Growth and differentiation of aggregating fetal brain cells in a serum-free defined medium

Synapse formation and development of neurotransmitter functions in neuronal cells from chick brain cultured in a serum-free, defined medium

Cells dissociated from cerebral hemispheres of 8-day-old chick embryos were seeded on poly-L-lysine coated Petri dishes in serum-containing medium. After 24 hr the culture medium was switched to a serum-free, chemically defined medium. These cultures contain mainly neuronal cells until day 14, characterized by the presence of acetylcholinesterase activity and neurofilament proteins. After 2 weeks glial cells progressively contaminated the neuronal culture. Cultures were maintained for a period of 4 weeks. From day 6 on numerous synapses with clear vesicles were observed. The activity of choline acetyltransferase remained low throughout the culture period, while GABA levels increased in parallel with synaptogenesis. Our observations indicate that chick cerebral hemisphere neuronal cultures grown in serum-free, chemically defined medium contain GABAergic neurons that undergo maturation.

Nutrition and fetal brain maturation. I. Responses in vitro and in vivo

The glycolytic enzyme enolase increases during the perinatal period of brain development and was utilized as a marker for examining the effect of culture environment on differentiation of cells from 20-day fetal rat brain. Enolase activity in cell cultures increased from 0.91 +/- 0.03 (Day 0) to 2.11 +/- 0.10 mumol/min/mg protein (Day 6). Comparable levels were not reached in vivo until neonatal pups were 15 days old. The in vitro increase was inhibited by both cycloheximide and actinomycin D. Enolase activity in the cells responded to alterations in both incubation media and homologous serum. After 6 days in culture, cells incubated in rat serum (10%) added to MEM or RPMI produced twice as much enolase activity as cells incubated similarly in Ham's medium, i.e., 1.96 +/- 0.09 and 1.85 +/- 0.21 vs 1.02 +/- 0.09, P less than 0.001. Results of a comparable magnitude were obtained when fetal calf serum replaced adult rat serum, but enolase production was somewhat lower when newborn calf serum replaced adult rat or fetal calf serum. When cells were incubated for 6 days with graded concentrations of adult rat serum (2.5-15%), enolase activity increased progressively. The pattern of enolase response suggests that the fetal rat brain cell model described herein will provide a sensitive probe with which to gain insight into nutrition and fetal brain development.

Neurotrophic effects of hippocampal target cells on developing septal cholinergic neurons in culture

The influence of hippocampal target cells on the development of cholinergic septal neurons was studied in rotation-mediated reaggregating cell cultures. Brain cells from 15-day-old mouse embryos were obtained from: septum, containing cholinergic cells which project to the hippocampus; hippocampus which contains target cells for the septal cholinergic neurons; and cerebellum, containing cells which are not targets for the septal cholinergic cells. The cells were then cultured for 3 weeks in a rotary incubator in the following combinations: septal cells alone; hippocampal cells alone; cerebellar cells alone; septal-hippocampal cells together; and septal-cerebellar cells together. After harvesting, fixation, and embedding, 50 micron sections were cut and processed for visualization of acetylcholinesterase activity. Sections from reaggregates containing either hippocampal or cerebellar cells alone contained only a few acetylcholinesterase-positive cells, but no positive fibers. Sections from septal-hippocampal coaggregates revealed a pattern of well-defined, fine-caliber acetylcholinesterase-positive fibers with extensive arborizations and varicosities suggesting axonal proliferation. In septal-cerebellar coaggregates, acetylcholinesterase-positive fibers appeared to be degenerating and distinct areas were observed which were essentially devoid of acetylcholinesterase fibers. In some experiments, either cerebellar or hippocampal cells were labeled with wheatgerm agglutinin-rhodamine prior to culture in order to identify these cells in the resulting reaggregates. Analysis of sections from these studies showed that acetylcholinesterase fibers were excluded from regions of coaggregates containing cerebellar cells, but were present in regions of coaggregates containing hippocampal cells. Finally, cell counts of acetylcholinesterase-positive cells in the various combinations revealed that these putative cholinergic neurons were significantly more numerous in septal-hippocampal coaggregates (271 +/- 19 per 10(6) septal cells added) than in septal reaggregates (38 +/- 6 per 10(6) septal cells added) or septal-cerebellar coaggregates (85 +/- 29 per 10(6) septal cells added). These results, taken together, suggest that hippocampal target cells influence the development and survival of cholinergic neurons.

Brain development in relation to fetal weight and maternal glucose tolerance during normal gestation

Parameters of brain development were studied in near term guinea-pigs in relation to fetal weight and maternal glucose tolerance during normal gestation. Seven litters (22 fetuses) were studied. Fetal weight ranged from 43 to 94 g (119% variability) and the maternal glucose index (sum of the 7 serum glucose levels during the oral glucose tolerance tests) from 921 to 1,528 mg/dl (66% variability). The weights of the cerebrum and cerebellum were less affected by changes of fetal weight compared to other fetal organs. Significant correlations were observed between the maternal glucose index and brain cell number (DNA) and myelination (cerebroside-sulfatide). These variables did not correlate with fetal weight. Liver weight (% fetal weight) and cell number also correlated with the maternal glucose index. It is speculated that the amount of glucose available to the brain could be responsible for the relative protection of the brain to fetal malnutrition and also for the link between maternal glucose index and parameters of fetal brain development.

