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D J Price

Publications and source records attributed to D J Price.

At least 55 records · Page 3Linked to original sources
PubMed1997

Roles of Pax-6 in murine diencephalic development.

Pax-6 is one of the earliest regulatory genes to be expressed in the diencephalon. We tested whether normal Pax-6 protein is required for early diencephalic development by examining morphology, precursor proliferation and patterns of regulatory gene expression in the embryonic diencephalon of Small-eye mice (Pax-6 mutants). In Small-eye mice, diencephalic morphology was abnormal at all the embryonic ages studied (days 10.5, 12.5 and 14.5). Regional differences in diencephalic cell density were lost, the diencephalon/mesencephalon boundary was unclear and the third ventricle was enlarged. We estimated diencephalic proliferative rates after labelling with bromodeoxyuridine and found that they were abnormally low in mutants aged embryonic day 10.5. In older mutants, the diencephalon contained fewer cells than normal. In wild-type E14.5 diencephalon, Pax-6, Dlx-2 and Wnt-3 are expressed in discrete regions along the rostrocaudal and dorsoventral axes. In situ hybridizations for these genes in E14.5 Small-eye mice revealed discrete zones of diencephalic expression that had similar relative positions to those in wild-type mice. Some differences of detail in their expression were seen: Pax-6 had an expanded rostral domain of expression and an abnormally indistinct caudal boundary; Dlx-2 had a diffuse, rather than a sharp, caudal boundary of expression; the normally high dorsal midline expression of Wnt-3 was lost. We conclude that normal expression of Pax-6 is required for the correct regulation of diencephalic precursor proliferation. Pax-6 may also control some aspects of diencephalic differentiation, but its mutation in Small-eye mice does not preclude the development of a degree of diencephalic regionalization resembling that in normal mice.

Animals↗
PubMed1996

Influences of the thalamus on the survival of subplate and cortical plate cells in cultured embryonic mouse brain.

The afferent and efferent connections of the cerebral neocortex develop simultaneously toward the end of embryogenesis. At this stage, the neocortex comprises two main cell-dense layers: the thicker and more superficial cortical plate (future layers 2-6) and the thinner underlying subplate. Many early thalamocortical projections temporarily innervate the subplate before leaving it to locate their ultimate targets in the overlying cortical plate. The subplate then disappears. In this study, we performed in vitro experiments on late embryonic murine brain to test whether the thalamus can influence the survival of cortical plate and subplate cells at this stage. In isolated organotypic cortical explants from embryonic day 19 mice, most of the cells that had formed the subplate died. Coculture with a thalamic explant prevented this loss; coculture with additional cortical or cerebellar explants did not. By contrast, many cells in or destined for the cortical plate survived even in isolated cortical explants; coculture with a thalamic explant did not alter the numbers of these cells that survived. Our results suggest that the thalamus provides trophic support for subplate cells but not for late embryonic cortical plate cells. In vivo, a loss of thalamic-derived trophic support for the subplate late in embryogenesis, consequent on the movement of thalamocortical axons into the cortical plate, may contribute to subplate death.

Animals↗
PubMed1996

Effects of subcortical structures on the growth of cortical neurites in vitro.

Cortical efferents grow from deep cortical layers to innervate numerous subcortical structures late in embryogenesis. The mechanisms that control their development are poorly understood. We co-cultured organotypic embryonic cortical explants with other tissues, maintaining a distance between them to avoid contact-mediated interactions. At embryonic day 15, when the cortical plate comprises only cells of the deep cortical layers, outgrowth from cultured cortex was stimulated by co-cultured subcortical structures, but not by additional cortex or liver. These data support the hypothesis that diffusible factors from subcortical structures, and not from the cortex itself, enhance cortical efferent growth.

Animals↗
PubMed1996

Modulation of megakaryocytopoiesis by human macrophage-stimulating protein, the ligand for the RON receptor.

