“Trophic” Functions

Abstract

The concept of neurotrophic function is an old one indeed. For over half a century, the term “trophic” has been used to describe a variety of phenomena whose mechanisms are not yet understood. However, it eventually became clear that the term “trophic” had to be either defined better or discarded, and in 1968, at a meeting called to address itself to this very issue, it was agreed that for scientific as well as historical reasons this undeniably vague term should be retained (Guth, 1969). Several of the phenomena to which it has been applied, viz., the neural regulation of differentiation of vertebrate taste buds, the neural regulation of amphibian limb regeneration, and the neural regulation of certain physiological and metabolic properties of mammalian muscles, all have in common certain features which fit the following definition of “neurotrophic” effects: “interactions between nerves and other cells which initiate or control molecular modification in the other cell” (Guth, 1969). Trophic influences can thus be distinguished operationally from other neurophysiological phenomena by the long-term nature of their effects even though the fundamental mechanisms that are responsible for these effects are not yet known.