Neuronal properties of clonal hybrid cell lines derived from central cholinergic neurons

Clonal cell lines derived from specific types of central neurons can be used to identify and characterize properties specific to those neurons. With somatic cell fusion techniques, nine clonal hybrid cell lines have been developed from the septal region of the mouse basal forebrain. Two lines express characteristics typical of cholinergic neurons--choline acetyltransferase activity and immunoreactivity, neurite formation with neurofilament protein immunoreactivity, and aggregation in rotation-mediated cell culture. These cell lines may be useful for studying the trophic interactions that support the development and maintenance of central cholinergic connections.

Cholinergic neurons of fetal rat telencephalon in aggregating cell culture respond to NGF as well as to protein kinase C-activating tumor promoters

Serum-free aggregating cell cultures of fetal rat telencephalon treated with the potent tumor promoter phorbol 12-myristate 13-acetate (PMA) showed a dose-dependent, persistent stimulation of the enzymes choline acetyltransferase (ChAT), glutamic acid decarboxylase and glutamine synthetase. After elimination of the proliferating cells by treatment of the cultures with Ara-C (0.4 microM) only the cholinergic marker enzyme, ChAT, could be stimulated by tumor promoters. The non-promoting phorbol ester, 4 alpha-phorbol 12,13-didecanoate proved to be inactive in these cultures, whereas the potent non-phorbol tumor promoter, mezerein, produced an even greater stimulatory effect than PMA. Since PMA and mezerein are potent and specific activators of protein kinase C, the present results suggest a role for this second messenger in the development of cholinergic telencephalon neurons. Stimulation of ChAT required prolonged exposure (48 h) of the cultures to PMA and the responsiveness of the cholinergic neurons to the tumor promoters decreased with progressive cellular maturation. The cholinergic telencephalon neurons showed the same pattern of responsiveness for tumor promoters as for nerve growth factor (NGF). However, the combined treatment with NGF and either PMA or mezerein produced an additive stimulatory effect, suggesting somewhat different mechanisms of action.

Protein kinase C-activating tumor promoters enhance the differentiation of astrocytes in aggregating fetal brain cell cultures

Serum-free aggregating cell cultures of fetal rat telencephalon treated with the potent tumor promoter phorbol 12-myristate 13-acetate (PMA) showed a marked, rapid, and sustained increase in the activity of the astrocyte-specific enzyme glutamine synthetase (GS). This effect was accompanied by a small increase in RNA synthesis and a progressive reduction in DNA synthesis. Only mitotically active cultures were responsive to PMA treatments. Since in aggregate cultures astrocytes are the preponderant cell type, both in number and mitotic activity, it can be concluded that PMA induces and/or enhances the terminal differentiation of astrocytes. The developmental expression of GS was also greatly stimulated by mezerein, a potent nonphorbol tumor promoter, but not by 4 alpha-phorbol 12,13-didecanoate, a nonpromoting phorbol ester. Since both tumor promoters, PMA and mezerein, are potent and specific activators of C-kinase, it is suggested that C-kinase plays a regulatory role in the growth and differentiation of normal astrocytes.

In vivo and in vitro development of alpha-MSH and ACTH in the embryonic and postnatal rat brain

The appearance of immunoreactive alpha-melanotropin (alpha-MSH) and adrenocorticotropin (ACTH) during development was studied in 3 areas of the rat brain--cerebral hemispheres, midbrain and hindbrain--from embryonic day (ED) 13-14 until day 21 postnatally. The alpha-MSH content in vivo was always highest in the midbrain; a peak content at birth was followed by a transient decline and a later, higher plateau from postnatal day 7 onwards. The alpha-MSH content in the cerebral hemispheres rose progressively after birth reaching a peak at day 21. Values in the hindbrain rose at day 3 and changed relatively sue taken at ED 15-16 showed a gradual increase in alpha-MSH content over the 20 days. The alpha-MSH content of hindbrain cultures remained at constant low levels, while no alpha-MSH was detectable in cerebral hemisphere cultures. ACTH appeared in vivo earlier than alpha-MSH and was detectable in embryonic brains at ED 13-14. A transient rise was seen at ED 17-18 and major peaks at birth, day 2 and day 3, in the midbrain, hemispheres and hindbrain, respectively. In vitro, the ACTH content increased in all brain regions during the first 5 days in culture and showed no further change thereafter. Comparisons of the in vivo and in vitro development of alpha-MSH and ACTH demonstrate that (i) these two peptide systems are independent in respect to their localization and time of appearance; (ii) they undergo maturation both in vivo and in vitro; (iii) epigenetic factors, such as interactions with other neurotransmitter systems may modulate the developmental pattern of these two peptides.

