bluuebunny/crossref_metadata_2025 huggingface dataset:
Acid-Base Regulation and Ion Transfers in the Carp (Cyprinus Carpio) During and After Exposure to Environmental Hypercapnia
Authors: Claiborne J. B. , Heisler Norbert
Published: April 2021

Acid-base balance and ion transfers were studied in the carp, Cyprinus carpio L., during and after 48 h of exposure to environmental hypercapnia ( Torr). Plasma pH, [HCO3−], and net transfers of HCO3−, NH4+, Cl− and Na+ between the fish and the environmental water were measured periodically throughout the experiment.

Over the first 8 h of hypercapnia, plasma increased by 7·6 Torr with a concurrent decrease in plasma pH of 0·28 units. Plasma [HCO3−] was slowly elevated from about 14 to 22 mm after 48 h, at which point 50% of the pH depression expected at constant bicarbonate concentration had been compensated. The net amount of H+ transferred to the water was 3 ·3 mmol kg−1 fish, representing a 115 % increase in the rate of cumulative H+ efflux, and inducing an elevation of both intracellular and extracellular [HCO3−]. Cl− transfer was reversed from a net uptake to a net efflux, while net Na+ influx was increased slightly.

Following hypercapnia, plasma pH returned to control values within 1 h, while the plasma [HCO3−], which was elevated during hypercapnia, fell continuously to reattain pre-hypercapnic control values after 20 h. The [HCO3−] decrease was due to the net gain of H+ ions from the water during this period. Cl− transfer returned to a net uptake, while the original Na+ influx was reversed to a net loss.

Acid-base regulatory responses in the carp are qualitatively similar to those observed in other fish, though the time required for compensatory pH adjustment is longer. It is concluded that alterations in the rates of Cl −/HCO3− and Na+/H+ exchanges during hypercapnia and Na+/H+ exchange following hypercapnia, play a significant role in the compensation of respiratory acid-base disturbances in these animals.
Lateral-Line Input and Stimulus Localization in the African Clawed Toad Xenopus Sp.
Authors: Görner Peter , Moller Peter , Weber Wolfgang
Published: April 2021

Intact Xenopus sp. responded to a train of surface waves with a single, stimulus-directed motor response which consisted of a turning component and a displacement component. The turning angle increased in a linear fashion with the stimulus angle. The magnitude of the turning angle was not affected by (a) the size of the animal, (b) the way the surface wave was elicited (with a drop of water or by dipping a rod into the water), (c) reflected waves and (d) the number of successively administered stimuli. With no lateral-line organs left intact Xenopus could still localize the origin of a surface wave, but with reduced accuracy. With only two stitches left intact on the left and on the right occipital lines, the turning angles were more widely scattered for stimuli placed at angles larger than 90°. The scatter was even larger than that of the equivalent responses from animals without a functional lateral-line system, i.e. the directional responsiveness in the partly lesioned animals was less accurate than in those with their entire lateral-line inoperative. Xenopus with four or two ipsilateral occipital stitches left intact were no longer able to orientate accurately. When the animal was stimulated on the lesioned side it frequently turned to the wrong side. These errors were absent or less frequent when the animal was stimulated on the intact side. The lesion experiments indicated that (a) a few organs provide sufficient information for an appropriate turning response, but the turnings were only roughly directed towards the stimulus, and (b) the decision whether Xenopus localizes a stimulus on the left or right side depends on whether the central nervous system receives information from one or both sides.
α-Aminoisobutyric Acid Transport In The Midgut Of Two Lepidopteran Larvae
Authors: Sacchi V. F. , Hanozet G. M. , Giordana B.
Published: April 2021

A net absorption of a-aminoisobutyric acid (AIB) takes place in vitro in the midgut of two lepidopteran larvae, Philosamia cynthia Drury and Bombyx mori L. In P. cynthia the midgut epithelium accumulates AIB from the lumen, while in the same conditions AIB accumulation is not observed in B. mori midgut cells. In P. cynthia, when the lumen is bathed with a low K solution, the net absorption of AIB is reduced and the intracellular accumulation from the lumen is abolished. Brush border membrane vesicles, prepared from the midgut of both species, show a transient K-dependent concentrative uptake of AIB. The relationship between AIB uptake and AIB concentration in the presence of a transmembrane K gradient was studied inB. mori vesicles and the kinetic constants were calculated. These results confirm that there is a K-amino acid co-transport system on the brush border of columnar cells in the midgut of both larvae.
A Sensory System Initiating Swimming Activity in the Medicinal Leech
Authors: Brodfuehrer Peter D. , Friesen W. Otto
Published: April 2021

