GAP-43 immunoreactivity is widespread in the autonomic neurons and sensory neurons of the rat

GAP-43 is a membrane-bound phosphoprotein generally associated with axon growth during development and regeneration. Using immunohistochemical and immunoblotting techniques this study shows that GAP-43 is expressed extensively in the unperturbed adult autonomic nervous system. Strong immunoreactivity was seen in the developing and mature enteric subdivision of the autonomic nervous system and in nerves of the iris and various blood vessels. The presence of GAP-43 immunoreactivity in varicose nerve fibres, and a comparison of the labelling pattern of GAP-43 with the nerve associated marker PGP 9.5 suggests that GAP-43 is present in most or all autonomic nerve fibres in these organs. Immunoblotting of gut samples on 10% polyacrylamide gels revealed a single band of approximately 45,000 mol. wt that co-migrated with pure central nervous system GAP-43. Surgical sympathectomy experiments resulting in almost complete elimination of sympathetic fibres did not markedly affect the pattern of GAP-43 immunoreactivity in the iris, indicating that GAP-43 is expressed not only in sympathetic nerves but also in parasympathetic and sensory fibres. These findings show that GAP-43 is expressed extensively in autonomic nerves of the adult rat, at levels comparable to those seen during development. High levels of GAP-43 are not therefore restricted to development and regeneration in this part of the nervous system.

GAP-43 is expressed by nonmyelin-forming Schwann cells of the peripheral nervous system

Recently it has been demonstrated that the growth-associated protein GAP-43 is not confined to neurons but is also expressed by certain central nervous system glial cells in tissue culture and in vivo. This study has extended these observations to the major class of glial cells in the peripheral nervous system, Schwann cells. Using immunohistochemical techniques, we show that GAP-43 immunoreactivity is present in Schwann cell precursors and in mature non-myelin-forming Schwann cells both in vitro and in vivo. This immunoreactivity is shown by Western blotting to be a membrane-associated protein that comigrates with purified central nervous system GAP-43. Furthermore, metabolic labeling experiments demonstrate definitively that Schwann cells in culture can synthesize GAP-43. Mature myelin-forming Schwann cells do not express GAP-43 but when Schwann cells are removed from axonal contact in vivo by nerve transection GAP-43 expression is upregulated in nearly all Schwann cells of the distal stump by 4 wk after denervation. In contrast, in cultured Schwann cells GAP-43 is not rapidly upregulated in cells that have been making myelin in vivo. Thus the regulation of GAP-43 appears to be complex and different from that of other proteins associated with nonmyelin-forming Schwann cells such as N-CAM, glial fibrillary acidic protein, A5E3, and nerve growth factor receptor, which are rapidly upregulated in myelin-forming cells after loss of axonal contact. These observations suggest that GAP-43 may play a more general role in the nervous system than previously supposed.

Rat Schwann cells produce interleukin-1

There is increasing evidence that Schwann cells of peripheral nerves may be able to function as accessory cells, interacting with the immune system in T cell-mediated immune responses, by expression of the major histocompatibility complex (MHC) class II molecules. In addition to MHC class II-associated presentation of antigen to T lymphocytes, the release of a co-stimulatory factor, interleukin-1 (IL-1), is an essential function of accessory cells for T cell activation. In this study, we investigated if Schwann cells were able to produce IL-1. Purified cultures of neonatal and adult rat Schwann cells were incubated with various stimulatory agents. Supernatants and cell lysates were collected from these cultures and IL-1 activity was assayed. Both neonatal and adult rat Schwann cells produced IL-1 activity in response to bacterial antigens and the IL-1 activity was often higher in the cell lysate than in the supernatant. When stimulated neonatal or adult rat Schwann cells were examined with antibody against IL-1, strong immunolabelling was seen intracellularly, but no IL-1 was detected on the cell surface. Since IL-1 plays an important role in the initiation of immune responses, these observations support the view that Schwann cells may function as antigen-presenting cells, thereby taking part in neuroimmunological responses within peripheral nerves.

