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Biomedical subjects

C Hildebrand

Publications and source records attributed to C Hildebrand.

At least 19 recordsLinked to original sources
PubMed2004

Early detection of diabetes retinopathy by new algorithms for automatic recognition of vascular changes.

Diabetes mellitus often results in diabetic retinopathy caused by pathological changes of the retinal vessel tree. Early detection of these changes can delay the disease. Image processing can reduce the workload of screeners and can play a central role in quality assurance tasks. Therefore we aimed at the refinement and development of image processing algorithms to improve the quality and cost effectiveness of screening and diagnosis of diabetic retinopathy. In order to support ophthalmologists in their routine and to enable the quantitative assessment of vascular changes in colour fundus photographs a multi-resolution approach was developed which segments the vessel tree efficiently and precisely into digital images of the retina. The vessel tracker aims at determining as correctly as possible the retinal vascular network captured on a digital image irrespective of its origin. In addition to the tracker, algorithms were developed to detect the optic disk, bright lesions such as cotton wools spots, and dark lesions such as haemorrhages. The following classification of veins and arteries identifies arteries in 78.4 % and veins in 66.5% correctly. This helps selecting conspicuous images from a great number of patients.

Algorithms↗
PubMed2003

Neuropeptide effects on rat chondrocytes and perichondrial cells in vitro.

This study examines if cultured chondrocytes and perichondrial cells change the level of cAMP and/or cGMP in response to application of the neuropeptide calcitonin gene-related peptide (CGRP). Cells collected from the knee region of 4-8 days old rat pups were cultured in vitro. Cultures were exposed to 10(-10)-10(-6) M CGRP during 10 minutes. The levels of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in the cultures and in controls were determined by radioimmunoassay. The results show that application of CGRP causes a distinctly increased level of cAMP, that was absent when CGRP was applied together with the CGRP(1) receptor antagonist. The level of cGMP was not obviously altered. Hence, it is possible that terminals of primary sensory neurones present in developing cartilage influence chondrocytes and perichondrial cells via local release of CGRP.

Animals↗
PubMed2003

Responses of rat trigeminal neurones to dental pulp cells or fibroblasts overexpressing neurotrophic factors in vitro.

The adult dental pulp is innervated by sensory trigeminal axons and efferent sympathetic axons. Rat trigeminal ganglia extend neurites when co-cultivated in vitro with pulpal tissue explants, suggesting that pulpal cells secrete soluble molecules that stimulate the growth of trigeminal ganglion axons. In addition, cultured pulpal cells produce mRNAs for neurotrophins and glial cell line-derived neurotrophic factor-family members. These data suggest that neurotrophic factors are involved in the formation of a pulpal innervation. Here, we examine how pulpal cells and 3T3 fibroblasts overexpressing certain neurotrophic factors (nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, neurotrophin-4, glial cell line-derived neurotrophic factor or neurturin) influence survival and growth of single trigeminal ganglion neurones in vitro in quantitative terms. The results show that most of the neurotrophic factor-overexpressing fibroblasts induce similar neuronal soma diameters, but higher survival rates and neurite lengths compared with pulpal cells. With respect to neurite growth pattern, trigeminal ganglion neurones co-cultured with fibroblasts overexpressing nerve growth factor develop a geometry that is most similar to that seen in co-cultures with pulpal cells. We conclude that none of the fibroblasts overexpressing neurotrophic factors can fully mimic the effects of pulpal cells on trigeminal ganglion neurones, and that nerve growth factor promotes a neurite growth pattern most similar to the picture seen in co-cultures with pulpal cells.

3T3 Cells↗
PubMed2001

Changes in a rat facial muscle after facial nerve injury and repair.

This study describes changes in a rat facial muscle innervated by the mandibular and buccal facial nerve branches 4 months after nerve injury and repair. The following groups were studied: (A) normal controls; (B) spontaneous reinnervation by collateral or terminal sprouting; (C) reinnervation after surgical repair of the mandibular branch; and (D) chronic denervation. The normal muscle contained 1200 exclusively fast fibers, mainly myosin heavy chain (MyHC) IIB fibers. In group B, fiber number and fiber type proportions were normal. In group C, fiber number was subnormal. Diameters and proportions of MyHC IIA and hybrid fibers were above normal. The proportion of MyHC IIB fibers was subnormal. Immediate and delayed repair gave similar results with respect to the parameters examined. Group D rats underwent severe atrophic and degenerative changes. Hybrid fibers prevailed. These data suggest that spontaneous regeneration of the rat facial nerve is superior to regeneration after surgical repair and that immediacy does not give better results than moderate delay with respect to surgical repair. Long delays are shown to be detrimental.

