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

Mary Jane Hogue (1883-1962): A pioneer in human brain tissue culture

The ability to maintain human brain explants in tissue culture was a critical step in the use of these cells for the study of central nervous system disorders. Ross G. Harrison (1870-1959) was the first to successfully maintain frog medullary tissue in culture in 1907, but it took another 38 years before successful culture of human brain tissue was accomplished. One of the pioneers in this achievement was Mary Jane Hogue (1883-1962). Hogue was born into a Quaker family in 1883 in West Chester, Pennsylvania, and received her undergraduate degree from Goucher College in Baltimore, Maryland. Research with the developmental biologist Theodor Boveri (1862-1915) in Würzburg, Germany, resulted in her Ph.D. (1909). Hogue transitioned from studying protozoa to the culture of human brain tissue in the 1940s and 1950s, when she was one of the first to culture cells from human fetal, infant, and adult brain explants. We review Hogue's pioneering contributions to the study of human brain cells in culture, her putative identification of progenitor neuroblast and/or glioblast cells, and her use of the cultures to study the cytopathogenic effects of poliovirus. We also put Hogue's work in perspective by discussing how other women pioneers in tissue culture influenced Hogue and her research.

Chick Heart Invasion Assay for Testing the Invasiveness of Cancer Cells and the Activity of Potentially Anti-invasive Compounds

The goal of the chick heart assay is to offer a relevant organ culture method to study tumor invasion in three dimensions. The assay can distinguish between invasive and non-invasive cells, and enables study of the effects of test compounds on tumor invasion. Cancer cells - either as aggregates or single cells - are confronted with fragments of embryonic chick heart. After organ culture in suspension for a few days or weeks the confronting cultures are fixed and embedded in paraffin for histological analysis. The three-dimensional interaction between the cancer cells and the normal tissue is then reconstructed from serial sections stained with hematoxylin-eosin or after immunohistochemical staining for epitopes in the heart tissue or the confronting cancer cells. The assay is consistent with the recent concept that cancer invasion is the result of molecular interactions between the cancer cells and their neighbouring stromal host elements (myofibroblasts, endothelial cells, extracellular matrix components, etc.). Here, this stromal environment is offered to the cancer cells as a living tissue fragment. Supporting aspects to the relevance of the assay are multiple. Invasion in the assay is in accordance with the criteria of cancer invasion: progressive occupation and replacement in time and space of the host tissue, and invasiveness and non-invasiveness in vivo of the confronting cells generally correlates with the outcome of the assay. Furthermore, the invasion pattern of cells in vivo, as defined by pathologists, is reflected in the histological images in the assay. Quantitative structure-activity relation (QSAR) analysis of the results obtained with numerous potentially anti-invasive organic congener compounds allowed the study of structure-activity relations for flavonoids and chalcones, and known anti-metastatic drugs used in the clinic (e.g., microtubule inhibitors) inhibit invasion in the assay as well. However, the assay does not take into account immunological contributions to cancer invasion.

Chick heart invasion assay

Tumors are microecosystems in which a continuous cross talk between cancer cells and host cells decides on the invasive behavior of the tumor cell population as a whole (Mareel et al., Encyclopedia of cancer, San Diego, CA, Academic Press, 1997). Both compartments secrete activating and inhibitory factors that modulate activities such as cell-extracellular matrix (ECM) interaction, cell-cell adhesion, remodeling of the ECM, and cell motility. For this reason, confrontations of cancer cells with a living normal host tissue in organ culture have been introduced by several groups: Wolff and Schneider in France (Wolff and Schneider, C R S Soc Biol (Paris) 151:1291-1292, 1957), Easty and Easty in the United Kingdom (Easty and Easty, Nature 199:1104-1105, 1963), and Schleich in Germany (Schleich et al., J Natl Cancer Inst 56:221-237, 1976). Embryonic chick heart fragments in organ culture maintain many histological features of their tissue of origin: They are composed of myocytes, fibroblasts, and endothelial cells, and their ECM contains fibronectin, laminin, and several collagen types. Moreover, the fragments remain contractile, and this activity allows the monitoring of their functional integrity during organ culture.

