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J E Treherne

Publications and source records attributed to J E Treherne.

At least 19 recordsLinked to original sources
PubMed1990

Cell proliferation in the repairing adult insect central nervous system: incorporation of the thymidine analogue 5-bromo-2-deoxyuridine in vivo.

Uptake of the thymidine analogue 5-bromo-2-deoxyuridine into non-neuronal cells of the insect central nervous system has been examined following a controlled lesioning of the glial elements. The pattern of BUdR labelling along the penultimate abdominal connective was examined over a period of 17 days. Cell proliferation occurred in and immediately around the site of damage in both perineurial and subperineurial glial cells but at different times post-lesion for the two regions. Proliferation in the perineurial zone was maximal at 6-8 days post-lesion but continued for at least 17 days. Subperineurial proliferation was less dramatic and peaked between days 8-11 post-lesion. In both areas division appears to be confined to the reactive glial cells. These results are discussed in the context of past research on this system, particularly with regard to the restoration of the blood-brain barrier.

Animals↗
PubMed1988

Cell recruitment during glial repair: the role of exogenous cells.

Selective disruption of the neuroglia in penultimate abdominal connectives of the cockroach nerve is followed by a rapid accumulation of cells in the perineurial layer of the lesion. Subsequently, there is an abrupt, secondary, rise in cell numbers in the undamaged perineurial tissues, anterior to the lesion and adjacent to the 4th abdominal ganglia. By 7 days the increased cell numbers are again effectively confined to the original lesion zone. The initial rise in cell numbers is postulated to result from an invasion by blood-borne haemocytes and the subsequent increase, in undamaged perineurial tissues, from the mobilization of endogenous reactive cells. Recruitment of the endogenous cells is inhibited if the haemocytes are excluded from the lesion. There is a slower mobilization of sub-perineurial cells, which, again, is inhibited following exclusion of haemocytes from the lesion zone. It is postulated that the recruitment of the endogenous reactive cells is initiated by the invading haemocytes which transform to granule-containing cells and release diffusible morphogenic and/or mitogenic factors.

Animals↗
PubMed1987

Mechanisms of glial regeneration in an insect central nervous system.

As in other repairing systems, glial regeneration in insect central nervous connectives, following selective chemical lesioning, involves both exogenous and endogenous elements. Our current evidence, including that obtained with monoclonal antibodies, indicates that the reactive, granule-containing cells are derived from a sub-population of circulating haemocytes which, within 24 h, invade, and are restricted to, the lesion zone. The granule-containing cells are involved in the initial repair of the perineurial region. They also contribute to the first stage in the restoration of the blood-brain barrier and are responsible for recruiting reactive endogenous glia, apparently from the vicinity of the anterior abdominal ganglion. The granule-containing cells transform into or are replaced by functional glia between 3 and 5 days after selective glial disruption, coincident with the appearance in the lesion zone of dividing reactive cells.

Animals↗
PubMed1987

Glial repair in an insect.

The repair of cockroach central nervous connectives, following selective glial disruption, involves an initial invasion of the lesion by a novel cell class. The available evidence, including that obtained using monoclonal antibodies, shows that these cells arise from circulating haemocytes. These invasive exogenous cells are restricted to the lesion zone. They are not only involved in initial repair of the peripheral glial elements, but may also be responsible for initiating recruitment and division of endogenous reactive cells. There is a clear anterior polarity in this recruitment, with significantly higher numbers of cells appearing anterior to, and then within, the lesion area. Characteristically, recognizable exogenous cells decline in number after 3 days, although there is no overall reduction in cell numbers within the lesion at this stage, nor has significant cell division begun. This suggests that the haemocyte-derived cells transform into, or are replaced by, functional perineurial glia, between 3 and 5 days, coincident with the restoration of the blood-brain barrier and the onset of endogenous cell division. Glial repair in the insect CNS can thus be divided into three phases which show striking similarities to the repair sequence in vertebrate brain. These include: an initial invasion of the lesion by exogenous cells, subsequent glial proliferation and then longer term fluxes in cell numbers and distribution.