We observed that human megakaryocytes expressed the heterodimeric tyrosine kinase RON, which serves as a receptor for macrophage-stimulating protein (MSP). MSP appears to be structurally related to hepatocyte growth factor (HGF), which is a pleiotropic growth factor for a broad spectrum of tissues and cell types. The effects of human rMSP and rHGF on permanent human megakaryocytic cell lines as well as on human and murine primary marrow megakaryocytes were studied. MSP enhanced the maturation of the primary bone marrow megakaryocytes and human megakaryocytic cell lines, CMK and DAMI, as assessed by an increase in ploidy content. The increase in ploidy was blocked by specific Abs for MSP and by anti-IL-6 Abs. MSP treatment of primary human marrow megakaryocytes, DAMI cells, or CMK cells resulted in enhanced secretion of IL-6. The addition of MSP to cultures of immature murine megakaryoblasts showed a significant growth response, similar to that of exogenous IL-6. This increased growth of immature murine megakaryoblasts in response to MSP was abrogated either by Abs against MSP or by neutralizing mAbs to IL-6. HGF, over a range of concentrations (10 to 100 ng/ml) alone or in combination with IL-3, granulocyte-macrophage-CSF, or IL-6, had no effect on differentiation of human or murine marrow megakaryocytes. These results indicate that megakaryocytes express a novel tyrosine kinase receptor (RON), and that its ligand, MSP, appears capable of regulating megakaryocyte maturation, possibly via an autocrine mechanism mediated by induction of the cytokine IL-6.

Animals↗
PubMed1996

Estimates of the convergence of association projections from area 17 to rostral area 18 in the cat depend on injection site size.

To estimate the degree of convergence of corticocortical projections from area 17 to the rostral part of area 18 in the cat, we injected the retrograde tracer diamidino yellow either at single or multiple adjacent sites in area 18. We measured the diameters of the individual or larger composite injections and the diameters of the labelled regions in area 17; from these values we estimated convergence factors. Small injections led to underestimates of the overall convergence of this pathway. A maximal value for convergence (about 3 mm) was obtained with larger composite injections (above about 3 mm in diameter). These results indicate that some area 17-to-18 projections may arborize widely in area 18. Their detection may require that injected tracer covers a large portion of their arbors.

Amidines↗
PubMed1996

The organization of visual corticocortical connections in early postnatal kittens.

We tested the hypothesis that, in newborn kittens, superficial layers of the extrastriate cortex receive more specific patterns of corticocortical innervation from the striate cortex than deep layers. First, we injected retrogradely transported tract-tracers at a range of depths in area 18 to label area 17. All injections were of similar tangential diameter and were in the same region of rostral area 18, where the visual field 10-20 degrees below the horizontal meridian is represented. Injections that involved only the superficial layers of area 18 labelled cells mainly in the superficial layers (future layers 2-4) of area 17, across a region that was 2-3 mm wider than the diameter of the injection site in the rostrocaudal direction. Injections that involved all layers of area 18 labelled cells in both superficial and deep layers (5 and 6) of area 17, across a region that was 6-9 mm wider than the diameter of the injection site in the rostrocaudal direction. These values demonstrate that, in neonates, the convergence of projections from area 17 to the superficial layers of area 18 is less than that to the deep layers of area 18. The lower values for convergence obtained by injecting only the superficial layers of area 18 in kittens were similar to those obtained by injecting all layers of area 18 in adult cats; the values obtained by injecting all layers of area 18 in kittens were much higher. Second, we injected the full depth of area 17 in newborn kittens with labels that travel anterogradely and retrogradely. Confirming the conclusions from the use of retrograde tracers, these focal injections produced very widespread labelling of the deep layers of area 18, but much more localized and topographically organized labelling of its superficial layers. These results indicate that there is a considerable postnatal improvement in the accuracy with which corticocortical cells in striate visual cortex target appropriate regions in extrastriate cortex, in agreement with previous findings. They also demonstrate that this change occurs mainly among those striate cortical neurons that innervate a wide region of the deep layers of extrastriate cortex at birth. The innervation of the superficial layers of extrastriate cortex is much more accurate from the outset.