Water-wave stimulation, which was previously shown to elicit swimming in intact leeches, can initiate swimming in a semi-intact leech preparation via activation of the sensillar movement receptors (SMRs), provided that 50 μ-serotonin is added to the physiological saline. The neuronal responses resulting from near-field stimulation of the leech body wall with a vibrating probe were recorded in peripheral nerves and in nerve-cord connectives. The response in the dorsal posterior nerve to a single vibratory pulse consists of a graded compound action potential. The units contributing to this action potential have a much lower threshold for near-field stimulation than do touch cells. They appear to be the same sensory units, the SMRs, that mediate leech sensitivity to water waves. The frequency domain of the SMR sensitivity extends as low as 1 Hz. Thus, leeches could receive self-stimulation from the water vibrations created by their own swimming movements. Leech physiological saline containing 20–40 m-Mg2 does not eliminate the SMR response to near-field stimulation recorded in the DP nerve; however, elevated Mg2 concentrations do eliminate the neuronal responses in the nerve cord connectives. Thus, while no chemical synapse occurs between the peripherally situated SMRs and nerve cord ganglia, a synapse may be interposed between the SMRs and the intersegmental neurones activated by near-field stimulation. The swim-facilitating action of serotonin occurs at unidentified sites within the ventral nerve cord, since serotonin does not alter the sensitivity of the SMRs.
Changes in Activity and Ventilation in Response to Hypoxia in Unrestrained, Unoperated Dogfish (Scyliorhinus Canicula L.)
Authors: Metcalfe J. D. , Butler P. J.
Published: April 2021

Daily activity cycles, together with changes in activity and ventilation frequency in response to hypoxia ( about 8 kPa), have been measured in unrestrained, unoperated dogfish. Continuous recording of activity over 48 h reveals that dogfish are essentially nocturnal, being three to four times more active at night than during the day. In relatively inactive, diurnal dogfish, rapid reduction of environmental does not cause any significant increase in swimming activity, whereas prolonged hypoxia actually appears to suppress activity. In more active, nocturnal dogfish, rapid reduction of environmental causes an immediate reduction in activity which remains suppressed throughout the hypoxic period. It is concluded therefore that increases in circulating catecholamines in response to hypoxia are the result of hypoxia alone, rather than of any increase in locomotory activity.

In resting diurnal dogfish, ventilation frequency is lower than has previously been reported for this species and, contrary to previous reports, increases markedly by 49% in response to hypoxia. It appears that in previous studies on confined dogfish, respiratory frequency, and probably ventilation volume, may have been elevated to near maximum levels even in ‘resting’ normoxic fish. This may have profound effects on so-called resting values for oxygen transfer in this species.
Heart Rate and Aerobic Metabolism in Humboldt Penguins, Spheniscus Humboldti, During Voluntary Dives
Authors: Butler P. J. , Woakes A. J.
Published: April 2021

Heart rate and aerobic metabolism have been recorded from three Humboldt penguins, Spheniscus humboldti, freely diving on a freshwater pond (9 × 4·6 × 2·7 m deep), using an implanted radiotransmitter and an open circuit respirometer. Oxygen uptake at mean dive duration (46·2 s) was 26 % greater than the resting value, but the difference was not statistically significant. Heart rate was also similar to the resting value. It is concluded that voluntary dives of penguins are completely aerobic and that oxygen stores are sufficient to allow metabolism to continue at the rate estimated in the present study for 2·27 min during voluntary submersion. This is longer than that calculated for tufted ducks, probably because the penguins are more efficient at underwater locomotion and because they are almost neutrally buoyant.
A Comparison of Neuronal and Behavioural Thresholds in the Displacement-Sensitive Pathway of the Crayfish Procambarus
Authors: Ebina Yoshio , Wiese Konrad
Published: April 2021

Velocity thresholds of neurones in the displacement-sensitive pathway of the crayfish were investigated using a stimulus programme of ramp fluid movements, with a range of velocities from 0·01–55 cm s−1 at the source (in both forward and backward directions). The velocity of the stimulus was calculated to produce particle movements with velocities of between 0·001–1·0 cms−1 at the receptors of the telson. The distribution of threshold values for afferents in the fourth root of the sixth abdominal ganglion and interneurones of abdominal 4–5 connectives was plotted. Thresholds were similar for afferents and interneurones, differing in absolute value from 0·001–1·0 cm s−1. Although neurones had threshold values throughout this range, there were peaks in the distributions. For the sample of 143 interneurones these were at 0·002–0·004, 0·01–0·08, 0·1–0·4 cm s−1. In the sample of 43 afferents the middle peak fell at 0·02–0·06 cm s−1, but the other two were the same as those for the interneurones. The threshold for a behaviour pattern which makes crayfish turn to face the water current was around 0·1 cm s−1 continuous fluid speed. Escape behaviour elicited by pure displacement stimuli was observed in our experiments only in animals of 2–3 cm body length which responded to displacement amplitudes of 28 mm s−1 and 6·7 cm s−1 maximum particle velocity. Strongly phasic interneurones in the pathway obviously contribute significantly in triggering escape and need high acceleration transients to become fully active.
A Method for the Neurophysiological Study of Reflexes Elicited by Natural Statocyst Stimulation in Lobsters
Authors: Miyan Jaleel Ahmad
Published: April 2021

In the neurophysiological investigation of crustacean statocyst function, the requirement to administer a physiological stimulus is not easy to reconcile with the need to maintain a stable preparation for microelectrode recordings. In studies of sensory activity this dilemma has been overcome by using an isolated statocyst preparation with its associated sensory nerve (Cohen, 1955). In many cases where such preparations have been used, stimulation has nevertheless been by artificial means: irrigation of the statocyst sac (Sandeman & Okajima, 1972; Silvey & Sandeman, 1976), magnetic attraction of an artificial iron lith (Ozeki, Takahata & Hisada, 1978) or displacement of individual hairs with a needle (Cohen, 1960; Takahata & Hisada, 1979; Takahata, 1981). For studying reflex activity, it has proved possible to record with needle electrodes from large statocyst interneurones in dissected crabs mounted on pivoted platforms (Fraser, 1974, 1977; Fraser & Sandeman, 1975).
The Extent Of Short-Term And Long-Term Compensation To Temperature Shown By Frog And Toad Sartorius Muscle
Authors: Renaud J. M. , Stevens E. D.
Published: April 2021

