bluuebunny/crossref_metadata_2025 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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.
The Effect of Dietary Protein Levels and Haemolymph Composition on the Sensitivity of the Maxillary Palp Chemoreceptors of Locusts
Authors: Abisgold J. D. , Simpson S. J.
Published: April 2021

Previous work has shown that fifth-instar nymphs of Locusta migratoria (L.) compensate for a dilution of their dietary protein by reducing intermeal interval (Simpson & Abisgold, 1985). The effect of dietary protein on intermeal interval is regulated, either directly or indirectly, by the osmolality and free amino acid content of the haemolymph (Abisgold & Simpson, 1987). The possibility that levels of dietary protein and haemolymph composition affect the response of the maxillary palp gustatory receptors is investigated. Insects fed a low-protein diet had a significantly greater receptor response (measured as the total number of spikes in the first second of stimulation of a sensillum) to stimulation with 0·0125 moll-1 leucine in 0·05 moll-1 NaCl, 0·05 mol 1-1 NaCl alone or 0·025 mol 1-1 sucrose in 0·05 mol 1-1 NaCl than did insects fed a high-protein diet, although for both diets the response to sucrose was significantly lower than the response to the other two solutions. Increasing the free amino acid profile of the haemolymph of a low-protein-fed locust up to that of a high-protein-fed locust by injection markedly reduced the response of the receptors to subsequent stimulation with a 0·0125 mol 1-1 mix of eight of the 10 amino acids injected, but did not reduce the response to stimulation with 0·025 mol 1-1 sucrose in 0·05 mol 1-1 NaCl. This reduction was independent of the effect of injection on blood osmolality and was sustained for 50 min after the injection. The response to 0·05 mol 1-1 NaCl alone was influenced both by increases in blood amino acid levels and by osmolality, but the effect was less marked than the specific reduction in response to amino acid stimulation. The possible significance of a reduction in receptor sensitivity on feeding behaviour and the relative roles of blood osmolality and free amino acid content are discussed.
Electrophysiology of K+ Transport by Midgut Epithelium of Lepidopteran Insect Larvae I. The Transbasal Electrochemical Gradient
Authors: Moffett David F. , Koch Alan R.
Published: April 2021

Basal membrane potential (Vb) and intracellular K+ activity [(K+)i] were recorded, using microelectrodes, in isolated, superfused, short-circuited midgut of fifth instar larvae of Manduca sexta. The electrochemical gradient across the basal membrane was favourable for K+ entry as long as [K+]b was 32mequivl-1 or greater. In 20mequivl-1 K+ Vb rose so that in some cells the basal electrochemical gradient was unfavourable for K+ entry. In 10mequivl-1 K+, the basal electro-chemical gradient of all cells was unfavourable for K+ entry. This result suggests that an active K+ pump may augment passive basal K+ entry.

Addition of 2 mmol 1-1 Ba2+ to midgut resulted in substantial hyperpolarization of Vb accompanied by relatively small changes in (K+)i; the net effect was to move (K+)i farther away from electrochemical equilibrium with external K+.

Identification of recorded cells by ionophoretic injection of Lucifer Yellow showed that both major cell types of the epithelium (goblet and columnar cells) had similar control values of Vb and (K+)i and responded similarly to Ba2+, suggesting the presence of effective chemical or electrical coupling between the transporting goblet cells and the non-transporting columnar cells.

Hypoxia reduced transepithelial K+ transport, both in the absence and in the presence of Ba2+. In the absence of Ba2+, (K+)i was within a few millivolts of equilibrium and the effect of hypoxia was small. In the presence of Ba2+, when (K+)i was far from equilibrium with extracellular K+, hypoxia markedly depolarized the basal membrane.

The results are compatible with the suggestion that Ba2+ partially blocks basal K+ entry, but does not directly affect the apical pump. Hypoxia inhibits the apical pump. Since the active transepithelial transport of K+ was reduced after Ba2+ treatment even though (K+)i was unchanged, it appears that the activity of the apical pump is primarily controlled by the voltage step across the apical membrane.
Wind Tunnel Experiments to Assess the Effect of Back-Mounted Radio Transmitters on Bird Body Drag
Authors: Obrecht Holliday H. , Pennycuick C. J. , Fuller Mark R.
Published: April 2021

