bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Presence of Gap Junctions in the Septate Desmosomes of the Salivary Apparatus of the Cockroach, Nauphoeta Cinerea
Authors: Maxwell David J. 
Published: April 2021

ABSTRACT
The acini of the cockroach salivary apparatus consists of two morphologically distinct types of cell. These have been described by Bland & House (1971) and have been called peripheral and central cells. Ducts which convey the saliva to the hypopharynx are also associated with the acini. Electrophysiological experiments (Ginsborg, House & Silinsky, 1974) have demonstrated the presence of low-resistance junctions between the cells of the acini (coupling resistance of less than 0·2 MΩ). Septate desmosomes are a common feature of the acini and ducts and have been observed to link all of the cell types (Bland & House, 1971). Although in the past several authors suggested that septate desmosomes could act as low-resistance couplings between cells (e.g. Loewenstein, 1966; Gilula, Branton & Satir, 1970), it now seems probable that gap junctions are the sites of low-resistance pathways between cells (for reviews see : Sotelo & Korn, 1978; Peracchia, 1980). Gap junctions are often incorporated in septate desmosomes (Berridge & Oschmann, 1972; Satir & Gilula, 1973; Noirot-Timothée et al. 1978).
Neuroglia And Spinal Fluids
Authors: Somjen George G. 
Published: April 2021

ABSTRACT
It is quite usual to see clear fluid collecting continuously on the surface of the spinal cord of ‘functionally decapitate’ cat preparations which have no functioning choroid plexus. The activity of potassium and calcium ions in interstitial fluid of these decapitate spinal cords is equal to that in spinal cords of cats with intact choroid plexus function, similar to normal cerebrospinal fluid, and different from blood plasma. It follows that fluid is being formed within the spinal cord by a process different from ultrafiltration. Endothelial cells seem likely to form this interstitial fluid by actively transporting Na+, with water following by osmotic force. Potassium and other ion concentrations may be adjusted by independent transport processes. A role could be attributed to glial cells in these transports if exchange of material could be demonstrated between glia and endothelium.
Comparative Studies on Glial Markers
Authors: Roots Betty I. 
Published: April 2021

ABSTRACT
Macromolecular markers for glial cells have been sought for a variety of reasons. One of the earliest was the need for a means of assessing the purity of cell and subcellular fractions prepared from nervous tissue. While there is still a requirement for this kind of tool, emphasis has shifted towards seeking information on biochemical differentiation among cells and their functional interactions. A brief general review will be made of glial markers and two of these, 2′,3′-cyclic nucleotide 3′-phosphohydrolase (CNP) and glutamine synthetase (GS), will be considered in detail. Until recently studies of markers have been concentrated on the higher vertebrates and those on lower vertebrates and invertebrates have hardly begun. However, such comparative studies may lead to fresh insight into old problems. For example, CNP has long been regarded as a marker for myelin and oligodendrocytes but it has not been possible to attribute a functional role to it and its relation to myelination has remained obscure. The finding that it is present in the glia of a moth Manduca sexta which lacks myelin provides a stimulus for a fresh approach to the problem. Another example is provided by studies on GS. This enzyme is found in astrocyte feet and preliminary results indicate that it is localized also in the perineurial glia of Aplysia ganglia. These results lead to a reconsideration of the perennial question of the possible role of astrocyte feet in barrier mechanisms. Extension of comparative studies may not only raise, new questions but also provide some answers.
Effect of Non-Neuronal Cells on Peptide Content of Cultured Sensory Neurones
Authors: Mudge Anne W. 
Published: April 2021

