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D J Price

Publications and source records attributed to D J Price.

At least 73 records · Page 4Linked to original sources
PubMed1993

The effect of high pressure on glycine- and kainate-sensitive receptor channels expressed in Xenopus oocytes.

The effect of high pressure on the response to glycine or kainate of voltage-clamped Xenopus oocytes micro-injected with messenger-RNA derived from either rat spinal cord or whole brain, respectively, has been investigated. Current responses were measured at 1 bar (= 10(5) Pa), 50 bar, 100 bar and 150 bar, with PO2 fixed at 1 bar and the balance helium. Glycine elicited a depolarizing current response which was antagonized by nanomolar concentrations of strychnine. The responses reversibly desensitized, with a decay constant of 0.01 s-1, when glycine concentrations greater than 250 microM were used. The decay constant was insensitive to both glycine concentration and pressure. Resensitization was complete within 4 min. Kainate elicited a depolarizing current which was non-desensitizing. The response was slightly sensitive to glutamate diethyl ester (50 microM), which increased the EC50 by 25%. The action of glycine was highly pressure sensitive. The dose-response curves established at 50 bar, 100 bar and 150 bar were shifted progressively to the right, with no effect on the maximal current. The EC50 increased from 216 microM to 296 microM at 50 bar, to 345 microM at 100 bar, and to 425 microM at 150 bar. The action of kainate was unaffected by pressure. No shift in the dose-response curves was established, nor was there any effect on the maximum current. The EC50 was 113 microM at 1 bar, and 111 microM at both 50 bar and 100 bar.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Regulation of an epitope-tagged recombinant Rsk-1 S6 kinase by phorbol ester and erk/MAP kinase.

Phorbol ester tumor promoters (TPA) activate the endogenous erk/MAP kinases and Rsk S6 kinases but not the p70S6 kinase in COS cells. DNA sequences encoding the rat Rsk-1 S6 kinase (homologous to Xenopus rsk alpha), modified by insertion of a peptide epitope at the polypeptide aminoterminus, were expressed transiently in COS cells. TPA stimulates the 40S and peptide kinase activity of the recombinant epitope-tagged Rsk-1, as well as the extent of Rsk-1 autophosphorylation in vitro (32P-Ser >> 32P-Thr). Indications that the conformation of the recombinant Rsk-1 polypeptide is substantially changed after activation by TPA in situ include a retarded mobility of the Rsk-1 polypeptide on SDS-PAGE and the appearance of new 32P-peptides during autophosphorylation in vitro. All these features of the TPA-activated Rsk-1 S6 kinase are abolished by dephosphorylation of the kinase in vitro with Ser/Thr phosphatase-2A. TPA increases 32P incorporation into recombinant Rsk-1 by 2-3-fold (32P-Ser >> 32P-Thr). Peptide mapping exhibits a single major 32P-peptide in Rsk-1 isolated from unstimulated cells and 10-12 additional 32P peptides after TPA treatment in situ. Phosphorylation of basal or phosphatase-2A-treated recombinant Rsk-1 in vitro with erk2/MAP kinase increases Rsk-1 40S kinase, peptide kinase, and autophosphorylating activity, retards migration of Rsk-1 polypeptides on SDS-PAGE, and generates new sites of Rsk-1 autophosphorylation in vitro. By contrast, TPA-activated Rsk-1 is not altered in these properties by autophosphorylation in vitro. By contrast, TPA-activated Rsk-1 is not altered in these properties by phosphorylation in vitro with erk2/MAP kinase. Activation of Rsk-1 in situ with TPA diminishes by over 90% the extent of Rsk-1 phosphorylation achieved in vitro by erk2/MAP kinase, as compared to the parallel phosphorylation of a phosphatase-2A-treated Rsk-1; basal Rsk-1 is intermediate. Peptide maps of phosphatase-2A-treated Rsk-1 after phosphorylation in vitro with erk2/MAP kinase exhibit 32P-peptides that comigrate with nearly all of the 32P-peptides present in TPA-activated-32P Rsk-1 labeled in situ, plus several 32P-peptides characteristic of Rsk-1 autophosphorylation in vitro.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1993

Effects of neonatal ablation of area 18 on corticocortical projections from area 17 to extrastriate visual areas in cats.

