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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 axons from VGluT2-TH neurons segregate dopaminergic markers and VGluT2 to different micro-domains (wild type rats)(a-c) Pre-embedding detection of VGluT2-IR in axon terminals lacking dopaminergic markers, which establish asymmetric synapses (green arrows) on dendritic spines (orange outlines). The VGluT2-IR (gold particles) is confined to the axon terminals. The contiguous axon segments to these VGluT2 terminals contain TH-IR (scattered dark material in a), DAT-IR (scattered dark material in b) or VMAT2-IR (scattered dark material in c). Note that the axon containing TH-IR establishes a symmetric synapse (blue arrow in a). ATs were quantified from the nAcc of rats (n = 4).(d) Post-embedding detection of VGluT2-IR (18 nm gold particles, black arrows) in an axon terminal lacking VMAT2-IR and establishing an asymmetric synapse (green arrow) on a dendritic spine (orange outline). The contiguous axon segment to this VGluT2-IR terminal contains VMAT2-IR (12 nm gold particles, black arrowheads).(e) Bars indicating the frequency (mean + s.e.m.) of axon terminals (ATs) containing VGluT2-IR or VMAT2-IR from a total of 257 ATs. Out of these ATs, 85.48 ± 3.03% have VGluT2-IR; 13.37 ± 2.78% have VMAT2-IR and 1.15 ± 0.40% appear to co-express VGluT2-IR and VMAT2-IR (paired t-test, t(3) = 12.42, p = 0.0011). ATs were quantified from the nAcc of rats (n = 4).Bars: (a, b, c, and d) 200 nm.
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Figure 2: Mesoaccumbens axons from VGluT2-TH neurons segregate dopaminergic markers and VGluT2 to different micro-domains (wild type rats)(a-c) Pre-embedding detection of VGluT2-IR in axon terminals lacking dopaminergic markers, which establish asymmetric synapses (green arrows) on dendritic spines (orange outlines). The VGluT2-IR (gold particles) is confined to the axon terminals. The contiguous axon segments to these VGluT2 terminals contain TH-IR (scattered dark material in a), DAT-IR (scattered dark material in b) or VMAT2-IR (scattered dark material in c). Note that the axon containing TH-IR establishes a symmetric synapse (blue arrow in a). ATs were quantified from the nAcc of rats (n = 4).(d) Post-embedding detection of VGluT2-IR (18 nm gold particles, black arrows) in an axon terminal lacking VMAT2-IR and establishing an asymmetric synapse (green arrow) on a dendritic spine (orange outline). The contiguous axon segment to this VGluT2-IR terminal contains VMAT2-IR (12 nm gold particles, black arrowheads).(e) Bars indicating the frequency (mean + s.e.m.) of axon terminals (ATs) containing VGluT2-IR or VMAT2-IR from a total of 257 ATs. Out of these ATs, 85.48 ± 3.03% have VGluT2-IR; 13.37 ± 2.78% have VMAT2-IR and 1.15 ± 0.40% appear to co-express VGluT2-IR and VMAT2-IR (paired t-test, t(3) = 12.42, p = 0.0011). ATs were quantified from the nAcc of rats (n = 4).Bars: (a, b, c, and d) 200 nm.

Mentions: We next explored the possibility that segregation between dopaminergic and glutamatergic signaling may occur within the same axon. We first determined the distribution of TH-IR and VGluT2-IR in serial sections of nAcc from wild type rats, immunolabeled prior to ultrathin sectioning (“pre-embedding” immunolabeling). In this procedure the antigen-antibody complexes were identified by silver intensified gold or peroxidase reaction. We occasionally observed TH-IR axon segments contiguous with VGluT2-IR ATs (Fig. 2a and Supplementary Fig. 1). In some instances a TH-IR axon segment making a symmetric synapse (within this domain) was contiguous with a VGluT2-IR AT; in this case the axon-terminal established an asymmetric synapse with a dendritic spine (Supplementary Fig. 1). From these findings, we conclude that under normal conditions axons from rat VGluT2-TH neurons maintain in the nAcc independent but adjacent cellular compartments containing either TH-protein, or VGluT2-protein, but not both. Thus, the presence of TH-IR and VGluT2-IR within the same axon provides evidence supporting the idea that some VGluT2-TH neurons can synthesize dopamine and also sustain dopamine vesicular release11.