Animals↗
PubMed1985

Octopamine reduces potassium permeability of the glia that form the insect blood-brain barrier.

Octopamine caused only a slight reduction in the potential across the perineurial glia of the cockroach, had no effect upon sodium-induced changes in potential, but did reduce potassium-induced changes (at 10(-7) M and above). The effect of 10(-7) M octopamine was accompanied by a rise in resistance, was mimicked by 10(-7) M synephrine and blocked by 10(-6) M phentolamine. Transperineurial potassium permeability was reduced by 10(-6) M octopamine. It is concluded that octopamine receptors mediate a reduction in potassium conductance of the basolateral membrane of these glia, and a reduction in the net potassium permeability of the barrier.

Animals↗
PubMed1984

Glial repair in an insect central nervous system: effects of surgical lesioning.

Surgical lesioning of central nervous connectives in the cockroach (Periplaneta americana (L.], although causing only local glial damage, resulted in complex and prolonged cellular changes. An early response to mechanical disruption was the appearance of granule-containing cells within the damaged perineurium, among adjacent, undamaged, perineurial cells, and between glial processes deep within the connectives. These cells, which were strikingly similar to hemocytes, were clearly involved in phagocytic activity and persisted in the damaged regions for more than a month after lesioning. There was only a slow restoration of organized perineurial glia and re-establishment of the blood-brain barrier, as indicated by the exclusion of an extracellular tracer, ionic lanthanum. These observations contrast with the speedy, ordered repair of the neuroglia observed following selective glial disruption and suggest that undamaged axons and/or the extracellular matrix exert a profound influence on the mechanisms of glial repair.

Animals↗
PubMed1984

Glial repair in an insect central nervous system: effects of selective glial disruption.

In vivo application of ethidium bromide to cockroach central nervous connectives caused extensive disruption of the neuroglia within 24 hr. Axonal conduction persisted following treatment with the glial toxin. A consistent feature of glial damage and repair was the prominent involvement of granule-containing cells. These cells (which were never seen in control cords) shared a number of cytological features with hemocytes that were seen adhering to and penetrating the neural lamella, in the early stages of glial damage. The granule-containing cells appear to serve dual functions: phagocytosis and structural repair. After 48 hr, granule-containing cells, or their processes, formed layers at the periphery of the connectives. By 4 to 6 days after treatment, the peripheral cells had assumed the morphological characteristics of normal perineurial cells and by 28 days were indistinguishable, ultrastructurally, from those of the perineurium of normal, untreated animals. These structural changes paralleled the re-establishment of the normal permeability properties of the blood-brain interface revealed by the exclusion of an extracellular tracer, ionic lanthanum, and electrophysiological observations.

Animals↗
PubMed1980

Electrical interactions between the giant axons of a polychaete worm (Sabella penicillus L.).

Intracellular recordings demonstrated a transfer of impulses between the paired giant axons of Sabella, apparently along narrow axonal processes contained within the paired commissures which link the nerve cords in each segment of the body. This transfer appears not to be achieved by chemical transmission, as has been previously supposed. This is indicated by the spread of depolarizing and hyperpolarizing voltage changes between the giant axons, the lack of effects of changes in the concentrations of external divalent cations on impulse transmission and by the effects of hyperpolarization in reducing the amplitude of the depolarizing potential which precedes the action potentials in the follower axon. The ten-to-one attenuation of electronic potentials between the giant axons argues against the possibility of an exclusively passive spread of potential along the axonal processes which link the axons. Observation of impulse traffic within the nerve cord commissures indicates, on the other hand, that transmission is achieved by conduction of action potentials along the axonal processes which link the giant axons. At least four pairs of intact commissures are necessary for inter-axonal transmission, the overall density of current injected at multiple sites on the follower axon being, it is presumed, sufficient to overcome the reduction in safety factor imposed by the geometry of the system in the region where axonal processes join the giant axons. The segmental transmission between the giant axons ensures effective synchronization of impulse traffic initiated in any region of the body and, thus, co-ordination of muscular contraction, during rapid withdrawal responses of the worm.