Using retrogradely transported fluorescent dyes, we investigated the distributions of corticocortical neurones in area 17 projecting to area 19 and to the lateral suprasylvian visual area in a normal cat and two cats in which area 18 had been ablated at 4 days old. Cells projecting to area 19 were distributed in a much more continuous manner in the lesioned cats than in the normal one, whereas those projecting to the lateral suprasylvian cortex were located in discrete patches in all three cats. Neonatal ablation of area 18 can thus prevent the normally occurring developmental removal of neurones or their axons projecting from area 17 to area 19, but not the removal occurring in the projection from area 17 to the lateral suprasylvian cortex.

Animals↗
PubMed1993

The incidence of bifurcation among corticocortical connections from area 17 in the developing visual cortex of the cat.

In newborn kittens, cells in the striate cortex (visual area 17) that project to area 18 (part of extrastriate cortex) are distributed with uniform density in the superficial and in the deep layers. During postnatal weeks 2-3, some of these corticocortical connections are removed to generate an adult-like projection in which association cells are clustered mainly in the superficial layers of area 17. Axonal elimination, without cell death, is the major factor sculpting patches of corticocortical cells in superficial layers. In adult cats, few cells in area 17 (approximately 5%) have axons that bifurcate to multiple extrastriate areas. We have studied the possibility that the early exuberant innervation of area 18 by neurons in area 17 is largely from the transient collaterals of axons that also project to other visual areas. Kittens aged 2-21 days were each injected with a pair of retrogradely transported tracers, either diamidino yellow and fast blue, or diamidino yellow and a carbocyanine dye, at retinotopically corresponding points in area 18 and either area 19 or the posteromedial lateral suprasylvian cortex (PMLS). As for injections in area 18, those in area 19 and PMLS in kittens aged < or = 5 days labelled cells in continuous bands in area 17; in older kittens neurons projecting from area 17 to extrastriate regions were in patches, mainly in superficial layers. In each animal, the labelling from the two injections overlapped by 51-92%.(ABSTRACT TRUNCATED AT 250 WORDS)

Amidines↗
PubMed1993

The fates of cells in the developing cerebral cortex of normal and methylazoxymethanol acetate-lesioned mice.

We are interested in the mechanisms that generate the mature cerebral cortex. We used bromodeoxyuridine (BrdU) to label cortical cells as they were being born. We followed the fates of specific sets of cortical precursors in normal mice and in mice in which other groups of cortical progenitors had been destroyed with the antimitotic agent methylazoxymethanol acetate (MAM Ac). In normal mice, most cells destined for the cerebral cortex were produced from embryonic day 12 (E12) to E16 in the expected inside-to-outside sequence (deep layers first, superficial layers last). Injection of MAM Ac at E13 killed cells that would normally have contributed to the deep cortical layers. As a consequence, the cortex was thinned by approximately 25% at postnatal day 21 (P21). However, all laminae were present and had normal connections with subcortical structures, although all were proportionately thinner. BrdU injected on E16 labelled a normally sized complement of cells that spanned a larger proportion of the depth of the thinned cortex. Thus, the deep cortical layers comprised many cells that were born several days later than normal. At embryonic ages prior to E12, a transient set of cells is produced in the early telencephalon. After injection with MAM Ac at E10, the cortex appeared histologically and histochemically normal at P21. However, many cells that would normally have contributed to superficial cortex (born on E15) were significantly deeper than normal. These results suggest that, during the early stages of cortical development, the nervous system is sufficiently plastic to compensate to some extent for the destruction of specific precursor cells by altering the fates of neurons born later. They indicate that the embryonic date on which a cortical cell is born does not necessarily determine its eventual phenotype.

Animals↗
PubMed1993

Cell migration and subplate loss in explant cultures of murine cerebral cortex.

We studied whether cortical cells migrate and subplate cells are lost in explants of murine cortex cultured for up to 14 days in defined serum-free medium. We gave bromodeoxyuridine (BrdU) to mice on embryonic days 12-13 (E12-13), to label subplate cells, or E17, to label cells destined for superficial cortical layers. We started culturing on E18-20. We left some mice to develop and provide in vivo data. At E18-20, most cells born on E17 lay below the cortical plate. During the following days in vitro, many of them moved to the cortical plate's superficial edge, although an abnormally high number remained in the ventricular zone. There was a selective loss of BrdU labelled cells from the subplate in culture; this occurred more rapidly than in vivo. Factors absent from our cultures may normally enhance migration and prolong the survival of subplate cells.

