Neuronal polarity during development

A spinal motor neuron. Sodium channels red MAP2 green.

Early in neuronal development, neurites become polarized into dendrites and the axon. One fundamental event involves the targeting of sodium channels to the initial segment of the axon, a site that may function as the zone of action potential initiation. In the figure above a motor neuron has been cultured from embryonic spinal cord. After 4 days in vitro the cell was labeled with antibodies against sodium channels (red) and MAP2, a somatodendritic marker (green). Only one neurite, destined to be the axon, has the cluster of sodium channels. In contrast with the situation at nodes of Ranvier, this channel clustering occurs independently of glial cells.

Cell labeled with antibodies against neurofilaments red and
sodium channels green after 4 days in vitro.

Our laboratory is interested in the mechanisms by which neurites become polarized, and in particular, how ion channels are targeted to specific processes. We are also studying the electrophysiological consequences of the 10-30 micron region of the axon that is devoid of sodium channels and could serve to limit excitability. These spinal motor neurons are further of considerable interest since they are primary targets of the disease process in amyotrophic lateral sclerosis.

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