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Maturation of silent synapses in amygdala-accumbens projection contributes to incubation of cocaine craving.

Lee BR, Ma YY, Huang YH, Wang X, Otaka M, Ishikawa M, Neumann PA, Graziane NM, Brown TE, Suska A, Guo C, Lobo MK, Sesack SR, Wolf ME, Nestler EJ, Shaham Y, Schlüter OM, Dong Y - Nat. Neurosci. (2013)

Bottom Line: However, the circuit-level adaptations mediating this plasticity remain elusive.We studied silent synapses, often regarded as immature synapses that express stable NMDA receptors with AMPA receptors being either absent or labile, in the projection from the basolateral amygdala to the NAc in incubation of cocaine craving.As the withdrawal period progressed, these silent synapses became unsilenced, a process that involved synaptic insertion of calcium-permeable AMPA receptors (CP-AMPARs).

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Molecular Therapeutics, Scripps Research Institute, Jupiter, Florida, USA. [2] Program in Neuroscience, Washington State University, Pullman, Washington, USA. [3].

ABSTRACT
In rat models of drug relapse and craving, cue-induced cocaine seeking progressively increases after withdrawal from the drug. This 'incubation of cocaine craving' is partially mediated by time-dependent adaptations at glutamatergic synapses in nucleus accumbens (NAc). However, the circuit-level adaptations mediating this plasticity remain elusive. We studied silent synapses, often regarded as immature synapses that express stable NMDA receptors with AMPA receptors being either absent or labile, in the projection from the basolateral amygdala to the NAc in incubation of cocaine craving. Silent synapses were detected in this projection during early withdrawal from cocaine. As the withdrawal period progressed, these silent synapses became unsilenced, a process that involved synaptic insertion of calcium-permeable AMPA receptors (CP-AMPARs). In vivo optogenetic stimulation-induced downregulation of CP-AMPARs at amygdala-to-NAc synapses, which re-silenced some of the previously silent synapses after prolonged withdrawal, decreased incubation of cocaine craving. Our findings indicate that silent synapse-based reorganization of the amygdala-to-NAc projection is critical for persistent cocaine craving and relapse after withdrawal.

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Related in: MedlinePlus

Insertion of CP-AMPARs within BLA-to-NAc synapses after 45 withdrawal days(A) Example EPSCs elicited at −70 to +50 mV (with 10 mV increment) from BLA-to-NAc synapses; data were collected on withdrawal day 45 in rats previously trained to self-administer saline or cocaine. Whole-cell voltage-clamp recordings were made in the presence of the GABAA receptor-selective antagonist picrotoxin (100 µM) and the NMDA receptor-selective antagonist D-APV (50 µM). (B, C) I–V curves of EPSCs from BLA-to-NAc synapses; the influence of reversal potentials of EPSCs was factored in for each recorded neuron (see Methods). (D) Summary showing that on withdrawal day 45 an increased rectification of EPSCs was detected at BLA-to-NAc synapses from cocaine- but not saline-experienced rats. Scattered dots indicate the values of individual cells. (E–F) Example EPSCs (E) and EPSC peak over trials (F) before and during perfusion of Naspm (a selective antagonist of CP-AMPARs) in saline-trained rats; EPSCs were induced in BLA-to-NAc synapses. (G–H) Example EPSCs (G) and EPSC peak over all trials (H) before and during perfusion of Naspm in cocaine-experienced rats. (I) Summary showing that EPSCs from BLA-to-NAc synapses became sensitive to Naspm on withdrawal day 45 after cocaine self-administration, indicating insertion of CP-AMPARs to BLA-to-NAc excitatory synapses. Error bar, s.e.m. ** p<0.01.
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Figure 3: Insertion of CP-AMPARs within BLA-to-NAc synapses after 45 withdrawal days(A) Example EPSCs elicited at −70 to +50 mV (with 10 mV increment) from BLA-to-NAc synapses; data were collected on withdrawal day 45 in rats previously trained to self-administer saline or cocaine. Whole-cell voltage-clamp recordings were made in the presence of the GABAA receptor-selective antagonist picrotoxin (100 µM) and the NMDA receptor-selective antagonist D-APV (50 µM). (B, C) I–V curves of EPSCs from BLA-to-NAc synapses; the influence of reversal potentials of EPSCs was factored in for each recorded neuron (see Methods). (D) Summary showing that on withdrawal day 45 an increased rectification of EPSCs was detected at BLA-to-NAc synapses from cocaine- but not saline-experienced rats. Scattered dots indicate the values of individual cells. (E–F) Example EPSCs (E) and EPSC peak over trials (F) before and during perfusion of Naspm (a selective antagonist of CP-AMPARs) in saline-trained rats; EPSCs were induced in BLA-to-NAc synapses. (G–H) Example EPSCs (G) and EPSC peak over all trials (H) before and during perfusion of Naspm in cocaine-experienced rats. (I) Summary showing that EPSCs from BLA-to-NAc synapses became sensitive to Naspm on withdrawal day 45 after cocaine self-administration, indicating insertion of CP-AMPARs to BLA-to-NAc excitatory synapses. Error bar, s.e.m. ** p<0.01.

