Nerve growth factor in mouse saliva. Rapid isolation procedures for and characterization of 7 S nerve growth factor

Epigenetic control of neurobehavioural plasticity: the role of neurotrophins

Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are two neurotrophins involved in the differentiation, growth and maintenance of selected peripheral and central populations of neuronal cells, during development and at adulthood. Furthermore, neuronal activity enhances expression and action of these neurotrophins, modifying synaptic transmission and connectivity. Neurotrophin production has been shown to be experience-dependent. In particular, during early developmental phases, experiences such as maternal deprivation or exposure to an enriched environment markedly affect NGF and BDNF levels. At adulthood, psychosocial stress has been shown to markedly alter NGF and BDNF levels, both in plasma and selected brain areas, including the hypothalamus and hippocampus. These results have been extended to humans, showing that NGF levels are enhanced by emotional stress induced by parachute jumping. Overall, these findings suggest a role of neurotrophins as factors mediating both short- and long-term effects of experience on brain structure and function.

Spatial and temporal localization of secretory IgA in healing tooth extraction sockets in a rabbit model

PURPOSE

The purpose of this study was to look at the spatial and temporal localization of secretory IgA in healing tooth extraction sockets in a rabbit model.

MATERIALS AND METHODS

Twenty-four male New Zealand White rabbits were used in the study. Incisor teeth were extracted from both jaws, and the healing extraction socket with the surrounding jaw bone was harvested at 48 hours, 4 days, and 1, 2, 4, 8, 12, and 16 weeks. Tissues were fixed, decalcified, and processed for hematoxylin and eosin and immunohistochemical staining. The sections were stained to detect secretory IgA. The stained sections were then imaged, and an automated computer program was used to detect the brown 3,3'-diaminobenzidine stain that represented the secretory IgA. The data were obtained in the form of percentage area and intensity of stain and analyzed using analysis of variance (Tukey-Kramer and Scheffé's tests).

RESULTS

Spatial and temporal differences in localization of secretory IgA were observed across time frames in both jaws.

CONCLUSION

The results of this study showed definite trends in the spatial and temporal localization of secretory IgA in healing tooth extraction sockets in a rabbit model.

Mast cells, neuropeptides, histamine, and prostaglandins in UV-induced systemic immunosuppression

There is a direct correlation between dermal mast cell prevalence in dorsal skin of different mouse strains and susceptibility to UVB-induced systemic immunosuppression; highly UV-susceptible C57BL/6 mice have a high dermal mast cell prevalence while BALB/c mice, which require considerable UV radiation for 50% immunosuppression, have a low mast cell prevalence. There is also a functional link between the prevalence of dermal mast cells and susceptibility to UVB- and cis-urocanic acid (UCA)-induced systemic immunosuppression. Mast cell-depleted mice are unresponsive to UVB or cis-UCA for systemic immunosuppression unless they are previously reconstituted at the irradiated or cis-UCA-administered site with bone marrow-derived mast cell precursors. cis-UCA does not stimulate mast cell degranulation directly. Instead, in support of studies showing that neither UVB nor cis-UCA was immunosuppressive in capsaicin-treated, neuropeptide-depleted mice, cis-UCA-stimulated neuropeptide release from sensory c-fibers which, in turn, could efficiently degranulate mast cells. Studies in mice suggested that histamine, and not tumor necrosis factor alpha (TNF-alpha), was the product from mast cells that stimulated downstream immunosuppression. Histamine receptor antagonists reduced by approximately 60% UVB and cis-UCA-induced systemic immunosuppression. Indomethacin administration to mice had a similar effect which was not cumulative with the histamine receptor antagonists. Histamine can stimulate keratinocyte prostanoid production. We propose that both histamine and prostaglandin E(2) are important in downstream immunosuppression; both are regulatory molecules supporting the development of T helper 2 cells and reduced expression of type 1 immune responses such as a contact hypersensitivity reaction.

Nerve growth factor, neuropeptides, and mast cells in ultraviolet-B-induced systemic suppression of contact hypersensitivity responses in mice

The induction of systemic immunosuppression following ultraviolet B radiation exposure has been linked with the release of inflammatory and immunomodulatory mediators by cells of the epidermis and dermis. Nerve growth factor has not previously been linked with ultraviolet-B-induced immunosuppressive effects. Nerve growth factor antibodies abrogated ultraviolet-B-induced systemic suppression of contact hypersensitivity responses in BALB/C mice. Subcutaneous injection of nerve growth factor (20 microg per mouse) into dorsal skin 5 d before hapten sensitization on ventral skin suppressed contact hypersensitivity responses in mast-cell-replete but not Wf/Wf mast-cell-depleted mice. Nerve growth factor injected 24 h prior to challenge was not able to suppress the efferent phase of the contact hypersensitivity response. Subcutaneous injection of nerve growth factor (20 microg per mouse) did not suppress contact hypersensitivity responses in capsaicin-pretreated (neuropeptide-depleted) BALB/c mice, and thus sensory c-fibers are necessary for nerve-growth-factor-mediated systemic suppression of contact hypersensitivity responses. Increased concentrations of nerve growth factor within epidermal keratinocytes 8 h after ultraviolet B irradiation were confirmed immunohistochemically. These findings support a role for keratinocyte-derived nerve growth factor via its action on sensory c-fibers, and subsequent release of neuropeptides to mediate mast cell degranulation in systemic suppression of contact hypersensitivity responses in mice following ultraviolet B exposure.

Early days of the nerve growth factor proteins

Adult male mouse submaxillary glands served as the preferred starting material for the isolation of the nerve growth factor (NGF) proteins in most of the isolation studies done. Two types of NGF proteins were isolated from extracts of the gland, a high-molecular-weight 7S NGF complex and a low-molecular-weight protein variously called NGF, betaNGF, or 2.5S NGF. The latter, which mediated all known biological functions of NGF, were closely related forms of a basic NGF dimer in which the N and C termini of two monomers (chains) were modified by proteolytic enzymes to different extents with no effect on biological activity. The betaNGF dimer showed a novel protein structure in which the two chains interacted non-covalently over a wide surface. Correspondingly, the betaNGF dimer was found to be unusually stable and the form through which NGFs actions were mediated at physiological concentrations. The betaNGF dimer was one of three subunits in 7S NGF; the other two were the gamma subunit, an arginine esteropeptidase or kallikrein, and the alpha subunit, an inactive kallikrein. Two zinc ions were also present in the complex and contributed greatly to its stability. There was much debate about whether 7S NGF was a specific protein complex of interacting subunits and, if so, what functions it might play in the biology of NGF. Observations of the inhibition of the enzyme activity of the gamma subunit and of the biological activity of betaNGF in 7S NGF were important in determining that 7S NGF was a naturally occurring complex and the sole source of NGF in the gland extract or in saliva. Specific interactions between the active site of the gamma subunit and the C-terminal arginine residues of the NGF chains, confirmed in the three-dimensional structure of 7S NGF, suggested a role for the gamma subunit in pro-NGF processing during the assembly of 7S NGF. In spite of the detailed knowledge of 7S NGF structure, no information on the role of this complex in the neurobiology of NGF has emerged. With the exception of the submaxillary gland of an African rodent, no other source of NGF has been convincingly shown to synthesize the alpha and gamma subunits, and they may well be irrelevant to NGFs actions.

