Studying synaptic plasticity in the human brain and opportunities for drug discovery

Repetitive Transcranial Magnetic Stimulation-Induced Neuroplasticity and the Treatment of Psychiatric Disorders: State of the Evidence and Future Opportunities

Neuroplasticity, or activity-dependent neuronal change, is a crucial mechanism underlying the mechanisms of effect of many therapies for neuropsychiatric disorders, one of which is repetitive transcranial magnetic stimulation (rTMS). Understanding the neuroplastic effects of rTMS at different biological scales and on different timescales and how the effects at different scales interact with each other can help us understand the effects of rTMS in clinical populations and offers the potential to improve treatment outcomes. Several decades of research in the fields of neuroimaging and blood biomarkers is increasingly showing its clinical relevance, allowing measurement of the synaptic, functional, and structural changes involved in neuroplasticity in humans. In this narrative review, we describe the evidence for rTMS-induced neuroplasticity at multiple levels of the nervous system, with a focus on the treatment of psychiatric disorders. We also describe the relationship between neuroplasticity and clinical effects, discuss methods to optimize neuroplasticity, and identify future research opportunities in this area.

Synaptic plasticity and mental health: methods, challenges and opportunities

Activity-dependent synaptic plasticity is a ubiquitous property of the nervous system that allows neurons to communicate and change their connections as a function of past experiences. Through reweighting of synaptic strengths, the nervous system can remodel itself, giving rise to durable memories that create the biological basis for mental function. In healthy individuals, synaptic plasticity undergoes characteristic developmental and aging trajectories. Dysfunctional plasticity, in turn, underlies a wide spectrum of neuropsychiatric disorders including depression, schizophrenia, addiction, and posttraumatic stress disorder. From a mechanistic standpoint, synaptic plasticity spans the gamut of spatial and temporal scales, from microseconds to the lifespan, from microns to the entire nervous system. With the numbers and strengths of synapses changing on such wide scales, there is an important need to develop measurement techniques with complimentary sensitivities and a growing number of approaches are now being harnessed for this purpose. Through hemodynamic measures, structural and tracer imaging, and noninvasive neuromodulation, it is possible to image structural and functional changes that underlie synaptic plasticity and associated behavioral learning. Here we review the mechanisms of neural plasticity and the historical and future trends in techniques that allow imaging of synaptic changes that accompany psychiatric disorders, highlighting emerging therapeutics and the challenges and opportunities accompanying this burgeoning area of study.

GluA3-containing AMPA receptors: From physiology to synaptic dysfunction in brain disorders

In the mammalian brain, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors (AMPARs) play a fundamental role in the activation of excitatory synaptic transmission and the induction of different forms of synaptic plasticity. The modulation of the AMPAR tetramer subunit composition at synapses defines the functional properties of the receptor. During the last twenty years, several studies have evaluated the roles played by each subunit, from GluA1 to GluA4, in both physiological and pathological conditions. Here, we have focused our attention on GluA3-containing AMPARs, addressing their functional role in synaptic transmission and synaptic plasticity and their involvement in a variety of brain disorders. Although several aspects remain to be fully understood, GluA3 is a widely expressed and functionally relevant subunit in AMPARs involved in several brain circuits, and its pharmacological modulation could represent a novel approach for the rescue of altered glutamatergic synapses associated with neurodegenerative and neurodevelopmental disorders.

Neuroplasticity as a convergent mechanism of ketamine and classical psychedelics

The emerging therapeutic efficacy of ketamine and classical psychedelics for depression has inspired tremendous interest in the underlying neurobiological mechanisms. We review preclinical and clinical evidence supporting neuroplasticity as a convergent downstream mechanism of action for these novel fast-acting antidepressants. Through their primary glutamate or serotonin receptor targets, ketamine and psychedelics [psilocybin, lysergic acid diethylamide (LSD), and N,N-dimethyltryptamine (DMT)] induce synaptic, structural, and functional changes, particularly in pyramidal neurons in the prefrontal cortex. These include increased glutamate release, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) activation, brain-derived neurotrophic factor (BDNF) and mammalian target of rapamycin (mTOR)-mediated signaling, expression of synaptic proteins, and synaptogenesis. Such influences may facilitate adaptive rewiring of pathological neurocircuitry, thus providing a neuroplasticity-focused framework to explain the robust and sustained therapeutic effects of these compounds.

