Hedgehog-interacting protein acts in the habenula to regulate nicotine intake.

Hedgehog-interacting protein (HHIP) sequesters Hedgehog ligands to repress Smoothened (SMO)-mediated recruitment of the GLI family of transcription factors. Allelic variation in HHIP confers risk of chronic obstructive pulmonary disease and other smoking-related lung diseases, but underlying mechanisms are unclear. Using single-cell and cell-type-specific translational profiling, we show that HHIP expression is highly enriched in medial habenula (MHb) neurons, particularly MHb cholinergic neurons that regulate aversive behavioral responses to nicotine. HHIP deficiency dysregulated the expression of genes involved in cholinergic signaling in the MHb and disrupted the function of nicotinic acetylcholine receptors (nAChRs) through a PTCH-1/cholesterol-dependent mechanism. Further, CRISPR/Cas9-mediated genomic cleavage of the Hhip gene in MHb neurons enhanced the motivational properties of nicotine in mice. These findings suggest that HHIP influences vulnerability to smoking-related lung diseases in part by regulating the actions of nicotine on habenular aversion circuits.

α3* Nicotinic Acetylcholine Receptors in the Habenula-Interpeduncular Nucleus Circuit Regulate Nicotine Intake.

Allelic variation in CHRNA3, the gene encoding the α3 nicotinic acetylcholine receptor (nAChR) subunit, increases vulnerability to tobacco dependence and smoking-related diseases, but little is known about the role for α3-containing (α3*) nAChRs in regulating the addiction-related behavioral or physiological actions of nicotine. α3* nAChRs are densely expressed by medial habenula (mHb) neurons, which project almost exclusively to the interpeduncular nucleus (IPn) and are known to regulate nicotine avoidance behaviors. We found that Chrna3tm1.1Hwrt hypomorphic mice, which express constitutively low levels of α3* nAChRs, self-administer greater quantities of nicotine (0.4 mg kg-1 per infusion) than their wild-type littermates. Microinfusion of a lentivirus vector to express a short-hairpin RNA into the mHb or IPn to knock-down Chrna3 transcripts markedly increased nicotine self-administration behavior in rats (0.01-0.18 mg kg-1 per infusion). Using whole-cell recordings, we found that the α3ß4* nAChR-selective antagonist α-conotoxin AuIB almost completely abolished nicotine-evoked currents in mHb neurons. By contrast, the α3ß2* nAChR-selective antagonist α-conotoxin MII only partially attenuated these currents. Finally, micro-infusion of α-conotoxin AuIB (10 µm) but not α-conotoxin MII (10 µm) into the IPn in rats increased nicotine self-administration behavior. Together, these data suggest that α3ß4* nAChRs regulate the stimulatory effects of nicotine on the mHb-IPn circuit and thereby regulate nicotine avoidance behaviors. These findings provide mechanistic insights into how CHRNA3 risk alleles can increase the risk of tobacco dependence and smoking-related diseases in human smokers.SIGNIFICANCE STATEMENT Allelic variation in CHRNA3, which encodes the α3 nicotinic acetylcholine receptor (nAChR) subunit gene, increases risk of tobacco dependence but underlying mechanisms are unclear. We report that Chrna3 hypomorphic mice consume greater quantities of nicotine than wild-type mice and that knock-down of Chrna3 gene transcripts in the habenula or interpeduncular nucleus (IPn) increases nicotine intake in rats. α-Conotoxin AuIB, a potent antagonist of the α3ß4 nAChR subtype, reduced the stimulatory effects of nicotine on habenular neurons, and its infusion into the IPn increased nicotine intake in rats. These data suggest that α3ß4 nAChRs in the habenula-IPn circuit regulate the motivational properties of nicotine.

Synaptic Microtubule-Associated Protein EB3 and SRC Phosphorylation Mediate Structural and Behavioral Adaptations During Withdrawal From Cocaine Self-Administration.

