GABA, Glycine, and Glutamate Co-Release at Developing Inhibitory Synapses

Neurobiologists have long classified synaptic phenotype by a single neurotransmitter released at that synapse. Research over the past two decades has made it clear, however, that the classification of neurons and synapses as purely GABAergic, or even as purely inhibitory or excitatory, is no longer valid. In this chapter we review evidence showing that inhibitory synapses co-release multiple inhibitory neurotransmitters, and that some classical inhibitory synapses also release excitatory neurotransmitters. As multiple transmitter release is particularly prevalent at immature synapses, we pay special attention to developmental plasticity in considering possible mechanisms and functions for release of these seemingly antagonistic neurotransmitters.