Determinants of Neural Plastic Changes Induced by Motor Practice

Short-term motor practice leads to plasticity in the primary motor cortex (M1). The purpose of this study is to investigate the factors that determine the increase in corticospinal tract (CST) excitability after motor practice, with special focus on two factors; “the level of muscle activity” and “the presence/absence of a goal of keeping the activity level constant.” Fifteen healthy subjects performed four types of rapid thumb adduction in separate sessions. In the “comfortable task” (C) and “forceful task” (F), the subjects adducted their thumb using comfortable and strong forces. In the “comfortable with a goal task” (CG) and “forceful with a goal task” (FG), subjects controlled the muscle activity at the same level as in the C and F, respectively, by adjusting the peak electromyographic amplitude within the target ranges. Paired associative stimulation (PAS), which combines peripheral nerve (median nerve) stimulation and transcranial magnetic stimulation (TMS), with an inter-stimulus interval of 25 ms (PAS25) was also done. Before and after the motor tasks and PAS25, TMS was applied to the M1. None of the four tasks showed any temporary changes in behavior, meaning no learning occurred. Motor-evoked potential (MEP) amplitude increased only after the FG and it exhibited a positive correlation with the MEP increase after PAS25, suggesting that FG and PAS25 share at least similar plasticity mechanisms in the M1. Resting motor threshold (RMT) decreased only after FG, suggesting that FG would also be associated with the membrane depolarization of M1 neurons. These results suggest task-dependent plasticity from the synergistic effect of forceful muscle activity and of setting a goal of keeping the activity level constant.

Optimising Cognitive Enhancement: Systematic Assessment of the Effects of tDCS Duration in Older Adults

Transcranial direct current stimulation (tDCS) has been shown to support cognition and brain function in older adults. However, there is an absence of research specifically designed to determine optimal stimulation protocols, and much of what is known about subtle distinctions in tDCS parameters is based on young adult data. As the first systematic exploration targeting older adults, this study aimed to provide insight into the effects of variations in stimulation duration. Anodal stimulation of 10 and 20 min, as well as a sham-control variant, was administered to dorsolateral prefrontal cortex. Stimulation effects were assessed in relation to a novel attentional control task. Ten minutes of anodal stimulation significantly improved task-switching speed from baseline, contrary to the sham-control and 20 min variants. The findings represent a crucial step forwards for methods development, and the refinement of stimulation to enhance executive function in the ageing population.

CRISPR/Cas9: Nature's gift to prokaryotes and an auspicious tool in genome editing

Clustered regularly interspaced short palindromic repeats (CRISPR) is a family of DNA direct repeats found in many prokaryotic genomes. It was discovered in bacteria as their (adaptive) immune system against invading viruses. Cas9 is an endonuclease enzyme linked with the CRISPR system in bacteria. Bacteria use the Cas9 enzyme to chop viral DNA sequences by unwinding it and then finding the complementary base pairs to the guide RNA. CRISPR/Cas9 is a modern and powerful molecular biology approach that is widely used in genome engineering (to activate/repress gene expression). It can be used in vivo to cause targeted genome modifications with better efficiency as compared to meganucleases, zinc-finger nucleases and transcription activator-like effector nucleases. CRISPR/Cas9 is a simple, reliable, and rapid method for causing gene alterations that open new horizons of gene editing in a variety of living organisms, including humans, for the treatment of several diseases. In this short review, we explored the basic mechanisms underlying its working principles along with some of its current applications in a number of diverse fields.

Alcohol and the Developing Brain: Why Neurons Die and How Survivors Change

The consequences of alcohol drinking during pregnancy are dramatic and usually referred to as fetal alcohol spectrum disorders (FASD). This condition is one of the main causes of intellectual disability in Western countries. The immature fetal brain exposed to ethanol undergoes massive neuron death. However, the same mechanisms leading to cell death can also be responsible for changes of developmental plasticity. As a consequence of such a maladaptive plasticity, the functional damage to central nervous system structures is amplified and leads to permanent sequelae. Here we review the literature dealing with experimental FASD, focusing on the alterations of the cerebral cortex. We propose that the reciprocal interaction between cell death and maladaptive plasticity represents the main pathogenetic mechanism of the alcohol-induced damage to the developing brain.

