Reward learning requires activity of matrix metalloproteinase-9 in the central amygdala

The Role of Cerebellar Intrinsic Neuronal Excitability, Synaptic Plasticity, and Perineuronal Nets in Eyeblink Conditioning

Evidence is strong that, in addition to fine motor control, there is an important role for the cerebellum in cognition and emotion. The deep nuclei of the mammalian cerebellum also contain the highest density of perineural nets-mesh-like structures that surround neurons-in the brain, and it appears there may be a connection between these nets and cognitive processes, particularly learning and memory. Here, we review how the cerebellum is involved in eyeblink conditioning-a particularly well-understood form of learning and memory-and focus on the role of perineuronal nets in intrinsic membrane excitability and synaptic plasticity that underlie eyeblink conditioning. We explore the development and role of perineuronal nets and the in vivo and in vitro evidence that manipulations of the perineuronal net in the deep cerebellar nuclei affect eyeblink conditioning. Together, these findings provide evidence of an important role for perineuronal net in learning and memory.

Optogenetic and chemogenetic approaches reveal differences in neuronal circuits that mediate initiation and maintenance of social interaction

For social interaction to be successful, two conditions must be met: the motivation to initiate it and the ability to maintain it. This study uses both optogenetic and chemogenetic approaches to reveal the specific neural pathways that selectively influence those two social interaction components.

MMP-9 plasma level as biomarker of cochlear implantation outcome in cohort study of deaf children

PURPOSE

If before cochlear implantation it was possible to assay biomarkers of neuroplasticity, we might be able to identify those children with congenital deafness who, later on, were at risk of poor speech and language rehabilitation outcomes.

METHODS

A group of 40 children aged up to 2 years with DFNB1-related congenital deafness was observed in this prospective cohort study over three follow-up intervals (0, 8, and 18 months) after cochlear implant (CI) activation. Children were assessed for auditory development using the LittlEARS Questionnaire (LEAQ) score, and at the same time, measurements were made of matrix metalloproteinase-9 (MMP-9) plasma levels.

RESULTS

There were significant negative correlations between plasma levels of MMP-9 at 8-month follow-up and LEAQ score at cochlear implantation (p = 0.04) and LEAQ score at 18-month follow-up (p = 0.02) and between MMP-9 plasma levels at 18-month follow-up and LEAQ score at cochlear implantation (p = 0.04). As already reported, we confirmed a significant negative correlation between MMP-9 plasma level at cochlear implantation and LEAQ score at 18-month follow-up (p = 0.005). Based on this latter correlation, two clusters of good and poor CI performers could be isolated.

CONCLUSIONS

The study shows that children born deaf who have an MMP-9 plasma level of less than 150 ng/ml at cochlear implantation have a good chance of attaining a high LEAQ score after 18 months of speech and language rehabilitation. This indicates that MMP-9 plasma level at cochlear implantation is a good prognostic marker for CI outcome.

Extracellular zinc regulates contextual fear memory formation in male rats through MMP-BDNF-TrkB pathway in dorsal hippocampus and basolateral amygdala

Large amount of zinc (100 µM even up to 300 µM) is released from the nerve terminals in response to high frequency neuronal stimulation in certain brain regions including hippocampus and amygdala. However, its precise pharmacological effect is poorly understood. Here, we investigated the role of extracellular zinc (endogenous zinc) and exogenous zinc in memory formation using contextual fear conditioning (CFC) model. Male Sprague Dawley rats were trained for fear conditioning followed by in vivo microdialysis for collection of microdialysate samples from CA1 and CA3 regions of hippocampus and basolateral amygdala (BLA). Extracellular zinc chelator CaEDTA, BDNF scavenger TrkB-Fc, exogenous 7,8-DHF and matrix metalloproteinases (MMP) inhibitor were infused into the CA1 and CA3 regions of hippocampus and BLA after CFC. Different doses of exogenous zinc hydroaspartate were administered intraperitoneally immediately after CFC. We found that CFC increased the level of extracellular zinc in the hippocampus and BLA. Infusing the CaEDTA, TrkB-Fc and MMP inhibitor into the CA1 and CA3 regions of hippocampus and BLA disrupted the fear memory formation. Furthermore, administration of TrKB agonist 7,8-DHF reversed the inhibitory effect of CaEDTA on fear memory formation, suggesting that extracellular zinc may regulate fear memory formation via the BDNF-TrKB pathway. We also found that high dose of exogenous zinc hydroaspartate supplementation increased extracellular zinc levels in brain and enhanced fear memory formation. Altogether, these findings indicate that extracellular zinc may participate in formation of contextual fear memory through MMP-BDNF-TrkB pathway in the hippocampus and BLA.

Whole-brain tracking of cocaine and sugar rewards processing

Natural rewards, such as food, and sex are appetitive stimuli available for animals in their natural environment. Similarly, addictive rewards such as drugs of abuse possess strong, positive valence, but their action relies on their pharmacological properties. Nevertheless, it is believed that both of these kinds of rewards activate similar brain circuitry. The present study aimed to discover which parts of the brain process the experience of natural and addictive rewards. To holistically address this question, we used a single-cell whole-brain imaging approach to find patterns of activation for acute and prolonged sucrose and cocaine exposure. We analyzed almost 400 brain structures and created a brain-wide map of specific, c-Fos-positive neurons engaged by these rewards. Acute but not prolonged sucrose exposure triggered a massive c-Fos expression throughout the brain. Cocaine exposure on the other hand potentiated c-Fos expression with prolonged use, engaging more structures than sucrose treatment. The functional connectivity analysis unraveled an increase in brain modularity after the initial exposure to both types of rewards. This modularity was increased after repeated cocaine, but not sucrose, intake. To check whether discrepancies between the processing of both types of rewards can be found on a cellular level, we further studied the nucleus accumbens, one of the most strongly activated brain structures by both sucrose and cocaine experience. We found a high overlap between natural and addictive rewards on the level of c-Fos expression. Electrophysiological measurements of cellular correlates of synaptic plasticity revealed that natural and addictive rewards alike induce the accumulation of silent synapses. These results strengthen the hypothesis that in the nucleus accumbens drugs of abuse cause maladaptive neuronal plasticity in the circuitry that typically processes natural rewards.

Blueprints for measuring natural behavior

Until recently laboratory tasks for studying behavior were highly artificial, simplified, and designed without consideration for the environmental or social context. Although such an approach offers good control over behavior, it does not allow for researching either voluntary responses or individual differences. Importantly for neuroscience studies, the activity of the neural circuits involved in producing unnatural, artificial behavior is variable and hard to predict. In addition, different ensembles may be activated depending on the strategy the animal adopts to deal with the spurious problem. Thus, artificial and simplified tasks based on responses, which do not occur spontaneously entail problems with modeling behavioral impairments and underlying brain deficits. To develop valid models of human disorders we need to test spontaneous behaviors consistently engaging well-defined, evolutionarily conserved neuronal circuits. Such research focuses on behavioral patterns relevant for surviving and thriving under varying environmental conditions, which also enable high reproducibility across different testing settings.

