Dissociation, fractionation, and culture of embryonic brain cells

Drosophila CASK regulates brain size and neuronal morphogenesis, providing a genetic model of postnatal microcephaly suitable for drug discovery

BACKGROUND

CASK-related neurodevelopmental disorders are untreatable. Affected children show variable severity, with microcephaly, intellectual disability (ID), and short stature as common features. X-linked human CASK shows dosage sensitivity with haploinsufficiency in females. CASK protein has multiple domains, binding partners, and proposed functions at synapses and in the nucleus. Human and Drosophila CASK show high amino-acid-sequence similarity in all functional domains. Flies homozygous for a hypomorphic CASK mutation (∆18) have motor and cognitive deficits. A Drosophila genetic model of CASK-related disorders could have great scientific and translational value.

METHODS

We assessed the effects of CASK loss of function on morphological phenotypes in Drosophila using established genetic, histological, and primary neuronal culture approaches. NeuronMetrics software was used to quantify neurite-arbor morphology. Standard nonparametric statistics methods were supplemented by linear mixed effects modeling in some cases. Microfluidic devices of varied dimensions were fabricated and numerous fluid-flow parameters were used to induce oscillatory stress fields on CNS tissue. Dissociation into viable neurons and neurite outgrowth in vitro were assessed.

RESULTS

We demonstrated that ∆18 homozygous flies have small brains, small heads, and short bodies. When neurons from developing CASK-mutant CNS were cultured in vitro, they grew small neurite arbors with a distinctive, quantifiable "bushy" morphology that was significantly rescued by transgenic CASK+. As in humans, the bushy phenotype showed dosage-sensitive severity. To overcome the limitations of manual tissue trituration for neuronal culture, we optimized the design and operation of a microfluidic system for standardized, automated dissociation of CNS tissue into individual viable neurons. Neurons from CASK-mutant CNS dissociated in the microfluidic system recapitulate the bushy morphology. Moreover, for any given genotype, device-dissociated neurons grew larger arbors than did manually dissociated neurons. This automated dissociation method is also effective for rodent CNS.

CONCLUSIONS

These biological and engineering advances set the stage for drug discovery using the Drosophila model of CASK-related disorders. The bushy phenotype provides a cell-based assay for compound screening. Nearly a dozen genes encoding CASK-binding proteins or transcriptional targets also have brain-development mutant phenotypes, including ID. Hence, drugs that improve CASK phenotypes might also benefit children with disorders due to mutant CASK partners.

In Vitro Testing of Neurotoxicity

Many of the toxic compounds that are at large in the environment represent a risk to our neuronal functions. Chemicals may have a direct or indirect effect on the nervous system and they may interfere with general biochemical properties or specific neuronal structures and processes. In this review, a brief presentation of the major neurotoxicological targets is given, together with a discussion of some aspects of the use of different in vitro models for screening purposes and mechanistic studies. It is believed that in vitro methods offer special opportunities for the development of new neurotoxicological assays, and that this development will mainly involve cultured model systems. Therefore, a presentation of nerve and glia tissue culture methods is given, followed by an overview of how information on the action of mercury and mercurials, excitotoxins and acrylamide has been obtained through the use of cultured cell models. It is concluded that the developmental potential in cell neurotoxicology lies within the areas of separation and identification of cells representative for different structures in the nervous system, co-cultivation of different cell types, in vivo/in vitro (ex vivo) procedures, chemically defined media, metabolic competent cultures of human cells and improved physiological conditions for cultivation and exposure.

Organotypic cultures of cerebellar slices as a model to investigate demyelinating disorders

INTRODUCTION

Demyelinating disorders, characterized by a chronic or episodic destruction of the myelin sheath, are a leading cause of neurological disability in young adults in western countries. Studying the complex mechanisms involved in axon myelination, demyelination and remyelination requires an experimental model preserving the neuronal networks and neuro-glial interactions. Organotypic cerebellar slice cultures appear to be the best alternative to in vivo experiments and the most commonly used model for investigating etiology or novel therapeutic strategies in multiple sclerosis. Areas covered: This review gives an overview of slice culture techniques and focuses on the use of organotypic cerebellar slice cultures on semi-permeable membranes for studying many aspects of axon myelination and cerebellar functions. Expert opinion: Cerebellar slice cultures are probably the easiest way to faithfully reproduce all stages of axon myelination/demyelination/remyelination in a three-dimensional neuronal network. However, in the cerebellum, neurological disability in multiple sclerosis also results from channelopathies which induce changes in Purkinje cell excitability. Cerebellar cultures offer easy access to electrophysiological approaches which are largely untapped and we believe that these cultures might be of great interest when studying changes in neuronal excitability, axonal conduction or synaptic properties that likely occur during multiple sclerosis.