The aerodynamic drag of bird bodies was measured in a wind tunnel, with and without back-mounted dummy radio transmitters. Flight performance estimates indicate that the drag of a large transmitter can cause a substantial reduction of a migrant’s range, that is, the distance it can cover in non-stop flight. The drag of the transmitter can be reduced by arranging the components in an elongated shape, so minimizing the frontal area. The addition of a rounded fairing to the front end, and a pointed fairing behind, was found to reduce the drag of the transmitter by about one-third, as compared with an unfaired rectangular box.
Metabolic Control of Spontaneous Glowing in Isolated Photophores of Porichthys
Authors: Rees J. F. , Baguet F.
Published: April 2021

Isolated photophores of the epipelagic fish Porichthys notatus become spontaneously luminescent after a few hours in saline at 20°C. This luminescence is not significantly affected by the adrenergic antagonists propranolol and phentolamine. The addition of glucose, mannose, fructose or galactose in saline inhibits glowing according to their respective rates of metabolism in fishes. Glycolytic metabolites, such as phosphoenolpyruvate and pyruvate, prevent or abolish the spontaneous glowing. Monoiodoacetate (IAA), the classical inhibitor of glycolysis, reverses the inhibitory effect of glucose but not of pyruvate. We suggested that glycolysis provides an energy supply to an inhibitory mechanism that keeps the Porichthys photophore in a non-luminescent state.
Connections of Hindwing Tegulae with Flight Neurones in the Locust, Locusta Migratoria
Authors: Pearson K. G. , Wolf H.
Published: April 2021

The connections of afferents from the hindwing tegulae to flight motoneurones and interneurones in the locust, Locusta migratoria, have been determined by selectively stimulating the tegula afferents while recording intracellularly from identified neurones in the meso- and metathoracic ganglia. Electrical stimulation of the hindwing tegula nerve (nerve ICla) revealed two groups of afferents distinguished by a difference in their conduction velocities. Both groups of afferents made excitatory connections to hindwing elevator motoneurones in the ipsilateral half of the metathoracic ganglion. Latency measurements indicated that these connections were monosynaptic. Stimulation of the hindwing tegula nerve also evoked excitatory postsynaptic potentials (EPSPs) in elevator motoneurones in the mesothoracic ganglion and in the contralateral half of the metathoracic ganglion, and inhibitory postsynaptic potentials (IPSPs) in forewing and hindwing depressor motoneurones. The latencies of these evoked EPSPs and IPSPs indicated that the initial responses were produced via interneuronal pathways. None of the recordings revealed EPSPs in depressor motoneurones or IPSPs in elevator motoneurones in response to hindwing tegula stimulation. This observation differs from that in Schistocerca gregaria where it has been reported that the large tegula afferents produce EPSPs in depressors and IPSPs in elevators (Kien & Altman, 1979). Some of the interneurones in disynaptic excitatory and inhibitory pathways to motoneurones were identified. These interneurones received input from both hindwing tegulae and were readily excited beyond threshold by mechanical stimulation of the tegulae or by electrical stimulation of the tegula afferents. The contribution of one excitatory interneurone to the electrically evoked EPSPs was assessed by blocking spike initiation in the interneurone while recording simultaneously from a flight motoneurone. Based on our observations of the central connections of tegula afferents to flight motoneurones and the previously reported discharge patterns of these afferents during tethered flight (Neumann, 1985), we propose that a major function of the hindwing tegulae in L. migratoria is to generate the initial depolarizations in forewing and hindwing elevator motoneurones during flight. Consistent with this proposal was our finding that ablation of the hindwing tegulae delayed the onset of elevator activity relative to the onset of the preceding depressor activity.
Learning by the Aplysia Model System: Lack of Correlation Between Gill and Gill Motor Neurone Responses
Authors: Colebrook Elaine , Lukowiak Ken
Published: April 2021

A semi-intact preparation of Aplysia californica was used to monitor simultaneously behavioural and motor neurone responses during classical conditioning of the gill withdrawal reflex. Gill motor neurone responses and gill withdrawal responses were both capable of enhancement in response to the conditioned stimulus after associative training. The neuronal and behavioural responses did not, however, correlate. In 32% of the conditioned (paired) preparations and 27% of the control (unpaired) preparations, the neuronal response was facilitated whereas the gill withdrawal response did not change, or decreased. In addition, amongst those preparations that showed behavioural enhancement, the acquisition of learning of gill withdrawal followed a different pattern from that displayed by the central neurones. This suggests that facilitation of the central sensory-motor neurone synapses is not primarily responsible for conditioning of the gill withdrawal reflex. The gill withdrawal response elicited by direct depolarization of the central motor neurones decreased following the unpaired (control) presentations of the conditioned and unconditioned stimuli, and remained unchanged following paired presentations, suggesting that there is a site of neuronal plasticity in the gill.
Induced Drag Savings From Ground Effect and Formation Flight in Brown Pelicans
Authors: Hainsworth F. Reed
Published: April 2021

