bluuebunny/crossref_metadata_2025_split huggingface dataset:
Coding of Directional Information by Single Neurones in the S-Segment of the Fm Bat, Myotis Lucifugus
Authors: Jen Philip H.-S. 
Published: April 2021

ABSTRACT
Response parameters of S-segment neurones of the FM bat Myotis lucifugus were measured as a sound was delivered from different azimuthal angles around the animal’s head. The response parameters investigated were the amplitude and threshold of the evoked potential (N3) of the S-segment, together with the threshold, latency and number of impulses (per stimulus pulse) of single units. All the neurones studied had their lowest thresholds either at 20–40° contralateral, or 20–40° ipsilateral or at the front (o°). The amplitude of the sound affected the relationship between stimulus direction and the amplitude of a non-monotonic N3, and the relationship between stimulus direction and the number of impulses of a non-monotonic single unit. It had no such effects with a monotonic N3 and a monotonic single unit. From a study of N3 amplitudes and numbers of impulses of single neurones, it appeared that an azimuthal difference as small as 3° could be easily coded at a 95% correct level with stimuli presented at around 20° ipsilateral, 20° contralateral, and at the front. The inter-aural pressure difference (IPD), which is considered an essential cue for echolocation in Myotis (Shimozawa et al. 1974), changed linearly with angle from 0 to 40° lateral at a rate of 0·4 dB/degree for sounds between 33·5 and 49·0 kHz. Assuming the just-detectable IPD to be 0·5 dB (as in man), the minimum detectable azimuthal difference of Myotis around the median plane would be 1·25°.
Cardiovascular Dynamics and Adrenergic Responses of the Rainbow Trout In Vivo
Authors: Wood Chris M. , Shelton Graham 
Published: April 2021

ABSTRACT
Cardiac output and dorsal aorta, ventral aorta, caudal artery, caudal vein, and subintestinal vein pressures have been directly measured in intact unanaesthetized trout. Cardiac output (Q̇) averaged 36·7 ml/kg.min. The pressure drop across the systemic vascular resistance (Rs) was approximately twice that across the gill resistance (Rg), and a significant positive pressure persisted in the venous system. α-Adrenergic blockade revealed a considerable endogenous vasomotor tone resulting from latent adrenergic constriction of RS. Intravenous adrenaline caused a pressor response throughout the circulatory system which has been analysed in detail with the aid of previous studies on isolated parts of the trout circulation. The complex and variable form of the pressor response reflected differential contributions from changes in Q̇, Rg, and Rs. Increases in R3 (α-receptor activation) were the principal cause of all pressor responses. Rg usually declined slightly due to passive dilation and/or β-receptor stimulation, but occasionally increased due to a-receptor activation. The cardiac response reflected a varying balance between a direct β-stimulatory effect of adrenaline on Q̇ and an indirect passive inhibition of Q̇ by the increase in peripheral resistance. Both effects were mediated through changes in stroke volume. Occasional tachycardia or more frequent reflex bradycardia were minor components of the cardiac response. The in vivo actions of other adrenergic agents have been similarly analysed.
The Reflex Control of Heart Rate and Cardiac Output in the Rainbow Trout: Interactive Influences of Hypoxia, Haemorrhage, and Systemic Vasomotor Tone
Authors: Wood Chris M. , Shelton Graham 
Published: April 2021

ABSTRACT
In cannulated trout there was no cholinergic vagal tone as revealed by atropine blockade during normal heart rates. Reductions in heart rate occasionally occurred under normoxia without apparent external stimuli (‘spontaneous’ bradycardia) and always occurred under environmental hypoxia (hypoxic bradycardia) due to the imposition of significant vagal tone. Direct measurements of cardiac output during these bradycardias showed that increases in cardiac stroke volume compensated for the falls in heart rate so that total remained unchanged or increased slightly. Sudden experimental reductions in arterial blood pressure via blockade of systemic vasomotor tone with yohimbine or via haemorrhage had no effect on heart rate during normal rates, but caused cardioacceleration during both types of bradycardia. These increases in heart rate never exceeded the point of zero vagal tone (normal heart rate) and were largely or wholly due to reductions in endogenous vagal tone. These cardioaccelerations were temporary; spontaneous bradycardia could re-occur at any time, while hypoxic bradycardia always re-occurred if the hypoxic stimulus were maintained. The results are interpreted in terms of a central interaction between the baroreceptor and chemoreceptor reflexes.
A Simple Method to Determine Drag Coefficients in Aquatic Animals
Authors: Bilo D. , Nachtigall W. 
Published: April 2021