The effect of pH at different temperatures was studied on the force velocity characteristics of the sartorius muscle to estimate short-term compensation to temperature. The effect of thermal acclimation was also studied in order to estimate long-term compensation. A decrease in either pH or temperature reduced both tetanic tension and shortening velocity. There was a significant pH-temperature interaction for tetanic tension and for maximum mechanical power, but not for Vmax It is shown that this pH-temperature interaction was large enough to provide a mechanism for short term compensation only for the maximum strength (tetanic tension) in both species. Shortening velocities at small loads of the sartorius muscle of frogs and toads acclimated to 25 C were faster than those acclimated to 5 C. The difference between the two acclimation groups increased with test temperature and was almost 1 muscle length per second (m.l. s−1) at 25 C for both species. Acclimation temperature had no significant effect on tetanic tension or on maximum mechanical power at any of the test temperatures. It is proposed that the small capacity for long-term compensation in frog and toad sartorius muscles is related to the strategy employed during winter: frogs and toads hibernate.
Bluefin Tuna Warm Their Viscera During Digestion
Authors: Carey Francis G. , Kanwisher John W. , Stevens E. Don
Published: April 2021

Acoustic telemetry showed that stomach temperature from large bluefin tuna, Thunnus thynnus, held in an impoundment, changes markedly during feeding. The stomach cools rapidly on ingesting cold food. It then warms to a maximum of 10–15 °C above water temperature over a period of 12–20 h. Temperature decreases slowly over the next 20–30 h to a final state where it remains 3–6 °C above water temperature. The viscera are thermally isolated. Conductive heat losses are reduced by an overlying gas bladder and by the thick fatty muscle of the body wall. Convective heat losses are prevented by heat exchangers in the circulation. The temperature rise can be accounted for by heat released in the hydrolytic processes of digestion and by an increase in metabolic rate. The elevated temperatures should speed digestion and allow the tuna to feed frequently when food is abundant.
Fiddler Crab Exercise: the Energetic Cost of Running Sideways
Authors: Full Robert J. , Herreid Clyde F.
Published: April 2021

The fiddler crab, Uca pugilator, used sideways octapedal locomotion during 15 min of treadmill exercise. At each velocity tested (0·06, 0·11 and 0·16 km h−1), oxygen consumption showed only a modest, sluggish elevation; a ‘steady-state’ was never attained. The highest recorded, 0·22 ml O2g−1 h−1, was 4·4 times the resting rate. Net whole body lactate (WBL) was found to increase at a constant rate throughout the exercise period.

During recovery, and WBL removal followed a similar time course and returned to pre-exercise rates in 30–45 min. Although the fate of lactate after exercise is unknown for crustaceans, calculations suggest that not enough oxygen is consumed by the crab during recovery to oxidize lactate completely to CO2 and H2O. A gluconeogenic fate is compatible with the data.

As running velocity was increased, increased only slightly, while the net rate of WBL production showed a substantial elevation. At low velocity aerobic metabolism accounted for 60 % of the ATP produced when aerobic metabolism and anaerobic fermentation are considered. Anaerobic fermentation dominated at medium and high velocity and produced 60 and 70 % of the ATP, respectively.

The minimum cost of transport, the least amount of energy required to transport a given mass a distance, was determined using both aerobic and anaerobic sources. This estimation of locomotion economy for Uca pugilator was within the range predicted for a vertebrate of a similar mass.
Fast Continuous Swimming of Two Pelagic Predators, Saithe (Pollachius Virens) and Mackerel (Scomber Scombrus): a Kinematic Analysis
Authors: Videler J. J. , Hess F.
Published: April 2021

Straight, forward, unrestrained swimming behaviour, with periodic lateral oscillations of body and tailfin, was described and compared for saithe and mackerel. A method was developed for kinematic analysis of forward motion, lateral displacements and body curvature, based on a Fourier-series approach.

The dimensionless kinematic quantities showed relatively small variations over large ranges of swimming speeds. The speed range of mackerel was twice as fast as that of saithe. The main difference in swimming style between the species was a somewhat greater tail amplitude and a correspondingly stronger curvature near the caudal peduncle in mackerel than in saithe.

The swimming style of both species yields a Froude efficiency close to the maximum value possible, given the observed amplitude increase in the posterior part.
Crayfish extraretinal photoreception. I. Behavioral and motorneuronal responses to abdominal illumination
Authors: Edwards D. H.
Published: April 2021