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.

Reaggregation of fetal rat brain cells in a stationary culture system. II: Ultrastructural characterization

Ultrastructural characteristics of fetal rat brain cell aggregates in a three-dimensional stationary culture system are described. Transmission electron microscopy showed immature cells which developed into mature astrocytes, oligodendrocytes, and neurons during 20 d in culture. This was accompanied by the development of a neuropil where myelinated axons and synaptic complexes were observed. In addition to confirming earlier ultrastructural investigations on fetal rat brain cell aggregates, the stationary culture system also showed the presence of histiotypic regions within the aggregates. These regions consisted of ependymal cells where cilia were observed on the cell surfaces. Structures resembling subependymal basement membrane labyrinths were also observed. Macrophages seemed to be more numerous in the stationary cultures as compared to other culture systems. The stationary culture system may provide aggregates that are ultrastructurally more complex than those obtained by rotation mediated systems.

Some electrophysiological properties of cultured rat cerebral cortical neurons dissociated from fetuses at various gestational ages

Neurons from dissociated cerebral cortex of fetal rat of different gestational ages were grown in culture for up to 4 weeks. Studies of membrane and action potentials, input resistance, neuron size and neurite outgrowth showed that neurons from 7-day fetuses develop rapidly both electrophysiologically and morphologically, but are maintained for only about 2 weeks. In contrast, neurons from 14 to 17 day fetuses mature slowly, but can be maintained for at least 4 weeks. Neurons from both young and old fetuses show an increase in resting Em with age, the maximum value of -60 to -65 mV being attained by about 2 weeks. While neurons can be maintained in serum-free medium, their membrane electrical properties deteriorate with time. Thus, appropriate development of neurons in culture depends upon both the age of the starting tissue, and the presence of adequate, but still undefined factors found in animal serum for at least the first several days in culture.

Effects of polyunsaturated fatty acids and hormones on synaptogenesis in serum-free medium cultures of mouse fetal hypothalamic cells

The effects of soluble factors on synaptogenesis by mouse fetal hypothalamic cells cultured in chemically defined conditions have been examined using transmission electron microscopy. Hypothalami taken on the 16th day of gestation were mechanically dissociated and cells were seeded in a minimum serum-free medium supplemented or not with the following components: triiodothyronine, corticosterone and a mixture of polyunsaturated fatty acids (arachidonic acid plus docosahexaenoic acid bound to defatted bovine serum albumin). In the minimum serum free medium synapses were found after 10 days in culture. However, the development of synaptic vesicles was very limited, whereas that of the presynaptic and postsynaptic densities was apparently normal. Supplementation of the minimum serum-free medium with triiodothyronine, corticosterone and polyunsaturated fatty acids added simultaneously, permitted a full development of synapses as attested to by the increase in number and the regular shape and diameter of synaptic vesicles as well as by the complexity and diversity of synapse configurations. Among those three factors, polyunsaturated fatty acids clearly played a key role. The ability of synapses formed in culture to respond to potassium evoked depolarization was examined on cultures grown for 12 days in the simultaneous presence of the three above mentioned supplements. Exposure for 3 min to 60 mM potassium chloride induced in synaptic boutons vesicular depletion, apposition of vesicle clusters onto the presynaptic grid, appearance of a rich filamentous network and of some coated vesicles. Return to 3mM potassium chloride induced in 3 min a massive restoration of the population of vesicles which slightly differed from synaptic vesicles in control cultures. These results show that: (1) the formation of synaptic vesicles in this system is regulated by soluble factors among which polyunsaturated fatty acids play a major role, and (2) synapses formed de novo in chemically defined conditions of culture display the same ability to respond to and to recover from potassium evoked depolarization as adult axon terminals. Thus, they offer a suitable model for analysis of the mechanisms involved in membrane traffic in central neurons.

Tissue culture analysis of neurite outgrowth in the presence and absence of serum: possible relevance for central nervous system regeneration

A tissue culture model has been developed to examine the hypothesis that axons can only regenerate when their growing tips are surrounded by extracellular fluid containing proteins derived from the blood. Fetal rat cerebral explants were cultured in serum medium for 10 days, followed by serum-free (SF) medium (from which serum had been removed) until 18 days in vitro (DIV). All explants cultured in serum medium for 0-10 DIV exhibited greater than 77% neurite viability (neurite viability ratio, NVR, 3.10). This degree of neurite viability was maintained for those explants exposed to serum until 18 DIV (NVR 2.82 at 18 DIV). By contrast, explants maintained in SF medium from 10-18 DIV had a much lower NVR, which, by 18 DIV, had declined to 0.30 (7.5% viability). Transmission electron microscopic analysis of explants fixed at 18 DIV confirmed these phase-contrast results and also showed a predominance of axonal profiles within the neurite population. In the center of explants, tissue viability was in excess of 75% in both the serum and SF media, suggesting that serum is of primary importance for axonal extension rather than neuronal survival. These data strengthen the hypothesis that blood-derived proteins may be needed for prolonged regeneration.

