data, together with other recent results, indicate that the teleost red blood cell does play a role in plasma dehydration and CO2 excretion, and therefore opposes the theory of Haswell & Randall (1978) that the erythrocyte is functionally impermeable to .
Water Vapour Absorption by the Desert Burrowing Cockroach, Arenivaga Investigata: Evidence Against A Solute Dependent Mechanism
Authors: O’donnell M. J.
Published: April 2021

Solute concentrations were measured in the frontal bodies and hypopharyngeal bladder surfaces, which form the absorption system of Arenivaga. Measured values were compared with the concentrations necessary to lower relative humidity to the absorption threshold, 81% R.H. The predominant inorganic solutes, measured by instrumental neutron activation analysis, were Na, K, and Cl. Their concentrations were 2–3 orders of magnitude below those necessary for absorption. Quantities of a variety of hydrophilic organic molecules were determined with fluorometric reagents. Concentrations of free amino acids, peptides, reducing sugars and polyhydroxyl alcohols were negligible in frontal bodies and on bladder surfaces. Frontal bodies did not appear to be active sites of protein or polysaccharide synthesis, because they did not accumulate significant amounts of radio-labelled amino acids and glucose injected into the hemolymph. The results of this and previous studies indicate strongly that absorption in Arenivaga differs markedly from the solute-dependent schemes which have been proposed for other arthropods.
Ventricular Haemodynamics in the Monitor Lizard Varanus Exanthematicus: Pulmonary and Systemic Pressure Separation
Authors: Burggren Warren , Johansen Kjell
Published: April 2021

The haemodynamics of the anatomically undivided ventricle of the monitor lizard Varanus exanthematicus have been examined by measurements of blood pressure and flow. Central blood , and pH were also measured.

Intracardiac pressure measurements show the ventricle to be functionally divided throughout systole into a high pressure pump (cavum arteriosum : ‘mean’ pressure 89 cm H2O) perfusing the systemic circulation, and a low pressure pump (cavum pulmonale: ‘mean’ pressure 40 cm H2O) perfusing the pulmonary circulation. Hypoxia produced by asphyxia or N2 breathing changed systolic pressures in the ventricular cava, but never resulted in superimposable pressure waveforms which would have indicated a break-down from ventricular division into two pressure pumps. Diastolic pressures were superimposable in the ventricular cava under all conditions.

Analysis of blood and O2 content revealed the potential for nearly complete separation of left and right atrial blood in the ventricle, but both left-to-right and right-to-left shunts of considerable magnitude could also develop.

The varanid heart with its systolic pressure separation allows the development of high blood pressure gradients capable of driving a large cardiac output through the high impedance systemic vascular beds. Concurrently, the low impedance pulmonary circuit is perfused at a much reduced blood pressure, circumventing filtration of plasma into the lungs and impairment of gas exchange. Haemodynamically this situation resembles that present in crocodilians and the homeothermic vertebrates.
Non-Spiking Stretch-Receptors in the Crayfish Swimmeret System
Authors: Heitler W. J.
Published: April 2021

Two neurones have been encountered with the properties of non-spiking stretch-receptors on both sides of each swimmeret-bearing segment of the crayfish Pacifastacus leniusculus. Each neurone depolarizes by up to 35 mV (measured intracellularly in the ganglionic neuropil) in response to experimentally imposed retraction of the appropriate swimmeret, but does not generate spikes. Depolarizing and hyperpolarizing current injected into these neurones can excite or inhibit the spike activity of several swimmeret motorneurones. Intracellular injection of dye shows that both non-spiking stretch-receptors have large diameter axons in the anterior branch of the first root and central cell bodies. One has a cell body in the anterior ipsilateral quadrant of the ganglion (NSSR-A), while the other has a cell body in the posterior ipsilateral quadrant (NSSR-P). Both neurones innervate a peripheral elastic strand which spans the base of the swimmeret, with its posterior attachment on the sternal rib at the posterior rim of the swimmeret socket, and its anterior attachment on the swimmeret basipodite. This strand (S1) is stretched by retraction of the swimmeret. A second strand (S2) stretches from the anterior rim of the swimmeret socket to the mid point of Si, and is innervated by several small diameter axons which also do not appear to have cell bodies in the periphery.
Drosophila Flight Motor Pattern: The Evidence from Interspike Intervals
Authors: Wyman Robert J. , Tanouye Mark A.
Published: April 2021