Psychosocial vs. "physical" stress situations in rodents and humans: role of neurotrophins

Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are well-studied polypeptide growth factors involved in the development and maintenance of specific peripheral and central populations of neuronal cells. In addition to its role as a neurotrophic agent, NGF controls very complex functions in vertebrate physiology. A variety of cells outside the nervous system are in fact able to synthesize NGF including epithelial cells, fibroblasts, lymphocytes, and macrophages. NGF target cells have been identified in the nervous, immune, and endocrine systems, suggesting that NGF may operate through multiple paths to ultimately regulate physiological homeostasis and behavioral coping. We used a mouse model of social stress to demonstrate that NGF levels increase both in plasma and in the hypothalamus following intermale aggressive interactions. The investigation has been extended to other species, including humans, to show that labour, lactation, and the anticipation of the first jump with a parachute also result in increased NGF plasma levels and in changes in the distribution of NGF receptors on lymphocytes. BDNF activation is caused by both physical and social stress events. The aim of this review is to (1) outline the current understanding of the roles of NGF and BDNF in stress-related physiological changes in vertebrates, in particular for physical vs. psychological stressors, which may activate both similar and different neurobiological pathways, and (2) summarize recent efforts to derive pharmacological strategies from the increasing body of BDNF and NGF neurobehavioral data.

Adaptation after small bowel resection is attenuated by sialoadenectomy: the role for endogenous epidermal growth factor

BACKGROUND

Epidermal growth factor (EGF) is likely involved during adaptation after small bowel resection (SBR) because some studies have shown enhanced adaptation by EGF administration. Because the major source of endogenous EGF in mice is the submandibular glands, we sought to determine the effect of submandibular gland excision (SAL) and luminal or systemic EGF replacement on adaptation after SBR.

METHODS

A 50% proximal SBR or Sham-SBR (bowel transection and reanastomosis) was performed on male C57BL/6 mice after either SAL or gland mobilization only. Additional mice underwent both SBR and SAL and then received daily EGF or saline solution by intraperitoneal or orogastric administration. At 1 week, adaptation was characterized in the ileum as changes in villus height, DNA, and protein content.

RESULTS

SAL significantly attenuated the increase in ileal villus height, total protein, and DNA content after SBR. Both systemic and oral EGF reversed these findings equally and significantly augmented all parameters of intestinal adaptation after SAL.

CONCLUSIONS

Submandibular EGF is important for the adaptive response to massive SBR. As both luminal and systemic EGF equally reversed the findings following SAL and SBR, the specific site of action for endogenous EGF during adaptation is either the luminal or basolateral surface of the enterocyte.

NGF regulatory role in stress and coping of rodents and humans

Nerve growth factor (NGF) is a polypeptide growth factor which exerts trophic and differentiative effects on specific peripheral and central populations of neurons. Recent data showing that various cellular types of the endocrine and immune systems are able to synthesize and release NGF have suggested that this neurotrophic factor may also play an important role in vertebrate physiologic homeostasis. Previous studies using a mouse model of aggressive behavior have shown that NGF levels increase in both plasma and the CNS following intermale agonistic encounters. More recently, we have extended this research area to include other species: in particular, humans. The data now available indicate that labour and lactation, or the occurrence of a stressful event such as the very first jump with a parachute causes in NGF plasma levels as well as changes in the distribution of NGF receptors on lymphocytes. This review aimed to outline the current understanding of NGF role in vertebrates in stress-related events.

Evidence of a role for nerve growth factor in the effect of sialoadenectomy on body temperature of parasite-infected mice

Mice infected with Schistosoma mansoni were used to investigate the role of the submaxillary salivary gland and nerve growth factor (NGF) in temperature response. The results showed that the infection increased (36.5 +/- 0.3 vs 35.7 +/- 0.2), while sialoadenectomy decreased (34.4 +/- 0.2 vs 35.1 +/- 0.2) body temperature. These temperature changes were associated with high or low circulating NGF levels, respectively. It was also found that infection altered the distribution of oxytocin-positive neurones in the hypothalamus and that administration of 20 mu g of purified NGF in normal mice raised (36.1 +/- 0.2 vs 35.1 +/- 0.2) and of NGF antibodies decreased (34.0 +/- 0.2 vs 35.1 +/- 0.2) body temperature. Taken together, these observations suggest that salivary NGF influences the temperature set-point in adult rodents, but the mechanism regulating these events remains to be elucidated.

Membrane properties of cultured glial cells obtained mechanically or by enzymatic dissociation: differential alterations by gangliosides

Rat astroglial cells were obtained either mechanically or by enzymatic dissociation and some properties of the primary and secondary cultures were studied. Differences in the ganglioside amount, taurine uptake, membrane fluorescence anisotropy, or their respective modulation by total brain gangliosides confirmed that although the two types of cultures are morphologically similar, they are biochemically distinct.

Evidence for an NGF-induced autocrine neurotrophic potential of glial cells in nervous system development

NGF receptor bearing peripheral glial cells, purified from chicken embryo dorsal root ganglia, were found to secrete neurite growth promoting activity (NGPA) but no NGF (detection limit 1 pM). If, however, minute concentrations of NGF (2 pM) were added to the glial cultures, an autocrine response was observed. Levels of NGF-like activity in the medium rose up to 50-fold. Induction of this autocrine response occured within a narrow range of NGF concentrations. NGPA production was not affected by addition of NGF. Coculture with neurons influenced the neurotrophic factor production. The data suggest that glial cells can "sense" traces of NGF and regulate its availability during neural development.

Distribution and metabolism patterns of plasma 7S- and beta-NGF in the adult male rat

There is a great deal of controversy on the existence of NGF in body fluids and tissues. To date it remains unknown whether this peptide accumulates preferentially at significant levels in different organs. Thus we undertook the evaluation of kinetic parameters of the disappearance of blood of 125I-7S-NGF and 125I-beta-NGF after intravenous injection in male adult rats. Our results indicate that the plasma half-life of 125I-7S-NGF is approximately twice as long as for 125I-beta-NGF (respectively 61.7 +/- 11.7 min and 36.3 +/- 2.2 min) while the distribution volume is not significantly different between both peptides. Furthermore, the uptake of radioactive NGF by different tissues seems very low as shown by 125I-7S-NGF and 125I-beta-NGF content of the sampled organs compared to the plasma concentration at the same time. These results indicate that the tissue uptake of circulating 7S and beta-NGF is very low in the adult rat. Thus in these animals NGF did not cross the blood-brain barrier and did not accumulate in peripheral organs which are known to contain subsequent amounts of this peptide. This lack of deposition might be due to a binding with plasma proteins (probably alpha 2-macroglobulin).

Basic fibroblast growth factor promotes adhesive interactions of neuroepithelial cells from chick neural tube with extracellular matrix proteins in culture

Fibroblast growth factors have been increasingly assigned mitogenic and trophic roles in embryonic and postnatal development of the nervous system. Little is known, however, of their functional roles in early embryonic neural development at the neural tube stage. We have examined the effect of basic fibroblast growth factor (bFGF) on the adhesive behavior in culture of dissociated brachio-thoracic neural tube cells from 26- to 30-somite stage chick embryos. Cells plated on collagen-coated substratum at a low density attach to the substratum but show poor cell spreading. Addition of bFGF markedly promotes cell spreading, yielding an epithelial morphology. This effect becomes discernible 6–8 hours after cell plating with bFGF and is completed by 24 hours, with half-maximal and maximal effects attained at around 0.4 and 10 ng/ml, respectively. The number of cells remain largely constant up to 24 hours, and then cell survival and/or mitogenic effects of bFGF become apparent. The cell spreading effect is abolished by cycloheximide treatment, inhibited by the anti-beta 1-integrin antibody CSAT, and accompanied by about twofold increases in the expression of beta 1-integrin and vinculin, components of focal adhesion complexes. Cells cultured with bFGF for 24 hours exhibit enhanced cell attachment and cell spreading with little time lag following cell plating. In earlier embryonic stages, developmentally less mature cells depend much more on bFGF for their cell spreading and survival, while in later stages the cell spreading response to bFGF becomes undetectable as neural tube develops to spinal cord. The cell spreading effect of bFGF is realized on specific extracellular matrix proteins including laminin, fibronectin and collagen, but not on vitronectin, arg-gly-asp peptide (PepTite-2000), poly-L-ornithine or others. These results suggest that, in an early stage of neural tube development, bFGF is involved in the developmental regulation of adhesive interactions between neuroepithelial cells and the extracellular matrix, thereby controlling their proliferation, migration and differentiation.