Age Factors↗
PubMed1996

Trophic and outgrowth-promoting effects of K(+)-induced depolarization on developing thalamic cells in organotypic culture.

The aim of this study was to investigate how different levels of K(+)-induced depolarization affect the survival and growth of isolated, cultured thalamic explants from mice aged embryonic day 13 to postnatal day 2. K+ was added to explants in serum-free culture medium. After culture for three days, explants were sectioned and Nissl-stained or photographed under phase contrast for quantification of neurite outgrowth. Viable and pyknotic cells were counted in sectioned material. The results revealed that, with no added K+, both viability and neurite outgrowth decreased as the age of the thalamic explant increased: most cells survived in embryonic day 13 explants, most died in postnatal day 2 explants. Adding K+ had an age- and dose-dependent effect on viability and neurite outgrowth. The greatest viability-promoting effect of adding K+ was at embryonic day 19: adding 5 mM K+ rescued the majority of these cells, although there was no effect on neurite outgrowth at this age (i.e., enhanced viability did not necessarily produce increased outgrowth). This same dose of K+ had its greatest effect on neurite outgrowth at embryonic day 17. No dose of added K+ had a stimulatory effect on viability and neurite outgrowth after embryonic day 19. The highest dose of K+ used here (50 mM) inhibited thalamic cell survival. We suggest that the survival and growth of the prenatal thalamus can occur without external influences. This intrinsic control may use an autocrine mechanism that becomes increasingly reliant on neural activity for its maintenance as it ages. After birth, when thalamic cells may switch their dependence to cortex-derived growth factors, this intrinsic control may become ineffective.

Animals↗
PubMed1995

Lesions of area 17 in newborn kittens cause selective changes in the development of area 18.

In the cat, areas 17 and 18 interconnect soon after birth. To test the hypothesis that the normal development of area 18 depends on interactions with area 17, unilateral lesions of area 17 were created in newborn kittens, and the animals allowed to mature. Horseradish peroxidase was then injected into both lateral geniculate nuclei. The major abnormalities of area 18 in the lesioned hemispheres were a thinning of specifically layers 2 and 3 and abnormally faint geniculocortical labelling of layer 4. Cell densities in layers 2 and 3 of the lesioned hemispheres were similar to or lower than normal. Neonatal destruction of area 17 therefore produced a selective loss of cells in layers 2 and 3 in area 18 (the layers that normally interconnect with area 17), and may have reduced thalamic innervation of layer 4.

Animals↗
PubMed1995

Purification of a major tyrosine kinase from RBL-2H3 cells phosphorylating Fc epsilon RI gamma-cytoplasmic domain and identification as the Btk tyrosine kinase.

Immunoglobulin E high affinity receptor-mediated signal transduction in mast cells results in a number of protein tyrosine kinases being activated as very early events in the process leading to degranulation. Some of these, such as the src kinases and the syk kinase, are known to be involved in this receptor-associated activation. In this paper we describe the search for other activation-associated tyrosine kinases by the ability to phosphorylate a cytoplasmic domain peptide of the Fc epsilon RI gamma-subunit. In utilizing a purification step previously used to isolate the 72 kDa syk kinase, we detected another kinase of molecular weight 79 kDa which we designated cd gamma kinase. The kinase was purified to near homogeneity by Heparin-agarose, Mono Q, and CM Sepharose chromatographies. The yield of enzyme was approx. 200 micrograms/10(9) cells. We characterized this kinase by its ability to phosphorylate both the cd gamma peptide (Km = 0.2 mM) and the cytoplasmic fragment of the Band III protein. The cd gamma kinase was distinguished from syk by inability to be precipitated by anti-syk antiserum and by partial peptide mapping. Cd gamma kinase was also distinguished from syk by cd gamma peptide and Band III substrate specificity. We identified the cd gamma kinase by Western blotting and by partial phosphopeptide mapping as Btk, the B-cell tyrosine kinase found to be defective in X-linked agammaglobulinemia.

