bluuebunny/crossref_metadata_2025 huggingface dataset:
From Embryonic Fascicles to Adult Tracts: Organization of Neuropile From a Developmental Perspective
Authors: Bastiani Michael , Pearson Keir G. , Goodman Corey S.
Published: April 2021

We discuss ideas emerging from our studies on selective axonal fasciculation in the grasshopper embryo that have implications for the organization of the adult neuropile in insects and perhaps other animals. While one of our laboratories has been studying the embryonic development of the G neurone (in the mesothoracic segment) and its lineal homologues (in other segments), the other has been studying the morphology and physiology of this same neurone and its segmental homologues in the adult nervous system. Our embryonic studies show that the growth cone of the G neurone selectively fasciculates with the A/P fascicle in preference to all other longitudinal axon fascicles as it turns anteriorly. The homologues of G in other thoracic and abdominal segments fasciculate in this same bundle. However, early in their morphological differentiation, they reveal interesting segmental differences. Our studies on the adult nervous system show that the segmental homologues of the G neurone share many properties in common (e.g. axons in the LDT : lateral dorsal tract) while other features are quite different. The notion emerging from these studies is that a basic segmentally-repeated pattern arises during embryogenesis: a stereotyped axonal scaffold upon which growth cones faithfully fasciculate. Evolutionary plasticity allows the specialization of lineally equivalent neurones in different segments within the context of the neuropilar neighbourhood that they find themselves in as a consequence of their selective fasciculation.
Neurogenetics and Behaviour in Insects
Authors: Fischbach K. F. , Heisenberg M.
Published: April 2021

The importance of the genome for behaviour has been amply demonstrated by the tools of population genetics. A deeper understanding of the relationship between genes and behaviour requires an investigation of how they influence brain development and neuronal function. This is the objective of neurogenetics.

Rigid genetic control of brain structure in insects is indicated by bilateral symmetry and by the similarity of isogenic brains (in locust). In large parts of the brain (e.g. optic lobes) the role of developmental variability seems to be as limited as in nematodes, but at closer inspection, the growth of at least some brain structures (e.g. mushroom bodies) is influenced by experience, similar to the growth of some vertebrate systems.

The role of individual genes for brain development and brain function is being studied in Drosophila melanogaster. Here, many single gene mutations affecting the brain and behaviour have been isolated. They either alter the development of neural circuits or modify cellular functions of neurones. Mutations of both categories are often remarkably specific (i.e. they influence only certain functional subsystems, leaving others unaffected). Therefore, functional subsystems are to some degree ontogenetic units under independent genetic control. Telling examples are sexual dimorphisms of behaviour and brain structure. The already peripheral separation of functional pathways in the brain seems to be partially due to the selective advantage of independent genetic modifiability of functions.
The Effects of Temperature on the Characteristics of the Dogfish Oculomotor System
Authors: Montgomery J. C. , Paulin M. G.
Published: April 2021

The dogfish oculomotor system can be modelled as a first order linear system (Montgomery, 1983) and hence can be specified by its characteristic frequency and gain. This paper describes the effect of temperature on these two parameters. The characteristic frequency is directly related to temperature, and decreases from 0·31 Hz at 20°C to 0·15 Hz at 10°C. The gain is inversely related to temperature, increasing approximately 2·5 times over a temperature drop from 20 °C to 10 °C. It is argued that the increase in gain with falling temperature can be attributed to an increase in relaxation time of the muscle, and that it is likely to be of biological significance in maintaining reflex performance in a poikilothermic animal.
Temporal and Spatial Spread of an Intersegmental Reflex in Crayfish
Authors: Page Charles H. , Gadaleta Dominick , Iacopino Anthony
Published: April 2021

An intersegmental reflex initiated by flexing a crayfish leg at the mero-carpal joint was examined by recording reflex response latencies of cephalic, thoracic and abdominal muscles. The first response was an intrasegmental resistance reflex in the extensor muscle of the stimulated leg. Spread of the intersegmental reflex occurred in both cephalic and caudal directions. Activation of the cephalic appendages occurred first (antennal levators, with latencies of 14–18 ms) while the abdominal musculature was activated last (superficial extensors, with latencies of 51–62ms). Shift of the stimulus site from the second to the fifth leg resulted in shorter latencies of the fifth leg and abdominal muscle responses while the latency for second leg extensor muscle discharge increased.

Low correlation coefficients between the response latencies of pairs of cephalic and abdominal muscles, and thoracic and abdominal muscles, indicate that reflex pathways which initiate the abdominal responses are different from those that evoke the cephalic and thoracic responses. High correlation coefficients indicate common reflex pathways for activating either ipsilateral or contralateral pairs of extensors or flexors in the second and fifth legs. High correlations suggesting common reflex pathways or cross-coupling were also obtained for bilateral pairs of abdominal extensors. Low correlation coefficients for the response latencies of paired muscles indicate separate reflex pathways for (1) bilaterally homologous leg muscles and (2) first–fifth segment abdominal extensors.

