Adult Neurogenesis and Neurogenic Plasticity in the Zebrafish Brain

Adult neurogenesis is a conserved feature of the central nervous system across the animal kingdom. This process takes place in restricted neurogenic niches of the brain, where active populations of adult stem/progenitor cells are capable of producing newborn neurons. The niche is tightly controlled by intrinsic signals within the microenvironment and from stimuli arising from the external world, which together determine the cellular behaviour of the niche and neuronal output. Currently, our understanding of the biological properties of adult neurogenesis rests mainly on two niches of the vertebrate forebrain. To broaden our view of the diversity of this trait comparative models and new niches must be explored. Here, I have taken advantage of the robust neurogenic capacity of the adult zebrafish brain to examine differences in forebrain and sensory neurogenic niches in regards to cytoarchitectural organization, neurogenic plasticity, and regulation. Five principle findings emerge: (1) up to six morphologically distinct cell types compose forebrain and sensory niches, and are devoid of ependymal cells; (2) heterogeniety in the phenotype of the stem/progenitor cell exists across niches; some having radial glial characteristics; (3) active populations of proliferating stem/progenitor cells reside within primary sensory structures of the adult brain, forming a “sensory neurogenic niche”; different from other models of adult neurogenesis; (4) changes in the social environment induce neurogenic plasticity in sensory niches more readily than integrative niches of the forebrain, and occur independently of cortisol levels; (5) modality-specific stimulation influences stages of adult neurogenesis exclusively in corresponding primary sensory niches as a result of sensory-dependent neurogenic plasticity. Additionally, I have shown that Fibroblast Growth Factor signalling may not be involved in maintaining cell proliferation in sensory niches. These studies showcase the diverse properties of forebrain and sensory neurogenic niches and provide a new perspective concerning the functional role of adult neurogenesis.Ph