PubMed Health⌕ Search

Biomedical subjects

E A Howes

Publications and source records attributed to E A Howes.

15 recordsLinked to original sources
PubMed1992

Cell specific DNA-labelling in the repairing blood-brain barrier of the insect Periplaneta americana.

This study uses a recently developed technique for preserving the ultrastructure of cells in the insect CNS during immunohistochemical processing for 5-bromo-2-deoxyuridine incorporation into newly synthesised DNA. The results allow us to identify the proliferating cell classes in the regenerating blood-brain barrier. High resistance barrier cells do not label with the antibody but sheath cells clearly do. Intermediate cell types appearing during repair are identified. It is hypothesised that these cells generate matrix molecules for neural lamella repair and may represent transitional forms as invasive blood cells transdifferentiate into functional sheath cells.

Animals↗
PubMed1991

Long-term growth in vitro of isolated, fully differentiated neurones from the central nervous system of an adult insect.

A method is described for the isolation and growth in vitro of fully differentiated neurones from the thoracic ganglia of adult cockroaches. The presence of insect blood in the culture system is shown to promote growth. The morphology of the growing neurones and the plasticity of the branching processes are described and growth rates are measured. Using a fluorescent Ca2+ indicator dye, changes of intracellular calcium levels in the growing neurones in response to K+ depolarization have been measured. The results, indicating the presence of voltage-dependent Ca2+ channels on neuronal processes in vitro, show that neurones can be maintained in a functional state for several weeks by this technique. Such preparations could prove useful for studying a variety of physiological and pharmacological properties of neurones, including the mechanisms controlling growth, synapse formation and neuronal interactions with other cell types.

Animals↗
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

Organ culture of adult cockroach CNS: ultrastructural and physiological characteristics.

The abdominal nerve cord of adult Periplaneta americana has been maintained in culture for up to 5 weeks. The ultrastructural appearance of in vitro cords resembles that of in vivo cords although some degeneration of glia may occur during the first 2 weeks in culture. The glial cells most affected are those which make up the perineurium. The blood-brain barrier, formed by the perineurium in vivo, breaks down in vitro. Despite this, normal action potentials were recorded from giant axons in 1 month old cultured connectives.

Action Potentials↗
PubMed1984

Relationship between lipofuscin granules and polyunsaturated fatty acids in the housefly, Musca domestica.

The fractional volume occupied by lipofuscin granules in epithelial cells of the midgut or oenocytes of abdominal fat body of 3-day-old and 13-day-old male houseflies was determined in two groups of flies by electron microscopic morphometry. One group had developed from larvae reared on diets containing no added polyunsaturated fatty acids and the second from larvae reared on diets containing added linoleic acid. No polyunsaturated fatty acids could be detected in the lipids of the first group of flies using a method which would have detected their presence in amounts greater than 0.1% of the total esterified fatty acids. The second group contained at least two hundred times more than this minimal level. The volume of lipofuscin granules increased significantly (p less than 0.01) (about threefold for the fat body and twofold in midgut cells) between 3 days and 13 days of age but no statistically significant difference was seen between the two groups of flies at the same age. The results show that if lipofuscin formation depends on the oxidation of polyunsaturated fatty acids in the housefly, then extremely small amounts of the acids are involved which lie below the detection limit of the methods employed. The age-associated small increase of extractable fluorescence seen previously in the linoleic acid group of flies is not associated with an increase in the lipofuscin granules.

Adipose Tissue↗
PubMed1984

Glial toxin effect on protein synthesis in an insect connective.

Analysis of electron autoradiographs from the nerve cord of the insect, Periplaneta americana (L.) shows a significant incorporation of 3H-labelled protein in the axons. The axonal activity is greatly reduced after treatment of the cord with the glial toxin ethidium bromide. This is interpreted as substantiating the possibility that adaxonal glia can transfer proteins to the axons.

Animals↗
PubMed1981

The concentration of choline into specific regions of the thoracic ganglion in B-methylcholine fed houseflies.

When larvae of the housefly, Musca domestica, are reared on a diet in which most of the choline has been replaced by a choline analogue, B-methylcholine, the small amount of choline available to the insect is largely taken up into the nervous system where it is incorporated into phosphatidylcholine and acetylcholine. Using autoradiographic techniques it is shown that, in the thoracic ganglion, the phosphatidylcholine component of this preferentially accumulated choline is not evenly distributed throughout the tissue but that a well-defined pattern of patches of silver grains is found over certain areas of the neuropile. Underlying this pattern are axons and glial processes structurally indistinguishable from the axons and glia of adjacent areas which show a much lighter autoradiographic reaction. It is concluded that the axons which produce this high density of silver graining are cholinergic and have a high affinity for choline.

Animals↗
PubMed1975

The permeability to ions of the neural lamella and the extracellular spaces in the C.N.S. of Anodonta cygnea.

Rapid axonal depolarization follows the elevation of [K+]o in the Ringer bathing the surfaces of the connectives of both intact and desheathed cerebrovisceral connectives of Anodonta cygnea. Potassium movements between the blood or medium bathing the surface of the connectives and the axonal membranes can be accounted for in terms of a first-order diffusion process. No visible structural barriers to prevent free movements of materials through the neural lamella and the extracellular spaces can be detected in electron micrographs of the cerebro-visceral connectives. In desheathed preparations fast action potentials are conducted in sodium-free (dextran) Ringer. Mechanisms of axona .l function and ionic regulation in this and other invertebrate central nervous tissues are discussed in the light of these observations.

Action Potentials↗