ABSTRACT
The peptide substances P (SP) and somatostatin (SOM) are present in small-diameter neurones of dorsal root ganglia (DRG) and in small-diameter fibres that project to the spinal cord dorsal horn. It is not known whether SP or SOM coexist with other transmitter molecules but, since both peptides can be released from sensory neurones and both can alter neuronal firing rates in the dorsal horn, it seems likely that they are involved in some way in synaptic transmission in the spinal cord. SP has generally excitatory effects in the spinal cord whereas SOM exerts inhibitory effects, and it is not at all clear which subclass of nociceptive afferents contain SP or SOM.
Mudge, Leeman & Fischbach (1979) have studied sensory neurones derived from chick DRG grown in dissociated cell culture. When the neurones are grown in the absence of non-neuronal cells, they contain SP but relatively little SOM. The amount of SOM produced by these neurones is greatly increased (c. 50-fold) when the neurones are grown together with ganglionic non-neuronal cells or with medium ‘conditioned’ by incubation with such cells. The increase in SOM content is not accompanied by an increase in SP content or a detectable change in neuronal survival.
The DRG non-neuronal cells consist of two major cell types-glial cells and fibroblasts. Indirect evidence suggests that glial cells rather than fibroblasts are responsible for the increased production of SOM by the neurones. Raff and his colleagues (Brockes, Fields & Raff, 1979) have used immunological techniques to obtain purified cultures of these two cell types. Work currently in progress is aimed at extending the above observations to the rat and firmly establishing whether glial cells can indeed influence SOM production in sensory neurones.
Influences of the Glial Environment on the Elongation of Axons After Injury: Transplantation Studies in Adult Rodents
Authors: Aguayo Albert J. , David Samuel , Bray Garth M. 
Published: April 2021

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 or 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 oblangata. 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.
Membrane Properties of Neuroglia in the Optic Nerve of Necturus
Authors: Orkand R. K. , Orkand P. M. , Tang C.-M. 
Published: April 2021

ABSTRACT
The optic nerve of Necturus has proved a useful preparation for the study of glial cell membranes in vivo and in vitro with anatomical relations to axons intact and isolated following axon degeneration. The glial membrane potential behaves as a selective potassium diffusion potential; there is no evidence of a significant permeability to other naturally occurring ions. The specific membrane resistance of the glial cells is high compared to that of neurones; there are low-resistance intercellular connexions among the cells which permit the passage of both ions and the dye Lucifer Yellow. The cells are readily and reversibly uncoupled by procedures which decrease the intracellular pH. There is no evidence for voltage-sensitive sodium channels in the membrane. Following sodium gain and potassium loss the membrane displays a potassium-dependent strophanthidin-sensitive electrogenic sodium pump. The glial membrane is depolarized by potassium released from active axons as well as by glutamate. The glial depolarization contributes to potentials recorded with surface electrodes. Depolarization by K+ plays a role in the redistribution of K+ which locally accumulates around active neurones and also affects glial metabolism and glucose uptake.
Ionic and Possible Metabolic Interactions Between Sensory Neurones and Glial Cells in the Retina of the Honeybee Drone
Authors: Coles J. A. , Tsacopoulos M. 
Published: April 2021

ABSTRACT
This is a review paper that includes original calculations and figures. The drone retina is composed of two essentially uniform populations of cells, the photoreceptors and the glial cells. The photoreceptors contain many mitochondria but no glycogen has been detected; the glial cells contain much glycogen and very few mitochondria. The oxygen consumption of the photoreceptors in the dark is 20 μl min−1 per g of retinal tissue and in response to a single flash of light there is an extra consumption that reaches a maximum of 40 μl min−1 per g. In addition, light stimulation of the photoreceptors leads to changes in the glycogen metabolism of the glial cells, and to movements of K+. Measurements with intracellular Insensitive micro-electrodes showed that during light stimulation with a series of flashes the K+ activity (aK) in the photoreceptors fell by an average of 27% while in the glial cells aK rose by an amount that is estimated to correspond to most of the quantity of K+ lost by the photoreceptors. The relative contributions to the clearance of extracellular K+ of extracellular diffusion, spatial buffering and possible net K+ uptake by glial cells are discussed.
Induced Magnetization in the Monarch Butterfly, Danaus Plexippus (Insecta, Lepidoptera)
Authors: Jones Douglas S. , Macfadden Bruce J. 
Published: April 2021

