The Anatomy of Multiple Gabaergic and Glycinergic Pathways in the Inner Plexiform Layer of The Goldfish Retina

Abstract

Glycine and τ-aminobutyric acid (GABA) are the dominant and perhaps the only fast inhibitory neurotransmitters for vertebrate interneurons. Why are even two such transmitters necessary? One compelling explanation is that a greater range of additivity of inhibitory currents is achieved by having two different pre-synaptic systems converge on the same kind of post-synaptic mechanism, as demonstrated by Gold and Martin (1984) for Muller cells in the lamprey medulla. Thus, in spite of tremendous molecular and biophysical similarity of the channels gated by glycine and GABA, their relative contributions to post-synaptic responses can be independent over a large range. In the vertebrate retina, and especially in the goldfish retina, there are multiple types of GABAergic and glycinergic amacrine cells (ACs) that constitute the fundamental assortment of inhibitory devices in the inner plexiform layer (IPL).