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Biomedical subjects

A Bergström

Publications and source records attributed to A Bergström.

45 records · Page 3Linked to original sources
PubMed1991

Ultrastructure of human retinal cell transplants with long survival times in rats.

Human fetal retinas (6-12 weeks post-conception) were obtained from elective abortions, transplanted to rat retinas and examined by electron microscopy. The oldest transplants that form the basis of this report were obtained 40 and 41 total weeks post-conception. The host rats were immunosuppressed with cyclosporin A. The transplants developed according to their intrinsic, genetically determined timetable. The development was heterogeneous with some parts showing almost normal differentiation and others, little. Both rods and cones developed with inner and outer segments and synaptic terminals. In regions corresponding to the inner plexiform layer, bipolar cell processes were seen in the typical dyad arrangement. Likewise, amacrine cell processes formed typical conventional synapses. Serial synapses were seen, engaging amacrine cell synapses as well as a few reciprocal synapses at the bipolar cell dyads. Monad-type synaptic complexes, a sign of immaturity, were common in bipolar cell processes. Similarly, incompletely differentiated synapses of both the amacrine and bipolar cell types were often observed. Ganglion cell processes could not be identified with certainty. A structure with morphological characteristics similar to the inner limiting membrane was noted to form inside the transplant. Both epi-retinal and sub-retinal transplants were obtained. Transplant cells touched host photoreceptor cells or pigment epithelium without any obvious specializations. The host pigment epithelium microvilli were absent adjacent to the graft. However, graft cells did appear in the host retina, and nerve cell processes were observed to cross the membrane separating the transplant and host.

Animals↗
PubMed1990

Neuronal markers in rat retinal grafts.

Rat E15 retina was grafted to the retina of adult rat hosts. After varying survival times (1 week-6 months), grafts were stained by immunohistochemistry for neurofilament 160 kDa (NF), HPC-1 (an amacrine cell marker), choline acetyltransferase (ChAT), tyrosine hydroxylase (TH), glutamic acid decarboxylase (GAD) and somatostatin-28 (SS-28). The first differentiating graft amacrine cells (cholinergic and dopaminergic) could be seen 1 week after transplantation (corresponding to postnatal day 1 = P1). The inner plexiform layer of the graft started to differentiate at 2 weeks (corresponding to P8) seen by HPC-1 and GAD staining. ChAT, TH and SS-28 immunostaining revealed an abnormal lamination pattern in the graft inner plexiform layer. Also by 2 weeks, the outer plexiform layers of the graft contained NF-immunoreactive horizontal cells. No NF-stained retinal ganglion cells could be observed in the graft. Five and 7 weeks after grafting, the transplants had obtained the same staining intensity with different markers as the host retina.

Animals↗
PubMed1986

Structural and pharmacological differences between codfish and rat brain alpha 1-adrenergic receptors revealed by photoaffinity labeling with 125I-APDQ.

The photoaffinity probe 125I-APDQ has been used to characterize alpha 1-receptor peptides in the cod and rat brains. In the cod brain a major specific peptide of Mr = 68,000 could be covalently labeled by 125I-APDQ as revealed by SDS-PAGE. In the rat brain a specific peptide with Mr = 77,000 was instead labeled. When a number of adrenergic agonists and antagonists were tested for their ability to protect the labeling by 125I-APDQ their potencies were those expected for alpha 1-receptors in both species. The ligand binding peptide in the cod brain also distinguished between stereoisomers of epinephrine as expected for a physiological receptor. However, there was a distinct difference between the cod and rat alpha 1-receptor in that the beta-agonist 1-isoprenaline was equipotent to 1-norepinephrine in the cod whereas it was less potent in the rat. The protecting ability of the tested agents were also matched by their ability to displace the alpha 1-adrenergic ligand 3H-prazosin from alpha 1-receptor binding sites in brain membranes from both species. Thus, the codfish alpha 1-receptor seems to be different from mammalian alpha 1-receptors both structurally and pharmacologically.

Affinity Labels↗
PubMed1986

Guanine nucleotides regulate both agonist and antagonist binding to cod brain alpha 1-adrenoceptors.

The effect of guanine nucleotides on the binding of 3H-prazosin and its displacement by various agonists and antagonists were studied in membranes prepared from the cod brain. When cod brain membranes were maintained in a buffer containing 8 mM Mg2+, GTP (1 mM) was found to increase the specific binding of 3H-prazosin Computer modelling 3H-prazosin saturation curves, suggested that the number of binding sites for 3H-prazosin was increased by 18 +/- 5% by GTP without affecting the affinity for 3H-prazosin (dissociation constant, Kd, 56 +/- 3 pM). Displacement of 3H-prazosin by adrenaline produced shallow displacement curves. Computer modelling these curves suggested that adrenaline bound to two sites - one high and one low affinity site - the Kd's being 0.14 +/- 0.03 (KH) and 7.6 +/- 0.5 microM (KL), respectively. When 1 mM GTP was present the displacement curves were shifted to the right and became steeper. Computer modelling these curves suggested that adrenaline now bound to only one low affinity site with a Kd of 7.6 +/- 0.5 microM. When unlabelled prazosin was used to displace 3H-prazosin the displacement curves were uniphasic and steep, irrespective of whether GTP was present or not. Computer modelling these curves suggested that prazosin bound to only one site with a Kd of 68 +/- 11 pM. In the absence of Mg2+ and in the presence of EDTA (0.8 mM) the displacement curve of adrenaline became steeper and the effect of GTP was almost abolished. During these conditions the ability of GTP to enhance 3H-prazosin binding was also abolished.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Agonists↗
PubMedDate not supplied

The nuclear issue in Swedish schools.