ABSTRACT
Eighteen preserved monarch butterflies, Danaus plexippus L., were analysed for their magnetic characteristics using a superconducting cryogenic magnetometer. These dead butterflies were either non-magnetic or possessed a natural remanent magnetization (NRM) indistinguishable from the background noise of the magnetometer (2 × 10−8 e.m.u. or less). Using a 500-gauss magnet, each specimen was induced with a magnetization which had a mean value of 1·27 × 10−6 e.m.u., indicating the presence of magnetic material in the monarch body.
Cutting the specimens into pieces, re-applying a strong field, and remeasuring revealed that most (about two-thirds or more) of the magnetization is concentrated in the head-thorax rather than the abdomen in contrast to the opposite situation reported for honey bees. The direction of the induced NRM, particularly in the horizontal plane, closely tracked the direction of the applied field. The intensities of induced magnetization and tracking of the applied field are similar to those reported for honey bees. There is no significant difference in the intensity or alignment of induced magnetization between males and females.
The Effects of Cooling On an Identified Reflex Pathway in the Cockroach (Periplaneta Americana), in Relation to Chill-Coma
Authors: Bradfisch G. A. , Drewes C. D. , Mutchmor J. A. 
Published: April 2021

ABSTRACT
The effects of cooling were studied in relation to (a) the impairment of locomotion (i.e. chill-coma) and (b) the functioning of various components of the monosynaptic trochanteral hair plate reflex in the cockroach, Peri-planeta americana. The mean temperature for onset of chill-coma was 10·5 °C. At this temperature animals were unable to right themselves and visible tremors of the legs and body occurred. Extracellular recordings from metathoracic nerve 5 indicated that cooling from 24 to 15 °C caused a decrease in the background spiking rate of motor neurone Ds. However, cooling from 12 to 9 °C caused a marked increase in the spiking frequency of both Ds and other unidentified neurones. This increase in spiking activity is the probable basis of leg and body tremors that occur during chill-coma. Monosynaptic coupling between hair plate afferent spikes and Ds spikes (following electrical stimulation of the hair plate) was markedly affected by cooling. At 25 °C, hair plate afferent and Ds spikes were always tightly coupled to one another, whereas at 10 °C coupling was very weak. Several lines of evidence suggest that this loss of coupling was the result of failure of central synaptic transmission. The reduced effectiveness of central synaptic transmission during cooling may be a critical factor in the impairment of locomotor ability associated with chill-coma.
Respiration and Acid-Base Physiology of the Spotted Gar, A Bimodal Breather
Authors: Smatresk Neal J. , Cameron J. N. 
Published: April 2021

ABSTRACT
In normally aerated water, at 20 °C, gar accounted for 42 % of their MO2 from their lungs, while in hypoxic water (PO2≃ 12 torr) their entire MO2 was from the lung, and O2 was lost through the gills. CO2 excretion in both normoxia and hypoxia was primarily via the gills.
Lung ventilation increased 1150%, accompanied by an elevation of pulmonary perfusion from 5·9 to 12·1 ml · kg−1 · min−1 in hypoxia, which accounts for the enhanced pulmonary MO2. Cardiac output increased from 31 to 40·5 ml · kg−1 · min−1 and systemic perfusion was maintained in hypoxia.
The difference in acid-base status between pre-and post-branchial blood (PCO2, pH and total CO2), changed only slightly during hypoxia, but the oxygen difference reversed. Normal dorsal aortic (DA) PCO2 was 23·8 torr, ventral aortic (VA) 20·3; during aquatic hypoxia the mean values were 21·9 and 22·6, respectively. Blood pressure rose in both the VA and DA in hypoxia but the branchial vascular resistance did not change. The oxygen transfer factor did not change significantly between normoxia and hypoxia.
Anatomical studies of the gill microvasculature revealed a reduced and channelized lamellar circulation. No respiratory shunt pathways were found around the lamellae.
The physiological and anatomical data indicated that the gar did not change lamellar perfusion or use shunt pathways to avoid hypoxic O2 loss.
Respiration and Acid-Base Physiology of the Spotted Gar, A Bimodal Breather
Authors: Smatresk Neal J. , Cameron James N. 
Published: April 2021