Targeted therapy of cognitive deficits in fragile X syndrome

Breaking an impasse in finding mechanism-based therapies of neuropsychiatric disorders requires a strategic shift towards alleviating individual symptoms. Here we present a symptom and circuit-specific approach to rescue deficits of reward learning in Fmr1 knockout mice, a model of Fragile X syndrome (FXS), the most common monogenetic cause of inherited mental disability and autism. We use high-throughput, ecologically-relevant automated tests of cognition and social behavior to assess effectiveness of the circuit-targeted injections of designer nanoparticles, loaded with TIMP metalloproteinase inhibitor 1 protein (TIMP-1). Further, to investigate the impact of our therapeutic strategy on neuronal plasticity we perform long-term potentiation recordings and high-resolution electron microscopy. We show that central amygdala-targeted delivery of TIMP-1 designer nanoparticles reverses impaired cognition in Fmr1 knockouts, while having no impact on deficits of social behavior, hence corroborating symptom-specificity of the proposed approach. Moreover, we elucidate the neural correlates of the highly specific behavioral rescue by showing that the applied therapeutic intervention restores functional synaptic plasticity and ultrastructure of neurons in the central amygdala. Thus, we present a targeted, symptom-specific and mechanism-based strategy to remedy cognitive deficits in Fragile X syndrome.

Brain size, gut size and cognitive abilities: the energy trade-offs tested in artificial selection experiment

The enlarged brains of homeotherms bring behavioural advantages, but also incur high energy expenditures. The ‘expensive brain’ (EB) hypothesis posits that the energetic costs of the enlarged brain and the resulting increased cognitive abilities (CA) were met by either increased energy turnover or reduced allocation to other expensive organs, such as the gut. We tested the EB hypothesis by analysing correlated responses to selection in an experimental evolution model system, which comprises line types of laboratory mice selected for high or low basal metabolic rate (BMR), maximum (VO_2max) metabolic rates and random-bred (unselected) lines. The traits are implicated in the evolution of homeothermy, having been pre-requisites for the encephalization and exceptional CA of mammals, including humans. High-BMR mice had bigger guts, but not brains, than mice of other line types. Yet, they were superior in the cognitive tasks carried out in both reward and avoidance learning contexts and had higher neuronal plasticity (indexed as the long-term potentiation) than their counterparts. Our data indicate that the evolutionary increase of CA in mammals was initially associated with increased BMR and brain plasticity. It was also fuelled by an enlarged gut, which was not traded off for brain size.

Progresses and Prospects of Neuroprotective Agents-Loaded Nanoparticles and Biomimetic Material in Ischemic Stroke

Ischemic stroke remains the leading cause of death and disability, while the main mechanisms of dominant neurological damage in stroke contain excitotoxicity, oxidative stress, and inflammation. The clinical application of many neuroprotective agents is limited mainly due to their inability to cross the blood-brain barrier (BBB), short half-life and low bioavailability. These disadvantages can be better eliminated/reduced by nanoparticle as the carrier of these drugs. This review expounded the currently hot researched nanomedicines from the perspective of the mechanism of ischemic stroke. In addition, this review describes the bionic nanomedicine delivery strategies containing cells, cell membrane vesicles and exosomes that can effectively avoid the risk of clearance by the reticuloendothelial system. The potential challenges and application prospect for clinical translation of these delivery platforms were also discussed.

Prospective cohort study reveals MMP-9, a neuroplasticity regulator, as a prediction marker of cochlear implantation outcome in prelingual deafness treatment

Because of vast variability of cochlear implantation outcomes in prelingual deafness treatment, identification of good and poor performers remains a challenging task. To address this issue, we investigated genetic variants of matrix metalloproteinase 9 (MMP9) and brain-derived neurotrophic factor (BDNF) and plasma levels of MMP-9, BDNF, and pro-BDNF that have all been implicated in neuroplasticity after sensory deprivation in the auditory pathway. We recruited a cohort of prelingually deaf children, all implanted before the age of 2, and carried out a prospective observation (N = 61). Next, we analyzed the association between (i) functional MMP9 (rs20544, rs3918242, rs2234681) and BDNF (rs6265) gene variants (and their respective protein levels) and (ii) the child’s auditory development as measured with the LittlEARS Questionnaire (LEAQ) before cochlear implant (CI) activation and at 8 and 18 months post-CI activation. Statistical analyses revealed that the plasma level of MMP-9 measured at implantation in prelingually deaf children was significantly correlated with the LEAQ score 18 months after CI activation. In the subgroup of DFNB1-related deafness (N = 40), rs3918242 of MMP9 was significantly associated with LEAQ score at 18 months after CI activation; also, according to a multiple regression model, the ratio of plasma levels of pro-BDNF/BDNF measured at implantation was a significant predictor of overall LEAQ score at follow-up. In the subgroup with DFNB1-related deafness, who had CI activation after 1 year old (N = 22), a multiple regression model showed that rs3918242 of MMP9 was a significant predictor of overall LEAQ score at follow-up.

Extracellular Metalloproteinases in the Plasticity of Excitatory and Inhibitory Synapses

Long-term synaptic plasticity is shaped by the controlled reorganization of the synaptic proteome. A key component of this process is local proteolysis performed by the family of extracellular matrix metalloproteinases (MMPs). In recent years, considerable progress was achieved in identifying extracellular proteases involved in neuroplasticity phenomena and their protein substrates. Perisynaptic metalloproteinases regulate plastic changes at synapses through the processing of extracellular and membrane proteins. MMP9 was found to play a crucial role in excitatory synapses by controlling the NMDA-dependent LTP component. In addition, MMP3 regulates the L-type calcium channel-dependent form of LTP as well as the plasticity of neuronal excitability. Both MMP9 and MMP3 were implicated in memory and learning. Moreover, altered expression or mutations of different MMPs are associated with learning deficits and psychiatric disorders, including schizophrenia, addiction, or stress response. Contrary to excitatory drive, the investigation into the role of extracellular proteolysis in inhibitory synapses is only just beginning. Herein, we review the principal mechanisms of MMP involvement in the plasticity of excitatory transmission and the recently discovered role of proteolysis in inhibitory synapses. We discuss how different matrix metalloproteinases shape dynamics and turnover of synaptic adhesome and signal transduction pathways in neurons. Finally, we discuss future challenges in exploring synapse- and plasticity-specific functions of different metalloproteinases.

The IntelliCage System: A Review of Its Utility as a Novel Behavioral Platform for a Rodent Model of Substance Use Disorder

The use of animal models for substance use disorder (SUD) has made an important contribution in the investigation of the behavioral and molecular mechanisms underlying substance abuse and addiction. Here, we review a novel and comprehensive behavioral platform to characterize addiction-like traits in rodents using a fully automated learning system, the IntelliCage. This system simultaneously captures the basic behavioral navigation, reward preference, and aversion, as well as the multi-dimensional complex behaviors and cognitive functions of group-housed rodents. It can reliably capture and track locomotor and cognitive pattern alterations associated with the development of substance addiction. Thus, the IntelliCage learning system offers a potentially efficient, flexible, and sensitive tool for the high-throughput screening of the rodent SUD model.

