Showing papers in "The Journal of Experimental Biology in 1981"

Instantaneous Measurements of Oxygen Consumption During Pre-Flight Warm-Up and Post-Flight Cooling in Sphingid and Saturniid Moths

Abstract: A method for instantaneous measurement of oxygen consumption in an open flow respirometry system is described. During pre-flight warm-up in both sphingids and saturniids, oxygen consumption reaches levels 20 to 70 times resting values. V O O2 required to maintain the thorax at flight temperature by intermittent wing-quivering and fluttering is about one-third the maximum V O O2 during warm-up. The Q 10 of resting V O O2 averages 2·4 in both sphingids and saturniids. At any given thoracic temperature, V O O2 during post flight-cooling exceeds V O O2 at rest. Factorial scope (maximum V O O2 ÷resting V O O2 ) during warm-up is independent of mass and thoracic temperature. In sphingids it averages 39, in saturniids, 43. Absolute metabolic scope in both groups increases with thoracic temperature and is roughly proportional to V O O2 . In saturniids about 49% of the heat produced during warm-up is stored in the thorax; in sphingids the figure is about 73%. The data on metabolic scope, power requirements for flight, Q 10 and body mass are used to develop equations that predict thoracic temperature during flight for both sphingids and saturniids.

Dynamic tensile properties of the plantaris tendon of sheep (Ovis aries)

Abstract: 1. The stresses applied during fast locomotion are sufficient to stretch the tendon far into the linear region of the load-extension plot. 2. The tangent modulus in the linear region is about 1.65 GN.m-2 and is independent of frequency for oscillations in the range 0.22 to 11 Hz. 3. Internal damping dissipates about 7% of the mechanical energy applied during oscillations. The load range (0 to about 1 kN) and frequencies (0.22 to 11 Hz) were comparable to those arising during locomotion. 4. The rate of rise of temperature, during the initial period of an oscillation, was consistent with the mechanical measurement of power loss. 5. The dynamic mechanical properties are appropriate for the hypothesis of energy saving by storage in tendons during fast locomotion.

Influences of the glial environment on the elongation of axons after injury: transplantation studies in adult rodents

Abstract: Tissue transplantation methods, previously used to study neural development, myelination and inherited disorders of myelin can be applied also to the investigation of repair and regeneration in the mammalian CNS. The elongation of axons from injured peripheral nerve of CNS has been studied in adult mice and rats by observing the growth of axons into PNS or CNS tissue grafts. Following spinal cord injury and also after transplantation of optic nerves into the PNS there is axonal sprouting but these neuronal processes fail to elongate more than a few mm into the surrounding glia. On the other hand if segments of a peripheral nerve are grafted into the transected spinal cord, axons arising from spinal neurons and dorsal root ganglia become associated with the transplanted Schwann cells and elongate along the graft, approximately 1 cm. Recently the elongation of axons from spinal and medullary neurones was studied using a new experimental model which employed PNS grafts as 'bridges' to connect the spinal cord and the brain stem. In a series of adult C57BL/6J mice and Sprague Dawley rats, autologous segments of sciatic nerve were used to create 'bridges' between the lower cervical or upper thoracic spinal cord and the medulla oblongata. The spinal cord between these two levels was left intact. Grafted segments examined by light and electron microscope 1-7 months after surgery were well innervated by Schwann cell ensheathed axons that had grown the entire length of the graft (2 cm in mice and 3.5 cm in rats). The origin and termination of these axons were determined by transecting the regenerated grafts and applying horseradish peroxidase to the cut ends. Retrogradely labelled neurones were found to be distributed widely in the gray matter of the spinal cord and medulla near the sites of insertion of the graft. Anterogradely labelled fibres coursing within the graft penetrated the CNS for short distances, approximately 2 mm. These new results indicate that following CNS injury a conducive glial environment does allow spinal and brain stem neurones to elongate axons for distances that can be greater than those they usually extend for in the intact animal. This evidence that the regenerative response of similar axons differs in CNS and PNS neuroglia supports the hypothesis that influences arising from the environment play an important role in the success or failure of regeneration. The regenerative potentiality of central neurones may be expressed only when the CNS neuroglial environment is changed to resemble that in the PNS.