In a variety of Diptera there are five motomeurones which innervate the wing depressor muscle (DLM) (Ikeda, Koenig & Tsuruhara, 1980; King & Wyman, 1980). During flight these motorneurones fire in a repeating cycle. Each motorneurone fires once per cycle. The firing times of the different motorneurones are separated so that no neurone fires immediately before or after any other (Wyman, 1965, 1969a, b). Wyman and co-workers have proposed that this spacing is due to mutual inhibition between the motorneurones (Wyman, 1969a, b;Harcombe & Wyman, 1977; Tanouye & Wyman, 1981). Koenig & Ikeda (1980) have now challenged this theory. They have presented data on the interspike intervals during flight that they believe do not fit the mutual inhibition hypothesis: they suggest that an ‘excitatory effect’ causes the spacing. The present communication argues that the two sets of data are consistent with each other and with the mutual inhibition theory.
A Comparison of Two Methods for Measurement of O2 Content of Small (20 μl) Samples of Fish Blood
Authors: Hughes G. M. , Belaud A. , Peyraud C. , Adcock P. J.
Published: April 2021

Measurements of the oxygen content of blood have been carried out for many years using a variety of methods many of which may be described as volumetric methods, e.g. Van Slyke and Natelson. In recent years methods applicable to small samples (10–20 μl blood) have been developed especially in relation to studies of comparative physiology. Volumetric methods depend upon the release of oxygen chemically bound with haemoglobin, which is frequently achieved by treatment with ferricyanide. With the release of oxygen the resulting increase in can be measured. If the volume is known then the quantity of oxygen released can be estimated. Methods using this principle have been developed by a number of authors including Fabel & Liibbers (1964) and a method using a small cuvette has been described by Tucker (1967).
Scanning Eye Movements in A Heteropod Mollusc
Authors: Land M. F.
Published: April 2021

The eyes of the heteropod molluscs are unusually large and complex, compared with those of other gastropods (Hesse, 1900). They have a basic design not unlike fish eyes, with a large spherical lens of short focal length that forms an image on a retina of highly ciliated photoreceptors (Dilly, 1969). Perhaps the strangest feature of the eyes is the shape of the retina. It is not a hemispherical cup as in fish, cephalopods and alciopid worms, but a long narrow ribbon only a few receptors wide (6 in Pterotrachea coronata, only 3 in Oxygyrus). The ribbon is several hundred receptors long and in some species it is straight whilst in others it is curved into a horseshoe configuration. In either case this means that the field of view of the eye is a narrow strip of space a few degrees high and 80–180° long. Most of the surroundings are therefore not seen by the animal at any given time. In this paper I show that the problem of the narrow field of view is solved in one heteropod species at least by systematic scanning movements of the eyes, in which each retina ‘sweeps’ through a 90° arc.
A Simple Method for Studying the Innervation of A Complex Muscle
Authors: Theophilidis G.
Published: April 2021

The innervation of an insect muscle can be studied by correlating the evoked spikes in neuronal cell bodies with extracellular or intracellularly recorded events in various parts of the muscle (Burrows & Hoyle, 1973; Hoyle & Burrows, 1973 ; Phillips, 1980). However, when a muscle is innervated by a large number of neurones, difficulties may occur: first, in the reliable identification of the neurones (especially when their cell bodies are closely clustered) and secondly, in maintaining stable records from the cell bodies for a sufficient period of time to permit reliable investigation of the muscle.
On the Indentation Hardness of Insect Cuticle
Authors: Hillerton J. E. , Reynolds S. E. , Vincent J. F. V.
Published: April 2021