Effects of Mephedrone and Amphetamine Exposure during Adolescence on Spatial Memory in Adulthood: Behavioral and Neurochemical Analysis

A synthetic cathinone, mephedrone is widely abused by adolescents and young adults. Despite its widespread use, little is known regarding its long-term effects on cognitive function. Therefore, we assessed, for the first time, whether (A) repeated mephedrone (30 mg/kg, i.p., 10 days, once a day) exposure during adolescence (PND 40) induces deleterious effects on spatial memory and reversal learning (Barnes maze task) in adult (PND 71-84) rats and whether (B) these effects were comparable to amphetamine (2.5 mg/kg, i.p.). Furthermore, the influence of these drugs on MMP-9, NMDA receptor subunits (GluN1, GluN2A/2B) and PSD-95 protein expression were assessed in adult rats. The drug effects were evaluated at doses that per se induce rewarding/reinforcing effects in rats. Our results showed deficits in spatial memory (delayed effect of amphetamine) and reversal learning in adult rats that received mephedrone/amphetamine in adolescence. However, the reversal learning impairment may actually have been due to spatial learning rather than cognitive flexibility impairments. Furthermore, mephedrone, but not amphetamine, enhanced with delayed onset, MMP-9 levels in the prefrontal cortex and the hippocampus. Mephedrone given during adolescence induced changes in MMP-9 level and up-regulation of the GluN2B-containing NMDA receptor (prefrontal cortex and hippocampus) in young adult (PND 63) and adult (PND 87) rats. Finally, in adult rats, PSD-95 expression was increased in the prefrontal cortex and decreased in the hippocampus. In contrast, in adult rats exposed to amphetamine in adolescence, GluN2A subunit and PSD-95 expression were decreased (down-regulated) in the hippocampus. Thus, in mephedrone-but not amphetamine-treated rats, the deleterious effects on spatial memory were associated with changes in MMP-9 level. Because the GluN2B-containing NMDA receptor dominates in adolescence, mephedrone seems to induce more harmful effects on cognition than amphetamine does during this period of life.

Chronic fluoxetine treatment impairs motivation and reward learning by affecting neuronal plasticity in the central amygdala

BACKGROUND AND PURPOSE

The therapeutic effects of fluoxetine are believed to be due to increasing neuronal plasticity and reversing some learning deficits. Nevertheless, a growing amount of evidence shows adverse effects of this drug on cognition and some forms of neuronal plasticity.

EXPERIMENTAL APPROACH

To study the effects of chronic fluoxetine treatment, we combine an automated assessment of motivation and learning in mice with an investigation of neuronal plasticity in the central amygdala and basolateral amygdala. We use immunohistochemistry to visualize neuronal types and perineuronal nets, along with DI staining to assess dendritic spine morphology. Gel zymography is used to test fluoxetine's impact on matrix metalloproteinase-9, an enzyme involved in synaptic plasticity.

KEY RESULTS

We show that chronic fluoxetine treatment in non-stressed mice increases perineuronal nets-dependent plasticity in the basolateral amygdala, while impairing MMP-9-dependent plasticity in the central amygdala. Further, we illustrate how the latter contributes to anhedonia and deficits of reward learning. Behavioural impairments are accompanied by alterations in morphology of dendritic spines in the central amygdala towards an immature state, most likely reflecting animals' inability to adapt. We strengthen the link between the adverse effects of fluoxetine and its influence on MMP-9 by showing that behaviour of MMP-9 knockout animals remains unaffected by the drug.

CONCLUSION AND IMPLICATIONS

Chronic fluoxetine treatment differentially affects various forms of neuronal plasticity, possibly explaining its opposing effects on brain and behaviour. These findings are of immediate clinical relevance since reported side effects of fluoxetine pose a potential threat to patients.

IntelliCage as a tool for measuring mouse behavior - 20 years perspective

Since the 1980s, we have witnessed the rapid development of genetically modified mouse models of human diseases. A large number of transgenic and knockout mice have been utilized in basic and applied research, including models of neurodegenerative and neuropsychiatric disorders. To assess the biological function of mutated genes, modern techniques are critical to detect changes in behavioral phenotypes. We review the IntelliCage, a high-throughput system that is used for behavioral screening and detailed analyses of complex behaviors in mice. The IntelliCage was introduced almost two decades ago and has been used in over 150 studies to assess both spontaneous and cognitive behaviors. We present a critical analysis of experimental data that have been generated using this device.

The role of matrix metalloproteinase-9 in negative reinforcement learning and plasticity in alcohol dependence

A role for matrix metalloproteinases (MMPs) in plasticity-dependent learning has been established. MMPs degrade the extracellular matrix (ECM) when synaptic reorganization is warranted. Previously, we showed that escalation of alcohol self-administration is a learned plasticity-dependent process that requires an intact MMP system. To identify the MMP subtypes within specific brain regions that are associated with plasticity underlying the negative reinforcing effects of alcohol (as measured by escalated alcohol self-administration) during acute withdrawal in alcohol dependence, male Wistar rats were trained to self-administer alcohol in an operant paradigm, subjected to one month of intermittent alcohol vapor exposure to induce alcohol dependence and then allowed to self-administer alcohol during repeated acute withdrawal self-administration sessions. Subsequently, rat brains were extracted after initial or stable escalated alcohol self-administration phases of acute withdrawal and analyzed by immunoblot to detect MMP-2, -3, and -9 levels in the anterior cingulate cortex (ACC), bed nucleus of the stria terminalis, central amygdala (CeA), hippocampus, and nucleus accumbens (NAc). The results showed that MMP-9 expression in the CeA and NAc of alcohol-dependent rats was increased, however, MMP-9 expression in the ACC was decreased during negative reinforcement learning. Subsequently, the importance of plasticity mediated by MMP-9 in escalated alcohol self-administration during acute withdrawal was functionally assessed through site-specific intra-CeA MMP-9 inhibition during repeated acute withdrawal self-administration sessions. MMP-9 inhibition prevented acute withdrawal-induced escalation of alcohol self-administration in a manner that was not confounded by locomotor effects or a permanent inability to learn about the negative reinforcing effects of alcohol.

Threat Memory Reminder Under Matrix Metalloproteinase 9 Inhibitor Doxycycline Globally Reduces Subsequent Memory Plasticity

Associative memory can be rendered malleable by a reminder. Blocking the ensuing reconsolidation process is suggested as a therapeutic target for unwanted aversive memories. Matrix metalloproteinase-9 (MMP-9) is required for structural synapse remodeling involved in memory consolidation. Inhibiting MMP-9 with doxycycline is suggested to attenuate human threat conditioning. Here, we investigated whether MMP-9 inhibition also interferes with threat memory reconsolidation. Male and female human participants (N = 78) learned the association between two visual conditioned stimuli (CS⁺) and a 50% chance of an unconditioned nociceptive stimulus (US), and between CS^- and the absence of US. On day 7, one CS⁺ was reminded without reinforcement 3.5 h after ingesting either 200 mg of doxycycline or placebo. On day 14, retention of CS memory was assessed under extinction by fear-potentiated startle. Contrary to our expectations, we observed a greater CS⁺/CS^- difference in participants who were reminded under doxycycline compared with placebo. Participants who were reminded under placebo showed extinction learning during the retention test, which was not observed in the doxycycline group. There was no difference between the reminded and the nonreminded CS⁺ in either group. In contrast, during relearning after the retention test, the CS⁺/CS^- difference was more pronounced in the placebo group than in the doxycycline group. To summarize, a single dose of doxycycline before threat memory reminder appeared to have no specific impact on reconsolidation, but to globally impair extinction learning, and threat relearning, beyond drug clearance.SIGNIFICANCE STATEMENT Matrix metalloproteinase-9 inhibition appears to attenuate memory consolidation. It could also be a target for blocking reconsolidation. Here, we test this hypothesis in human threat conditioning. We find that doxycycline has no specific impact on a reminded cue, but confers a global reduction in extinction learning and threat learning beyond the clearance of the drug. This may point toward a more long-lasting impact of doxycycline treatment on memory plasticity.

