bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Chemical Synapse Between Two Motion Detecting Neurones in the Locust Brain
Authors: Rind F. Claire 
Published: April 2021

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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 &lt;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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACTThe 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

ABSTRACT
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

ABSTRACT
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

Abstract
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.
Water Flow Patterns During Prey Capture By Teleost Fishes
Authors: Lauder George V. , Clark Brian D. 
Published: April 2021

Abstract
Water flow into the mouth cavity during suction feeding in centrarchid sunfishes was studied by mapping the trajectories of small particles in the water during prey capture. In Lepomis, a circulation develops as the mouth opens, and water is drawn into the mouth from above, below and in front of the head. Water displaced by movement of the body as the prey is approached during the strike is entrained into the circulation towards the mouth. The parcel of water sucked into the mouth has a diameter approximately one-tenth that of the predator’s length.