Branchial and Renal Acid and Ion Fluxes in the Rainbow Trout, Salmo Gairdneri, at Low Environmental pH

Abstract: Rainbow trout were exposed for 4 days to an environmental pH averaging 4.2, an exposure which resulted in a continuous net branchial influx of acid. The influx provoked a progressive depression in blood pH and [HCO3−], virtually complete by 48 h, and a marked increase in renal acid excretion, also complete by 48 h. The increase in the latter was sufficient to remove, at maximum, about half of the protons entering at the gills; those remaining were buffered in body fluids. The low pH exposure also impaired gill ion regulation as indicated by continuous net branchial losses of Na+, Cl− and K+ and by a progressive decline in plasma Na+ and Cl− levels. Evidence is presented which indicates that there was a significant contribution by the intracellular compartment both to the total body ion losses and to the buffering of the body acid load.

Electrical activity and relative length changes of dog limb muscles as a function of speed and gait

Abstract: SUMMARY Electrical activity and length changes of 11 muscles of the fore- and hindlimbs of dogs walking, running, and galloping on a treadmill, were measured as a function of forward speed and gait. Our purpose was to find out whether the activity patterns of the major limb muscles were consistent with the two mechanisms proposed for storage and recovery of energy within a stride: a 'pendulum-like' mechanism during a walk, and a 'spring-like' mechanism during a run. In the stance phase of the walking dog, we found that the supraspinatus, long head of the triceps brachii, biceps brachii, vastus lateralis, and gastrocnemius underwent only minor length changes during a relatively long portion of their activity. Thus, a major part of their activity during the walk seems consistent with a role in stabilization of the joints as the dog 'polevaulted ' over its limbs (and thereby conserved energy). In the stance phase of trotting and/or galloping dogs, we found that the supraspinatus, lateral head of the triceps, vastus lateralis, and gastrocnemius were active while being stretched prior to shortening (as would be required for elastic storage of energy), and that this type of activity increased with increasing speed. We also found muscular activity in select limb flexors that was consistent with storage of kinetic energy at the end of the swing phase and recovery during the propulsive stroke. This activity pattern was apparent in the latissimus dorsi during a walk and trot, and in the biceps femoris during a trot and gallop. We conclude that, during locomotion, a significant fraction of the electrical activity of a number of the dog's limb muscles occurs while they undergo little or no length change or are being stretched prior to shortening and that these types of activities occur in a manner that would enable the operation of pendulum-like and spring-like mechanisms for conserving energy within a stride. Therefore these forms of muscular activity, in addition to the more familiar activity associated with muscle shortening, should be considered to be important during locomotion.

Differentiation of the Chloride Extrusion Mechanism During Seawater Adaptation of a Teleost Fish, The Cichlid Sarotherodon Mossambicus

Abstract: Opercular membranes isolated from the freshwater-adapted euryhaline teleost, Sarotherodon mossambicus , and mounted in Ussing-style chambers, have low conductance and current and do not actively transport chloride. In contrast, membranes isolated from seawater-adapted S. mossambicus have high conductance and generate large currents representing net chloride extrusion. Full development of this chloride secretion process requires 1-2 weeks, the time-course of which provides the first unambiguous measurement of changes in net extrarenal salt secretion associated with a teleost's adaptation to seawater. Tissues from seawater-adapted fish contain typical chloride cells, when observed with the electron microscope, which appear as large cells with fluorescence microscopy after staining with dimethylaminostyrylaethylpyridiniumiodine. These cells are absent from the freshwater tissue, although rudimentary chloride cells are present, appearing as small cells with fluorescence microscopy. Following seawater transfer, the number of chloride cells increases only during the first 3 days. Subsequent chloride cell hypertrophy is highly correlated with the quantity of chloride extrusion. These data strongly implicate the chloride cell as the salt-secretory cell-type. When cortisol was injected into freshwater fish, chloride cell density increased but chloride secretion was not activated. It appears that development of salt extrusion involves increased numbers (controlled, at least in part, by cortisol) and differentiation of chloride cells, including activation of membrane active-transport sites. The opercular membrane from S. mossambicus provides a valuable model for studying these physiological and morphological events.

Contribution of Compound Eyes and Ocelli to Steering Of Locusts in Flight: I. Behavioural Analysis

Abstract: Locusts (Orthoptera, Acrididae) were tethered inside a simulated horizon visual display. Rotation of the horizon elicited following motions of the animal's head and rudderlike movements during flight. Head and steering motions were still elicited after either the compound eyes or the ocelli were surgically ablated. Head motions after ocellar cautery suggested that the ocelli may function synergistically with the compound eyes to (a) minimize the delay of visual responses and (b) augment visual responses when no sharp horizontal border is present. Flight steering motions were found not to depend on proprioception of head position. Three other species (Diptera and Odonata) also followed horizon rotations with head motion after their compound eyes had been ablated.