Mephedrone Impact on Matrix Metalloproteinases Activity - Do they Influence the Memory Processes?

BACKGROUND

The use of drugs of addiction, as mephedrone, is associated with functional neuronal disorders due to remodeling of the nervous tissue. Key enzymes in remodeling are extracellular matrix (ECM) proteases like matrix metalloproteases (MMPs). Recently, MMPs have been of great interest as some studies point to a fact that the alterations in structural remodeling of synaptic connections modify learning-dependent changes, which remain active even after a prolonged period of abstinence. This entails a continuous development of dependence.

OBJECTIVES

The aim of the study was to determine the influence of subchronic exposure to three different doses of mephedrone on the activity of MMP-2 and 9 in hippocampus and prefrontal cortex and how this was correlated with memory processes in mice.

METHODS

The homogenates of hippocampus and cortex were assayed for MMP-2 and MMP-9 activity by gelatin zymography. Memory consolidation processes were evaluated in the passive avoidance (PA) test.

RESULTS

The study confirmed the dose-dependent increase in activity of MMP-2 and -9 exerted by subchronic administration of mephedrone. Moreover, the highest dose of mephedrone attenuated consolidation of memory and learning processes.

CONCLUSIONS

We could hypothesize that inhibition of MMPs can be considered as a therapeutic option for the treatment of addictive behaviors associated with cognitive processes. Moreover, further studies are required to find out if elevated activities of MMPs contribute to brain damage or recovery from brain damage caused directly by mephedrone.

Demystifying the extracellular matrix and its proteolytic remodeling in the brain: structural and functional insights

The extracellular matrix (ECM) plays diverse roles in several physiological and pathological conditions. In the brain, the ECM is unique both in its composition and in functions. Furthermore, almost all the cells in the central nervous system contribute to different aspects of this intricate structure. Brain ECM, enriched with proteoglycans and other small proteins, aggregate into distinct structures around neurons and oligodendrocytes. These special structures have cardinal functions in the normal functioning of the brain, such as learning, memory, and synapse regulation. In this review, we have compiled the current knowledge about the structure and function of important ECM molecules in the brain and their proteolytic remodeling by matrix metalloproteinases and other enzymes, highlighting the special structures they form. In particular, the proteoglycans in brain ECM, which are essential for several vital functions, are emphasized in detail.

MMPs in learning and memory and neuropsychiatric disorders

Matrix metalloproteinases (MMPs) are a group of over twenty proteases, operating chiefly extracellularly to cleave components of the extracellular matrix, cell adhesion molecules as well as cytokines and growth factors. By virtue of their expression and activity patterns in animal models and clinical investigations, as well as functional studies with gene knockouts and enzyme inhibitors, MMPs have been demonstrated to play a paramount role in many physiological and pathological processes in the brain. In particular, they have been shown to influence learning and memory processes, as well as major neuropsychiatric disorders such as schizophrenia, various kinds of addiction, epilepsy, fragile X syndrome, and depression. A possible link connecting all those conditions is either physiological or aberrant synaptic plasticity where some MMPs, e.g., MMP-9, have been demonstrated to contribute to the structural and functional reorganization of excitatory synapses that are located on dendritic spines. Another common theme linking the aforementioned pathological conditions is neuroinflammation and MMPs have also been shown to be important mediators of immune responses.

PyMICE: APython library for analysis of IntelliCage data

IntelliCage is an automated system for recording the behavior of a group of mice housed together. It produces rich, detailed behavioral data calling for new methods and software for their analysis. Here we present PyMICE, a free and open-source library for analysis of IntelliCage data in the Python programming language. We describe the design and demonstrate the use of the library through a series of examples. PyMICE provides easy and intuitive access to IntelliCage data, and thus facilitates the possibility of using numerous other Python scientific libraries to form a complete data analysis workflow.

Blocking human fear memory with the matrix metalloproteinase inhibitor doxycycline

Learning to predict threat is a fundamental ability of many biological organisms, and a laboratory model for anxiety disorders. Interfering with such memories in humans would be of high clinical relevance. On the basis of studies in cell cultures and slice preparations, it is hypothesised that synaptic remodelling required for threat learning involves the extracellular enzyme matrix metalloproteinase (MMP) 9. However, in vivo evidence for this proposal is lacking. Here we investigate human Pavlovian fear conditioning under the blood-brain barrier crossing MMP inhibitor doxycyline in a pre-registered, randomised, double-blind, placebo-controlled trial. We find that recall of threat memory, measured with fear-potentiated startle 7 days after acquisition, is attenuated by ~60% in individuals who were under doxycycline during acquisition. This threat memory impairment is also reflected in increased behavioural surprise signals to the conditioned stimulus during subsequent re-learning, and already late during initial acquisition. Our findings support an emerging view that extracellular signalling pathways are crucially required for threat memory formation. Furthermore, they suggest novel pharmacological methods for primary prevention and treatment of posttraumatic stress disorder.

Releasing Addiction Memories Trapped in Perineuronal Nets

Drug addiction can be conceptualized at a basic level as maladaptive learning and memory. Addictive substances elicit changes in brain circuitry involved in reward, cognition, and emotional state, leading to the formation and persistence of strong drug-associated memories that lead to craving and relapse. Recently, perineuronal nets (PNNs), extracellular matrix (ECM) structures surrounding neurons, have emerged as regulators of learning, memory, and addiction behaviors. PNNs do not merely provide structural support to neurons but are dynamically remodeled in an experience-dependent manner by metalloproteinases. They function in various brain regions through constituent proteins such as brevican that are implicated in neural plasticity. Understanding the function of PNN components in memory processes may lead to new therapeutic approaches to treating addiction.

The Search for an Effective Therapy to Treat Fragile X Syndrome: Dream or Reality?

Fragile X Syndrome (FXS) is the most common form of intellectual disability and a primary cause of autism. It originates from the lack of the Fragile X Mental Retardation Protein (FMRP), which is an RNA-binding protein encoded by the Fragile X Mental Retardation Gene 1 (FMR1) gene. Multiple roles have been attributed to this protein, ranging from RNA transport (from the nucleus to the cytoplasm, but also along neurites) to translational control of mRNAs. Over the last 20 years many studies have found a large number of FMRP mRNA targets, but it is still not clear which are those playing a critical role in the etiology of FXS. So far, no therapy for FXS has been found, making the quest for novel targets of considerable importance. Several pharmacological approaches have been attempted, but, despite some promising preclinical results, no strategy gave successful outcomes, due either to the induction of major side effects or to the lack of improvement of the phenotypes. However, these studies suggested that, in order to measure the effectiveness of a specific treatment, trials should be redesigned and new endpoints defined in FXS patients. Nevertheless, the search for new therapeutic targets for FXS is very active. In this context, the advances in animal modeling, coupled with better understanding of neurobiology and physiopathology of FXS, are of crucial importance in developing new selected treatments. Here, we discuss the pathways that were recently linked to the physiopathology of FXS (mGluR, GABAR, insulin, Insulin-like Growth Factor 1 (IGF-1), MPP-9, serotonin, oxytocin and endocannabinoid signaling) and that suggest new approaches to find an effective therapy for this disorder. Our goal with this review article is to summarize some recent relevant findings on FXS treatment strategies in order to have a clearer view of the different pathways analyzed to date emphasizing those shared with other synaptic disorders.

