Influence of nerve activity of the macromolecular content of neurons and their effector organs.

The term "plasticity" is sometimes used to refer exclusively to anatomical changes in the nervous system that occur, in response either to neural damage or to changes in an animal's environment. However, in a more general sense, the term can encompass long-term changes in the biochemi­ cal and electrophysiological properties of neurons that occur under these same circumstances. One experimental approach to the study of biochemi­ cal plasticity has been to ask what effects periods of "use" or "disuse" have on the biochemistry of neurons and their effector cells. Biochemical changes following repeated activation of a neural circuit have often been postulated to underlie long-term changes in an animal's behavior and physiology (e.g. learning, adaptation to environmental change) (see 44). Such activity­ dependent changes have thus far been most successfully studied in the peripheral nervous system-particularly in skeletal muscle, the superior cervical ganglion, and the pineal gland. This brief review summarizes evi­ dence that the level of neural stimulation of these tissues affects the concen­ trations of certain proteins important in regulating the tissues' function.