The exoskeleton and insect proprioception. i. responses of tibial campaniform sensilla to external and muscle-generated forces in the american cockroach, periplaneta americana

Abstract: 1. 1. The tibial campaniform sensilla are a group of mechanoreceptors in the cockroach leg that respond to cuticular strain. Each sensillum consists of a single bipolar neurone whose dendrite inserts into an ovoid cuticular cap embedded in the exoskeleton. 2. 2. The tibial campaniform sensilla are consistently separable into two subgroups with mutually perpendicular cap orientation: the long axis of the caps of proximal subgroups are oriented perpendicular to the tibial long axis; caps of the distal subgroup are parallel to the tibia. 3. 3. The responses of individual, identified sensilla from both subgroups were tested to the following forces: bending forces (perpendicular to the leg long axis), axial forces (parallel to the leg axis), torques (twisting about the leg long axis) and forces generated by the tibial muscles. 4. 4. The tibial campaniform sensilla respond vigorously to bending forces imposed in the plane of movement of the adjacent femorotibial joint. Individual sensilla exhibit orientation-dependent directional sensitivity in their response: the proximal sensilla respond only to dorsal bending; the distal sensilla respond only to ventral bending. Sensilla respond less vigorously to bending forces in other planes. 5. 5. Responses are weak but directionally sensitive to axial forces: the proximal sensilla fire upon axial compression; the distal sensilla fire upon axial tension. 6. 6. Both subgroups respond simultaneously but weakly to imposed torques. 7. 7. Contractions of the tibial muscles produce strong orientation dependent responses: the proximal sensilla respond only to flexor muscle contractions; the distal sensilla respond only to extensor muscle contractions. 8. 8. These responses are accurately predicted from a simple model in which the tibia behaves as a cylinder under stress. The tibial campaniform sensilla respond as directionally sensitive strain gauges. Each individual sensillum responds only to compressions perpendicular to the long axis of its cuticular cap. 9. 9. Tibial campaniform sensilla respond best to those forces that the animal can most effectively control.

Possible roles of vertebrate neuroglia in potassium dynamics, spreading depression and migraine.

Abstract: SUMMARY The membranes of glial cells are highly selectively permeable to potassium. The implications of this and the possible reasons for it are discussed. Glial cells may contribute to buffering the extracellular K+ concentration of brain tissue through several mechanisms. However, the only one that benefits from the K + selective permeability is the so-called 'spatial' buffer mechanism, which acts more effectively than extracellular diffusion in many situations to speed the dispersal of local accumulations of potassium. The role of glial cells in buffering the extracellular K+ concentration may help to prevent the occurrence of a phenomenon called Leab's spreading depression (SD). A K+-induced K + efflux from neurones, occurring when the EC K + concentration rises above critical levels, is probably crucial in causing SD. The models that have been proposed to describe this process are discussed and related. Spreading depression is not known definitely to occur in man. It seems probable, however, that it occurs during attacks of' classical' migraine, associated with neurological symptoms. These neurological symptoms have often been attributed to vasoconstriction rather than to SD since certain vasodilators can relieve the symptoms. Experiments with SD in anaesthetized rats show that at least one of these vasodilator interventions (administration of a CO 2/O2 mixture) stops also the propagation of a wave of SD. This strengthens the evidence for a possible relationship between migraine and SD. The involvement of SD in migraine probably deserves more critical attention than has hitherto been devoted to it.

An Aerodynamic Analysis of Bird Wings as Fixed Aerofoils

Abstract: The aerodynamic properties of bird wings were examined at Reynolds numbers of 1-5 × 10 4 and were correlated with morphological parameters such as apsect ratio, camber, nose radius and position of maximum thickness. The many qualitative differences between the aerodynamic properties of bird, insect and aeroplane wings are attributable mainly to their differing Reynolds numbers. Bird wings, which operate at lower Reynolds numbers than aerofoils, have high minimum drag coefficients (0·03-0·13), low maximum lift coefficients (0·8-1·2) and low maximum lift/drag ratios (3–17). Bird and insect wings have low aerofoil efficiency factors (0·2-0·8) compared to conventional aerofoils (0·9-0·95) because of their low Reynolds numbers and high profile drag, rather than because of a reduced mechanical efficiency of animal wings. For bird wings there is clearly a trade-off between lift and drag performance. Bird wings with low drag generally had low maximum lift coefficients whereas wings with high maximum lift coefficients had high drag coefficients. The pattern of air flow over bird wings, as indicated by pressure-distribution data, is consistent with aerodynamic theory for aeroplane wings at low Reynolds numbers, and with the observed lift and drag coefficients.