Ciné films of brown pelicans flying in formation were used to measure altitudes and wing tip spacing (WTS, distance perpendicular to the flight path between wing tips of adjacent birds at maximum span) for birds flying in ground effect, and vertical displacements and WTS for birds flying out of ground effect. Views were near coplanar with the plane of flight paths, and maximum wing span was used for scale. Induced drag savings in ground effect averaged 49% for gliding. Average WTS varied considerably with no evidence for systematic positioning near an optimum. There were also no differences in average WTS between flapping and gliding in or out of ground effect. Vertical displacements out of ground effect varied less than WTS but more than vertical displacements in ground effect. Few birds had wing beat frequencies similar to the bird ahead as would be needed to track vertical variation in trailing wing tip vortex positions. Imprecision in WTS may be due to unpredictable flow fields in ground effect, and difficulty in maintaining position under windy conditions out of ground effect.
The Aerobic Capacity of Locomotory Muscles in the Tufted Duck, Aythya Fuligula
Authors: Turner D. L. , Butler P. J.
Published: April 2021

The locomotory muscles of the tufted duck, Aythya fuligula (L.), were analysed for mass, aerobic and anaerobic enzyme activities, fibre-type proportions, capillarity, mitochondrial and myoglobin content. The estimated aerobic capacity of the muscles correlated well with the muscles’ maximal oxygen uptake both when measured during swimming and when predicted for steady-state flight. The results suggest that exercise performance in birds cannot be predicted purely on the basis of muscle mass (see Butler & Woakes, 1985); the specific enzyme complement of each muscle must also be taken into account.

The delivery of oxygen to mitochondria is facilitated by the dense capillarity and high myoglobin content of the muscles.
Regional Distribution of Blood Flow During Swimming in the Tufted Duck (Aythya Fuligula)
Authors: Butler P. J. , Turner D. L. , Al-Wassia A. , Bevan R. M.
Published: April 2021

The distribution of blood flow to a number of organs and tissues of the tufted duck was determined (by the microsphere technique) before and while the birds were swimming at close to their maximum sustainable velocity (i.e. at 0·69 ± 0·01 ms−1).

During swimming, oxygen uptake was twice the pre-exercise value. Cardiac output increased by 70%, there was no significant change in arterial blood pressure and total systemic conductance increased by 44 %. There were no significant changes in blood flow to the brain, liver, adrenal glands, spleen and respiratory muscles. Not surprisingly, there were increases in blood flow to the heart (30 % increase) and to the muscles of the hindlimbs (to 3·1 times the pre-exercise value). Significant reductions in flow occurred to various parts of the gastrointestinal tract (although not to the gastrointestinal tract as a whole), to the pancreas and to the pectoralis muscles. In the case of the flight musculature as a whole, the reduction was to approximately 40% of the values in the ducks before exercise.

Thus, despite the fact that cardiac output was some three times lower than it would have been during flight, there was a clear redistribution of blood away from some visceral organs and inactive muscles during surface swimming in the tufted duck. This lends support to the suggestion that blood is selectively directed to the legs, as well as to the brain and central nervous system (CNS) and away from the visceral organs and inactive muscles during voluntary diving in these birds.
Anomalous Behaviour of 86Rb as a Tracer for Transintestinal Potassium Transport in the Fowl, Gallus Domesticus
Authors: Grubb Barbara R. , Brown Helen V. , Bentley P. J.
Published: April 2021

Fluxes of potassium ions across biological membranes can be measured using 42K as a tracer. This isotope, however, has a half-life of only 12-4 h and it is expensive. Rubidium belongs to the alkali metal series of elements and rubidium ions behave in many respects, physicochemically and biologically, like K+. Furthermore, 86Rb has a half-life of 18-7 days and is less expensive than 42K. Thus 86Rb has been used quite widely as a tracer for estimating K+ transport. In mammals this usage has included erythrocytes (Beauge & Adragna, 1971), the crystalline lens (Becker, 1962), renal tubules (Ellison, Velazquez & Wright, 1986) and large intestine (Tannen, Marino & Dawson, 1986; Freel, 1987). In these instances, the ratios of the measured fluxes, JK/JRb were not found to differ significantly from unity. In non-mammals, 86Rb has been shown to be a useful substitute for K+ in transport studies using flounder intestine (Frizzell et al. 1984), salmon erythrocytes (Bourne & Cossins, 1984) and frog skin (Zerahn, 1983). In fish gills, the ratio JK/JRB was consistently found to be about 1·3 (Sanders & Kirschner, 1983), thus allowing for correction of estimates of K+ flux based on the use of 86Rb as a tracer. In the American silkworm (Hyalophora cecropia) gut, this ratio was 1·1 in a flat-sheet preparation (Wood & Harvery, 1979), but in a spherical preparation it was rather unpredictable with a mean of 1 -7 (Zerahn, 1980). None of these authors considered 86Rb to be a reliable substitute for 42K. Eddy (1985) has drawn attention to such possible disparities of K+ metabolism estimated by the use of 86Rb in fish. We have also found differences in estimates of K+ transport using 42K and 86Rb as tracers in the avian intestine.
A Simple Analyser for Gases In Mixed Samples
Authors: Kozacik John J.
Published: April 2021