PC12 cells can be induced to produce, but do not process, the neurotensin/neuromedin N precursor

Neurotensin and neuromedin N are two biologically active, related peptides that are encoded in the same precursor molecule. In the rat, the precursor consists of a 169-residue polypeptide containing in its C-terminal region one copy each of neurotensin and neuromedin N. Four Lys-Arg sequences, which are thought to represent putative processing sites, occur in the precursor molecule. Studies by others have shown that rat pheochromocytoma PC12 cells produced neurotensin and dramatically increased their neurotensin/neuromedin N precursor mRNA content in response to a combination of nerve growth factor, dexamethasone, forskolin, and Li+. Here, we investigated the effects of this combination of inducers on the posttranslational processing of the neurotensin/neuromedin N precursor in PC12 cells. Radioimmunoassays coupled to HPLC and arginine-directed tryptic cleavage of cell extracts were performed with five antisera specific for precursor sequences adjacent to basic doublets. Thus, mature neurotensin and neuromedin N represented less than 1% of the total precursor content in PC12 cells. The PC12 cell line may represent an interesting model with which one could transfect the recently cloned prohormone convertases PC1 and PC2, thereby allowing the study of the role of these enzymes in the processing of the neurotensin/neuromedin N precursor.

Nerve growth factor and a fibroblast growth factor-like neurotrophic activity in cerebrospinal fluid of brain injured human patients

We report here the presence of nerve growth factor (NGF) in the cerebrospinal fluid (CSF) of some brain-injured human patients soon after injury. The NGF was quantified against a recombinant human NGF standard in a two-site enzyme-linked immunoabsorbent assay using antibodies against murine B NGF. None of the samples collected more than 2 days after injury contained detectable levels of NGF. When the CSF was assayed for the ability to promote neurite outgrowth from PC12 cells, neurite outgrowth was reduced, but not completely blocked, by antibodies to B NGF, suggesting that there were other biologically active factors present. Fibroblast growth factor (FGF) also promotes neurite outgrowth in PC12 cells. In an initial screening for the presence of FGF, we employed PC12 cells and NR119 cells, PC12 variants in which recombinant human B NGF, but not recombinant human basic FGF, promotes neurite outgrowth. CSF from brain injury patients promoted greater neurite outgrowth from PC12 cells than from NR119 cells, suggesting that some of the biological activity associated with the injury CSF may be due a FGF. This possibility is further supported by the observation that the biological activity of the injury CSF significantly reduced by batch absorption with heparin Sepharose, suggesting the presence of a heparin binding neurotrophic factor. Neurotrophic factors appear in CSF as a consequence of diverse types of brain injury, including head trauma, intracerebral hemorrhage and subarachnoid hemorrhage. The appearance of these factors may reflect important common elements in the complex series of cellular changes occurring in response to acute brain injury.

Biochemical characterization of recombinant human nerve growth factor

Recombinant human nerve growth factor (rhNGF) was expressed and secreted by Chinese hamster ovary cells and purified to homogeneity using ion-exchange and reversed-phase (RP) chromatography. The isolated product was shown to be consistent with a 120-amino-acid residue polypeptide chain by amino acid composition, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), RP-HPLC, and mass spectrometry and with an N-terminal sequence consistent with that expected from the cDNA for human nerve growth factor. By size-exclusion chromatography, rhNGF behaves like a noncovalent dimer. Limited enzymatic digests of the 120-residue monomer produced additional species of 118 (trypsin, removal of the C-terminal Arg119-Ala120 sequence) and 117 (trypsin plus carboxypeptidase B, removal of the C-terminal Arg118-Arg119-Ala120 sequence) residues. Each of these species was isolated by high-performance ion-exchange chromatography and characterized by amino acid and N-terminal sequence analyses, SDS-PAGE, RP-HPLC, and mass spectrometry. All three species were present in the digests as both homodimeric and heterodimeric combinations and found to be equipotent in both the chick dorsal root ganglion cell survival and rat pheochromocytoma neurite extension assays.

Activity and biospecificity of proteolyzed forms and dimeric combinations of recombinant human and murine nerve growth factor

Purified recombinant human nerve growth factor (rhNGF) and submaxillary gland-derived murine NGF (muNGF) were characterized by amino acid composition, polyacrylamide gel electrophoresis (PAGE), reversed-phase HPLC (RP-HPLC), and high-performance ion-exchange chromatography (HPIEC). Limited tryptic digest of the N and C termini of the 120-residue form of rhNGF produced a species of 109 residues (10-118). The previously observed natural murine analogue of this variant, muNGF lacking the first eight N-terminal amino acids, was also isolated as a homodimer. Both species were purified using HPIEC and characterized by amino acid analysis, N-terminal sequence, PAGE, and RP-HPLC analysis. Each of the four homodimeric species was evaluated in some or all of the following biological assays for NGF: chick dorsal root and sympathetic ganglion assays and rat pheochromocytoma-12 cell line neurite extension assay. The 118-residue homodimeric versions of both rhNGF and muNGF displayed equivalent bioactivity, whereas the N terminal-modified molecules presented activity reduced by 50- to 100-fold. Utilizing HPIEC, we have examined the ability of the monomeric forms of any two of the homogeneous dimeric species of rhNGF to recombine. We have shown that not only can all of the previously described species form dimers by recombination, but an interspecies dimer can be created between muNGF and rhNGF.

Nerve growth factor: increased angiogenesis without improved nerve regeneration

Nerve growth factor (NGF) and laminin are important factors for neural development and regeneration. We examined the effects of increasing the local concentration and duration of action of NGF and laminin on peripheral nerve regeneration in the adult mouse sciatic nerve. A Silastic (silicone rubber) channel with intraluminal NGF solution was secured between transected nerve ends. The second channel tested, formed from a polysaccharide called chitosan, was prepared with NGF and laminin in the channel walls and provided a sustained release of NGF. At six weeks post-implantation, no improvement in nerve regeneration was identified in those channels prepared with NGF when comparing electromyographic thresholds (microA), maximum potentials (mV), nerve diameter, myelin sheath thickness, myelinated axon counts, or diameter. However, increased angiogenesis was demonstrated within the chitosan and Silastic channels prepared with NGF compared to those channels without NGF. Silastic exhibited minimal inflammation. Chitosan was associated with inflammation in many nerve channels.

beta-NGF-endopeptidase: structure and activity of a kallikrein encoded by the gene mGK-22