In vitro responses of sympathetic neurons to nerve growth factor and other macromolecular agents

Cells in the dissociated state from the sympathetic ganglia (SG) of 11-day-old chick embryos, and monolayer cultures of these cells are used to illustrate some of th extrinsic influences that regulate neuronal performance. In culture, the survival of SG neurons can be measured, as an assay for survival-promoting agents. Among the requirements of the SG discussed are: (1) nerve growth factor and other trophic factors that can replace it, (2) serum, and a defined mixture (N1) that can substitute for it, and (3) a minimal presence of non-neuronal cells. Also reviewed are factors that confer neurite-promoting competence on certain culture substrata. Suspensions of SG cells permit analysis of "short-latency" events triggered within minutes of the presentation of nerve growth factors and provide an insight into its possible mode of action. The most striking such event is its control over Na+/K+ pumps, since ionic control is a fundamental feature of living cells and may well mediate their regulation by trophic factors, hormones or mitogens.

Aggregating neural cell cultures

When freshly dissociated embryonic tissues are kept under gyratory agitation, the cells aggregate to form three-dimensional spheroids in which the cells can migrate and organize themselves, attaining maximal cellular differentiation after weeks of culture. The three-dimensional architecture of the aggregates permits direct cell-to-cell interactions and the formation of a natural cell matrix, which is fundamental to the acquisition of the histotypic properties of the aggregates. This unit describes protocols for preparing forebrain cells from embryonic rodents for aggregating cultures and maintaining these cultures to the differentiated state.

Establishment of pure neuronal cultures from fetal rat spinal cord and proliferation of the neuronal precursor cells in the presence of fibroblast growth factor

A primary culture system of nearly pure neuronal cells from 14-day-old fetal rat spinal cord has been developed by combining a preplating step, the use of a chemically defined serum-free medium, and borated polylysine-coated dishes that prevented the formation of cell aggregates. About 98% of the cells were found to be immunostained with neuron-specific enolase antibodies, confirming their neuronal nature. The cultures are composed essentially of a population of non-motoneurons and contain few motoneurons, characterized by their large size and multipolar aspect, the presence of acetylcholinesterase (AChE), and the intense immunoreaction for growth-associated protein GAP-43. Neuronal precursor cells are also present in these cultures and proliferate during the first 3 days. The addition of bovine brain basic fibroblast growth factor (bFGF) stimulates their proliferation over a period of 2 days, as determined by measurement of [125I]iododeoxyuridine incorporation and by immunocytochemical reaction after bromodeoxyuridine incorporation into nuclei. The proliferating cells were characterized as neurons by immunostaining against neuron-specific enolase. Recombinant human bFGF and bovine brain acidic FGF (aFGF) exerted similar effects. Other growth factors, including epidermal growth factor (EGF), transforming growth factor beta 1 (TGF-beta 1), and thrombin, were without effect on the proliferative activity of these neuronal cells. bFGF has no effect on the survival of motoneurons and on the fiber outgrowth of the whole neuronal population. However, bFGF affects the development of bipolar AChE-positive neurons, probably belonging to the non-motoneuron population. The data indicate that bFGF and aFGF are mitogens for neuroblasts from rat spinal cord in culture and that bFGF influences the development of a subpopulation of spinal neurons that are AChE-positive.

