Which neurotransmitter is released by most spiny striatal neurons?

The primary neurotransmitter released by most spiny striatal neurons is gamma-aminobutyric acid (GABA).1

While these neurons are chemically heterogeneous and often contain more than one neurotransmitter, they frequently co-release other substances, such as substance P and enkephalin. As the main output cells of the striatum, these neurons utilize GABA to exert inhibitory effects on their target areas, including the globus pallidus and the substantia nigra.1