Forebrain cell proliferation, behavior, and physiology of zebrafish, Danio rerio, kept in enriched or barren environments

Comparative studies on neural plasticity in non-mammalian vertebrates are increasingly promoted as an important complement to mammalian models. In teleost fishes the number of brain cells increases with age, body weight, and body length throughout life. Neurogenesis persists to a large degree, and both neuron replacement and net brain growth occur during adulthood. Whether environmental factors affect brain cell proliferation has however been scarcely investigated in this animal group. In the current study adult male zebrafish were kept in social isolation in different environments (enriched vs. barren) for one week. Telencephalic cell proliferation was investigated by proliferating cell nuclear antigen (PCNA) immunohistochemistry. Higher numbers of PCNA positive nuclei and significantly increased inter-individual variability was observed in fish kept in aquaria enriched with artificial plants and gravel. Zebrafish rapidly regained feed intake after transfer to social isolation. Whole-body cortisol levels were also generally low in isolated fish, although slightly elevated in fish from enriched environments. In summary, this study demonstrates that environmental alterations can rapidly alter cell cycle dynamics in the zebrafish brain. Furthermore, the results support the idea that mild short-term stressors and concomitant small increases in corticosteroid exposure stimulate brain cell proliferation.