Surgical isolation of the supraoesophageal ganglion from the ventral nerve cord eliminated the responses of the antennal levators while producing a substantial increase in the response latencies of both maxilliped extensors and the contralateral second leg extensor and flexor, as well as a small but significant decrease in the contralateral first abdominal extensor. The synaptic input zones of the interneurones that mediate the thoracic and abdominal responses are located in the ventral nerve cord and not in the supraoesophageal ganglion.
Thermal Dependence of Contractile Properties of Red and White Fibres Isolated From the Iliofibularis Muscle of the Desert Iguana (Dipsosaurus Dorsalis)
Authors: Johnston Ian A. , Gleeson Todd T.
Published: April 2021

Single fibres were isolated from the ‘red’ and ‘white’ portions of the iliofibularis muscle from the desert iguana (Dipsosaurus dorsalis). Muscle fibres were chemically skinned with the non-ionic detergent Brij. 58.

Maximal Ca2+-activated tensions at 40°C were 32·3 ± 1·5 N cm-2 for red and 33·0 ± 24 N cm-2 for white muscle fibres (mean ± S.E. mean). Unloaded contraction velocities (Vmax) were determined by the ‘slack-test’ method. Average values for Vmax at 40°C were 7·1 ±0·4 and 164 ± 14 muscle length s-1 (Lo s-1) for red and white fibres respectively. The red portion of the iliofibularis contained fibres with Vmax values between 14 and 12·9 Los-1. Around 18% of the red fibre population had maximum contraction velocities less than 4·0Los-1. These slower fibres were principally located in the region closest to the femur in situ. They probably correspond to the multiply-innervated ‘tonic type’ fibres that can be identified histochemically.

Q10 values for Vmax over the range 5·15 °C were higher for red (4·2) than white (2·3) muscle fibres. Above 25·30 °C Q10 values for Vmax were in the range 1·3−1·9 for both fibre types. Maximum Ca2+-activated tensions were largely independent of temperature between 20 and 45 °C. Dipsosaurus is maximally active in the field at 35·42 °C, which corresponds to a 2one of relative thermal independence of muscle contractile properties and locomotory performance.
Oxygen Consumption and Swimming Performance in Hypoxia-Acclimated Rainbow Trout Salmo Gairdneri
Authors: Bushnell P. G. , Steffensen J. F. , Johansen K.
Published: April 2021

Swimming performance and oxygen consumption of normoxic (control) and hypoxia-acclimated rainbow trout, Salmo gairdneri Richardson, were monitored at >145, 60 and 40mmHg. Maximum swimming velocity at 40 mmHg was reduced from >54·8cms−1 to 41·4cms−1 in controls and to 40·6cms−1 in hypoxia-acclimated fish. Normoxic oxygen consumption of control fish ranged from 97·5mg O2 kg−1 h−1 (5·5cms’1) to 318-5mg O2 kg−1 h−1 (54·8cms−1) and did not differ significantly from that of hypoxia-acclimated fish in normoxia. Reduction of ambient from normoxia to 60 mmHg or 40 mmHg did not significantly change oxygen consumption in control animals, although no fish (control or hypoxia acclimated) completed swimming trials at 54·8 cms−1 in 40mmHg. Oxygen consumption of hypoxia-acclimated fish at 5·5cms−1 and 40 mmHg was significantly higher than oxygen uptake in normoxia at the same speed. This relative increase was not maintained, however, as oxygen consumption at higher swimming speeds was similar to that in normoxia. Blood studies showed that hypoxia-acclimated fish had lower ATP concentrations and P50 values. While these factors may increase the blood oxygen loading capacity, the change is apparently not enough markedly to improve swimming performance or oxygen consumption in hypoxia and/or exercise.
Whole Body Calcium Flux Rates in Freshwater Teleosts as A Function of Ambient Calcium and Ph Levels: A Comparison Between the Euryhaline Trout, Salmo Gairdneri and Stenohaline Bullhead, Ictalurus Nebulosus
Authors: Hōbe Helve , Laurent Pierre , Mcmahon Brian R.
Published: April 2021

The exchange of calcium between the blood and external medium following intravascular injection of 45Ca was investigated in adult fresh water rainbowtrout (Salmogairdneri) acclimated to ambient [Ca2+] of 0.18, 0.65 and 5.0 mequivl−1, and in bull heads (Ictalurus nebulosus) at external [Ca2+] of 0.17 mequivl−1, each at near-neutral ambient pH, 11–12°C and constant Na+ and Cl− levels of 0.06 and 0.03 mequivl−1, respectively.

The dispersal volume of isotope exhibited a slow exponential increase with 8–9 h required for 95% of the radiospace to be filled, irrespective ofthe acclimation medium or fish species. Equilibrium radiospaces in trout (range 1600–2000 ml kg−1) were independent of ambient [Ca2+] but 1.4 -fold higher than in bullheads. In all cases, whole body exchangeable calciumcontent was low, representing ≃3 % of total body calcium content. The whole body calcium exchange rates (mean ranges; influx or efflux) in trout of 7–22μequiv kg−1 h−1 were largely independent of ambient Ca2+ levels; lower values of 2–10μequiv kg−1 h were found in bullheads.

Acute exposure (24 h) to low ambient pH 4.0-4.2 at external [Ca2+] ≃ 0.18 mequivl−1 resulted in whole body ion loss in both species. Net Ca2+ losses in trout were due to a reduction in influx whereas both increased efflux and depressed influx accounted for the response in bullheads. These changes were transitory (12 h) and minor in comparison with concomitantnet Na+ and Cl− losses which unlike Ca2+, exhibited no recovery within 24 h of acid exposure.

