Nicotine abuse and addiction is a major health liability. Nicotine, an active alkaloid in tobacco, is self-administered by animals and produces cellular adaptations in brain regions associated with ...drug reward, such as the nucleus accumbens. However, it is unknown whether, akin to illicit drugs of abuse such as cocaine or heroin, the adaptations endure and contribute to the propensity to relapse after discontinuing nicotine use. Using a rat model of cue-induced relapse, we made morphological and electrophysiological measures of synaptic plasticity, as well as quantified glutamate overflow, in the accumbens after 2 wk of withdrawal with extinction training. We found an enduring basal increase in dendritic spine head diameter and in the ratio of AMPA to NMDA currents in accumbens spiny neurons compared with yoked saline animals at 2 wk after the last nicotine self-administration session. This synaptic potentiation was associated with an increase in both AMPA (GluA1) and NMDA (GluN2A and GluN2B) receptor subunits, and a reduction in the glutamate transporter-1 (GLT-1). When nicotine seeking was reinstated by presentation of conditioned cues, there were parallel increases in behavioral responding, extracellular glutamate, and further increases in dendritic spine head diameter and ratio of AMPA to NMDA currents within 15 min. These findings suggest that targeting glutamate transmission might inhibit cue-induced nicotine seeking. In support of this hypothesis, we found that pharmacological inhibition of GluN2A with 3-Chloro-4-fluoro-N-4-2-(phenylcarbonyl)hydrazinocarbonylbenzylbenzenesulfonamide (TCN-201) or GluN2B with ifenprodil abolished reinstated nicotine seeking. These results indicate that up-regulated GluN2A, GluN2B, and rapid synaptic potentiation in the accumbens contribute to cue-induced relapse to nicotine use.
Relapse to cocaine use necessitates remodeling excitatory synapses in the nucleus accumbens and synaptic reorganization requires matrix metalloproteinase (MMP) degradation of the extracellular matrix ...proteins. We found enduring increases in MMP-2 activity in rats after withdrawal from self-administered cocaine and transient increases in MMP-9 during cue-induced cocaine relapse. Cue-induced heroin and nicotine relapse increased MMP activity, and increased MMP activity was required for both cocaine relapse and relapse-associated synaptic plasticity.
Comparatively little is known about how new instrumental actions are encoded in the brain. Using whole-brain c-Fos mapping, we show that neural activity is increased in the anterior dorsolateral ...striatum (aDLS) of mice that successfully learn a new lever-press response to earn food rewards. Post-learning chemogenetic inhibition of aDLS disrupts consolidation of the new instrumental response. Similarly, post-learning infusion of the protein synthesis inhibitor anisomycin into the aDLS disrupts consolidation of the new response. Activity of D1 receptor-expressing medium spiny neurons (D1-MSNs) increases and D2-MSNs activity decreases in the aDLS during consolidation. Chemogenetic inhibition of D1-MSNs in aDLS disrupts the consolidation process whereas D2-MSN inhibition strengthens consolidation but blocks the expression of previously learned habit-like responses. These findings suggest that D1-MSNs in the aDLS encode new instrumental actions whereas D2-MSNs oppose this new learning and instead promote expression of habitual actions.
Vulnerability to relapse during periods of attempted abstinence from cocaine use is hypothesized to result from the rewiring of brain reward circuitries, particularly ventral tegmental area (VTA) ...dopamine neurons. How cocaine exposures act on midbrain dopamine neurons to precipitate addiction-relevant changes in gene expression is unclear. We found that histone H3 glutamine 5 dopaminylation (H3Q5dop) plays a critical role in cocaine-induced transcriptional plasticity in the midbrain. Rats undergoing withdrawal from cocaine showed an accumulation of H3Q5dop in the VTA. By reducing H3Q5dop in the VTA during withdrawal, we reversed cocaine-mediated gene expression changes, attenuated dopamine release in the nucleus accumbens, and reduced cocaine-seeking behavior. These findings establish a neurotransmission-independent role for nuclear dopamine in relapse-related transcriptional plasticity in the VTA.
Abstract Synaptic plasticity has long been known to involve three key elements of neuropil, the presynapse, the postsynapse and adjacent glia. Here we review the role of the extracellular matrix in ...synaptic plasticity as a necessary component forming the tetrapartite synapse. We describe the role of matrix metalloproteinases as enzymes sculpting extracellular proteins and thereby creating an extracellular signaling domain required for synaptic plasticity. Specifically we focus on the role of the tetrapartite synapse in mediating the effects of addictive drugs at cortico-striatal synapses, and conclude that the extracellular signaling domain and its regulation by matrix metalloproteinases is critical for developing and expressing drug seeking behaviors. This article is part of a Special Issue entitled SI:Addiction circuits.
The distinction between acquired aplastic anemia (AA) and hypocellular myelodysplastic syndrome (hMDS) is often difficult, especially nonsevere AA. We postulated that somatic mutations are present in ...a subset of AA, and predict malignant transformation. From our database, we identified 150 AA patients with no morphological evidence of MDS, who had stored bone marrow (BM) and constitutional DNA. We excluded Fanconi anemia, mutations of telomere maintenance, and a family history of BM failure (BMF) or cancer. The initial cohort of 57 patients was screened for 835 known genes associated with BMF and myeloid cancer; a second cohort of 93 patients was screened for mutations in ASXL1, DNMT3A, BCOR, TET2, and MPL. Somatic mutations were detected in 19% of AA, and included ASXL1 (n = 12), DNMT3A (n = 8) and BCOR (n = 6). Patients with somatic mutations had a longer disease duration (37 vs 8 months, P < .04), and shorter telomere lengths (median length, 0.9 vs 1.1, P < .001), compared with patients without mutations. Somatic mutations in AA patients with a disease duration of >6 months were associated with a 40% risk of transformation to MDS (P < .0002). Nearly one-fifth of AA patients harbor mutations in genes typically seen in myeloid malignancies that predicted for later transformation to MDS.