Interaction between cAMP elevation, identified growth factors, and serum components in regulating Schwann cell growth

Most previous studies on Schwann cell proliferation in vitro have used serum-containing media. This complicates the analysis of agents required for cell division since serum contains an ill-defined mixture of hormones and growth factors. Serum-free medium has therefore been used to analyse the response of Schwann cell to previously identified Schwann cell mitogens. Serum factors were not necessary for DNA synthesis in response to platelet-derived growth factor, basic fibroblast growth factor, or glial growth factor, provided they were used in combination with forskolin to elevate intracellular cAMP. Transforming growth factor beta 1, a Schwann cell mitogen in serum, was not mitogenic under these conditions. Neither the growth factors nor forskolin were effective when used alone. Growth control was analysed further using long-term cultured Schwann cells that had spontaneously immortalized. Measurements of endogenous cAMP levels in short- and long-term Schwann cells revealed that long-term cells had two to three times higher basal cAMP levels. As predicted by these findings, platelet-derived growth factor, basic fibroblast growth factor, and glial growth factor stimulated DNA synthesis in long-term cells without requiring costimulation by agents which elevate cAMP (while transforming growth factor beta 1 had no effect).(ABSTRACT TRUNCATED AT 250 WORDS)

Spontaneous immortalisation of Schwann cells in culture: short-term cultured Schwann cells secrete growth inhibitory activity

In the developing peripheral nerve, Schwann cells proliferate rapidly and then become quiescent, an essential step in control of Schwann cell differentiation. Cell proliferation is controlled by growth factors that can exert positive or inhibitory influences on DNA synthesis. It has been well established that neonatal Schwann cells divide very slowly in culture when separated from neurons but here we show that when culture was continued for several months some cells began to proliferate rapidly and non-clonal lines of immortalised Schwann cells were established which could be passaged for over two years. These cells had a similar molecular phenotype to short-term cultured Schwann cells, except that they expressed intracellular and cell surface fibronectin. The difference in proliferation rates between short- and long-term cultured Schwann cells appeared to be due in part to the secretion by short-term cultured Schwann cells of growth inhibitory activity since DNA synthesis of long-term, immortalised Schwann cells was inhibited by conditioned medium from short-term cultures. This conditioned medium also inhibited DNA synthesis in short-term Schwann cells stimulated to divide by glial growth factor or elevation of intracellular cAMP. The growth inhibitory activity was not detected in the medium of long-term immortalised Schwann cells, epineurial fibroblasts, a Schwannoma (33B), astrocytes or a fibroblast-like cell-line (3T3) and it did not inhibit serum-induced DNA synthesis in epineurial fibroblasts, 33B cells or 3T3 cells. The activity was apparently distinct from transforming growth factor-beta, activin, IL6, epidermal growth factor, atrial natriuretic peptide and gamma-interferon and was heat and acid stable, resistant to collagenase and destroyed by trypsin treatment. We raise the possibility that loss of an inhibitory autocrine loop may contribute to the rapid proliferation of long-term cultured Schwann cells and that an autocrine growth inhibitor may have a role in the cessation of Schwann cell division that precedes differentiation in peripheral nerve development.

The effects of cAMP on differentiation of cultured Schwann cells: progression from an early phenotype (04+) to a myelin phenotype (P0+, GFAP-, N-CAM-, NGF-receptor-) depends on growth inhibition

The present experiments were designed to clarify the relationship between cAMP elevation, proliferation and differentiation in Schwann cells. They were carried out on short-term cultures of cells obtained from neonatal rat sciatic nerves. It was found that the myelin-related phenotype was expressed in response to agents that elevate or mimic intracellular cAMP (forskolin, cholera toxin, cAMP analogues), provided cell division was absent. This phenotype included upregulation of the major myelin protein P0 and downregulation of GFAP, N-CAM, A5E3, and NGF receptor. In contrast, when cells were cultured in conditions where cell division occurred, elevation of intracellular cAMP produced an alternative response, characterized by DNA synthesis and absence of myelin-related differentiation. The cAMP mediated induction of an early Schwann cell antigen, 04, followed a different pattern since it was induced equally in dividing and nondividing cells. These observations are consistent with the proposal that during development of the rat sciatic nerve: (a) cAMP elevation, possibly induced by axon-associated factors, is a primary signal responsible for the induction of 04 expression in proliferating Schwann cells during the premyelination period; (b) subsequent withdrawal of cells associated with the larger axons from the cell cycle acts as a permissive secondary signal for induction of myelination, since in quiescent cells the ongoing cAMP elevation will trigger myelination.