Neural plasticity and network remodeling: From concepts to pathology

Neuroplasticity has been subject to a great deal of research in the last century. Recently, significant emphasis has been placed on the global effect of localized plastic changes throughout the central nervous system, and on how these changes integrate in a pathological context. Specifically, alterations of network functionality have been described in various pathological contexts to which corresponding structural alterations have been proposed. However, considering the amount of literature and the different pathological contexts, an integration of this information is still lacking. In this paper we will review the concepts of neural plasticity as well as their repercussions on network remodeling and provide a possible explanation to how these two concepts relate to each other. We will further examine how alterations in different pathological contexts may relate to each other and will discuss the concept of plasticity diseases, its models and implications.

Stimulating somatosensory psychophysics: a double-blind, sham-controlled study of the neurobiological mechanisms of tDCS

The neuromodulation technique transcranial direct current stimulation (tDCS) is thought to produce its effects on behavior by altering cortical excitability. Although the mechanisms underlying the observed effects are thought to rely on the balance of excitatory and inhibitory neurotransmission, the physiological principles of the technique are not completely understood. In this study, we examine the influence of tDCS on vibrotactile adaptation, using a simple amplitude discrimination paradigm that has been shown to exhibit modifications in performance due to changes in inhibitory neurotransmission. Double-blind tDCS (Anodal/Sham) of 1 mA was delivered for 600 s to electrodes positioned in a somatosensory/contralateral orbit montage. Stimulation was applied as part of a pre/post design, between blocks of the behavioral tasks. In accordance with previous work, results obtained before the application of tDCS indicated that amplitude discrimination thresholds were significantly worsened during adaptation trials, compared to those achieved at baseline. However, tDCS failed to modify amplitude discrimination performance. Using a Bayesian approach, this finding was revealed to constitute substantial evidence for the null hypothesis. The failure of DC stimulation to alter vibrotactile adaptation thresholds is discussed in the context of several factors that may have confounded the induction of changes in cortical plasticity.

Relationship Between Non-invasive Brain Stimulation-induced Plasticity and Capacity for Motor Learning

BACKGROUND

Cortical plasticity plays a key role in motor learning (ML). Non-invasive brain stimulation (NIBS) paradigms have been used to modulate plasticity in the human motor cortex in order to facilitate ML. However, little is known about the relationship between NIBS-induced plasticity over M1 and ML capacity.

HYPOTHESIS

NIBS-induced MEP changes are related to ML capacity.

METHODS

56 subjects participated in three NIBS (paired associative stimulation, anodal transcranial direct current stimulation and intermittent theta-burst stimulation), and in three lab-based ML task (serial reaction time, visuomotor adaptation and sequential visual isometric pinch task) sessions.

ANALYSIS

After clustering the patterns of response to the different NIBS protocols, we compared the ML variables between the different patterns found. We used regression analysis to explore further the relationship between ML capacity and summary measures of the MEPs change. We ran correlations with the "responders" group only.

RESULTS

We found no differences in ML variables between clusters. Greater response to NIBS protocols may be predictive of poor performance within certain blocks of the VAT. "Responders" to AtDCS and to iTBS showed significantly faster reaction times than "non-responders." However, the physiological significance of these results is uncertain.

CONCLUSION

MEP changes induced in M1 by PAS, AtDCS and iTBS appear to have little, if any, association with the ML capacity tested with the SRTT, the VAT and the SVIPT. However, cortical excitability changes induced in M1 by AtDCS and iTBS may be related to reaction time and retention of newly acquired skills in certain motor learning tasks.

Increased prefrontal cortex neurogranin enhances plasticity and extinction learning

Increasing plasticity in neurons of the prefrontal cortex (PFC) has been proposed as a possible therapeutic tool to enhance extinction, a process that is impaired in post-traumatic stress disorder, schizophrenia, and addiction. To test this hypothesis, we generated transgenic mice that overexpress neurogranin (a calmodulin-binding protein that facilitates long-term potentiation) in the PFC. Neurogranin overexpression in the PFC enhanced long-term potentiation and increased the rates of extinction learning of both fear conditioning and sucrose self-administration. Our results indicate that elevated neurogranin function within the PFC can enhance local plasticity and increase the rate of extinction learning across different behavioral tasks. Thus, neurogranin can provide a molecular link between enhanced plasticity and enhanced extinction.