The indentation hardness of locust cuticle was measured using a Vickers diamond applied to the surface of the cuticle. A number of areas of cuticle showed similar hardness values, approximately 24 kg mm−2, for the dehydrated cuticle but the mandibles (29·8 kg mm−2) and the dorsal mesothorax (33·3 kg mm−2) were harder. The mandibles have localized areas of hardness which are related to their function. It is suggested that the hardness of the dorsal thorax may be related to its function as an energy storing structure in flight. The measured hardness of cuticle depends on the hydration of the material but relative differences between cuticles from different parts of the locust persist whether tested fresh or after dehydration. Hardness is correlated with the dihydroxyphenol content of cuticle (unlike stiffness), conversely it is not correlated with the hydrophobicity of the matrix proteins (unlike stiffness). It is emphasized that hardness and stiffness are very different mechanical properties.
Inhibitors of protein synthesis on 80S ribosomes phase shift theGonyaulaxclock
Authors: Taylor Walter R. , Dunlap Jay C. , Hastings J. W.
Published: April 2021

One-hour pulses of anisomycin (0· 3 μM), streptimidone (30 μM) and cycloheximide (5 μM) caused strong phase-shifts (either advances or delays, of up to 12 h) in the circadian rhythm of the bioluminescence glow in the marine photosynthetic dinoflagellate, Gonyaulax polyedra. Similar pulses of emetine (0·1–100 μM) caused small ( < 4 h) phase shifts. Drug pulses have quantitatively different effects when applied at different phases of the circadian cycle, thus giving rise to ‘phase response curves’ (PRC’s). The results lend additional support to the generalization, based on results from several different organisms, that 80s ribosome protein synthesizing system is of key importance in the mechanism responsible for circadian rhythms.
Hypoxic Vasoconstriction and the Effects of Adrenaline on Gas Exchange Efficiency In Fish Gills
Authors: Pettersson Knut , Johansen Kjell
Published: April 2021

A gill perfusion technique allowing control of flow and in the ventral aorta and in the irrigating water is described. The procedure includes measurements of flow and in the dorsal aorta and the inferior jugular vein. Pressure recordings were made in the ventral and dorsal aortas.

Lowering the perfusion fluid and/or the irrigating water increased the branchial vascular resistance, without altering flow distribution. This response is probably released by vasoconstriction proximal to the arteriovenous anastomoses in the gill filaments.

Adrenaline acted on receptors both proximal and distal to the arteriovenous anastomoses: branchial vascular resistance decreased, dorsal aortic flow increased and oxygenation of the perfusion fluid increased.

It is suggested that a combination of a direct myogenic response to hypoxia and release of adrenaline serve to increase O2 uptake efficiency when fish are exposed to hypoxic stress.
The Respiration ofCancer PagurusUnder Normoxic and Hypoxic Conditions
Authors: Bradford S. M. , Taylor A. C.
Published: April 2021

The respiration of Cancer pagurus under normoxic conditions and its respiratory responses to hypoxia are described. Respiration of quiescent crabs is characterized by a rhythmic pattern of ventilation and cardiac activity in which periods of apnoea and bradycardia of approximately 5 min duration alternate with longer periods of active ventilation and cardiac activity. The significance of this rhythmic ventilatory behaviour is discussed and evidence is presented to account for this behaviour in terms of allowing energy savings to be made during periods of inactivity. During a ventilatory pause the of the post-branchial blood falls from its normal level of 94 + 5 torr to only 24 ± 3 torr. The blood of Cancer provides a store of oxygen which is used during pausing to maintain aerobic metabolism. Anaerobic metabolism does not appear to contribute significantly to energy production during these periods since no increase in the blood lactate concentration was recorded.

Cancer haemocyanin has a high oxygen affinity (P50 = 5–10 torr) and exhibits a large, positive Bohr shift (Δ log P50/pH = – 1·18). However, under normal conditions the pigment has only a minor role in supplying oxygen to the tissues, since over 91 % is carried in solution.