Primary culture of glial cells from mouse sympathetic cervical ganglion: a valuable tool for studying glial cell biology

Central nervous system glial cells as astrocytes and microglia have been investigated in vitro and many intracellular pathways have been clarified upon various stimuli. Peripheral glial cells, however, are not as deeply investigated in vitro despite its importance role in inflammatory and neurodegenerative diseases. Based on our previous experience of culturing neuronal cells, our objective was to standardize and morphologically characterize a primary culture of mouse superior cervical ganglion glial cells in order to obtain a useful tool to study peripheral glial cell biology. Superior cervical ganglia from neonatal C57BL6 mice were enzymatically and mechanically dissociated and cells were plated on diluted Matrigel coated wells in a final concentration of 10,000cells/well. Five to 8 days post plating, glial cell cultures were fixed for morphological and immunocytochemical characterization. Glial cells showed a flat and irregular shape, two or three long cytoplasm processes, and round, oval or long shaped nuclei, with regular outline. Cell proliferation and mitosis were detected both qualitative and quantitatively. Glial cells were able to maintain their phenotype in our culture model including immunoreactivity against glial cell marker GFAP. This is the first description of immunocytochemical characterization of mouse sympathetic cervical ganglion glial cells in primary culture. This work discusses the uses and limitations of our model as a tool to study many aspects of peripheral glial cell biology.

Immunophenotypic and ultrastructural validation of a new human glioblastoma cell line

1. A human glioma cell line, NG97, was established by Grippo et al. in 2001 from tissue obtained from a grade III astrocytoma (WHO, 2000). In this first study, the cell line grew as two morphologically distinct subpopulations: dendritic/spindle cells and small round cells. The injection of NG97 cells into nude mice induced an aggressive tumor characterized by: severe cytological atypia, vascular proliferation and pseudopalisading necrosis (glioblastoma multiforme features). 2. The purpose of the present study was to characterize the immunophenotype and ultrastructural aspects of this cell line, using the parental tumor, cultured cells and the xenotransplant, in order to assess its glial nature and possible divergent differentiation. 3. NG97 cells and xenotransplant expressed the main neuroglial markers (GFAP, S-100 protein, NSE and Leu-7) and showed no aberrant expression of other histogenetic markers. GFAP was similarly expressed in the parental tumor and in the cells in culture, but decreased in the xenotransplant. NSE expression was reduced in NG97 cells, but substantially recovered in the xenotransplant. This variability in expression of GFAP and NSE was interpreted as either a phenomenon of dedifferentiation or to microenvironmental selection of specific subclones. S-100 was equally expressed in the three contexts. The xenotransplant's ultrastructural features were those of a highly undifferentiated tumor. No significant immunophenotypic or ultrastructural differences between the two morphologically distinct populations were found. 4. Thus, our data demonstrate that NG97 cells constitute a pure glial-committed cell line, which may prove useful as a malignant glioma model in studies addressing pathophysiological, diagnostic and therapeutic issues.

Human central nervous system tissue culture: a historical review and examination of recent advances

Tissue culture has been and continues to be widely used in medical research. Since the beginning of central nervous system (CNS) tissue culture nearly 100 years ago, the scientific community has contributed innumerable protocols and materials leading to the current wide variety of culture systems. While nonhuman cultures have traditionally been more widely used, interest in human CNS tissue culture techniques has accelerated since the middle of the last century. This has been fueled largely by the desire to model human physiology and disease in vitro with human cells. We review the history of human CNS tissue culture summarizing advances that have led to the current breadth of options available. The review addresses tissue sources, culture initiation, formats, culture ware, media, supplements and substrates, and maintenance. All of these variables have been influential in the development of culturing options and the optimization of culture survival and propagation.

A reliable primary human CNS culture protocol for morphological studies of dendritic and synaptic elements

Primary dissociated human fetal forebrain cultures were grown in defined serum-free conditions. At 4 weeks in vitro the cultures contained abundant morphologically well differentiated neurons with complex dendritic arbors. Astrocytic proliferation was negligible without the use of antimitotic agents. Confocal scanning laser microscopy (CSLM) and electron microscopy confirmed the presence of a dense neuropil, numerous cell-cell contacts and synapses. Neurons expressed a variety of proteins including growth associated protein-43 (GAP43), microtubule associated protein-2ab (MAP), class-III beta tubulin (C3BT), neurofilaments (NF), synaptophysin (SYN), parvalbumin (PA) and calbindin (CB). The cultures have proven to be reliable and simple to initiate and maintain for many weeks without passaging. They are useful in investigations of dendritic growth and injury of primary human CNS neurons.

