Selective brain distribution and distinctive synaptic architecture of dual glutamatergic-GABAergic neurons

Even though VTA axons express both vGluT2 and vGAT, synaptic vesicles and transporters are largely segregated into distinct pools for release rather than released together at the same synapse.

“Together, these studies suggest that even though individual axons from the VTA express both vGluT2 and vGAT, synaptic vesicles and vesicular transporters are largely segregated into distinct pools for release, rather than released together at the same synapse.”

LHb-projecting EP neurons have single axon terminals that make both symmetric and asymmetric synapses, as determined by EM.

“Similar to LHb-projecting VTA neurons, LHb-projecting EP neurons have single axon terminals that make both symmetric (GABAergic) and asymmetric (glutamatergic) synapses, as determined by EM. 33”

Immunogold EM shows that more than 60% of VTA axon terminals in LHb are positive for both vGAT and vGluT2, with smaller subsets positive for one transporter.

“Immunogold EM indicates that >60% of the axon terminals in LHb from VTA are positive for both vGAT and vGluT2, while smaller subsets label for one or the other transporter.”

Immunogold EM and immunoprecipitation of LHb synaptic vesicles found vesicles largely vGluT2 or vGAT positive, rarely copositive, suggesting GABA and glutamate are typically packaged into separate vesicles in LHb.

“Finally, immunogold EM and immunoprecipitation of synaptic vesicles from LHb found that vesicles were largely vGluT2 or vGAT positive, but rarely copositive, suggesting that GABA and glutamate are typically packaged into separate vesicles in the LHb.33”

These VTA neurons are distributed mostly in medial subregions including the interfascicular, paranigral, and rostral linear raphe nuclei.

“These neurons are distributed mostly in the medial subregions of the VTA, including the interfascicular nucleus, paranigral nucleus, and rostral linear nucleus of the raphe.33”

Immunogold EM indicates that single axon terminals make both symmetric and asymmetric synapses, suggesting segregation of vesicles into GABAergic and glutamatergic synapses within the same axon and bouton.

“Interestingly, immunogold EM also indicated that single axon terminals make both symmetric (GABAergic) and asymmetric (glutamatergic) synapses (see Figure 5 in Root et al. 33 ), suggesting segregation of synaptic vesicles into glutamatergic and GABAergic synapses within the same axon and bouton.”

The GABA/Glu cluster, representing 0.08% (32 of 39,411) of cells in the scRNA-seq dataset, corresponds to a bona fide and previously unrecognized neuronal cell type within the DRN.

“Thus, this cluster, representing just 0.08% (32 of 39,411) of cells in the scRNA-seq dataset, corresponds to a bona fide and previously unrecognized neuronal cell type within the DRN that may be a caudal extension of the recently described GABA/Glu neuron group of the ventral midbrain (Root et al., 2018).”