Transplantation of postnatal rat enteric ganglia into denervated adult rat hippocampus

These experiments explore the possible value of the myenteric plexus as a source of donor cells for autografting into the central nervous system. Neurons and glia from 10-12-day postnatal rat myenteric plexus survive for at least one month after transplantation into cholinergically denervated syngeneic adult rat hippocampus. A population of donor cholinergic neurons has acetylcholinesterase-positive processes, but these appear not to innervate host tissue. Host gliosis in response to these implants seems to be less than that seen with other peripheral ganglia, and unlike Schwann cells, the enteric glia form end-feet on brain capillaries.

Schwann cell precursors and their development

During development of peripheral nerves, an apparently homogeneous pool of embryonic Schwann cells gives rise to two morphologically and antigenically distinct mature Schwann cell types. These are the myelin-forming cells associated with axons of larger diameter and the non-myelin-forming cells associated with axons of smaller diameter. The development of these cells from precursors that can be identified in early embryonic nerves can be followed with the help of antigenic differentiation markers. This development depends on Schwann cells retaining a close association with axons. The effect of axons can be mimicked in vitro by agents that elevate cAMP levels. This has given rise to the idea that the effects of axon-associated signals in Schwann cell development are to a significant extent mediated via elevation in Schwann cell cAMP levels. In vitro, the cAMP induced progression of cells from a premyelination state to a myelination state depends on withdrawal from the cell cycle. It is therefore possible that in vivo, the timing of myelin formation by individual Schwann cells is determined by signals that suppress proliferation.

04 and A007-sulfatide antibodies bind to embryonic Schwann cells prior to the appearance of galactocerebroside; regulation of the antigen by axon-Schwann cell signals and cyclic AMP

In the rat sciatic nerve, the relationship between Schwann cells, axons, the extracellular matrix and perineurial sheath cells undergoes extensive modification between embryo day 15 and the onset of myelination during the first postnatal day. Little is known about molecular changes in Schwann cells in this important prenatal period. In the present paper, we use immunofluorescence to study the prenatal development and postnatal regulation of the antigen(s) recognized by the 04 monoclonal antibody and a well-characterized rat monoclonal antibody to sulfatide, A007. We show that, in a series of immunochemical tests, the 04 antibody recognizes only sulfatide in neonatal and adult rat nerves. Both antibodies first bind to Schwann cells in the sciatic nerve at embryo day 16–17, and all Schwann cells bind both antibodies at birth. In the adult nerve, both nonmyelin-forming and myelin-forming cells are labelled with the antibodies. Schwann cells dissociated from embryo day 15 nerves and cultured in the absence of axons develop neither 04 nor A007 binding on schedule, and 04-positive and A007-positive Schwann cells from postnatal nerves lose the ability to bind these antibodies during the first few days in culture. Schwann cells in the distal stump of transected nerves also sharply down-regulate cell surface binding of 04. High numbers of 04-positive or A007-positive Schwann cells reappear in cultures treated with agents that mimic or elevate intracellular cAMP. We conclude that two anti-sulfatide antibodies 04 and A007, recognize an antigen, probably sulfatide, that appears very early in Schwann cell development (one to two days prior to galactocerebroside) but is nevertheless subject to upregulation by axonal contact or elevation of intracellular cAMP.

Three markers of adult non-myelin-forming Schwann cells, 217c(Ran-1), A5E3 and GFAP: development and regulation by neuron-Schwann cell interactions