Bilirubin exerts additional toxic effects in hypoxic cultured neurons from the developing rat brain by the recruitment of glutamate neurotoxicity

Both hypoxia and bilirubin are common risk factors in newborns, which may act synergistically to produce anatomical and functional disturbances of the CNS. Using primary cultures of neurons from the fetal rat brain, it was recently reported that neuronal apoptosis accounts for the deleterious consequences of these two insults. To investigate the influence of hypoxia, bilirubin, or their combination on the outcome of neuronal cells of the immature brain, and delineate cellular mechanisms involved, 6-d-old cultured neurons were submitted to either hypoxia (6 h), unconjugated bilirubin (0.5 microM), or to combined conditions. Within 96 h, cell viability was reduced by 22.7% and 24.5% by hypoxia and bilirubin, respectively, whereas combined treatments decreased vital score by 34%. Nuclear morphology revealed 13.4% of apoptotic cells after hypoxia, 16.2% after bilirubin, and 22.6% after both treatments. Bilirubin action was specifically blocked by the glutamate receptor antagonist MK-801, which was without effect on the consequences of hypoxia. Temporal changes in [(3)H]leucine incorporation rates as well as beneficial effects of cycloheximide reflected a programmed phenomenon dependent upon synthesis of selective proteins. The presence of bilirubin reduced hypoxia-induced alterations of cell energy metabolism, as reflected by 2-D-[(3)H]deoxyglucose incorporation, raising the question of free radical scavenging. Measurements of intracellular radical generation, however, failed to confirm the antioxidant role of bilirubin. Taken together, our data suggest that low levels of bilirubin may enhance hypoxia effects in immature neurons by facilitating glutamate-mediated apoptosis through the activation of N:-methyl-D-aspartate receptors.

Transient hypoxia may lead to neuronal proliferation in the developing mammalian brain: from apoptosis to cell cycle completion

Cerebral hypoxia/ischemia was shown to induce delayed, apoptotic neuronal death occurring through biochemical pathways potentially sharing common events with cell proliferation. This study was designed to test the hypothesis that a sublethal hypoxia may promote mitotic activity in developing central neurons. After six days in vitro, cultured neurons from the forebrain of 14-day-old rat embryos were exposed to hypoxia (95% N2/5% CO2) for 3 h and re-oxygenated for up to 96 h. Controls were kept in normoxia. As a function of time, cell viability was measured by diphenyltetrazolium bromide, and rates of DNA and protein synthesis were monitored using [3H]thymidine and [3H]leucine, respectively. Morphological features of apoptosis, necrosis and mitosis were scored under fluorescence microscopy after nuclear staining with 4,6-diamidino-2-phenylindole, and the expression profile of proliferating cell nuclear antigen, a cofactor for DNA polymerase, was analysed by immunohistochemistry. Data were compared to those obtained after transient hypoxia for 6 h followed by re-oxygenation for 96 h and which was shown to induce apoptosis. Whereas a 6-h insult reduced cell viability, with 23% of the neurons exhibiting apoptosis by the end of re-oxygenation, a 3-h hypoxia led to a cycloheximide-sensitive increase in the final number of living neurons compared to controls (13%, P < 0.01), with no signs of apoptosis, significantly increased thymidine incorporation into acid-precipitable fraction, and persistent over-expression of proliferating cell nuclear antigen. Accordingly, final score of mitotic nuclei was significantly enhanced. In addition, the cell cycle inhibitor olomoucine (50 microM) prevented apoptosis consecutive to a 6-h hypoxia, but impaired the stimulatory effects of a 3-h insult. These findings support the conclusion that some neurons exposed to sublethal hypoxia may dodge apoptotic death by fully achieving the cell cycle.

