NeoTherapeutics Inc. shares rose nearly 21% after the company said tests of its Neotrofin drug in animals suggested the compound could stimulate nerves to grow again after they have been damaged. Shares in the Irvine-based biotechnology company rose $2.31 to close at $13.50 on Nasdaq. More than 566,000 shares changed hands, more than four times the average trading volume for the stock over the last six months. The animal research--a vote of confidence in the drug's ability to improve nerve function and help repair damaged neurons--comes as NeoTherapeutics works to complete the second of the three stages of drug testing in humans required by the Food and Drug Administration. The company is studying Neotrofin for use in treating patients who have mild to moderate Alzheimer's disease. "These results indicate that Neotrofin may provide therapeutic benefit in several different neuro-degenerative diseases such as Alzheimer's disease, spinal cord injury and stroke," said company President and Chief Executive Alvin Glasky.