Amino Acid Sequence↗
PubMed1995

The stimulation of thalamic neurite outgrowth by cortex-derived growth factors in vitro: the influence of cortical age and activity.

Recent in vitro experiments have provided useful insights into the development of connections between the thalamus and the cortex. While most of these previous studies focused on neurite guidance and target recognition, our experiments used a serum-free culture system to examine the possible roles of unidentified diffusible cortex-derived growth factors. We demonstrated that occipital cortical explants release diffusible growth factors that enhance neurite outgrowth from explants of the posterior thalamus (the region around the developing lateral geniculate nucleus). The amount of thalamic outgrowth was dependent on the age of the cocultured cortical slices. Our results suggest that there is an overall increase in the release of cortex-derived growth factors during the first three postnatal weeks in mice; this parallels known postnatal increases in the production of several identified growth factors. We found evidence for two peaks in the release of cortex-derived growth factors during the general upward trend, the first at around postnatal day 6 (shortly after thalamocortical innervation of layer 4) and a second between postnatal days 14 and 18 (just after eye-opening). The increased release of cortex-derived growth factors was not found when cortical slices were from mice that had been dark-reared from birth, suggesting that neural activity may be important for enhancing release. Other regions of the central nervous system, including the cerebellum and medulla, were also capable of stimulating some thalamic outgrowth; neither additional explants of the thalamus nor hepatic explants enhanced outgrowth. Fibroblast growth factor is one substance that is distributed preferentially among those tissues that were stimulatory in our experiments. Its level of transcription is known to increase in the brain during the first three postnatal weeks and to be influenced by neural activity. At low doses, fibroblast growth factor greatly increased outgrowth from isolated posterior thalamic explants. Nerve growth factor, another candidate molecule, was less effective. Overall, our results complement the in vivo observations of others on the synthesis of identified growth factors in the cortex and the factors that influence their production. They suggest that growth factors may influence thalamic neurons, and indicate that fibroblast growth factor, and possibly nerve growth factor, are two candidates for molecules mediating the in vitro effects.

Animals↗
PubMed1995

The roles of growth factors and neural activity in the development of the neocortex.

Previous research on primarily the peripheral nervous system has shown that soluble growth factors help control key developmental events by contributing to dynamic autocrine and paracrine signalling systems. Much less is known about the roles of these substances in neocortical development. Using cell and tissue culture paradigms, we have demonstrated that soluble growth factors are produced by the neocortex and its subcortical targets, and that these tissues can respond to them. There are several possible functions for these factors in neocortical development in vivo: they may initiate axonal growth from neocortical neurons and/or their afferents; accelerate or guide that growth; and/or play a role in the later refinement of connections. Although none of these possibilities can be excluded, the existing evidence strengthens the hypothesis that soluble growth factors are important for the early postnatal growth and refinement of neocortical connections, when their levels of release may be regulated by neocortical activity. At present we do not know which growth factors are involved in these processes, but the results of preliminary experiments indicate that neurotrophins and fibroblast growth factor are prime candidates.

Animals↗
PubMed1995

Damage to red blood cells induced by acoustic cavitation.

This experimental study has revealed damage to red blood cells that is quantitatively related to the acoustic pressure during irradiation with 0.75-MHz continuous-wave ultrasound, using a range of intensities comparable to those employed by ultrasonic physiotherapy equipment (0.25 to 7 W cm-2 spatial average temporal average). Damage to the red blood cells was investigated by measuring the extent of haemolysis using a UV/VIS spectrophotometer. There was a clear correlation between the amount of haemoglobin released and the intensity of harmonic emissions recorded from the sample during irradiation. The observed degree of haemolysis could not be produced by temperature rises in the absence of the sound field. This suggests that the damage was a direct result of acoustic cavitation.

Acoustics↗
PubMed1994

Evidence that molecules influencing axonal growth and termination in the developing geniculocortical pathway are conserved between divergent mammalian species.