Stimulation of blinded and sighted crayfish with ventrally directed light evokes a slow tail flexion response or a tail flexion accompanied by backward walking. The response latencies and durations of sighted animals are shorter than those of blinded animals, which indicates that visual inputs can speed a response which can be released by extraretinal photoreceptors alone. Recordings from electrodes implanted in intact, freely behaving animals demonstrate that ventral illumination tonically excites abdominal postural flexor motoneurones. The motoneurone discharge occurs first in caudal segments and then spreads rostrally, as does abdominal flexion around each segmental joint. Illumination of individual abdominal ganglia (A2–A5) tonically excites a similar flexor motoneurone response in cells of the stimulated ganglion and more caudal ganglia. Swimmeret motoneurones are also tonically excited by this stimulus. These responses can be evoked in isolated abdominal nerve cords, indicating that extraretinal photoreceptors present in these ganglia activate motor circuits that are local to the abdomen. Stimulation of A6 excites the caudal photoreceptor neurones, but only excites flexor motoneurones if the abdominal ventral nerve cord is connected to the rostral part of the CNS. The motoneurones respond with repeated bursts of activity that long outlast the stimulus or the initial high-frequency burst of the caudal photoreceptor neurones. These motoneurone responses are similar to those evoked by stimulation of command fibres that also evoke backward walking (Kovac, 1974a).
Chloride transport in toad skin (Bufo viridis) The effect of salt adaptation
Authors: Katz U. , Larsen E. H.
Published: April 2021

The steady-state Cl− current across the skin of Bufo viridis adapted to tap water was found to be rectified. In skins bathed with NaCl Ringer on both sides, a large outward current, carried by influx of Cl−, was observed at a clamping voltage (V) of < − 50mV (outside of the skin negative). For V = −50 mV the transepithelial Cl− conductance calculated from isotope flux measurements was 2·5 ± 0·3 mS cm−2, N= 10. When the skin was clamped at +50 mV the net flux of Cl− was reversed, but Cl− conductance was only 0·3 ± 0·1 mS cm−2. Flux ratio analysis indicated that the potential-activated Cl− conductance carries Cl− ions by way of passive transport. With NaCl Ringer bathing the outer surface of the skin the spontaneous potential was about −30 mV. At this potential the Cl− conductance of the skin was about half of its maximum value. The time course of Cl− current activation following a fast, stepwise change of V from 50 mV to a potential below 0 mV showed an initial delay of a few seconds, and proceeded with a halftime (T1/2) which varied as a bellshaped function of V. The maximum T1/2 was about 100 s for V = −10 mV in skins exposed to KCL Ringer on the outside. Following adaptation of the toads to a 250 mm-NaCl solution, the fully activated Cl− conductance of the skin was greatly reduced, and the conductance-voltage curve was shifted to the left along the voltage-axis. With NaCl Ringer on the outside the spontaneous potential was about −20 mV, and Cl− conductance activation was possible only outside the physiological range of potentials. The time constant of Cl− conductance activation from closed to fully activated state was more than doubled following salt adaptation of the toads. The active inward Cl− flux disappeared in skins of toads adapted to a 250 mm-NaCl solution, and apparent leakage conductance was reduced. Application of the phosphodiesterase inhibitor 3-isobutyl-l-methylxanthine to skin of fully salt-adapted toads increased the transepithelial Cl− conductance, and the time courses of voltage clamp currents became more like those of water-adapted toads. Apparent leakage conductance was increased. Salt adaptation of B. viridis was followed by a statistically significant reduction in the number of mitochondria-rich cells relative to the number of granulosum cells of the replacement layer, from a ratio of 0·50 to 0·25. The volume of the mitochondria-rich cells was reduced following salt adaptation of the toads.
The Electrical Properties of Isolated Frog Skin
Authors: Francis W. L.
Published: April 2021

The relation of the electrical potential across isolated frog skin in Ringer to oxygen concentration and oxygen pressure has been experimentally investigated. The dependence of the respiration of isolated frog skin in Ringer on oxygen concentration has also been determined. The potential and respiration depend in the same way on the oxygen concentration. The potential is diminished by inhibitors of respiratory processes.

The rôle of oxygen consumption in maintaining the skin potential is discussed.
Histological Changes in the Ovaries and Ovarian Blood Vessels of Xenopus Laevis Associated With Hypophysectomy, Captivity and the Normal Reproductive Cycle
Authors: Shapiro B. G. , Shapiro H. A.
Published: April 2021

Seasonal changes in the ovaries of Xenopus laevis (the South African clawed toad) are described. Degenerative changes in the large mature central ova occur more rapidly as a result of hypophysectomy than as a result of captivity. The suggestion is made that the pituitary may be concerned with the maturation of ova in Xenopus laevis. Hypophysectomy results in severe arteriosclerotic changes in the ovarian blood supply as early as 412 months after the operation. Control animals show no such changes. The histological changes observed in the ovaries after hypophysectomy, whether total or partial, are probably due to the removal of the anterior lobe alone.
The Physiology of Contractile Vacuoles
Authors: Kitching J. A.
Published: April 2021

The rate of output of fluid from the contractile vacuole of a fresh-water Peritrich Cihate was decreased to a new steady value immediately the organism was placed in a mixture of tap water and sea water. The rate of output returned to its original value immediately the organism was replaced in tap water. The contractile vacuole was stopped when the organism was treated with a mixture containing more than 12 per cent, of sea water. Transference of various species of marine Peritricha from 100 per cent, sea water to mixtures of sea water and tap water led to an immediate increase of the body volume to a new and generally steady value. Return of the organism to 100 per cent, sea water led to an immediate decrease of the body volume to its original value or less. Marine Peritricha showed little change in rate of output when treated with concentrations of sea water between 100 and 75 per cent. In more dilute mixtures the rate of output was immediately increased, and then generally fell off slightly to a new steady value which was still considerably above the original (100 per cent, sea water) value. The maximum sustained increase was approximately x 80. Return of the organism to 100 per cent, sea water led to an immediate return of the rate of output to approximately its original value. When individuals of some marine species were placed in very dilute concentrations of sea water, the pellicle was frequently raised up in blisters by the formation of drops of fluid underneath it, and the contractile vacuole stopped. Evidence is brought forward to suggest that in the lower concentrations of sea water marine forms lost salts. The contractile vacuole probably acts as an osmotic controller in fresh-water Protozoa. Its function in those marine Protozoa in which it occurs remains obscure.
Effects of Body Size and Slope on Acceleration of a Lizard (Stellio Stellio)
Authors: Huey Raymond B. , Hertz Paul E.
Published: April 2021