Possible mechanisms of Ca2+ regulation in fresh water fish are discussed.
Octopamine Release From an Identified Neurone in the Locust
Authors: Morton David B. , Evans Peter D.
Published: April 2021

The release of octopamine from the extensor-tibiae muscle preparation of the locust in response to high K+ saline and DUMETi stimulation has been demonstrated. This release has been measured using a radioenzyme assay for octopamine. Both forms of stimulated release have been shown to be calcium sensitive. Three potential problems of studying the release of transmitters from neuromuscular preparations using radiolabelled compounds have been identified, (a) The cellular location of the labelled compounds is unknown, (b) The site of the high K induced release is unknown, (c) The contraction of the muscle could cause nonspecific release of radioactivity from the muscle.
Ionic Dependence of Secretory and Electrical Activity Evoked by Elevated K+ in a Peptidergic Neurosecretory System
Authors: Cooke Ian M. , Haylett Beverley A.
Published: April 2021

Secretion of the octapeptide erythrophore-(red pigment-) concentrating hormone (ECH, RPCH) and extracellularly monitored electrical activity were followed simultaneously from individual, isolated sinus glands (neurohaemal organs), of the crab Cardisoma carnifex. Following introduction of saline having elevated [K], 100–196 mmol I−1 (5–11× normal), secretion (bioassayed from 1-min fractions during continuous perfusion) increases from barely detectable (<1 fmol min−1) to a peak, average 31fmolmin−1, within 5 min, and immediately subsides. Additional responses are obtainable following a period, >30 min, of normal saline perfusion. Secretory responses to K are Ca-dependent. If Ca is restored (in high K) following perfusion in 0-Ca, high K, only a small secretory response is observed. Addition of Mn (10mmol I−1, normal Ca) reduces secretion to one-tenth. Increased net uptake of 45Ca of 2·5- to 6-fold is observed in individual sinus glands exposed to 10× K compared to paired, unstimulated organs. The pattern and Ca-dependence of secretory responses to K are unaffected, but the amount of secretion is augmented in Na-deficient or TTX-containing salines. Intracellular recording confirms that brief (10–40 s) bouts of intense firing recorded extracellularly upon commencing a high K perfusion include repetitive firing by terminals, superimposed on rapid depolarization. Firing ceases as the membrane potential reaches a depolarized value (–18 to –15 mV for [K] 100–176 mmol I−1), which is then maintained until restoration of normal saline, when slow repolarization ensues. In 0-Ca, spontaneous impulse firing is increased, resting potential depolarized by 5 to 15 mV, but the bout of impulse firing and the maintained depolarization in response to K are similar. Thus, mechanisms of secretion of a crustacean peptide neurohormone appear closely similar to those of other systems characterized: responsiveness to elevated K, dependence on Ca, depolarization-, but not secretion-dependent inactivation, and lack of dependence on Na inward current. Intracellular recording here permits direct observation of electrical responses of terminals.
Vascular And Renal Actions Of Salmon Calcitonin In Freshwater- and Seawater-Adapted European Eels (Anguilla Anguilla)
Authors: Wales N. A. M.
Published: April 2021

When freshwater eels were given either 5 or 15 i.u. calcitonin kg−1 body weight, there was an increase in dorsal aortic blood pressure as well as a rise in urine volume, glomerular filtration rate and electrolyte excretion rate, 1 h after injection. None of these changes was shown by seawater-adapted eels. When freshwater-adapted eels received 15 i.u. calcitonin kg−1 body weight there were significant changes in plasma electrolyte levels, again a response not shown by seawater-adapted fish. These changes occurred in 1 h after the injection of hormone, during which time plasma levels of sodium, chloride and calcium fell whilst plasma potassium levels increased.

At no time within the first hour were there changes in the relative handling of electrolytes. However, seawater-adapted eels showed hypercalcaemia and a reduced relative calcium clearance 3 h after receiving 15 i.u. calcitonin kg−1 body weight.
Synapses Between an Identified Giant Interneurone and A Filiform Hair Sensory Neurone in the Terminal Ganglion of First Instar Cockroaches (Periplaneta Americana L.)
Authors: Blagburn J. M. , Beadle D. J. , Sattelle D. B.
Published: April 2021

The ultrastructure of input and output synapses of various identified insect neurones has recently been studied (for example Titmus & Hoyle, 1977; Altman, Shaw & Tyrer, 1980; Phillips, 1980; Watson & Burrows, 1981, 1982, 1983; Tolbert & Hildebrand, 1981) and connections between anatomically and physiologically defined axons have been described (King & Wyman, 1980). To date though, synapses have not been visualized in an insect central pathway in which aspects of the anatomy, physiology, pharmacology and associated behaviour have been investigated. The cereal afferent, giant interneurone synapses in the sixth abdominal (A6) ganglion of the cockroach Periplaneta americana are well suited for such studies. Using cobalt staining (Pitman, Tweedle & Cohen, 1972) of single neurones, seven giant interneurones (GIs 1–7) can be identified on the basis of their morphology (Harrow, Hue, Pelhate & Sattelle, 1980; Daley, Vardi, Appignani & Camhi, 1981). In adult cockroaches these interneurones receive sensory input from numerous cereal mechanoreceptor afferents (Callec, Guillet, Pichon & Boistel, 1971 ; Daley et al. 1981). There is considerable evidence for cholinergic monosynaptic transmission at these synapses (Callec, 1974; Sattelle, 1980) and postsynaptic acetylcholine receptors sensitive to the nicotinic cholinergic antagonist a-bungarotoxin are present on GI2 and GI 3 (Harrow, Hue, Pelhate & Sattelle, 1979; Sattelle, David, Harrow & Hue, 1980; Harrow & Sattelle, 1983 ; Sattelle et al. 1983). It has been shown that the cereal afferent, giant interneurone pathways play a part in mediating the escape response of the cockroach following stimulation of the cereal mechanoreceptors (Ritzmann & Camhi, 1978; Camhi, Tom & Volman, 1978).
Ion Transport in the Midgut of the Cockroaches Leucophaea Maderae And Blabera Gigantea
Authors: Giordana B. , Sacchi V. F. , Zerahn K.
Published: April 2021

