DEVELOPMENT OF SPINAL-CORD IN THE ISOLATED CNS OF A NEONATAL MAMMAL (THE OPOSSUM MONODELPHIS-DOMESTICA) MAINTAINED IN LONG-TERM CULTURE

The CNS of the newly born opossum removed in its entirety survives and maintains its electrical excitability in suitable culture media for u p to ten days at 25 degrees C. The structure of the developing neonata l spinal cord has been studied in the intact animal and in the culture d CNS. The differentiation and survival of individual cells and subcel lular structures were followed at the light and electron microscopic l evel. The expression of cell markers in neuronal and glial cells was s tudied immunocytochemically using commercially available antibodies. B oth mono- and polyclonal antibodies raised against antigens from sever al other species cross-reacted with Monodelphis antigens. The spinal c ord of preparations removed from three-day-old-animals showed many neu ron specific enolase-positive large neurons in the ventral horn as wel l as vimentin- and glial fibrillary acidic protein-positive radial gli al cells and numerous small diameter unmyelinated axons, abundant dend rites and synaptic structures. From post natal day 5 to post natal day 8 continued differentiation of neurons and differentiation of radial glial cells into astrocytes were apparent. Radial glial fibres and ast rocytes reacted positively to antibodies against glial fibrillary acid ic protein. Myelin had not appeared at 8 days. A comparison of materia l obtained from postnatal day 3-postnatal day 4 preparations fixed imm ediately after dissection and from postnatal day 3-postnatal day 4 pre parations fixed after 5 days in culture showed growth with continued m itotic activity of the neuroepithelial cells and further neuronal and glial maturation in the spinal cord especially in the more rostral end . In successful experiments in vitro, the preservation of individual c ells, organelles, membranes and synapses was similar in the freshly di ssected and cultured preparations apart from a distinct loss of the yo ungest and some of the oldest neurons in the spinal cord. Also the mai n fibre tracts (dorsal, lateral and ventromedial funiculus) survived. Virtually all preparations that had not been damaged or injured showed these results. Possible reasons for the death or survival of individu al neuronal or glial cell populations in these preparations are discus sed.