Mentions: During brain development, silent synapses can be either pruned away or mature into fully functional synapses by recruiting AMPARs, resulting in very low levels of silent synapses in adulthood14,30. While both processes may occur simultaneously after withdrawal from cocaine, the second possibility is supported by evidence of elevated cell surface/synaptic levels of CP-AMPARs in the NAc after prolonged withdrawal from cocaine6,31–34. We therefore tested whether cocaine-generated silent synapses were ‘un-silenced’ during the withdrawal period by recruiting these receptors. CP-AMPARs conduct minimal current at depolarized membrane potentials35. Therefore, synaptic insertion of these receptors can be detected by increased rectification of EPSCs at positive membrane potentials35. In rats trained with the same cocaine regimen (Fig. S1), we found increased rectification of AMPAR EPSCs at BLA-to-NAc synapses after 45 withdrawal days [t(27)=3.5, p=0.002, Fig. 3A–D]. Furthermore, AMPAR EPSCs at these synapses became sensitive to Naspm (200 µM), a selective antagonist of CP-AMPARs35 [t(7)=3.8, p=0.007, Figs. 3E–I]. These data, obtained from rats trained to self-administer cocaine under limited access 2-h daily sessions, are different from those of a recent report34 in which accumulation of CP-AMPARs in NAc after 45 withdrawal days was observed in rats trained to self-administer cocaine for 6-h/d but not 2-h/d. These differences might be due to the fact that we initiated the training phase with an overnight extended access cocaine self-administration. Another difference between our study and previous studies is that we assessed accumulation of CP-AMPARs specifically in the BLA-to-NAc projection, increasing our ability to detect small changes in CP-AMPAR levels, assuming that CP-AMPARs do not accumulate in all NAc synapses after our limited access cocaine self-administration training procedure. Furthermore, the rats used in this study were younger than those previously used in studies on the role of CP-AMPARs in incubation of cocaine craving3,7, and thus may be more susceptible to withdrawal-induced CP-AMPAR accumulation.


Maturation of silent synapses in amygdala-accumbens projection contributes to incubation of cocaine craving.

Lee BR, Ma YY, Huang YH, Wang X, Otaka M, Ishikawa M, Neumann PA, Graziane NM, Brown TE, Suska A, Guo C, Lobo MK, Sesack SR, Wolf ME, Nestler EJ, Shaham Y, Schlüter OM, Dong Y - Nat. Neurosci. (2013)

Insertion of CP-AMPARs within BLA-to-NAc synapses after 45 withdrawal days(A) Example EPSCs elicited at −70 to +50 mV (with 10 mV increment) from BLA-to-NAc synapses; data were collected on withdrawal day 45 in rats previously trained to self-administer saline or cocaine. Whole-cell voltage-clamp recordings were made in the presence of the GABAA receptor-selective antagonist picrotoxin (100 µM) and the NMDA receptor-selective antagonist D-APV (50 µM). (B, C) I–V curves of EPSCs from BLA-to-NAc synapses; the influence of reversal potentials of EPSCs was factored in for each recorded neuron (see Methods). (D) Summary showing that on withdrawal day 45 an increased rectification of EPSCs was detected at BLA-to-NAc synapses from cocaine- but not saline-experienced rats. Scattered dots indicate the values of individual cells. (E–F) Example EPSCs (E) and EPSC peak over trials (F) before and during perfusion of Naspm (a selective antagonist of CP-AMPARs) in saline-trained rats; EPSCs were induced in BLA-to-NAc synapses. (G–H) Example EPSCs (G) and EPSC peak over all trials (H) before and during perfusion of Naspm in cocaine-experienced rats. (I) Summary showing that EPSCs from BLA-to-NAc synapses became sensitive to Naspm on withdrawal day 45 after cocaine self-administration, indicating insertion of CP-AMPARs to BLA-to-NAc excitatory synapses. Error bar, s.e.m. ** p<0.01.
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Related In: Results  -  Collection