The presence of a cation pump on the apical membrane of epithelial cells in insects, responsible for the extrusion of K or Na, has been proposed for Malpighian tubules (Maddrell, 1977) and salivary glands (Berridge, Lindley & Prince, 1976). An essential role of the midgut in K homeostasis has been established only for the phytophagous larvae of Lepidoptera (Harvey & Nedergaard, 1964). The main features of the rheogenic, luminally-directed potassium pump of this tissue have been extensively studied (Zerahn, 1978; Harvey, Cioffi, Dow & Wolfersberger, 1983). Since the midgut of these animals is also peculiar in that it does not actively absorb Na, the presence of the K pump could be the sole example in insect gut physiology. Na absorption in the midgut has been demonstrated in several species of insects (O’Riordan, 1969; Sauer, Schlenz True & Mills, 1969; Farmer, Maddrell & Spring, 1981 ; Dow, 1981a; Koefoed & Zerahn, 1982) while K secretion has been suggested for Periplaneta americana (Sauer & Mills, 1969), Leucophaea maderae (Sacchi & Giordana, 1979) and Schistocerca gregaria (Dow, 1981b).
Do the Motoneurones Constitute A Part of the Spinal Network Generating the Swimming Rhythm in the Lamprey?
Authors: Wallén P. , Lansner A.
Published: April 2021

In the study of the neural control of rhythmic motor acts, the operation of the central neuronal networks that produce the motor pattern is an area of considerable interest (cf. Delcomyn, 1980; Grillner, 1981). The motor pattern underlying swimming in the lamprey, a primitive vertebrate, can be produced in the isolated spinal cord in vitro (Cohen & Wallén, 1980; Wallén & Williams, 1984). The capacity to generate the rhythmic pattern is distributed throughout the spinal cord, and short pieces of just a few segments may produce a coordinated pattern (Cohen & Wallén, 1980; Grillner & Sigvardt, in Grillner et al. 1982).
Analysis of the Scaphognathiteventilatory Pump in the Shore Crab Carcinus Maenas I. Work and Power
Authors: Mercier A. Joffre , Wilkens Jerrel L.
Published: April 2021

Measurements of branchial pressure and ventilation volumes were used to calculate the work and power of gill ventilation in Carcinus maenas, during spontaneous as well as forced unilateral ventilation. With increasing ventilation rate (fR), the stroke work increases as a result of an elevated gradient of branchial pressure, while power output increases as a result of enhancement of both the pressure gradient and the flow rate. To a first approximation, the stroke work is proportional to fR1·5, and the power output is proportional to fR2·5. The available evidence suggests that flow is mainly laminar through the branchial chamber but turbulent through the pumping chamber. Evidence is presented which suggests that the crab is able to vary the resistance to the flow of branchial water.

The increased branchial pressure at elevated ventilation rates constitutes an increased load on the ventilatory muscles. Measurements of isometric tension confirm that the muscles compensate for this increased load by generating greater force. Electromyograms support the notion that the change in force results from appropriate changes in the output from the central pattern generator.
Structural Variability of an Identified Interneurone in Locusts From a Wild Population
Authors: Satterlie Richard A.
Published: April 2021

One property of invertebrate nervous systems used to great experimental advantage is the ‘identifiability’ of individual neurones. A principal tenet of the ‘identified neurone’ concept is that a certain degree of structural regularity can be expected when investigating an identified cell in individual members of a single species. Yet in organisms that reproduce sexually some degree of structural variability should be expected over and above that attributed to developmental noise. Genotypic lineage appears to be a strong determinant of neurone structure. Recent studies using controlled lineages through selective and parthenogenetic breeding have indicated a fairly strong genetic influence on neurone number, structure and interconnections (Macagno, Lopresti & Levinthal, 1973; Goodman, 1977, 1978; Steeves & Pearson, 1983). In wild populations, however, some genetic variability may be selectively eliminated through environmental factors as well as intra-and interspecific biological interactions.
Differences in metabolic potential of skeletal muscle fibres and their significance for metabolic control
Authors: Gollnick P. D. , Riedy M. , Quintinskie J. J. , Bertocci L. A.
Published: April 2021

When exposed to chronic overloads skeletal muscle is remodelled, thereby equipping it to better meet the stresses it is encountering. Examples abound in nature of the adaptive response of muscle exposed to different tasks (i.e. Armstrong, lanuzzo & Kutz, 1977; Newsholme & Start, 1973). The principles that are outlined in this paper for the relationship between metabolic potential and control of metabolism apply to all situations where differences in metabolic potential exist. The basic model discussed is that of physical training, particularly endurance training, on skeletal muscle and metabolic control. Training was selected as the model as it is a convenient method for inducing changes in skeletal muscle and for illustrating the consequences of these adaptations on the local and total body metabolism. Thus, heavy resistance exercise taxes the tension development capacity but not prolonged energy production so the fibres enlarge without a significant modification in the metabolic systems (Gollnick et al. 1972). In contrast, endurance training stresses energy production, particularly aerobic energy production, but not the tension developing capacity, with the end result being augmentation of the aerobic energy-producing systems. Corollaries of these exist throughout the animal kingdom.
Metabolic and circulatory limitations to at the whole animal level
Authors: di Prampero P. E.
Published: April 2021