Target cell stimulation of dissociated serotonergic neurons in culture

Dissociated mesencephalic raphe cells from fetal rats (14-18 days) were grown in culture in 96 well Linbro plates. The maturation of serotonergic cells was qualitatively studied using immunocytochemistry with a serotonin antibody and quantitatively by measuring the retention of radioactivity following incubation in the presence of a low concentration of [3H]5-hydroxytryptamine (6 X 10(-8) M). The 5-hydroxytryptamine immunoreactive neurons showed specific staining in the perikaryon, nucleus, dendrites, axons and growth cones. These neurons formed varicose fibers and growth cones after 18 h in culture and survived for up to 21 days in culture. Each serotonergic neuron concentrated approximately 1 fmol of serotonin after 20 min of incubation. Maturation of mesencephalic serotonergic neurons was increased in co-cultures of both normal (hippocampus, cerebral cortex, olfactory bulb and striatum) and abnormal (spinal cord) target neurons. The best stimulation was produced by dissociated hippocampal neurons (14-18 days of gestation) on mesencephalic raphe cells (14 days of gestation) after 4 days in culture. This stimulation was seen in culture conditions which favored neuronal but not glial survival. Our results obtained using cultures of dissociated serotonergic cells are consistent with an expansive network pattern developed by this chemical transmitter system in the adult brain.

Ultrastructural investigation of fetal rat brain hemisphere tissue in nonadherent stationary organ culture

Fetal rat brain fragments grown in nonadherent stationary organ culture for 50 days have been investigated ultrastructurally. Synaptogenesis and myelin formation occurred at the same time as the corresponding time-dependent events in the developing brain in vivo. Intermediate junctions were observed between cellular processes lining a central cavity in the fragments and later associated with astrocytes at the surface. Gap junctions and tight junctions were also present. In some fragments cilia were observed in the central cavity. Subependymal basement membrane labyrinths were observed in all fragments after 10 days in culture. The ultrastructural characteristics and the tissue-like structure in general were preserved for at least 50 days in this tissue culture system. The brain fragments may therefore be a valuable supplement to existing culture methods for nervous tissue.

Reaggregation of fetal rat brain cells in a stationary culture system. I: Methodology and cell identification

A stationary tissue culture system for reaggregation cultures of rat brain cells is described. Aggregates were formed by placing cells at high concentration in liquid overlay cultures on a nonadherent nutrient agar surface. No physical stress in the form of rotation or shaking was applied to the aggregating cell population. Transmission electron microscopy and immunohistochemistry showed that the cells developed from homogeneously dispersed, immature cells in Day 4 aggregates, to mature astrocytes, oligodendrocytes, and neurons in Day 20 aggregates. Twenty days older aggregates had a tightly packed neuropil which was most prominent in a cell-sparse outer layer of the aggregates. When the aggregates were allowed to adhere to a substrate, both glial fibrillary acidic protein (GFAP) positive and negative cells were observed migrating out from the aggregates. Cells giving a positive reaction for neuron specific enolase (NSE) were also present. This reaggregation procedure, with transfer of selected brain cell aggregates into agar-coated multiwells is an alternative three-dimensional culture system which can be potentially useful in the study of morphogenesis and cell interactions in the nervous system.

Development of taurine biosynthesizing system in cerebral cortical neurons in primary culture

Developmental patterns of taurine biosynthesizing system were investigated using primary cultured neurons prepared from the neopallium of 15-day-old fetal mice by a trypsin treatment in comparison with those in cerebral cortices obtained from age-matched fetal and neonatal mice. The morphological observations by phase contrast and scanning electron micrographies indicated that the cells in primary culture used in the present study possessed typical features of neurons. In addition, the immunohistochemical studies using the antibody to glial fibrillary acidic protein (GFAP), a specific marker for astroglia, revealed that the contamination of astroglias was negligible. The contents of taurine and metabolic intermediates in taurine biosynthesis, cysteine sulfinic acid and cysteic acid, in primary cultured neurons showed decreases during their development, especially during the first week after the inoculation. Similar developmental patterns of these amino acids were observed in cerebral cortices in vivo during perinatal stage, which corresponded to the first week of neuronal growth in vitro. On the other hand, the activities of cysteine sulfinic acid decarboxylase and cysteine dioxygenase, both of which are involved in the biosynthesis of taurine, were found to be increased progressively both in primary cultured neurons and in cerebral cortices in vivo during their growth. The immunohistochemical study using antitaurine antibody obtained from rabbit clearly demonstrated that immunoreactive materials were localized in cell bodies and the processes of neurons, and the intensity of the immunoreactivity in primary cultured neurons also showed a reduction with time of culture. These results indicate that primary cultured neurons used in this study possess a similar capacity to synthesize taurine from cysteine as developing brains in vivo. The present results also strongly suggest the well known decrease in cerebral taurine content in vivo during neonatal stages may be predominantly due to the decrease of taurine in neuronal cells.