ABSTRACT
Transfer from fresh water to 50% sea water (SW) at 26 °C increased the blood osmolarity of spotted gar (Lepisosteus oculatus) from 275 to 310 mosmol during the first 24 h. It then returned slowly to freshwater levels by 5 days after the transfer. The arterial pH dropped sharply, from 7·69 in fresh water to 7·46 in 50% SW, as a result of a small elevation in the blood CO2 partial pressure, and a marked metabolic acidosis. The respiratory (CO2) portion of the acidosis appeared to be a result of the reduction in branchial ventilation, and possibly permeability as well. The metabolic portion of the acidosis was not due to the accumulation of lactic acid, but probably involved a disruption of the extracellular strong ion difference in the saltier medium. The metabolic acidosis did not diminish during 5 days.
The rate of air breathing rose from 7 to 20 bph during 50% SW exposure. The control of pulmonary ventilation was directly responsive to the availability of O2, in general increasing when O2 was limiting (e.g. 50% SW transfer, hypoxia) and decreasing in hyperoxia. CO2 had no affect on the rate of air breathing. Withdrawal from 5–20% of total lung volume elicited an immediate air breath during hypoxia, but the response was inconsistent in normally aerated water. Lung inflation with O2 prolonged the interval between air breaths, but inflation with N2 did not change the rate of air breathing. Thus, pulmonary ventilation was secondarily controlled by lung volume. Gill ventilation frequency fell in 50 % SW, despite a respiratory and metabolic acidosis, while gill ventilation increased in response to treatment with acetazolamide. Hyperoxia caused a marked depression of gill ventilation, despite a respiratory acidosis. The gill ventilation rate appears to be most closely linked to oxygen, but may be affected indirectly by CO2 through the Root or Bohr effects.
Inhibition of Active K Transport in the Isolated Midgut of Hyalophora Cecropia by T1+
Authors: Zerahn Karl 
Published: April 2021

ABSTRACT
The midgut of the American silkworm transports potassium actively from blood side to lumen. The active K transport was measured by short-circuiting the gut.
The K transport is inhibited by T1 in the lumen solution. A Lineweaver-Burk plot showed that the inhibition with T1 is competitive with the active K transport. The Km was found to be 5·7 ± 0·7 and Ki = 0·1. It was concluded that T1 acts on the K pump which is located close to the lumen of the gut. When T1 was applied to the blood-side, only about half inhibition is found, yet, paradoxically, T1 concentration in the gut tissue was ten times as high as when T1 was applied to the lumen side.
Respiration in Exercising Fowl. III. Ventilation
Authors: Brackenbury J. H. , Gleeson M. , Avery P. 
Published: April 2021

ABSTRACT
Minute volume , respiratory frequency (f) and tidal volume (VT) were continuously measured in domestic fowl running on a treadmill at speeds of 1·24–4·3 km h−1 in air temperatures of 18 ± 2 °C and 35 ± 2 °C. Oxygen extraction (E) was estimated using previously measured values of oxygen consumption. At 18±2 °C and VT rose abruptly at the start of exercise and and f continued to rise except at the slower running speeds. and f continued to rise throughout exercise at all speeds in the heat-stressed birds. In both groups VT reached a maximum at the start of exercise then fell to a new steady-state level. Steady-state ,f and VT increased with exercise speed at 18 ±2 °C. At 35-37 °C steady-state and VT increased with speed but f changed relatively little. E remained close to resting (0·21) at low speeds in room temperatures but decreased to 0·17 at 4·3 km h−1. In contrast E rose from 0·05 at rest in heat-stressed birds to 0·14 at 3·6 km h−1. The changes in oxygen extraction and respiratory pattern in the two groups during exercise are discussed in connexion with the control of ventilation by thermal and non-thermal factors. It is suggested that the latter play a predominant role during heavy exercise and that this accounts for the convergence of respiratory patterns in both heat-stressed and non heat-stressed birds at maximum work rates.
The Function of Photomechanical Movements in the Retina of the Rainbow Trout (Salmo Gairdneri)
Authors: Douglas R. H. 
Published: April 2021

