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Biomedical subjects

M R Bennett

Publications and source records attributed to M R Bennett.

At least 217 records · Page 12Linked to original sources
PubMed1987

Motoneurone survival and neurite regeneration requirements: the role of dorsal root ganglion cells during development.

The effect of dissociated dorsal root ganglion cells on the survival of motoneurones in vitro from differently aged chick embryos has been studied. Homogeneous cultures of motoneurones were prepared from 5-8-day embryos, using a cell sorter; dorsal root ganglion cells were obtained from 8-day embryos. The survival of motoneurones from 5-day and 6-day embryos was not enhanced above controls by the presence of dorsal root ganglion cells; however, the survival of motoneurones from older embryos was greatly increased, reaching a maximum of over 80% for 8-day embryonic motoneurones. In contrast, the number of motoneurones that had regenerated neurites when co-cultured with dorsal root ganglion cells for 24 h decreased with the motoneurone age at plating, from 51% at 5 days to less than 10% for 7- and 8-day motoneurones. The survival-enhancing effects were probably mediated by cell contact between the motoneurones and processes of the dorsal root ganglion cells: conditioned media from high-density cultures of dorsal root ganglion cells could not be shown to significantly enhance the survival of motoneurones above that of control levels. The possibility that the ganglion cells exert this survival enhancing effect by depolarizing the motoneurones was examined by exposing 8-day sorted motoneurones to 47 mM potassium; this did not effect the survival of the motoneurones relative to control levels. The stage dependency of the survival of motoneurones on different neurotrophic factors and the dorsal root ganglion cell is discussed.

Animals↗
PubMed1987

Loss of polyneuronal innervation and establishment of a topographical map in the glutaeus muscle of Bufo marinus during generation of secondary muscle cells.

The development of synaptic connections to the toad (Bufo marinus) glutaeus magnus from segmental nerves 8 (N8) and 9 (N9) was determined in the postmetamorphic period. Three different-size toads were studied: small (0.3-2.0 g), medium-size (5-15 g) and large (greater than 20 g). The number of cells in the glutaeus increased about 9-fold during development; this involved the appearance and subsequent maturation of secondary fibres throughout the muscle. The glutaeus in small toads, which consisted almost entirely of primary fibres, was innervated to a similar extent by N8 and N9 as assessed by tetanic contraction measurements. During late development there was a progressive increase in the percentage of the muscle innervated by N9 and a decrease in the percentage innervated by N8. This change in the segmental innervation was accompanied by changes in the innervation of the ventral glutaeus as assessed by intracellular recording. In small toads this surface of the muscle was innervated predominantly by N8, with N9 frequently appearing as a low-efficacy terminal on dually innervated fibres. With further development there was a progressive reduction in the percentage of dually innervated fibres and a concomitant decrease in the percentage innervation of the entire ventral glutaeus by N8. These results suggest that the topographical projection is established by the initial distribution of N9 terminals on the primary fibres of the muscle. The multiple innervation of newly generated fibres and the on-going process of terminal elimination results in N9 terminals, many of which were initially weak, preserving their position in the muscle. This occurs at the expense of N8 terminals, whose relative incidence declines during development. The competitive advantage of N9 motoneurones may be due to their greater capacity to lay down axon collaterals and preferentially innervate newly generated fibres; alternatively N9 terminals may displace N8 terminals, which were initially more efficacious, from dually innervated fibres. Secondary muscle fibres generated throughout the muscle are thus incorporated into an increasingly precise topographical map.

Animals↗
PubMed1987

Occult pneumococcal bacteremia and empyema without preceding pulmonary parenchymal involvement.

We have presented a case of pneumococcal empyema without evidence of pulmonary parenchymal infection. We postulate that the pleural space was hematogenously seeded from an unexplained pneumococcemia. This manifestation of pneumococcal infection is unusual, particularly since the patient was receiving adequate antibiotic therapy before the radiologic or clinical appearance of the empyema. This emphasizes the need for diagnostic thoracentesis when the clinical situation changes, even after appropriate antimicrobial therapy is begun.

Ampicillin↗
PubMed1986

Retinal ganglion cell survival requirements: a major but transient dependence on Müller glia during development.

Neonatal rat retinal ganglion cells (RGC), identified by a retrograde horseradish peroxidase labelling technique, survived over a 16-h culture period when cultured on monolayers of rat Müller glia or in conditioned media derived from these cells. Maximal survival of neonatal RGC was obtained at 1:4 dilution of conditioned media. However, extensive neurite outgrowth from RGC was seen only when they were cultured on glial monolayers. Homogeneous cultures of RGC, obtained using cell sorting techniques, also survived in Müller-conditioned media. This indicates that other intrinsic cells of the retina do not mediate the effect of Müller-conditioned media on RGC. Conditioned media from Müller glia do not significantly enhance the survival of RGC from 6 day retinae. However, these older RGC are supported in culture by extracts derived from their target tissue. These results suggest that as development proceeds RGC survival is dependent on factors produced by target rather than those produced by Müller glia.