It is often necessary to measure the concentration of a single gas in a sample of mixed gases. Dalton’s Law of Partial Pressures indicates that this may be done by measuring the volume of a sample before and after absorption of the gas of interest; the ratio of the difference between the two volumes to the original volume stating exactly the concentration of the absorbed gas.
Central Coordination of Buccal and Pedal Neuronal Activity in the Pond Snail Lymnaea Stagnalis
Authors: Kyriakides M. A. , McCROHAN C. R.
Published: April 2021

Cyclical synaptic inputs were recorded from identified giant neurones and neuronal cluster cells in the pedal ganglia of Lymnaea stagnalis. They occurred in phase with rhythmical inputs to buccal ganglion motoneurones, which have been shown to originate from interneurones of the buccal central pattern generator for feeding. In pedal neurones, the cyclical inputs were mainly inhibitory, and occurred predominantly during the radula retraction phase of the feeding cycle.

Tonic depolarization of higher-order interneurones in the feeding system, to activate the buccal central pattern generator, led to the onset of cyclical inputs to pedal neurones. These inputs were abolished after cutting the cerebrobuccal connectives, supporting the hypothesis that they originate from the buccal ganglia. The possible role of these inputs in coordinating foot and body wall movements with the buccal feeding rhythm is discussed.
Induction of Potential for Sperm Motility by Bicarbonate and pH In Rainbow Trout and Chum Salmon
Authors: Morisawa Sachiko , Morisawa Masaaki
Published: April 2021

Spermatozoa of rainbow trout and chum salmon, which have no potential for motility in the testis, acquire that potential in the sperm duct. This paper demonstrates that there is little difference between the levels of sodium, potassium, calcium, magnesium, chloride and osmolality of the seminal plasma in the testis and in the sperm duct. However, the bicarbonate concentration of the seminal plasma and the pH value of semen were higher in the sperm duct than in the testis. When immotile spermatozoa obtained from the testis were incubated in artificial seminal plasma with a high pH and containing HCO3−, spermatozoa became motile within 1 h. These results suggest that spermatozoa of salmonid fish acquire the potential for motility as a result of the increase in seminal bicarbonate concentration and pH that occurs as spermatozoa pass from the testis to the sperm duct.
Unpaired Median Neurones in a Lepidopteran Larva (Antheraea Pernyi): II. Peripheral Effects and Pharmacology
Authors: Brookes S. J. H.
Published: April 2021

Two unpaired median cells (MCI and MC2) had a temporal pattern of firing that correlated with phasic muscular activity in preparations of larval Antheraea pernyi, and previous work has indicated that the axons of median cells are associated with nerve trunks innervating blocks of muscle. In spite of this, action potentials in median cells were not found to have any one-for-one effects on either the tension or the electrical activity of somatic muscle fibres. However, bursts of action potentials in MC2 were shown to modulate both tension production and electrophysiological activity of a number of motor units. These effects consisted of an increase in twitch tension, a relaxation of basal resting tension, an increase in relaxation rate following contractions, a hyperpolarization of some muscle fibres and an increase in amplitude of excitatory junction potentials. The relative potency of these different effects varied between fast and slow muscles. All of these effects were mimicked by the application of octopamine and synephrine, and in higher concentrations by a number of other biogenic amines and adrenergic agonists. The possibility that the effects of median cell activity were mediated by the release of endogenous octopamine was supported by the observation that phentolamine (10−5moll-1) blocked the effects of both MC2 impulses and the application of exogenous octopamine, whereas propanolol affected neither set of responses. This observation also indicated a pharmacological similarity with a number of other octopamine-sensitive insect tissue preparations. MCI had similar effects to MC2 on the electrical activity of a number of muscles, suggesting that these two cells play a similar role. These observations provide strong evidence for the presence of an identifiable octopaminergic system of neurones, similar to the dorsal unpaired median (DUM) neurones that have been extensively studied in the locust.
Spectral Sensitivity of Photoreceptors and Colour Vision in the Solitary Bee, Osmia Rufa
Authors: Menzel R. , Steinmann E. , De Souza J. , Backhaus W.
Published: April 2021