Adenosine Triphosphatases↗
PubMed2001

Sorting of regenerating rat sciatic nerve fibers with target-derived molecules.

The functional outcome of microsurgical repair of divided nerves is disappointing since many regenerating axons fail to reach appropriate targets. Sorting of regenerating axons according to target tissue might be used to improve functional regeneration. The aim of the present study is to see if regenerating axons can be sorted into functionally different bundles with target-derived molecules. The proximal stump of the adult rat sciatic nerve was sutured into the inlet of a silicon Y-tube. The two branches of the Y-tube were filled with agarose primed with filtrates prepared from skin and muscle homogenates from the operated rat. The tibial and sural nerves were inserted in the two branches of the Y-tube. Six weeks later the sciatic nerve axons showed vigorous regeneration into both branches. Electron microscopic examination of regenerated nerve segments showed numerous myelinated and unmyelinated axons. The proportion of myelinated axons was significantly larger in the muscle-gel branch than in the skin-gel branch. Retrograde tracing from the nerve regenerates with Fast Blue and Fluoro-Ruby showed that ventral horn neurons at L4-L5 segmental levels were preferentially labeled from the muscle-gel branch. Neurons in corresponding dorsal root ganglia were labeled from both Y-tube branches (no significant numerical difference). A few neurons of both types contained both tracers. Measurements revealed that sensory neurons labeled from the muscle-gel branch were significantly larger (mean perikaryal area 870 microm(2)) than neurons labeled from the skin-gel branch (mean area 580 microm(2)). We conclude that regenerating motor and sensory axons can be sorted with target-derived molecules.

Animals↗
PubMed2000

[Schwann cells promote development and repair of nerve cells].

During early development Schwann cells have trophic effects on neurons with outgrowing axons. Later these cells are responsible for myelination and formation of nodes of Ranvier in the peripheral nervous system, a developmental process with considerable functional significance. In adult nerves, Schwann cells and axons cooperate closely. After nerve injuries, axons degenerate while Schwann cells proliferate and dedifferentiate. The stimulating effects these cells have on axonal regeneration are exploited clinically through the use of nerve grafts for repair. Schwann cells are used experimentally to enhance regeneration of axons in the central nervous system. Tomorrow this may be used clinically--an exciting development.

Axons↗
PubMed2000

Penguins use the two-voice system to recognize each other.

The sound-producing structure in birds is the syrinx, which is usually a two-part organ located at the junction of the bronchi. As each branch of the syrinx produces sound independently, many birds have two acoustic sources. Thirty years ago, we had anatomical, physiological and acoustical evidence of this two-voice phenomenon but no function was known. In songbirds, often these two voices with their respective harmonics are not activated simultaneously but they are obvious in large penguins and generate a beat pattern which varies between individuals. The emperor penguin breeds during the Antarctic winter, incubating and carrying its egg on its feet. Without the topographical cue of a nest, birds identify each other only by vocal means when switching duties during incubation or chick rearing. To test whether the two-voice system contains the identity code, we played back the modified call of their mate to both adults and also the modified call of their parents to chicks. Both the adults and the chicks replied to controls (two voices) but not to modified signals (one voice being experimentally suppressed). Our experiments demonstrate that the beat generated by the interaction of these two fundamental frequencies conveys information about individual identity and also propagates well through obstacles, being robust to sound degradation through the medium of bodies in a penguin colony. The two-voice structure is also clear in the call of other birds such as the king penguin, another non-nesting species, but not in the 14 other nesting penguins. We concluded that the two-voice phenomenon functions as an individual recognition system in species using few if any landmarks to meet. In penguins, this coding process, increasing the call complexity and resisting sound degradation, has evolved in parallel with the loss of territoriality.

Animals↗
PubMed2000

Developing chicken oligodendrocytes express the type IV oligodendrocyte marker T4-O in situ, but not in vitro.