Mouse nerve growth factor (NGF) is cleaved at a histidine-methionine bond to release an NH2-terminal octapeptide (NGF1-8). The enzyme responsible, beta-NGF-endopeptidase, is structurally and functionally similar to gamma-NGF and epidermal growth factor-binding protein (EGF-BP) and cleaves mouse low molecular weight kininogen to produce bradykinin-like activity. These data have suggested that, like gamma-NGF and EGF-BP, beta-NGF-endopeptidase is a mouse glandular kallikrein. Evidence for a physiological role for NGF1-8 encouraged studies to further characterize the structure and function of this enzyme. Purified beta-NGF-endopeptidase migrated as a single band on isoelectric focusing and reducing SDS-polyacrylamide gels. As was expected, it removed NGF1-8 from NGF. Interestingly, enzymatic activity on an artificial substrate, and on NGF, was inhibited by NGF1-8 and by bradykinin. These studies further supported the view that beta-NGF-endopeptidase acts on both NGF and kininogen. The first 30 NH2-terminal amino acids of beta-NGF-endopeptidase were sequenced. This analysis demonstrated that the enzyme is encoded by the gene designated mGK-22 (Evans et al., 1987). The sequence of this gene corresponds to that of EGF-BP type A (Anundi et al., 1982; Drinkwater et al., 1987), and so studies were performed to determine whether or not beta-NGF-endopeptidase participates in EGF complex formation. Chromatographic and kinetic data gave no evidence that beta-NGF-endopeptidase is an EGF-binding protein. Our studies suggest that contamination of high molecular weight (HMW) EGF preparations with beta-NGF-endopeptidase erroneously led to earlier designation of the product of mGK-22 as an EGF-BP.(ABSTRACT TRUNCATED AT 250 WORDS)

Merkel cells in vitro: production of nerve growth factor and selective interactions with sensory neurons

A method has been developed for obtaining mixed primary cultures of dissociated epidermis enriched in Merkel cells. Merkel cells obtained from embryonic rat buccal pads were grown in serum-free medium and identified in vitro using a variety of histological and immunohistochemical markers. Quinacrine, a fluorescent amine, which has been used to identify Merkel cells in situ, labeled a morphologically distinct population of cells in vitro. Cells labeled with quinacrine had a large, phase bright nucleus with prominent nucleoli, surrounded by a phase dark perinuclear ring. Antibodies directed against neuron-specific enolase, another marker for Merkel cells in situ, and antibodies against a well-characterized neuroendocrine vesicle antigen also labeled this population of quinacrine fluorescent cells. Electron microscopic examination of our cultures indicated that cells containing characteristic features of Merkel cells including cytoplasmic dense-cored granules were present. A small but significant increase in the number of Merkel cells was observed over time in culture. Merkel cells supported the survival and outgrowth of both trigeminal ganglion sensory neurons and sympathetic neurons from the superior cervical ganglion in serum-free medium in the absence of exogenous nerve growth factor (NGF). Immunoblots probed with antibodies directed against NGF demonstrated that NGF was present in the medium taken from these cultures. NGF-like immunoreactivity colocalized to cells containing quinacrine fluorescence in situ and in vitro. Addition of antibodies directed against NGF to cocultures of Merkel cells and neurons decreased survival of sympathetic neurons by 90% and decreased survival of sensory neurons by 60%. These results suggest that Merkel cells are capable of providing trophic support for their normal complement of sensory neurons by producing NGF. Selective recognition of these targets was studied in vitro by characterizing the interactions between Merkel cells and growth cones from sensory or sympathetic neurons using both time-lapse videomicroscopy and standard morphometry of fixed cocultures. The majority of trigeminal ganglion sensory neurons (approximately 60%) extended growth cones onto clusters of Merkel cells. Neurites which contacted clusters of Merkel cells were significantly more highly branched than those growing on collagen. In contrast, the majority of sympathetic neurons (greater than 90%) failed to grow onto Merkel cells. Growth cones of sympathetic neurons often "collapsed" and retracted when contact was made with a cluster of Merkel cells. Fixation of Merkel cells with paraformaldehyde prior to coculture did not affect this difference between sensory and sympathetic neurite extension onto the Merkel cells. However, prior fixation of Merkel cells eradicated the apparent Merkel ce-induced branching of sensory neurites.(ABSTRACT TRUNCATED AT 400 WORDS)

Phosphatidylinositol is involved in the attachment of tailed asymmetric acetylcholinesterase to neuronal membranes

1. We analyzed the mode of attachment of 16 S tailed acetylcholinesterase (AChE; EC 3.1.1.7) to rat superior cervical ganglion (SCG) neuronal membranes. Using extractions by high-salt (HS) and nonionic detergent (Triton X-100), we found two pools of 16 S AChE. 2. The detergent-extracted (DE) 16 S AChE was tightly bound to membranes through detergent-sensitive, high-salt insensitive interactions and was distinct from high-salt-soluble 16 S AChE. The detergent-extracted (DE) 16 S AChE constituted a significant proportion of about one-third of the total 16 S AChE. 3. Treatment of the neuronal membranes by a phosphatidylinositol-specific phospholipase C (PIPLC) resulted in the release of some, but not all DE 16 S AChE, indicating that a significant amount of the neuronal DE 16 S AChE, about one-third, is anchored to membranes through a phosphatidylinositol containing residue. Thus, a covalent association of a glycolipid and catalytic or structural AChE polypeptidic chains occurs not only for dimeric AChE but also for the asymmetric species of AChE. 4. The complex polymorphism of AChE is due not only to different globular or asymmetric associations of catalytic and structural subunits but also to the alternative existence of a transmembrane domain or a glycolipid membrane anchor.

Structure and biosynthesis of nerve growth factor

Most of our knowledge about NGF comes from extensive study of the mouse submaxillary gland protein. NGF from this source is isolated as a high molecular weight complex consisting of beta-NGF and two subunits, alpha and gamma, belonging to the kallikrein family of serine proteases. There are few other tissues where NGF is found in sufficient quantities for protein purification and study, although new molecular biological techniques have accelerated the study of NGFs from a variety of species and tissues. Mouse submaxillary gland NGF is synthesized as a large precursor that is cleaved at both N- and C-terminals to produce mature NGF. This biologically active molecule can be further cleaved by submaxillary gland proteases. The roles of the alpha and gamma subunits in the processing of the beta-NGF precursor, the modulation of the biological activity of beta-NGF, and the protection of mature beta-NGF from degradation have been well studied in the mouse. However, the apparent lack of alpha and gamma subunits in most other tissues and species and the existence of a large family of murine kallikreins, many of which are expressed in the submaxillary gland, challenge the relevance of murine high molecular weight NGF as a proper model for NGF biosynthesis and regulation. It is important therefore to identify and characterize other NGF complexes and to study their subunit interactions, biosynthesis, processing, and regulation. This review points out a number of other species and tissues in which the study of NGF has just begun. At this time, there exist many more questions than answers regarding the presence and the functions of NGF processing and regulatory proteins. By studying NGF in other species and tissues and comparing the processing and regulation of NGF from several sources, we will discover the unifying concepts governing the expression of NGF biological activity.

Evidence that the B2 chain of laminin is responsible for the neurite outgrowth-promoting activity of astrocyte extracellular matrix

Extracellular matrix (ECM) derived from cerebral cortical astrocytes stimulates neurite outgrowth from pheochromocytoma (PC12) cells in the absence of the classical nerve growth factor (NGF). We have shown here that astrocyte ECM can also stimulate neurite outgrowth from primary cultures of central nervous system (CNS) neurons. Using PC12 cells for a quantitative assay, we also demonstrated that the neurite growth-promoting activity increased as the astrocytes matured in vitro: ECM from older astrocytes (3-12 weeks in vitro) exhibited two-fold more neurite growth-promoting activity than ECM for younger astrocytes (5 days to 2 weeks in vitro). We applied various antibodies to identify the neurite growth-promoting factor of astrocyte ECM and found that anti-laminin inhibited neurite outgrowth by 50%, whereas anti-fibronectin and anti-NGF had no effect. Immunoblots, using laminin chain-specific antibodies, and cDNA hybridization of laminin mRNA demonstrated that cultured astrocytes synthesize only the B2 chain of laminin. This suggests that the B2 chain of laminin suffices to stimulate neurite outgrowth.