Animals↗
PubMed1993

Plasticity of an aberrant geniculocortical pathway in neonatally lesioned cats.

Geniculocortical afferents to the lateral suprasylvian (LS) visual area come only from the C layers in normal adult cats. After neonatal lesions of areas 17 and 18, inputs to the LS area also arise from the A layers. We studied the plasticity of this aberrant pathway. We made lesions in areas 17 and 18 of newborn kittens, some of which were then monocularly deprived. In lesioned undeprived cats, retrograde tracing confirmed projections to the LS area from both the A and A1 as well as the C geniculate layers. In lesioned deprived cats, geniculate afferents from the A layers to the LS area came mainly from the layer receiving a normal visual input. We conclude that the development of the abnormal pathway from the A layers to the LS area is influenced by patterned visual activity.

Animals↗
PubMed1992

Rapamycin-induced inhibition of the 70-kilodalton S6 protein kinase.

The immunosuppressant rapamycin inhibited proliferation of the H4IIEC hepatoma cell line. Rapamycin, but not its structural analog FK506, also inhibited the basal and insulin-stimulated activity of the p70 ribosomal protein S6 kinase. By contrast, insulin stimulation of the p85 Rsk S6 kinase and mitogen-activated protein (MAP) kinase activity were unaffected by drug. Rapamycin treatment of COS cells transfected with recombinant p70 S6 kinase completely inhibited the appearance of the hyperphosphorylated form of p70 S6 kinase concomitant with the inhibition of enzyme activity toward 40S subunits. Thus, rapamycin inhibits a signal transduction element that is necessary for the activation of p70 S6 kinase and mitogenesis but unnecessary for activation of p85 Rsk S6 kinase or MAP kinase.

Animals↗
PubMed1992

Evidence that the earliest generated cells of the murine cerebral cortex form a transient population in the subplate and marginal zone.

We used bromodeoxyuridine to label the earliest generated cells of the murine cerebral cortex while they were dividing, and then observed their distributions at several instances later in development. Shortly before birth, many of the labelled cells were either above the cortical plate, in the marginal zone, or below it, in the region known as the subplate in other species. These cells had disappeared by postnatal day 21.

Animals↗
PubMed1992

Organization of association projections from area 17 to areas 18 and 19 and to suprasylvian areas in the cat's visual cortex.

Cells in area 17 that are labelled by single, discrete injections of retrogradely transported tracers into extrastriate visual areas are discontinuously distributed in dense patches. In this study we made multiple, closely spaced injections of fluorescent dyes into extrastriate areas, to generate large deposits that would reveal whether the distributions of corticocortical cell bodies in area 17 are truly patchy or appear clustered only after small injections. By injecting a different tracer into each extrastriate area, or group of areas, we examined the spatial relationships between the populations of association cells. All deposits of tracers in areas 18, 19, or suprasylvian cortex, irrespective of size, label cells in a series of clusters in topographically related parts of area 17. We conclude that the complete populations of cells in area 17 that project to areas 18, 19, and the lateral suprasylvian cortex are all genuinely distributed in a patchy fashion. There appears to be a complex relationship between the sets of association cells projecting to different extrastriate regions: they do not completely overlap, only partially, and share some cortical zones but not others. In these experiments, only tiny percentages (2-5%) of labelled cells in the overlapping regions were filled with both tracers, suggesting that very few association cells in area 17 project to more than one of the extrastriate areas we studied. By comparing the dimensions of each injection site and of the labelled region in area 17, we estimated the extent of the convergence from area 17 to areas 18, 19, and posteromedial suprasylvian areas in retinotopic terms. The functional convergence was very similar in these pathways.

Amidines↗
PubMed1992

An array of insulin-activated, proline-directed serine/threonine protein kinases phosphorylate the p70 S6 kinase.