Sweden is almost unique in that its government through its foreign office gave financial support to a carefully thought out proposal from Svenska Läkare Mot Kärnvapen (Swedish Physicians against Nuclear Weapons) for a youth education project on the nuclear issue. The Swedish Board of Education has agreed to provide: 1. In-service training for teachers on current affairs; 2. Up-to-date teaching resources and materials, such as the booklet, Facts and Reflections on Nuclear Weapons; 3. A curriculum stating that education on nuclear and other environment issues should not be a special subject but should be involved in many school activities-for example the learning of foreign languages, biology, physics, science and even physical education. The Board's recommendations have been sent to every Swedish school, together with the booklet, but each school decides for itself whether or not to implement them. However, some teachers do some education on the nuclear issue in most Swedish schools.

Adolescent↗
PubMedDate not supplied

Function and structure in retinal transplants.

Embryonic mammalian donor retina transplanted into the subretinal space of a mature host develops into a graft with well-organized, but atypical retinal structure. We tested the effect of this organization on rabbit-to-rabbit graft functional properties, isolating the graft to avoid contamination of graft responses by host retinal activity. Transient ON or ON-OFF spike-like responses and local electroretinograms (L-ERGs) were recorded simultaneously via a single electrode on the graft surface. These response components depended on stimulus diameter, sometimes in a way indicating antagonistic center-surround receptive field organization and spatial tuning (43%). Other times, the responses were an increasing function of stimulus diameter which saturated for large spots (57%). Response amplitudes were a monotonically-increasing function of light intensity over the narrow range tested. The L-ERGs were reminiscent of the proximal negative response or M-wave seen in normal retinas, which reflect light-induced amacrine cell activity. Thus, for the first time, we have shown that these subretinal grafts possess light-transduction and complex functional properties like those in normal retinas. They also possess the cellular complement and synaptic microcircuitry needed to form these physiological properties, Therefore, these results demonstrate a functional ability and capacity in transplants that is required if nerve cell transplantation surgery is to be done with therapeutic aims.

Action Potentials↗
PubMedDate not supplied

Ultrastructure of retinal cells transplanted to the rabbit choroid.

PURPOSE: Allogenic rabbit-to-rabbit retinal cell transplants survive in the choroid, which is not as expected because it has not been shown that this is an immune-privileged site. We have therefore examined the ultrastructure of such transplants, looking for features that might explain the phenomenon. METHODS: Rabbit retinal tissue fragment transplants were produced with previously described methods. The donor age was 15 days and the transplants were examined by standard electron microscopy when the transplants were 1-2 months (3 transplants) or 3-4 months old, of postconception age (3 transplants). RESULTS: The transplants survived and developed as expected from previous observations. Rosettes were seen, but they were not as common as in transplants produced with the same technique in the subretinal space of rabbits. Photoreceptor outer segments were not seen in the transplants. At 1 month, there was an incomplete sheath of Müller cells around the transplants, and a complete one at 3-4 months. There was also a well-developed basement membrane around the transplant at 3-4 months, but less so at 1 month. Blood vessels did not enter the transplant. The fenestrations in the choriocapillaris were not affected as long as the pigment epithelium was normal. CONCLUSIONS: The enclosure of the transplants by Müller cells might help to insulate them from the immune system of the host, but it is a late phenomenon and it is not likely to have much effect for the first few weeks after the transplantation. We suspect that either the rabbit choroid is an immune-privileged site, even though there is no previous direct evidence for this, or that the retinal tissue itself is responsible for the prolonged survival at this site.

Animals↗
PubMedDate not supplied

Cellular organization in retinal transplants using cell suspensions or fragments of embryonic retinal tissue.

We have investigated the cellular organization in two different types of retinal transplants using cell type-specific monoclonal antibodies. Both fragments and cell suspensions of E17-E19 Sprague-Dawley rat retina were transplanted to a subretinal site in congenic adult rat hosts. After a survival time of 28 days, the transplants were stained by immunocytochemistry with antibodies against rhodopsin, which stained rods; with antibodies against HPC-1, which stained amacrine cells and outer and inner plexiform layers; and with antibodies against vimentin, which stained Müller cell fibers and horizontal cells. In the host retina, the distribution of immunocytochemical staining was similar, irrespective of transplantation technique. In the transplants, the anti-rhodopsin staining showed that fragment transplants developed photoreceptors in rosettes, whereas in cell suspension transplants, this staining showed a scattered distribution of photoreceptors. The HPC-1 staining showed that regions corresponding to the inner nuclear layer surrounded both types of transplants and made large invaginations into them. In one case, using the cell suspension technique, fibres were found to run from the inner plexiform layer of the transplant to the outer plexiform layer of the host. The vimentin staining revealed a disorganized array of Müller cell fibres in both types of transplants, but with some concentration to the regions corresponding to the inner plexiform layer.

Animals↗