A compound represented by the general formula (I): (wherein R represents optionally protected hydroxy or oxo; indicates alpha configuration, beta configuration, or a mixture of these in an arbitrary proportion; n is an integer of 1 to 3; and m is an integer of 0 to 10, provided that two or more R 's are not bonded to the same carbon atom other than the terminal carbon atoms), a salt of the compound, or a prodrug of either. The compound represented by the general formula (I) is effective in, e.g., improving the function of astrocytes. It is useful as a preventive and/or therapeutic agent for brain infarction or nerve function disorders after brain infarction and for neurodegenerative diseases such as Parkinson's disease, Parkinson's syndrome, amyotrophic lateral sclerosis, and Alzheimer's disease.