Development of neuronal markers in aggregating fetal rat telencephalon cells cultured in the presence of triiodothyronine

The concentrations of the general neuronal markers D2-protein (N-CAM), D3-protein and neuron specific enolase (NSE) in reaggregating cultures of fetal rat telencephalon cells were affected by the presence of 30 nM triiodothyronine in the defined culture medium. The extent of normal developmental changes were enhanced by triiodothyronine, as demonstrated by crossed immunoelectrophoresis. From 13 to 19 days in culture, the concentration of D2-protein decreased, and the concentrations of both D3-protein and NSE increased. Nerve growth factor (NGF) was without effect on the development of these general neuronal markers. However, as shown previously both triiodothyronine and NGF increased the activity of choline acetyltransferase, a marker for cholinergic neurons. The results suggest an enhanced overall differentiation of several types of telencephalon neurons in the presence of triiodothyronine, and a specific stimulation of cholinergic telencephalon neurons by NGF.

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.

Epidermal growth factor and bovine growth hormone stimulate differentiation and myelination of brain cell aggregates in culture

Bovine growth hormone (bGH) and epidermal growth factor (EGF) increased the activity of ornithine decarboxylase (ODC) in brain cell aggregates cultured in a serum-free chemically defined medium. ODC is considered as a marker of cell growth and differentiation. The effect of bGH and EGF on myelination was investigated by measuring two myelin markers, 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) and myelin basic protein (MBP). EGF treatment at days 2 and 5 caused a dose-dependent increase of both myelin markers at culture day 12. This increase could still be observed at culture day 19, indicating a prolonged action of EGF. The continual presence of bGH in the culture medium produced a large accumulation of MBP at day 19. This effect was dose-dependent and required the presence of triiodothyronine (T3). In contrast, the effect of bGH on CNP activity did not require the presence of T3. This is the first report showing a direct effect of bGH on CNS myelination in vitro and of EGF on both MBP accumulation and ODC activity.

Growth and myelination of explant cultures in defined medium

The purpose of this study was to compare the development of organotypic cultures in defined medium versus nutrient containing serum and embryo extract (EE). Explant cultures of cerebellum with or without locus ceruleus were grown in the Maximow system and monitored in the living state and with histological stains. Thinner explants, fibronectin and a more frequent feeding schedule were required to overcome the growth differences encountered using a defined medium. The final medium formulation was arrived at by evaluation of living cultures and consisted of a basal medium (Dulbecco's minimal essential medium), a number of hormones and other supplements, and a final glucose concentration of 750 mg%. Using a Golgi stain and histofluorescence, it was shown that the three major types of neurons - Purkinje, deep nuclear, and locus ceruleus - developed similarly in the defined medium and in serum-EE cultures. Myelination occurred in virtually all cerebellar cultures in defined medium and the onset was earlier than in serum-EE cultures. These results indicate that differentiation of oligodendroglia and maturation of neurons occur in a defined medium. Elimination of thyroid hormone delayed the maturation of the cultures, both neurons and myelin, by 3-4 days.

Towards an improved serum-free, chemically defined medium for long-term culturing of cerebral cortex tissue

The present study describes a series of experiments which have led to a substantially improved serum-free, chemically defined medium (CDM) for long-term culturing of reaggregated fetal rat cerebral cortex tissue. A reduction of the original medium concentrations of the hormones insuline, T3 and corticosterone, on the one hand, and an enrichment of the medium with the vitamins A, C and E, the unsaturated fatty acids linoleic and linolenic acid, and biotin, L-carnitine, D(+)-galactose, glutathione (reduced) and ethanolamine, on the other hand, formed the most important chemical adjustments of the medium. With the aid of this CDM (encoded R12), the light- and electron microscopic architecture of the tissue could be kept in a good condition (superior to that seen earlier in serum-supplemented medium) up to 23 days in vitro. From that time on, the neuronal network lying between the reaggregates degenerated for the largest part, while a portion of the large neurons (probably pyramidal cells) plus some of the neuronal network within the reaggregates degenerated too. This degeneration process continued during the following weeks, but the reaggregates nevertheless retained most of their mass, so that both small and large neuronal cell bodies (visible in transparent regions at the edge of the reaggregates) remained in good condition up to at least 103 DIV. Stout, thick nerve bundles interconnecting the reaggregates, also survived up to this point. Electron microscopic evaluation of such 'aged' reaggregates revealed degenerating as well as healthy regions. The latter had indeed retained healthy-looking pyramidal and non-pyramidal neurons, embedded within a dense neuropil which was often traversed by myelinated axons. The numerical synapse density in such selected, healthy tissue regions reached its maximum during the sixth week in vitro, followed by a rapid decrease and a stabilization at about half the peak values. The present culture system has opened the possibility for performing controlled quantitative studies on the relationship between structure and function of cerebral cortex tissues during development and aging, on its dependence on nutrients, hormones and drugs, and on special factors synthesized by the tissue and released into the nutrient medium.

