The long term goal of this project is to study the development and regulation of electrical activity and synapse formation using dissociated mammalian central neurons in cell culture as a model system. Previous studies of these fundamental neurobiological questions have used preparations from the peripheral nervous system, i.e. sensory and autonomic ganglion cells or the neuromuscular junction. Our approach has been to use spinal cord neurons taken from mouse embryos at an early developmental stage (day 13) and use the subsequent changes that occur with time in culture as a model of development. Studies have shown that early in development, spinal cord neurons have voltage-dependent sodium, potassium and calcium channels. Recent studies have examined the chemosensitivity of these developing neurons to excitatory amino acids, which are likely to be major excitatory transmitters in this system. For both voltage-dependent sodium channels and for ion channels gated by excitatory amino acids, the major change observed during the initial 21 days in culture was an increase in receptor/channel number, whereas no change in the basic features of the ion channels (voltage-dependence and ion selectivity) was observed. In the case of sodium channels, the increase in channel number correlates with the period of synapse formation and development of spontaneous electrical activity; this suggests that regulation of ion channel density may be related to electrical activity. However, in preliminary studies we have been unable to demonstrate a similar correlation of amplitude of response to excitatory amino acids with synapse formation.