Immunohistochemical methods are used to investigate in detail the development and regulation of three proteins (217c(Ran-1), A5E3 and GFAP) specifically associated with adult non-myelin-forming Schwann cells in the rat sciatic nerve, from embryo day 15 to maturity. 217c(Ran-1), which is probably the NGF-receptor, and A5E3 are expressed by the majority of cells in the nerve at embryo day 15 and by essentially all cells at embryo day 18. GFAP first appears at embryo day 18; this is an intrinsically programmed developmental event which occurs in cultured Schwann cells even in the absence of serum. Postnatally, the expression of 217c(Ran-1), A5E3 and GFAP is suppressed in cells that form myelin but retained in non-myelin-forming Schwann cells. Mature myelin-forming cells nevertheless maintain the potential to express all three proteins but will only do so if removed from contact with myelinated axons. In neuron-free cultures Schwann cells express all three proteins. This work, together with our previous observations on N-CAM, shows that removal of a diverse set of surface proteins and a change in intermediate filament expression is one of the major consequences of axon to Schwann cell signalling during myelination in the rat sciatic nerve. Unlike myelin-forming cells, adult non-myelin-forming Schwann cells remain very similar to embryonic and newborn cells with respect to expression of surface proteins, in contrast to the previously established developmental changes that occur in their surface lipids.

Transforming growth factor-beta and gamma-interferon have dual effects on growth of peripheral glia

The influence of transforming growth factor-beta (TGF-beta) and gamma-interferon on DNA synthesis in Schwann cells and enteric glia in culture has been studied. TGF-beta stimulated the DNA synthesis of short-term (less than 2 weeks in culture) Schwann cells, whereas gamma-interferon was ineffective. The stimulatory effect of TGF-beta was additive to the stimulation of DNA synthesis due to axonal membrane fragments. In contrast to their effect on short-term Schwann cells, both TGF-beta and gamma-interferon inhibited DNA synthesis in enteric glial cells and in long-term (over 3 months in culture) Schwann cells. When short-term Schwann cells were stimulated to divide by axolemma or glial growth factor, gamma-interferon did not inhibit this enhanced DNA synthesis although it suppressed DNA synthesis induced by cAMP analogues. These results raise the possibility that TGF-beta and gamma-interferon might have a role in controlling glial proliferation during development and/or regeneration of the peripheral nervous system.

Control of peripheral glial cell proliferation: enteric neurons exert an inhibitory influence on Schwann cell and enteric glial cell DNA synthesis in culture

Neuronal membranes from rat dorsal root ganglia provide a mitogenic signal to cultured Schwann cells and it has been suggested this is an important factor in regulating Schwann cell numbers during development. In this study, the influence of enteric neurons on the DNA synthesis of both Schwann cells and enteric glia has been investigated as well as the effect of axonal membrane fractions (axolemma) on enteric glia. The proliferation rate of rat Schwann cells and enteric glia was assessed in culture using [3H]thymidine uptake and autoradiography in combination with immunolabelling to identify cell types. When purified rat Schwann cells were co-cultured with guinea pig enteric neurons, their DNA synthesis rate was reduced compared with control cultures of pure Schwann cells or Schwann cells not close to neurites or neuronal cell bodies. Nevertheless, in accordance with previous findings that sensory neurons stimulate Schwann cell division, these Schwann cells increased their DNA synthesis rate when in contact with neurites from purified guinea pig or adult rat dorsal root ganglion neurons and on exposure to bovine axolemmal fractions. The enteric neurons also suppressed the DNA synthesis of enteric glia in co-cultures of purified enteric neurons and enteric glia, while bovine axolemma stimulated their DNA synthesis. These results indicate that a mitotic inhibitory signal is associated with enteric neurons and can exert its effect on both Schwann cells and enteric glia, and that enteric glia, like Schwann cells, are stimulated to divide by axolemmal fractions. It thus seems possible that during development glial cell numbers in the peripheral nervous system may be controlled by both positive and negative regulators of cell growth.

Type I collagen preparations inhibit DNA synthesis in glial cells of the peripheral nervous system

The mechanisms underlying cessation of glial proliferation in the developing peripheral nervous system are obscure. One possibility, as yet little explored, is that mitotic inhibitory signals play a part in regulating glial cell numbers. In this study we demonstrate that type I collagen preparations from several different sources can inhibit the rate of DNA synthesis in purified populations of enteric glia and both short-term and long-term secondary Schwann cells in dissociated cell cultures. When these cells are grown on gelled or dried type I collagen substrata, they proliferate at substantially lower rates than on polylysine substrata. In contrast, type III or V collagen preparations do not inhibit glial DNA synthesis and laminin, fibronectin, type IV collagen, and secreted matrix from bovine corneal endothelial cells all stimulate thymidine incorporation. The inhibitory effect is not observed with heat denatured type I collagen preparations, but is seen equally in serum-containing medium, in medium containing fibronectin-free serum, or in serum-free medium, suggesting that the interaction of collagen with the cells requires structurally intact collagen molecules and does not occur via intermediary linkage to fibronectin. The inhibition on collagen is accompanied by a shape change from a more flattened morphology to a narrow spindle form. The labeling index of a rat Schwannoma cell line, 33B, is not inhibited on type I collagen substrata. These results demonstrate that type I collagen preparations inhibit the DNA synthesis levels of early postnatal peripheral glial cells in vitro. It remains to be determined whether this effect occurs via direct collagen-cell membrane interactions or whether it depends on accessory molecules, perhaps present in the collagen preparations themselves, since these are not purified to absolute homogeneity.