The Mechanisms and Energetics of Honeybee Swarm Temperature Regulation

Abstract: 1. 1. Free (active) honeybee swarms regulated their core temperature ( T c) generally within 1 °C of 35 °C. They maintained the same temperature around freshly built honeycomb, and in the brood nest of the hive, from ambient temperatures of between at least 1 and 25 °C. Captive (inactive) swarms in the laboratory often allowed T c to decline below 35 °C. 2. 2. The temperature of the swarm mantle ( T m) varied with the general activity of the swarm as well as with ambient temperature ( T A), but in captive swarms (and sometimes at night in free swarms), T m was generally held above 17 °C, even at T A < 5 °C. 3. 3. Within the swarm, temperatures varied between 36 °C, an upper temperature set-point, and 17 °C, a lower temperature set-point. 4. 4. Before swarm take-off, all temperature gradients in the swarm were abolished and T m equalled T c. 5. 5. The regulated T c and T m were unrelated to size and passive cooling rates in swarms ranging from 1000 to 30000 bees. 6. 6. The weight-specific metabolic rate of swarms was correlated with T A and T c, but relatively little affected by swarm size. 7. 7. Bees on the mantle experiencing low temperatures pushed inward, thus contracting the mantle, diminishing the mantle porosity, and filling interior passageways. As a result, their own rate of heat loss, as well as that from the swarm core, decreased. 8. 8. In large tightly clumped swarms, even at T A < 5 °C, the resting metabolic rate of the bees in the swarm core was more than sufficient to maintain T c at 35 °C or above. The active thermoregulatory metabolism was due to the bees on the swarm mantle. 9. 9. There was little physical exchange of bees between core and mantle at low (< 5 °C) T A. In addition, there was no apparent chemical or acoustic communication between the bees in the swarm mantle that are subjected to the changes of the thermal environments and the bees in the swarm interior that constantly experience 35 °C regardless of T A. 10. 10. The data are summarized in a model of T c control indicating a primary role of the mantle bees in controlling heat production and heat loss. 11. 11. The possible ecological significance of swarm temperature regulation is discussed.

Reversal of a Walking Leg Reflex Elicited by a Muscle Receptor

Abstract: Passive movement of the basal (thoracic-coxal) leg joint in the shore crab Carcinus maenas normally elicits a resistance reflex in the promotor and remotor motoneurones. Remotion of the joint excites promotor moto-neurones and promotion excites remotor motoneurones. This reflex behaviour may reverse and become an assistance reflex, where movement of the joint excites the motoneurones innervating the muscle which would assist the passive movement. This reversal of reflex activity appears to be dependent upon the central state of activity of the animal.

Membrane structure in mammalian astrocytes: a review of freeze-fracture studies on adult, developing, reactive and cultured astrocytes.

Abstract: The application of freeze-fracture techniques to studies of brain structure has led to the recognition of two unsuspected specializations of membrane structure, each distributed in a specific pattern across the surface of astrocytes. 'Assemblies' (aggregates of uniform, small particles packed in orthogonal array into rectangular or square aggregates) are found to characterize astrocytic plasma membranes apposed to blood vessels or to the cerebrospinal fluid at the surface of the brain. These particle aggregates are much less densely packed in astrocytic processes in brain parenchyma. Assemblies are not fixation artifacts, have been shown to extend to the true outer surface of the membrane, are remarkably labile in the setting of anoxia, and are at least in part protein. The function of assemblies is unknown, but their positioning suggests that they may have a role in the transport of some material into or out of the blood and cerebrospinal fluid compartments. A second specialization of intramembrane particle distribution, the polygonal particle junction, links astrocytic processes at the surface of the brain, and also links proximal, large caliber astrocytic processes in brain parenchyma. The function of this membrane specialization also is unknown, but it may subserve a mechanical role.

Contribution of Compound Eyes and Ocelli to Steering of Locusts in Flight: II. Timing Changes in Flight Motor Units

Abstract: Locusts (Orthoptera, Acrididae) were induced to fly while tethered within a simulated horizon display. Rotation of the horizon about the animal9s long axis caused changes in the relative timing of the spikes of homologous flight muscles of either side. Changes in relative timing paralleled the pattern of head motions (Taylor, 1981) elicited by horizon rotation. Systematic changes in relative spike timing were also seen after the compound eyes were surgically disconnected and in response to forced head rotation. These results are discussed in relation to the functions of the compound eyes, the ocelli, and the cervical proprioceptive hairs for visual flight stabilization.

