Isolation and transplantation of oligodendrocyte precursor cells

Cell of all trades: oligodendrocyte precursor cells in synaptic, vascular, and immune function

Oligodendrocyte precursor cells (OPCs) are not merely a transitory progenitor cell type, but rather a distinct and heterogeneous population of glia with various functions in the developing and adult central nervous system. In this review, we discuss the fate and function of OPCs in the brain beyond their contribution to myelination. OPCs are electrically sensitive, form synapses with neurons, support blood-brain barrier integrity, and mediate neuroinflammation. We explore how sex and age may influence OPC activity, and we review how OPC dysfunction may play a primary role in numerous neurological and neuropsychiatric diseases. Finally, we highlight areas of future research.

Myelination of axons within cytosine arabinoside treated mouse cerebellar explants by cultured rat oligodendrocytes

Cell suspensions of cultured purified rat oligodendrocytes prepared by the differential substrate adhesion method were applied to neonatal mouse cerebellar explant cultures in which myelination and oligodendrocyte maturation had been irreversibly inhibited by exposure to cytosine arabinoside. Myelination of Purkinje cell axons within 92% of the host explants was observed 2-5 days after oligodendrocyte application. Ultrastructurally, mature oligodendrocytes and axons surrounded by compact myelin, as well as spherules of compact myelin membranes without axons, were present within the cerebellar explants. It is evident that cultured dissociated purified oligodendrocytes retain the ability to myelinate appropriate axons. Such oligodendrocytes may be hyperreactive with regard to myelin membrane formation, as suggested by the presence of spheres of compact myelin without axons.

Survival and function of dissociated rat dopamine neurones grafted at different developmental stages or after being cultured in vitro

The in vitro culture approach was combined with the cell suspension grafting technique to examine whether the maturation of dopamine (DA) neurones in vitro imposed similar limitations on their ability to survive grafting as when they are allowed to develop in situ in the fetus. The functional capacity, survival and growth of DA neurones from 2.5- and 7-day-old cultures, grafted to rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal pathway, was compared with similar grafts freshly prepared from fetal donors of embryonic days 14, 16 and 20. Grafts of freshly dissociated mesencephalic DA neurones, taken from embryonic day 14-16 donors and 2.5-day-old cultures, generally survived well and markedly reduced amphetamine-induced rotational asymmetry in the recipient rats. However, when cultured for 7 days prior to grafting, or when taken from 20-day-old fetuses, the mesencephalic DA neurones survived very poorly and the grafts did not have any functional effects. Plating of aliquots of cell suspension used for grafting indicated that the survival rate of dissociated DA neurones is in the same order of magnitude when grown in vitro (about 2 DA neurones per 1000 cells) as when grafted in vivo to the rat striatum (about 1-5 DA neurones per 1000 cells). When the number of surviving grafted DA neurones was plotted against the behavioural effects of the grafts, a threshold number of around 100-200 DA neurones was found necessary to obtain a marked reduction (greater than 50%) in amphetamine-induced rotational asymmetry. Moreover, the survival of 300-500 DA neurones seemed to produce a 'ceiling effect' beyond which additional surviving DA neurones gave rise to little or no further effect on the amphetamine-induced rotational behaviour.

Transplantation of oligodendrocytes in the newborn mouse brain: extension of myelination by transplanted cells. Anatomical study

The shiverer model allows for the immunocytochemical staining of the patches of myelin formed by transplanted oligodendrocytes from a normal newborn mouse. Fragments of the olfactory bulb were transplanted into various parts of the brain to place the myelinating cells in different anatomical conditions. Whole brains were horizontally sectioned in order to study the full pattern of migration and myelination of the grafted oligodendrocytes. Transplanted oligodendrocytes were capable of short and long distance migration before their differentiation. Long distance migration occurred in the caudal as well as in the rostral direction and into the contralateral part of the brain through the commissures. The patches of immunoreactive myelin were mainly found in the large myelinated bundles: corpus callosum, internal capsule, fimbria-fornix, medial lemniscus, cerebellar peduncles and spinal cord funiculi. Some sites of migration indicate that oligodendrocytes followed at least two different axonal pathways successively. The thalamic area which contained numerous patches could be a place where oligodendrocytes switch from one fasciculus to another.

Effects of neuron-conditioned medium and fetal calf serum content on glial growth in dissociated cultures

The influence of the microenvironment as assessed by medium conditioned by 6-day-old chick embryo neurons in culture and of the nutrients derived from fetal bovine serum was evaluated in cultures of primary chick embryo glial cells. Glia-enriched cultures from 15-day-old chick embryo were incubated from culture days 3-9 with various concentrations of neuron-conditioned medium, with or without 10% fetal bovine serum in the final culture medium. Also, glial growth was studied in cultures with 5%, 10% or 20% fetal bovine serum in the medium. Glutamine synthetase and 2',3',-cyclic nucleotide 3'-phosphohydrolase were used as astrocytic and oligodendrocytic markers, respectively. Cultures were harvested at day 9. The presence of neuron-conditioned medium in the cultures was associated with persistence of immature glioblast-like cells. This persistence of glial immature cells was also reflected by the lower glutamine synthetase activity in the cultures with neuron-conditioned medium as compared to cultures with neuron-conditioned medium and fetal calf serum. In cultures with 5% neuron-conditioned medium without fetal bovine serum, cyclic nucleotide phosphohydrolase activity was increased. We are assuming that the input of neurons to the microenvironment is partially mediated through the neuron-conditioned medium. Thus, the present findings show that neurons influence the growth and differentiation of glial cells in culture.

