Long-term culture of human fetal spinal cord neurons: morphological, immunocytochemical and electrophysiological characteristics.

Cultures were prepared from ventral spinal cord tissue from 8-11-week gestational human fetuses and grown for a period of up to 6 months. These cultures were studied by morphological, immunocytochemical and intracellular electrophysiological techniques. From 2 weeks in vitro and onward, small bipolar cells were found in outgrowths of spinal cord explants and were identified as neurons by positive immunoreactions with an antibody specific for neurofilament protein. In addition, a large population of glial fibrillary acidic protein-positive astrocytes and a smaller number of galactocerebroside-positive oligodendrocytes were recognized in these cultures. The development of synaptic terminals was also studied by electron microscopy. The first appearance of synaptic terminal was found in a 3-week culture and was an axo-dendritic synapse. During the next 2 months, there was a steady increase in number and structural maturation of synaptic profiles. In addition to axo-dendritic synapses, which were most common, axo-somatic and axo-axonic synapses were demonstrated. After 3 months in culture, the occurrence of large neurons possessing the characteristic features of mature neurons was also noted. Although the occurrence of oligodendrocytes in these cultures was confirmed, no myelination of axons was demonstrated by electron microscopy. Intracellular recordings were obtained from the cultured spinal cord cells, and these cells were identified clearly as neurons by their action potential responses to depolarizing current pulses. The average input resistance of these neurons was 31 M omega with resting membrane potential of -52 +/- 2.3 mV.