TRANSIENT COUPLING OF NG-CAM EXPRESSION TO NGCAM-DEPENDENT CALCIUM SIGNALING DURING MIGRATION OF NEW NEURONS IN THE ADULT SONGBIRD BRAIN

The adult avian forebrain continues to generate neurons from subependy mal zone (SZ) precursor cells, whose neuronal progeny migrate into the brain upon radial guide fibers, These neurons express the immunoglobu lin-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 wit h 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 res tricted, 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 pers isted tonically thereafter. The period during which NgCAM elicited a c alcium signal corresponded to the postmitotic age at which new, bipola r neurons leave the adult SZ to enter the brain parenchyma in vivo. Ac cordingly, the calcium response to NgCAM was largely limited to morpho logically 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 c alcium-dependent signal transduction pathways to a stably expressed su rface adhesion molecule, whose function in a given neuron may therefor e evolve with cellular maturation.