Enucleation of the rat pheochromocytoma clonal cell line, PC12: effect on neurite outgrowth

The effect of removal of PC12 cell nuclei on neurite outgrowth was studied. Enucleation (80-90%) was accomplished in the presence of cytochalasin B using a centrifugation technique that exploited the very tight adhesivity of PC12 cells for a substratum composed of an extracellular matrix secreted by bovine corneal endothelial cells in response to epidermal growth factor treatment. Neither nucleated nor enucleated PC12 cells showed significant neurite outgrowth on this particular matrix in the absence of nerve growth factor. In the presence of nerve growth factor both PC12 cell types initiated neurite outgrowth, but whereas neurites from nucleated cells grew continuously for two days, those from enucleated cells reached a maximum length after one day. The results suggest that neurite initiation but not continued neurite growth or stabilization can occur in the absence of transcription.

Growth cone-growth cone interactions in cultures of rat sympathetic neurons

Growth cones of sympathetic neurons from the superior cervical ganglia of neonatal rats were studied using video-microscopy to determine events following contact between growth cones and other cell surfaces, including other growth cones and neurites. A variety of behaviors were observed to occur upon contact between growth cones. Most commonly, one growth cone would collapse and subsequently retract upon establishing filopodial contact with the growth cone of another sympathetic neuron. Contacts resulting in collapse and retraction were often accompanied by a rapid and transient burst of lamellipodial activity along the neurite 30-50 microns proximal to the retracting growth cone. In no instances did interactions between growth cones and either fibroblasts or red blood cells result in the growth cone collapsing, suggesting that a specific recognition event was involved. On several occasions, growth cones were seen to track other growth cones, although fasciculation was rare. In some cases, there was no obvious response between contacting growth cones. Growth cone-growth cone contact was almost four times more likely to result in collapse and retraction than was growth cone-neurite contact (45% vs 12%, respectively). These observations suggest that the superior cervical ganglion may be composed of neurons with different cell surface determinants and that these determinants are more concentrated on the surface of growth cones than on neurites. These results further suggest that contact-mediated inhibition of growth cone locomotion may play an important role in growth cone guidance.

Effect of nerve growth factor on the synthesis of amino acids in PC12 cells

Radioactive short-chain fatty acids preferentially label glutamine relative to glutamate in brain due to compartmentation of glutamine and glutamate. To determine whether this phenomenon occurs in a single cell culture model, we examined the effect of fatty acid chain length on the synthesis as well as pool size of selected amino acids in rat pheochromocytoma PC12 cells, a cell culture model of the large glutamate compartment in neurons. Intracellular 14C-amino acids were quantitated by HPLC, and the incorporation of [U-14C]-glucose, [1-14C]-butyrate, [1-14C]-octanoate, and [1-14C]-palmitate into five amino acids was measured in native and NGF-treated PC12 cells. NGF pretreatment decreased the intracellular concentration of amino acids as did addition of fatty acids but these effects were not additive. Specific activities of amino acids in native cells labelled by 14C-octanoate were 1,300 DPM/nmol, 490 DPM/nmol, 200 DPM/nmol, and 110 DPM/nmol for glutamate, aspartate, glutamine, and serine, respectively. No radioactivity was detected in alanine. Similar specific activities were noted when 14C-butyrate was the precursor; however, there was at least 5-fold less if 14C-palmitate was the precursor. Pretreatment of cells with NGF decreased the specific activity of amino acids by 25-65%. Specific activities of amino acids synthesized from 14C-glucose decreased in the following order: glutamate, 1,640 DPM/nmol; aspartate, 1,210 DPM/nmol; alanine, 580 DPM/nmol; glutamine, 275 DPM/nmol; and serine, 80 DPM/nmol for native cells. NGF pretreatment decreased the specific activities of glutamate and glutamine, but not of the other 3 amino acids. The preferred precursor for glutamate synthesis in native PC12 cells was glucose followed by octanoate, butyrate and palmitate (16:6:3:1).

Catecholaminergic cells and support cell precursors in neural crest cultures differentially express nerve growth factor receptors

Long-term neural crest cultures grown in the continuous absence of exogenous nerve growth factor (NGF) contain a subpopulation of cells with NGF receptors exclusively of the low affinity subtype (Kd of approximately 3.2 nM). The current studies combined immunocytochemistry, using GIN1 (a support cell marker) or tyrosine hydroxylase antibodies, with radioautography following exposure to iodinated nerve growth factor (125I-NGF). The majority of cells specifically binding 125I-NGF were found to be immunoreactive for GIN1, indicating that the primary cell phenotype expressing receptors for NGF appear to be support cell precursors, at least under these conditions. These cells are likely to be responsive to and/or dependent upon NGF; the nature of this response or dependency remains to be determined. Some cells exhibiting silver grains were not immunoreactive for GIN1, suggesting that other cell phenotypes in neural crest cultures also have NGF receptors. In addition, some neural crest cells were found that stained with GIN1 and lacked 125I-NGF binding. Tyrosine hydroxylase-like immunoreactive cells apparently did not bind 125I-NGF under these culture conditions. Catecholaminergic sympathetic and sensory neurons from embryonic ganglia, derived from the neural crest, express both the high and low affinity forms of the NGF receptor. In order to determine whether the microenvironment played a role in the type of catecholaminergic cells appearing in culture, neural crest cells were grown in the continuous presence of exogenous NGF. Under these conditions, many tyrosine hydroxylase-like immunoreactive cells were found that specifically bound 125I-NGF. In addition, silver grains were still detected on these cells following a chase with nonradioactive NGF, designed to eliminate 125I-NGF bound to low affinity sites. Therefore, the catecholaminergic cells possess both the low and high affinity forms of the receptor. NGF's ability to modulate tyrosine hydroxylase activity, as it does in mature catecholaminergic neurons, was tested in this system. Surprisingly, there was no statistically significant difference in tyrosine hydroxylase activity in cultures grown in the absence or presence of exogenous NGF. This raises the possibility that embryonic catecholaminergic cells are unable to respond to NGF in this specific way, even though the receptors for the factor are present.

Localization of high-affinity and low-affinity nerve growth factor receptors in cultured rat basal forebrain

Previous work has indicated that nerve growth factor specifically and selectively increases choline acetyltransferase and acetylcholinesterase in organotypic cultures of rat basal forebrain-medial septal area. To determine whether these actions are potentially receptor-mediated, organotypic and dissociated basal forebrain-medial septal area cultures were examined. Two independent methods, [125I]nerve growth factor binding and immunocytochemistry with a monoclonal nerve growth factor receptor antibody (192-IgG), detected specific receptors. The nerve growth factor receptors were localized to two different cellular populations: flat, large, non-neuron-like cells, and small, round, process-bearing, neuron-like cells. Dissociation studies with [125I]nerve growth factor suggested that high-affinity receptors were localized to the neuron-like population, while only low-affinity receptors were localized to the non-neuron-like cells. We tentatively conclude that nerve growth factor may elicit cholinergic effects by directly binding to high-affinity receptors on neurons. To begin examining receptor regulation, cultures were exposed to exogenous, unlabeled nerve growth factor continuously for 10 days before binding studies were performed. Prior exposure to nerve growth factor did not alter binding characteristics of the receptor, using the present methods.