This study characterizes the insulin-activated serine/threonine protein kinases in H4 hepatoma cells active on a 37-residue synthetic peptide (called the SKAIPS peptide) corresponding to a putative autoinhibitory domain in the carboxyl-terminal tail of the p70 S6 kinase as well as on recombinant p70 S6 kinase. Three peaks of insulin-stimulated protein kinase active on both these substrates are identified as two (possibly three) isoforms of the 40-45-kDa erk/microtubule-associated protein (MAP)-2 kinase family and a 150-kDa form of cdc2. Although distinguishable in their substrate specificity, these protein kinases together with the p54 MAP-2 kinase share a major common specificity determinant reflected in the SKAIPS peptide: the requirement for a proline residue immediately carboxyl-terminal to the site of Ser/Thr phosphorylation. In addition, however, at least one peak of insulin-stimulated protein kinase active on recombinant p70, but not on the SKAIPS peptide, is present although not yet identified. MFP/cdc2 phosphorylates both rat liver p70 S6 kinase and recombinant p70 S6 kinase exclusively at a set of Ser/Thr residues within the putative autoinhibitory (SKAIPS peptide) domain. erk/MAP kinase does not phosphorylate rat liver p70 S6 kinase, but readily phosphorylates recombinant p70 S6 kinase at sites both within and in addition to those encompassed by the SKAIPS peptide sequences. Although the tryptic 32P-peptides bearing the cdc2 and erk/MAP kinase phosphorylation sites co-migrate with a subset of the sites phosphorylated in situ in insulin-stimulated cells, phosphorylation of the p70 S6 kinase by these proline-directed protein kinases in vitro does not reproducibly activate p70 S6 kinase activity. Thus, one or more erk/MAP kinases and cdc2 are likely to participate in the insulin-induced phosphorylation of the p70 S6 kinase. In addition to these kinases, however, phosphorylation of the p70 S6 kinase by other as yet unidentified protein kinases is necessary to recapitulate the multisite phosphorylation required for activation of the p70 S6 kinase.

Amino Acid Sequence↗
PubMed1991

Insulin-activated protein kinases phosphorylate a pseudosubstrate synthetic peptide inhibitor of the p70 S6 kinase.

p70 S6 kinase, a major insulin-mitogen-activated ribosomal S6 protein kinase in mammalian cells, is activated by phosphorylation of multiple Ser/Thr residues on the enzyme polypeptide. A synthetic peptide, corresponding to a 37-residue segment from the carboxyl-terminal tail of the kinase which resembles the sequence phosphorylated in S6, acts as a competitive inhibitor of p70 S6 kinase without itself being phosphorylated by the enzyme. This synthetic peptide is phosphorylated by an array of protein kinases which are rapidly activated by insulin. Thus, these sequences of p70 S6 kinase constitute a potential autoinhibitory pseudosubstrate site, whose phosphorylation is catalyzed by candidate upstream-activating protein kinases.

Amino Acid Sequence↗
PubMed1991

Purification and characterisation of the insulin-stimulated protein kinase from rabbit skeletal muscle; close similarity to S6 kinase II.

The insulin-stimulated protein kinase (ISPK) was purified over 50,000-fold from extracts of rabbit skeletal muscle by a procedure involving chromatography on phosphocellulose, fractionation with ammonium sulphate, and further chromatography on DEAE-cellulose, phenyl-Superose, Mono S and Mono Q. About 10 micrograms enzyme was isolated from 800 g muscle (one rabbit) in four days with an overall recovery of 5%. The purified enzyme showed a single protein-staining band of apparent molecular mass 91 kDa when analysed by SDS/polyacrylamide gel electrophoresis. The ISPK comigrated during SDS/polyacrylamide gel electrophoresis with the enzyme S6 kinase II from Xenopus eggs, and was recognised in immunoblotting and immunoprecipitation experiments by antibodies raised against S6 kinase II. The substrate specificities of ISPK and S6 kinase II were also very similar and like S6 kinase II, ISPK that had been inactivated by protein phosphatase 2A could be reactivated by incubation with mitogen-activated protein kinase and MgATP. ISPK was distinct from an insulin-stimulated 70-kDa S6 kinase from rat liver in both substrate specificity and immunological cross reactivity. It is concluded that ISPK is closely related in structure to S6 kinase II and may be a mammalian equivalent of this enzyme. The possibility that ISPK is involved in mediating a number of the actions of insulin is discussed.

Amino Acid Sequence↗
PubMed1991

Cloning and sequencing of a leech homolog to the Drosophila engrailed gene.