The agamid lizard Stellio ( = Agama) stellio L. accelerated quickly on a level track. Lizards reached 95 % of maximum speed in an average of only 0·31 m and 0·19s. Large lizards had higher initial accelerations (∼M1/3) and accelerated over longer distances and times than did small lizards. As a result, larger lizards achieved higher maximum speeds. Lizards of a given size that accelerated quickly also achieved high maximum speeds. Acceleration was also measured on slopes ranging from −15° to +60°. Steep inclines did not differentially reduce the initial acceleration of large versus small lizards, a result which contrasts with a previous demonstration that such inclines significantly reduce the maximum speed of only large lizards. Simulations of simple predatory-prey chases suggest that large lizards will be more successful if they attack distant prey on level or downhill slopes and that small lizards will be more likely to escape larger quadrupedal predators by fleeing uphill, unless the predators are near.
A Chemical Synapse Between Two Motion Detecting Neurones in the Locust Brain
Authors: Rind F. Claire
Published: April 2021

The LGMD is the major source of visual input from the compound eye to the ipsilateral DCMD. Inactivating the LGMD or hyperpolarizing it, so it no longer spikes, abolishes the response of the DCMD to the visual stimulus. Synaptic transmission between the LGMD and DCMD neurones is chemical. A spike in the LGMD terminals induces a postsynaptic potential in the DCMD dendrites, with a transmission delay of 1 ms. There is a conductance increase in the DCMD during an LGMD-mediated PSP. The conductance increase occurs at membrane potentials when the current/voltage relationship of the DCMD membrane is linear, and at several different membrane potentials. The LGMD-mediated PSP within the dendritic region of the DCMD has a rise time of 1·3 ms, a half-time for decay of 2·2 ms and a total duration of 8·3 ms. In the cell body it has a rise time of 3·3 ms, a half-time for decay of 8 ms and a total duration of 21·3 ms. The amplitude of the LGMD-mediated PSP depends on the membrane potential of the DCMD. The PSP amplitude is increased by membrane hyperpolarization and decreased by membrane depolarizations. At a membrane potential 30 mV more positive than resting potential the extrapolated size of the PSP is zero. The synaptic efficiency of the LGMD-DCMD connection is usually 1·2. There is a threshold of 13 mV in the LGMD before synaptic transmission occurs. Currents less than 13 mV are not transmitted in either direction across the synapse although they do reach the synaptic region if they are injected at the extremities of the neurones within the brain. Length constants for the LGMD are 0·36 mm between points c and d (see Fig. 4) in the protocerebrum and 0-63 mm between point b in the optic lobe and point d in the protocerebrum. The length constant measured between the dendrite region of the DCMD and its cell body is 1·34mm. DCMD spikes and PSPs follow spikes in the LGMD at a constant latency at frequencies up to 400 Hz. Usually a spike in the LGMD induces a spike in the DCMD.
An Anticalmodulin Drug, W-7, Inhibits the Voltage-Dependent Calcium Current in Paramecium Caudatum
Authors: Hennessey Todd M. , Kung Ching
Published: April 2021

The anticalmodulin drug, W-7 [N--(6 aminohexyl)-5-chloro-l-naph-thalenesulphonamide] specifically inhibits the voltage-dependent Ca-current of Paramecium as well as the behavioural consequence of Ca2+ influx, backward swimming. The dechlorinated analogue, W-5, is four to five times less effective. Analysis of membrane currents under voltage clamp shows that W-7 not only reversibly inhibits the voltage-dependent Ca-current but also shifts the voltage sensitivity of this Ca-current towards less negative voltages in a concentration-dependent manner. We suggest that Paramecium can be used as a system to screen behaviourally for other Ca-channel blockers as well as to study the mechanism of action of these drugs.
Geotaxis in the Ciliated Protozoon Loxodes
Authors: Fenchel T. , Finlay B. J.
Published: April 2021

Geotaxis is demonstrated in the ciliated protozoon Loxodes. This behaviour is mediated by a mechanoreceptor which is probably the Müller body, an organelle characteristic of loxodid ciliates. The geotactic response is sensitive to dissolved oxygen tension: in anoxia or at very low O2 tensions the ciliates tend to swim up and at higher O2 tensions they tend to swim down. This behaviour, in conjunction with a kinetic response allows the ciliates to orientate themselves in vertical O2 gradients and to congregate in their optimum environment. In two appendices, models of the behaviour predicting vertical distribution patterns and considerations of the minimum size of a functional statocyst are offered.
Secretion By The Malpighian Tubules Of Rhodnius Prolixus Stal: Electrical Events
Authors: O’Donnell M. J. , Maddrell S. H. P.
Published: April 2021