Role of microtubules in the cytoplasmic compartmentation of neurons. II. Endocytosis in the growth cone and neurite shaft

We investigated the role of microtubules in the compartmentation of motility and endocytosis in the neurite shaft and growth cone of cultured chick sensory neurons. As reported previously by Letourneau and Ressler (J. Cell Biol., 98 (1984) 1355-1362), stimulating microtubule polymerization with taxol inhibits growth cone motility. In neurons that had grown for 18-30 h, taxol treatment caused growth cones to round up forming an obvious varicosity (taxol bulb) at the terminal. Removal of taxol allowed nearly immediate resumption of cortical motility in all 17 neurons observed by time-lapse videomicroscopy. However, only one of the 17 neurites was observed to elongate measurably even after 5 h of observation. In 14 cases taxol was rinsed out and the concentration of nerve growth factor was increased 10x, 11/14 neurites retracted within the next hour. Endocytic activity was investigated by incubating control and taxol treated neurons in either cationized ferritin or horseradish peroxidase for 30 min. The number and area of label-containing vesicles was measured along with the total area of the growth cone or taxol bulb. We found that taxol treatment caused a 7-fold decrease in the ratio of the area of the labeled vesicles to the area of growth cone or taxol bulb. Conversely, in neurite shafts, normally relatively quiescent with respect to endocytosis, those regions devoid of microtubules in both control and nocodazole-treated cells contained a high concentration of label-containing vesicles. We conclude that the presence of microtubules plays a role in regulating endocytic activity by the overlying cell cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of organophosphates and nerve growth factor on muscarinic receptor binding number in rat pheochromocytoma PC12 cells

Muscarinic receptor binding in PC12 cells is influenced by both nerve growth factor (NGF) and organophosphates. Treatment of PC12 cells with a single dose of NGF (50 ng, 7S NGF/ml) increased [3H]N-methylscopolamine ([3H]-NMS) binding sites approximately two-fold at 48 hr but did not change the Kd for this ligand. Exposure of PC12 cells to soman, 50 microM, decreased [3H]-NMS binding in both undifferentiated and NGF-treated cells; however, decreases in muscarinic binding induced by the organophosphate were only minimal after the first hour after treatment and were maximal at about 24 hr. Other organophosphates including sarin, tabun, and VX as well as the carbamate, pyridostigmine, also reduced [3H]-NMS binding in PC12 cells measured 24-48 hr after treatment. The order of potency of organophosphates in lowering [3H]-NMS binding was soman greater than sarin greater than VX greater than tabun greater than DFP. High amounts of VX (200 microM) but not the other organophosphates inhibited [3H]-NMS binding when added to cells during the course of binding assays. Decreases in muscarinic receptor binding induced by the organophosphates differed markedly from that produced by carbamylcholine, which decreased [3H]-NMS binding maximally 30 min after addition to the cells. Decreases in [3H]-NMS binding produced by carbamylcholine were antagonized by atropine, but reductions in muscarinic binding produced by the organophosphates were not reversed by atropine. Thus, decreases in muscarinic receptor binding induced in PC12 cells by organophosphates occur via a novel mechanism that does not involve agonist-induced receptor desensitization.

Developmental changes of nerve growth factor levels in sympathetic ganglia and their target organs

The predominant source of nerve growth factor (NGF) used by mature sympathetic neurons originates in their target organs (Heumann, R., Korsching, S., Scott, J., and Thoenen, H. (1984), EMBO J. 3, 3183-3189; Korsching, S., and Thoenen, H. (1985), J. Neurosci. 5, 1058-1061). We have determined the NGF content of two sympathetically innervated mouse organs, submandibular gland and heart ventricle, and of sympathetic ganglia from mouse and rat between embryonic Day 12 (E12) and adulthood. NGF levels were measured by a two-site enzyme immunassay (Korsching, S., and Thoenen, H. (1983), Proc. Natl. Acad. Sci. USA 80, 3513-3516). In heart ventricle and submandibular gland, NGF first became detectable around the time of initial innervation by sympathetic neurons (E12 and E13, respectively) and increased respectively 14- and 7-fold in the following 2 days, to reach adult levels already at E14 for heart ventricle (1.4 +/- 0.2 ng NGF/g wet wt). NGF in the superior cervical ganglion (SCG) was first detected at the same time as in its target organ, the submandibular gland. NGF content in the SCG then increased 6-fold during the next 2 days and continued to increase until the end of the third postnatal week, when adult levels were reached. Although the levels of NGF in the adult mouse submandibular gland are sexually dimorphic and six orders of magnitude higher than those in other sympathetic target organs, no sex difference in the NGF content was found in either developing submandibular gland or SCG until the end of the third postnatal week. Moreover, the steep NGF increase observed in the male submandibular gland after postnatal Day 18 (250-fold within the following 3 days and up to the 55,000-fold in the next 7 days) was not reflected in a corresponding increase in the NGF content of the male SCG. These data indicate that, in accordance with earlier findings (see Levi-Montalcini, R., and Angeletti, P. U. (1968), Physiol. Rev. 48, 534-569), SCG neurons do not have access to the large amounts of NGF synthesized during and after adolescence in the mouse submandibular gland. Our results support the concept that initial fiber outgrowth of sympathetic neurons is neither dependent on NGF nor mediated by it. The time course of NGF levels in the SCG is consistent with the concept that sympathetic neurons are provided with NGF by means of retrograde axonal transport from the innervated organs already early in development.

Cultured rat Schwann cells express low affinity receptors for nerve growth factor

Schwann cell cultures prepared from postnatal Sprague-Dawley rat sciatic nerves were used to demonstrate the presence of specific receptors for the beta-subunit of nerve growth factor (NGF) on rat Schwann cells. Indirect immunofluorescence microscopy with a monoclonal antineuronal NGF receptor (NGFR) antibody indicated that NGFR antigen was expressed on the surface of Schwann cells but not of endoneurial fibroblasts. Studies with 125I-NGF confirmed this distribution of NGFR in the cultures and showed that the Schwann cell NGFR had a single NGF binding affinity (Kd of 1.8 x 10(-9) M). 125I-NGF binding by the cultured Schwann cells increased with time in vitro, reaching a plateau level on the 4th day, but decreased with increasing age, reaching 40% of the neonatal value in Schwann cells isolated from 12-day-old rats. Treatment of the cultures with NGF did not alter Schwann cell phenotype, survival or proliferation.

Detection of molecules with nerve growth factor binding activity in medium conditioned by L-929 fibroblasts

L-929 fibroblasts (L cells) secrete a high molecular weight form of nerve growth factor (NGF) that is non-covalently bound and contains as part of its structure a molecule similar, if not identical, to beta-NGF in mouse submandibular glands. The other components of the NGF complex have not been characterized. In this study we used radiolabeled beta-NGF as a probe to detect molecules with NGF binding activity in L cell conditioned medium. The L cell NGF complex was dissociated at low pH, or with denaturants or detergents, and allowed to reassociate in the presence of 125I-beta-NGF. Radioactivity became associated with a complex that eluted in a high molecular weight volume on columns of Sephadex G-200 and Sephacryl S-500. Incorporation was saturable and did not occur under non-dissociating conditions. The complex was affinity cross-linked and studied by SDS gel electrophoresis. Radiolabeled molecules were observed with molecular weights of 151,000, 56,000 and 53,000. Labeling did not occur in the presence of excess unlabeled NGF or when cross-linking was done with fetal bovine serum, indicating that binding is specific and that binding activity is not derived from serum added to tissue culture medium. Solutions containing 7S NGF from mouse salivary glands were cross-linked by similar procedures but different banding patterns were observed. The data show that NGF binding molecules dissimilar from those in salivary glands are present in L cell conditioned medium.