ABSTRACT
The function of photomechanical movements in the retina of rainbow trout (Salmo gairdneri) was investigated by determining both the effect of light on the level of extractable visual pigment, and the electroretinographic b-wave sensitivity, during various stages of photomechanical light and dark adaptation. Dark-adapted fish, light-adapted fish, and dark-adapted fish exposed to ten minutes direct sunlight had on average visual pigment concentrations of 100, 82 and 36% respectively. The intensity of illumination required to bleach a specified amount of visual pigment in the light-adapted retina was found to be 1·29 log units higher than that needed to bleach the same amount of visual pigment in a dark-adapted eye. The level of extractable visual pigment was observed to be relatively constant over natural twilight periods. A close temporal correlation was observed between the time course of electroretinographic adaptation, measured by the b-wave sensitivity, and photomechanical changes. All these observations tend to support the hypothesis that photo-mechanical movements serve, at least in part, to protect the rod visual pigment from overstimulation in the light-adapted retina.
pHi, Contractility and Ca-Balance Under Hypercapnic Acidosis in the Myocardium of Different Vertebrate Species
Authors: Gesser H. , Jørgensen E. 
Published: April 2021

ABSTRACTThe influence of hypercapnic acidosis upon the heart was examined in four vertebrate species. The CO2 in the tissue bath was increased from 2·7 to 15 % at 12 °C for flounder (Platichthys flesus) and cod (Gadus morhua) and from 3 to 13% at 22 °C for turtle (Pseudemys scripta) and rainbow trout (Salmo gairdneri).During hypercapnia, as previously described, there was a decline and recovery of contractility in heart strips of flounder and turtle, and a sustained decrease in cod and rainbow trout.At high CO2 the increase in contractile force following increases in the extracellular Ca-concentration were smaller for the cod myocardium than for the other myocardia.The intracellular pH (pHi), measured with the DMO method, in heart strips of turtle and trout was significantly lower at high than at low CO2. This acidifying effect expressed as the increase in the intracellular concentration of hydrogen ions was larger in the turtle than in the trout myocardium.Intracellular Ca-activity, measured by efflux of 45Ca from preloaded heart strips, was unaffected by high CO2 in trout, but was raised in the other three species.Thus the ability to counteract the negative inotropic effect of hypercapnia is apparently not due to cellular buffering or extrusion of hydrogen ions. More probably it involves (a) a release of intracellular Ca; (b) a positive inotropic effect of an increase in intracellular Ca-activity.
The Effects of Osmoregulatory Solutes On Tension Generation by Dogfish Skinned Muscle Fibres
Authors: Altringham J. D. , Yancey P. H. , Johnston I. A. 
Published: April 2021

ABSTRACT
Many marine organisms accumulate high concentrations of solutes in their tissues to maintain osmotic balance. Osmoregulatory solutes are usually end-products of metabolism rather than inorganic ions (Prosser, 1973). For example, skeletal muscle from marine elasmobranchs, holocephalans and the coelacanth contains high concentrations of both urea (300–600 mm) and methylamine compounds, such as trimethylamine oxide (175–250 mm) (Pang, Griffith & Atz, 1977). Urea is a potent protein destabilizer, and most elasmobranch enzymes examined are inhibited by urea (Yancey, 1978). However, it has recently been found that TMAO acts as a general protein stabilizer and can offset the effects of urea on enzyme Km and maximal velocity in vitro (Yancey & Somero, 1979, 1980).