The spectral sensitivity of single photoreceptors of Osmia rufa was determined by a fast voltage-clamp technique. Three receptor types were found whose spectral sensitivity functions followed a rhodopsin-like photopigment absorption function with λmax values at 348nm (ultraviolet receptor), 436nm (blue receptor) and 572nm (green receptor). The λmax of the green receptor in Osmia rufa is shifted to much longer wavelengths compared with other insect species. Discrimination of colour signals was tested after training a bee at the entrance to its nest. The colour signals were filter discs (70 mm in diameter) with a hole (10 mm in diameter) in the centre and the bees quickly learned to use the coloured disc as a marker of the nest entrance. Tests were dual forced-choice tests with two coloured discs closely positioned next to each other. 94 different tests were each repeated 5–15 times and were performed after training to 12 different colour signals.

A photoreceptor model was used to calculate the loci of the colour signals in a three-dimensional colour space and in a chromaticity diagram. The perceptual distance between the colour loci was calculated as line elements (minimum number of just noticeable difference, jnd-steps), which were based on the noise properties of the photoreceptors. The discrimination determined by the behavioural tests correlated very well with the jnd-steps. The correlation was better for the line elements in the colour plane than in the colour space. Osmia rufa was compared with the honeybee Apis mellifera and the stingless bee Melipona quadrifasciata. There is no difference in colour selection between Osmia and Apis, whereas Melipona discriminates less well in the violet-blue region. The model calculation was used to compare the chromaticity diagrams and the spectral discrimination functions of the three species. It is concluded that the receptor model used in this study predicts the discrimination behaviour of the three bee species very well. Therefore, comparative studies on colour vision in flower visiting insects may be based on spectral measurements of the photoreceptors, and in many cases this reduces the extent of laborious behavioural studies.
The Adrenergic Responses of Carp (Cyprinus Carpio) Red Cells: Effects of and pH
Authors: Salama Annika , Nikinmaa Mikko
Published: April 2021

Carp (Cyprinus carpio) red cells do not show β-adrenergic responses when incubated with 10−5moll−1 adrenaline at atmospheric oxygen tension and a pH value close to the in vivo resting pH (approx. 8·1). However, when either the pH or the oxygen tension of the incubation medium is decreased, the adrenergic responses appear, showing that oxygen or an oxygen-linked phenomenon has a direct influence on the response. Once present, the adrenergic red cell response is similar to that of trout: cellular water content, sodium content and intracellular pH all increase. Quantitatively the effect appears to be much smaller in carp than in trout. Adrenaline induces an increase in red cell oxygen content when the oxygen content is plotted as a function of extracellular pH. This effect coincides with the onset of the Root effect and is caused by the adrenaline-induced increase in intracellular pH, since it disappears when the oxygen content is plotted as a function of intracellular pH. The red cell ATP content decreases metabolically during adrenaline incubations. In contrast, cellular GTP content is not metabolically reduced in adrenaline-treated cells, showing that the rapid and selective decrease in red cell GTP concentration, observed in hypoxic cyprinids, is not adrenergically induced.
Quantitative Analysis of Resting Membrane Electrogenesis in Insect (Diptera) Skeletal Muscle I. Intracellular K+, Na+ and Cl- Activities, Measured Using Liquid Ion-Exchanger and Neutral Ion-Carrier Microelectrodes
Authors: Dawson Jill , Djamgoz M. B. A.
Published: April 2021

Electrophysiological properties of skeletal body-wall muscles of prepupal Calliphora erythrocephala were investigated using double-barrelled intracellular ion-sensitive microelectrodes. The most realistic estimate of the intracellular K+ activity, obtained using K+-sensitive microelectrodes based on a neutral carrier, was 115mmoll-1. The K+ equilibrium potential was consistently more negative than the prevailing resting potential, the average difference being —15 mV. The intracellular Na+ activity and the Na+ equilibrium potential were 7 mmol 1-1 and +46 mV on average, respectively. The mean value of the intracellular Cl- activity was 40 mmol 1-1, and this was apparently higher than that required for passive distribution of Cl-. However, when reversibly exposed to a Ringer containing no Cl-, cells could rapidly exchange most of their intracellular Cl-, although the resting membrane potentials were only transiently affected. It is concluded that an anionic interferent exists inside muscles, that this artefactually elevates the measured intracellular Cl- activities, and that Cl- makes no contribution to resting membrane electrogenesis.