The Developmental Influence of Inhibitory Synaptic Transmission

Abstract

Environmental manipulations that affect brain development form the primary evidence for “activity-dependent” mechanisms. Manipulations of this sort probably alter the normal amount or the pattern of synaptic transmission and action potentials, and this altered activity state somehow influences the growth and differentiation of synaptic connections. The first studies to draw a strong causal relationship between environmental stimulation and the development of connections were performed in the cat visual system (Wiesel and Hubel, 1963, Wiesel and Hubel, 1965; Hubel and Wiesel, 1965). In control animals, extracellular recordings from cortex show that most neurons fire action potentials in response to stimulation of either eye. However, when visual stimulation to one eye is decreased during development, there is a dramatic loss in the ability of that eye to activate cortical neurons. While these changes are striking, the cellular mechanisms whereby differences in neural activity are translated into structural or functional changes are far from clear. To date, most studies have focused on the cellular mechanisms that might operate at developing excitatory synapses, such as the nerve-muscle junction. In contrast, little is known about the maturation of inhibitory synaptic contacts, and whether they too can exhibit “activity-dependent” mechanisms. This chapter summarizes experimental findings from a developing inhibitory projection in the auditory system, and provides evidence that inhibitory transmission plays an active role during ontogeny.