•Acquired mutations of myeloid-related genes are present in a proportion of AA patients.•Somatic mutations in AA predict higher risk of transformation to MDS.
Relapse to drug use can be initiated by drug-associated cues. The intensity of cue-induced relapse is correlated with the induction of transient synaptic potentiation (t-SP) at glutamatergic synapses ...on medium spiny neurons (MSNs) in the nucleus accumbens core (NAcore) and requires spillover of glutamate from prefrontal cortical afferents. We used a rodent self-administration/reinstatement model of relapse to show that cue-induced t-SP and reinstated cocaine seeking result from glutamate spillover, initiating a metabotropic glutamate receptor 5 (mGluR5)-dependent increase in nitric oxide (NO) production. Pharmacological stimulation of mGluR5 in NAcore recapitulated cue-induced reinstatement in the absence of drug-associated cues. Using NO-sensitive electrodes, mGluR5 activation by glutamate was shown to stimulate NO production that depended on activation of neuronal nitric oxide synthase (nNOS). nNOS is expressed in ∼1% of NAcore neurons. Using a transgene strategy to express and stimulate designer receptors that mimicked mGluR5 signaling through Gq in nNOS interneurons, we recapitulated cue-induced reinstatement in the absence of cues. Conversely, using a transgenic caspase strategy, the intensity of cue-induced reinstatement was correlated with the extent of selective elimination of nNOS interneurons. The induction of t-SP during cued reinstatement depends on activating matrix metalloproteinases (MMPs) and selective chemogenetic stimulation of nNOS interneurons recapitulated MMP activation and t-SP induction (increase in AMPA currents in MSNs). These data demonstrate critical involvement of a sparse population of nNOS-expressing interneurons in cue-induced cocaine seeking, revealing a bottleneck in brain processing of drug-associated cues where therapeutic interventions could be effective in treating drug addiction.
Relapse to cocaine use in a rat model is associated with transient increases in synaptic strength at prefrontal cortex synapses in the nucleus accumbens. We demonstrate the sequence of events that mediates synaptic potentiation and reinstated cocaine seeking induced by cocaine-conditioned cues. Activation of prefrontal inputs to the accumbens by cues initiates spillover of synaptic glutamate, which stimulates metabotropic glutamate receptor 5 (mGluR5) on a small population of interneurons (∼1%) expressing neuronal nitric oxide synthase. Stimulating these glutamate receptors increases nitric oxide (NO) production, which stimulates matrix metalloprotease-2 (MMP-2) and MMP-9 activity in the extracellular space. Manipulating the interaction between mGluR5, NO production, or MMP-2 and MMP-9 pharmacologically or genetically is sufficient to recapitulate transient synaptic potentiation and reinstate cocaine seeking.
Potassium channels of the Two-Pore Domain (K2P) subfamily, KCNK1-KCNK18, play crucial roles in controlling the electrical activity of many different cell types and represent attractive therapeutic ...targets. However, the identification of highly selective small molecule drugs against these channels has been challenging due to the high degree of structural and functional conservation that exists not only between K2P channels, but across the whole K
channel superfamily. To address the issue of selectivity, here we generate camelid antibody fragments (nanobodies) against the TREK-2 (KCNK10) K2P K
channel and identify selective binders including several that directly modulate channel activity. X-ray crystallography and CryoEM data of these nanobodies in complex with TREK-2 also reveal insights into their mechanisms of activation and inhibition via binding to the extracellular loops and Cap domain, as well as their suitability for immunodetection. These structures facilitate design of a biparatropic inhibitory nanobody with markedly improved sensitivity. Together, these results provide important insights into TREK channel gating and provide an alternative, more selective approach to modulation of K2P channel activity via their extracellular domains.
Cocaine addiction remains a major health concern with limited effective treatment options. A better understanding of mechanisms underlying relapse may help inform the development of new ...pharmacotherapies. Emerging evidence suggests that collapsin response mediator protein 2 (CRMP2) regulates presynaptic excitatory neurotransmission and contributes to pathological changes during diseases, such as neuropathic pain and substance use disorders. We examined the role of CRMP2 and its interactions with a known binding partner, CaV2.2, in cocaine-seeking behavior. We employed the rodent self-administration model of relapse to drug seeking and focused on the prefrontal cortex (PFC) for its well-established role in reinstatement behaviors. Our results indicated that repeated cocaine self-administration resulted in a dynamic and persistent alteration in the PFC expression of CRMP2 and its binding partner, the CaV2.2 (N-type) voltage-gated calcium channel. Following cocaine self-administration and extinction training, the expression of both CRMP2 and CaV2.2 was reduced relative to yoked saline controls. By contrast, cued reinstatement potentiated CRMP2 expression and increased CaV2.2 expression above extinction levels. Lastly, we utilized the recently developed peptide
myr-TAT-CBD3
to disrupt the interaction between CRMP2 and CaV2.2 in vivo
.
We assessed the reinstatement behavior after infusing this peptide directly into the medial PFC and found that it decreased cue-induced reinstatement of cocaine seeking. Taken together, these data suggest that neuroadaptations in the CRMP2/CaV2.2 signaling cascade in the PFC can facilitate drug-seeking behavior. Targeting such interactions has implications for the treatment of cocaine relapse behavior.
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