ABSTRACT
The drag coefficient CD= 2.D/(Aρν2) (D drag, A characteristic area of the object, ρ density of medium, ν relative speed between object and medium) is important in determining energetic requirements of a biological or technical ‘construction’ that is moving in a fluid. A small value indicates low energetic requirements. Before World War II drag coefficients of cares were usually determined by deceleration measurements. We have modified the measuring system and developed a simple method of analysis to determine CD values without influencing the swimming animal in any way. Gentoo penguins (Pygoscelis papua) were filmed during decelerating underwater gliding (‘Ausgleiten’) without any movements of extremities, parallel to a large underwater window of a penguinarium. From these films distance-time functions were plotted (Fig. 1 a). Using distance-differences Ax and time differences Δt between two points, momentary velocity ν = Δx/Δt can be determined. The reciprocal velocity ν-1 as a function of time t gives a straight line in the case of undisturbed deceleration as explained by the following.
The Influence of Calcium on the Physiological Responses of the Rainbow Trout, Salmo Gairdneri, to Low Environmental pH
Authors: McDONALD D. G. , Hobe H. , Wood C. M. 
Published: April 2021

ABSTRACT
The physiological responses of 1- to 2-year-old rainbow trout to low pH are dependent on the environmental calcium concentration. Trout, maintained for 5 days in moderately hard water ([Ca2+] = 1·6 −2·7 m-equiv/1) at a mean pH of 4·3, developed a major blood acidosis but exhibited only a minor depression in plasma ion levels. In acidified soft water ([Ca2+] = 0·3 m-equiv/1), only a minor acidosis occurred, but plasma ion levels fell and there were substantially greater mortalities. Lethal bioassays performed on fingerling trout over a range of pH levels (3·0−4·8) revealed an important influence of external [Ca2+] on resistance to acid exposure. Terminal physiological measurements on adult fish succumbing to low pH in soft water indicate the singular importance of iono-regulatory failure as the toxic mechanism of action under these circumstances.
The Transepithelial Potential and Osmotic Regulation in the Green Hydra
Authors: Chain Benjamin M. 
Published: April 2021

ABSTRACT
The properties of the ion-transporting systems in the green Hydra were investigated by measuring the trans-epithelial potential and the potential profile across the body wall. The major potential step occurs across the inner ectodermal membrane, and is produced by an inwardly directed electrogenic sodium pump, which is sensitive to ethacrynic acid but not to ouabain. Calcium ions inhibit sodium transport across the epithelium. Calculations using data for the short-circuit current across the epithelium show that sodium transport requires a relatively high rate of energy expenditure, as would be expected ‘a priori’ for a small organism.
Ventilatory and Circulatory Responses to Hyperthermia in the Mute Swan (Cygnus Olor)
Authors: Bech C. , Johansen K. 
Published: April 2021

ABSTRACT
Ventilatory parameters of mute swans were measured at thermoneutral conditions and during heat stress. Deep body temperature increased from 39·5 to 41·1 °C. Breathing frequency increased 29 times, compared to the thermoneutral condition. Tidal volume decreased to 18 % of the pre-panting value, and the total ventilatory volume increased by 5·4 times. End-tidal and , values decreased and increased, respectively.
The swans developed a slight respiratory alkalosis; arterial decreased from an average of 27·1 to 25·7 mmHg and arterial pH increased from 7·501 to 7·559
Cardiac output, heart rate and stroke volume were 106%, 154%, and 70%, respectively, of the values at thermoneutrality. Mean arterial blood pressure and total peripheral resistance were slightly reduced.
It is concluded that the increased ventilation during panting mainly constitutes dead space ventilation resulting from the great reduction in tidal volume. Parabronchial ventilation remains nearly unchanged, resulting in only a slight hypocapnic alkalosis.
Mechanisms of Resorption and Deposition of Calcium in the Carapace of the Crab Carcinus Maenas
Authors: Roer Robert D. 
Published: April 2021