The differentiation of oligodendrocytes in a serum-free hormone-supplemented medium

Primary mixed cultures of trypsin-dissociated fetal and newborn rat brain and spinal cord have been grown in a serum-free medium. This medium, containing insulin, selenium, transferrin and triiodothyronine, was optimized for oligodendrocyte survival by determining the number of cells which expressed surface galactocerebroside. Comparison of cultures in serum-containing and serum-free media revealed that galactocerebroside positive (GalC+) oligodendrocytes could be detected earlier in the absence of serum. This early differentiation occurred in the absence of the added hormones and nutrients, whose main function appeared to be to prolong survival of the cells. The effect of serum on the differentiation of oligodendrocytes was studied by comparing the expression of surface GalC in media containing 2.5% or 10% fetal calf serum. At a given time a much greater number of GalC+ oligodendrocytes could be detected at the lower serum concentration. However, when cultures were transferred from 10% serum to serum-free medium (or 1% serum) large numbers of GalC+ oligodendrocytes subsequently appeared, showing that precursors were present in the high-serum medium, but that they were unable to differentiate. Possible explanations of the effect of serum on oligodendrocyte differentiation are discussed.

Characterization and down-regulation of opiate receptors in aggregating fetal rat brain cells

Aggregating brain cells prepared from embryonic rats bind radioactive opiates in a stereospecific manner. The drug selectivity, receptor content during culturing and down-regulation of these apparent opiate receptors were studied in aggregates prepared from the embryonic hindbrain or forebrain. The receptor content in hindbrain but not forebrain aggregates was increased up to 3-fold after 21 days in culture. Differences between the receptors of the two types of aggregates were also observed in the affinity of opiate alkaloids and D-Ala2,D-Leu5-enkephalin (DADL). The potent opiate alkaloid etorphine induced down-regulation of opiate receptors in aggregates prepared from either brain region whereas DADL was a potent down-regulator in the forebrain but not in the hindbrain aggregates and morphine had no effect in both tissues. The implications of these results concerning the control of various types of opiate receptors in the whole animal are discussed.

Isolation and cultivation of mature oligodendroglial cells

CNS axons are ensheathed by myelin which is produced and maintained by oligodendrocytes. A disorder of this assembly results in functional disturbances, e.g., paralysis in multiple sclerosis. Methods are now available to isolate and cultivate oligodendrocytes in vitro. Thus, basic oligodendroglial properties can be now investigated: signals for oligodendroglial gene expression and their role in myelinogenesis and the interaction between oligodendrocytes and other neural cells by, e.g., the release of informational substances.

The neuronal adhesion protein D2 in differentiating aggregates of brain cells

The D2-protein is a high molecular weight protein involved in interneuronal adhesion. The concentration of D2-protein was measured both in aggregates of fetal rat telencephalic cells cultured in a chemically defined medium and in developing forebrain. Both the concentration of the D2-protein and the degree of sialylation were changed in the cultures in parallel with the corresponding values obtained from postnatal forebrain. In the cultures the highest specific concentration of D2-protein was observed after 12 days in culture. This value was 2.7 times higher than the average value of adult rat forebrain. Antibodies to D2-protein have previously been shown to inhibit fasciculation of neuritic fibers extending from cultured explants of sympathetic ganglia. We investigated the effect of such antibodies on the differentiation of aggregating telencephalic cells. By adding surplus antibodies to the cultures from day 11 to day 16 we were able to decrease the specific concentration of D2-protein on the neurons by 53% measured at day 19. The decrease was not compensated fully even after further 10 days in the culture. Although the concentration of D2-protein was decreased during the period of synaptogenesis no change was found in the specific concentration of a marker of mature synapses, the D3-protein. Thus, in this culture system synaptogenesis could proceed to an unimpaired extent in the presence of a decreased concentration of a putatively involved adhesion molecule. However, the specific concentration of two markers of myelination, 2',3'-cyclic nucleotide 3'-phosphodiesterase and myelin basic protein, were both increased, suggesting an antibody-induced stimulation of myelination in the cultured aggregates.

Regulation of arylsulphatase A and sulphogalactolipid turnover by cortisol in myelinogenic cultures of cells dissociated from embryonic mouse brain

Myelinogenic cultures of cells dissociated from embryonic mouse brain were used to study the regulation of myelination-associated molecules by cortisol. Cortisol in physiological concentrations (0.03 microM) caused an increased accumulation of myelination-associated sulphogalactolipids. It also stimulated the myelin- and oligodendroglia-specific cyclic nucleotide phosphohydrolase. The increase in sulphogalactolipid content was caused by a cortisol-concentration-dependent inhibition in arylsulphatase A activity and not by an increase in either cerebroside sulphotransferase activity or an increase in availability of adenosine 3'-phosphate 5'-phosphosulphate. Of several steroid hormones tested only the glucocorticoid types brought about these changes. The relationship between net sulphogalactolipid accumulation and arylsulphatase A inhibition induced by cortisol was confirmed by sulphogalactolipid turnover studies. Depending on whether a single-phase or a two-phase decay calculation is used, the turnover of sulphogalactolipid with cortisol present was decreased at 22 days in culture by either 62% or 65% respectively of that without cortisol. This decrease in turnover can be attributed completely to the decrease of arylsulphatase activity by cortisol to 63% of the value for normal cells grown under the same conditions.