Animals↗
PubMed1986

The growth of muscle nerves in relation to the formation of primary myotubes in the developing chick forelimb.

A study has been made of the development of muscle nerves to primary myotube clusters destined to become the flexor carpi ulnaris (fcu) and flexor digitorum profundus (fdp) muscles in the avian forelimb. Myotubes and nerves were identified by immunofluorescent techniques using antibodies to the heavy and light subunits of myosin and neurofilament, respectively. At stage 24 the main ventral nerve trunk (the brachialis longus inferior nerve; bli n) had entered the limb before the appearance of myotubes in the limb. At stage 25/26 the bli n within the ventral compartment of the forearm had given rise to the interosseus nerve (in n) and the medial-ulnar nerve (m-u n) at the junction of the stylopodium and zeugopodium. The first few myotubes of the fdp and fcu muscles were observed at this level within the ventral premuscle cell mass; however, no nerves projected toward these myotubes from either the in n or the m-u n at this time. At stage 26/27 the fcu and the fdp muscles each consisted of clusters of 20-40 myotubes; each cluster was clearly delineated within the ventral premuscle cell mass. By this time small groups of axons had left the in n and the m-u n to grow into the fdp and fcu myotube clusters, respectively; these axons formed the muscle nerves. At stage 28/29 the number of primary myotubes in the clusters composing the fdp and fcu muscles had greatly increased, as did the size of the muscle nerves; each muscle was still clearly identifiable within the ventral muscle mass. By stage 32 the fdp and fcu muscles had clearly separated and the muscle nerves had divided into several well-spaced branches within each muscle. The present observations show that the main nerve trunks grow into the limb before the formation of myotubes expressing myosin isozymes. When myotubes do form they appear in small clusters at specific sites within the premuscle mass, before muscle nerves appear; a distinct muscle is destined to form from each of these clusters. Muscle nerves first branch from the main limb nerves when the myotube cluster contains more than about ten myotubes.

Animals↗
PubMed1986

Motoneurone numbers in rat neonatal lateral motor columns: use of antibody to choline acetyltransferase to identify motoneurones.

The number of motoneurones in the rat lumbosacral and brachial motor columns were determined during the neonatal period, following identification of the motoneurones with antibodies to the enzyme choline acetyltransferase. Motoneurone numbers declined by less than 15% between 21 days embryonic and 4 days postnatal. These observations suggest that there is little change in the population of motoneurones during the period of extensive loss of polyneuronal innervation of muscle.

Animals↗
PubMed1986

The role of innervation in the establishment of the topographical distribution of primary myotube types during development.

Many avian muscles contain a characteristic topographical distribution of fibre types. In order to study the role of nerves in the establishment and distribution of these fibre types, monoclonal antibodies (McAb) to the heavy chain subunit of myosin (MHC) were produced. The anti-fast McAb (2B12) bound to adult fast MHC and cross-reacted with the embryonic isoform of MHC. The anti-slow McAb (3D1) bound specifically to the heavy chain of slow myosin 2. By indirect immunofluorescence, anti-fast (2B12) stained all myotubes in the anterior latissimus dorsi and triceps and biceps muscles at stage 37 (11 days embryonic), whilst anti-slow (3D1) staining was largely restricted to the future slow fibres of these muscles. Brachial levels of the neural tube were surgically removed at stage 12 (2 days embryonic) so that muscles developed aneurally. Muscles at aneural stage 37 were smaller than normal, but the distribution of myotube types was not altered; all myotubes present still stained with anti-fast antibody while anti-slow staining was restricted to the anterior latissimus dorsi and myotubes in the deep parts of the triceps brachii pars scapularis, triceps brachii par humeralis and biceps brachii muscles (the future slow fibres of normal muscles). The results suggest that despite an overall reduction in MHC in aneural muscles, specialized fast and slow primary myotubes arise independently of the nerve in appropriate regions of the muscle.

Animals↗
PubMed1986

Motoneurone survival requirements during development: the change from immature astrocyte dependence to myotube dependence.

