Development of “Organotypic” Bioelectric Activities in Central Nervous Tissues During Maturation in Culture

Abstract

This chapter discusses the bioelectric activities that develop in explants of vertebrate central nervous tissues during differentiation and maturation in vitro. The chapter also focuses on the remarkable degree of intrinsic self-differentiation, which has been demonstrated in long-term cultures of explants from various parts of the vertebrate neuraxis—spinal cord to cerebral cortex. Correlative electrophysiological and electron-microscopic analyses demonstrate that neurons in embryonic spinal-cord explants can form organized synaptic networks in vitro. Dorsal-root ganglia attached to these cord cross sections can develop functional connections with cord neurons. Axons from the latter may, in turn, grow into attached skeletal muscle tissue, leading to characteristic neuromuscular transmission. The entire spinal reflex arc is thus available for direct study during its formation in vitro. Bioelectric and ultrastructural data obtained during the growth of neonatal mouse cerebral cortex in culture reveal that a similar process of self-differentiation occurs. Primary evoked potentials and secondary oscillatory afterdischarges develop in cerebral explants and display a remarkable similarity to recordings from cerebral cortex in situ. Characteristic sensitivity of these complex bioelectric activities to various neuropharmacological agents provides further evidence of their organotypic nature.