Non-myelin-forming Schwann cells proliferate rapidly during Wallerian degeneration in the rat sciatic nerve

Transection of a mixed peripheral nerve results in the degeneration of axons and breakdown of myelin in the distal stump. These events are accompanied by a sharp but transient Schwann cell proliferation. The present study seeks to determine whether both myelin-forming and non-myelin-forming Schwann cells enter a proliferative phase under these conditions, or whether the dividing cells are chiefly recruited from one or other of the Schwann cell populations. The macrophage recruitment into the transected distal stumps has also been timed and quantitated, since it has been suggested that macrophages are an important source of Schwann cell mitogens in degenerating peripheral nerves. Incorporation of [3H]-thymidine and autoradiography was used as a measure of cell proliferation, and cell type markers and immunohistochemistry were used to identify myelin-forming and non-myelin-forming Schwann cells. The cells were removed from the distal stump of the rat sciatic nerve and sympathetic trunk at various times after transection and proliferation measured during the first 24 h in culture. It was found that in the sciatic nerve, which contains a mixture of myelinated and unmyelinated fibres, both myelin-forming cells, identified by presence of the myelin protein Po, and non-myelin-forming cells (Po- cells) showed a substantial elevation in [3H]-thymidine labelling index at day 2 postoperatively, which was similar in magnitude for the two categories of cell. The proliferation rate of both Po+ and Po- cells remained elevated for up to 8 days after transection.(ABSTRACT TRUNCATED AT 250 WORDS)

Schwann cells co-cultured with stimulated T cells and antigen express major histocompatibility complex (MHC) class II determinants without interferon-gamma pretreatment: synergistic effects of interferon-gamma and tumor necrosis factor on MHC class II induction

Schwann cells (SC) do not express major histocompatibility complex (MHC) class II antigens under normal culture conditions. SC can, however, be induced in vitro to express MHC class II molecules by exposure to high concentrations of interferon-gamma (IFN-gamma) and can present antigens to antigen-specific T cell lines. In the present study immunohistochemical labeling showed that most SC (greater than 90%) prepared from rat neonatal sciatic nerves expressed MHC class II molecules when cultured together with mycobacterial antigen and T cells, and as a consequence were able to function as antigen-presenting cells in lymphoproliferation assays, without requiring pretreatment with IFN-gamma. Antigen or T cells alone were ineffective in stimulating MHC class II expression and induction of class II molecules was MHC restricted, requiring the presence of syngeneic T cells. Addition of monoclonal antibody DB1, directed against IFN-gamma to co-cultures of SC and T lymphocytes stimulated with antigen, prevented the induction of MHC class II antigen on SC. When SC were incubated with recombinant (r)IFN-gamma alone, up to 50% of SC showed positive labeling for MHC class II antigen. This level of expression was enhanced to greater than 80% when recombinant tumor necrosis factor (rTNF) was also added. rTNF alone had no effect, and addition of DBI antibody inhibited the synergistic effects of rTNF on MHC class II expression. The effects of rIL 4 were also investigated but neither rIL 4 alone nor rIL 4 in combination with rIFN-gamma induced MHC class II expression by SC. These results show that in the presence of sensitized T lymphocytes and antigen, SC do not require pretreatment with exogenous rIFN-gamma to express MHC class II antigens and function as antigen-presenting cells. T cell-derived TNF and IFN-gamma appear to act as mediators of the T cell-induced expression of MHC class II by SC.