Transepithelial and intracellular potentials have been simultaneously recorded from Rhodnius upper Malpighian tubules before and after stimulation of fluid secretion. The transepithelial electrical response to the diuretic hormone mimic 5-hydroxytryptamine (5-HT) was triphasic; recordings of intracellular potential changes indicated that the three phases represented successive events at the apical membrane. Depolarizations produced by increasing the bathing medium potassium concentration indicated that the basal membrane was much more permeable to potassium than to sodium. Electrical responses to chloride-free saline were inconsistent with a significant basal membrane chloride permeability. Chloride movements across the basal membrane were opposed by an electrical gradient of about 65 mV. The results of experiments in which tubules were exposed to chloride-free saline or sodium-free saline suggested that chloride entry into the cells was linked to the entry of Na+ and K The effects of furosemide and bumetanide upon secretion and potential changes suggested that chloride crossed the basal membrane through co-transport with Na+ and K+. Chloride probably crosses the apical membrane into the lumen passively in response to a favourable electrical gradient of about 35 mV. Cations must be actively pumped into the lumen against an electrical gradient of 35 mV. Our results support previous evidence for an apical cation pump which actively transports Na and K into the lumen. A tentative model of ionic movements during fluid secretion is presented. It is suggested that the apical cation pump maintains sodium at low intracellular concentrations, thereby maintaining a favourable gradient for entry of Na+ through the proposed basal co-transport step. The suggested stoichiometry is Na+ : K+ : 2Cl−.
Plasma and Red Cell Ionic Composition in Rainbow Trout Exposed to Progressive Temperature Increases
Authors: Houston A. H. , Koss T. F.
Published: April 2021

Yearling rainbow trout, Salmogairdneri Richardson, were exposed to progressive increases in temperature from 10 to 26·1 °C, and variations in haemoglobin, haematocrit and plasma and erythrocytic concentrations of Na+, K+, Ca, Mg2+ and Cl− were compared with those of animals maintained at 10 °C. Despite the effects which increases in temperature are known to have on branchial ventilation, perfusion and effective exchange area, and consequently upon passive water and electrolyte fluxes, plasma ion concentrations were little affected at other than acutely stressful temperatures. Presumably this reflects the consequences of previously demonstrated changes in branchial, renal and erythrocytic (Na+/K+)- and (HCO3−)-activated ATPase and carbonic anhydrase activities. Haemoglobin and haematocrit were also little influenced by increases in temperature between 10 °C and about 25 °C. It is unclear whether the decreases seen at higher temperatures reflected accelerated ageing and breakdown of circulating red cells or were a consequence of changes in tissue water content and distribution with resulting haemodilution. Red cell levels of Cl− and K+ increased more or less steadily at temperatures exceeding 16–18°C. So also did [Cl−] : [Hb] and [Kj:[Hb], Sodium and [Na+]: [Hb] were essentially constant up to about 25 °C, but thereafter increased sharply. Much the same was true of Ca2+. However, red cell Ca2+ concentrations were normally <0·15 mmol l−1 cell water, and may be physiologically insignificant in the context of the present study. A more complex pattern of change was encountered in the case of Mg2+. Concentrations of this ion and the [Mg2+] : [Hb] ratio declined between 10 °C and 20–22°C and thereafter increased. A significant positive correlation existed between red cell levels of Cl− and K+, significant negative correlations between Cl− and Mg2+ and K+ and Na+. Negative, but insignificant correlations were also seen between Ca2+ and both Cl− and K+. Given the known direct and indirect effects of inorganic ions upon haemoglobin-oxygen affinity, the reductions in intraerythrocytic pH which accompany increases in temperature and the effects of temperature per se on affinity, the compositional changes observed in this study would be expected to prompt reductions in haemoglobin-oxygen affinity and increases in P50 values. Previous studies have, however, revealed little thermo-acclimatory variation in the P50 of this species. Thus, some as yet unidentified factor or factors may operate in opposition to these influences.
Radial Symmetry and the Organization of Central Neurones in A Hydrozoan Jellyfish
Authors: Spencer A. N. , Arkett S. A.
Published: April 2021

Two discrete networks of neurones in the outer nerve-ring of Polyorchis penicillatus can be identified by their physiological and morphological characteristics. The ‘B’ system is characterized by the regular, spontaneous firing pattern that can be recorded intracellularly. Bursts of up to six spikes are produced in response to a rapid reduction in the light intensity. Neurones of the ‘B’ system are electrically coupled to one another. Action potentials in the ‘B’ system produce unitary EPSPs in swimming motor neurones and in epithelial cells overlying the outer nerve-ring. Lucifer Yellow injected into a ‘B’ neurone diffuses rapidly through neighbouring neurones to reveal a condensed network of neurones in the centre of the nerve-ring and a more diffuse network passing up and around each tentacle. The ‘O’ system is characterized by very regular (approx. 1 Hz), spontaneous membrane potential oscillations. Action potentials are never recorded. Neurones of the ‘O’ system are electrically coupled to one another. There is evidence of interaction between the ‘O’ system and swimming motor neurones. Lucifer Yellow injected into an ‘O’ neurone diffuses through member neurones to show an anastomosing network of neurones extending across the width of the outer nerve-ring and tracts of neurones extending up the sides of each tentacle towards the ocelli. The restriction of injected Lucifer Yellow to each of the networks and the blockade of interaction between systems by Mg2+ anaesthesia are evidence that signalling between different central networks is by chemical means. The adaptive advantages of this type of functional organization of central neurones in radially symmetrical animals are discussed. Such an organization is compared with that found in bilateral animals.
The Role of the Gills and Branchiostegites in Gas Exchange in a Bimodally Breathing Crab, Holthuisana Transversa: Evidence for a Facultative Change in the Distribution of the Respiratory Circulation
Authors: Taylor H. H. , Greenaway Peter
Published: April 2021