ABSTRACT
Premoult resorption of Ca from the carapace of Carcinus involves the active inward transport of Ca by the hypodermis with maximal rates occurring in stage D2 of the moult cycle. Postmoult calcification of the carapace involves the active outward transport of Ca by the hypodermis with maximal rates occurring in stages A1 and A2 of the moult cycle. Bidirectional active transport of Ca by Carcinus hypodermis may be accomplished by means of a quercitin-sensitive Ca-ATPase and a Na/Ca exchange mechanism in conjunction with observed changes in epithelial cell shape and size.
A Micropuncture Study of Kidney Function in the River Lamprey Lampetra Fluviatilis Adapted to Sea Water
Authors: Logan A. G. , Morris R. , Rankin J. C. 
Published: April 2021

ABSTRACT
Micropuncture techniques have been used to investigate kidney function in lampreys adapted to hyperosmotic media. Plasma electrolyte concentrations were maintained well below corresponding concentrations in the external environment. Urine composition was variable, but generally showed high concentrations of magnesium, sulphate and chloride ions. Lampreys in 50% sea water produced urine which was hypo or iso-osmotic to plasma, whereas those in 100% sea water produced hyperosmotic urine. Urine flow rate in 50% sea water was one tenth of that in fresh water, due to a reduction in filtration rate and an increase in water reabsorption by the kidney. As in fresh water, little if any filtered water was reabsorbed by the proximal segment. Almost 90% of filtered water was reabsorbed by the kidney of 100% sea water lampreys and most of this must have occurred in the distal and collecting segments.
An Arthropod Muscle Innervated by Nine Excitatory Motor Neurones
Authors: Phillips Christine E. 
Published: April 2021

ABSTRACT
The anatomical and physiological organization of the locust metathoracic flexor tibiae was examined by a combination of intracellular recording and electron microscopy. Nine excitatory motor neurones, three fast, three intermediate and three slow innervate the muscle ; each is uniquely identifiable using a combination of physiological response and soma location. A simple spatial distribution of inputs to the muscle from the individual motor neurones was not found. Individual muscle fibres responded to as many as seven of the motor neurones in various combinations.
The muscle fibres are heterogeneous, ranging from slow (tonic) to fast (phasic) in a continuum from predominantly phasic proximally to tonic distally. This is demonstrated by contraction and relaxation rates to direct and indirect stimulation, as well as contraction elicited by action potentials in a single flexor motor neurone. The fast and slow contractile properties of the muscle fibres are matched by appropriate ultrastructures.
Such a high degree of complexity of neuromuscular innervation as that found in the metathoracic flexor tibiae has not previously been described for an arthropod muscle.
Cholinergic Motor Control of Sea Urchin Tube Feet: Evidence for Chemical Transmission Without Synapses*
Authors: Florey E. , Cahill M. A. 
Published: April 2021

ABSTRACT
Isolated tube feet of Strongylocentrotus franciscanus contract briefly when the outer epithelium is touched. Similar twitch-like contractions can be induced by electrical stimulation of the outer surface of the tube foot. These responses appear to be chemically mediated. The following evidence indicates that the transmitter substance may be acetylcholine (ACh): ACh causes muscle contraction. This effect and that of electrical stimuli is potentiated by anticholinesterase agents and is antagonized by cholinergic blocking agents. Anaesthesia with chloralhydrate or chloretone abolishes responsiveness to mechanical or electrical stimulation but not to ACh. Desensitization with carbachol prevents responses to ACh and to mechanical or electrical stimulation.
There are no neuromuscular synapses and no axons can be detected which cross the connective tissue layer which separates the muscle fibres from the subepithelial nerve plexus. The latter is known to contain conspicuous amounts of ACh ; nerve terminals containing clear vesicles invest the outer surface of the connective tissue layer. All evidence indicates that chemical transmission involves diffusion of ACh (released from activated nerve terminals) across this connective tissue layer which is around 5 μm thick in fully extended tube feet but may have a thickness of 20 or even 25 μm in less extended ones. Calculations based on equations describing transmitter diffusion prove the feasibility of such a mechanism.
A Ca-Induced Na-Current In Paramecium
Authors: Saimi Yoshiro , Kung Ching 
Published: April 2021