Action Potentials↗
PubMed1979

Distribution and environmental synchronization of the marine insect, Halobates robustus, in the Galapagos islands.

The following three aspects of the biology of the marine insect Halobates robustus were studied, during a two week observation period, at several sites in the Galapagos Islands: distribution, aggregation behaviour and rhythmicity of locomotory activity. H. robustus occurred in highest numbers on the water surface at shores fringed with mangroves. The aggregations of H. robustus varied according to their location and density. Copulating adults formed dense, floating aggregations, which tended to be close to rocks or mangroves. Late instar nymphs were less aggregated and, in lagoons (where there was some shelter from direct tidal forces), were furthest from the shore. In two types of habitat (mangrove-fringed, sandy shores and rocky shores) the aggregations of H. robustus showed a pronounced ability to maintain a floating station in relation to the surrounding environment, irrespective of tidal movements (in one case at 34 m from the nearest fixed objects). Evidence of the ability of the aggregations to maintain station on the water surface was also obtained by comparing the movements of H. robustus with those of floating polystyrene particles, which move passively with wind and tide. Laboratory observations and experiments indicated no clear periodicity in locomotory movements throughout a 24 h period. However, the frequency of encounters between individuals showed two daily peaks, post-dawn and pre-dusk, with fewer encounters during the day and only occasional encounters during the night. By shifting the light-dark cycle it was demonstrated that the daily bimodal rhythm of encounters is triggered by dawn and, since it is not maintained in constant light or dark, an 'hour-glass' mechanism is suggested. The contributions of single adults, of copulating pairs and of immature stages to the overall pattern of activity were also determined. Immature stages did not affect the overall rate of encounters significantly and the interactions between single and copulating pairs of adults appear to have been responsible for the bimodal pattern.

Animals↗
PubMed1979

Physiologically induced changes in intramembranous particle frequency in the axons of an osmoconforming bivalve.

Freeze-fractured axonal membrane surfaces from the connectives of Mytilus edulis show an increment in particle frequency of 52% (fixed tissues) or 68% (unfixed tissues) after long-term adaptation to low salinity. Particle size distribution was unaffected by osmotic adaptation, but was significantly different in fixed and unfixed material. The possibility that these structural changes reflect the known increase in sodium pump frequency in this osmoconforming tissue is considered.

Adenosine Triphosphatases↗
PubMed1978

Kinetics of sodium and lithium movements across the blood-brain barrier of an insect.

The electrical responses of axons were used to monitor the time-course of a change in the concentration of an ion species in the fluid bathing the axons in connectives of isolated cockroach nerve cords. Initial exposure of the connectives to sodium-deficient Ringer resulted in a depletion of extra-axonal sodium which was much slower than the restoration observed on return of the sodium Ringer. It is suggested that this asymmetry could result from a sodium reservoir which delays the initial decline. Subsequent net inward and outward movements of sodium ions were rapid and symmetrical. Unlike sodium ions, lithium ions were apparently unable to reach the axon surfaces following sodium depletion. In view of the similar properties of sodium and lithium ions in many biological systems it is therefore unlikely that the sodium movements were passive. Instead, the results support the idea of net sodium transport by the perineurial and/or glial elements.

Action Potentials↗
PubMed1978

Axonal adaptations to osmotic and ionic stress in an invertebrate osmoconformer (Mercierella enigmatica Fauvel). I. Ultrastructural and electrophysiological observations on axonal accessibility.

The giant axons in Mercierella are overlaid by narrow glial processes which provide an incomplete covering of the axonal surface. Where more complete covering occurs the intercellular clefts are not sealed by tight junctional complexes. Ionic lanthanum penetrates to the surfaces of axons from sea-water-adapted animals (in normal saline and during initial exposure to hyposmotic saline) and, also, to the surface of hyposmotically adapted axons. A relatively free intercellular access to the axon surfaces is also indicated by the rapid electrical responses of sea-water-adapted axons to hyposmotic dilution and of hyposmotically adapted axons to sodium-deficient saline. The giant axon possesses an unusual ultrastructural specialization: hemidesmosome-like structures (associated with the axon membrane) which are connected to a network of neurofilaments within the axon. Theoretical considerations suggest that these structures could enable the axons to withstand appreciable excesses in intracellular hydrostatic pressure resulting from osmotic imbalance during hyposmotic stress.

