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P Bernd

Publications and source records attributed to P Bernd.

31 records · Page 2Linked to original sources
PubMed1988

Selective expression of high-affinity nerve growth factor receptors on tyrosine hydroxylase-containing neuron-like cells in neural crest cultures.

A subpopulation of cultured neural crest cells undergoing differentiation have receptors for nerve growth factor (NGF) that exhibit a binding constant similar to that of the low-affinity NGF binding site (3.2 nM). Recent studies have shown that NGF receptors are not present on neuron-like cells immunoreactive for tyrosine hydroxylase (TH), serotonin, or vasoactive intestinal polypeptide. Since tissues innervated by sympathetic neurons in vivo produce NGF, we sought to determine whether NGF deficits in the tissue culture microenvironment may be one parameter preventing the expression of NGF receptors on TH-containing neuron-like cells. Neural crest cultures were therefore grown in complete tissue culture medium (15% fetal bovine serum and 5% chicken embryo extract), with or without exogenous NGF (50 ng/ml). Examination of light-microscopic radioautographs following incubation with 125I-NGF revealed that, if the cultures were supplemented with NGF for 7 d, approximately 33% of neuron-like cells exhibiting TH-like immunoreactivity possessed NGF receptors. There were no obvious morphological differences between TH-containing cells that did or did not have NGF receptors. Scatchard analysis of cultures grown under these conditions again demonstrated the sole presence of the low-affinity form of the NGF receptor (Kd, 3.4 nM). Embryonic catecholaminergic sympathetic neurons exhibit both high- and low-affinity forms of the NGF receptor, raising the possibility that the Scatchard analysis may not have been sensitive enough to detect the high-affinity form of the receptor on a relatively small population of cells. Therefore we used a morphological approach that took advantage of the different dissociation rates of the 2 receptor types.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Neuron-like cells in long-term neural crest cultures are not targets of nerve growth factor.

It has been shown previously that a subpopulation of long-term (7-14 days) cultured neural crest cells undergoing differentiation possesses receptors for nerve growth factor (NGF). These cells are likely to be targets of NGF during the early stages of embryonic development. This study was conducted to determine whether cells exhibiting neuron-like characteristics (i.e. process formation, presence of putative neurotransmitters) in neural crest cultures have NGF receptors. This was accomplished by combining 125I-NGF radioautography and immunocytochemistry using antibodies against tyrosine hydroxylase, serotonin, and vasoactive intestinal polypeptide. Examination of light microscopic radioautographs revealed that none of the neuron-like cells with tyrosine hydroxylase-like, serotonin-like, or vasoactive intestinal polypeptide-like immunoreactivity bound 125I-NGF, and, therefore, do not possess NGF receptors. It is not known whether the lack of NGF receptors on neuron-like cells is due to the early developmental stage of these cells, or is caused by a difference in the microenvironment in vitro as compared to in vivo. The identity of the cultured neural crest cells which do possess NGF receptors remains to be determined.

Animals↗
PubMed1986

Characterization of nerve growth factor binding to cultured neural crest cells: evidence of an early developmental form of the NGF receptor.

Cultured neural crest cells undergoing differentiation have been shown to contain a subpopulation of cells with specific receptors for nerve growth factor (NGF). These cells are the potential targets of NGF during differentiation and development. This study was done to pharmacologically characterize the binding of NGF to long-term (1- to 3-week) cultures of quail neural crest cells. The data indicate that 125I-NGF binding was specific and saturable, with less than 20% nonspecific binding. Scatchard analysis revealed the presence of one type (class) of receptors with a binding constant (Kd) similar to that of the low-affinity binding site described for embryonic dorsal root and sympathetic ganglia (approximately 3.2 nM). This was corroborated by displacement experiments (Kd of 1.3 nM), in which 125I-NGF binding was measured in the presence of increasing concentrations of nonradioactive NGF. In addition, affinity labeling revealed that the 125I-NGF-receptor complex had a molecular weight of about 93K, characteristic of the low-affinity NGF receptor of PC12 cells. The NGF receptor of cultured neural crest cells was trypsin-sensitive, as is typical of the low-affinity NGF binding sites. These findings indicate that differentiating neural crest cells lack high-affinity 125I-NGF binding sites. In contrast, embryonic dorsal root and sympathetic ganglia cells, known NGF targets, have both high- and low-affinity receptors. Measurements of the differential release of surface-bound 125I-NGF indicated that a relatively small amount (about 14%) of NGF is internalized over a 1-hr period. Cultured neural crest cells which bear NGF receptors were also shown by light microscopic radioautographic techniques to incorporate [3H]thymidine. I suggest, therefore, that cultured neural crest cells which have not terminally differentiated, as judged by morphological criteria and continued proliferation, may express an early developmental form of the NGF receptor.