Maximal O2 consumption increases with increasing O2 partial pressure in inspired air (Bannister & Cunningham, 1954; Fagraeus, Karlsson, Linnarsson & Saltin, 1973; Kaijser, 1970; Margaria, Camporesi, Aghemo & Sassi, 1972; Margaria, Cerretelli, Marchi & Rossi, 1961 ; Nielsen & Hansen, 1937 ; Welch & Pedersen, 1981) and following the transfusion of red blood cells (Buick et al. 1980 ; Ekblom, Goldbarg & Gullbring, 1972; Ekblom, Wilson & Åstrand, 1976); it decreases in hypoxia (both acute and chronic) (see Cerretelli, 1981 for review), following CO inhalation (Ekblom & Huot, 1972; Ekblom, Huot, Stein & Sthorstenson, 1975; Pirnay, Dujardin, Deroanne & Petit, 1971; Raven et al. 1974; Vogel & Gleser, 1972) and after acute anaemia (Woodson, Wills & Lenfant, 1978).
Temperature and muscle
Authors: Bennett A. F.
Published: April 2021

Rates of force development, contraction and relaxation of vertebrate skeletal muscle are temperature dependent with Q10 values of approximately 2. Maximal forces developed have a low or negative thermal dependence. The functional basis of these patterns is poorly understood. Muscle performance generally does not acclimate. There appears to have been some evolutionary adaptation among species and classes to different thermal regimes, such that muscles from cold-adapted species maintain better mechanical performance at low temperatures than do those from warm-adapted animals. However, rate processes remain strongly thermally dependent even in animals with low or variable body temperatures. This thermal dependence of muscle in vitro is reflected in behavioural performance: maximal force generation in vivo is temperature independent and time-dependent activities are more rapid at higher muscle temperatures.
Malleability of the system in overcoming limitations: functional elements
Authors: Saltin B.
Published: April 2021

Three different views can be found in the literature concerning the classical question in exercise physiology: what limits maximal oxygen uptake in man? Some authors believe that the limitation is the maximal rate of oxygen delivery by the cardiovascular system. Others argue that oxygen uptake is limited by the capillary bed or metabolic capacity of skeletal muscle, and the third line of thought is that no single factor can be found to be directly limiting as all links in the oxygen transport are so closely matched. The stand taken in this paper is that the skeletal muscle of man can be excluded as a limiting factor for maximal oxygen uptake in whole body exercise. It can be shown, by direct measurements, that in sedentary and in trained man maximal perfusion and oxygen utilization of skeletal muscle is so high that if all muscles in the body were engaged in intense exercise, the cardiac pump function would have to be 2-3 fold larger than it is. What happens in whole body exercise is that each muscle group receives only a fraction of the blood it can accommodate. The primary role for a larger capillary network observed in trained muscles is to keep or extend mean transit time. Elevated mitochondrial enzyme activities affect the metabolic response (i.e. lipid oxidation is elevated in trained muscles). However, these adaptations are not necessary for increasing the maximal oxygen uptake of man, as the capacity of the heart is limiting. Improved training techniques (which induce even larger improvements in cardiac pump function) may reveal that pulmonary diffusion capacity is the limiting factor.
Malleability of the motor system: training for maximizing power output
Authors: Howald H.
Published: April 2021

Power output is very high in international athletes and their performances are still improving in most sports. Such improvement is possible because of the remarkable malleability of the human motor system in response to highly specific training methods. Skeletal muscle of man can adapt to the needs for either short maximum effort (e.g. weightlifting, sprinting, etc.) or prolonged exercise (e.g. long-distance running, cycling, cross-country skiing, etc.). In many sports, however, performance capacity depends on both strength and endurance of the muscles involved (e.g. in rowing, middle-distance running, swimming and ball games), whereas in others the success of an athlete is mainly a question of optimized neuromuscular control (e.g. in gymnastics and figure skating). At the level of the muscle cell, training-induced adaptations occur in structure as well as in metabolic function and the changes are highly specific to the particular training stimulus. Some of the cellular adaptations are accompanied by adaptive processes in the cardiovascular and respiratory system, since skeletal muscle must be provided with both energy-supplying substrates and oxygen during exercise of more than one or two minutes.
Developmental Changes in the Interference Reflectors and Colorations of Tiger Beetles (Cicindela)
Authors: Schultz T. D. , Rankin M. A.
Published: April 2021

Samples of cicindelid cuticle were examined at various stages of adult ecdysis. The multilayered potential reflector was secreted in the initial stages of the moult, verifying that it is not tectocuticle and supporting the contention that it is a form of inner epicuticle. At early stages of ecdysis, the electron-dense layers were visible only when the section was post-stained. During post-ecdysial colour development, the dense layer increased in in-herent electron density. Concurrently, the reflector increased in refractive index and the interference coloration increased in intensity and wavelength of maximum reflectance. Black pigment was also deposited simultaneously within the outer portion of the cuticle. It is proposed that electron-dense material was deposited in situ within the inner epicuticle after ecdysis, thereby increasing the wavelength and reflectance of interference colour.
An Investigation of Haemocyanin Oxygen Affinity in the Semi-Terrestrial Crab Ocypode Saratan Forsk
Authors: Morris S. , Bridges C. R.
Published: April 2021

The oxygen affinity of the haemocyanin in the supralittoral crab Ocypode saratan was investigated at temperatures between 20 and 35 °C. The effect of L-lactate on dialysed and undialysed haemolymph oxygen affinity was also examined.