Cell and tissue culture of the central nervous system: recent developments and current applications

A survey of methods for cell and tissue culture of the central nervous system (CNS) is given. This includes a brief historical outline and description of methods in current use. Recent methodological improvements are emphasized, and it is shown how these are applied in modern neurobiological research. Both monolayer cell cultures and three-dimensional organ culture systems are widely used, each having advantages and limitations. In recent years, there has been considerable improvement of culture for prolonged periods in chemically defined media. Brain tissue from a wide spectrum of species have been used, including different types of human brain cells which can be propagated for several months. At present, these culture systems are employed for dynamic studies of the developing, the adult and ageing brain. It is possible to select neurons and the different classes of glial cells for culture purposes. Cell culture of the CNS has given new insights into the biology of brain tumours. Culture systems for experimental tumour therapy in vitro are also available. Recently, it has been shown that organ cultures of brain tissue can be used as targets for invasive glioma cells, enabling a direct study of the interactions between tumour cells and normal tissue to take place.

Cyclic morphological changes of glial cells in long-term cultures of rat brain

Brain cells from embryonic rats were dissociated with trypsin, cultivated under constant conditions in Falcon flasks, and studied for periods of one year or more. Antisera against glial fibrillary acidic protein (GFA) and myelin basic protein (MBP) were used to identify glial cell types. For scanning electron microscopical (SEM) observation an embedding method in resin was developed that allows good preservation of the fine ultrastructural features of the cultivated cells and precise characterization of the cell types. Under our culture conditions, after four subcultures and 8-10 weeks of cultivation, the following cell types can be distinguished. (a) Flat epitheloid cells. From an immunocytological point of view these cells form a heterogeneous population composed of GFA- and MBP-positive and negative cells. They are the precursors of the following cell types. (b) Astroglial cells. SEM observations show a characteristic network of radially orientated prolongations. 92% of these cells are GFA-positive. (c) Oligodendroglial cells with characteristic dichotomously dividing branches. Secondary and tertiary branches end in flat amoeboid prolongations. These cells are MBP-positive. After approximately six weeks the most prominent cells are the flat epitheloid cells. The astroglial cells originate continuously from the epitheloid cells during the whole cultivation time. The formation of oligodendroglial cells, on the other hand, takes place at relatively precise intervals of time (approximately every 20-30 days) over the entire cultivation period (of more than one year).

Cellular composition of a cerebral hemisphere primary culture

In this overview attention is given to available markers and methods for characterizing cell elements in a culture system. Primary cultures from newborn rat cerebral hemispheres were grown for 14 days. The population of cells was dominated by astrocytic glial cells (60-70%), but cells with properties of macrophages, endothelial-like cells, mesenchymal-like cells, ependymal-like cells, and oligoblasts were also found. Neither mature neurons nor oligodendroglial cells were observed. The enrichment in astroglial-like cells makes the cultures a satisfactory astroglial-cell model, at least for some purposes.

Growth requirements of immature astrocytes in serum-free hormonally defined media

A chemically defined serum-free medium is described that has been optimized for the selective growth of immature astrocytes starting from early postnatal mouse cerebellar cultures. The medium is a modification of one described recently [Fischer et al, 1982] and consists of epidermal growth factor (EGF, 10 nM), transferrin (10 micrograms/ml), insulin (10 micrograms/ml), and bovine serum albumin (BSA, 1 mg/ml) in BME with Earle's salts. None of these constituents of the medium alone nor combinations of two of them can stimulate the proliferation and survival of immature astrocytes. Only with a combination of EGF and transferrin together with either insulin or BSA can proliferation of the cells be obtained. For optimal growth all four constituents are needed. However, the immature astrocytes can only grow for a limited time period of about 2-3 wk in this medium. Therefore they can be selected for and characterized but not continuously cultivated in this medium.