Endogenous cardiotonic steroids in kidney failure: a review and an hypothesis

In response to progressive nephron loss, volume and humoral signals in the circulation have increasing relevance. These signals, including plasma sodium, angiotensin II, and those related to volume status, activate a slow neuromodulatory pathway within the central nervous system (CNS). The slow CNS pathway includes specific receptors for angiotensin II, mineralocorticoids, and endogenous ouabain (EO). Stimulation of the pathway leads to elevated sympathetic nervous system activity (SNA) and increased circulating EO. The sustained elevation of circulating EO (or ouabain) stimulates central and peripheral mechanisms that amplify the impact of SNA on vascular tone. These include changes in synaptic plasticity in the brain and sympathetic ganglia that increase preganglionic tone and amplify ganglionic transmission, amplification of the impact of SNA on arterial tone in the vascular wall, and the reprogramming of calcium signaling proteins in arterial myocytes. These increase SNA, raise basal and evoked arterial tone, and elevate blood pressure (BP). In the setting of CKD, we suggest that sustained activation/elevation of the slow CNS pathway, plasma EO, and the cardiotonic steroid marinobufagenin, comprises a feed-forward system that raises BP and accelerates kidney and cardiac damage. Block of the slow CNS pathway and/or circulating EO and marinobufagenin may reduce BP and slow the progression to ESRD.

Abnormality of the corpus callosum in coalmine gas explosion-related posttraumatic stress disorder

Abnormal corpus callosum (CC) has been reported in childhood trauma-related posttraumatic stress disorder (PTSD); however, the nature of white matter (WM) integrity alterations in the CC of young adult-onset PTSD patients is unknown. In this study, 14 victims of a coal mine gas explosion with PTSD and 23 matched coal miners without experiencing the coal mine explosion were enrolled. The differences in fractional anisotropy (FA) within 7 sub-regions of the CC were compared between the two groups. Compared to the controls, PTSD coal miners exhibited significantly reduced FA values in the anterior sub-regions of the CC (P < 0.05, Bonferroni-corrected), which mainly interconnect the bilateral frontal cortices. Our findings indicated that the anterior part of the CC was more severely impaired than the posterior part in young adult-onset PTSD, which suggested the patterns of CC impairment may depend on the developmental stage of the structure when the PTSD occurs.

Higher integrity of the motor and visual pathways in long-term video game players

Long term video game players (VGPs) exhibit superior visual and motor skills compared with non-video game control subjects (NVGCs). However, the neural basis underlying the enhanced behavioral performance remains largely unknown. To clarify this issue, the present study compared the whiter matter integrity within the corticospinal tracts (CST), the superior longitudinal fasciculus (SLF), the inferior longitudinal fasciculus (ILF), and the inferior fronto-occipital fasciculus (IFOF) between the VGPs and the NVGCs using diffusion tensor imaging. Compared with the NVGCs, voxel-wise comparisons revealed significantly higher fractional anisotropy (FA) values in some regions within the left CST, left SLF, bilateral ILF, and IFOF in VGPs. Furthermore, higher FA values in the left CST at the level of cerebral peduncle predicted a faster response in visual attention tasks. These results suggest that higher white matter integrity in the motor and higher-tier visual pathways is associated with long-term video game playing, which may contribute to the understanding on how video game play influences motor and visual performance.

The pain of pain: challenges of animal behavior models

Berend Olivier has had a long-standing interest in the utility of animal models for a wide variety of therapeutic indications. His work has spanned multiple types of models, blending ethological, or species typical and naturalistic behaviors, along with methodologies based on learned behavior. He has consistently done so, from an analytical as well as predictive perspective, and has made multiple contributions while working in both the pharmaceutical industry and within an academic institution. Although focused primarily on psychiatric disorders, Berend has conducted research in the area of pain in humans and in animals, demonstrating an expansive appreciation for the breadth, scope and significance of the science and applications of the discipline of pharmacology to these diverse areas. This review focuses on the use of animal models in pain research from the perspective of the long-standing deficiencies in the development of therapeutics in this area and from a preclinical perspective where the translational weaknesses have been quite problematic. The challenges confronting animal models of pain, however, are not unique to this area of research, as they cut across several therapeutic areas. Despite the deficiencies, failures and concerns, existing animal models of pain continue to be of widespread use and are essential to progress in pain research as well as in other areas. Although not focusing on specific animal models of pain, this paper seeks to examine general issues facing the use of these models. It does so by exploring alternative approaches which capture recent developments, which build upon principles and concepts we have learned from Berend's contributions, and which provide the prospect of helping to address the absence of novel therapeutics in this area.

