Growth and myelination of explant cultures in defined medium

Effect of altered thyroid status on neurotrophin gene expression during postnatal development of the mouse cerebellum

Thyroid hormone (TH) plays an important role in brain development. The rodent cerebellum has been an excellent model for the study of the molecular mechanisms of TH action in brain. However, most studies have utilized the rat rather than the mouse. Considering the usefulness of mice with regard to diverse genetic models, the study of TH effect on mouse cerebellar development is needed. Thus, we examined the effect of perinatal hypothyroidism on the expression of neurotrophin-3 (NT-3) and brain-derived neurotrophic factor (BDNF) genes, which play critical roles in cerebellar development. Newborn mice were rendered hypothyroid by administering methimazole and perchlorate in drinking water to their mothers. The growth of hypothyroid mice was retarded, which was reversed by daily thyroxine administration. NT-3 and BDNF gene expression was depressed in the perinatal hypothyroid cerebellum. Furthermore, the expression of retinoid-receptor-related orphan nuclear hormone receptor-alpha (RORalpha), an orphan nuclear receptor that plays critical roles in Purkinje cell development, was also decreased. Morphologically, disappearance of the external granule cell layer was retarded and arborization of Purkinje cell dendrite was decreased, events that were also observed in hypothyroid rats. These results indicate that the mouse cerebellum is comparable to the rat cerebellum as a model for the examination of the molecular mechanisms of TH action in brain development.

Myelination in cerebellar slice cultures: development of a system amenable to biochemical analysis

Myelin deposition and maintenance are critical to proper function of the mammalian nervous system. Previous investigations of myelination in the central nervous system (CNS) were hampered by the lack of an in vitro system that can faithfully reproduce in vivo events yet is amenable to biochemical investigation. We have developed a procedure, based on organotypic cultures, which permits efficient preparation of large numbers of cerebellar slice cultures that can be easily manipulated. Cultures have been examined to document myelination biochemically (by incorporation of [35S]sulfate into sulfolipids), immunohistochemically (by labeling the myelin components myelin basic protein and galactocerebroside), and morphologically (by both light and electron microscopy). We tested the effects of biologically active peptides and antibodies on myelination in the thin slices. The results indicate that the cultures provide an in vitro system that can be used to examine specific cellular events that occur during CNS myelination.

An in vitro model to study diabetic neuropathy

Adult dorsal root ganglion (DRG) neurons from diabetic and normal C57BL mice were cultured and compared for survival and neurite extension. Neurons from diabetic mice have improved their survival and neurite extension when the insulin concentration was increased but it was never as good as that of controls. The increase of glucose concentration in serum-free media to ten times higher than normal improved both survival and neurite extension of neurons from diabetic animals.

Myelination requirements of central nervous system glia in vitro: statistical validation of differences between glia from adult and immature mice

Glia from adult optic nerve, like those from immature nerve, have been shown to colonize and myelinate cerebellar axons in combined cultures. Preliminary experiments suggested, however, that the glia from adults might require the added nutrients and/or chemical signals present in a serum and embryo extract containing medium to produce myelin, whereas glia from immature animals could form myelin in a chemically defined medium described by Hendelman et al. (1985). This observation demanded rigorous confirmation, since it depended on the meaning of a negative result (the absence of myelin), which could be produced by many factors other than the composition of the medium in this complex culture system. Here we report an extensive series of experiments, with controls for all other factors, that provide unquestionable statistical validation of the additional myelination requirements of the glia from adult nerves. The cultures can now be used to identify these required substances, which may be limiting factors for central nervous system myelin regeneration in situ.

Cytology and organization of rat cerebellar organ cultures

Roller tube cultures of parasagittal cerebellar slices were taken from young rats aged 9-11 days, and maintained in vitro for 1-2 weeks. Morphological aspects of cell types and synaptic relationships in such organ cultures were examined at light and electron microscopic levels. Some neurons were marked by intracellular injections of horseradish peroxidase for subsequent identification of their connection patterns. Cytoarchitecture of the cerebellar cortex was largely preserved in the organ cultures. Dendritic trees of Purkinje cells exhibited isoplanar organizations that often resembled their orientation at the time of explanation. Other cerebellar neurons, namely granule cells, Golgi cells, basket cells, stellate cells, all differentiated within the organ cultures. In addition, some neurons of the deep cerebellar nuclei remained viable during the period of culture. Mossy fibers most probably of cerebellar nuclear origin were found terminating on the dendrites of granule cells and Golgi cells. Quite unexpected were certain types of direct synapses of afferent fibers on short necked spines arising from Purkinje cell smooth dendrites and somata. Such terminals resembled climbing fibers. They were most likely modified mossy fiber afferents, since the organ cultures did not include neurons of the inferior olive which are well spearated from the cerebellar mass at postnatal stages. These "ascending" mossy fibers presumably occupied postsynaptic surfaces that were either vacated by deafferentation or induced by the afferent fibers themselves. Intracellularly labeled Purkinje cells had widely distributed axonal collateral branches. Labeled axons were distributed within the Purkinje cell layer. Several recurrent Purkinje cell axon collaterals stained with reaction products of horseradish peroxidase tracer were followed at the ultrastructural level. In one case, labeled terminals were examined in an area of approximately 2 mm2. Terminals of Purkinje cell collaterals formed symmetric synapses with somata of basket cells and dendrites of Golgi cells, but not Purkinje cell somata. Some large boutons of serially traced Purkinje cell axon collaterals formed asymmetric contacts with profiles interpreted as Golgi cell dendrites. In contrast to the apparent axonal sprouting in cerebellar organ cultures, maturation of dendritic processes remained static. Astroglia cells of diverse shapes were observed following immunocytochemical staining with antisera to glia filament proteins. The distribution patterns of immunoreactive astrocytes changed dramatically in cerebellar slice cultures maintained for 3-6 weeks in vitro.