Culture of purified rat astrocytes in serum-free medium supplemented with mitogen

We have obtained a highly purified astrocyte population in cultures originating from neonatal (2-5 days) rat cerebrum by use of the selection process provided by a serum-free chemically defined medium (DM). The addition of a glial growth factor isolated from bovine pituitary glands to DM induced in these astrocyte cultures both a stimulation of astrocytic proliferation and a morphological transformation of the astrocytes from flat fibroblastic form to multipolar stellate form.

Isolation of a protein from bovine brain which promotes neurite extension from chick embryo cerebral cortex neurons in defined medium

Seven-day-old chick embryo cerebral cortex neurons cultured at low density (10,000 cells/16 mm well) in defined medium in polylysine-coated wells fail to extend neurites and assume a flattened phase-dark morphology. Addition of soluble bovine brain extract promotes neurite outgrowth and rounding of the cell body (which becomes phase-bright). A quantitative bioassay was utilized to purify this neurite extension factor (NEF), based on counting the number of phase-bright neurons with processes at least equal to one cell body diameter after 20 h in culture. Using a combination of heat treatment, DEAE-cellulose chromatography, and gel filtration, an acidic protein with a native Mr = 75,000 has been purified. Upon reduction it yields subunits of Mr = 37,000. Purified fractions are active at 100 ng/ml in inducing neurite outgrowth in this bioassay.

Astrocyte cultures from adult rat brain. Derivation, characterization and neurotrophic properties of pure astroglial cells from corpus callosum

It has not as yet been routinely possible to derive primary cultures of glial cells from adult rat brain tissue even when adopting strategies that have proven successful with perinatal tissue. We now report that in response to a surgical lesion and a period of postoperative 'priming' in vivo, proliferating cultures of astroglial cells can be derived from the normally quiescent glia of the corpus callosum region of the adult rat brain. In such cultures the predominance of astroglia and the virtual absence of oligodendroglia and neurons has been established by the use of a variety of cell-type specific antisera. Fibroblasts, the only other cell type identified, when not numerous could be successfully eliminated by treatment of the cultures with anti-Thy-1 antibodies and guinea pig complement. Pure astroglial cells from adult brain have been sub-cultured and maintained for up to 4 months in vitro, providing suitable quantities of cells for studies on the trophic interaction between glia and neurons. In long-term culture the adult astrocytes maintain a flattened undifferentiated morphology but readily assume a stellate shape with long branching processes upon the addition of a crude homogenate from bovine pituitary.

Preparation and partial characterization of highly purified primary cultures of neurons and non-neuronal (glial) cells from embryonic chick cerebral hemispheres and several other regions of the nervous system

Purified cultures of neurons and non-neuronal (glial) cells were prepared from the cerebral hemispheres of 10-day chick embryos by a method previously used for embryonic chick sympathetic ganglia 16. This technique separates these cell types on the basis of both: (1) differences in the adhesiveness of neurons and non-neuronal cells to a collagen substrate; and (2) the capacity of neurons to form homotypic aggregates. Purity of the cerebral non-neuronal cultures was determined to be greater than or equal to 99.5% by microscopic examination, while that of the cerebral neuronal cultures was only 92%. Modification of the technique by periodic redissociation of the neuronal aggregates during cell separation increased the purity of the neuronal cultures to greater than or equal to 97% as determined both by microscopic examination and by measurement of levels of butyrylcholinesterase, an enzyme present in the non-neuronal cells. Highly purified cultures of neurons were also prepared from the optic lobes of 10-day chick embryos (greater than or equal to 98%), but attempts to obtain non-neuronal cultures of reasonable density from this tissue were unsuccessful. In addition, highly purified non-neuronal cultures (greater than or equal to 99.5%) were prepared from the dorsal root ganglia of 12-day chick embryos, but cultures enriched with dorsal root neurons could only be partially purified (82%). Specific activity of butyrylcholinesterase in cerebral non-neuronal cells was found to vary inversely with the density of non-neuronal cells.

