The injury of the CA1 region of the adult rat hippocampus causes cognitive impairment. In this study, animal models were established by mechanically injuring the CA1 region of the adult rat hippocampus, and into the injured area were implanted chitosan carriers loaded either with or without NT-3. Immunohistochemical and nerve tracer methods were adopted to observe the role of the above-mentioned carriers in repairing the injured brain and to observe the scar formation after the injury, and Morris water maze (MWM) tests were performed to evaluate the recovery degree of the cognitive function. The results showed that NT-3-chitosan carriers stimulated regeneration of a large amount of NF-positive nerve fiber and neuron-like cells into the injured area. The newly regenerated NF-positive nerve fibers in the injured area rebuilt a neural circuit with the contralateral CA1 region via corpus callosum. Comparison of the lesion control rats and the treated rats indicates that the chitosan carriers loaded either with or without NT-3 may significantly improve the cognitive function after the hippocampus injury. (C) 2009 Elsevier Ltd. All rights reserved.