Role of extracellular matrix in tumor invasion: migration of glioma cells along fibronectin-positive mesenchymal cell processes

OBJECTIVE

The major morbidity of glioma lies in its infiltrative growth. One of the major patterns of this invasive growth is the formation of Scherer's secondary structures associated with the blood vessels and the leptomeninges. To better understand the role of extracellular matrix (ECM) in glioma invasion, we investigated in vitro the interaction between glioma cells and the meningeal mesenchymal tissue from the brain. As an aid to this study, ECM in glioma cell line spheroids was compared with that in primary fetal brain aggregates.

METHODS

To study the expression of ECM, four glioma cell lines (U-87 MG, U-251 MG, AN1/lac-z, and HF-66) and primary cells from fetal rat brain were grown as spheroids and monolayers. To sudy the role of ECM in glioma invasion, spheroids from the glioma cell lines were grown over established cultures of fetal meningeal and mesenchymal tissue. Expression of fibronectin, laminin, tenascin, collagen VI, and chondroitin sulfate proteoglycan was studied by immunofluorescence.

RESULTS

Expression of ECM by the spheroids was variable. U-87 MG expressed most of the ECM components robustly, whereas AN1/lac-z expressed them all weakly. Fetal rat brain aggregates produced minimal ECM. In cocultures of glioma spheroids and fetal meningeal mesenchymal tissue, individual cells from the glioma spheroids that expressed least fibronectin (AN1/lac-z and U-251 MG) migrated along the fibronectin-positive mesenchymal cells in the culture dish. Cells from the other two lines (U-87 MG and HF-66) that expressed fibronectin strongly did not demonstrate such behavior. None of the other ECM components showed a similar association; mesenchymal cells did not express laminin as strongly as fibronectin, and glioma cells were not observed to align with the laminin-positive structures.

CONCLUSION

This study suggests that fibronectin may play a key role in intracerebral invasion of glioma cells.

Influence of post-hypoxia reoxygenation conditions on energy metabolism and superoxide production in cultured neurons from the rat forebrain

Brain reperfusion and/or reoxygenation may be of particular importance in the etiology of neuronal damage after hypoxic-ischemic insult in neonates, especially with reference to the generation of free radicals. To investigate this issue, the influence of either standard reoxygenation or transient hyperoxia was studied on the consequences of severe hypoxia in a model of cultured neurons isolated from the fetal rat brain. Culture dishes were exposed for 6 h to hypoxia (95% N2/5% CO2). They were then placed under normoxia (95% air/5% CO2) or hyperoxia (95% O2/5% CO2) for 3 h, and finally returned to normoxia. Control cultures were kept under normoxic conditions. Cell morphology, protein concentrations, lactate dehydrogenase leakage, energy metabolism, as reflected by specific transport and incorporation of 2-D-[3H]deoxyglucose, as well as superoxide radical formation were analyzed as a function of time. Po2 values in the cell incubating medium were decreased by 78% by hypoxia and increased by 221% by hyperoxia. No morphologic alteration could be noticed before 72 h posthypoxia, when cell degeneration became apparent, with a concomitant reduction in protein contents. Hypoxia-reoxygenation induced a transient cellular hypermetabolism, as shown by a 36% increase in 2-D-[3H]deoxyglucose uptake 24 h after hypoxia, and then a 23% decrease below control values at 72 h. It also led to a sharp increase in the formation of superoxide radicals (+108%). Transient hyperoxia during reoxygenation did not exacerbate these events, and thus would not enhance their deterimental effects on cell integrity.

Analysis of glutamate receptors in primary cultured neurons from fetal rat forebrain

In order to further analyze the development of glutamatergic pathways in neuronal cells, the expression of excitatory amino acid receptors was studied in a model of neurons in primary culture by measuring the specific binding of L-[3H]glutamate under various incubation conditions in 8-day-old intact living neurons isolated from the embryonic rat forebrain, as well as in membrane preparations from these cultures and from newborn rat forebrain. In addition, the receptor responsiveness to glutamate was assessed by studying the uptake of tetraphenylphosphonium (TPP+) which reflects membrane polarization. In the presence of a potent inhibitor of glutamate uptake, the radioligand bound to a total number of sites of 36.7 pmol/mg protein in intact cells incubated in a Tris buffer containing Na+, Ca2+, and Cl-, with a Kd around 2 microM. In the absence of the above ions, [3H]glutamate specific binding diminished to 14.2 pmol/mg protein with a Kd-value of 550 nM. Under both of the above conditions, similar Kd were obtained in membranes isolated from cultures and from the newborn brain. However, Bmax-values were significantly lower in culture membranes than in intact cells or newborn membranes. Displacement studies showed that NMDA was the most potent compound to inhibit [3H]glutamate binding in membranes obtained from cultured neurons as well as from the newborn brain, whereas quisqualate, AMPA, kainate and trans-ACPD were equally effective.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of adenosine receptors in a model of cultured neurons from rat forebrain