In general, the temperature sensitivity of the haemocyanin was low: ΔH was —3·1 kJ mol-1, between 25 and 30°C. Temperature sensitivity was temperature-dependent, being larger at the extreme temperatures (ΔH = — 26kJmol-1). The Bohr effect (ΔlogP50/ΔpH) was temperature-independent and averaged — 0·67.

No specific effect of CO2 on oxygen affinity was observed but L-lactate increased oxygen affinity in both dialysed and undialysed haemolymph. The maximal effect of lactate on oxygen affinity was similar in dialysed and undialysed haemolymph, but was evident at a lower lactate concentration (4 mmol I-1) in dialysed, compared with undialysed, haemolymph (7 mmol I-1). Dialysed haemolymph showed a higher oxygen affinity than undialysed haemolymph at low lactate concentration (<4mmoll-1). The Bohr effect and buffer value both decreased with increasing lactate concentration in both dialysed and undialysed haemolymph. The physiological implications of these findings are discussed.
Postsynaptic Potentials of Limited Duration in Visual Neurones of a Locust
Authors: Simmons Peter J.
Published: April 2021

Large, second-order neurones of locust ocelli (‘L-neurones’) make both excitatory and inhibitory connections amongst each other. A single L-neurone can be presynaptic at both types of connection. At the excitatory connections, transmission can be maintained for long periods without decrement. In contrast, inhibitory postsynaptic potentials (IPSPs) never last for more than 15–35 ms. This paper examines mechanisms which could limit the duration of these IPSPs.

An IPSP begins 4-5 ms after a presynaptic neurone starts to depolarize from its resting potential, and the time-to-peak is 7 ms. The amplitude of an IPSP depends both upon the amplitude of the peak presynaptic potential and upon the potential at which a presynaptic neurone is held before it is depolarized. The rate at which a postsynaptic neurone hyperpolarizes to produce an IPSP is proportional to the rate at which the presynaptic neurone depolarizes, independent of the potential from which the presynaptic depolarization starts. A maximum rate of postsynaptic hyperpolarization is reached when the presynaptic neurone depolarizes at 10 mV ms−1. Once an IPSP has occurred, both the amplitudes and the rates of hyperpolarization of subsequent IPSPs are depressed. The connection recovers its full ability to transmit over a period of 1-5 s. Larger IPSPs are followed by initially greater depression than smaller IPSPs. A connection can begin to recover from depression while the presynaptic neurone is held depolarized from resting. Transmission fails when a presynaptic neurone is depolarized by pulses shorter than 2 ms. The most likely reason why the duration of the IPSPs is limited is that calcium channels in the presynaptic terminal inactivate within 7 ms of first opening.
The Neural Basis of Escape Swimming Behaviour in the Squat Lobster Galathea Strigosa
Authors: Sillar Keith T. , Heitler William J.
Published: April 2021

The anatomy and physiology of neurones underlying escape swimming behaviour in the squat lobster, Galathea strigosa, have been investigated, and the results are discussed in the context of the evolution of decapod escape behaviour. In contrast to crayfish, hermit crabs and a number of other related decapods, Galathea does not possess a giant fibre system for escape. Fast flexor motor neurones (FFs) and fast extensor motor neurones (FEs) have been shown, by cobalt backfilling, to be homologous with crayfish FFs and FEs in number, size and distribution of somata. A small degree of intersegmental and interspecific variation is noted. The flexor inhibitor (FI) neurone is described in terms of its central anatomy, peripheral function and peripheral branching pattern. In each of these respects the neurone is found to be homologous with the crayfish FI The neurone homologous with the crayfish motor giant (MoG) in its soma size and position is found to be a typical FF in Galathea. This ‘MoGH’ contrasts with the crayfish MoG in having central neuropilar arborization and in lacking axonal branches in the connectives. These differences can be accounted for by the absence of cord giant axons.
Pressure-Induced Changes in Ca2+-Channel Excitability inParamecium
Authors: Otter T. , Salmon E. D.
Published: April 2021

The behaviour of swimming Paramecium is markedly affected by hydro-static pressure (50-200atm, 1 atm = 101 325Pa). To investigate whether pressure might alter behaviour by acting directly on specific ion channels that mediate the behavioural responses, we examined the effects of K+, Na+ and Ba2+ ions on swimming speed and the reversal response during pressurization and decompression. If pressure acted on the channels that transport these ions, then the pressure-induced responses of swimming Paramecium should be exaggerated or diminished, according to which ions were present in the experimental buffer. Pressurization to 100 atm in standard buffer inhibited the brief reversal of swimming direction that occurred at atmospheric pressure when a paramecium encountered the wall of the pressure chamber. To determine whether pressure impaired mechanoreceptor function or directly blocked the Ca2+-channels that control ciliary reversal, we added Ba2+ or Na+ to standard buffer to induce multiple spontaneous reversals. Pressurization blocked these reversals, suggesting that channel opening is directly inhibited by pressure. Decom-pression in standard buffer elicited momentary ciliary reversal and backward swimming. Buffers with a high ratio of K+ to Ca2+ suppressed this response, and the decompression-induced reversal was exaggerated in the presence of Ba2+ or Na+, consistent with the effects that these ions are known to have on Paramecium’s reversal response. These data imply that, upon decompression, the Ca2+-channels that mediate ciliary reversal open transiently. In addition to blocking the reversal response, pressurization slowed forward swimming. By examining the response to pressurization of Paramecium immobilized by Ni2+, we found that hydrostatic pressure apparently slows swimming by reorientating the direction of ciliary beat.
The Mechanical Power Output of A Tettigoniid Wing Muscle During Singing and Flight
Authors: Josephson Robert K.
Published: April 2021