Immunocytochemical localization of the glucose-transport protein in mammalian brain capillaries

The endothelial cells of mammalian brain capillaries, which form the anatomical basis of the blood-brain barrier, have been investigated by immunocytochemical methods to determine the distribution of the glucose-transport protein. A monoclonal antibody raised against the intact human erythrocyte glucose-transport protein and polyclonal antibodies raised against a synthetic peptide corresponding to the C-terminal sequence of the human erythrocyte glucose-transport protein were used for immunofluorescent staining of isolated human and bovine cerebral cortex microvessels. The pattern of fluorescence with both antibodies demonstrated the antigen to be distributed throughout the plasma membrane of the capillary endothelial cells. These results provide further evidence for the homology between the human erythrocyte and brain capillary glucose-transport protein, and confirm its abundance in brain capillaries.

GABA immunoreactivity and 3H-GABA uptake in mucosal epithelial cells of the rat stomach

GABA, best known as a neurotransmitter in the central nervous system, is also present in various peripheral tissues including the gastrointestinal tract, where there is strong evidence that GABA acts as a transmitter in some intrinsic myenteric neurones. Several studies indicate that the gastric mucosa is one of the sites of action of GABA in the gut. Highly specific anti-GABA antibodies have been used to detect endogenous GABA in the mucosa of the rat gastrointestinal tract, and 3H-GABA uptake followed by autoradiography has been used to localise cells with uptake sites for exogenous GABA. It was found that although GABA immunoreactive nerve fibres are essentially absent from this site, some mucosal cells are strongly GABA-immunoreactive. These cells are common in the pyloric stomach and upper part of the small intestine. The autoradiographic experiments provide evidence that these cells also possess high-affinity GABA uptake sites. These observations raise the possibility that in the gastrointestinal tract GABA acts as a gut hormone in a subpopulation of mucosal endocrine cells, in addition to its role as an enteric neurotransmitter.

Macrophage-like cells in muscularis externa of mouse small intestine: immunohistochemical localization of F4/80, M1/70, and Ia-antigen

Macrophage-like cells (MLC) in mouse small intestine are situated in the muscularis externa in the subserosal layer at the level of Auerbach's plexus, and at the level of the deep muscular plexus. By combined labelling with FITC-dextran and immunohistochemical techniques, the MLC were shown to express the macrophage markers F4/80 and M1/70.15. The MLC appeared to be constitutively IE-antigen-positive, but did not contain lysozyme. It is suggested that MLC, like Langerhans cells, belong to a specialized class of cells in the mononuclear phagocyte system.

Immunohistochemical localisation and electrophysiological actions of GABA in prevertebral ganglia in guinea-pig

Immunohistochemical techniques were used to detect the presence of a GABA-like material in prevertebral sympathetic ganglia in guinea-pigs. Varicose, immunolabelled nerve fibres were observed in close proximity to sympathetic neurones in inferior mesenteric ganglia and coeliac ganglia. Non-varicose, immunolabelled nerve fibres were observed in lumbar colonic nerves and superior coeliac nerves, i.e. in nerve bundles peripheral to prevertebral ganglia. Immunolabelling was also present in neurones in the myenteric plexus and in nerve fibres in the circular muscle of the colon, as shown previously (Hills et al., Neuroscience, 22 (1987) 301-312). However, GABA-like immunoreactivity was not observed in the cell bodies of prevertebral ganglia nor in splanchnic nerves central to prevertebral ganglia. It was concluded from these results that prevertebral ganglia in guinea-pig receive a GABAergic innervation from neurones peripheral to the ganglia, possibly from GABA-containing neurones in the myenteric plexus of the gastrointestinal tract. Intracellular recordings were made from sympathetic neurones in the inferior mesenteric ganglion (IMG). Application of GABA onto the IMG caused a slow depolarisation of sympathetic neurones, during which there was a marked decrease in the input resistance of IMG cells. Application of GABA also depressed excitatory postsynaptic potentials (EPSPs) and action potentials in sympathetic neurones excited by cholinergic nerve fibres in the lumbar colonic nerves. The reversal potential of the GABA-induced slow depolarisation was -37 mV, a value close to the chloride equilibrium potential for sympathetic neurones. The actions of GABA were reversibly reduced by the GABAA antagonist, bicuculline, and were modulated in a predictable manner by substituting chloride ions with methane-sulphonate ions. These results indicated that GABA, and presumably GABAergic nerves in prevertebral ganglia, modulate the excitability of sympathetic neurones by acting on GABAA receptors linked to a chloride ionophore.