Multifaceted Roles of Metzincins in CNS Physiology and Pathology: From Synaptic Plasticity and Cognition to Neurodegenerative Disorders

The extracellular matrix (ECM) and membrane proteolysis play a key role in structural and functional synaptic plasticity associated with development and learning. A growing body of evidence underscores the multifaceted role of members of the metzincin superfamily, including metalloproteinases (MMPs), A Disintegrin and Metalloproteinases (ADAMs), A Disintegrin and Metalloproteinase with Thrombospondin Motifs (ADAMTSs) and astacins in physiological and pathological processes in the central nervous system (CNS). The expression and activity of metzincins are strictly controlled at different levels (e.g., through the regulation of translation, limited activation in the extracellular space, the binding of endogenous inhibitors and interactions with other proteins). Thus, unsurprising is that the dysregulation of proteolytic activity, especially the greater expression and activation of metzincins, is associated with neurodegenerative disorders that are considered synaptopathies, especially Alzheimer's disease (AD). We review current knowledge of the functions of metzincins in the development of AD, mainly the proteolytic processing of amyloid precursor protein, the degradation of amyloid β (Aβ) peptide and several pathways for Aβ clearance across brain barriers (i.e., blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier (BCSFB)) that contain specific receptors that mediate the uptake of Aβ peptide. Controlling the proteolytic activity of metzincins in Aβ-induced pathological changes in AD patients' brains may be a promising therapeutic strategy.

Matrix Metalloproteinase-9 and Synaptic Plasticity in the Central Amygdala in Control of Alcohol-Seeking Behavior

BACKGROUND

Dysfunction of the glutamatergic system has been implicated in alcohol addiction; however, the molecular underpinnings of this phenomenon are still poorly understood. In the current study we have investigated the possible function of matrix metalloproteinase-9 (MMP-9) in alcohol addiction because this protein has recently emerged as an important regulator of excitatory synaptic plasticity.

METHODS

For long-term studies of alcohol drinking in mice we used IntelliCages. Dendritic spines were analyzed using Diolistic staining with DiI. Whole-cell patch clamp was used to assess silent synapses. Motivation for alcohol in human subjects was assessed on the basis of a Semi-Structured Assessment for the Genetics of Alcoholism interview.

RESULTS

Mice devoid of MMP-9 (MMP-9 knockout) drank as much alcohol as wild-type animals; however, they were impaired in alcohol seeking during the motivation test and withdrawal. The deficit could be rescued by overexpression of exogenous MMP-9 in the central nucleus of the amygdala (CeA). Furthermore, the impaired alcohol seeking was associated with structural alterations of dendritic spines in the CeA and, moreover, whole-cell patch clamp analysis of the basal amygdala to CeA projections showed that alcohol consumption and withdrawal were associated with generation of silent synapses. These plastic changes were impaired in MMP-9 knockout mice. Finally, C/T polymorphism of MMP-9 gene at position -1562, which upregulates MMP-9 expression, correlated with increased motivation for alcohol in alcoholics.

CONCLUSIONS

In aggregate, our results indicate a novel mechanism of alcohol craving that involves MMP-9-dependent synaptic plasticity in CeA.

Abundant collateralization of temporal lobe projections to the accumbens, bed nucleus of stria terminalis, central amygdala and lateral septum

Behavioral flexibility is subserved in part by outputs from the cerebral cortex to telencephalic subcortical structures. In our earlier evaluation of the organization of the cortical-subcortical output system (Reynolds and Zahm, J Neurosci 25:11757-11767, 2005), retrograde double-labeling was evaluated in the prefrontal cortex following tracer injections into pairs of the following subcortical telencephalic structures: caudate-putamen, core and shell of the accumbens (Acb), bed nucleus of stria terminalis (BST) and central nucleus of the amygdala (CeA). The present study was done to assess patterns of retrograde labeling in the temporal lobe after similar paired tracer injections into most of the same telencephalic structures plus the lateral septum (LS). In contrast to the modest double-labeling observed in the prefrontal cortex in the previous study, up to 60-80 % of neurons in the basal and accessory basal amygdaloid nuclei and amygdalopiriform transition area exhibited double-labeling in the present study. The most abundant double-labeling was generated by paired injections into structures affiliated with the extended amygdala, including the CeA, BST and Acb shell. Injections pairing the Acb core with the BST or CeA produced significantly fewer double-labeled neurons. The ventral subiculum exhibited modest amounts of double-labeling associated with paired injections into the Acb, BST, CeA and LS. The results raise the issue of how an extraordinarily collateralized output from the temporal lobe may contribute to behavioral flexibility.

Thalamic Regulation of Sucrose Seeking during Unexpected Reward Omission

The paraventricular nucleus of the thalamus (PVT) is thought to regulate behavioral responses under emotionally arousing conditions. Reward-associated cues activate PVT neurons; however, the specific PVT efferents regulating reward seeking remain elusive. Using a cued sucrose-seeking task, we manipulated PVT activity under two emotionally distinct conditions: (1) when reward was available during the cue as expected or (2) when reward was unexpectedly omitted during the cue. Pharmacological inactivation of the anterior PVT (aPVT), but not the posterior PVT, increased sucrose seeking only when reward was omitted. Consistent with this, photoactivation of aPVT neurons abolished sucrose seeking, and the firing of aPVT neurons differentiated reward availability. Photoinhibition of aPVT projections to the nucleus accumbens or to the amygdala increased or decreased, respectively, sucrose seeking only when reward was omitted. Our findings suggest that PVT bidirectionally modulates sucrose seeking under the negative (frustrative) conditions of reward omission.

The BTBR mouse model of idiopathic autism - Current view on mechanisms

Autism spectrum disorder (ASD) is the most commonly diagnosed neurodevelopmental disorder, with current estimates of more than 1% of affected children across nations. The patients form a highly heterogeneous group with only the behavioral phenotype in common. The genetic heterogeneity is reflected in a plethora of animal models representing multiple mutations found in families of affected children. Despite many years of scientific effort, for the majority of cases the genetic cause remains elusive. It is therefore crucial to include well-validated models of idiopathic autism in studies searching for potential therapeutic agents. One of these models is the BTBR T⁺Itpr3^tf/J mouse. The current review summarizes data gathered in recent research on potential molecular mechanisms responsible for the autism-like behavioral phenotype of this strain.

Altered serum level of matrix metalloproteinase-9 and its association with decision-making in eating disorders

AIM

The aims of this study were to determine whether the serum levels of precursor brain-derived neurotrophic factor (proBDNF), mature BDNF (mBDNF), and matrix metalloproteinase-9 (MMP-9) are altered in patients with eating disorders (ED), including anorexia nervosa (AN) and bulimia nervosa (BN), and to explore whether those levels are associated with decision-making abilities.