Na + FLUXES ACROSS ISOLATED PERFUSED GILLS OF THE CHINESE CRAB ERIOCHEIR SINENSIS

Abstract: Sodium transport processes in the branchial epithelium of euryhaline crustaceans have been investigated using a perfused preparation of gills isolated from Chinese crabs Eriocheir sinensis acclimated to dilute (FW) and to concentrated (SW) media. The results clearly establish the existence of a functional difference between the different pairs of branchiae with respect to their participation in the regulation of the blood Na + content. In FW-acclimated animals, the Na + active uptake which counter-balances the salt loss along the concentration gradient is mostly achieved across the three posterior pairs of gills. Conversely, the Na + fluxes measured in the three anterior pairs are essentially passive and carrier-mediated. Further characterization of the Na + uptake system present in the posterior gills by means of inhibitors like ouabain and ethacrynic acid indicates the existence of at least two spatially separated components of the Na + carrying system. It is shown that NH 4 + may be used as co-ion for Na + but that such a coupling can only account for a very small part of the Na + actively transported inward. The existence of an electrogenic mechanism or of another coupled system has thus to be postulated but remains at present a matter of speculation. To study FW-to-SW and SW-to-FW acclimation, Na + fluxes were measured in isolated gills of SW-acclimated crabs and of FW crabs perfused and incubated in SW conditions. During acclimation to SW the Na + active uptake in the posterior gills is abolished primarily as a result of inhibition of the Na + carrier activity.

The Functional Design of the Insect Excretory System

Abstract: Insects have a slowly operating excretory system in which the passive rate of movement of haemolymph solutes into a slowly secreted primary excretory fluid is restricted by a reduction in the area available for passive transfer. They may have come to possess such an energy-saving system as a result of their evolution as small animals in osmotically and ionically stressful environments. Although the possession of a waxy cuticle is a major element in their ability to live in such environments, insects have a very high surface-area/volume ratio and this is likely to have conferred a selective advantage on individuals able to withstand unusually variable extracellular conditions. Among their major adaptations evolved to allow them to tolerate such conditions are the lack of a blood-borne respiratory pigment to be affected and the development of a system whereby their most sensitive tissues are protected by the regulatory activities of special covering epithelia. Because of these features it follows that there has been less evolutionary pressure for rapid excretory control of the haemolymph composition. With an excretory system that only slowly filters the haemolymph, less energy expenditure is involved in the production of the primary excretory fluid and in reabsorption of useful substances from it. In addition, insects are able to maintain in circulation high concentrations of substances such as amino acids, trehalose, and lipids. They can also eliminate excess fluid at very high rates with the loss of only trace amounts of haemolymph solutes. It is argued that terrestrial insects owe much of their success to their ability to recover virtually all the water from the slow flow of primary excretory fluid. The hindgut cells that are responsible for this recovery are aided by their cuticular lining which protects them from contact with the very high concentrations of potentially interfering compounds in the excretory material.

Interneuronal control of feeding in the pond snail lymnaea stagnalis i. initiation of feeding cycles by a single buccal interneurone

Abstract: SUMMARY The Lymnaea buccal ganglion is organized such that the basic feeding rhythm is generated by an interneuronal network which imposes its activity on a set of follower cells. In this paper we extend our earlier observations (Benjamin & Rose, 1979) on the follower cells to show that they receive four consecutive synaptic inputs. The main objective of the paper is to describe the properties of an interneurone called the 'slow oscillator' which is capable of initiating feeding cycles. This interneurone will be used in the following paper (Rose & Benjamin, 1981) to drive other members of the interneuronal network in order to determine how it is organized, and to understand the origin and timing of the four synaptic inputs to the follower cells.

Mechanisms of ionic homeostasis in the central nervous system of an insect

Abstract: Extracellular ionic homeostasis in an insect central nervous system involves a peripheral intercellular diffusion barrier, an extracellular matrix and neuroglial cation transport. The peripheral location of the barrier in the superficial neuroglia is confirmed by intracellular recording from glial cells identified by peroxidase injection. This barrier protects the underlying neurones from large changes in ionic composition of the blood-plasma, but renders them more susceptible to fluctuations in ion composition resulting from neuronal signalling within the very restricted extracellular system. Because of the peripheral intercellular barrier, sodium movements between the blood and the extracellular fluid are largely transcellular and are mediated by ion pumps on the perineurial and underlying glial membranes. It is suggested that the homeostatic role of the neuroglial ion pumps is augmented by an anion matrix which functions as an extracellular sodium reservoir. It is proposed that during depletion of extracellular sodium, this cation is released by the matrix to maintain the sodium activity in the fluid at the axon surfaces.

