The finding's right there in the title: dopamine is a neurotransmitter, and so is glutamate. Stuber et al found (in mice) that many of the cells that release dopamine also simultaneously release glutamate - specifically, almost all of the cells that project to the nucleus accumbens, involved in pleasure and motivation, also release glutamate. By contrast none of the dopaminergic neurons projecting to the nearby dorsal striatum, involved in movement regulation do this.Previous work had provided some suggestive evidence for some degree of glutamate/dopamine co-release but this is the first hard evidence and the fact that basically all the dopamine input to the nucleus accumbens is also glutamate input is especially striking.
This is important because it overturns the idea that neurons only release one neurotransmitter each. In fact, it's been clear for a while that this isn't strictly true: there are various little-understood peptide transmitters or "neurohormones" that are known to be co-released, but their function is obscure in most cases.
Dopamine and glutamate on the other hand are both extremely well studied neurotransmitters in their own right. Glutamate's the single most common transmitter in the brain while dopamine is famous for its role in motor control, motivation, Parkinson's disease, mental illness and the action of recreational drugs, just for starters.
What exactly the glutamate does in the nucleus accumbens is completely mysterious at present but future work will no doubt shed light on this. More generally, this paper is a reminder of the fact that our knowledge of the brain is still in its infancy...
Stuber, G., Hnasko, T., Britt, J., Edwards, R., & Bonci, A. (2010). Dopaminergic Terminals in the Nucleus Accumbens But Not the Dorsal Striatum Corelease Glutamate Journal of Neuroscience, 30 (24), 8229-8233 DOI: 10.1523/JNEUROSCI.1754-10.2010
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