The somatosensory cortex of mammals is famous for its map-like representation of the parts of the body responsive to touch. This area also was one of the first used to show what is now known as a common cortical property called experience-dependent plasticity, which is a change in the sensitivity of cortical responses to a particular spatial stimulus. If an area of the body is deprived of touch for a long time, the responsive area in the cortex becomes less sensitive and may decrease; if the area of the body is continually stimulated, the cortical sensitivity increases and the cortical area may expand. A simple model system for showing the plasticity is the facial whisker array of rodents, which maps in a very distinctive way in what are called "barrel fields" for their shape. The long whiskers easily can be trimmed daily, so that the intact whiskers receive much more of natural sensory stimulation than the trimmed ones, and it turns out that the central responses to neighboring trimmed versus untrimmed whiskers show significant changes. This project investigates the role of a biochemical compound called acetylcholine (ACh) in the experience-dependent plasticity. ACh is known to affect the transmission of excitatory impulses between nerve cells. A novel specific immunotoxin is used to pharmacologically block ACh inputs from a part of the brain that provides the major source of ACh inputs to the cortex. Electrophysiological recordings measure the responsiveness of central cortical nerve cells to give a quantitative assay of the plasticity with and without the precise and specific ACh blockage. Results will be important to understanding the nature of cortical function, and have potential impact not only on recovery from cortical deficits, but also on mechanisms of development and perhaps learning.