Microtubule stability in severed axons

We examined severed axons of cat sympathetic nerves and severed neurites of cultured chick sensory neurons for evidence of extensive microtubule depolymerization. Cat sympathetic fibres fixed at various times after severing were cross-sectioned for electron microscopy from both cut ends. The number density of microtubules was determined at various times after severing for matched proximal and distal regions equidistant from cut ends. These data show that the number density of microtubules was nearly identical in proximal and distal fragments at 10, 20 and 60 min and at distances between 10 and 50 micron from the cut ends. In chick sensory neurites the microtubule array was examined in longitudinal sections. In order to define objectively a normal microtubule array, the distance between 100 microtubule pairs was measured in seven control neurites, giving a mean distance (+/- S.D.) of 33 nm +/- 19 nm. A normal array of microtubules was defined as having microtubules within 52 nm of their nearest lateral neighbour. Among 11 neurites at times from 1 to 15 min after transection, the mean distance from the cut tip to the first microtubule was 1.3 micron in proximal fragments and 0.5 micron in distal fragments. The mean distance to the normal microtubule array was 2.8 micron in proximal fragments and 2.1 micron in distal fragments. There was no trend or pattern with respect to the times after severing that the neurite was fixed and the amount of microtubule depolymerization. Our results show no evidence for stabilization of axonal/neurite microtubules by capping structures at their ends. We conclude that microtubule instability is unlikely to play a role in the response of axons to axotomy.

Nerve growth factor modulates tubulin transcript levels in pheochromocytoma PC12 cells

We report that nerve growth factor (NGF) can elevate tubulin transcript levels in cultured rat pheochromocytoma PC12 cells in a manner which correlates with its capacity to enhance neurite formation. The elevation is due, at least in part, to transcript stabilization. We have previously shown that insulin and its homologs can similarly enhance neurite outgrowth and tubulin mRNA levels in human neuroblastoma cells. Insulin by itself can neither induce neurite formation nor increase tubulin transcript levels in PC12 cells. However, both responses are potentiated in cells treated with the combination of insulin and NGF. The results together support the generalization that tubulin transcript levels are specifically elevated whenever neurite elongation is initiated by polypeptide neuritogenic factors.

Role of microtubules in the cytoplasmic compartmentation of neurons

We have examined the role of microtubules (MTs) in the development and maintenance of the cytoplasmic compartmentation of ribosomes in cultured embryonic chick sensory neurons. Control neurons show a sharp cytoplasmic demarcation between the ribosome-rich/MT-deficient 'translational' cytoplasm of the perikaryon and the ribosome-deficient/MT-rich 'expressional' cytoplasm of the axon-like neurites. Neurites treated with 1.0 microgram/ml nocodazole for 15-20 min show in addition to the depolymerization of MTs a clear loss of the cytoplasmic demarcation between the soma and neurite. We found a decreasing density of ribosomes with increasing distance from the soma in the nocodazole treated neurites. Ribosomes, as confirmed by their diameter and sensitivity to ribonuclease treatment, populated the first 100 microns of neurites at roughly the same density as found in the soma (150-300 ribosomes per microns2 in 50 mm longitudinal thin sections). The second 100 microns contained a lower density of ribosomes than the first, 20-60 per microns2, but still higher than controls. Distances past 200 microns were devoid of unambiguous ribosomes. Neurites amputated between 50 and 150 microns from the soma then treated with nocodazole contained a dense population of ribosomes in the proximal segment still attached to the soma, but few or none in the distal segment. We interpret these findings as evidence that ribosomes are able to move from the soma down the neurite after MT disassembly.(ABSTRACT TRUNCATED AT 250 WORDS)

Heparin modulation of the neurotropic effects of acidic and basic fibroblast growth factors and nerve growth factor on PC12 cells

Nerve growth factor (NGF) and acidic or basic fibroblast growth factor (aFGF and bFGF, respectively) induce neurite outgrowth from the rat pheochromocytoma cell line, PC12. The neurites induced by these three factors are stable for up to a month in cell culture in the continued presence of any of the above growth factors. bFGF (ED50 = 30 pg/ml) is 800 fold more potent in stimulating neurite outgrowth than aFGF (ED50 = 25 ng/ml) and 260 fold more potent than NGF (ED50 = 8 ng/ml). While the neurotropic activities of aFGF and NGF are potentiated by heparin, that of bFGF is both partially inhibited or stimulated, depending upon the concentration of bFGF. Radioreceptor binding experiments show that aFGF and bFGF bind to a common binding site on the PC12 cell surface. Affinity labeling studies demonstrate a single receptor with an apparent molecular weight of 145,000 daltons, which corresponds to the high molecular weight receptor identified in BHK-21 cells. NGF does not appear to compete with aFGF or bFGF for binding to the receptor. Heparin blocked the binding of bFGF to the receptor but had only a small inhibitory effect on the binding of aFGF to the receptor. Thus, it appears that heparin inhibition of the neurotropic effects of bFGF occurs, at least in part, by impairing the interaction of bFGF with the receptor, while having little effect on that of aFGF. The stimulatory effects of heparin on the neurotropic activity of aFGF, bFGF, and NGF may occur through a site not associated with the respective cellular receptor for the growth factors.

Nerve growth factor (NGF) receptor expression in chicken cranial development

In order to map the expression of receptors for nerve growth factor (NGF) during brain and cranial ganglia development, iodinated NGF (125I beta NGF) was used as a probe in an autoradiographical analysis performed between embryonic day 3 (E3) and posthatching day 3 (P3) of chicken development. Heavy autoradiographic labelling was observed at the classical NGF target sites, the proximal cranial sensory ganglia and the sympathetic superior cervical ganglion, throughout development and after hatching. In contrast, only weak labelling could be detected during a restricted time span in the vestibulocochlear (E4-E8) and the distal cranial sensory ganglia (E4-E10), the neurons of which originate from the otic and epibranchial placodes. Specific 125I beta NGF binding was also observed in various brain regions during early brain development. NGF receptor expression there followed a characteristic pattern. The neuroepithelial layer displayed very low levels of specific 125I beta NGF binding, while strong 125I beta NGF labelling was found in the mantle layer. Brainstem somatomotor nuclei, visceromotor columns, brainstem alar plate, cerebellar anlage, tectum, and basal forebrain (epithalamus, striatum) were found to be transiently labelled by 125I beta NGF in early development (E4-E12). Non-nervous tissues such as parts of the otic vesicle epithelium and skeletal muscle anlagen of the head were also labelled. These results, showing specific binding of 125I beta NGF to cranial cells of different origin (neural tube, neural crest, placode, and possibly mesoderm) strengthen the concept that NGF may have diverse functions in growth and differentiation of various tissues and cell types.

