BACKGROUND: Previous experiments have confirmed bone morphogenetic proteins (BMPs) upregulate cholinergic expression in neurons isolated from the embryonic rat hippocampus and cerebral cortex. Therefore, BMPs could be useful for treating Alzheimers disease and other neurodegenerative diseases. OBJECTIVE: BMP-4 was infused into the hippocampal dentate gyrus of fornix-fimbria transected rats to test the effects of BMP-4 on cholinergic expression in dentate gyrus neurons, and to observe changes in spatial memory behavior. DESIGN: A randomized controlled animal experiment. SETTING: Department of Neurosurgery and Laboratory for Cell Biology, Institute of Geriatrics, General Hospital of Chinese PLA.MATERIALS: Twenty-seven healthy adult male Sprague Dawley (SD) rats, weighing 250-300 g, were provided by the Laboratory Animal Center of the General Hospital of Chinese PLA. Reagents: BMP-4 (B-2680, Sigma Company) and choline acetyl transferase (ChAT) antibody (AB5042, Chemicon Company) were used in this study. Equipments: a rat stereotaxic instrument (type: SN-2N, Narushige Group, Japan) and Image-prog-plus image analysis software (Media Cybernetics company, USA) were used in this study. The protocol was carried out in accordance with ethical guidelines for the use and care of animals.METHODS: This experiment was performed in the Institute of Geriatrics, General Hospital of Chinese PLA between July 2004 and March 2005. Rats were randomly divided into 4 groups: Alzheimers disease group (n = 7), normal control group (n = 5), BMP-4-Alzheimers disease group (n = 8), and model group (n = 7). In the Alzheimers disease group, the left hippocampal fornix-fimbria of rats was transected to mimic Alzheimers disease symptoms. In the BMP-4-Alzheimers disease group, 1 μL BMP-4 (10 mg/L) was perfused into the left dentate gyrus with a microinjector at 1 μL/min. In the model group, 1 μL saline was perfused into the same position by the same method. Twenty-eight days after injection, Morris water maze test was performed in all rats to test spatial memory. Time-to-platform and swim-path length were recorded. Immunohistochemical staining of cholinergic neurons was performed on brain sections containing dentate gyrus. The area covered by ChAT-positive cells was analyzed using an Image-prog-plus image analysis software. MAIN OUTCOME MEASURES: Area covered by ChAT-positive cells in the dentate gyrus. Time-to-platform and swim path-length.RESULTS: Twenty-seven rats were included in the final analysis. In the Alzheimers disease group, the area covered by ChAT-positive cells was significantly smaller compared with the normal control group (F = 76.03, P < 0.01). The area covered by ChAT-positive cells was significantly larger in the BMP-4- Alzheimers disease group than in the model group (F = 35.17, P < 0.05), but significantly smaller than in the normal control group (F = 40.17, P < 0.05). Time-to-platform and swim-path length were significantly longer in the Alzheimers disease group than in the normal control group (F =24.62 and 631.58, respectively, both P < 0.05). Time-to-platform and swim-path length were significantly shorter in the BMP4-Alzheimers disease group compared with the model group (F = 22.06 and 606.89, respectively P < 0.05).CONCLUSION: Injection of BMP-4 into the dentate gyrus of Alzheimers disease model rats alleviates central cholinergic system injury and concomitantly improves spatial memory.