Immunoselection of oligodendrocytes by magnetic beads. I. Determination of antibody coupling parameters and cell binding conditions

Oligodendrocytes from early postnatal mouse cerebellum were isolated using polyacrylamide-coated magnetic beads carrying monoclonal antibody to 04 cell surface antigen. Oligodendrocytes were enriched to a purity of 91 +/- 4% starting from a mixed cell population containing approximately 1.5% antigen-positive oligodendrocytes. Viability of 04 antigen-positive oligodendrocytes was approximately 90% as judged by exclusion of trypan blue. Oligodendrocytes were recovered after detachment from the beads with a yield of 19 +/- 6% and after collection by centrifugation onto glass coverslips with yields of approximately 6% of all 04 antigen-positive cells. The final cell yield of oligodendrocytes is approximately 8 x 10(5) cells/gram fresh cerebellar tissue.

Molecular requirements for survival of cultured avian and rodent dorsal root ganglionic neurons responding to different trophic factors

We have previously demonstrated that both peripheral and central neurons from 8 day embryonic chick and newborn mouse can be maintained in a serum-free medium using the N1 supplement consisting of insulin, transferrin, putrescine, progesterone, and selenite. In the present studies we show that dorsal root ganglionic (DRG) neurons from embryonic chick (E7-E15) and neonatal mouse can be cultured in a serum-free environment with only the addition of insulin and transferrin, plus Nerve Growth Factor (NGF). Chick DRG from E10-E15 contain a population of neurons sensitive to a chick embryo eye-derived ganglionic neuronotrophic factor (GNTF), which is distinct from the neuronal subset dependent upon NGF. The GNTF-dependent chick neurons can also be maintained in culture with insulin and transferrin supplements. Neonatal mouse DRG neurons, whether supported by NGF or eye-derived GNTF, likewise survive in serum-free medium with only insulin and transferrin. Limited numbers of neurons survive for the first 24 hours in a serum-free medium lacking insulin or transferrin, but failed to display neurite outgrowth even in the presence of added trophic factor.

Growth regulator from spinal cord: produced in cultures of glial cells

Spinal cord cultures produced a regulatory factor which inhibited myogenesis. After serial passage (x 3) production of this factor continued as neuronal cells disappeared and large, pale polygonal cells rich in cytoplasmic microfilaments with morphology of astrocyte precursors became predominant. These glial cells responded to dibutyryl cyclic AMP by assuming a star-shaped appearance with multiple, radiating cytoplasmic processes. Cultures active in production of the growth regulator also produced nonneuronal-type enolase and glutamine synthetase. It is suggested that the growth regulator is produced by astrocytic glia in culture.

Complete replacement of serum in primary cultures of chick embryo brain cells by growth-promoting alpha-globulin

Growth-promoting alpha-globulin (GPAG), a specific serum protein complex which induces mitotic activity in continually replicating metazoan cells in vitro, was shown in this study to support growth of astrocytes and mesenchymal cells as well as process formation of nerve cells isolated from cerebral hemispheres of chick embryos.

Method for preparing cultures of central neurons: cytochemical and immunochemical studies

We report a simplified method for culturing fetal central nervous system cells predominantly inducing neurons that grow, differentiate, and live in vitro for as long as 10 weeks. These central nervous system cells form a confluent cell culture in which about 80% of the cells are fully differentiated neurons producing interconnecting axons and dendrite processes and live upon a sparse underlying population of fibrillary and protoplasmic astrocytes, oligodendrocytes, and fibroblasts. Morphological and cytochemical characteristics of these cell types, based on immunofluorescent cell specific markers and silver staining of neurons, are presented.

Demonstration of enkephalin-, substance P- and glutamate decarboxylase-like immunoreactivity in cultured cells derived from newborn rat neostriatum

The presence of cells exhibiting leucine-enkephalin-, substance P- and glutamate decarboxylase-like immunoreactivity was demonstrated in dissociated cultures from newborn rat neostriatum. The size and shape of the enkephalin-immunoreactive cells varied, but they were generally larger than substance P- and glutamate decarboxylase-immunoreactive cells, which formed relatively uniform cell populations. Cells of apparently non-neuronal origin did not show any immunoreactivity. It is unlikely that enkephalin is present in the same cells that contain substance P or glutamate decarboxylase because of morphological differences between these cells. The possible coexistence of substance P and glutamate decarboxylase in the same cells however, could not be excluded. The results of this study confirm that the cell bodies of neurons containing three possible neurotransmitters are located in the neostriatum.

