Scientists have identified a backup supply of stem cells that can repair the most severe damage to the nerves responsible for our sense of smell. These reservists normally lie around and do nothing, but when neighboring cells die, the scientists say, the stem cells jump into action.

A new pill makes normal mice resistant to weight gain even when they are fed a high-fat diet. The synthetic drug is designed to mimic fat, and allows scientists to chemically switch on PPAR-d, the master regulator that controls the ability of cells to burn fat. Even when the mice are not active, turning on the chemical switch activates the same fat-burning process that occurs during exercise. The resulting shift in energy balance (calories in, calories burned) makes the mice resistant to weight gain on a high fat diet.

Mice whose brains had lost a large number of neurons due to neurodegeneration regained long-term memories and the ability to learn after their surroundings were enriched with toys and other sensory stimuli, new studies have shown. The scientists were able to achieve the same results when they treated the mice with a specific type of drug that encourages neuronal growth. The studies suggest two promising avenues for treatments for neurodegenerative diseases such as Alzheimer's disease.