Culture of rat cerebral oligodendrocytes in a serum-free, chemically defined medium

Oligodendrocytes were isolated from the cerebra of young rats (5-10 days old) by trypsinization of the tissue followed by cell separation on Percoll gradients. The isolation was carried out in physiological, isotonic media. The cell yield was 2-4 X 10(6) cells per brain; the plating efficiency was greater than or equal to 70%. Isolated cells were seeded on poly-L-lysine-coated culture dishes and maintained in a serum-free, chemically defined medium for at least 30 days. After 10 days in culture 67 +/- 10% of the surviving cells were oligodendrocytes, as judged by immunocytochemical and morphological criteria, whereas most of the other cells reacted positively with antiserum against glial fibrillary acidic protein. The expression of typical oligodendrocyte markers (2':3'-cyclic-nucleotide 3'-phosphodiesterase, galactocerebrosides and myelin basic protein) was greatly enhanced under these serum-free conditions as compared with cultures in serum-containing medium. The antigenic markers (galactocerebrosides, myelin basic protein) were absent in the freshly isolated cells but could be detected after 3 days in culture by immunocytochemistry. The activity of 2':3'-cyclic-nucleotide 3'-phosphodiesterase increased from 75 nmol min-1 mg-1 protein on day 4 to 400 nmol min-1 mg-1 protein on day 14 in culture.

Epidermal growth factor (EGF) stimulation of cultured brain cells. II. Increased production of extracellular soluble proteins

The production of extracellular soluble proteins was studied in serum-free aggregating cell cultures of fetal rat telencephalon labeled on culture day 7 with a mixture of radioactive amino acid precursors. Cultures treated continuously with epidermal growth factor (EGF; 20 ng/ml) showed a generally increased protein secretion and a particularly enhanced production of a few distinct extracellular proteins. The time lag of this response after an initial dose of EGF (25 ng/ml) on day 7 was 48 h. The total macromolecular radioactivity that accumulated within 96 h of labeling in the media of EGF-treated cultures was 175% of untreated controls, whereas no difference was found in the proportions of intracellular amino acid incorporation. Cultures which received a single dose of EGF (25 ng/ml) on day 1 showed still a greatly increased protein secretion on day 7. Prevention of extracellular protein accumulation by reducing the initial cell number and increasing the rate of media changes did not affect the EGF-induced stimulation of the two glial enzymes, glutamine synthetase and 2',3'-cyclic nucleotide 3'-phosphohydrolase. The results suggest that both the increased production of extracellular proteins and the enhanced development of glial enzymatic activities reflect the stimulated phenotypic expression of EGF-sensitive brain cells.

Epidermal growth factor (EGF) stimulation of cultured brain cells. I. Enhancement of the developmental increase in glial enzymatic activity

Serum-free aggregating cell cultures of fetal rat telencephalon grown in the presence of 3 ng/ml (5 X 10(-10) M) epidermal growth factor (EGF) until day 12 showed 2- to 3-fold increased activities in the two glial enzymes, glutamine synthetase (GLU-S) and 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNPase). This effect was concentration-dependent, with maximal stimulation in cultures treated daily with 3 ng/ml EGF. Addition of EGF during the first 10 culture days was sufficient to produce a maximal stimulation of both GLU-S and CNPase on day 19, whereas treatments starting on day 12 were ineffective. The stimulation of GLU-S preceded that of CNPase. The EGF-induced increase in GLU-S activity was not directly dependent on the presence of insulin, triiodothyronine, or hydrocortisone in the medium, whereas insulin was required for the stimulation of CNPase. A single dose of 5 ng/ml EGF on day 2 caused a slight but significant decrease in DNA synthesis after day 6. The present results indicate that in serum-free aggregating cell cultures of fetal rat telencephalon EGF partially inhibits DNA synthesis, and stimulates an early step in glial differentiation.

Serum-free medium for cultures of the postnatal mouse cerebellum: only insulin is essential

Serum-free culture conditions for dissociated postnatal mouse cerebellar cells were investigated. This study demonstrates that among various supposed growth-promoting factors only insulin is required as an additive to the basic medium. If viewed by phase contrast microscopy, cultures kept in insulin-supplemented basic medium looked identical to those maintained in the presence of a mixture of growth-promoting factors (insulin, putrescine, transferrin, progesterone, triiodothyronine, selenium). In addition, quantitative evidence is provided indicating that cellular survival is supported to the same extent by insulin as by this admixture. Insulin concentrations required ranged between 0.3-20 micrograms/ml. By contrast to serum-supplemented culture conditions, no significant proliferation of non-neuronal cells was observed in serum-free culture media. It is expected that by these findings attention will be focused again to the exact role insulin plays in the central nervous system.