The general architecture of the visual system is similar for all species of mammal. To determine if the development of connections in the visual system might be under the influence of conserved molecules, we co-cultured explants of the murine lateral geniculate nucleus with slices from either murine or feline occipital cortex. Neurite outgrowth from embryonic murine geniculate explants was significantly enhanced by slices of newborn mouse occipital cortex or kitten visual cortex or by medium previously conditioned by these slices. Slices of similar volume but from sites other than occipital cortex had less or no effect on the murine geniculate explants. Fibers from murine geniculate explants grew freely on cortical slices from the kitten. They terminated mainly in layer 4 and also in layer 6, in both murine and feline visual and frontal cortical slices, irrespective of whether they entered through the white matter or pial side. Only the deep layers of the kitten's cortex sent projections to co-cultured murine geniculate explants. We suggest that the diffusible factors released by the cortex that stimulate the growth of axons from the lateral geniculate nucleus and the molecules that mark specific cortical laminae as targets for ingrowing afferents, are conserved in divergent species. We also found that murine geniculate axons grew freely on feline cerebellar slices. It is known from previous co-culture experiments that rodent geniculate axons are inhibited on rodent cerebellum and we suggest that the inhibitory factors involved are not conserved.

Animals↗
PubMed1994

Monitoring of cerebrospinal dynamics using continuous analysis of intracranial pressure and cerebral perfusion pressure in head injury.

Cerebrospinal dynamics has been investigated by statistical analysis of results of computerised monitoring of 80 head injured patients admitted to the Intensive Care Unit at Pinderfields General Hospital. One minute average values of intracranial pressure (ICP), systemic arterial pressure (ABP), cerebral perfusion pressure (CPP), amplitude of the fundamental component of the intracranial pressure pulse wave and the short-term moving correlation coefficient between that amplitude and mean ICP (RAP) were recorded. It was found that reduction of CPP down to 40 mmHg was more often caused by decrease in ABP than increase in ICP. Further falls in CPP below 40 mmHg were caused by substantial increases in ICP above 25 mmHg. The relationship between the ICP pulse wave amplitude and CPP showed a significant gradual increase in amplitude with CPP decreasing from 75 to 30 mmHg. For CPP below 30 mmHg there is a sharp decrease in amplitude followed by a change in the coefficient RAP from positive to negative values. This was interpreted as a sign of critical disturbance in cerebral circulation.

Blood Pressure↗
PubMed1994

Growth-promoting interactions between the murine neocortex and thalamus in organotypic co-cultures.

The aim of this study was to assess whether developing cerebral cortex produces diffusible factors that can affect the growth of thalamic cells and, if so, what the role of these factors might be during the formation of thalamocortical connections. We studied interactions between cultured organotypic explants from mice maintained in defined serum-free medium. First, we cultured explants of embryonic dorsolateral thalamus in isolation from any other tissue; after culture, these explants were viewed intact and then sectioned. We estimated the numbers of healthy and pyknotic cells before and after culture, and the rates of mitosis in the explants during culture (using bromodeoxyuridine). Based on these data, we concluded that the majority of cells in the thalamic explants survived, although significant numbers of pyknotic cells did accumulate. Thalamic explants extended either very few or no neurites when cultured alone. We then cultured explants of embryonic thalamus near to explants from other tissues. A gap was always maintained between the explants, and we measured the length and density of neurite outgrowth from each thalamic explant. Slices of embryonic cortex promoted a small but significant increase in the amount of growth from thalamic explants. Postnatal cortex stimulated much more profuse neurite outgrowth; postnatal cerebellum had less of an effect, and postnatal medulla or liver had none. We showed that there was significantly more outgrowth from thalamic explants cultured in medium that had been preconditioned with cortical slices than from thalamic explants cultured in control medium, confirming that diffusible factors were produced by the cortex. The survival and mitotic rates of thalamic cells were unaffected by co-culture with the cortex. We conclude that the developing cortex releases diffusible factors that stimulate the growth of thalamic neurites and that other regions of the brain may also release the same substance(s). The lack of a specific source of thalamic growth promoting factor(s) argues against a role for these factors in guiding thalamic axons to specific targets; indeed, we were unable to demonstrate any chemotropic guidance of thalamic axons towards cortical explants in collagen gels. Since postnatal cortex has a more potent stimulatory effect than prenatal cortex, it seems possible that, in vivo, the cortical-derived factors act mainly on thalamocortical axons that have located their targets and are in the process of arborizing and refining their connections.