Cancer pagurus exhibits quite a high degree of respiratory independence and is able to maintain its rate of oxygen consumption approximately constant over a wide range of ambient oxygen tension, down to a of 60–80 torr, below which it declines. Similarly there was little change in heart rate during hypoxia until a of 20–40 torr was reached below which it also declined sharply. Oxygen consumption during hypoxia was maintained primarily as a result of an increase in ventilation volume and oxygen extraction. During hypoxia the of both the pre- and post-branchial blood declined and resulted in a reduction in the gradient across the respiratory surface . Oxygen uptake during hypoxia was facilitated, however, by an increase in the transfer factor .
The respiratory responses of the fowl to hot climates
Authors: Kassim H. , Sykes A. H.
Published: April 2021

Respiratory rate (f) and tidal volume (VT) have been measured at normal and at warm ambient temperatures (Ta) in adult domestic fowl by means of a whole body plethysmograph. Resting values of f = 23 ± 9 min−1 and of VT = 25·6 ± 0·9 ml min−1 were found. At Ta 30, 35 or 40 °C f increased in direct relation to the severity of the heat stress reaching a maximum value of 273 ±12 min−1; VT fell uniformly in all three climates to a minimum of 9·0 ± 0·5 ml. Total ventilation showed a linear relation with f during first-phase panting. Second-phase panting occurred only at Ta 40 °C ; K increased at first but subsequently fell as the decline in f became more pronounced.
The effect of changes in blood oxygen-carrying capacity on ventilation volume in the rainbow trout (Salmo gairdneri)
Authors: Smith Frank M. , Jones David R.
Published: April 2021

Changes in ventilation volume of rainbow trout caused by hypercapnia, hypoxia and anaemia were measured directly by collection of expired water. Exposure to hypercapnic water ( range 0·5–2 kPa) increased (by up to four times) by augmenting ventilatory stroke volume; breathing frequency remained constant. O2 added to the inspired water in maintained hypercapnia reduced at all but the highest level of . increased when blood oxygen content was decreased by exposure to normoxic hypercapnia, but addition of O2 to the water increased blood oxygen content and decreased. When blood oxygen-carrying capacity was depressed by hypoxia or anaemia, increased as it did during normoxic hypercapnia. We suggest that ventilatory responses to low levels of hypercapnia, to hyperoxic hypercapnia, to hypoxia, and to anaemia in trout are related to changes in levels of blood oxygen content under these conditions.
Relationship between muscle force and muscle area showing glycogen loss during locomotion
Authors: Armstrong R. B. , Taylor C. R.
Published: April 2021

This experiment was designed to study the relationship between the crosssectional area of rat skeletal muscle showing glycogen loss and the muscle forces exerted during exercise. Muscular force exerted by the extensors of the elbows and ankle was increased by 24 % by loading rats with 24 % of their body mass while running them on a treadmill at 30 m. min−1. increased by 24 % and stride frequency was unchanged when the rats ran with loads. Cross-sectional areas of the elbow and ankle extensor muscles showing glycogen loss were compared from rats running with and without the load. We found a nearly direct proportionality between the changes in force and the changes in muscle area showing glycogen loss, i.e. when the force of the extensors was increased by 24%, the cross-sectional area of the elbow extensors showing glycogen loss increased by 28%, and that of the ankle extensor group increased by 24%. The more peripheral muscles in each group accounted for a greater proportion of the increase in cross-sectional area of the group showing glycogen loss (i.e. lateral and long heads of triceps brachii muscle accounted for 91 % of the increase in the elbow extensor group, and gastrocnemius muscle accounted for 84 % of the increase in the ankle extensor group). Most of the increases in muscle area showing glycogen loss occurred in fast-twitch-glycolytic fibres (84% in the elbow and 88 % in the ankle). The data suggest that increasing muscle force requirements by 24 % by loading resulted in proportional increases in cross-sectional area of muscles recruited to produce the force, i.e. that spatial recruitment primarily accounted for the elevation in force. The relatively greater increases in cross sectional area showing glycogen loss of peripheral muscles within a group indicate the importance of studying whole groups of muscles when considering muscular recruitment patterns during exercise.
Morphology of identified cercal afferents and giant interneurones in the hatchling cockroachPeriplaneta americana
Authors: Blagburn J. M. , Beadle D. J.
Published: April 2021