Action Potentials↗
PubMed1978

Axonal adaptations to osmotic and ionic stress in an invertebrate osmoconformer (Mercierella enigmatica Fauvel). II. Effects of ionic dilution on the resting and action potentials.

The giant axon of this extreme euryhaline osmoconformer possess an unusual ability to produce action potentials of large amplitude over a wide range of ionic dilution when constant osmotic concentration is maintained by the addition of mannitol to the bathing medium. Ionic dilution under these circumstances causes a decline in the overshoot of the action potential (resulting largely from reduction in [Na+]o) and an appreciable axonal hyperpolarization (primarily as a result of decrease in [K+]O). This hyperpolarization tends to compensate for the reduction in the extent of the overshoot and so maintains the amplitude of the sodium-mediated action potentials during isosmotic dilution of the bathing medium. The axonal hyperpolarization also appears to reduce sodium inactivation so as to maintain a rapid rate of rise of the action potential despite drastic reduction in the ionic concentration of the bathing medium. Prolonged exposure to reduced ionic concentrations appears to induce a ouabain sensitive reduction in intracellular sodium concentration which increases the sodium gradient across the axon membrane during isosmotic dilution of the external medium.

Action Potentials↗
PubMed1978

Axonal adaptation to osmotic and ionic stress in an invertebrate osmoconformer (Mercierella enigmatica Fauvel). III. Adaptations to hyposmotic dilution.

The giant axons of this extreme osmoconformer were adapted, in vitro, to progressive hyposmotic dilution of the bathing medium (from 1024 m-Osmol to concentrations as low as 76.8 m-Osmol). Hyposmotic adaptation is associated with reductions in the intracellular concentrations of both sodium and potassium ions. These reductions do not appear to result from appreciable axonal swelling. The different electrical responses to isosmotic and hyposmotic dilution suggest that reduction in [Na+]1 results from ouabain-dependent sodium extrusion, in response to ionic dilution, and that reduction in [K+]1 is induced by a combination of ionic and osmotic dilution. The reduced level of intracellular potassium achieved during hyposmotic adaptation represents a balance between the necessity to contribute to osmotic equilibration and to maintain a potassium gradient across the axon membrane sufficient to produce appreciable axonal hyperpolarization during dilution of the bathing medium. This hyperpolarization tends to maintain the amplitude of the action potential, by compensating for reduction in overshoot (with decline in E(Na), and by reducing sodium inactivation. This, together with the reduction in [Na+]1, enables overshooting action potentials of relatively large amplitude and rapid rise time to be maintained during more than tenfold dilution of the ionic and osmotic concentration of the bathing medium.

Action Potentials↗
PubMed1977

Ionic basis of axonal excitability in an extreme euryhaline osmoconformer, the serpulid worm Mercierella enigmatica (Fauvel).

Despite the extreme fluctuations in blood concentration experienced by this marine osmoconformer, essentially 'conventional' ionic mechanisms are involved in conduction by the giant axons in isosmotic conditions. The resting axonal membrane approximates to an ideal potassium electrode, with a 58-8 mV slope for decade change in [K+]O above 10 mM. The action potential overshoot shows a 55-8 mV decline with decade reduction in [Na+]O and the action potentials are blocked by tetrodotoxin at around 5 X 10(-7) M. The rising phase and overshoot of the action potential remain constant at potassium concentrations up to the relatively high level of 30 mM found in the blood, indicating an unusual absence of sodium inactivation over a wide range of resting potentials. Relatively rapid, symmetrical movement of potassium ions between the bathing medium and the axon surface is deduced from the potential changes induced by alterations in [K+]O. Outward movement of sodium ions (t0-5 = 33-5 s) occurs at a similar rate to that of potassium, but inward movement of Na+ is relatively slow and complex. It is concluded that the ability of axons to function in dilute media must involve specific adaptations to osmotic and ionic stress.

Action Potentials↗