Animals↗
PubMed1986

Nerve growth factor receptors on dissociated neurofibroma Schwann-like cells.

Neurofibromatosis is a disorder which predominantly involves cellular elements of peripheral neural sheaths. Little is known about the regulation of differentiation and proliferation of cells comprising neurofibromas. Because nerve growth factor-like activity may be present in neurofibromas and the cells comprising neurofibromas are neural crest derivatives, we have investigated whether nerve growth factor (NGF) receptors are present on cells from dissociated dermal neurofibromas. Using 125I-NGF to measure binding to cultured cells in suspension and for autoradiography, we identified a population of cells having characteristics of Schwann cells which exhibited saturable 125I-NGF binding. This binding is characteristic of the "fast" (low affinity) NGF receptor, having a Kd of approximately 1 nM and a Bmax of at least 120 fmol/10(6) cells. Less than 20% of the bound 125I-NGF (5 ng/ml) is not displaced when transferred to 0 degrees C by an excess of unlabeled NGF (10 micrograms/ml) and is therefore bound to either "slow" (high affinity) sites or is rapidly internalized. NGF receptors with characteristics of fast sites have recently been reported on Schwann-like cells from chick dorsal root ganglia [Zimmerman, A., and Sutter, A. Beta nerve growth factor (beta NGF) receptors on glial cells. Cell-cell interaction between neurones and Schwann cells in culture of chick sensory ganglia. EMBO J., 2: 879-885, 1983]. The identification of NGF receptors on both fetal chick dorsal root ganglia and neurofibroma Schwann-like cells suggests that NGF may have a role in the regulation of Schwann cell function in both normal development and in neurofibromatosis.

Cells, Cultured↗
PubMed1985

Appearance of nerve growth factor receptors on cultured neural crest cells.

Light microscopic radioautography of differentiating quail neural crest cultures (1 to 2 weeks after explanation) incubated with Iodine-125-labeled nerve growth factor (125I-NGF) revealed that approximately 35% of the cells bound NGF. The binding was specific and saturable; it was blocked by an excess of nonradioactive NGF, and was not detected following incubation with biologically inactive 125I-NGF. In addition, the binding did not appear to be blocked or diminished by insulin. Cell cultures prepared from somites or notochord showed no specific binding of 125I-NGF. Melanocytes comprised approximately 10% of the cell population in these cultures and appeared to be unlabeled. The subpopulation of cells with NGF receptors that were morphologically similar to other non-melanocyte unlabeled cells present in the neural crest cultures are probably the targets of the factor during differentiation and development. In contrast, there was no evidence of 125I-NGF binding by premigratory neural crest (adherent to the isolated neural tube) or by early migratory neural crest cells (24 hr after explantation). Both of these types of neural crest cells are relatively undifferentiated. The cells of the neural tube were also unlabeled. The binding of 125I-NGF to differentiating neural crest cells was not noticeably diminished by a brief pretreatment with trypsin or Dispase, enzymes used in the isolation of neural tubes. Hence, the absence of NGF receptors on premigratory neural crest and early migratory neural crest cultures was not due to enzymatic alterations of the receptor. It seems, therefore, that receptors for NGF appear on neural crest cells during the time when these cells are acquiring their phenotypic characteristics.

Animals↗
PubMed1984

Association of 125I-nerve growth factor with PC12 pheochromocytoma cells. Evidence for internalization via high-affinity receptors only and for long-term regulation by nerve growth factor of both high- and low-affinity receptors.

Association of 125I-nerve growth factor (NGF) with PC12 pheochromocytoma cells was studied. Surface-bound and internalized NGF were distinguished by differential release of the former at low pH, high salt. Binding to the surface was rapid; at 0.2 nM (5 ng/ml) 125I-NGF, this was near-maximal within 5 min. Internalization, in contrast, did not start until about 2 min after NGF exposure and, thereafter, proceeded linearly for at least 1/2-1 h. By the latter time, approximately 75% of total bound NGF was within rather than on the surface of the cells. Binding versus concentration experiments indicated two distinct classes of surface binding sites. For both naive cells and cells treated with NGF for at least a week (primed cells), about 7% of the receptors had an apparent binding constant of about 0.3 nM; the remaining sites half-saturated at approximately 4 nM NGF. The number of each type of site was 3--4-fold higher/mg of protein in primed cells. For both naive and primed cultures, internalization appeared to be mediated by a single class of uptake sites which half-saturated at about 0.3 nM. The maximal rate of uptake by primed cells (200 fmol/h/mg protein) was about twice that for naive cells. Light and electron microscopic autoradiography indicated that the density of binding was substantially higher in primed cultures and that this increase took place over a time course of days to weeks. These findings suggest that NGF brings about long-term increases in its own high- and low-affinity surface receptors, but is internalized only via the high-affinity sites.