Addictive behaviors, including relapse, are thought to depend in part on long-lasting drug-induced adaptations in dendritic spine signaling and morphology in the nucleus accumbens (NAc). While the influence of activity-dependent actin remodeling in these phenomena has been studied extensively, the role of microtubules and associated proteins remains poorly understood. We report that pharmacological inhibition of microtubule polymerization in the NAc inhibited locomotor sensitization to cocaine and contextual reward learning. We then investigated the roles of microtubule end-binding protein 3 (EB3) and SRC kinase in the neuronal and behavioral responses to volitionally administered cocaine. In synaptoneurosomal fractions from the NAc of self-administering male rats, the phosphorylation of SRC at an activating site was induced after 1 d of withdrawal, while EB3 levels were increased only after 30 d of withdrawal. Blocking SRC phosphorylation during early withdrawal by virally overexpressing SRCIN1, a negative regulator of SRC activity known to interact with EB3, abolished the incubation of cocaine craving in both male and female rats. Conversely, mimicking the EB3 increase observed after prolonged withdrawal increased the motivation to consume cocaine in male rats. In mice, the overexpression of either EB3 or SRCIN1 increased dendritic spine density and altered the spine morphology of NAc medium spiny neurons. Finally, a cocaine challenge after prolonged withdrawal recapitulated most of the synaptic protein expression profiles observed at early withdrawal. These findings suggest that microtubule-associated signaling proteins such as EB3 cooperate with actin remodeling pathways, notably SRC kinase activity, to establish and maintain long-lasting cellular and behavioral alterations following cocaine self-administration.SIGNIFICANCE STATEMENT Drug-induced morphological restructuring of dendritic spines of nucleus accumbens neurons is thought to be one of the cellular substrates of long-lasting drug-associated memories. The molecular basis of these persistent changes has remained incompletely understood. Here we implicate for the first time microtubule function in this process, together with key players such as microtubule-bound protein EB3 and synaptic SRC phosphorylation. We propose that microtubule and actin remodeling cooperate during withdrawal to maintain the plastic structural changes initially established by cocaine self-administration. This work opens new translational avenues for further characterization of microtubule-associated regulatory molecules as putative drug targets to tackle relapse to drug taking.

Transient synaptic potentiation in nucleus accumbens shell during refraining from cocaine seeking.

Repeated exposure to drug-associated cues without reward (extinction) leads to refraining from drug seeking in rodents. We determined if refraining is associated with transient synaptic plasticity (t-SP) in nucleus accumbens shell (NAshell), akin to the t-SP measured in the NAcore during cue-induced reinstatement of drug seeking. Using whole cell patch electrophysiology, we found that medium spiny neurons (MSNs) in NAshell expressed increased ratio of AMPA to NMDA glutamate receptor currents during refraining, which normalized to baseline levels by the end of the 2-hour extinction session. Unlike t-SP observed in NAcore during reinstated drug seeking, neither dendrite spine head enlargement nor activation of matrix metalloproteases (MMP2/9) accompanied the increased AMPA:NMDA in NAshell during refraining. Refraining was also not associated with changes in paired pulse ratio, NMDA receptor current decay time, or AMPA receptor rectification index in NAshell MSNs. Our preliminary data in transgenic mice suggest that t-SP may increase D2-MSN inputs relative to D1-MSN inputs.

Accumbens nNOS Interneurons Regulate Cocaine Relapse.

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. SIGNIFICANCE STATEMENT: 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.

Sequential drain amylase to guide drain removal following pancreatectomy.

BACKGROUND: Although used as criterion for early drain removal, postoperative day (POD) 1 drain fluid amylase (DFA) ≤ 5000 U/L has low negative predictive value for clinically relevant postoperative pancreatic fistula (CR-POPF). It was hypothesized that POD3 DFA ≤ 350 could provide further information to guide early drain removal. METHODS: Data from a pancreas surgery consortium database for pancreatoduodenectomy and distal pancreatectomy patients were analyzed retrospectively. Those patients without drains or POD 1 and 3 DFA data were excluded. Patients with POD1 DFA ≤ 5000 were divided into groups based on POD3 DFA: Group A (≤350) and Group B (>350). Operative characteristics and 60-day outcomes were compared using chi-square test. RESULTS: Among 687 patients in the database, all data were available for 380. Fifty-five (14.5%) had a POD1 DFA > 5000. Among 325 with POD1 DFA ≤ 5000, 254 (78.2%) were in Group A and 71 (21.8%) in Group B. Complications (35 (49.3%) vs 87 (34.4%); p = 0.021) and CR-POPF (13 (18.3%) vs 10 (3.9%); p < 0.001) were more frequent in Group B. CONCLUSIONS: In patients with POD1 DFA ≤ 5000, POD3 DFA ≤ 350 may be a practical test to guide safe early drain removal. Further prospective testing may be useful.

Reinstatement of nicotine seeking is mediated by glutamatergic plasticity.

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)hydrazino]carbonyl]benzyl]benzenesulfonamide (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.

