The Effects of Environmental Enrichment and Age-Related Differences on Inhibitory Avoidance in Zebrafish (Danio rerio Hamilton)

Abstract

The inhibitory avoidance paradigm allows the study of mechanisms underlying learning and memory formation in zebrafish (Danio rerio Hamilton). For zebrafish, the physiology and behavior associated with this paradigm are as yet poorly understood. We therefore assessed the effects of environmental enrichment and fish age on inhibitory avoidance learning. Fish raised in an environmentally enriched tank showed decreased anxiety-like behavior and increased exploration. Enrichment greatly reduced inhibitory avoidance in 6-month (6M)- and 12-month (12 M)-old fish. Following inhibitory avoidance, telencephalic mRNA levels of proliferating cell nuclear antigen (pcna), neurogenic differentiation (neurod), cocaine- and amphetamine-regulated transcript 4 (cart4), and cannabinoid receptor 1 (cnr1) were lower in enriched-housed fish, while the ratios of mineralocorticoid receptor (nr3c2)/glucocorticoid receptor α [nr3c1(α)] and glucocorticoid receptor β [nr3c1(β)]/glucocorticoid receptor α [nr3c1(α)] were higher. This was observed for 6M-old fish only, not for 24-month (24 M) old fish. Instead, 24 M-old fish showed delayed inhibitory avoidance, no effects of enrichment, and reduced expression of neuroplasticity genes. Overall, our data show strong differences in inhibitory avoidance behavior between zebrafish of different ages and a clear reduction in avoidance behavior following housing under environmental enrichment.

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“…However, similar effect was reported in Manuel et al (2015) where it was attributed to the inhibition of avoidance behavior in fish subjected to EE. Thus, we may conclude that EE-induced reduction in NeuroD1 hippocampal expression in Aβ-treated or aging rats could reflect some adaptive behavioral reactions needed in further investigation.…”

Housing Environment Affects Baseline Anxiety in Zebrafish

“…Zebrafish age is an important consideration, as indicated by one study showed that age does impact anxiety parameters [14] but that study involved an age difference of six months (approx. 180 days).…”

Conserved regulators of cognitive aging: From worms to humans

“…Zebrafish exhibit decreased associative learning with age, with defects in spatial learning evident at around 18 months [180, 235, 237]. Inhibitory avoidance is also reduced by 24 months of age [122], and there is a corresponding reduction in the expression of plasticity-associated genes in the zebrafish telencephalon, such as bdnf , cart4 , and pcna [122]. Killifish also display reduced performance on an active avoidance task by 9 weeks of age [218, 219].…”