GABA is an endogenous ligand for synaptic glycine receptors

Experimental evidence refuting Dale's principle, the notion that each neuron synthesizes and releases only one neurotransmitter, has accumulated in the past four decades, and cotransmission by multiple neurotransmitters from the same axon terminal (and even from the same vesicle) now is well documented. Heretofore, in all examples of cotransmission, each released neurotransmitter acted on a different receptor. Lu, Rubio, and Trussell, however, demonstrate in this issue of Neuron the first instance of cotransmission in which two neurotransmitters act on the same postsynaptic receptor.