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Dopaminergic and glutamatergic microdomains in a subset of rodent mesoaccumbens axons.

Zhang S, Qi J, Li X, Wang HL, Britt JP, Hoffman AF, Bonci A, Lupica CR, Morales M - Nat. Neurosci. (2015)

Bottom Line: However, the mechanism is unclear, and co-release by mesoaccumbens fibers has not been documented.In vivo overexpression of VMAT2 did not change the segregation of the two vesicular types, suggesting the existence of highly regulated mechanisms for maintaining this segregation.Using optogenetics, we found that dopamine and glutamate were released from the same mesoaccumbens fibers.

View Article: PubMed Central - PubMed

Affiliation: National Institute on Drug Abuse, Neuronal Networks Section, US National Institutes of Health, Baltimore, Maryland, USA.

ABSTRACT
Mesoaccumbens fibers are thought to co-release dopamine and glutamate. However, the mechanism is unclear, and co-release by mesoaccumbens fibers has not been documented. Using electron microcopy, we found that some mesoaccumbens fibers have vesicular transporters for dopamine (VMAT2) in axon segments that are continuous with axon terminals that lack VMAT2, but contain vesicular glutamate transporters type 2 (VGluT2). In vivo overexpression of VMAT2 did not change the segregation of the two vesicular types, suggesting the existence of highly regulated mechanisms for maintaining this segregation. The mesoaccumbens axon terminals containing VGluT2 vesicles make asymmetric synapses, commonly associated with excitatory signaling. Using optogenetics, we found that dopamine and glutamate were released from the same mesoaccumbens fibers. These findings reveal a complex type of signaling by mesoaccumbens fibers in which dopamine and glutamate can be released from the same axons, but are not normally released at the same site or from the same synaptic vesicles.

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Mesoaccumbens neurons establish either VGluT2-asymmetric synapses or TH-symmetric synapses (wild type rats)(a) VTA inputs to nAcc identified by PHA-L- or mCherry-immunoreactivity (IR). VTA neurons were tagged with PHA-L (n = 3) or AAV5-CaMKII-ChR2-mCherry (n = 2). Within the nAcc, PHA-L-IR axon terminals make asymmetric or symmetric synapses on dendrites or dendritic spines.(b) nAcc axon terminal 1 (AT1, green outline) co-expressing PHA-L-IR (scattered dark material) and VGluT2-IR (gold particles, green arrowhead) makes an asymmetric synapse (green arrow) with a dendrite (De, orange outline). AT2 (yellow outline) contains only VGluT2-IR.(c) nAcc AT1 (blue outline) co-expressing PHA-L-IR (scattered dark material) and TH-IR (gold particles, blue arrowhead) makes a symmetric synapse (blue arrow) on the side of a dendritic spine (sp, orange outline) with spine apparatus (sa). The head of this dendritic spine also makes an asymmetric synapse (green arrow) with the unlabeled AT2 (green outline). AT3 (yellow outline) has only TH-IR.(d-f) Triad arrangement in which ATs from VTA neurons are converging on the same dendritic spine and establishing different types of synapses. Serial sections of two ATs from VTA neurons expressing mCherry-IR (scattered dark material) under the control of the CaMKII promoter (d and e). Both ATs are making synapses on the same dendritic spine (sp, orange outline); AT1 (green outline) makes an asymmetric synapse (green arrow) on the head of the spine and AT2 (blue outline) makes a symmetric synapse (blue arrow) on the side of the same dendritic spine.Bars: (b, c, d, and e) 200 nm.
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Figure 1: Mesoaccumbens neurons establish either VGluT2-asymmetric synapses or TH-symmetric synapses (wild type rats)(a) VTA inputs to nAcc identified by PHA-L- or mCherry-immunoreactivity (IR). VTA neurons were tagged with PHA-L (n = 3) or AAV5-CaMKII-ChR2-mCherry (n = 2). Within the nAcc, PHA-L-IR axon terminals make asymmetric or symmetric synapses on dendrites or dendritic spines.(b) nAcc axon terminal 1 (AT1, green outline) co-expressing PHA-L-IR (scattered dark material) and VGluT2-IR (gold particles, green arrowhead) makes an asymmetric synapse (green arrow) with a dendrite (De, orange outline). AT2 (yellow outline) contains only VGluT2-IR.(c) nAcc AT1 (blue outline) co-expressing PHA-L-IR (scattered dark material) and TH-IR (gold particles, blue arrowhead) makes a symmetric synapse (blue arrow) on the side of a dendritic spine (sp, orange outline) with spine apparatus (sa). The head of this dendritic spine also makes an asymmetric synapse (green arrow) with the unlabeled AT2 (green outline). AT3 (yellow outline) has only TH-IR.(d-f) Triad arrangement in which ATs from VTA neurons are converging on the same dendritic spine and establishing different types of synapses. Serial sections of two ATs from VTA neurons expressing mCherry-IR (scattered dark material) under the control of the CaMKII promoter (d and e). Both ATs are making synapses on the same dendritic spine (sp, orange outline); AT1 (green outline) makes an asymmetric synapse (green arrow) on the head of the spine and AT2 (blue outline) makes a symmetric synapse (blue arrow) on the side of the same dendritic spine.Bars: (b, c, d, and e) 200 nm.