METHODS

Nineteen women with AN, 28 women with BN, and 22 age-matched healthy control women (HC) were enrolled in the current study. All participants had their decision-making abilities assessed using the Iowa Gambling Task (IGT). Their eating-related pathophysiology and depressive/anxiety symptoms were also evaluated.

RESULTS

The MMP-9 level in AN was significantly lower than that in either BN or HC, but the serum levels of proBDNF and mBDNF did not differ among the three groups. Investigation of the serum levels of proBDNF and MMP-9 in patients with ED and controls revealed a significant correlation between them. In the BN, there were positive correlations between mBDNF level and IGT performance and also between MMP-9 level and IGT performance, but these correlations did not occur in AN. The MMP-9 level was positively associated with the Symptom Scale, one of the subscales of the Bulimic Investigatory Test, Edinburgh, only in AN.

CONCLUSION

These results suggest that the serum level of MMP-9 plays a role in the pathophysiology of AN, and both the serum levels of mBDNF and MMP-9 may be associated with decision-making abilities in patients with BN.

Matrix Metalloproteinase 9 in Epilepsy: The Role of Neuroinflammation in Seizure Development

Matrix metalloproteinase 9 is a proteolytic enzyme which is recently one of the more often studied biomarkers. Its possible use as a biomarker of neuronal damage in stroke, heart diseases, tumors, multiple sclerosis, and epilepsy is being widely indicated. In epilepsy, MMP-9 is suggested to play a role in epileptic focus formation and in the stimulation of seizures. The increase of MMP-9 activity in the epileptic focus was observed both in animal models and in clinical studies. MMP-9 contributes to formation of epileptic focus, for example, by remodeling of synapses. Its proteolytic action on the elements of blood-brain barrier and activation of chemotactic processes facilitates accumulation of inflammatory cells and induces seizures. Also modification of glutamatergic transmission by MMP-9 is associated with seizures. In this review we will try to recapitulate the results of previous studies about MMP-9 in terms of its association with epilepsy. We will discuss the mechanisms of its actions and present the results revealed in animal models and clinical studies. We will also provide a comparison of the results of various studies on MMP-9 levels in the context of its possible use as a biomarker of the activity of epilepsy.

Spike Timing-Dependent Plasticity in the Mouse Barrel Cortex Is Strongly Modulated by Sensory Learning and Depends on Activity of Matrix Metalloproteinase 9

Experience and learning in adult primary somatosensory cortex are known to affect neuronal circuits by modifying both excitatory and inhibitory transmission. Synaptic plasticity phenomena provide a key substrate for cognitive processes, but precise description of the cellular and molecular correlates of learning is hampered by multiplicity of these mechanisms in various projections and in different types of neurons. Herein, we investigated the impact of associative learning on neuronal plasticity in distinct types of postsynaptic neurons by checking the impact of classical conditioning (pairing whisker stroking with tail shock) on the spike timing-dependent plasticity (t-LTP and t-LTD) in the layer IV to II/III vertical pathway of the mouse barrel cortex. Learning in this paradigm practically prevented t-LTP measured in pyramidal neurons but had no effect on t-LTD. Since classical conditioning is known to affect inhibition in the barrel cortex, we examined its effect on tonic GABAergic currents and found a strong downregulation of these currents in the layer II/III interneurons but not in pyramidal cells. Matrix metalloproteinases emerged as crucial players in synaptic plasticity and learning. We report that the blockade of MMP-9 (but not MMP-3) abolished t-LTP having no effect on t-LTD. Moreover, associative learning resulted in an upregulation of gelatinolytic activity within the "trained" barrel. We conclude that LTP induced by spike timing-dependent plasticity (STDP) paradigm is strongly correlated with associative learning and critically depends on the activity of MMP-9.

Transient ECM protease activity promotes synaptic plasticity

Activity-dependent proteolysis at a synapse has been recognized as a pivotal factor in controlling dynamic changes in dendritic spine shape and function; however, excessive proteolytic activity is detrimental to the cells. The exact mechanism of control of these seemingly contradictory outcomes of protease activity remains unknown. Here, we reveal that dendritic spine maturation is strictly controlled by the proteolytic activity, and its inhibition by the endogenous inhibitor (Tissue inhibitor of matrix metalloproteinases-1 – TIMP-1). Excessive proteolytic activity impairs long-term potentiation of the synaptic efficacy (LTP), and this impairment could be rescued by inhibition of protease activity. Moreover LTP is altered persistently when the ability of TIMP-1 to inhibit protease activity is abrogated, further demonstrating the role of such inhibition in the promotion of synaptic plasticity under well-defined conditions. We also show that dendritic spine maturation involves an intermediate formation of elongated spines, followed by their conversion into mushroom shape. The formation of mushroom-shaped spines is accompanied by increase in AMPA/NMDA ratio of glutamate receptors. Altogether, our results identify inhibition of protease activity as a critical regulatory mechanism for dendritic spines maturation.

Update of neurotrophic factors in neurobiology of addiction and future directions

Drug addiction is a chronic brain disease and drugs of abuse cause long lasting neuroadaptations. Addiction is characterized by the loss of control over drug use despite harmful consequences, and high rates of relapse even after long periods of abstinence. Neurotrophic factors (NTFs) are well known for their actions on neuronal survival in the peripheral nervous system. Moreover, NTFs have been shown to be involved in synaptic plasticity in the brain. Brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) are two of the most studied NTFs and both of them have been reported to increase craving when administered into the mesocorticolimbic dopaminergic system after drug self-administration. Here we review recent data on BDNF and GDNF functions in addiction-related behavior and discuss them in relation to previous findings. Finally, we give an insight into how new technologies could aid in further elucidating the role of these factors in drug addiction.

Differential effects of naloxone on rewarding electrical stimulation of the central nucleus of the amygdala and parabrachial complex in a place preference study

The central nucleus of the amygdala (CeA) is considered to be involved in different affective, sensory, regulatory, and acquisition processes. This study analyzed whether electrical stimulation of the PB-CeA system induces preferences in a concurrent place preference (cPP) task, as observed after stimulation of the parabrachial-insular cortex (PB-IC) axis. It also examined whether the rewarding effects are naloxone-dependent. The results show that electrical stimulation of the CeA and external lateral parabrachial subnucleus (LPBe) induces consistent preference behaviors in a cPP task. However, subcutaneous administration of an opiate antagonist (naloxone; 4mg/ml/kg) blocked the rewarding effect of the parabrachial stimulation but not that of the amygdala stimulation. These results are interpreted in the context of multiple brain reward systems that appear to differ both anatomically and neurochemically, notably with respect to the opiate system.

