Novel Enzyme Finding Points Way to Improved Cognitive Therapies

    An international scientific team altered a gene in mice to inhibit the activity of phosphodiesterase-4B (PDE4B), which is present in many organs of the vertebrate body, including the brain. In behavioral tests, the PDE4B-inhibited mice showed enhanced cognitive abilities. They tended to learn faster, remember events longer, and solve complex exercises better than ordinary mice.

    For example, the “brainy mice” showed a better ability than ordinary mice to recognize another mouse that they had been introduced to the day before. They were also quicker at learning the location of a hidden escape platform in a test called the Morris water maze. However, the PDE4B-inhibited mice also showed less recall of a fearful event after several days than ordinary mice.

    The findings in the study (“Specific inhibition of phosphodiesterase-4B results in anxiolysis and facilitates memory acquisition”), published in Neuropsychopharmacology, were limited to mice and have not been tested in humans, but PDE4B is present in people. The diminished memory of fear among mice with inhibited PDE4B could be of interest to researchers looking for treatments for pathological fear, typified by post-traumatic stress disorder.

    The PDE4B-inhibited mice also showed less anxiety. They spent more time in open, brightly-lit spaces than ordinary mice, which preferred dark, enclosed spaces. Ordinary mice are naturally fearful of cats, but the PDE4B-inhibited mice showed a decreased fear response to cat urine, suggesting that one effect of inhibiting PDE4B could be an increase in risk-taking behavior.

    So, while the PDE4B-inhibited mice excelled at solving complex exercises, their low levels of anxiety could be counterproductive for a wild mouse.

    The researchers point out that their work sheds light on the molecular underpinnings of learning and memory and could form the basis for research into new treatments for age-related cognitive decline, cognitive disorders such as Alzheimer’s disease and schizophrenia, and other conditions.

    “Cognitive impairments are currently poorly treated, so I’m excited that our work using mice has identified phosphodiesterase-4B as a promising target for potential new treatments,” said Steve Clapcote, lecturer in pharmacology in the school of biomedical sciences at the University of Leeds.

    The researchers are now working on developing drugs that will specifically inhibit PDE4B. These drugs will be tested in animals to see whether any would be suitable for clinical trials in humans.

    According to Alexander McGirr, M.D., a psychiatrist in training at the University of British Columbia, who co-led the study, “In the future, medicines targeting PDE4B may potentially improve the lives of individuals with neurocognitive disorders and life-impairing anxiety, and they may have a time-limited role after traumatic events.”