The use of a tyrosine-hydroxylase cDNA probe to study the neurotransmitter plasticity of rat sympathetic neurons in culture

We have compared quantitatively the effects of muscle-conditioned medium (CM) and elevated K+ concentration (40 mM) on the enzymatic activity of tyrosine hydroxylase (TH) and on TH-mRNA levels in primary cultures of rat sympathetic neurons. Northern blot analysis of RNA from cultured neurons with a 32P-labeled rat TH-cDNA probe was performed. The probe hybridized strongly with a single RNA species of 1.9 kb, similar in size to the TH-mRNA from PC12 pheochromocytoma cells. In agreement with earlier data both CM and a partially purified factor from CM increased choline acetyltransferase activity up to 200-fold and depressed TH activity by 2- to 7-fold in cultured sympathetic neurons. These effects were accompanied by a decrease in TH-mRNA level, which correlated with the decrease in TH activity. On the other hand, a culture medium supplemented with 40 mM KCl caused a 1.5- to 5-fold increase in TH activity, which was accompanied by an increase in TH-mRNA level of the same order of magnitude. As a working hypothesis, we suggest that CM and neuronal depolarization control the transcription of the TH gene in an antagonistic manner.

Purification and amino terminal sequencing of human melanoma nerve growth factor receptor

The nerve growth factor (NGF) receptor, solubilized with Triton X-100 detergent, has been purified from human melanoma cell line A875. Purification to near-homogeneity was achieved by chromatography on wheat germ agglutinin-agarose, followed by immunoaffinity chromatography on Sepharose columns coupled with anti-NGF receptor monoclonal antibody (MAb). The purified receptor, a 75,000-dalton protein, retains the capacity to bind NGF as well as anti-receptor MAbs. Final purification was achieved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The sequence of amino acid residues at the amino terminus has been determined. Possible sequence homology between the NGF receptor and several other proteins is discussed. Using the purified receptor as immunogen, new MAbs to the NGF receptor have been produced. The NGF receptor was visualized by immunoperoxidase staining in tissue sections of dorsal root ganglia from monkeys.

Nerve growth factor (NGF) in serum: evaluation of serum NGF levels with a sensitive bioassay employing embryonic sensory neurons

Considerable controversy surrounds the question of whether or not nerve growth factor (NGF) or a related nerve growth-promoting factor is present in serum. Recently, supporting its role as a local neuronotrophic factor, the presence of NGF in glial cells and its production in target tissues of NGF-responsive neurons were demonstrated [Rush: Nature 312:364-367, 1984; Heumann, Korsching, Scott, Thoenen: EMBOJ 3:3183-3189, 1984; Shelton and Reichardt: Proc Natl Acad Sci USA 81:7952-7955, 1984]. At the same time, the concept that NGF may play a role as a humoral factor has been questioned, since careful analyses of serum with specific and sensitive radioimmunoassays [Suda, Barde, Thoenen: Proc Natl Acad Sci USA 75:4042-4046, 1978; Korsching and Thoenen; Proc Natl Acad Sci USA 80:3513-3516, 1983; Furukawa, Kamo, Furukawa, Akazawa, Satoyoshi, Itoh, Hayashi: J Neurochem 40:734-744, 1983] as well as bioassays [Skaper and Varon: Exp Neurol 76:655-665, 1982] have not confirmed earlier reports [Levi-Montalcini and Booker; Proc Natl Acad Sci USA 46:373-391, 1960; Banks, Banthorpe, Charlwood, Pearce, Vernon: Nature 246:503-504, 1973; Hendry: Biochem J 128:1265-1272, 1972] on NGF's representation in serum. In this study serum from mouse, rat, and man was analyzed with an in vitro bioassay system which employs sensory neurons from chicken embyro dorsal root ganglia and which allows the measurement of NGF concentrations as low as 0.8 pM. It was found that sera from all these species contained neuronotrophic activity (S-NGF). The target cell spectrum as well as characteristic parameters of the neuronal growth response of S-NGF and of NGF were identical. S-NGF of mouse serum was completely inhibitable by polyclonal and monoclonal antibodies to mouse submandibular gland beta NGF. On polyacrylamide isoelectric focussing gels mouse and human S-NGF could be recovered from the same position as NGF as well as from the region where alpha 2-macroglobulin and serum albumin focused. In newborn and adult male and female mice basal S-NGF levels were equivalent to 10-50 pM NGF. A fraction of the serum samples of male mice showed elevated S-NGF levels. The incidence of high S-NGF levels was more frequent in NMRI and C57BL/6 males than in BALB/c males. Following sialectomy of male mice only basal S-NGF levels were observed up to 5 weeks after the operation. This indicates that although the submandibular gland may contribute to S-NGF levels in serum under certain conditions that appeared to be stress related, it cannot be the only source of S-NGF.

Altered cellular functions in a PC-12 cell clone chronically infected with retrovirus

We characterized retrovirus-induced changes in PC-12 cell function and neuronal differentiation. PC-12 cells were infected with a neurotropic retrovirus (temperature-sensitive Moloney murine leukemia virus, mutant BA-1). We isolated a cell clone from this infected culture that displayed altered response to nerve growth factor; increased choline acetyltransferase activity; and decreased basal and nerve growth factor-stimulated acetylcholinesterase activity. In addition, Kirsten murine sarcoma virus infection of and subsequent expression of the v-ras oncogene in PC-12 cells induced neurite extension, enhanced choline acetyltransferase activity, and limited the growth potential of the infected cells.

Conditions increasing the adrenergic properties of dissociated chick superior cervical ganglion neurons grown in long-term culture

Neurons dissociated from the embryonic chick superior cervical ganglion (SCG) were separated from ganglionic nonneuronal cells using a density gradient formed with Percoll. The sympathetic neurons were then grown for 3-4 weeks in serum containing medium on a polyornithine substrate precoated with heart-conditioned medium. Both catecholamine (CA) and acetylcholine (ACh) are synthesized and accumulated by these neurons, but the amount of CA is higher and increases much more over time in culture than the amount of ACh. The cultures become therefore more adrenergic with time. We report here that the adrenergic properties of these cells can be enhanced. A 3-fold increase in CA synthesis, as expressed on a per neuron basis, is obtained by increasing neuron cell density 3- to 4-fold. ACh synthesis, however, is decreased at high neuronal density. Optimal CA production is obtained at densities of 120-150,000 neurons/cm2. This effect is due to direct cell contact since it cannot be transferred to low density cultures by medium conditioned by high density cultures. Nerve growth factor concentrations 5-10-fold higher than the amount necessary for optimal neuronal survival (1 microgram/ml 7S NGF) increases CA production but do not affect ACh synthesis. This effect is highest at low plating densities (20-30,000 neurons/cm2, 10-fold increase) and progressively decreases with increasing neuronal density. No increase is obtained in high density cultures where CA production is maximal. In addition, we made the novel observation that medium conditioned by chick liver cells in culture (LCM) increases CA production approximately 4-fold, whereas it does not increase ACh production by the SCG neurons. Work is in progress to biochemically characterize the active component(s) present in the LCM and to determine whether they favor the survival of a subpopulation of adrenergic neurons possible present in these ganglia. Alternatively, the adrenergic differentiation of neurons initially capable of synthesizing both CA and ACh could be selectively increased by LCM.

Calcium-dependent activation of glycogen phosphorylase in rat pheochromocytoma PC12 cells by nerve growth factor

Glycogen phosphorylase in PC12 cells exists in two forms analogous to those found in brain and muscle. The active phosphorylated form of the enzyme, phosphorylase-a, represents about 20-30% of total glycogen phosphorylase in these cells. Incubation of PC12 cells with 100 ng 7S nerve growth factor/ml increased phosphorylase-a within minutes. In contrast to nerve growth factor, insulin (6 ng/ml) and epidermal growth factor (6 ng/ml) decreased phosphorylase-a. Activation of phosphorylase-a by nerve growth factor was not accompanied by increases in cyclic AMP; however, removal of extracellular Ca2+ or incubation of cells with calcium channel blockers inhibited activation of glycogen phosphorylase by nerve growth factor.

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.