The control of transepithelial potential oscillations in the salivary gland of calliphora erythrocephala

Abstract: The effects of the hormone 5-hydroxytryptamine, its analogues and its antagonists on the electrical activity and secretion rate of isolated salivary glands of the blowfly Calliphora erythrocephala were investigated. The secretion rate increases linearly with the logarithm of hormone concentration between 10−9 and 10−8M. At >10−8M the transepithelial potential depolarizes and rapidly attains a new stable value. However, at intermediate hormone concentrations, the potential does not maintain a stable intermediate value but displays sustained oscillations. These oscillations are not an artifact resulting from periodic variations in hormone concentration. The frequency of the oscillations increases with hormone concentration and with the concentration of external calcium and hormone analogues. The frequency decreases following the addition of lanthanum to the perfusion medium. The experimental results suggest that the potential oscillation may be driven by an oscillation in the intracellular concentrations of cyclic AMP and calcium. It is argued that oscillatory control provides a reliable, noise-resistant strategy for controlling secretion rate.

THE ROLE OF CaCO3 DISSOLUTION AS A SOURCE OF HCO3- FOR THE BUFFERING OF HYPERCAPNIC ACIDOSIS IN AQUATIC AND TERRESTRIAL DECAPOD CRUSTACEANS

Abstract: Blood calcium concentrations are elevated during a hypercapnic acidosis in the terrestrial crab Gecarcinus lateralis , but not in the aquatic Callincetes sapidus . The increase occurs concomitantly with a rise in blood HCO 3 - and partial restoration of resting blood pH values. It is believed that in G. lateralis that a source of CaCO 3 , possibly the shell, is being dissolved for buffering purposes.

Interneuronal Control of Feeding in the Pond Snail Lymnaea Stagnalis: II. The Interneuronal Mechanism Generating Feeding Cycles

Abstract: SUMMARY The feeding cycle of Lymnaea is generated by a network of three types of interneurone, Ni, N2 and N3. This network is driven by the slow oscillator (SO) interneurone described in the previous paper. Interaction between the different interneurones is dependent on both connectivity and endogenous properties, and utilizes such properties as post-inhibitory rebound and self-feedback within electrically-coupled populations. Each of the four components of the interneuronal network (SO, Ni, N2 and N3) is responsible for a different phase of synaptic input to the follower cell population which was previously shown to directly control feeding movements.

Acid-base and electrolyte status in carp (Cyprinus carpio) exposed to low environmental pH.

Abstract: Carp (Cyprinus carpio) were exposed to environmental water pH (pHw) step changes from 7.4 to 5.1, 5.1 to 4.0 and 4.0 to 3.5 pH, PCO2, PO2 and lactate in dorsal aortic blood, [Na+], [K+] and [Cl-] in dorsal aortic plasma, base loss, and ammonia excretion were determined as a function of time after each pHw step change. At pHw 5.1 the measured blood acid-base and electrolyte parameters remained essentially unchanged; the base loss, however, was increased by a factor of 2. When pHw was lowered to 4.0 an additional severe increase in the ‘net base loss’, expressed as the difference between base loss and ammonia excretion, resulted in progressive reduction of arterial pH and [HCO3-]. The electrolyte status was also severely disturbed by progressively falling plasma [Na+] and [Cl-], which is attributed to failure of the active H+/Na+ and HCO3-/Cl- exchange mechanisms in the gills. At pHw 4.0 the acid-exposure syndrome is characterized by acid-base and electrolyte disturbances apparently not related to hypoxia. However, at pHw 3.5, tissue hypoxia, due to disturbances of gill gas exchange and to Bohr and Root effects, appears to be an additional important factor aggravating the disturbances of acid-base and electrolyte status.

The Exoskeleton and Insect Proprioception: III. Activity of Tribal Campaniform Sensilla During Walking in the American Cockroach, Periplaneta Americana