Animals↗
PubMed1994

Functional organization of corticocortical projections from area 17 to area 18 in the cat's visual cortex.

We used anatomical and physiological methods to study the functional organization of the association projection from area 17 to area 18 in the cat's visual cortex. Neurons in area 17 projecting to area 18 (revealed by retrograde transport of fluorescent tracer) tend to be clustered over regions of layer 4 receiving input from the ipsilateral eye (visualized by anterograde transneuronal tracing). Since the contralateral input overlaps these ipsilateral patches, the association cells lie preferentially in regions that are likely to be binocularly innervated. Indeed, almost all cells recorded electrophysiologically within the association clusters were strongly binocular, whereas between the clusters, many neurons were dominated by the contralateral eye. There is sufficient jitter in the retinotopic organization of area 17 for the discontinuous distribution of association cells to provide a continuous representation of the visual field. Cells in each association cluster in the rostral part of area 17 project divergently to innervate a zone extending up to 3 mm wide, anteroposteriorly, in the superficial layers of area 18. The receptive fields of cells at any point in area 18 are larger than for the corresponding point in area 17. Neurons recorded at two points in area 18, separated by a distance equal to the limit of anatomical divergence of the projection from area 17, have receptive fields that overlap by an amount similar to the region of visual field covered by the receptive fields of cells in a single association cluster in area 17 at a similar retinotopic position. Thus, area 18 receives a full and strongly binocular representation of the visual field not only from the lateral geniculate nucleus but also from area 17. The divergence of the area 17 to 18 projection compensates for the difference in receptive field size by ensuring that the receptive fields of each cluster of projecting neurons overlap fairly precisely those of the recipient neurons in area 18.

Amidines↗
PubMed1994

Postnatal development and plasticity of corticocortical projections from area 17 to area 18 in the cat's visual cortex.

We used retrogradely transported fluorescent tracers to study the development of projections from area 17 to area 18 in normal and monocularly deprived kittens. In newborn animals, cells in area 17 that were labeled from small, discrete injections in area 18 were concentrated around the retinotopically corresponding zone, but distributed with lower density over a very wide surrounding area. Hence, the total convergence and divergence of the projection were initially enormous, but they decreased dramatically, mainly during the first postnatal month, through elimination of the sparse, widespread distribution of projections. Injections of two different tracers close together in area 18 produced very few double-labeled cells in area 17 at any age, implying that most individual axons arborize over very small territories even at birth. In normal kittens the peak density of association cells in the upper layers, corrected for the overall expansion of the cortex, doubled over the first postnatal month and then declined gradually over the following several months, presumably because of continuing selection and elimination. As shown in previous work (Price and Blakemore, 1985a), area 17 to 18 cells in newborn kittens were distributed in two continuous bands in supragranular and infragranular layers. During normal maturation, elimination of projections results in the formation of distinct clusters; these lie preferentially in the upper layers above patches of ipsilateral eye input to layer 4 (Price et al., 1994). Monocular deprivation, which causes the terminal patches representing the deprived eye to become much smaller than normal, did not stop the normal decrease in overall convergence/divergence or the appearance of clusters of association cells, but the clusters were distinctly larger than normal in both hemispheres. Monocular deprivation also prevented the normal reduction in density of association cells within clusters after 1 month of age. Comparison with results from binocularly deprived animals, where clusters also form but association cell density is low, suggests that the size of clusters and the density of association cells retained depend on the overall level of cortical activity.

Aging↗