Late granule cell genesis in quail cerebellum

Proliferation of avian cerebellar neurons, including granule cells, is thought to be completed during embryonic life, and aspects of cell addition in cerebellar lobules in posthatching life are unknown. The present study tested the hypothesis that cell genesis in late embryonic and posthatching stages of quail cerebellum occurs in parallel with the performance of motor programs. After exposure to bromodeoxyuridine, short (20 hours) and long survival time points were selected to investigate survival and migration of labeled cells. Quantitative analysis of the lobular distribution of labeled cells was performed with the stereological disector method. External granular layer (EGL) proliferation did not cease after hatching, indicating that there is an extended posthatching period, lasting until P20, when cells can be added into the internal granular layer, modifying the cerebellar circuitry and function. Indeed, long survival experiments suggested that EGL-labeled cells migrated into the internal granular layer and survived for a prolonged time, although many of the progenitor cells remained in the EGL for days. Double-labeling experiments revealed that most of the late-generated granule cells were NeuN positive, but only few expressed nitric oxide synthase. In addition to granule cells, the white matter and a glutamic acid decarboxylase (GAD)-positive cell population in the molecular layer around Purkinje somata showed bromodeoxyuridine labeling. Although all lobules showed significant posthatching proliferation, an anteroposterior gradient was evident. The index of granule cell production and survival supports a spatiotemporal pattern, in correlation with the functional division of cerebellum into anterior and posterior domains.