The respiratory circulation was investigated in air-breathing and waterbreathing Holthuisana transversa von Martens by analysis of the distribution of radioactive microspheres injected into the haemocoel at seven locations. The gills and putative lungs (branchiostegites and membraneous thoracic walls) both trap approximately 90 % of the microspheres entrained in their afferent circulations. The main blood supply to the branchiostegites is from the venous sinuses and constitutes a substantial fraction of the total venous return, which is consistent with earlier inferences, based on morphological information, of their possible involvement in gas exchange. In airbreathing crabs, a mechanism exists which directs a greater proportion of the total venous return via the lungs. From the sinus at the base of walking leg 2, the ratio lung: gill flow was estimated as 86·9: 13T ± 5·7 % in hydrated crabs that had been air-breathing for more than 1 day, and 19·5:80·5 ± 7·12 % in water-breathers. A factor in this circulatory switch may be an increase in branchial resistance in air caused by surface tension of water adherent to the gill lamellae. The direct arterial circulation to the gills represents about 3 % of cardiac output and is therefore an insignificant component of the total respiratory circulation. Patterns of microsphere distribution among different gills and different regions of the lung provide information on flow patterns within the thoracic sinus. Neither the thoracic sinus as a whole nor the infrabranchial sinuses can be considered as reservoirs of truly mixed venous blood in H. transversa.
Motor Patterns Induced in the Antenna of the Rock Lobster by Cuticular Vibration on the Cephalothorax
Authors: Vedel Jean-Pierre
Published: April 2021

In the rock lobster, Palinurus vulgaris, mechanical vibration applied to one point on the cuticle of the cephalothorax induced phasic sensory activity in numerous cuticular nerve branches innervating most of the carapace. The same vibratory stimulus produced two kinds of effect on the tonic activity of the motoneurones innervating the extensor and flexor muscles of the distal joints (J2 and J3) of the antenna: a reciprocal motor effect, decreasing the extensor motoneurone activity and increasing the flexor motoneurone discharge, or a diffuse facilitatory motor effect increasing both extensor and flexor motoneurone activity. The extensor and flexor excitatory motoneurones, like the inhibitory motoneurone common to the J2 and J3 extensor and flexor muscles, can be driven in a one-to-one manner by vibration at low frequency (5–10 Hz). Either motor effect of cuticular stimulation can be modified by other sensory stimuli, e.g. passive movements of the uropods. Cuticular vibration modulates the extensor and flexor resistance reflexes elicited by passive extension/flexion movements of the flagellum, the nature of this modulation depending upon which effect the vibratory stimulus alone produces. The functional significance of the cuticular motor effects is discussed.
Local Circuit Interactions in Synchronization of Cortical Neurones
Authors: Wong R. K. S. , Miles R. , Traub R. D.
Published: April 2021

Under certain circumstances large numbers of neurones in the mammalian central nervous system (CNS) can discharge simultaneously. An example of such activity is recorded from a hippocampal slice in the presence of agents which block synaptic inhibition. This synchronized discharge occurs spontaneously in a rhythmic fashion or may be triggered by stimulation of any afferent pathway. Its generation appears to involve local circuit interactions. The favourable conditions offered by an in vitro preparation have allowed the cellular events during this activity to be examined in some detail. Three factors appear to be critically involved in the synchronization process. Firstly, the intrinsic ability of neurones to generate bursts, secondly, the existence of powerful recurrent excitatory connections, and thirdly the absence of inhibition which normally prevents the spread of bursting activity through the recurrent connections. Computer simulations show that in a sparsely connected network of bursting neurones activity initiated in a few cells may spread through recurrent connections until eventually the whole population discharges simultaneously. Rhythmic discharges similar to those described here also underly various CNS functions including centrally-originating motor patterns. It remains to be determined whether neuronal properties and connectivity found to be important in this hippocampal rhythm may also play a role in the generation of other rhythmic activities in the mammalian CNS.
Neuronal Interactions Mediated by Neurally Evoked Changes in the Extracellular Potassium Concentration
Authors: Spira Micha E. , Yarom Y. , Zeldes D.
Published: April 2021

Neuronal interactions mediated by alteration of the extracellular K+ concentration [K+]o occur between populations as well as among single neurones in very restricted regions. The interactions mediated by K+ ions may range from low efficacy ones (in which the effects of increased [K+]o around the non-active cells can be recorded only after massive activity of a large population of neurones) to very effective interactions (in which a single action potential in a neurone is sufficient to produce a depolarization of several mV in a second one). Such efficient K+-mediated interactions cannot be unequivocally distinguished by shape, amplitude or time course from postsynaptic responses induced by chemical or electrotonic synapses.