Development, reactivity and GFA immunofluorescence of astroglia-containing monolayer cultures from rat cerebrum

This report describes detailed protocols for the dissociation, seeding and growth in vitro of monolayer cultures derived from neonatal rat cerebrum. Primary cultures derived by using different seeding densities and in vitro ages were examined qualitatively and quantitatively for morphological composition in terms of two major cell classes (flat cells and process-bearing cells) and for the presence within these classes of glial fibrillary acidic protein (GFA) as detected by immunofluorescence histochemistry. Also examined was the reaction of the cells to serum withdrawal plus the administration of dibutyryl cyclic AMP in terms of the conversion of flat cells into process-bearing cells. Conditions are defined for the generation of in vitro cell populations, more than 90% of which are GFA-containing flat cells which can all be experimentally converted into cells with processes. These well-defined culture preparations will serve as useful models for future studies of astroglial behaviour.

Fibronectin associated with the glial component of embryonic brain cell cultures

In the basic approach to investigations of neuronal--glial interactions during both normal brain development and its pathogenesis, embryonic brain cell populations were fractionated into purified neuronal and glial components. Using separation procedures based on differential adhesion and cytotoxicity, the isolated neuronal and glial phenotypes could be identified by distinct morphological and biochemical characteristics, including the visualization of glial fibrillary acid protein (GFA) within glial cells in immunohistochemical assays with monospecific anti-GFA serum. When unfractionated cerebrum cells dissociated from 10-day chick or 14-day mouse embryos were plated as monolayers and cultured for 1--14 days, monospecific antiserum against fibronectin (LETS glycoprotein) was found to react with many, but not all, of the cells as revealed by indirect immunofluorescence microscopy. The isolated neuronal and glial components of these populations were used to determine whether the appearance of membrane-associated fibronectin was characteristic of one cell type or the other, or both, and if neuronal--glial cell interaction was required for its expression. It was found that the surfaces of glial cells, completely isolated from neurons, showed an intense fluorescent reaction to the anti-fibronectin serum. In contrast, the purified neuronal cultures showed no fluorescence with either the anti-GFA or anti-fibronectin sera. These results demonstrate fibronectin as a cell surface protein associated primarily with glial cells and independent of neuronal--glial cell interaction for its expression. Furthermore, the results indicate that the fibronectin observed on glial cell surfaces in these cultures is produced endogenously and is not due to the preferential binding of fibronectin present in the culture medium. The role of fibronectin as an adhesive molecule in neuronal--glial interactions is discussed.

In vitro growth of glial cell-enriched and depleted populations from mouse cerebellum

Glial cell-enriched and -depleted populations isolated from 10-day-old mouse cerebella have been grown in vitro. There are marked differences in the cellular morphology between these two populations. The glial cell-enriched populations are very heterogeneous with respect to cell size, morphology and processes, whereas the glial cell-depleted populations are very homogeneous, containing a cell type with a small cell body and predominantly bipolar processes. Further characterization of the cell types has been affected using antiserum prepared against GFA protein and tubulin. The immunocytochemical localization of these proteins clearly identifies astrocytes and neurons. The glial cell enriched populations contain several types of astrocytes and neurons in addition to cells of non-ectodermal origin, whereas the glial cell-depleted populations contain predominantly a single neuronal cell type, the granule cells.