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 axons from VGluT2-TH neurons segregate dopaminergic markers and VGluT2 to different micro-domains (wild type rats)(a-c) Pre-embedding detection of VGluT2-IR in axon terminals lacking dopaminergic markers, which establish asymmetric synapses (green arrows) on dendritic spines (orange outlines). The VGluT2-IR (gold particles) is confined to the axon terminals. The contiguous axon segments to these VGluT2 terminals contain TH-IR (scattered dark material in a), DAT-IR (scattered dark material in b) or VMAT2-IR (scattered dark material in c). Note that the axon containing TH-IR establishes a symmetric synapse (blue arrow in a). ATs were quantified from the nAcc of rats (n = 4).(d) Post-embedding detection of VGluT2-IR (18 nm gold particles, black arrows) in an axon terminal lacking VMAT2-IR and establishing an asymmetric synapse (green arrow) on a dendritic spine (orange outline). The contiguous axon segment to this VGluT2-IR terminal contains VMAT2-IR (12 nm gold particles, black arrowheads).(e) Bars indicating the frequency (mean + s.e.m.) of axon terminals (ATs) containing VGluT2-IR or VMAT2-IR from a total of 257 ATs. Out of these ATs, 85.48 ± 3.03% have VGluT2-IR; 13.37 ± 2.78% have VMAT2-IR and 1.15 ± 0.40% appear to co-express VGluT2-IR and VMAT2-IR (paired t-test, t(3) = 12.42, p = 0.0011). ATs were quantified from the nAcc of rats (n = 4).Bars: (a, b, c, and d) 200 nm.
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Figure 2: Mesoaccumbens axons from VGluT2-TH neurons segregate dopaminergic markers and VGluT2 to different micro-domains (wild type rats)(a-c) Pre-embedding detection of VGluT2-IR in axon terminals lacking dopaminergic markers, which establish asymmetric synapses (green arrows) on dendritic spines (orange outlines). The VGluT2-IR (gold particles) is confined to the axon terminals. The contiguous axon segments to these VGluT2 terminals contain TH-IR (scattered dark material in a), DAT-IR (scattered dark material in b) or VMAT2-IR (scattered dark material in c). Note that the axon containing TH-IR establishes a symmetric synapse (blue arrow in a). ATs were quantified from the nAcc of rats (n = 4).(d) Post-embedding detection of VGluT2-IR (18 nm gold particles, black arrows) in an axon terminal lacking VMAT2-IR and establishing an asymmetric synapse (green arrow) on a dendritic spine (orange outline). The contiguous axon segment to this VGluT2-IR terminal contains VMAT2-IR (12 nm gold particles, black arrowheads).(e) Bars indicating the frequency (mean + s.e.m.) of axon terminals (ATs) containing VGluT2-IR or VMAT2-IR from a total of 257 ATs. Out of these ATs, 85.48 ± 3.03% have VGluT2-IR; 13.37 ± 2.78% have VMAT2-IR and 1.15 ± 0.40% appear to co-express VGluT2-IR and VMAT2-IR (paired t-test, t(3) = 12.42, p = 0.0011). ATs were quantified from the nAcc of rats (n = 4).Bars: (a, b, c, and d) 200 nm.
Mentions: We next explored the possibility that segregation between dopaminergic and glutamatergic signaling may occur within the same axon. We first determined the distribution of TH-IR and VGluT2-IR in serial sections of nAcc from wild type rats, immunolabeled prior to ultrathin sectioning (“pre-embedding” immunolabeling). In this procedure the antigen-antibody complexes were identified by silver intensified gold or peroxidase reaction. We occasionally observed TH-IR axon segments contiguous with VGluT2-IR ATs (Fig. 2a and Supplementary Fig. 1). In some instances a TH-IR axon segment making a symmetric synapse (within this domain) was contiguous with a VGluT2-IR AT; in this case the axon-terminal established an asymmetric synapse with a dendritic spine (Supplementary Fig. 1). From these findings, we conclude that under normal conditions axons from rat VGluT2-TH neurons maintain in the nAcc independent but adjacent cellular compartments containing either TH-protein, or VGluT2-protein, but not both. Thus, the presence of TH-IR and VGluT2-IR within the same axon provides evidence supporting the idea that some VGluT2-TH neurons can synthesize dopamine and also sustain dopamine vesicular release11.

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