Accumulating data suggest that the oligodendrocyte population includes morphological and biochemical subtypes. We recently reported that a polyclonal antiserum against an unknown antigen, the T4-O molecule, labels a subpopulation of chicken oligodendrocytes, obviously representing the type IV variety of Del Rio Hortega. The present study examines the developmental expression of the T4-O molecule in situ and in vitro. The results show that T4-O immunoreactive cells first appear at E15 in the ventral funiculus. But, oligodendrocytes cultured in vitro with or without neurones do not develop a T4-O immunoreactivity. We conclude that oligodendrocytes in the spinal cord of chicken embryos first express the T4-O molecule some time after onset of myelination, and that the T4-O immunoreactive phenotype does not develop in vitro.

Age Factors↗
PubMed2000

Hypoglycaemic neuropathy: occurrence of axon terminals in plantar skin and plantar muscle of diabetic BB/Wor rats treated with insulin implants.

It is generally believed that diabetic neuropathy is due to chronic hyperglycaemia. However, experience from insulinoma patients and experimental studies show that hypoglycaemia may also cause neuropathy. Accordingly, the plantar nerves of diabetic eu-/hypoglycaemic BB/Wor rats treated with insulin implants exhibit a distinct neuropathy. To what extent hypoglycaemic neuropathy affects axon terminals in skin and muscle is unknown. In the present study we examine the occurrence of epidermal axon profiles and the neuropeptide calcitonin gene-related peptide (CGRP) in plantar skin, and of end plate axon terminals in a plantar muscle of diabetic BB/Wor rats subjected to long periods of hypoglycaemia. The number of protein gene product-immunoreactive axon profiles was found to be normal in heel skin biopsy specimens from eu-/hypoglycaemic rats, but many profiles were short and thin. The content of CGRP in the skin biopsy samples was significantly below normal. After staining with antibodies against the vesicular acetylcholine transporter protein, the occurrence of end plate axon terminals was significantly reduced in sections from the flexor hallucis brevis muscle of eu-/hypoglycaemic rats. Moreover, the end plate axon terminals tended to be abnormally small in these rats. We conclude that the hypoglycaemic neuropathy seen in plantar nerve trunks of diabetic BB/Wor rats treated with insulin implants is accompanied by mild alterations in the epidermal innervation of plantar skin and a more obviously abnormal nerve terminal pattern in plantar muscle.

Animals↗
PubMed2000

Retrograde tracing and neuropeptide immunohistochemistry of sensory neurones projecting to the cartilaginous distal femoral epiphysis of young rats.

Although cartilage is considered to be devoid of innervation, axons occur in the perichondrium and during development in cartilage canals, thereby having a relatively close spatial relationship to chondroblasts and chondrocytes. The present study locates the source of the sensory innervation of the femoral cartilaginous epiphyses of young rats and investigates whether the neuropeptide calcitonin gene-related peptide (CGRP) can influence chondrocytes. Retrograde tracing from the distal femoral epiphysis of young rats with Fast Blue (FB) showed labelled neuronal profiles in the L2-L5 dorsal root ganglia. Sample countings indicated that 50% of the FB-labelled neuronal profiles were located at the L3 level and 25% at the L4 level. The labelled neurones had diameters of 15-40 microm, with a peak at 25-30 microm. Immunohistochemistry showed that about 50% of the FB-labelled profiles contained CGRP. Together with the finding that CGRP influences bone cells to generate the second messenger cAMP, this result suggested the hypothesis that chondrocytes might be similarly influenced by CGRP. However, stimulation of cartilage slices with CGRP in vitro followed by an assay of the cAMP content did not provide support for this hypothesis. We conclude that primary sensory neurones containing CGRP project to the perichondrium and to cartilage canals of growing cartilage, and that exogenous CGRP does not elevate the cAMP content of cartilage slices in vitro.

Amidines↗
PubMed2000

Fibroblast-like cells from rat plantar skin and neurotrophin-transfected 3T3 fibroblasts influence neurite growth from rat sensory neurons in vitro.