Cobalt backfills from the thoracic connectives of the hatchling Periplaneta americana allowed identification of giant interneurones in the terminal abdominal ganglion, morphologically comparable to GI 1, 2 and 3 in the adult. The bipolar neurone innervating each cereal filiform wind receptor ‘hair is ultrastructurally similar to the adult cell and possesses an individually identifiable afferent axon, four of which provide the behaviourally functional escape response system with a simplified sensory input. Both pre-and post-synaptic neurones can be identified and may provide a good preparation for the study of cholinergic synapses.
Tail Thrust of BluefishPomatomus SaltatrixAt Different Buoyancies, Speeds, and Swimming Angles
Authors: Ogilvy Christopher S. , DuBois Arthur B.
Published: April 2021

The tail thrust of bluefish Pomatomus saltatrix was measured using a body accelerometer at different water speeds, buoyancies, and angles of water flow to determine the contribution of tail thrust in overcoming parasitic drag, induced drag, and weight directed along the track. The lengths and weights of the fish averaged 0·52 m and 1·50 kg respectively. The tail thrust overcoming parasitic drag in Newtons, as measured during neutral buoyancy, was: 0·51 × speed+ 0·15, with a standard error of estimate of 0·09 N. When buoyancy was altered by the introduction or removal of air from a balloon implanted in the swim bladder, the tail thrust was altered by an amount of the same order as the value calculated for the induced drag of the pectoral fins. The component of weight directed backward along the track was the weight in water multiplied by the sine of the angle of the swimming tunnel relative to horizontal. When this force was added to the calculated induced drag and tail thrust measured at neutral buoyancy, the rearward force equal to the tail thrust, at 45 ml negative buoyancy, 0·5 m s−1, and 15°head up, was 0·12 N due to weight+ 0·05 N due to induced drag+ 0·40 N due to parasitic drag = 0·57 N total rearward force. The conditions required for gliding were not achieved in our bluefish because the drag exceeded the component of the weight in water directed forward along the track at speeds above the stalling speed of the pectoral fins.
Lability of Conduction Velocity During Repetitive Activation of an Excitable Epithelium
Authors: Schwab Walter E. , Josephson Robert K.
Published: April 2021

Conduction velocity lability was studied in the electrically excitable epithelium of Euphysa japonica by means of intracellular recordings. Three classes of response latency change were identified in response to bursts of stimuli: an initial jump, uniform drift and abrupt jumps in latency. In each case an increase in stimulus frequency produced an increase in latency. The initial jump in latency, which occurred between the first and second response of a series, was related to the afterpotential of the first response. The increased latency of the second response appears to result from the drop in membrane resistance during the hyperpolarizing afterpotential. The uniform drift in latency remains unexplained but may be the result of ion accumulation within the tissue, progressive inactivation of the ionic channels involved in producing the action potential, or junctional phenomena. The abrupt jumps in latency, which often preceded failure to respond, were found to be impulse initiation phenomena.
Oxygenation and Deoxygenation Kinetics of Red Cells In Isolated Lamellae of Fish Gills
Authors: Hills B. A. , Hughes G. M. , Koyama T.
Published: April 2021

The kinetics of oxygen transfer across the water-blood barrier in fish gills were studied by measuring oxygenation and deoxygenation of single red blood cells contained within isolated secondary lamellae using a microphotometric technique. Recordings of the overall time courses show that both oxygenation and deoxygenation are more rapid in the carp than in the eel. In both species the half-time for deoxygenation is about five times slower than for oxygenation. It is shown that the resistances to oxygenation and deoxygenation are identical ; the differences in the shapes of the O2v. time curves recorded being attributable to the influence of the HbO2 dissociation curve upon the driving force for diffusion. It is concluded that a diffusional as opposed to a chemical reaction resistance provides the main barrier to oxygen transfer in gill secondary lamellae.
Chemosensitivity of Walking Legs of the LobsterHomarus Americanus:Neurophysiological Response Spectrum and Thresholds
Authors: Derby Charles D. , Atema Jelle
Published: April 2021

