The adult avian forebrain continues to generate neurons from subependymal zone (SZ) precursor cells, whose neuronal progeny migrate into the brain upon radial guide fibers. These neurons express the immunoglobulin-family adhesion molecule NgCAM, and their migration in culture is disrupted by anti-NgCAM Fab. Confocal imaging of adult zebra finch SZ loaded with the calcium indicator fluo-3, as well as ratio imaging with the indicator fura-2, revealed that migrating new neurons responded to microgram amounts of NgCAM with reversible increments in cytosolic calcium. The calcium response to NgCAM antigen was developmentally restricted, in that it was only manifested by neurons for roughly the 3- to 4-day period between 6 and 9 DIV, even though NgCAM expression persisted tonically thereafter. The period during which NgCAM elicited a calcium signal corresponded to the postmitotic age at which new, bipolar neurons leave the adult SZ to enter the brain parenchyma in vivo. Accordingly, the calcium response to NgCAM was largely limited to morphologically bipolar cells. Anti-NgCAM IgG also evoked a neuronal calcium signal over the same restricted period that NgCAM protein exerted its effect. These findings suggest a dynamic coupling and uncoupling of calcium-dependent signal transduction pathways to a stably expressed surface adhesion molecule, whose function in a given neuron may therefore evolve with cellular maturation.
ASJC Scopus subject areas
- Molecular Biology
- Cellular and Molecular Neuroscience
- Cell Biology