Our previous finding that skin-derived and muscle-derived molecules can be used to sort regenerating rat sciatic nerve axons evoked questions concerning neuron-target interactions at the level of single cells, which prompted the present study. The results show that dorsal root ganglion (DRG) neurons co-cultured with fibroblast-like skin-derived cells emit many neurites. These have a proximal linear segment and a distal network of beaded branches in direct relation to skin-derived cells. Electron microscopic examination of such co-cultures showed bundles of neurites at some distance from the target cells and single profiles closely apposed to subjacent cells. RNase protection assay revealed that cultivated skin-derived cells express nerve growth factor (NGF), brain derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4 (NT-4). In co-cultures of DRG neurons and 3T3 fibroblasts overexpressing either of the neurotrophins produced by skin-derived cells the picture varied. NT-3 transfected 3T3 fibroblasts gave a growth pattern similar to that seen with skin-derived cells. Neurons co-cultured with mock-transfected 3T3 fibroblasts were small and showed weak neurite growth. In co-cultures with a membrane insert between skin-derived cells or 3T3 fibroblasts and DRG neurons few neurons survived and neurite growth was very sparse. We conclude that skin-derived cells stimulate neurite growth from sensory neurons in vitro, that these cells produce NGF, BDNF, NT-3 and NT-4 and that 3T3 fibroblasts producing NT-3 mimic the effect of skin-derived cells on sensory neurons in co-culture. Finally the results suggest that cell surface molecules are important for neuritogenesis.

3T3 Cells↗
PubMed2000

Myelination of prospective large fibres in chicken ventral funiculus.

In mammals, the oligodendrocyte population includes morphological and molecular varieties. We reported previously that an antiserum against the T4-O molecule labels a subgroup of oligodendrocytes related to large myelinated axons in adult chicken white matter. We also reported that T4-O immunoreactive cells first appear in the developing ventral funiculus (VF) at embryonic day (E)15, subsequently increasing rapidly in number. Relevant fine structural data for comparison are not available in the literature. This prompted the present morphological analysis of developing and mature VF white matter in the chicken. The first axon-oligodendrocyte connections were seen at E10 and formation of compact myelin had started at E12. Between E12 and E15 the first myelinating oligodendrocytes attained a Schwann cell-like morphology. At hatching (E21) 60% of all VF axons were myelinated and in the adult this proportion had increased to 85%. The semilunar or polygonal oligodendrocytes associated with adult myelinated axons contained many organelles indicating a vivid metabolic activity. Domeshaped outbulgings with gap junction-like connections to astrocytic profiles were frequent. Oligodendrocytes surrounded by large myelinated axons and those surrounded by small myelinated axons were cytologically similar. But, thick and thin myelin sheaths had dissimilar periodicities and Marchi-positive myelinoid bodies occurred preferentially in relation to large myelinated axons. We conclude that early oligodendrocytes contact axons and form myelin well before the first expression of T4-O and that emergence of a T4-O immunoreactivity coincides in time with development of a Type IV phenotype. Our data also show that oligodendrocytes associated with thick axons are cytologically similar to cells related to thin axons. In addition, the development of chicken VF white matter was found to be similar to the development of mammalian white matter, except for the rapid time course.

Aging↗
PubMed2000

Molecular signaling and pulpal nerve development.

The purpose of this review is to discuss molecular factors influencing nerve growth to teeth. The establishment of a sensory pulpal innervation occurs concurrently with tooth development. Epithelial/mesenchymal interactions initiate the tooth primordium and change it into a complex organ. The initial events seem to be controlled by the epithelium, and subsequently, the mesenchyme acquires odontogenic properties. As yet, no single initiating epithelial or mesenchymal factor has been identified. Axons reach the jaws before tooth formation and form terminals near odontogenic sites. In some species, local axons have an initiating function in odontogenesis, but it is not known if this is also the case with mammals. In diphyodont mammals, the primary dentition is replaced by a permanent dentition, which involves a profound remodeling of terminal pulpal axons. The molecular signals underlying this remodeling remain unknown. Due to the senescent deterioration of the dentition, the target area of tooth nerves shrinks with age, and these nerves show marked pathological-like changes. Nerve growth factor and possibly also brain-derived neurotrophic factor seem to be important in the formation of a sensory pulpal innervation. Neurotrophin-3 and -4/5 are probably not involved. In addition, glial cell line-derived neurotrophic factor, but not neurturin, seems to be involved in the control of pulpal axon growth. A variety of other growth factors may also influence developing tooth nerves. Many major extracellular matrix molecules, which can influence growing axons, are present in developing teeth. It is likely that these molecules influence the growing pulpal axons.

