Identification of Zeta (S) Opioid Receptor Binding Polypeptides in Rat Cerebellum

Abstract

Growth factors are known to be crucial in dictating the course of cellular proliferation and differentiation^1-4. Developing cells and tissues may be subjected to a host of elements that can stimulate or inhibit growth processes, ultimately serving to determine the number and type(s) of cells composing the mature organ. Nervous system development is a carefully orchestrated process that consists of a cascade of events (i.e., cell proliferation, migration, differentiation) which legd to the harmonious functioning unit vital to the organism⁵. One such event that is critical to achieving a successfully working nervous system is determination of the number of neuronal and glial cells. In humans, literally billions of cells are replicated and differentiated in a very short time, with most of the process of cellular replication occurring during prenatal life and in the early postnatal period. Indeed, by 18 months of age, the human nervous system has largely formed the neurons and many of the glia constituting the adult. Two forces are integral to determining the proper cell number. Cells must be allowed or even stimulated to proliferate, and repressed when the approporiate number has been achieved. Needless to say, if this process of cell replication malfunctions, short-and long-term damage may occur. Thus, dysfunction of these processes could lead to abnormally fewer cells which would compromise neural integration and signalling, or it could result in too many cells that may lead to neural neoplasia. While a number of growth factors are known to excite and stimulate cell proliferation, our knowledge of factors that curtail cell proliferation is extremely limited.