Role of serum-free defined medium in regulation of LH receptor in cultured rat granulosa cells

The induction of luteinizing hormone (LH) receptor by follicle-stimulating hormone (FSH) in granulosa cells was compared following culture in serum-free or serum-containing medium. Incubation of primary cultures of granulosa cells in serum-free defined medium with purified FSH resulted in dramatic increases in the level of functional LH receptors. This striking enhancement of LH receptor by FSH was completely abolished by concomitant incubation with serum (rat, horse, porcine, human or calf). The serum inhibition of FSH was not readily reversible and could be evoked throughout the culture period. The synthesis of cAMP by FSH was markedly suppressed by serum, suggesting that serum component(s) are inhibiting FSH action at the level of adenylate cyclase. Such an action, however, cannot be the sole mechanism because serum also blocked LH receptor induction by cyclic AMP analogs. In defined medium, addition of insulin, transferrin, dexamethasone or fibronectin alone had no effect on basal levels of LH receptor. However, following incubation with either insulin or dexamethasone, the FSH-induced increases in LH receptor were markedly suppressed. Insulin was found to markedly inhibit FSH-stimulated cyclic AMP formation; this was not the case with dexamethasone. The present results demonstrated the complete inhibition of FSH action by serum in cultured granulosa cells and suggest that the effect is caused by a combination of direct actions of common metabolic hormones which inhibit FSH action at multiple sites. These experiments clearly indicate the obligatory role of defined medium in the hormone-dependent differentiation of the granulosa cell in culture.

Insulin-like growth factor I (IGF I) stimulates DNA synthesis in fetal rat brain cell cultures

Addition of insulin, IGF I or IGF II to serum-free cultures of fetal rat brain cells (gestation day 15/16) significantly stimulates DNA synthesis. The dose-response curves show that IGF I is more potent than insulin; half maximal stimulation of [3H]thymidine incorporation is obtained at about 0.4 nM IGF I and 14 nM insulin, respectively. Cultures initiated 2 days later (gestation day 17/18) showed a decreased responsiveness to both peptides. No additive effect was observed after combined addition of both peptides at near-maximal doses. Both peptides show a latency of action of about 12-18 h. In the presence of either IGF or insulin, neuronal as well as glial enzymes are increased, suggesting that neuronal and glial precursor cell division is influenced. IGF I and IGF II interact with a specific binding site for which insulin competes very weakly; however IGF I and IGF II bind with relatively high affinity to the insulin specific binding site. The present results support the hypothesis that both insulin and IGF stimulate mitotic activity by interacting with specific somatomedin receptors and suggest a physiological role of IGF in the developing brain.

Cell proliferation in growing cultures of dissociated embryonic mouse brain: macromolecule and ornithine decarboxylase synthesis and regulation by hormones and drugs

Primary cultures of cells dissociated from embryonic mouse brain were demonstrated to be a useful system for studying cell proliferation and its regulation. Ornithine decarboxylase activity was closely correlated with the rate of DNA and RNA synthesis during cell growth, suggesting that the enzyme is as good an indicator of cell proliferation in these cultures as it is in vivo. Both DNA synthesis and ornithine decarboxylase activity were stimulated by insulin. The enzyme was stimulated five- to sixfold by insulin and approximately twofold by butyrate, cis-retinoic acid, and 12-O-tetradecanoylphorbol-13-acetate. No effect on the enzyme activity was observed with triiodothyronine, hydrocortisone, growth hormone, cyclic AMP, or cyclic GMP.

Serum-free growth of normal and tumor mouse mammary epithelial cells in primary culture

Freshly isolated normal and tumor mouse mammary epithelial cells embedded within a collagen gel matrix undergo sustained growth when cultured for as long as 3 wk in a serum-free medium composed of a 1:1 (vol/vol) mixture of Hepesbuffered Ham's F12 and Dulbecco's modified Eagle's medium supplemented with insulin, epidermal growth factor (EGF), transferrin, bovine serum albumin fraction V, and cholera toxin. Of these additives, only insulin, EGF, and albumin are required for the growth of most normal cells. Albumin is not always an absolute requirement for growth but greatly enhances it. Lithium has been found to stimulate the growth of normal cells and can replace EGF. The collagen matrix culture system allows sustained growth of primary cultures of both normal and neoplastic mammary epithelium in serum-free conditions. This serum-free system will be useful in identifying and investigating the role of hormones, growth factors, and nutritional factors in regulating the growth of mammary epithelial cells.

Cultivation of mouse cerebellar cells in serum free, hormonally defined media: survival of neurons

A hormonally defined medium is described which facilitates the survival of small neurons in primary cultures of mouse cerebellum. The defined medium consists of bovine serum albumin, insulin, transferrin, selenium, thyroxine, and the protease inhibitor aprotinin. About 95% of all cells were identified as neurons using tetanus toxin as a marker in an immunocytochemical assay. They survive for more than 4 weeks, showing a tendency to grow in cell clusters with a dense network of processes. The remaining cells (approximately 5%) were identified as astrocytes by their expression of vimentin and GFA protein and the lack of expression of fibronectin.