Abstract: 1.In the cockroach tibia, the activities of campaniform sensilla that monitor cuticular strain have been recorded in free-walking animals. 2.In walking, sensillum firing is correlated with myographic activity of the flexor and extensor tibiae muscles. 3.The specific activity of a single campaniform sensillum depends upon the orientation of its cuticular cap. 4.In slow walking, proximal sensilla, whose ovoid cuticular caps are oriented perpendicular to the leg long axis, fire in bursts that are initiated just prior to the onset of extensor tibiae activity in the stance phase of locomotion. The firing frequency within bursts of proximal sensilla is generally inversely related to the frequency of the slow extensor tibiae motoneurone and ceases when motoneurone activity exceeds 200 Hz. 5.Distal campaniform sensilla, oriented parallel to the leg long axis, only fire when slow extensor tibiae activity exceeds 300 Hz. In slow walking, distal sensillum activity typically occurs as a short intense burst near the end of the stance phase of the step cycle, when slow extensor frequency is maximal. Distal sensillum firing is greatly increased when forward progression is impeded. 6.The patterns of afferent activity seen in slow walking indicate that the campaniform sensilla function in load compensation and limitation of muscle tensions. The proximal sensilla respond to initial loading of the leg and can reflexly excite the slow extensor motoneurone in compensation. The distal sensilla respond to cuticular strains that result from large extensor contractions and can reflexly inhibit the slow motoneurone. 7.In rapid walking, activities of both subgroups of campaniform sensilla shift in phase relative to slow extensor firing. Proximal sensilla activity occurs after the onset of slow extensor firing. Distal sensilla bursts follow the termination of slow extensor activity. 8.These phase shifts limit the reflex functions of the tibial campaniform sensilla in rapid walking. Shifts in phase of afferent activity may contribute to the need for central programming of locomotion.

The Exoskeleton and Insect Proprioception: II. Reflex Effects of Tibial Campaniform Sensilla in the American Cockroach, Periplaneta Americana

Abstract: 1.Mechanical stimulation of individual tibial campaniform sensilla produces specific reflex effects upon motoneurones to leg muscles. 2.The reflex effects of a campaniform sensillum depend upon the orientation of its cuticular cap. The proximal sensilla, oriented perpendicular to the long axis of the tibia, excite slow motoneurones to the extensor tibiae and extensor trochanteris muscles and inhibit slow motoneurones to the flexor tibiae and flexor trochanteris muscles. The distal sensilla, oriented parallel to the tibia, exhibit reflexes of opposite sign, inhibiting the extensors and exciting the flexors. 3.These reflexes constitute a negative feedback system. Individual sensilla specifically excite motoneurones which innervate muscles whose resultant tensions decrease the firing of those sensilla. 4.It is postulated that individual campaniform sensilla can detect loading of the leg in various postures and can excite appropriate motoneurones in compensation. These receptors can also detect strains caused by large, resisted contractions of the antagonist muscles and inhibit the corresponding motoneurones.

Comparison of Potassium Transport in Three Structurally Distinct Regions of The Insect Midgut

Abstract: 1.Active potassium transport across the isolated midgut of the Tobacco Hornworm larva, Manduca sexta, was studied by measuring the short circuit current (ISC) and unidirectional 42-potassium fluxes. 2.The midgut is composed of structurally distinct anterior, middle and posterior regions, all of which are shown to transport potassium, so that by comparing and contrasting their structural and functional properties new information on the mechanism of midgut potassium transport was obtained. 3.It has previously been shown that the potassium pump is located on the apical membrane of the goblet cell. In the anterior and middle regions of the midgut the goblet cell has a large cavity and mitochondria are closely associated with the apical membrane while in the posterior midgut the goblet cavity is much smaller, and mitochondria are not associated with the apical membrane. However, the apical membrane particles which have been implicated in active potassium transport in a number of other insect epithelia are present in all three regions. This observation suggests that the particles are a structural requirement for active transport, and that close association between mitochondria and the transporting membrane is not essential. 4.Comparison of the kinetic influx pool size and the differences in the ISC decay profiles between the three midgut regions suggest that part of the influx pool is a transported pool located in the goblet cavity. 5.A new model to explain the driving force for potassium transport in the midgut is proposed, in which the rate of potassium transport controls the entrance of potassium into the cell, rather than the opposite, currently accepted view.

Invertebrate Neuroglia-Junctional Structure and Development

Abstract: The morphological characteristics of the neuroglial cells of invertebrates are reviewed, including the ultrastructural and enzyme cytochemical features of their cell bodies and attenuated cytoplasmic processes, the various ways they ensheath the nerve cells, including the loosely myelinated condition, their modifications due to intraganglionic localization and their interactions with other glial cells in the form of homocellular junctions. The spectrum of heterocellular axo-glial associations that occur in invertebrates is considered with particular reference to the different kinds of intramembranous organization they exhibit as revealed by freeze-fracture. Recent studies on glial cell development in a range of arthropods, during embryonic and pupal stages, reveal the importance of glial cell tight junctions in forming the tracer-excluding blood-brain barrier. These occluding junctions are now shown to be, in some cases, vertebrate-like in their complexity. The stages in their assembly, which may be concurrent with those of gap junction formation, reveal a number of differences from vertebrate glia. During metamorphosis, glial cells dissociate and the dynamics of the concomitant interglial junctional disruption and their intramembranous particle dispersal without apparent internalization, as well as their subsequent reassembly, are examined. The stimuli triggering these glial events and the physiological significance of the various glial modifications are considered.

