Our new paper is out! We identified concentrated populations of neurons that co-express molecular markers of GABA synthesis, accumulation of glutamate into synaptic vesicles, and accumulation of GABA into synaptic vesicles. These neurons that co-transmit glutamate and GABA belong to specific parts of the ventral tegmental area (VTA), supramammillary nucleus (SUM), and entopeduncular nucleus (EPN). We also found subsets of neurons in lateral habenula, pons, and elsewhere that accumulate glutamate into synaptic vesicles, synthesize GABA, but do not accumulate GABA into vesicles by VGaT, suggesting this type of glutamate-GABA neuron does not co-transmit glutamate and GABA.
Examining the axon terminals established by VTA, EPN, and SUM neurons we found a common synaptic structure of independent types of inhibitory or excitatory synapses from single axon terminals - suggesting a common mechanism for the co-transmission of glutamate and GABA from different sources of glutamate-GABA neurons. Finally, in lateral habenula that receives co-transmitted glutamate and GABA from VTA and EPN, we found that glutamate and GABA are accumulated into separate synaptic vesicles. This suggests that the co-transmission of glutamate and GABA arises from specific synaptic vesicles released at separate synapses within single axon terminals.
You can download the paper here at Cell Reports