Responses of chemoreceptors in the walking legs of the lobster Homarus americanus to 35 individual compounds and 3 mixtures (prey odours and extracts) were studied using extracellular recording techniques. Compared against a standard mussel (Mytilus edulis) extract, these receptors were most sensitive to the amino acids L-glutamate, hydroxy-L-proline, L-aspartate, L-arginine, glycine, taurine, and L-alanine, as well as such other compounds as ammonium chloride, betaine, and the tripeptide glutathione. Most of these excitants are among those compounds most prevalent in the prey of lobsters. Some proteins and odours from live prey were also effective stimuli. In general, carbohydrates, alcohols, nucleosides, and nucleotides were only slightly excitatory. The lowest thresholds for 10 compounds ranged from 3·5×10−6 to 3·5 × 10−14M; these thresholds are lower than previously reported for crustacean taste receptors.
The Effects of Axotomy Upon the Extrasynaptic Acetylcholine Sensitivity of An Identified Motoneurone in The Cockroach Periplaneta Americana
Authors: David J. A. , Pitman R. M.
Published: April 2021

The effects of axotomy on the sensitivity of the fast coxal depressor motoneurone (Df) of the cockroach (Periplaneta americana) to applied acetylcholine (ACh) and carbamylcholine (CCh) have been investigated.

ACh and CCh applied to the soma membrane either by bath perfusion or by ionophoresis caused depolarization; repeated application of large doses of these agonists resulted in a relatively rapid desensitization and depression of the response.

Axotomy performed 3-10 days before recordings were made caused an approximately threefold increase in the sensitivity to ACh but had no affect upon the sensitivity to CCh. The resting potential, input resistance and membrane time-constant remained within the normal range. In addition there was no change in the rise-times of the responses or of the ACh reversal potential, or in the apparent number of ACh molecules needed to combine with individual cholinoceptors to produce a response.

The anticholinesterases physostigmine and neostigmine potentiated the ACh response at relatively low concentrations (10−7 M-10−8 M). This potentiation was significantly greater in the normal cells than in the axotomized cells. It is therefore concluded that the increase in ACh sensitivity of this motoneurone results at least partly from a fall in the activity of choline esterase in the region of the applied drug.
Unstirred Mucus Layers: Ion Exchange Properties and Effect on Ion Regulation in Lymnaea Stagnalis
Authors: Schlichter L. C.
Published: April 2021

Mucus from the footsole of the freshwater snail Lymnaea stagnate behaves as a weak, negatively charged ion exchanger. Activities and concentrations of Na, K, Ca, and Cl were measured in mucus dialysed to equilibrium against artificial pond water or physiological saline. Observed activity coefficients (activity/concentration) in mucus were compared with those predicted by the Debye-Huckel theory to interpret the effects of electrostatic forces between the polyelectrolyte ions and small ions. The affinity of mucus for small ions decreased in the series, Ca2+, K+, Na+, Cl−.

The extent to which mucus can concentrate cations was measured using three different methods: by titrating the fixed acidic groups with K or Ca and by equilibrium dialysis after which the electrical potential difference was either measured directly or was calculated from the Nernst potential for Na. Ion exchange titration indicated a much smaller exchange capacity than did the other two methods.

Kinetics of cation uptake by the snail from dilute media were re-interpreted by considering the enhanced concentrations of cations in the mucus layer. It was shown that the presence of mucus in the unstirred layer adjacent to a transporting epithelium can result in an underestimate of the Michaelis constant (Km) determined from influx measurements.
Transport of Sodium and Potassium Across the Isolated Midgut of the Larvae of Tenebrio Molitor Related to the Fine Structure of the Epithelium
Authors: Koefoed Bodil M. , Zerahn Karl
Published: April 2021

For meal-worms, which are able to survive under extremely dry living conditions, the normal situation is that the K+ concentration of the haemolymph regulates the process of water conservation via the rectal complex (Grimstone, Mullinger & Ramsay, 1968; Koefoed, 1975). The aim of this paper has been to study the handling of sodium and potassium by the midgut epithelium of the larva of Tenebrio molitor and to discover if the transport of these ions is reflected in the structure of the epithelium.
Extracellular Fluid Volume Changes in Carcinus Maenas during Acclimation to Low and High Environmental Salinities
Authors: Harris R. R. , Andrews M. B.
Published: April 2021