The neuromodulator adenosine is acting through specific receptors coupled to adenylate cyclase via G-proteins. The expression of both adenosine receptors A1 and A2 as well as forskolin binding sites was investigated by radioligand binding techniques in 8-day-old neurons isolated from fetal rat forebrain and cultured in chemically-defined medium. Adenosine A1 receptors were specifically labeled with [3H]chloro-N6-cyclopentyladenosine (CCPA), whereas [3H]CGS 21680 was used for the analysis of A2 receptors. Cultured neurons exhibited high affinity binding sites for CCPA (Bmax = 160 fmol/mg protein; Kd = 2.9 nM), and for CGS 21680 (Bmax = 14 fmol/mg protein; Kd = 1.7 nM). These data correlate well with those obtained in crude membranes isolated from the newborn rat forebrain. The incubation of culture membranes in the additional presence of guanylyl-5'-imidodiphosphate (Gpp(NH)p, a GTP analogue) led to significantly increased Kd-values, suggesting the association of adenosine receptors with G-proteins. Finally, cultured neurons also bound specifically [3H]forskolin with characteristics close to those found in the newborn brain, indicating that cultured neurons appear as an appropriate model for studying the neuromodulatory properties of adenosine.

An aggregate brain cell culture model for studying neuronal degeneration and regeneration

Rotation-mediated aggregating cell cultures from fetal rat telencephalons containing glial and neuronal cells mature in a fashion comparable to that known to occur in brain in vivo. Large aggregates of 300-500 microM diameters can now reproducibly be cultivated and maintained for more than 40 days in a well defined serum free medium. Validity of the use of such cultures for in vitro studies of various physiological, pharmacological and toxicological phenomenon has already been demonstrated. In this communication some observations suggesting the usefulness of such cultures for pharmacological studies clarifying the possible effects of drugs and other agents on excitatory amino acid induced pathological processes will be presented. The advantages and limitations of the use of aggregated brain cell culture based models for the development of agents potentially useful for the treatment of aging and dementia will also be discussed.

Human fetal myelinated organotypic cultures

We have previously reported the establishment of organotypic cultures derived from human fetal brain tissue. Although these cultures permit the testing of multiple hypotheses about normal human neurodevelopment and neuropathologic conditions, they have the limitation of not being myelinated and therefore preclude the study of questions related to myelinogenesis and diseases of myelin. In the current communication, we describe recent developments that allow us to overcome this limitation and permit the establishment of a myelinated organotypic culture model. Sections of dorsal column dissected from the lumbar spinal cord of human fetuses ranging in age 21-23 weeks of gestation were placed in culture. The explants were maintained for up to 12 weeks during which time they were characterized and shown to express a number of CNS cell-type-specific markers including glial fibrillary acidic protein (astrocytes), nerve growth factor receptor and neurofilament protein (neurons), CD68 (microglia), and myelin basic protein, HNK-1 and galactocerebroside (oligodendrocytes). In addition, lectin histochemistry using Ricinus communis agglutinin-1 detected microglia and endothelial cells. Upon explantation, abundant myelin was seen by electron microscopy in the cultures. Although during the culture period there was degradation of myelin, there was also evidence of maintenance of intact myelin sheaths around small caliber axons and de novo myelin synthesis. This model system may permit the further use of human organotypic cultures to investigate issues related to neurodevelopment and to pathologic conditions including those relevant to dysmyelination and demyelination.

Neuronal cell cultures: a tool for investigations in developmental neurobiology

The aim of this review is to describe environmental requirements for survival of neuronal cells in culture, and secondly to survey the complex interplay between hormones, neurotrophic factors, transport- and extracellular matrix- proteins, which characterize the developmental program of differentiating neurons. An overall reconsideration of the literature in this vast field is above the limits of the present paper; since progress and refinement in the techniques of neuronal cell cultures have paralleled the advancement in Developmental Neurobiology, we will run instead through the main steps which form the conceptual framework of neuronal cell cultures.