Evidence against translational repression by the carboxyltransferase component of Escherichia coli acetyl coenzyme A carboxylase.

In Escherichia coli, synthesis of the malonyl coenzyme A (malonyl-CoA) required for membrane lipid synthesis is catalyzed by acetyl-CoA carboxylase, a large complex composed of four subunits. The subunit proteins are needed in a defined stoichiometry, and it remains unclear how such production is achieved since the proteins are encoded at three different loci. Meades and coworkers (G. Meades, Jr., B. K. Benson, A. Grove, and G. L. Waldrop, Nucleic Acids Res. 38:1217-1227, 2010, doi:http://dx.doi.org/10.1093/nar/gkp1079) reported that coordinated production of the AccA and AccD subunits is due to a translational repression mechanism exerted by the proteins themselves. The AccA and AccD subunits form the carboxyltransferase (CT) heterotetramer that catalyzes the second partial reaction of acetyl-CoA carboxylase. Meades et al. reported that CT tetramers bind the central portions of the accA and accD mRNAs and block their translation in vitro. However, long mRNA molecules (500 to 600 bases) were required for CT binding, but such long mRNA molecules devoid of ribosomes seemed unlikely to exist in vivo. This, plus problematical aspects of the data reported by Meades and coworkers, led us to perform in vivo experiments to test CT tetramer-mediated translational repression of the accA and accD mRNAs. We report that increased levels of CT tetramer have no detectable effect on translation of the CT subunit mRNAs.

A master regulator of opioid reward in the ventral prefrontal cortex.

In addition to their intrinsic rewarding properties, opioids can also evoke aversive reactions that protect against misuse. Cellular mechanisms that govern the interplay between opioid reward and aversion are poorly understood. We used whole-brain activity mapping in mice to show that neurons in the dorsal peduncular nucleus (DPn) are highly responsive to the opioid oxycodone. Connectomic profiling revealed that DPn neurons innervate the parabrachial nucleus (PBn). Spatial and single-nuclei transcriptomics resolved a population of PBn-projecting pyramidal neurons in the DPn that express µ-opioid receptors (µORs). Disrupting µOR signaling in the DPn switched oxycodone from rewarding to aversive and exacerbated the severity of opioid withdrawal. These findings identify the DPn as a key substrate for the abuse liability of opioids.

PiRATeMC: A highly flexible, scalable, and low-cost system for obtaining high quality video recordings for behavioral neuroscience.

With the rapidly accelerating adoption of machine-learning based rodent behavioral tracking tools, there is an unmet need for a method of acquiring high quality video data that is scalable, flexible, and relatively low-cost. Many experimenters use webcams, GoPros, or other commercially available cameras that can be expensive, offer minimal flexibility of recording parameters, and not optimized for recording rodent behavior, leading to suboptimal and inconsistent video quality. Furthermore, commercially available products are not conducive for synchronizing multiple cameras, or interfacing with third-party equipment to allow time-locking of video to other equipment such as microcontrollers for closed-loop experiments. We present a low-cost, customizable ecosystem of behavioral recording equipment, PiRATeMC (Pi-based Remote Acquisition Technology for Motion Capture) based on Raspberry Pi Camera Boards with the ability to acquire high quality recordings in bright/low light, or dark conditions under infrared light. PiRATeMC offers users control over nearly every recording parameter, and can be fine-tuned to produce optimal videos in any behavioral apparatus. This setup can be scaled up for synchronous control of any number of cameras via a self-contained network without burdening institutional network infrastructure. The Raspberry Pi is an excellent platform with a large online community designed for novice and inexperienced programmers interested in using an open-source recording system. Importantly, PiRATeMC supports TTL and serial communication, allowing for synchronization and interfacing of video recording with behavioral or other third-party equipment. In sum, PiRATeMC minimizes the cost-prohibitive nature of conducting and analyzing high quality behavioral neuroscience studies, thereby increasing accessibility to behavioral neuroscience.

High quality, high throughput, and low-cost simultaneous video recording of 60 animals in operant chambers using PiRATeMC.