The mesothoracic wings of tettigoniid insects are used in song production and flight; the metathoracic wings in flight only. In Neoconocephalus triops the wing stroke frequency during flight is about 25 Hz ; the frequency during singing about 100 Hz. The twitch duration of mesothoracic, first tergocoxal (Tcxl) wing muscles is only about one-half the duration of the upstroke or downstroke portion of the wing cycle. During tethered flight the Tcxl muscles are activated on each cycle with short bursts of action potentials, each burst typically containing four action potentials. Activating the muscles with brief, tetanizing bursts increases the duration of muscle activity and the mechanical power output per wing cycle above that obtainable with single twitch contractions of the muscle. The mechanical power output was determined for mesothoracic Tcxl muscles undergoing sinusoidal length change and stimulated phasically in the length cycle. At 25 Hz, the power at optimum muscle strain and optimum stimulus phase was 5 Wkg-1 at 30 °C for muscles activated with a single stimulus per cycle and about 33 W kg-1 for muscles activated with bursts of stimuli in the normal pattern of flight. The maximum power output at 100 Hz, the singing frequency, was 18 W kg-1. This was achieved with a single stimulus per wing cycle. From published values of oxygen consumption by tettigoniids during singing, it is concluded that the efficiency of conversion of metabolic to mechanical power during singing is about 3 %.
Temperature Acclimation: Influence on Transient Outward and Inward Currents in an Identified Neurone of Helix Pomatia
Authors: Zečević Dejan , Levitan Herbert , Pašlć Mira
Published: April 2021

To gain insight into the mechanisms underlying compensatory changes in excitability induced by thermal acclimation we examined the effects of short-term and long-term temperature transition on a transient outward potassium current (A-current) and the transient inward current in an identified neurone (Br) of the land snail Helix pomatia. The A-current in neurones from snails acclimated to 20°C was suppressed by cooling to 3°C, with a Q10 of 4.5 between 10°C and 20°C. This is consistent with suppression of the ability of these neurones to fire repetitively at low temperatures. Neurones acclimated to low temperature (5°C) partially recovered their ability to fire repetitively, but exhibited no A-current, at this temperature. Neither the equilibrium potential for the A-current (EA), the steadystate inactivation parameters of the A-current (Bo), nor the ratio of the time constants of A-current activation and inactivation (τA/τB) were affected by cooling, leading to the conclusion that the reduction of the A-current by cooling was due to a decrease in the A-current activation parameters (GAA∞). Cooling reduced the maximum peak inward current, with a Q10 of 2, in neurones from warm-acclimated animals. After acclimation to 5°C, maximum peak inward current partially recovered. Cooling neurones from warm-acclimated animals slowed the time course of the recovery of inward current from inactivation. Acclimation to the cold caused a partial, compensatory shortening of the inactivation removal process.
Characteristics of Mechanoreceptors in the Air-Breathing Organ of the Holostean Fish, Amia Calva
Authors: Milsom William K. , Jones David R.
Published: April 2021

Single nerve fibre discharge was recorded from mechanoreceptors associated with the air-breathing organ in double-pithed specimens of the bowfin, Amia calva L. These receptors were innervated by the vagus nerve and although their exact location was difficult to determine, most appeared to be located along the anterio-ventral wall of the single lung. All receptors increased tonic discharge with step increases in lung volume, above a threshold level, and were slowly adapting. There was a dynamic, rate-sensitive burst of activity associated with lung inflation and a dynamic, rate-sensitive inhibition of discharge associated with deflation. These responses were qualitatively similar to those of the tonic stretch receptors found in fish swimbladder and mammalian gut. All receptors were insensitive to changes in intrapulmonary partial pressures of oxygen and carbon dioxide. These observations suggest that receptors capable of transducing the rate, as well as the degree, of inflation and deflation are associated with primitive lungs, and may have arisen from tonic gut receptors.
Spontaneous Efferent Activity in Branches of the Vagus Nerve Controlling Heart Rate and Ventilation in the Dogfish
Authors: Barrett D. J. , Taylor E. W.
Published: April 2021