Human fetal central nervous system organotypic cultures

Many aspects of human neurodevelopment remain enigmatic. A main reason for this is, although there have been a significant number of morphologic and biochemical studies of neural tissues derived from human embryos and fetuses, this can only provide a static picture of the events at a given gestational age. Also, in vitro studies that focus on cells derived from these tissues have a limitation in that different cell types in dissociated tissue culture cannot interact in a 'normal' physiologic manner thereby, perhaps, altering their housekeeping and luxury functions. The present study focused on the development of a human explant organotypic culture model that may overcome the static limitation of the first example and permit a dynamic analysis of different cell types as they interact which may satisfy the second restriction. Because there is an array of developmental markers that define different cell phenotypes, this explant model may also provide a means of analyzing, for the first time, processes undefined in the human CNS. Human fetal CNS tissue obtained from second trimester abortuses was established in culture. The tissues were maintained for up to 12 weeks during which time they developed and differentiated. Sample cultures were harvested periodically and analyzed by light- and electron microscopy in combination with immunocytochemistry. Differentiation of neurons, astrocytes, oligodendrocytes and endothelial cells was documented using morphologic and biochemical criteria. As such, this model system may allow for the analysis of processes that occur during normal human fetal neurodevelopment and in pathologic conditions.

Cultivation of rat fetal spinal cord slices in a semi-solid medium: a new approach to studying axonal outgrowth and regeneration

A soft agar culture system was used for the cultivation of spinal cord slices with the purpose of improving the evaluation of the dynamics of axonal outgrowth and development. Slices of the spinal cord of 15-day-old fetal Wistar rats were cultured in a 0.5% agar culture medium. The sprouting and outgrowth of axons from the slices was observed at 6-24-h intervals. The morphology and growth rates of axons could be easily investigated by light microscopy. Quantification of growth parameters of individual neurites is made easy because no cells migrate out of the slices, so that the outgrowth is not masked by migrating neurons, fibroblasts, glial cells etc. The axons had well-developed growth cones, comparable to those observed in liquid medium; the daily growth rate was on average 318 microns during the 6 days of observation, with a maximum of 1050 microns per day. Back-labelling with a fluorescent dye (DiI) indicated that the longest neurites originated from motoneurons. Our experiments show that axons can develop and grow in a soft agar medium without the need for adding any growth promoting factor or substrate molecule.

A chemically-defined medium for organotypic slice cultures

Organotypic slice cultures provide an excellent system for the analysis of study of the molecular mechanisms of this development necessitates the use of a chemically defined culture medium. We report here the development of a medium, EOL1 defined medium, designed specifically for this purpose. Cultures of both cerebral cortex and basal forebrain demonstrate that this defined medium allows a high degree of cytoarchitectural maintenance while promoting neural metabolism and process outgrowth.

Multicellular tumor spheroids from human gliomas maintained in organ culture

Tumor tissue from seven human gliomas was maintained in long-term agar overlay culture as multicellular organotypic spheroids. Light microscopic and ultrastructural observation of the spheroids displayed morphological features similar to those of the original tumor tissue in vivo; in this respect they were different from spheroids obtained from permanent cell lines. The spheroids contained preserved vessels, connective tissue, and macrophages, revealing a close resemblance to the conditions in the original tumor. Flow cytometric deoxyribonucleic acid measurements of cells from the tumor spheroids and from biopsy material obtained directly from the operation revealed the same ploidy and the same amount of proliferating cells in the spheroids as in the original tumor. Fluorescence microscopy using bromodeoxyuridine (BUdR) incorporation and anti-BUdR monoclonal antibody confirmed the proliferative potential of tumor cells in the spheroids. Diameter measurements showed that the size of the spheroids from two of the tumors increased over time while in three other cases it decreased. Spheroids from the remaining two tumors showed no change in size, even after 80 days in culture. These growth data and the relatively high number of proliferating cells, as measured by flow cytometry, indicate that the degree of cell proliferation and cell loss from the spheroids are closely linked, as is the case for tumors in vivo. The culture system presented provides a valuable alternative to propagation of human tumors in animals.