Enzymatic and morphological properties of primary rat brain astrocyte cultures, and enzyme development in vivo

The development of (Na+ + K+) ATPase, carbonic anhydrase and HCO3--stimulated ATPase activity was studied in developing rat brain in vivo, and in primary astrocyte cultures from 1--3-day-old rat brain as a function of increasing cell growth. The primary cultures showed an increase in all the above enzyme activities during cell growth, with time courses which were qualitatively similar to their development in vivo. Cell cultures grown separately from the cerebellum plus brain stem regions showed greater carbonic anhydrase activity than cerebral cultures over the entire 4-week growth period, corresponding to development of this activity in these same regions in vivo, HCO3-stimulated ATPase activity was slightly greater in cerebellar cultures and (Na+ + K+) ATPase activity was greater in cerebral cultures up to the second week of growth, resembling development of the same enzyme activities in vivo. C6 glioma and neuroblastoma cells showed no and 10-fold lower carbonic anhydrase activities respectively, compared to the primary astrocyte cultures. Addition of 1 mM N6-2'-O-dibutyryladenosine-3',5'-monophosphate (DBcAMP) in the presence of serum caused marked formation of cellular processes and increased carbonic anhydrase and (Na+ + K+) ATPase activity. Maximum effects were found 2 h after addition of 1 mM DBcAMP and thereafter declined. In the absence of serum such effects persisted for at least 24 h. Electron microscope studies showed large numbers of microtubule (approximately 20 nm diameter) and filamentous structures (less than or equal to 10 nm diameter) in the cytoplasm, which showed changes in distribution in cells treated with DBcAMP. This study suggests that the increase in ATPase and carbonic anhydrase activities in rat brain with increasing age may be in part a reflection of proliferation and development of astroglia cells. Together with the morphological data, it also provides additional evidence that primary cultures derived from neonatal rats may closely resemble developing astroglia in vivo.

Induced glial differentiation of fetal rat brain cells in culture: an ultrastructural study

Primary and secondary cultures of fetal rat brain cells (FBC) from 18th day of gestation have been investigated by scanning and transmission electron microscopy. Primary cultures consisted of a monolayer of flat, undifferentiated epithelioid cells, with some oligodendrocytes, astrocytes and immature neuronal cells. In secondary cultures, cells with glia morphology disappeared. Following addition of extracts from adult rat brains to secondary cultures, a dramatic change of the epithelioid cells took place. They detached from the palstic surface, extruded long cytoplasmic processes with numerous microvilli and cytoplasmic blebs as well as parallel arrays of microtubules and filaments. The differentiated cells resembled astrocytes, and characteristic glia filaments were also observed. An increase of ribosomes and rough endoplasmatic reticulum suggested enhancement of protein synthesis. At the same time S-100 protein and glial fibrillary acidic protein accumulated within the cells. The morphological changes were mostly reversible within 48 h of removal of the brain extract.

Subcellular distribution of glutamyltransferase activities in embryonic cerebral hemispheres

Glutamyltransferase (GT) activities were examined in cell groups from embryonic cerebral hemispheres. During normal development, GT activities were highest in a mixed population of small neurons and non-neuronal cells (small cell group). In culture, in response to hydrocortisone, activities exceeded normal levels only in this small cell group. In view of these findings, the small cell population was used to study the subcellular distribution of the enzyme. At the subcellular level, GT activities in the small cell group were distributed differentially but increased generally during normal development. In vitro, hydrocortisone promoted a precocious increase in GT activity, under experimental conditions regarded as optimum, only in the subcellular fraction characterized by synaptic endings.

Neuroblasts-glia interaction in tissue culture as evidenced by the study of ectoenzymes. Ecto-ATPase activity of mouse neuroblastoma cells

Ecto-ATPase and ecto-5'-nucleotidase activities of hamster astroblasts, clonal line NN, and mouse neuroblasts, clonal line Ml in coculture, have been studied. The originally low ecto-ATPase activity in both cell lines increased many fold when these cell lines were cocultured. An increase of ecto-ATPase activity was also found in coculture of neuroblastoma cells with chick fibroblasts. Neuroblastoma Ml cells were separated from coculture with hamster astroblasts after 7 days and 2 months. Reisolated M1 cell lines exhibited higher ecto-ATPase activity than the original M1 cell line. The M1 cell line separated after 2 months of coculture had higher ecto-ATPase activity than the M1 cell line separated after 7 days of coculture with hamster astroblasts. This higher ecto-ATPase activity continued for more than 20 replications after separation of the M1 cells from the glial cells.