Adrenal Gland Neoplasms↗
PubMed1983

Receptor-mediated entry of beta-glucuronidase into the parasitophorous vacuoles of macrophages infected with Leishmania mexicana amazonensis.

125I-labeled rat preputial gland beta-glucuronidase was shown by light and electron microscopic radioautography to accumulate within the parasitophorous vacuoles of in vitro derived bone marrow macrophages infected with Leishmania mexicana amazonensis. beta-glucuronidase uptake was mediated by the mannose receptor, since the penetration of the ligand was inhibited by mannan. Uptake was detected as soon as 4 h after incubation of infected cells with the ligand, and increased at 24 and 48 h. The label persisted in the vacuoles for at least 24 h after a 24-h pulse with the ligand, a finding compatible with the relatively long half-life of labeled beta-glucuronidase in normal macrophages. Parasitophorous vacuoles were also labeled in macrophages exposed to the ligand only before infection, indicating that secondary lysosomes containing the ligand fused with the parasitophorous vacuoles. Another mannosylated ligand, mannose-BSA, which, in contrast to beta-glucuronidase, is rapidly degraded in macrophage lysosomes, did not detectably accumulate in the vacuoles. The results support and extend information previously obtained with electron opaque tracers that emphasizes the phagolysosomal nature of Leishmania parasitophorous vacuoles. In addition, the results suggest that appropriate mannosylated molecules may be used as carriers for targeting of leishmanicidal drugs to the parasitophorous vacuoles of infected macrophages.

Animals↗
PubMed1983

Electron microscopic radioautographic localization of iodinated nerve growth factor bound to and internalized by PC12 cells.

Nerve growth factor (NGF) has many effects on sympathetic and sensory neurons, but the mechanisms by which NGF exerts its actions are unknown. We have determined the localization of bound and internalized 125I-NGF by light and electron microscopic radioautography on a cell line derived from a rat pheochromocytoma (PC12). In response to NGF, PC12 cells cease mitosis and develop neuron-like processes. We have localized 125I-NGF (5 ng/ml) in cells without previous exposure to NGF (naive) after a continuous incubation with 125I-NGF for 2 min, 1 hr, 6 hr, 1 day and 1 week, as well as in cells that were grown with NGF (50 ng/ml) for 1 week (primed) and then exposed to 125I-NGF for 15 min, 1 hr, 6 hr, and 1 day. Examination of whole mount radioautographs revealed that all cells were labeled and that the distribution of grains was homogeneous. Primed cells were labeled on neurites and growth cones, as well as on cell bodies, and also had a greater density of labeling than naive cells. These patterns were identical for all time points studied, with the exception that "hot spots" of radioactivity appeared along neurites following a long incubation with 126I-NGF (longer than 6 hr). Electron microscopic radioautography revealed that these "hot spots" correspond to accumulation of grains in aggregates of lysosomes. The binding of 125I-NGF was specific, since control cultures (excess nonradioactive NGF) exhibited only background levels of grains. Quantification of electron microscopic radioautographs revealed that 70 to 95% of the grains were internalized after 15 min. The only cellular components labeled above random distribution levels were the plasma membrane, lysosomes, and the nuclear membrane. Each of these structures exhibited "down-regulation" of specific binding in naive cells after 6 hr of incubation. The cytosol, polyribosomes, dense cored granules, heterochromatin, and euchromatin showed labeling at or below the levels expected from random distribution of grains within the cell. The distribution of grains about the nuclear membrane also suggested an association with 125I-NGF. These data indicate that a large proportion of NGF "bound" to target cells is in fact internalized, and are consistent with some, but not other models for NGF's mechanism of action.

Adrenal Gland Neoplasms↗
PubMed1981

Separation of dissociated thyroid follicular and parafollicular cells: association of serotonin binding protein with parafollicular cells.