Establishment and properties of separate cultures of enteric neurons and enteric glia

In this paper methods are described for the preparation of two types of culture derived from myenteric explants: (a) highly enriched neuronal cell cultures, and (b) purified glial cells (greater than 98%). Both procedures combine the technique of antibody complement-mediated cytolysis with the use of an antimitotic agent. Immunohistochemical methods were used to compare the purified cells to their counterparts in mixed cultures (see accompanying paper). Antibodies to the glycoprotein Thy-1 and the monoclonal antibody A2B5 which recognizes gangliosides, labelled the cell surface of all enteric neurons in enriched cultures while subpopulations of the neurons expressed the Leu 7 carbohydrate epitope, the neurotransmitter 5-hydroxytryptamine and the neuropeptides substance P, methionine-enkephalin and vasoactive intestinal polypeptide. Autoradiographic experiments show that a subpopulation of enriched neurons exhibit high-affinity uptake sites for gamma-[3H]aminobutyric acid (GABA). All purified enteric glia continue to express the calcium binding protein S100, the basement membrane glycoprotein laminin and the antigens recognized by the A2B5 antibody, and subpopulations of glia are labelled by the monoclonal antibodies LB1 which binds to GD3 gangliosides, and Leu 7. Thus enteric neurons and glia can survive independently of each other and express molecular properties which are present in cultures normally containing both cell types.

Antigenic markers and laminin expression in cultured enteric neural cells

In this study, polyclonal and monoclonal antibodies have been used in conjunction with standard immunohistochemical methods to define markers which can be used to identify and study the main cell types present in the outgrowth area of explant cultures of myenteric plexus from newborn guinea pig. We show that all of the neurons binds antibodies to the glycoprotein Thy-1 and the antibody A2B5 which recognizes gangliosides. All enteric glial cells bind antibodies to the calcium-binding protein S100, and the A2B5 monoclonal antibody and ca. 95% of glia are labeled by the antibody LB1, which recognizes the GD3 ganglioside. Most fibroblasts are labelled by antibodies to Thy-1 and the matrix glycoprotein fibronectin. Thus enteric neurons can be defined serologically as Thy-1+/A2B5+/S100- cells; enteric glia as S100+ cells and fibroblasts as A2B5-/S100-cells. The markers have been used to demonstrate that laminin is made by both enteric glia and fibroblasts. They have also been used to show that ca. 5% of neurons and less than 5% of enteric glia bind the antibody Leu 7 (HNK-1, L2), thus revealing the subpopulations of neurons and glia show differential cell surface expression of the carbohydrate epitope recognized by the antibody. In the accompanying paper, we demonstrate that two of the antibodies (LB1 and Thy-1) can be used to generate purified populations of neurons and glia.

Control of peripheral glial cell proliferation: a comparison of the division rates of enteric glia and Schwann cells and their response to mitogens

The enteric nervous system comprises neurons and a relatively homogeneous population of glial cells, which differ considerably from those found in other parts of the peripheral nervous system and resemble more closely astrocytes from the central nervous system. It provides a simple model system for the study of neuron/glial interactions and glial cell development. In this study the proliferation rates of purified populations of enteric glia and Schwann cells and their response to several mitogens in vitro were compared. Enteric glial cells divided at a much higher rate than Schwann cells in both serum-containing and serum-free media. This difference in their basal proliferation rates was the major difference seen between the two cell types. Both cell populations were stimulated to divide by fibroblast growth factor and glial growth factor but not by epidermal growth factor. Enteric glial cells and Schwann cells proliferated at a greater rate on a basement membrane-like extracellular matrix produced by corneal endothelial cells, laminin, and fibronectin than on poly-L-lysine-coated glass coverslips. The magnitude of stimulation was greater for Schwann cells, presumably due to their lower basal division rates. Like Schwann cells, enteric glial cells were stimulated to divide by two agents which elevate intracellular cAMP, cholera toxin, and dibutyryl cAMP.