We have cloned and sequenced a homolog (ht-en) to the Drosophila engrailed (en) gene from the glossiphoniid leech, Helobdella triserialis. Amino acid comparisons of the ht-en homeodomain and C-terminal residues with the corresponding residues encoded by en-class genes of other species reveal 75-79% sequence identity. In addition, the ht-en sequence appears to have a serine-rich region 16 residues C-terminal from the homeodomain, which by analogy to Drosophila may be a target site for phosphorylation. The leech gene encodes some amino acid substitutions for residues that are highly conserved in other species. These are found within the second and third of the three putative helices of the homeodomain, and in both of the intervening turn regions.

Amino Acid Sequence↗
PubMed1991

Susceptibility of captive wildfowl to avian tuberculosis: the importance of genetic and environmental factors.

This study reports the findings of an epidemiological survey of death due to avian tuberculosis in the captive collection of wildfowl at The Wildfowl and Wetlands Trust Centre, Slimbridge, Gloucestershire. Both genetic and environmental factors have been shown to affect the incidence of, and the birds' susceptibility to, the disease. Seasonal body condition was related to the occurrence of death due to the disease in both males and females. Birds from either hot or cold climates appeared to have a higher incidence than those from temperate climates. What the birds ate did not affect incidence but the method they used for obtaining their food did. Higher susceptibility was found in those species evolved for marine or arboreal habitats. Anomalies in susceptibility which suggest a higher level of genetic immunity in some groups have also been found. Reasons are put forward to explain these findings.

Animals↗
PubMed1991

Sonoluminescence in water and agar gels during irradiation with 0.75 MHz continuous-wave ultrasound.

Free radicals, detected as light emissions (sonoluminescence), can be produced in both simple aqueous systems and agar gels by irradiation with 0.75 MHz continuous-wave (CW) ultrasound using acoustic pressures as low as 200 KPa. Although the acoustic pressures necessary for free radical formation in tap water gels (200 KPa), are considerably higher than those required for the formation of macroscopic visible bubbles (26 KPa), the sonoluminescence threshold (0.5 W/cm-2 SATA equivalent) falls at the lower end of the intensity range (0.5-3 W/cm-2) commonly used by ultrasonic physiotherapy equipment. In respect of the overall features of cavitation processes, agar gels appear to be suitable simple systems in which to model cavitation in vivo. However, cavitation processes leading to sonoluminescence are themselves complex as illustrated by the findings that small changes in ionic composition or pH have a significant effect on both the acoustic pressure threshold and the extent of sonoluminescence above this threshold.

Agar↗
PubMed1991

Regressive changes among corticocortical neurons projecting from the lateral suprasylvian cortex to area 18 of the kitten's visual cortex.

The postnatal development of corticocortical neurons projecting from the medial bank of the lateral suprasylvian cortex to area 18 of the kitten's visual cortex was examined using retrograde fluorescent tracers. Area 18 was injected in young kittens aged nine days or less and in older kittens aged 30 days or more. Many of the injected kittens were perfused with fixative four to five days later, but some of the youngest were killed after longer survival periods of 35-50 days (long-survival animals). Labelled neurons in the medial bank of the lateral suprasylvian cortex were densely distributed in both superficial layers (II and III) and deep layers (V and VI) in the kittens injected less than nine days postnatal, irrespective of whether survival was short or long, but they were found almost exclusively in layers V and VI in the old, short-survival animals. Only in the group of old kittens did we find a clear topographical arrangement of projections in the rostrocaudal direction and a correlation between the rostrocaudal lengths of the injection sites and labelled areas. In the other two groups, for a similarly sized injection site, the labelled areas were much longer rostrocaudally than in the old, short-survival kittens, and occupied roughly the posterior two-thirds of the medial bank of the lateral suprasylvian cortex, irrespective of the positions of the injections. In the frontal plane, topography was unclear in all groups. These findings demonstrate that there is considerable postnatal refinement of the projection from the medial bank of the lateral suprasylvian cortex to area 18. This involves a loss of connections originating from superficial layers and a decrease of convergence with the appearance of topography. Our results from long-survival kittens suggest that most of the early exuberant population of corticocortical neurons projecting from the medial bank of the lateral suprasylvian cortex to area 18 survive beyond the first postnatal month but undergo axonal elimination during this period.

Aging↗