Environmental enrichment attenuates cognitive deficits, but does not alter neurotrophin gene expression in the hippocampus following lateral fluid percussion brain injury

Abstract

Environmental enrichment attenuates neurological deficits associated with experimental brain injury. The molecular events that mediate these environmentally induced improvements in function after injury are largely unknown, but neurotrophins have been hypothesized to be a neural substrate because of their role in cell survival and neural plasticity. Furthermore, exposure to complex environments in normal animals increases neurotrophin gene expression. However, following an ischemic injury, environmental enrichment decreases neurotrophin mRNA levels. Whether these contrasting findings are attributable to differences between injured and uninjured animals or are dependent upon the specific type of brain injury has not been determined. We examined the effects of 14 days of environmental enrichment following a lateral fluid percussion brain injury on behavior and gene expression of brain-derived neurotrophic factor, its high-affinity receptor, TrkB, and neurotrophin-3 in the rat hippocampus. Environmental enrichment attenuated learning deficits in the injured animals, but neither the injury nor housing conditions influenced neurotrophin/receptor mRNA levels. From these data we suggest that following brain trauma, improvements in learning associated with environmental enrichment are not mediated by alterations in brain-derived neurotrophic factor, TrkB or neurotrophin-3 gene expression.