Parafollicular cells (PC) of the sheep thyroid gland are neural crest derivatives that synthesize and release the biogenic amine serotonin (5-HT) as well as the hormone calcitonin. The thyroid also contains a highly specific serotonin-binding protein (SBP). Separation of dissociated thyroid cells was done to study the cellular localization of SBP and to develop a means of isolating PC for study. Various methods were used to obtain an enriched and purified population of PC. Minced thyroid glands were enzymatically dissociated and the cells were layered on a Ficoll linear density gradient. Fractions obtained from the gradient were examined for cell number, viability, 5-HT concentration, SBP activity, and morphology by electron microscopy. One of the fractions was found to be enriched in PC. High levels of 5-HT and SBP were also found in this fraction, whereas these levels were low where the majority of cells were found. This PC-rich fraction, however, contained numerous follicular cells (FC); therefore, additional approaches to cell separation were used. FC can be stimulated in vitro with thyroid stimulating hormone (TSH) to become intensely phagocytic. When stimulated cells were incubated in the presence of silica microspheres, the FC engulfed the microspheres, which were toxic to them. PC did not become phagocytic and were unharmed by the microspheres. Suspended cells, after incubation with microspheres, were centrifuged on a discontinuous gradient, and a PC-rich fraction was obtained. Silica, however, interfered with analysis of SBP. Another method to take advantage of the phagocytic potential of FC was therefore used. TSH-stimulated cell suspensions were passed through a column of sepharose to which thyroglobulin had been coupled. Stimulated FC apparently adhered to the beads and were retained by the columns. Fractions eluting from the columns were greatly enriched with PC. These fractions contained high levels of 5-HT and SBP, and considerably reduced FC contamination was found by quantitative electron microscopy. It is concluded that SBP is localized to PC in the sheep thyroid. The idea that these cells resemble serotonergic neurons in their mechanisms of 5-HT storage is supported.

Animals↗
PubMed1980

Phylogeny of enteric serotonergic neurons.

Serotonergic neurons have previously been identified in the enteric nervous systems of humans, subhuman primates, rodents, and rabbits. The distribution of enteric serotonergic neurons in lower vertebrates was examined in order to determine if these neurons are restricted to mammals and, if they are found more generally amongst vertebrates, when they first appear in vertebrate phylogeny. Since mammalian enteric serotonergic neurons take up 3H-serotonin by a highly specific mechanism, the radioautographic demonstration of axonal uptake of 3H-serotonin was used as the primary tool in looking for these neurons. As controls, conditions known to interfere with 3H-serotonin uptake by mammalian enteric neurons were also examined. These controls included incubation with 10 microM fluoxetine, a specific antagonist, incubation in Na+-free medium, and incubation in the presence of a 100-fold excess of nonradioactive serotonin. Radio-autographic labeling had to be absent or greatly reduced under all three control conditions for labeling by 3H-serotonin to be considered specific. Labeled enteric axons were found in cyclostomes (hagfish), teleosts (goldfish), and amphibia (bull-frog) but not in tunicates (sea squirt; sea vase) or echinoderms (sea cucumber). In addition, the serotonin concentration was measured in the intestine of two vertebrates, hagfish and goldfish, that do not have serotonin-containing enterochromaffin cells. Serotonin was found in both; in hagfish, the amine concentration was highest in preparations of muscularis externa containing the myenteric plexus. It is concluded that enteric serotonergic neurons arose early in vertebrate evolution, possibly in an ancestral chordate resembling amphioxus, although probably not in more primitive prevertebrates, and that they are a general feature of the vertebrate bowel.

Animals↗
PubMed1979

Localization of a highly specific neuronal protein, serotonin binding protein, in thyroid parafollicular cells.

A highly specific serotonin binding protein (SBP) has been found in serotonergic neurons in both brain and gut. This protein has an extremely high affinity for serotonin and may be a storage protein. Serotonin is found in many endocrine cells, including parafollicular cells of the sheep thyroid, as well as in neurons. SBP is also present in sheep thyroid. The present study was done to localize the protein in the gland. Thyroid glands were divided into five segments. Concentrations of serotonin and SBP, as well as parafollicular cell volume were measured in each. Serotonin was assayed by enzymatic conversion to melatonin using tritiated S-adenosylmethionine. SBP was assayed by molecular sieve chromatography on sephadex G-50. The relative volume of parafollicular cells was obtained by stereological analysis of electron micrographs. Experiments were also done to demonstrate these cells by histofluorescence and radioautography following incubation with tritiated 5-hydroxytryptophan. Good correlations were found between serotonin and SBP concentrations, and parafollicular cell volume. These peaked in the rostro-central portion of the gland and were minimal at the poles. We conclude that thyroid SBP is probably localized in parafollicular cells.

Animals↗