Efferent activity was recorded from cranial nerves in the decerebrate dogfish (Scyliorhinus canicula) before and after injection of paralysing drugs. The recordings were made from the mandibular (Vth) and glossopharyngeal (IXth) nerves and the branchial (respiratory) and cardiac branches of the vagus (Xth) nerve. All the respiratory branches (Vth, IXth and Xth) and both cardiac branches fired rhythmic bursts of activity, synchronous with ventilation, which continued (at a higher rate) following paralysis, indicat-ing that they originated in the CN S rather than arising reflexly from stimula-tion of pharyngeal mechanoreceptors. A burst of activity in the Vth nerve was followed by a burst in the IXth then, after a 30-ms delay, simultaneous bursts in the three respiratory branches of the Xth. The bursts in the bran-chial cardiac branches had a fixed phase relationship with activity in the respiratory branches, the onset of each burst preceding that in the im-mediately adjacent branch (branchial III), whereas the bursts in the visceral cardiac branches had a variable phase relationship with all other branches. The branchial cardiac branches alone contained units which fired sporadi-cally between the bursts and increased their rate of firing during hypoxia. Both the bursting and non-bursting units responded to mechanical stimula-tion of the gill area. Separate oscillatory inputs driving the Vth, IXth and Xth respiratory motoneurones and an excitatory input to the bursting car-diac vagal motoneurones from expiratory motoneurones or the respiratory rhythm generator are implied by these relationships. The sporadically firing units in the branchial cardiac nerves clearly receive non-oscillatory inputs.
The Location of Cardiac Vagal Preganglionic Neurones in the Brain Stem of the Dogfish Scyliorhinus Canicula
Authors: Barrett D. J. , Taylor E. W.
Published: April 2021

The locations, within the brain stem, of vagal efferent preganglionic neurones with axons in the two pairs of cardiac vagal rami of the dogfish have been defined by the retrograde intra-axonal transport of horseradish peroxidase (HRP). HRP was applied to the cardiac rami in one of two ways: either as crystals placed on the cut central end of the nerve or as a dried concentrated solution administered into the nerve on the tip of a fine pin. No difference was observed in the number of labelled cell bodies identified using either method. Labelled branchial cardiac vagal motoneurones were found ipsilaterally in the medial division of the vagal motor column, in the lateral division of the vagal motor column, and scattered between these two locations. In contrast, visceral cardiac vagal motoneurones were confined to the ipsilateral medial division of the vagal motor column. We suggest that the dual location of cell bodies supplying axons to the branchial cardiac branch of the vagus may represent a separation of function with respect to the two types of activity conducted by this nerve. Cardiac efferent fibres are confined in their exit from the brain to a middle group of vagal rootlets. This corresponds to the topographical representation of cardiac efferent somata within the extent of the vagal motor column.
The Characteristics of Cardiac Vagal Preganglionic Motoneurones in the Dogfish
Authors: Barrett D. J. , Taylor E. W.
Published: April 2021

Preganglionic vagal motoneurones supplying the heart of the dogfish have been located in the medulla by antidromic stimulation of the central cut end of the branchial cardiac branch of the vagus. They supplied axons with conduction velocities between ·75 and 16·3 ms-1, which is similar to mam-malian B fibres. Motoneurones were found in two locations: the rostromedial (N=5) and lateral (N = 12) divisions of the vagal motor column. Their measured depths and rostrocaudal distributions with respect to obex corresponded with the location of branchial cardiac motoneurones determined by horseradish peroxidase (HRP) histochemistry. All the neurones located in the rostromedial division of the vagal motor column were spontaneously rhythmically active. Their activity contributed to the rhythmic, respiratory-related bursts in peripheral recordings of efferent activity from the branchial cardiac vagus. They could be induced to fire in a prolonged burst by mechanical stimulation of the gill arches. The neurones located lateral to the rostromedial division of the vagal motor column could be divided into three categories : (1) spontaneously, continuously active cells which could be induced to fire more frequently by mechanoreceptor stimulation, (2) silent cells which could be induced to fire by mechanoreceptor stimulation, (3) silent cells which did not respond to mechanoreceptor stimulation. It is concluded, from the response of the medial and two categories of lateral cells to mechanoreceptor stimulation (which results in a transient bradycardia), that branchial cardiac motoneurones from both these central locations exert a chronotropic influence on the heart.
Contractile Performance of Cephalopod Hearts Under Anoxic Conditions
Authors: Driedzic William R.
Published: April 2021

The cephalopod circulatory system includes an efferent systemic ventricle and two afferent branchial hearts. Branchial hearts lack coronary arteries and thus must be nourished by only venous blood. During routine metabolism in normoxic water, oxygen availability to branchial hearts is only a small percentage of that to the systemic heart; during hypoxic excursions the venous oxygen content may, at least transiently, approach zero (Johansen, Brix & Lykkeboe, 1982; Houlihan, Innes, Wells & Wells, 1982). The extreme difference in oxygen delivery to these tissues suggests that branchial hearts are better able to meet their energetic demands through anaerobic metabolism than are systemic hearts. This hypothesis was tested by following isometric force development of the cardiac tissue of the cuttlefish, Sepia officinalis, during cyanide poisoning. Experiments were also conducted with the systemic heart of Octopus vulgaris, in order to allow a comparison between a decapod and an octapod.
Continuous Recording of Arterial Blood in Octopus Vulgaris During Progressive Hypoxia and Movement
Authors: Smith P. J. S. , Duthie G. G. , Wells M. J. , Houlihan D. F.
Published: April 2021

The respiratory and acid-base status of the blood of animals continually changes in response to variations in internal and external conditions. Attempts to monitor transitory changes by repetitive sampling techniques can, however, lead to an unacceptable level of blood loss. An external circulatory shunt in which blood is continuously removed from one vessel, passed across monitoring electrodes and reintroduced into an appropriate second vessel would obviate this problem. Such a system has been developed to continuously monitor blood gas parameters and pH in fish (Belaud, Trotter & Peyraud, 1979; Thomas & Le Ruz, 1982). The present study attempts to apply a similar technique to an invertebrate, Octopus vulgaris.