MMP-9 in translation: from molecule to brain physiology, pathology, and therapy

Matrix metalloproteinase-9 (MMP-9) is a member of the metzincin family of mostly extracellularly operating proteases. Despite the fact that all of these enzymes might be target promiscuous, with largely overlapping catalogs of potential substrates, MMP-9 has recently emerged as a major and apparently unique player in brain physiology and pathology. The specificity of MMP-9 may arise from its very local and time-restricted actions, even when released in the brain from cells of various types, including neurons, glia, and leukocytes. In fact, the quantity of MMP-9 is very low in the naive brain, but it is markedly activated at the levels of enzymatic activity, protein abundance, and gene expression following various physiological stimuli and pathological insults. Neuronal MMP-9 participates in synaptic plasticity by controlling the shape of dendritic spines and function of excitatory synapses, thus playing a pivotal role in learning, memory, and cortical plasticity. When improperly unleashed, MMP-9 contributes to a large variety of brain disorders, including epilepsy, schizophrenia, autism spectrum disorder, brain injury, stroke, neurodegeneration, pain, brain tumors, etc. The foremost mechanism of action of MMP-9 in brain disorders appears to be its involvement in immune/inflammation responses that are related to the enzyme's ability to process and activate various cytokines and chemokines, as well as its contribution to blood-brain barrier disruption, facilitating the extravasation of leukocytes into brain parenchyma. However, another emerging possibility (i.e., the control of MMP-9 over synaptic plasticity) should not be neglected. The translational potential of MMP-9 has already been recognized in both the diagnosis and treatment domains. The most striking translational aspect may be the discovery of MMP-9 up-regulation in a mouse model of Fragile X syndrome, quickly followed by human studies and promising clinical trials that have sought to inhibit MMP-9. With regard to diagnosis, suggestions have been made to use MMP-9 alone or combined with tissue inhibitor of matrix metalloproteinase-1 or brain-derived neurotrophic factor as disease biomarkers. MMP-9, through cleavage of specific target proteins, plays a major role in synaptic plasticity and neuroinflammation, and by those virtues contributes to brain physiology and a host of neurological and psychiatric disorders. This article is part of the 60th Anniversary special issue.

Extracellular proteolysis in structural and functional plasticity of mossy fiber synapses in hippocampus

Brain is continuously altered in response to experience and environmental changes. One of the underlying mechanisms is synaptic plasticity, which is manifested by modification of synapse structure and function. It is becoming clear that regulated extracellular proteolysis plays a pivotal role in the structural and functional remodeling of synapses during brain development, learning and memory formation. Clearly, plasticity mechanisms may substantially differ between projections. Mossy fiber synapses onto CA3 pyramidal cells display several unique functional features, including pronounced short-term facilitation, a presynaptically expressed long-term potentiation (LTP) that is independent of NMDAR activation, and NMDA-dependent metaplasticity. Moreover, structural plasticity at mossy fiber synapses ranges from the reorganization of projection topology after hippocampus-dependent learning, through intrinsically different dynamic properties of synaptic boutons to pre- and postsynaptic structural changes accompanying LTP induction. Although concomitant functional and structural plasticity in this pathway strongly suggests a role of extracellular proteolysis, its impact only starts to be investigated in this projection. In the present report, we review the role of extracellular proteolysis in various aspects of synaptic plasticity in hippocampal mossy fiber synapses. A growing body of evidence demonstrates that among perisynaptic proteases, tissue plasminogen activator (tPA)/plasmin system, β-site amyloid precursor protein-cleaving enzyme 1 (BACE1) and metalloproteinases play a crucial role in shaping plastic changes in this projection. We discuss recent advances and emerging hypotheses on the roles of proteases in mechanisms underlying mossy fiber target specific synaptic plasticity and memory formation.

Matrix Metalloproteinase-9 as a Novel Player in Synaptic Plasticity and Schizophrenia

Recent findings implicate alterations in glutamate signaling, leading to aberrant synaptic plasticity, in schizophrenia. Matrix metalloproteinase-9 (MMP-9) has been shown to regulate glutamate receptors, be regulated by glutamate at excitatory synapses, and modulate physiological and morphological synaptic plasticity. By means of functional gene polymorphism, gene responsiveness to antipsychotics and blood plasma levels MMP-9 has recently been implicated in schizophrenia. This commentary critically reviews these findings based on the hypothesis that MMP-9 contributes to pathological synaptic plasticity in schizophrenia.

Activity dependent CAM cleavage and neurotransmission

Spatially localized proteolysis represents an elegant means by which neuronal activity dependent changes in synaptic structure, and thus experience dependent learning and memory, can be achieved. In vitro and in vivo studies suggest that matrix metalloproteinase and adamalysin activity is concentrated at the cell surface, and emerging evidence suggests that increased peri-synaptic expression, release and/or activation of these proteinases occurs with enhanced excitatory neurotransmission. Synaptically expressed cell adhesion molecules (CAMs) could therefore represent important targets for neuronal activity-dependent proteolysis. Several CAM subtypes are expressed at the synapse, and their cleavage can influence the efficacy of synaptic transmission through a variety of non-mutually exclusive mechanisms. In the following review, we discuss mechanisms that regulate neuronal activity-dependent synaptic CAM shedding, including those that may be calcium dependent. We also highlight CAM targets of activity-dependent proteolysis including neuroligin and intercellular adhesion molecule-5 (ICAM-5). We include discussion focused on potential consequences of synaptic CAM shedding, with an emphasis on interactions between soluble CAM cleavage products and specific pre- and post-synaptic receptors.

Matrix Metalloproteinase-9 Regulates Neuronal Circuit Development and Excitability

In early postnatal development, naturally occurring cell death, dendritic outgrowth, and synaptogenesis sculpt neuronal ensembles into functional neuronal circuits. Here, we demonstrate that deletion of the extracellular proteinase matrix metalloproteinase-9 (MMP-9) affects each of these processes, resulting in maladapted neuronal circuitry. MMP-9 deletion increases the number of CA1 pyramidal neurons but decreases dendritic length and complexity. Parallel changes in neuronal morphology are observed in primary visual cortex and persist into adulthood. Individual CA1 neurons in MMP-9(-/-) mice have enhanced input resistance and a significant increase in the frequency, but not amplitude, of miniature excitatory postsynaptic currents (mEPSCs). Additionally, deletion of MMP-9 significantly increases spontaneous neuronal activity in awake MMP-9(-/-) mice and enhances response to acute challenge by the excitotoxin kainate. Our data document a novel role for MMP-9-dependent proteolysis: the regulation of several aspects of circuit maturation to constrain excitability throughout life.

Matrix metalloproteinase 9 (MMP-9) is indispensable for long term potentiation in the central and basal but not in the lateral nucleus of the amygdala

It has been shown that matrix metalloproteinase 9 (MMP-9) is required for synaptic plasticity, learning and memory. In particular, MMP-9 involvement in long-term potentiation (LTP, the model of synaptic plasticity) in the hippocampus and prefrontal cortex has previously been demonstrated. Recent data suggest the role of MMP-9 in amygdala-dependent learning and memory. Nothing is known, however, about its physiological correlates in the specific pathways in the amygdala. In the present study we show that LTP in the basal and central but not lateral amygdala (LA) is affected by MMP-9 knock-out. The MMP-9 dependency of LTP was confirmed in brain slices treated with a specific MMP-9 inhibitor. The results suggest that MMP-9 plays different roles in synaptic plasticity in different nuclei of the amygdala.

