Development, Involution and Plasticity in the Central Nervous System

Smith, C

Abstract

The purpose of this project is to study the biochemical events associated with development, plasticity and involution of the nervous system. We have used the quantitative autoradiographic [1-14C]leucine method to study the sites of origin and the process underlying changes in nervous system organization that take place during these events and the [14C]deo- xyglucose method to examine the outcome of the changes, i.e. the func- tional reorganization. Our studies of normal development in rats show decreasing rates of protein synthesis in most brain regions from day 10 to the adult stage except in the paraventricular and supraoptic nuclei of the hypothalamus. We are studying the developing and adult mouse somato- sensory system as a model system of plasticity. Results of deoxyglucose studies on the effects of whisker follicle removal in neonatal mice show that when the lesioned mice reach adulthood metabolic maps in both somatosensory cortex and in trigeminal brainstem nuclei are altered. When adult mice are similarly lesioned metabolic maps in the cortical barrel field are also found to be altered after 160 days. Comparison of the number of nerve fibers innervating whisker follicles adjacent to those that had been lesioned suggests that in adult mice the reorganiza- tion may occur in the periphery; i.e., fibers that had originally inner- vated the lesioned follicles now innervated new targets, the adjacent follicles. In the neonatally lesioned mice no such supernumerary innerva- tion was found and it is hypothesized that in the neonate the reorganiza- tion had taken place in the central nervous system. These results indi- cate functional reorganization in both the neonatal and the adult whis- ker-barrel pathway in the mouse and they suggest that this system may serve as a useful model of both developmental and adult plasticity.