Changes in extracellular fluid (ECF) volume of Carcinus maenas (L.) were studied in vivo during acclimation to low and high environmental salinities. Initial investigations showed that there was a rapid equilibration into this compartment of the ECF markers used ([3H]inulin and [14C] hydroxymethyl inulin). Earlier reports of a relatively slow marker distribution, indicated from clearance curves, can be explained by high clearance rates occurring when frequent blood sampling was carried out. After transfer of the crabs to media hyposmotic to the haemolymph, ECF volumes decreased transiently to 74·8% of the initial volume, but within 40 h in 26% sea water original volumes were restored. Calculation of intracellular water contents suggests that a volume limitation phase precedes the regulatory return to the original volume. In hyperosmotic media, the ECF volumes increased significantly (to a maximum of 143 %) but, in contrast to the response in hyposmotic conditions, showed only a partial return to the original volumes.
The neuromuscular basis of swimming movements in embryos of the amphibian Xenopus Laevis
Authors: Kahn J. A. , Roberts A. , Kashin S. M.
Published: April 2021

When removed from their egg membranes, Xenopus embryos can swim. High-speed cinematography shows that, in swimming, lateral undulations pass rostro-caudally down the body. The swimming rhythm period is 40-100 ms. In swimming, electrical activity in myotomal muscles alternates on opposite sides of a segment and sweeps rostro-caudally in ipsilateral myotomes.

Myotome muscle physiology was examined. Muscle fibres are electrically coupled to each other, and the fibres are able to spike. The possible role of a myotomal conduction pathway in swimming is discussed.
Regulation of Blood Oxygen Affinity in the Australian Blackfish Gadopsis Marmoratus
Authors: Dobson G. P. , Baldwin J.
Published: April 2021

The effects of thermal acclimation on whole blood oxygen affinity were examined in the freshwater blackfish Gadopsis marmoratus. Oxygen equilibrium curves for 20 °C-acclimated fish were shifted to the right of curves obtained for 10 °C-acclimated fish when determined at both 20 °C and 10 °C. Oxygen equilibrium curves obtained for solutions of stripped haemoglobin prepared from blood of 20 °C- and 10 °C-acclimated fish did not show the differences observed for whole blood. Thermal acclimation did not alter the number, migration rates, or relative amounts of the five electrophoretic forms of haemoglobin present in blackfish blood. The intraerythrocytic concentration of nucleoside triphosphates was higher in the 20 °C-acclimated fish than in 10 °C-acclimated fish, while the whole blood haemoglobin concentration was lower in the 20 °C-acclimated fish. These differences gave NTP : Hb4 molar ratios of 1·68 for the 20 °C-acclimated fish and 1·32 for 10 °C-acclimated fish. The effects of nucleoside triphosphates on oxygen affinity were similar for stripped haemoglobins of both acclimation groups. The change in NTP:Hb4 molar ratios with acclimation temperature acts to enhance oxygen unloading to the tissues rather than oxygen uptake at the gills at the higher acclimation temperature. As the waters inhabited by the blackfish retain high oxygen tensions at 20 °C, these changes in blood oxygen affinity could be considered adaptive if they were associated with elevated rates of oxygen-dependent metabolism at the higher temperatures.
Blood Gas Transport in the Cephalopod, Sepia Officinalis
Authors: Johansen Kjell , Brix O. L. E. , Lykkeboe Gunnar
Published: April 2021

Blood gas transport was studied in unrestrained free-swimming cuttlefish, Sepia officinalis, following cannulations of an efferent branchial (arterial) vessel and the vena cava cephalica with indwelling catheters.