Animals↗
PubMed1999

Noradrenaline-induced pigment aggregating response of melanophores in normal, denervated and reinnervated cichlid skin.

The present study examines noradrenaline (NA) effects on melanophore pigment aggregation in normal, denervated and reinnervated teleost skin in vitro. Many axons were present in the melanophore-containing layer of normal skin. One week after a nerve crush lesion the skin was devoid of axons. By 1 month the skin was partly reinnervated. One day after nerve crush NA-sensitivity was markedly increased compared to controls. Sensitivity then approached normality but it remained elevated for at least one month. We conclude that melanophore supersensitivity develops very rapidly upon denervation and then gradually fades away during reinnervation.

Animals↗
PubMed1999

Denervation does not affect the growth of rat vibrissae.

This study examines the hypothesis that neural factors influence the growth of rat vibrissae. We divided the vibrissae in rows alpha-delta, 1 and 2 and examined their regrowth during the first complete growth period in normal and nerve-lesioned rats. The lesions used were denervation through neonatal capsaicin treatment, surgical sympathecomy in adult rats, neurectomy of the mandibular and buccal branches of the facial nerve in adult rats or division of the infraorbital nerve in adult rats. Normal vibrissae developed a length of 51.1 mm and a diameter of 178 microm (row alpha-delta), 44.1 mm and 181 microm (row 1) and 33.2 mm and 165 microm (row 2). In all experimental groups the examined vibrissae developed a normal final length and proximal diameter. This indicates that local nerves do not influence vibrissal growth to any major extent.

Animals↗
PubMed1999

Increased occurrence of PGP 9.5-immunoreactive epidermal Langerhans cells in rat plantar skin after sciatic nerve injury.

This study examines the occurrence and distribution of epidermal dendritic cells (DCs) in cryostate sections from plantar skin in normal rats and in rats with a crush injury or neurotomy and suture of the sciatic nerve. The dendritic cells were visualized with antibodies against protein-gene product 9.5 (PGP 9.5). Counts under the fluorescence microscope showed that the occurrence of dendritic cells is increased and that the proportion of dendritic cells in the basal layer is elevated 3 months after sciatic neurotomy and suture but not after a crush lesion. The countings also revealed that the number of cells is elevated as soon as 1 week after neurotomy and suture. Labelling with specific antibodies showed that the dendritic cells examined represent Langerhans cells (LCs). These observations show that there is a neural influence on the occurrence and distribution of PGP 9.5-immunoreactive epidermal Langerhans cells. Whether this influence is direct or indirect remains to be ascertained.

Animals↗
PubMed1999

Tooth pulp tissue promotes neurite outgrowth from rat trigeminal ganglia in vitro.

The mammalian tooth pulp becomes innervated by nociceptive and sympathetic axons relatively late during development, when part of the root has formed. In the adult, regenerating axons from an injured tooth nerve or sprouting axons from uninjured nerves in the vicinity rapidly reinnervate denervated tooth pulps. These observations indicate that tooth pulp tissue can use molecular factors to attract pulpal axons from local nerve trunks. The present study examines the hypothesis that these factors include nerve growth factor (NGF), brain derived neurotrophic factor (BDNF) and glial cell line derived neurotrophic factor (GDNF). Explants of trigeminal ganglia from neonatal rat pups showed a distinct neurite outgrowth when co-cultured with pulpal explants collected from molar teeth of 12-day old pups, or after application of a pulpal extract. Control cultures, containing single ganglionic explants, or explants co-cultured with heat-treated pulpal tissue, exhibited a sparse neurite outgrowth. Exogenous NGF and/or GDNF, but not exogenous BDNF, stimulated neurite outgrowth from ganglionic explants. Unexpectedly, application of antibodies against NGF, BDNF and/or GDNF to co-cultures of ganglionic and pulpal explants did not inhibit neuritogenesis. Control experiments showed that IgG molecules readily penetrate the gel used for culture and that even very high concentrations of NGF and GDNF antibodies in combination failed to block neurite growth. On the basis of these data we suggest that other as yet unknown neurite-promoting factors might be present and active in TG/pulpal co-cultures.

Animals↗