Cellular discrimination processes in metal accumulating cells

Abstract: SUMMARY A technique is described for investigating cellular fluxes and the accumulation of metal ions in the hepatopancreas of the snail Helix aspersa. The method involves the simultaneous administration of double isotopes into the haemocoel and the subsequent detection of these metals in tissues and granule materials. By comparing in vivo and in vitro data it is possible to detect two separate accumulation systems which appear to correspond with metallothionein and pyrophosphate granules. It is also possible to obtain some information of the nature of possible cellular transport systems.

The Effect of Progressive Hypoxia on Heart Rate, Ventilation, Respiratory Gas Exchange and Acid-Base Status in the Crayfish Austropotamobius Pallipes

Abstract: 1. 1. Male and female crayfish, Austropotamobius pallipes (Lereboullet) maintained a constant rate of O2 uptake ( M oo2) during a progressive reduction in ambient O2 tension down to a critical tension ( Pc ) of 40 mmHg at15 °C. 2. 2. Heart rate ( fH ) slowed progressively during hypoxia but blood flow was maintained by an increase in cardiac stroke volume. 3. 3. At a P I , oo2, of 50; mmHg the rate of ventilation ( Vw ) had increased to 2.8 times the normoxic value. This was effected by a doubling in respiratory frequency ( fR ) accompanied by increases in both the mean amplitude of the pressure pulse and the mean hydrostatic pressure recorded in the branchial chambers. The effectiveness of removal of O2 from the water ventilating the gills was maintained ( Ew ), and there is evidence that the ability of the respiratory surface to transfer O8 ( T OO2) improved during hypoxia. 4. 4. The hyperventilation enhanced CO2 elimination so that CO2 tensions were halved and respiratory alkalosis occurred in the haemolymph. 5. 5. This alkalosis had the effect of increasing the affinity of the blood pigmentfor O2, reducing the half saturation pressure ( P 50) from 8 to 4.5 mmHg. Thus despite reductions in pre- and post branchial O2 tensions by 50% the arteriovenous O2 content difference was maintained and the effectiveness of removal of O2 into the blood ( Eb ) remained high in moderately hypoxic water ( P OO2 63 ± 1 mmHg). 6. 6. At P I, OO2, levels below 40 mmHg, when crayfish were denied access to air, they were unable to sustain the hyperventilation. Haemolymph O2 content and the a - v O2 content difference decreased, and as the haemolymph was no longer saturated with O2 on its passage through the gills, Eb was reduced. As a consequence of these changes M OO2 fell. 7. 7. Under these conditions a partial switch to anaerobic metabolism occurred, with lactic acid accumulating in the haemolymph. The resultant metabolic acidosis partially off set the respiratory alkalosis.

Physiology of water motion detection in the medicinal leech.

Abstract: 1.Neuronal activity resulting from stimulation by water waves occurs in ventral nerve cord-body wall preparations of the medicinal leech, Hirudo medicinalis. In segmental nerves, this activity consists of afferent compound action potentials with graded amplitudes resulting from simultaneous action potentials in many small sensory axons. Afferent input impinging on one segmental ganglion activates neuronal activity along much of the ventral nerve cord. 2.Previously identified tactile mechanoreceptors are insensitive to low-amplitude wave stimulation. Touch-cell impulse activity can be evoked by moderate or strong wave stimulation, but these impulses appear to arise near the cell body, not from the peripheral receptor endings. 3.The transduction sites for wave stimulation are localized at or very near the segmental sensilla. Because of their location and modality the receptors were named ‘sensillar movement receptors’ (SMR). 4.S cells (Rohde9s fibre) receive suprathreshold excitatory input during SMR activation without concomitant activity in the tactile mechanoreceptors. 5.The annulus erector motor neurones contralateral to the afferent SMR inflow are inhibited by SMR activation. This inhibition is also observed in ganglia adjacent to the ganglion receiving the afferent input and provides a neuronal basis for reflexive smoothing of the leech body wall. 6.Two neurones in the anterior median packet of segmental ganglia receive powerful synaptic input during SMR activation. One, cell 202, receives 10 mV excitatory potentials while the other, cell 201, receives 10 mV inhibitory potentials.