In well-aerated water the arterial averaged about 100·00 mmHg and was fully saturated with O2. Mixed venous varied between 17 and 40 mmHg, typically corresponding to blood O2 utilizations of 80% or higher. Some blood samples showed venous pH to exceed arterial, a tendency becoming more distinct during exposure to hypoxic water. The resulting higher O2 affinity of venous compared to arterial blood discourages O2 unloading in the tissues, while promoting efficient O2 loading in the gills. A high n-value of Sepia blood (n = 4·7) is important for maintaining a large arteriovenous O2 content difference and a high utilization of circulating O2.
Hydrophilic Cuticle - The Basis for Water Vapour Absorption by the Desert Burrowing Cockroach,Arenivaga Investigata
Authors: O’Donnell M. J.
Published: April 2021

A micro-method has been developed for measuring the water content of materials over a range of humidities. A vapour pressure osmometer measures the equilibrium humidity in a sealed chamber containing the sample and an accurately known volume of water. The cuticle of the hypopharyngeal bladders, which are the sites for atmospheric water absorption in Arenivaga, has a water affinity much greater than that of unspecialized cuticle from this and other species. This difference is also found in washed samples. The hydrophilic properties of the bladder cuticle are therefore not due to dissolved salts in the frontal body fluid which is applied to the bladders during absorption in vivo. Dissolved salts reduce cuticle water affinity. The basis for this effect is discussed with reference to known properties of polyelectrolytes. A model of in vivo absorption is proposed. It is suggested that the cyclical addition of frontal body fluid alters the water affinity of bladder cuticle so that condensed water is released. Some of the water is then swallowed.
Responses to Hypersaline Exposure in the Euryhaline CrayfishPacifastacus Leniusculus
Authors: G. Wheatly Michèle , McMahon B. R.
Published: April 2021

The effect of 48 h of hypersaline exposure (25, 50 and 75% SW) on haemocyanin oxygenation properties in the euryhaline crayfish Pacifastacus leniusculus was investigated in vitro and in vivo. In vitro significant increases in affinity and cooperativity were measured, although the magnitude of the Bohr shift was unaffected. In vitro dialysis of haemolymph against physiological salines of variable ionic composition proved that these changes were only partly attributable to altered levels of haemolymph ions, implicating the existence of modulators other than H+ and inorganic ions, the possible identities of which are discussed. Significant depressions of both pre- and postbranchial oxygen tensions ( and ) were observed, but O2 delivery was maintained by utilization of the venous reserve and by an increase in haemocyanin O2 affinity. This occurred despite a concomitant acidosis whose effect on O2 affinity was directly opposed by the ‘salt’ effect. Under hypersaline conditions, haemocyanin played an increasingly important role in O2 delivery in vivo. Despite a reduction in the concentration of combined O2 at complete saturation of the pigment (), indicating lowered haemocyanin concentration, compensatory changes in O2-binding and cardiac output precluded an impairment to O2 transfer. Equilibration at the tissues () in FW was less effective than at the gills () but progressively improved with hypersaline exposure reversing this trend. Although effects of increased salinity on O2 equilibrium characteristics were qualitatively similar in vivo and in vitro, some interesting quantitative differences are discussed.
Intracellular and extracellular acid-base regulation in the tropical fresh-water teleost fishSynbranchus marmoratusin response to the transition from water breathing to air breathing
Authors: Heisler Norbert
Published: April 2021

In the tropical fresh water fish, Synbranchus marmoratus, transition from water breathing to air breathing, induced by reduction of oxygen partial pressure () in the environmental water below 16 mmHg, causes a considerable rise in the arterial partial pressure of carbon dioxide () from 5·6 to 26 mmHg on the average (half time of the rise between 2 and 6·5 h). The associated fall in arterial plasma pH by about 0·6 units is not compensated by an increase in plasma bicarbonate concentration, whereas the intracellular pH of white skeletal muscle and heart muscle is kept almost constant by elevation of the intracellular bicarbonate concentration. The additional bicarbonate is generated by intracellular non-bicarbonate buffering, and by net transfer into the intracellular space of bicarbonate formed by buffering in blood. Only a relatively small quantity of bicarbonate is taken up from environmental water.

This type of acid-base regulation, with almost complete intracellular pH compensation and only minor bicarbonate uptake (equivalent H+ release or OH− uptake) from water, is attributed to several factors. Probably the most important of these is the lack of continuous contact of the gills, which are the main site of ion transfer processes, with the environmental water during air breathing. Regardless of the mechanisms involved, this particular strategy of acid-base regulation provides a constant milieu for the intracellular structures and demonstrates the prevalence of intracellular over extracellular acid-base regulation.