Primary dissociated cell culture of fetal rat central nervous tissue. I. Immunocytochemical and ultrastructural studies of cell development and synaptogenesis

We have tried to establish a method of primary dissociated cell culture of the central nervous system (CNS) for successful development of large numbers of synapses and myelinated axons. Cerebra from 18-day-old fetal rats were enzymatically dissociated into single cells and plated onto poly-D-lysine-precoated coverslips at high cell density. With the progress of cell maturation, mixed neuronal and non-neuronal cell processes grew heavily and piled up on each other, making three-dimensional structures which corresponded to 'neuropil' in vivo. Within these structures we could observe not only many mature neurons and remarkable synaptogenesis but also many myelinated axons. The synapses were mainly axo-dendritic but axo-somatic synapses were also occasionally observed. Although most of the axon terminals contained many round clear vesicles which were about 30 nm in diameter, some of them contained both round clear vesicles and 50 nm in diameter vesicles with electron-dense cores. Also a small number of large electron-dense core vesicles (about 130 nm in diameter) were found in the perikarya of mature neurons. The numerous synapse formations observed in 3-dimensional structures suggest that neurons can remain in a stable state and carry out an active metabolism through neurotransmitters. So these structures are considered to provide a favorable microenvironment for both synaptogenesis and myelinogenesis.

Primary culture of the enteric nervous system from neonatal hamster intestine. Selection of vasoactive intestinal polypeptide-containing neurons

The enteric nervous system is a major division of the autonomic nervous system and is responsible for the regulation of gastrointestinal function. The objective of the present study was to develop a simple and effective technique for isolating and culturing neurons of the enteric nervous system that would permit characterization of their development and regulatory peptide content. This was accomplished using a dispersed intestinal cell preparation cultured under conditions designed to support the growth and differentiation of neurons and neuroendocrine cells. Newborn hamster intestine was digested in 0.1% collagenase, mechanically dispersed, and cultured in RPMI 1640 supplemented with 2.5% serum and other additives. Phase and bright-field microscopy demonstrated neuronal cells and fibers after the second day in culture. This was confirmed by immunohistochemistry using antibodies directed against neurofilament and vasoactive intestinal polypeptide. Acetic acid extracts of the culture indicated that during the first 4 days of the culture the content of vasoactive intestinal polypeptide increased, whereas the content of substance P, mammalian bombesin, and neurotensin declined. High-performance liquid chromatography and fast protein liquid chromatography confirmed that the immunoreactive vasoactive intestinal polypeptide coeluted with synthetic and iodinated forms of the peptide. This study describes a technique for primary culture of intestinal tissue that supports the survival of enteric neurons and permits analysis of the development and synthetic and secretory characteristics of the enteric nervous system.

A normal human brain cell aggregate model for neurobiological studies

A new in vitro model of normal human brain has been developed in which fetal human brain cells form three-dimensional aggregates that can be maintained for up to 60 days in culture. Cells appear fully differentiated at the time of initiation in culture; the predominant cells identified were astrocytes, neurons, and oligodendrocytes with myelin, with occasional ependymal cells and macrophages. The specific arrangement and numbers of neural cells within aggregates differed among brain specimens. Cell kinetics studies detected DNA synthesis throughout the culture interval. Aggregates cocultured with a human malignant glioma cell line (U251-MG) were progressively invaded by tumor cells. In aggregates infected with human cytomegalovirus (CMV), intracellular viral replication and morphologic changes characteristic of human brain infection with this pathogen were seen. This model of brain aggregates should prove valuable for multidisciplinary studies in human neurobiology, particularly in the fields of developmental neurobiology, neuro-oncogenesis, tumor cell invasion, and species-specific viral infection of the central nervous system.

Fetal rat brain hemisphere tissue in nonadherent stationary organ culture

A simple organ culture system for brain tissue is described. Fragments of fetal rat brain hemisphere tissue are explanted to multiwell dishes base-coated with semisolid agar. In this system nonadherent organ culture can be performed for at least 50 days. Cell migration, biochemical and morphological differentiation and the formation of a layered architecture seem to mimic some of the phenomena occurring in the developing rat brain in vivo. The fragments may therefore be a useful organ culture model for nervous tissue.