ABSTRACT
Under a voltage clamp, step depolarization and repolarization can induce a sustained inward current and a tail inward current in Paramecium tetraurelia bathed in a solution containing 8 mm-Na+. These currents are best seen in the ‘paranoiac’ mutant. The I-V plot of the sustained inward current can have a region of negative resistance around – 20 mV. This current is absent when Na+ is excluded from the bath solution, and it increases as the Na+ concentration increases from 2 to 8 mm. Injection of Na+ into the cell suppresses this inward current. This current develops very slowly, reaching its maximum seconds after the step depolarization and decays with a time constant of hundreds of milliseconds after the repolarization. This slow current is dependent on Ca2+. It can be suppressed by reduction or deletion of external Ca2+ or by iontophoretic injection of EGTA. ‘Pawn’ mutants with defective Ca-conductance also lack this current. We conclude that Paramecium has a Ca-induced conductance through which the Na-current flows. Although more prominent in the ‘paranoiac’ mutant, this Ca-induced Na-current is also seen in the wild type. This conductance may function in generating plateau depolarizations lasting seconds or even minutes and the corresponding prolonged backward swimming away from sources of irritation and stress.
Oxygen Consumption by the Sea Anemone Calliactis Parasitica (Couch)
Authors: Brafield A. E. 
Published: April 2021

ABSTRACT
Oxygen consumption by Calliactis parasitica, measured in a continuous-flow polarographic respirometer, yielded a slope of 0-92 when plotted against body weight on log scales. This high value is discussed in terms of the sea anemone’s basically laminate nature. Strip-chart records of the oxygen concentration of water which had just passed a specimen of Calliactis commonly showed rhythmic fluctuations, either of low amplitude and high frequency or high amplitude and low frequency (mean cycle lengths 11 and 34 min respectively). The fluctuations are explained in terms of rhythmic muscular contractions which irrigate the enteron for respiratory purposes. Analysis of the slow fluctuations indicates that the endoderm is responsible for about 18 % of the total oxygen consumption.
The oxygen concentration of water in the enteron, measured and recorded continuously, was 4–27% of the air-saturation level. These strip chart records also frequently showed rhythmic fluctuations (mean cycle length 12 min), apparently resulting from the muscular contractions.
The Physical Properties of the Pedal Mucus of the Terrestrial Slug, Ariolimax Columbianus
Authors: Denny Mark W. , Gosline John M. 
Published: April 2021

ABSTRACT
The pedal mucus of gastropods functions in locomotion by coupling the movements of the foot to the substratum. The pedal mucus of the terrestrial slug, Ariolimax columbianus, is suited to this role by the following unusual physical properties.
At small deformations the mucus is a viscoelastic solid with a shear modulus of 100–300 Pa. The mucus shows a sharp yield point at a strain of 5–6, the yield stress increasing with increasing strain rate. At strains greater than 6 the mucus is a viscous liquid (η = 30–50 poise). The mucus recovers its solidity if allowed to ‘heal’ for a period of time, the amount of solidity recovered increasing with increasing time.
Opioid Peptides: Aspects of Their Origin, Release and Metabolism
Authors: Hughes J. , Beaumont A. , Fuentes J. A. , Malfroy B. , Unsworth C. 
Published: April 2021

ABSTRACT
At the present time there is evidence for two families of related peptides which act as ligands for opiate receptor sites. The endorphin group of peptides are derived from the ACTH/LPH precursor pro-opiocortin. The enkephalins appear to be formed from a separate precursor or precursors that have yet to be fully characterized. There appear to be a number of different types of opiate receptors and this may be related to the multiplicity of peptide ligands that have so far been identified. The enkephalins and related peptides appear to have a much wider distribution than the endorphins but the latter may act as circulating hormones unlike the enkephalins. It is likely that both endorphins and enkephalins are involved in sensory modulation processes and release of these peptides has been demonstrated during brain stimulation for pain relief. The enkephalins are very rapidly inactivated by tissue proteases, the aminopeptidases appear largely responsible for the inactivation of exogenously administered enkephalins but the dipeptidyl carboxypeptidase, termed enkephalinase, may have a special inactivating function at enkephalinergic synapses.
Evidence will be presented for the biosynthesis, the release and inactivation of the enkephalins relating to the above points.
Development of an Amphibian Neuromuscular Junction in Vivo And in Culture
Authors: Cohen M. W. 
Published: April 2021