Mentions: We previously showed that two types of putative glutamatergic VTA neurons (expressing VGluT2 mRNA without TH-IR or co-expressing VGluT2 mRNA and TH-IR) innervate the nAcc7. Here we determined the type of synapses that these VTA neurons establish in the shell of the nAcc. We tagged axons from the rat VTA by intra-VTA injections of the anterograde tract tracer Phaseolus vulgaris leucoagglutinin (PHA-L) or an adeno-associated virus (AAV) encoding mCherry under the CaMKII promoter (Fig. 1a). With both tracers, we found that within the nAcc some ATs from VTA neurons containing VGluT2-immunoreactivity (VGluT2-IR) formed asymmetric synapses on the heads of dendritic spines or dendritic shafts (Fig. 1b). We determined that 96.09 ± 2.70% of the PHA-L positive ATs that established asymmetric synapses co-expressed VGluT2-IR [70 out of 72 ATs; n = 3 rats; t(2) = 17.07, p = 0.0034; Fig. 1b]. Among the few TH-IR ATs that formed synapses, most of those co-expressing PHA-L formed symmetric synapses (95.24 ± 4.76%; 17 from 18ATs; n = 3 rats; t(2) = 9.50, p = 0.0109; Fig. 1c). The infrequent detection of TH-IR terminals making synapses has been previously documented14. We also observed VGluT2-terminals and TH-terminals lacking PHA-L, indicating that not all mesoaccumbens cells were tagged, and in the case of VGluT2-terminals indicating that some of these terminals do not originate from the VTA. In addition, we found ultrastructural arrangements in which an mCherry-labeled terminal (from a VTA VGluT2 neuron) formed an asymmetric synapse on the head of a dendritic spine that also received a symmetric convergent mCherry input (from a VTA TH-neuron) on the neck of the spine (Fig. 1d-f). The convergence of glutamatergic-inputs and TH-inputs on a single postsynaptic target is well documented15, and has been proposed as a synaptic arrangement by which midbrain dopamine release modulates excitatory transmission at the level of individual dendritic spines16. Prior studies have shown that glutamatergic inputs from different brain areas synapse on nAcc neurons, and proposed to convey different types of reward-related information during goal-directed behavior. However, the contribution of VGluT2-terminals from VTA neurons to behavioral functions of the nAcc remains to be determined.


Dopaminergic and glutamatergic microdomains in a subset of rodent mesoaccumbens axons.

Zhang S, Qi J, Li X, Wang HL, Britt JP, Hoffman AF, Bonci A, Lupica CR, Morales M - Nat. Neurosci. (2015)