Nerve growth factor (NGF) stimulation of cholinergic telencephalic neurons in aggregating cell cultures

The addition of nerve growth factor (2.5S NGF) to serum-free aggregating cell cultures of fetal rat telencephalon greatly stimulated the developmental increase in choline acetyltransferase activity. Two other neuronal enzymes, acetylcholinesterase and glutamic acid decarboxylase, showed only slightly increased activities after NGF treatment whereas the total protein content of the cultures and the activity of 2',3'- cyclic nucleotide phosphodiesterase remained unchanged. The stimulation of choline acetyltransferase was dependent on the NGF media concentrations, showing a 50% maximum effect (120% increase) at approximately 3 ng/ml (10-10 M 2.5S NGF). NGF treatments during different culture periods showed that the cholinergic neurons remained responsive for at least 19 days. The continued treatment was the most effective; however, an initial treatment for only 5 days still caused a significant stimulation of choline acetyltransferase on day 19. The observed stimulation appeared to be specific to NGF. Univalent antibody fragments (Fab) against 2.5S NGF completely abolished the NGF-dependent increase in choline acetyltransferase activity, whereas Fab fragments of control IgG were ineffective. Furthermore, angiotensin II, added in high amounts to the cultures, showed no stimulatory effect. The present results suggest that certain populations of rat brain neurons are responsive to nerve growth factor.

Nerve outgrowth, synaptogenesis and bioelectric activity in fetal rat cerebral cortex tissue cultured in serum-free, chemically defined medium

Dissociated and non-dissociated cerebral cortex of fetal rat was successfully cultured in a serum-free, chemically defined medium for at least 18 days without any preincubation in serum-supplemented medium. Neurite outgrowth, synapse formation and spontaneous bioelectric activity, in its qualitative and quantitative aspects, were essentially the same as was observed in medium containing 20% heat-inactivated horse serum.

Growth of purified astrocytes in a chemically defined medium

Astrocytes purified from primary cultures of neonatal rat cerebrum can now be grown in a synthetic medium supplemented with putrescine, prostaglandin F2 alpha, insulin, fibroblast growth factor, and hydrocortisone. These five supplements have a marked synergistic effect on growth when used in combination but have little effect when used individually. Astrocytes grown in the defined medium exhibit dramatic changes in morphological characteristics in comparison to cells grown in serum-free or serum-supplemented medium. In addition, these cells express the astrocyte-specific marker glial fibrillary acidic protein and are estimated by several criteria to be greater than 95% astrocytes.

Selective cell culture of brain cells by serum-free, hormone-supplemented media: a comparative morphological study

We cultured single cell suspensions derived from enzymatically digested rat and mouse brains in the serum-free, hormone-supplemented media originally established for culturing glioma (C6) and neuroblastoma cell lines (B104). We succeeded in selecting different cell types by varying the hormones added to the culture medium. In addition to the medium the attachment factors used for coating the culture dishes proved important for the establishment of a selective culture system. In a comparative morphological study we show that different particular microenvironmental conditions determine the growth and/or survival of different cell types of dissociated brain cells.

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.

Requirements for growth of neurites from embryonic chick cerebellum in culture

Embryonic chick cerebella were cut into pieces and cultured under various conditions. Neurites were extended actively to collagen gel for a week or so and then degenerated. The neurite growth for the first two days was similar, also in the serum-free medium. Among 15 substances tested, insulin and cyclic AMP facilitated the growth.

An endocrine approach to the control of epidermal growth: serum-free cultivation of human keratinocytes

Human keratinocytes, derived from the skin of newborns and of adults, were grown in the complete absence of serum, in a hormone-supplemented medium on fibronectin-coated cell culture dishes at low seed density. The cell culture medium consisted of Medium 199 containing epidermal growth factor, triiodothyronine, hydrocortisone, Cohn fraction IV, insulin, transferrin, bovine brain extract, and trace elements. Removal of the brain extract from the hormone supplement had a greater negative impact on proliferation of the keratinocyte cultures than did the removal of epidermal growth factor, hydrocortisone, and triiodothyronine or Cohn fraction IV. The growth of keratinocytes in this hormone-supplemented medium suggests that control of keratinocyte growth depends in large part on endocrine stimulation by other body organs, including the brain.

Chemically defined medium enhances bioelectric activity in mouse spinal cord-dorsal root ganglion cultures

Co-cultures of mouse spinal cord with dorsal root ganglion (DRG) cultures were grown either in horse serum (HS)-supplemented medium or in a serum-free, chemically defined medium (CDM). The cytoarchitecture of cord--DRG explants was fully retained in CDM, with little or no distortion due to flattening of the explant, as is invariably observed in HS-supplemented cultures. Functional properties such as bioelectric activity and DRG--spinal cord interconnectivity were well sustained in CDM.