ABSTRACT
During normal development presumptive synaptic sites in the myotomes of Xenopus laevis begin to acquire a high density of ACh receptors within as little as 2 h after the arrival of the nerve fibres. Synaptic function also begins very shortly after the arrival of the nerve fibres. Initially synaptic currents are some eight times longer lasting than at maturity and are not prolonged by anticholinesterase. During the first day after nerve-muscle contact is made there is a considerable decrease in synaptic current duration, sensitivity to anticholinesterase develops, and synaptic ultrastructure becomes apparent. Schwann cells do not arrive until later. Synaptic development proceeds with a similar rapid time course in cultures of dissociated myotomes and spinal cord derived from Xenopus embryos. The cultured muscle cells also develop synaptic specializations in the absence of nerve including sites of high ACh receptor density, cholinesterase activity, and postsynaptic ultrastructure. Studies on mixed nerve and muscle cultures have further revealed that muscle impulse and contractile activity is unnecessary for the development of synaptic ultrastructure or for the localization of ACh receptors, that the localization of ACh receptors at nerve-muscle contacts is nerve-induced and involves a redistribution of surface receptors, and that the development of synaptic specializations does not occur at nerve-muscle contacts when the source of nerve is dorsal root ganglia or sympathetic ganglia rather than spinal cord.
Preliminary Studies On the Use of Monoclonal Antibodies as Probes for Sympathetic Development
Authors: Chun Linda L. Y. , Patterson Paul H. , Cantor Harvey 
Published: April 2021

ABSTRACT
The precise structural organization and proper functioning of the adult nervous system depend on the ability of neurones to make highly ordered synaptic connexions. To define molecules involved in the development of these connexions and to study their functional roles, we use primary cultures of dissociated rat sympathetic neurones grown in the virtual absence of nonneuronal cells. These neurones can develop adrenergic or cholinergic properties, depending on the environment in which they are grown.
This ability to manipulate neuronal phenotype is being used in an attempt to identify cell surface macromolecules that are important in the development or function of adrenergic and cholinergic properties. We have produced monoclonal antibodies against the surface membranes of these neurones and are in the process of characterizing them. Results are presented on the binding specificity of one of these antibodies and on the effect of two other antibodies on neurotransmitter synthesis, uptake, and release.
Cell Interactions in Nerve and Muscle Cell Cultures
Authors: Christian C. N. , Bergey G. K. , Daniels M. P. , Nelson P. G. 
Published: April 2021

ABSTRACT
The neurotransmitter synthesized by a given class of neurones is subject to modification and, indeed, a qualitative switchover in transmitter biochemistry recently has been demonstrated (Furshpan, Potter & Landis, 1980; Walicke, Campenot & Patterson, 1977). In conjunction with the specification of transmitter biosynthesis that becomes established in a given neurone, a complementary specification of appropriate receptor production is required in any cell functionally post-synaptic to that neurone. An additional requirement of peculiar force in the nervous system has to do with the spatial organization of the receptors in the surface membrane of the post-synaptic cell once the receptors are synthesized. Inappropriately distributed receptors are useless receptors. The perfect registration of a variety of types of presynaptic release sites with high post-synaptic concentrations of appropriate receptors constitutes one of the outstanding features of nervous-system organization that must be accounted for. We report some experiments directed toward understanding the cell biology of regulation of receptor distribution over the surface membrane of muscle cells.
The Physiological Significance of Urea
Authors: Simpson W. W. , Ogden Eric 
Published: April 2021

ABSTRACT
Inasmuch as they are the end products of katabolism, the carbon dioxide and urea in the blood have been regarded merely as waste products on their way to the excretory organs until the former was shown to play a very important role as the regulating stimulus to the respiratory apparatus. Urea, on the other hand, has not up to the present time been shown to subserve any useful function in the animal body. Nevertheless it is well known that the kidney maintains the concentration of urea in the blood at a remarkably constant level and that only very slight variations of this level are found in health.