The survival requirements of motoneurones obtained from differently aged avian embryos was analysed, in both heterogeneous cultures of motoneurones with spinal cord cells and homogeneous cultures of motoneurones obtained by cell sorting. It was found that medium conditioned by contact with immature astrocytes could maintain more than 75% of the motoneurones plated from 5-day embryos for two days; however, this astrocyte medium could not maintain motoneurones plated from 8-day embryos above control levels at two days. In contrast, medium conditioned by contact with myotubes could not maintain motoneurones plated from 5-day embryos above control levels for two days; this myotube medium could maintain more than 70% of the motoneurones plated from 8-day embryos for two days. The change in the receptivity of motoneurones to astrocyte-conditioned medium may be due to their ageing. Thus, motoneurones from 6-day embryos could not be sustained above control numbers in culture for 4 days with astrocyte media, in the same way as motoneurones from 8-day embryos degenerate by two days. In contrast, more than 70% of motoneurones plated from 6-day embryos could be maintained in culture for 4 days with myotube media in the same way as motoneurones from 8-day embryos for two days. The results indicate that motoneurones from 5-day embryos are dependent for their survival on immature astrocytes but that this switches to a dependence on myotubes during the normal motoneurone death period from 6 days to 10 days of embryonic age.

Age Factors↗
PubMed1986

Motoneurone survival activity in extracts of denervated muscle reduced by prior stimulation of the muscle.

Inactivation of skeletal muscle by denervation increases motoneurone survival activity in extracts of skeletal muscle. The present investigation shows that electrical stimulation of denervated muscle decreases motoneurone survival activity in extracts of these muscles. The result suggests that motoneurone survival is dependent on a factor(s) in muscle whose synthesis and/or release is regulated by muscle contraction.

Animals↗
PubMed1986

Elevated pleural fluid glucose: a risk for tension hydrothorax.

We have presented a case of tension hydrothorax that developed after hyperosmolar hyperalimentation fluids were infused into the pleural space through a misplaced jugular venous line. The hyperosmolar state of the pleural fluid appears to have played a prominent role in the development of the tension hydrothorax. We believe there is a risk of tension hydrothorax in any clinical situation in which the pleural fluid glucose concentration is significantly higher than the serum concentration.

Adult↗
PubMed1986

The probability of quantal secretion along visualized terminal branches at amphibian (Bufo marinus) neuromuscular synapses.

The number of quanta secreted from selected sites along terminal branches at toad (Bufo marinus) neuromuscular junctions was determined. Terminal branches were visualized by prior staining with the fluorescent dye, 3-3 Diethyloxadicarbocyanine iodide (DiOC2(5)); neither impulse conduction nor quantal release were affected by DiOC2(5) at concentrations less than 10 microM. The evoked quantal release recorded with an extracellular micro-electrode (me) at different sites along the length of terminal branches was determined in an external calcium concentration, [Ca]o, of 0.35-0.45 mM. For short branches (40-80 microns), me remained approximately constant for over 60% of the branches; for the rest, me declined approximately exponentially with an average length constant of 17 +/- 2 microns (mean +/- S.E. of mean). For both medium (81-120 microns) and long branches (121-160 microns), me declined in nearly all cases approximately exponentially with length constants of 39 +/- 5 and 54 +/- 8 microns respectively. These changes in me were observed at synapses having a wide range of terminal branching patterns. Some DiOC2(5)-stained branches possessed discontinuous cholinesterase staining. In general, me declined along these branches in the same way as along DiOC2(5)-stained branches with continuous cholinesterase staining. It is suggested that because of the decline in me along most medium and long terminal branches, many release sites have a very low probability for secretion in low [Ca]o. Release sites near the point of nerve entry, which have a relatively high probability, therefore make the main contribution to secretion recorded with an intracellular micro-electrode. As a consequence, transmitter secretion from the whole terminal does not fluctuate from impulse to impulse as much as expected if there were a large number of release sites, each with a low probability of secretion. Transmitter secretion then follows binomial rather than Poisson statistics.

Action Potentials↗
PubMed1985

Retinal ganglion cell survival is mediated by cell contact with immature rat astroglia.

The survival of identified retinal ganglion cells (RGGs) in vitro increased when they were plated over subcultured monolayers of astrocytes. Immunofluorescence labelling of these monolayers showed that over 85% of the cells were glial fibrillary acidic protein (GFAP) positive and consisted of large, flat immature astrocytes. Less than 7% of the total cell population in the monolayers were fibroblasts, leptomeningeal or endothelial cells. Coculturing of RGCs with subcultured astrocytes revealed that the trophic interaction between astrocytes and RGCs is mediated through cell contact.

Animals↗
PubMed1985

Development of the mature distribution of synapses on fibres in the frog sartorius muscle.

Most of the fibres in mature frog sartorius muscle possess two or more synapses separated by up to one-third the length of the muscle. The aim of the present work was to determine how the relative distances between these synapses changes during development in the frog (Limnodynastes tasmaniansis), as the fibres increase in length from 2 mm (stage 56) to 20 mm (1 year postmetamorphosis). At the earliest stage investigated (fibres 2.0-4.0 mm in length; stages 56-57) about 80% of the fibres were innervated at two endplates. The percentage of fibres with two endplates then remained approximately constant with further development. The polyneuronal innervation of endplates was almost eliminated by stage 57. Muscle fibres with two endplates had each situated on average about one-third the length of the fibre from a tendinous insertion; these relative positions did not change throughout development. Thus the distance between endplates increased linearly with an increase in fibre length. The size of terminals and the complexity of their branching also increased continually throughout development, independently of the location of the terminals on the fibres. The observations suggest that the distance between terminals increases during development because of the intercalation of new plasma membrane and basal lamina associated with the increase in length and diameter of fibres.