The rotating 6-hydroxydopamine-lesioned mouse as a model for assessing functional effects of neuronal grafting

Mice were first administered intrastriatal injections of 6-hydroxydopamine and subsequently a sub-group was given neural cell suspension grafts prepared from 14-day-old fetal ventral mesencephalic mouse tissue. Six and 8 weeks after transplantation the mice in the grafted group exhibited a significant reduction in amphetamine-induced turning behaviour towards the lesioned side compared to non-grafted lesioned controls. Six of the 7 mice that had surviving grafts containing histofluorescent dopamine neurons eventually showed a reversed motor side bias with more amphetamine-induced turning in a direction away from the transplant.

The generation and regeneration of oligodendroglia. A short review

During postnatal development of the higher vertebrate CNS, large populations of oligodendroglia are generated from precursor cells in a very dependable way. In adult lesioned CNS tissues, local populations of oligodendroglia are replenished by proliferation of this replenishment varies from one species to another and also from one lesion type another. Studies on the developmental generation of oligodendroglia are reviewed here, delineating what is known of the early relationships between the CNS glial lineages and of what regulates this development. Contributions from recent cell biological work are considered against the background of morphological and radioautographic results. The quiescent condition of extremely slow turnover in the normal adult CNS is noted, and the dramatic effects of lesions on the neural cell environment are considered. Lesions can trigger proliferation at a much greater rate in the mature oligodendroglial population, as observed both in situ and in tissue culture; in addition to persisting stem cells, the mature cells participate in replenishing the local oligodendroglial population. This regeneration from cells already committed to the oligodendroglial lineage may minimise such disturbing effects of the lesion environment as might distort replenishment of the population from precursor cells.

A procedure for long-term culture of oligodendrocytes

A procedure for long-term culture of oligodendrocytes is described, the starting material being 20-day-old primary mixed cultures of newborn rat brain. Cells were first incubated in a serum-free medium for 48 h before they were subcultured on poly-L-lysine coated plastic dishes. After this treatment, the oligodendrocytes developed well in Waymouth medium containing 10% (v/v) calf serum, while most of the astrocytes died. At 13 days in subculture more than 90% of the cells were identified as oligodendrocytes; the criteria for oligodendrocytes were based on their immunoreactivity to antisera against W1 Wolfgram protein, myelin basic proteins and the synthetic C-terminal hexapeptide of the major myelin proteolipid. At 13 and 19 days astrocytes were present, 7% and 20% respectively. The culture system described here may be useful to study the biochemical and immunological aspects of the oligodendrocytes.

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.

Rat oligodendroblasts in vitro as a long-term cell line

A stable line of oligodendrocyte-like cells has been derived by passaging methods from initial explant cultures of postnatal Lewis rat cerebellum. These cells resemble oligodendrocytes by both light and electron microscopy. However, their ultrastructure suggests immaturity, and they express no galactocerebroside at their surfaces. They do express surface tetrasialoganglioside. They contain no intermediate filaments, and show none of the ultrastructural characteristics of astrocytes. It is suggested that they represent immediate precursors to oligodendrocytes, or "oligodendroblasts". In addition, the cell line contains a small minority of astrocytes, and interactions between these and the oligodendroblasts are suggested to account for the highly differentiated ultrastructure maintained by the oligodendroblasts over hundreds of cell generations in vitro, as well as, possibly, the high proliferative rate of the oligodendroblasts. Conversely, the failure of the oligodendroblasts to mature is related to the absence of neurons.

Myelination of mouse cerebellar explants by rat cultured oligodendrocytes

It has been shown that transplanted central nervous system tissue containing oligodendrocytes will myelinate neuronal processes in vitro and in situ. In this study we propose to show that cultured rat oligodendrocytes have the capacity to myelinate mouse cerebellar neuronal processes in vitro. Cultured rat oligodendrocytes were transplanted to cytosine arabinoside-treated mouse cerebellar explant cultures, then observed for myelination. Ultrastructural examination showed myelin and myelin-like figures in co-cultures. Control cytosine arabinoside-treated cultures and cultured oligodendroglia were without compact myelin.

Tropic factors in reactive mammalian central nervous system tissue

Previous studies suggest that distal stumps of transected peripheral nerves contain diffusible factors which can attract/support axonal regeneration over distances of several mm in vivo. The present experiments were undertaken to determine if this is so for distal regions of traumatized central (i.e., optic) nerves. Proximal stumps of transected rat sciatic nerves were inserted into the single inlet ends of 6 mm long Y-shaped Silastic implants. Alternative 'lures' were attached to the paired outlets, the ability of these lures to attract/support regeneration of nerve fibers in their associated forks assessed 3.5 weeks postoperatively. Exclusive or preferential growth of nerve fibers occurred in implant forks associated with optic nerve grafts, of Elvax pellets containing homogenate obtained from previously crushed (reactive) optic nerves. Grafts of tendon, as well as homogenate from unoperated optic nerve had no effect. Results suggest that, with respect to the assay used, degenerating optic nerve tissue contains factor(s) which can attract/support regenerating nerve fibers.