Background: The development of Raspberry Pi-based recording devices for video analyses of drug self-administration studies has shown to be promising in terms of affordability, customizability, and capacity to extract in-depth behavioral patterns. Yet, most video recording systems are limited to a few cameras making them incompatible with large-scale studies. New Method: We expanded the PiRATeMC (Pi-based Remote Acquisition Technology for Motion Capture) recording system by increasing its scale, modifying its code, and adding equipment to accommodate large-scale video acquisition, accompanied by data on the throughput capabilities, video fidelity, synchronicity of devices, and comparisons between the Raspberry Pi 3B+ and 4B models. Results: Using PiRATeMC default recording parameters resulted in minimal storage (~350MB/h), high throughput (< ~120 seconds/Pi), high video fidelity, and synchronicity within ~0.02 seconds, affording the ability to simultaneously record 60 animals in individual self-administration chambers at a fraction of current commercial costs. No consequential differences were found between Raspberry Pi 3B+ and 4B models. Comparison with Existing Methods: This system allows greater acquisition of video data simultaneously than other video recording systems by an order of magnitude with less storage needs and lower costs. Additionally, we report in-depth quantitative assessments of throughput, fidelity, and synchronicity, displaying real-time system capabilities. Conclusions: The system presented is able to be fully installed in a month's time by a single technician and provides a scalable, low cost, and quality-assured procedure with a high-degree of customization and synchronicity between recording devices, capable of recording a large number of subjects with high turnover in a variety of species and settings.

Dimerization of the bacterial biotin carboxylase subunit is required for acetyl coenzyme A carboxylase activity in vivo.

Acetyl coenzyme A (acteyl-CoA) carboxylase (ACC) is the first committed enzyme of the fatty acid synthesis pathway. Escherichia coli ACC is composed of four different proteins. The first enzymatic activity of the ACC complex, biotin carboxylase (BC), catalyzes the carboxylation of the protein-bound biotin moiety of another subunit with bicarbonate in an ATP-dependent reaction. Although BC is found as a dimer in cell extracts and the carboxylase activities of the two subunits of the dimer are interdependent, mutant BC proteins deficient in dimerization are reported to retain appreciable activity in vitro (Y. Shen, C. Y. Chou, G. G. Chang, and L. Tong, Mol. Cell 22:807-818, 2006). However, in vivo BC must interact with the other proteins of the complex, and thus studies of the isolated BC may not reflect the intracellular function of the enzyme. We have tested the abilities of three BC mutant proteins deficient in dimerization to support growth and report that the two BC proteins most deficient in dimerization fail to support growth unless expressed at high levels. In contrast, the wild-type protein supports growth at low expression levels. We conclude that BC must be dimeric to fulfill its physiological function.

Survival Statistics of Digital Replantation in the UK.

Background Digital replantation is associated with a substantial risk of failure. There is considerable variation in survival rates globally, and the current data are limited by poor statistical methods and bias of selection, which limits its translation to Europe and the USA. We aimed to establish a more representative survival rate of digit replantation for western populations and evaluate espoused prognostic variables using robust statistical methodology. Materials and Methods Retrospective data were collected from 58 consecutive patients who underwent digital replantation following traumatic amputation in three tertiary care hand centres in the UK over seven years. The unit of analysis was the digit. Generalized linear modelling was used to estimate the odds ratio (OR) of digit survival. Results Forty-six of 68 replanted digits survived (68%). The typical replant candidate was a 40-year-old male manual worker. Digit survival was more likely with guillotine injuries (adjusted OR 25.5 [95% CI 5.60, 115]) and when intraoperative skeletal shortening was performed (adjusted OR 15.3 [95% CI 2.62, 89.5]). The age of the patient, seniority of the operating surgeon, and use of vein grafts was not associated with digit survival. Conclusion We provide robust data to show that guillotine amputations have more favourable survival rates, which can be further improved by skeletal shortening at the time of replantation. We suggest that research networks worldwide set up digit amputation registries to capture individual patient data on this uncommon injury.

Opposing roles for striatonigral and striatopallidal neurons in dorsolateral striatum in consolidating new instrumental actions.

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.

Dynamic CRMP2 Regulation of CaV2.2 in the Prefrontal Cortex Contributes to the Reinstatement of Cocaine Seeking.

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.

Dopaminylation of histone H3 in ventral tegmental area regulates cocaine seeking.

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.

HDAC5 Regulates the Formation of Drug Memories.

Cocaine-associated environmental cues can precipitate craving and relapse in addicted individuals even after years of abstinence, but the molecular mechanisms by which maladaptive drug memories are generated remain unclear. New findings suggest that histone deacetylase 5 (HDAC5) plays a key role in this process.

The tetrapartite synapse: Extracellular matrix remodeling contributes to corticoaccumbens plasticity underlying drug addiction.

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.

Synaptic plasticity mediating cocaine relapse requires matrix metalloproteinases.

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.