Estrogen promotes the initial migration and inception of NgCAM-dependent calcium-signaling by new neurons of the adult songbird brain

The adult avian forebrain continues to generate neurons from ventricular zo ne (VZ) precursor cells, whose neuronal progeny then migrate into the brain parenchyma, Migrating neurons respond to the Ig-family adhesion molecule N gCAM with increments in cytosolic calcium, and migration is disrupted by an ti-NgCAM Ig. The calcium response to NgCAM is developmentally restricted to bipolar migrants during a period spanning 6 to 9 DIV. This period correspo nds to the postmitotic age at which new neurons leave the adult VZ to trave rse a subjacent layer of estrogen-receptive "gatekeeper" neurons, Since neu ronal passage through this layer occurs concurrently with the onset of NgCA M-dependent calcium signaling, we asked whether acquisition of the calcium response to NgCAM required estrogen exposure. Among neurons arising from ex plants of the adult finch neostriatal VZ, only those supplemented with estr ogen developed calcium responses to NgCAM; neither explants raised in the a bsence of estrogen, nor those supplemented with testosterone, did so. Neuro ns in all three groups expressed NgCAM, had equivalent baseline calcium lev els, and responded identically to K+-depolarization. Nonetheless, many more neurons migrated from explants of both finch and canary VZ raised in estro gen-supplemented media than from their estrogen-deprived counterparts, even though no effect of estrogen on neuronal survival per se was noted. These findings suggest that estrogen encourages the initial departure and assumpt ion of signal competence by neurons arising from the adult avian VZ, thereb y promoting their parenchymal recruitment and migration success.