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Figure 3: Insertion of CP-AMPARs within BLA-to-NAc synapses after 45 withdrawal days(A) Example EPSCs elicited at −70 to +50 mV (with 10 mV increment) from BLA-to-NAc synapses; data were collected on withdrawal day 45 in rats previously trained to self-administer saline or cocaine. Whole-cell voltage-clamp recordings were made in the presence of the GABAA receptor-selective antagonist picrotoxin (100 µM) and the NMDA receptor-selective antagonist D-APV (50 µM). (B, C) I–V curves of EPSCs from BLA-to-NAc synapses; the influence of reversal potentials of EPSCs was factored in for each recorded neuron (see Methods). (D) Summary showing that on withdrawal day 45 an increased rectification of EPSCs was detected at BLA-to-NAc synapses from cocaine- but not saline-experienced rats. Scattered dots indicate the values of individual cells. (E–F) Example EPSCs (E) and EPSC peak over trials (F) before and during perfusion of Naspm (a selective antagonist of CP-AMPARs) in saline-trained rats; EPSCs were induced in BLA-to-NAc synapses. (G–H) Example EPSCs (G) and EPSC peak over all trials (H) before and during perfusion of Naspm in cocaine-experienced rats. (I) Summary showing that EPSCs from BLA-to-NAc synapses became sensitive to Naspm on withdrawal day 45 after cocaine self-administration, indicating insertion of CP-AMPARs to BLA-to-NAc excitatory synapses. Error bar, s.e.m. ** p<0.01.
Mentions: During brain development, silent synapses can be either pruned away or mature into fully functional synapses by recruiting AMPARs, resulting in very low levels of silent synapses in adulthood14,30. While both processes may occur simultaneously after withdrawal from cocaine, the second possibility is supported by evidence of elevated cell surface/synaptic levels of CP-AMPARs in the NAc after prolonged withdrawal from cocaine6,31–34. We therefore tested whether cocaine-generated silent synapses were ‘un-silenced’ during the withdrawal period by recruiting these receptors. CP-AMPARs conduct minimal current at depolarized membrane potentials35. Therefore, synaptic insertion of these receptors can be detected by increased rectification of EPSCs at positive membrane potentials35. In rats trained with the same cocaine regimen (Fig. S1), we found increased rectification of AMPAR EPSCs at BLA-to-NAc synapses after 45 withdrawal days [t(27)=3.5, p=0.002, Fig. 3A–D]. Furthermore, AMPAR EPSCs at these synapses became sensitive to Naspm (200 µM), a selective antagonist of CP-AMPARs35 [t(7)=3.8, p=0.007, Figs. 3E–I]. These data, obtained from rats trained to self-administer cocaine under limited access 2-h daily sessions, are different from those of a recent report34 in which accumulation of CP-AMPARs in NAc after 45 withdrawal days was observed in rats trained to self-administer cocaine for 6-h/d but not 2-h/d. These differences might be due to the fact that we initiated the training phase with an overnight extended access cocaine self-administration. Another difference between our study and previous studies is that we assessed accumulation of CP-AMPARs specifically in the BLA-to-NAc projection, increasing our ability to detect small changes in CP-AMPAR levels, assuming that CP-AMPARs do not accumulate in all NAc synapses after our limited access cocaine self-administration training procedure. Furthermore, the rats used in this study were younger than those previously used in studies on the role of CP-AMPARs in incubation of cocaine craving3,7, and thus may be more susceptible to withdrawal-induced CP-AMPAR accumulation.

Bottom Line: However, the circuit-level adaptations mediating this plasticity remain elusive.We studied silent synapses, often regarded as immature synapses that express stable NMDA receptors with AMPA receptors being either absent or labile, in the projection from the basolateral amygdala to the NAc in incubation of cocaine craving.As the withdrawal period progressed, these silent synapses became unsilenced, a process that involved synaptic insertion of calcium-permeable AMPA receptors (CP-AMPARs).

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Molecular Therapeutics, Scripps Research Institute, Jupiter, Florida, USA. [2] Program in Neuroscience, Washington State University, Pullman, Washington, USA. [3].

ABSTRACT
In rat models of drug relapse and craving, cue-induced cocaine seeking progressively increases after withdrawal from the drug. This 'incubation of cocaine craving' is partially mediated by time-dependent adaptations at glutamatergic synapses in nucleus accumbens (NAc). However, the circuit-level adaptations mediating this plasticity remain elusive. We studied silent synapses, often regarded as immature synapses that express stable NMDA receptors with AMPA receptors being either absent or labile, in the projection from the basolateral amygdala to the NAc in incubation of cocaine craving. Silent synapses were detected in this projection during early withdrawal from cocaine. As the withdrawal period progressed, these silent synapses became unsilenced, a process that involved synaptic insertion of calcium-permeable AMPA receptors (CP-AMPARs). In vivo optogenetic stimulation-induced downregulation of CP-AMPARs at amygdala-to-NAc synapses, which re-silenced some of the previously silent synapses after prolonged withdrawal, decreased incubation of cocaine craving. Our findings indicate that silent synapse-based reorganization of the amygdala-to-NAc projection is critical for persistent cocaine craving and relapse after withdrawal.

Show MeSH
Related in: MedlinePlus