Mesoaccumbens neurons establish either VGluT2-asymmetric synapses or TH-symmetric synapses (wild type rats)(a) VTA inputs to nAcc identified by PHA-L- or mCherry-immunoreactivity (IR). VTA neurons were tagged with PHA-L (n = 3) or AAV5-CaMKII-ChR2-mCherry (n = 2). Within the nAcc, PHA-L-IR axon terminals make asymmetric or symmetric synapses on dendrites or dendritic spines.(b) nAcc axon terminal 1 (AT1, green outline) co-expressing PHA-L-IR (scattered dark material) and VGluT2-IR (gold particles, green arrowhead) makes an asymmetric synapse (green arrow) with a dendrite (De, orange outline). AT2 (yellow outline) contains only VGluT2-IR.(c) nAcc AT1 (blue outline) co-expressing PHA-L-IR (scattered dark material) and TH-IR (gold particles, blue arrowhead) makes a symmetric synapse (blue arrow) on the side of a dendritic spine (sp, orange outline) with spine apparatus (sa). The head of this dendritic spine also makes an asymmetric synapse (green arrow) with the unlabeled AT2 (green outline). AT3 (yellow outline) has only TH-IR.(d-f) Triad arrangement in which ATs from VTA neurons are converging on the same dendritic spine and establishing different types of synapses. Serial sections of two ATs from VTA neurons expressing mCherry-IR (scattered dark material) under the control of the CaMKII promoter (d and e). Both ATs are making synapses on the same dendritic spine (sp, orange outline); AT1 (green outline) makes an asymmetric synapse (green arrow) on the head of the spine and AT2 (blue outline) makes a symmetric synapse (blue arrow) on the side of the same dendritic spine.Bars: (b, c, d, and e) 200 nm.
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Figure 1: Mesoaccumbens neurons establish either VGluT2-asymmetric synapses or TH-symmetric synapses (wild type rats)(a) VTA inputs to nAcc identified by PHA-L- or mCherry-immunoreactivity (IR). VTA neurons were tagged with PHA-L (n = 3) or AAV5-CaMKII-ChR2-mCherry (n = 2). Within the nAcc, PHA-L-IR axon terminals make asymmetric or symmetric synapses on dendrites or dendritic spines.(b) nAcc axon terminal 1 (AT1, green outline) co-expressing PHA-L-IR (scattered dark material) and VGluT2-IR (gold particles, green arrowhead) makes an asymmetric synapse (green arrow) with a dendrite (De, orange outline). AT2 (yellow outline) contains only VGluT2-IR.(c) nAcc AT1 (blue outline) co-expressing PHA-L-IR (scattered dark material) and TH-IR (gold particles, blue arrowhead) makes a symmetric synapse (blue arrow) on the side of a dendritic spine (sp, orange outline) with spine apparatus (sa). The head of this dendritic spine also makes an asymmetric synapse (green arrow) with the unlabeled AT2 (green outline). AT3 (yellow outline) has only TH-IR.(d-f) Triad arrangement in which ATs from VTA neurons are converging on the same dendritic spine and establishing different types of synapses. Serial sections of two ATs from VTA neurons expressing mCherry-IR (scattered dark material) under the control of the CaMKII promoter (d and e). Both ATs are making synapses on the same dendritic spine (sp, orange outline); AT1 (green outline) makes an asymmetric synapse (green arrow) on the head of the spine and AT2 (blue outline) makes a symmetric synapse (blue arrow) on the side of the same dendritic spine.Bars: (b, c, d, and e) 200 nm.
Mentions: We previously showed that two types of putative glutamatergic VTA neurons (expressing VGluT2 mRNA without TH-IR or co-expressing VGluT2 mRNA and TH-IR) innervate the nAcc7. Here we determined the type of synapses that these VTA neurons establish in the shell of the nAcc. We tagged axons from the rat VTA by intra-VTA injections of the anterograde tract tracer Phaseolus vulgaris leucoagglutinin (PHA-L) or an adeno-associated virus (AAV) encoding mCherry under the CaMKII promoter (Fig. 1a). With both tracers, we found that within the nAcc some ATs from VTA neurons containing VGluT2-immunoreactivity (VGluT2-IR) formed asymmetric synapses on the heads of dendritic spines or dendritic shafts (Fig. 1b). We determined that 96.09 ± 2.70% of the PHA-L positive ATs that established asymmetric synapses co-expressed VGluT2-IR [70 out of 72 ATs; n = 3 rats; t(2) = 17.07, p = 0.0034; Fig. 1b]. Among the few TH-IR ATs that formed synapses, most of those co-expressing PHA-L formed symmetric synapses (95.24 ± 4.76%; 17 from 18ATs; n = 3 rats; t(2) = 9.50, p = 0.0109; Fig. 1c). The infrequent detection of TH-IR terminals making synapses has been previously documented14. We also observed VGluT2-terminals and TH-terminals lacking PHA-L, indicating that not all mesoaccumbens cells were tagged, and in the case of VGluT2-terminals indicating that some of these terminals do not originate from the VTA. In addition, we found ultrastructural arrangements in which an mCherry-labeled terminal (from a VTA VGluT2 neuron) formed an asymmetric synapse on the head of a dendritic spine that also received a symmetric convergent mCherry input (from a VTA TH-neuron) on the neck of the spine (Fig. 1d-f). The convergence of glutamatergic-inputs and TH-inputs on a single postsynaptic target is well documented15, and has been proposed as a synaptic arrangement by which midbrain dopamine release modulates excitatory transmission at the level of individual dendritic spines16. Prior studies have shown that glutamatergic inputs from different brain areas synapse on nAcc neurons, and proposed to convey different types of reward-related information during goal-directed behavior. However, the contribution of VGluT2-terminals from VTA neurons to behavioral functions of the nAcc remains to be determined.

Bottom Line: However, the mechanism is unclear, and co-release by mesoaccumbens fibers has not been documented.In vivo overexpression of VMAT2 did not change the segregation of the two vesicular types, suggesting the existence of highly regulated mechanisms for maintaining this segregation.Using optogenetics, we found that dopamine and glutamate were released from the same mesoaccumbens fibers.

View Article: PubMed Central - PubMed

Affiliation: National Institute on Drug Abuse, Neuronal Networks Section, US National Institutes of Health, Baltimore, Maryland, USA.

ABSTRACT
Mesoaccumbens fibers are thought to co-release dopamine and glutamate. However, the mechanism is unclear, and co-release by mesoaccumbens fibers has not been documented. Using electron microcopy, we found that some mesoaccumbens fibers have vesicular transporters for dopamine (VMAT2) in axon segments that are continuous with axon terminals that lack VMAT2, but contain vesicular glutamate transporters type 2 (VGluT2). In vivo overexpression of VMAT2 did not change the segregation of the two vesicular types, suggesting the existence of highly regulated mechanisms for maintaining this segregation. The mesoaccumbens axon terminals containing VGluT2 vesicles make asymmetric synapses, commonly associated with excitatory signaling. Using optogenetics, we found that dopamine and glutamate were released from the same mesoaccumbens fibers. These findings reveal a complex type of signaling by mesoaccumbens fibers in which dopamine and glutamate can be released from the same axons, but are not normally released at the same site or from the same synaptic vesicles.

Show MeSH
Related in: MedlinePlus