Aging↗
PubMed1985

Spatial distribution and size of acetylcholine receptor clusters determined by motor nerves in developing chick muscles.

The size and distribution of acetylcholine receptor clusters (AChR-C) on normal and aneural developing muscle fibres of the chick wing were studied by labelling AChR with fluorescent conjugates of alpha-bungarotoxin (alpha-BGT). AChR-C of a size typical of initial synaptic contacts (5 micron long) were present at 7 days incubation, shortly after the appearance of nerves, and were grouped in bands corresponding to muscle nerve branches. A regular distribution of large (approximately equal to 5 micron) AChR-C separated by 100-200 micron had developed by 10-14 days in the slow-tonic anterior latissimus dorsi and ulnimetacarpalis dorsalis muscles. The role of motor innervation in the formation of AChR-C was assessed by removing the brachial neural tube at 2 days incubation in order to prevent nerves entering the wing. Neural-tube removal prevented the appearance of the large AChR-C normally associated with the early synaptic contacts. Small AChR-C (less than 2 micron long) appeared in aneural muscles, but these were not grouped into bands characteristic of the large AChR-C in normal muscles. The results suggest that the formation of junctional AChR-C is dependent on nerves.

Animals↗
PubMed1985

Motoneurone survival and neuritic outgrowth promoted by different cell types in embryonic muscle.

Different cell types within developing chick skeletal muscle were assayed for their ability to release factors into culture media which could affect the survival and neuritic development of labelled motoneurones and lateral motor column explants. Enriched cultures of myotubes, myoblasts, fibroblasts and mesenchyme were prepared by selective preplating and trypsinisation techniques. Degrees of enrichment were assessed immunofluorescently and morphologically; fibroblasts were the main contaminating cell type. Medium conditioned over each cell type was then tested in dose-response assay against both explants and dissociated motoneurones. In both cases the myotube conditioned medium (MCM) promoted the greatest levels of both survival and neuritic outgrowth, and had the greatest relative potency of all of the cell types. When MCM was preincubated over polycationic substrata, it lost the ability to promote neuritic growth; this could be restored if fresh conditioned medium (CM) was added to the cultures. Thus it was demonstrated that within the MCM there are physically separable agents responsible for neurone survival and neurite expression. The neurite-promoting factor (NPF) within the MCM was stable to collagenase, deoxyribonuclease, neuraminidase and chondroitinase ABC, but was destroyed by trypsin and heparinase. These results imply that a heparan sulfate proteoglycan is essential for the activity of the factor.

Animals↗
PubMed1985

Motoneurone survival is induced by immature astrocytes from developing avian spinal cord.

Dissociated spinal cords of 6-day chick embryos were grown on monolayers consisting primarily of either flat (relatively immature) or process-bearing (relatively mature) astrocytes. Cultures rich in flat astrocytes maintained about 80% of the motoneurones originally plated for 48 h in vitro. However, process-bearing astrocytes were unable to support motoneurone survival. Medium conditioned by contact with the monolayers of flat astrocytes also promoted motoneurone survival for 48 h. Maximal activity occurred over the concentration range 55-110 micrograms/ml protein. After 48 h, the number of motoneurones dropped to control levels both in the conditioned medium and on the monolayers. This effect could not be reversed by the introduction of fresh conditioned media at 48 h. This indicated a decrease in the requirements of more mature motoneurones for this media as muscle-conditioned medium could support 80% of the motoneurones initially plated for 96 h. Thus, relatively immature astrocytes were capable of supporting the survival of 6-day montoneurones in vitro for up to 48 h and this effect is mediated through the release of a soluble substance.

Animals↗
PubMed1985

Cytomegalovirus hemorrhagic colitis in a nontransplant patient.

A 75-year-old man with major colonic hemorrhage was found at exploratory laparotomy and colectomy to have acute sigmoid colitis induced by cytomegalovirus (CMV) infection. The usual risk factors for CMV colitis (previous mucosal injury, cytotoxic drug therapy, and transplantation) were absent. The stress and debility of an acute uremic state and a long hospital stay may have compromised the patient's immune system and allowed for viral invasion of the colon. This manifestation of cytomegalic disease is an extremely unusual but important clinical entity. Accurate and prompt diagnosis, which requires a high index of suspicion, is important, since in the majority of cases, colectomy is indicated for control of hemorrhage.

Aged↗