We review here experiments which demonstrate various levels of interactions mediated by changes in potassium ion concentration. The giant axons (Gax) and non-giant axons from the central nervous system of the cockroach Periplaneta americana were used. The types of interactions discussed are: (a) pathological interactions among populations of neurones induced by the convulsant drug picrotoxin; (b) restricted and limited interactions which are the consequence of the combination of the special geometry of Gaxs and increases in extracellular K+; and finally, (c) local and efficient interactions among Gaxs which are postulated to be mediated by K+ ions.

The experiments described in this review, as well as others, demonstrate that the extracellular spaces in the CNS serve as predetermined pathways for K+-mediated neuronal communication. When the extracellular space between two adjacent neurones is very small, the K+-mediated interaction may resemble the PSPs of chemical or electrotonic synapses. It is possible that because of this resemblance, other K+-mediated interactions in the CNS have not been identified as such.
Early Visual Processing in Insects
Authors: Shaw S. R.
Published: April 2021

The present account reviews some of the progress made recently towards understanding better the processing of visual information in the peripheral visual system of insects. To limit the scope, it concentrates mainly upon the group that has been the subject of the most intensive recent work, and that is better understood from most aspects: the Diptera, or true flies. The region discussed is the retina proper and first synaptic neuropile, the lamina, and thus encompasses visual processing up to the level of third-order visual neurones. A number of reviews give either wider or fuller accounts of the same area: those of Laughlin (1980) and Järvilehto (1984) are particularly wide-ranging, Shaw (1981) discusses the neural connections in detail, whilst Meinertzhagen & Frohlich (1983) and Meinertzhagen (1984) provide introductions to aspects of neural development. A recent NATO conference volume features this area (Ali, 1984).
Changes in Neuronal Circuits During Insect Metamorphosis
Authors: Levine Richard B.
Published: April 2021

During metamorphosis insects undergo dramatic changes in both form and behaviour. Cell birth and death, as well as neurone respecification all contribute to the overall reorganization of the nervous system. Within the visual and chemosensory processing areas of the insect brain large numbers of newly-generated adult neurones are incorporated into the larval nervous system. In the abdominal ganglia, however, identified larval neurones are retained to assume a new adult role. This respecification of motor neurone function involves not only the acquisition of a new target muscle, but also the reorganization of dendritic morphology, and alterations in the interconnections between neurones. For example, an identified abdominal motor neurone in the hawkmoth, Manduca sexta, grows new dendritic processes and changes its synaptic relationship with an abdominal stretch receptor such that an interaction that was inhibitory during larval life, becomes excitatory in the adult. In another example, identified sensory neurones that evoke a larval flexion behaviour, later participate in the defensive gin trap reflex that is characteristic of the pupa. In both instances the formation of new pathways is a two-step process in that the new circuits do not become behaviourally relevant as they are formed, but instead are activated abruptly at the appropriate time. For the gin trap reflex an identified peptide hormone is responsible for activating the circuit.
Neurospecificity in the Cricket Cercal System
Authors: Murphey R. K. , Walthall W. W. , Jacobs G. A.
Published: April 2021

Studies of neurospecificity in the cricket cereal sensory system are reviewed and a decade of experimentation is examined in the light of recently obtained anatomical data. The nearly complete description of the anatomy indicates that the excitatory receptive fields of directionally-selective interneurones are a joint function of an orderly afferent projection and the dendritic structure of the first order interneurones. The detailed understanding of the anatomy is shown to be a powerful tool in the interpretation of previously published physiological experiments and the design of new ones.

The mechanisms which shape the orderly afferent projection are then described and compared with the work on vertebrate sensory systems. It is concluded that both positional interactions of the type conceived by Sperry (1963) and competitive interactions of the type conceived by Hubel, Wiesel & LeVay (1977) are involved in producing the cereal afferent projection. Thus the two main components of the neurospecificity concept are shown to exist in the cricket nervous system. The limits of a purely anatomical approach to the study of neurospecificity are considered in light of the work on this cricket sensory system.
The Muscular Basis of Aquatic and Aerial Ventilation in the Air-Breathing Teleost Fish Channa
Authors: Liem Karel F.
Published: April 2021

The mechanisms of aquatic and aerial ventilation in four bimodally breathing species of teleosts of the genus Channa were studied by high-speed light and X-ray ciné films, pressure transducer recordings and electromyography. Neither inter- nor intraspecific differences were found in the pattern of aquatic and aerial ventilation. Aquatic ventilation proceeds with a partially air-filled buccopharyngeal cavity. The electromyographic patterns, pressure waveforms in the buccal and opercular cavities, and kinematics of jaw and opercula resemble those found for aquatically breathing teleosts. The pattern of aerial ventilation differs significantly from that of aquatic ventilation. Aerial ventilation is initiated by a reversed flow of water brought about by a low pressure in the buccal cavity. In this way the air in the suprabranchial cavity is moved forward and expelled from the mouth. The buccal, suprabranchial and opercular pressures are maintained at below ambient pressures throughout the aerial respiratory cycle. The kinematic pattern of bone movements, pressure waveforms and electromyographic profiles during air ventilation are identical to those of the cough and do not differ interspecifically. The complex aerial ventilation mechanism in Channa may be homologous with the primitive cough mechanism. Fishes employing the cough mechanism for air ventilation remain totally dependent on water and are therefore poorly adapted to explore terrestrial habitats.