Astrocyte mediated MMP-9 activation in the synapse dysfunction: An implication in Alzheimer disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that occurs due to spasms of the neurons, resulting in loss of memory and behavioral changes. In particular, synaptic loss has been described as an early event in the pathogenesis of AD. The increasing evidences have suggested the role of many matrix metalloproteinase (MMPs) in central nervous system (CNS) pathology. Many studies showed that MMPs enzymes are important for the pathophysiological process during Alzheimer's disease (AD). It is usually believed that the synaptic dysfunction and synapse loss contribute to the cognitive deficits of patients with AD. Cerebrovascular events such as blood-brain barrier (BBB) disruption lead to neuronal damage as well as neuroinflammation. BBB dysfunctions are observed at an early post injury time point, and are associated with activation of proteases, such as MMPs especially MMP-9 which is actively engage in a neuronal injury in the most of the neurodegenerative disorders. BBB opening is accompanied by astrocytic activation, BBB injury and dysregulation of cerebral blood flow. Activated MMPs disrupt neurovascular unit (NVU) which may starve the neurons and affect the synapse function by altering synaptic plasticity and ultimately lead to cognitive decline. However, how MMPs implicated in synaptic dysfunction what are the mechanism associated with this disparity needs to discuss for better understanding the role of MMP-9 in pathogenesis of AD. In this review, we focused on the role of astrocytes and MMP-9 in synaptic dysfunction. We also, underlined possible pharmacological strategies for drug development that might offer more insight into the pathogenesis of cerebrovascular disease such as stroke and Vascular dementia.

Acute nicotine administration increases BOLD fMRI signal in brain regions involved in reward signaling and compulsive drug intake in rats

BACKGROUND

Acute nicotine administration potentiates brain reward function and enhances motor and cognitive function. These studies investigated which brain areas are being activated by a wide range of doses of nicotine, and if this is diminished by pretreatment with the nonselective nicotinic receptor antagonist mecamylamine.

METHODS

Drug-induced changes in brain activity were assessed by measuring changes in the blood oxygen level dependent (BOLD) signal using an 11.1-Tesla magnetic resonance scanner. In the first experiment, nicotine naïve rats were mildly anesthetized and the effect of nicotine (0.03-0.6 mg/kg) on the BOLD signal was investigated for 10 min. In the second experiment, the effect of mecamylamine on nicotine-induced brain activity was investigated.

RESULTS

A high dose of nicotine increased the BOLD signal in brain areas implicated in reward signaling, such as the nucleus accumbens shell and the prelimbic area. Nicotine also induced a dose-dependent increase in the BOLD signal in the striato-thalamo-orbitofrontal circuit, which plays a role in compulsive drug intake, and in the insular cortex, which contributes to nicotine craving and relapse. In addition, nicotine induced a large increase in the BOLD signal in motor and somatosensory cortices. Mecamylamine alone did not affect the BOLD signal in most brain areas, but induced a negative BOLD response in cortical areas, including insular, motor, and somatosensory cortices. Pretreatment with mecamylamine completely blocked the nicotine-induced increase in the BOLD signal.

CONCLUSIONS

These studies demonstrate that acute nicotine administration activates brain areas that play a role in reward signaling, compulsive behavior, and motor and cognitive function.

Synapse rearrangements upon learning: from divergent-sparse connectivity to dedicated sub-circuits

Learning can involve formation of new synapses and loss of synapses, providing memory traces of learned skills. Recent findings suggest that these synapse rearrangements reflect assembly of task-related sub-circuits from initially broadly distributed and sparse connectivity in the brain. These local circuit remodeling processes involve rapid emergence of synapses upon learning, followed by protracted validation involving strengthening of some new synapses, and selective elimination of others. The timing of these consolidation processes can vary. Here, we review these findings, focusing on how molecular/cellular mechanisms of synapse assembly, strengthening, and elimination might interface with circuit/system mechanisms of learning and memory consolidation. An integrated understanding of these learning-related processes should provide a better basis to elucidate how experience, genetic background, and disease influence brain function.

DP-b99 modulates matrix metalloproteinase activity and neuronal plasticity

DP-b99 is a membrane-activated chelator of zinc and calcium ions, recently proposed as a therapeutic agent. Matrix metalloproteinases (MMPs) are zinc-dependent extracellularly operating proteases that might contribute to synaptic plasticity, learning and memory under physiological conditions. In excessive amounts these enzymes contribute to a number of neuronal pathologies ranging from the stroke to neurodegeneration and epileptogenesis. In the present study, we report that DP-b99 delays onset and severity of PTZ-induced seizures in mice, as well as displays neuroprotective effect on kainate excitotoxicity in hippocampal organotypic slices and furthermore blocks morphological reorganization of the dendritic spines evoked by a major neuronal MMP, MMP-9. Taken together, our findings suggest that DP-b99 may inhibit neuronal plasticity driven by MMPs, in particular MMP-9, and thus may be considered as a therapeutic agent under conditions of aberrant plasticity, such as those subserving epileptogenesis.

Tissue inhibitor of matrix metalloproteinases-1 loaded poly(lactic-co-glycolic acid) nanoparticles for delivery across the blood-brain barrier

Aim

The aim of this study was to develop poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) for delivery of a protein – tissue inhibitor of matrix metalloproteinases 1 (TIMP-1) – across the blood–brain barrier (BBB) to inhibit deleterious matrix metalloproteinases (MMPs).

Materials and methods

The NPs were formulated by multiple-emulsion solvent-evaporation, and for enhancing BBB penetration, they were coated with polysorbate 80 (Ps80). We compared Ps80-coated and uncoated NPs for their toxicity, binding, and BBB penetration on primary rat brain capillary endothelial cell cultures and the rat brain endothelial 4 cell line. These studies were followed by in vivo studies for brain delivery of these NPs.

Results

Results showed that neither Ps80-coated nor uncoated NPs caused significant opening of the BBB, and essentially they were nontoxic. NPs without Ps80 coating had more binding to endothelial cells compared to Ps80-coated NPs. Penetration studies showed that TIMP-1 NPs + Ps80 had 11.21%±1.35% penetration, whereas TIMP-1 alone and TIMP-1 NPs without Ps80 coating did not cross the endothelial monolayer. In vivo studies indicated BBB penetration of intravenously injected TIMP-1 NPs + Ps80.

Conclusion

The study demonstrated that Ps80 coating of NPs does not cause significant toxic effects to endothelial cells and that it can be used to enhance the delivery of protein across endothelial cell barriers, both in vitro and in vivo.

Neural ECM proteases in learning and synaptic plasticity

Recent studies implicate extracellular proteases in synaptic plasticity, learning, and memory. The data are especially strong for such serine proteases as thrombin, tissue plasminogen activator, neurotrypsin, and neuropsin as well as matrix metalloproteinases, MMP-9 in particular. The role of those enzymes in the aforementioned phenomena is supported by the experimental results on the expression patterns (at the gene expression and protein and enzymatic activity levels) and functional studies, including knockout mice, specific inhibitors, etc. Counterintuitively, the studies have shown that the extracellular proteolysis is not responsible mainly for an overall degradation of the extracellular matrix (ECM) and loosening perisynaptic structures, but rather allows for releasing signaling molecules from the ECM, transsynaptic proteins, and latent form of growth factors. Notably, there are also indications implying those enzymes in the major neuropsychiatric disorders, probably by contributing to synaptic aberrations underlying such diseases as schizophrenia, bipolar, autism spectrum disorders, and drug addiction.