Genetic risk for schizophrenia: convergence on synaptic pathways involved in plasticity

Recent large-scale genomic studies have revealed two broad classes of risk alleles for schizophrenia: a polygenic component of risk mediated through multiple common risk variants and rarer more highly penetrant submicroscopic chromosomal deletions and duplications, known as copy number variants. The focus of this review is on the emerging findings from the latter and subsequent exome sequencing data of smaller, deleterious single nucleotide variants and indels. In these studies, schizophrenia patients were found to have enriched de novo mutations in genes belonging to the postsynaptic density at glutamatergic synapses, particularly components of the N-methyl-D-aspartate receptor signaling complex, including the PSD-95 complex, activity-regulated cytoskeleton-associated protein interactors, the fragile X mental retardation protein complex, voltage-gated calcium channels, and genes implicated in actin cytoskeletal dynamics. The convergence of these implicated genes onto a coherent biological pathway at the synapse, with a specific role in plasticity, provides a significant advance in understanding pathogenesis and points to new targets for biological investigation. We consider the implications of these studies in the context of existing genetic data and the potential need to reassess diagnostic boundaries of neuropsychiatric disorders before discussing ways forward for more directed mechanistic studies to develop stratified, novel therapeutic approaches in the future.

Cannabinoids prevent the effects of a footshock followed by situational reminders on emotional processing

Posttraumatic stress disorder (PTSD) can develop following exposure to a traumatic event. Hence, what we do in the first few hours after trauma exposure may alter the trajectory of PTSD. We examined whether cannabinoids can prevent the effects of a single footshock followed by situational reminders (SRs) on emotional processing. Rats were exposed to a footshock (1.5 mA, 10 s) on day 1 followed by exposure to SRs of the shock on days 3 and 5. The CB1/2 receptor agonist WIN55,212-2 or vehicle were injected intraperitoneally 2 h after the shock. After 1 week, PTSD-like symptoms were examined. Exposure to SRs exacerbated the effects of the shock as rats exposed to shock and SRs, but not shock alone, showed impaired extinction of the traumatic event, impaired plasticity in the hippocmapal-accumbens pathway, enhanced latency to startle, and altered expression of CB1 receptors (CB1r) and glucocorticoid receptors (GRs) in the CA1, basolateral amygdala (BLA) and prefrontal cortex (PFC). WIN55,212-2 prevented the effects of the shock and SRs on extinction, plasticity, and startle response. WIN55,212-2 normalized the shock/SR-induced upregulation in CB1r in the PFC, and CA1 and GRs in the CA1, with no effect on BLA downregulation of CB1r and GRs. Shock and SRs caused lasting (1 week) alterations in emotional processing associated with changes in GR and CB1r expression in brain areas related to PTSD. WIN55,212-2 administered after trauma exposure prevented these alterations via PFC- and CA1-CB1r and CA1-GRs.

Late cortical plasticity in motor and auditory cortex: role of met-allele in BDNF Val66Met polymorphism

The brain-derived neurotropic factor (BDNF) Val66Met polymorphism has been associated with abnormalities of synaptic plasticity in animal models, and abnormalities in motor cortical plasticity have also been described in humans using transcranial direct current stimulation. No study has yet been done on plasticity in non-motor regions, and the effect of two Met alleles (i.e. 'Met dose') is not well understood. We studied the effect of the BDNF Val66Met polymorphism on the after-effects of transcranial direct current stimulation and tetanic auditory stimulation in 65 subjects (23; Val66Val, 22; Val66Met and 20; Met66Met genotypes). In the first session, motor evoked potentials (MEP) were recorded under stereotaxic guidance for 90 min after 9 min of anodal transcranial direct current stimulation (TDCS). In the second session, auditory-evoked potentials (AEP) were recorded before and after 2 min of auditory 13 Hz tetanic stimulation. There was a difference in MEP facilitation post-TDCS comparing Met carriers with non-Met carriers, with Met carriers having a modest late facilitation at 30-90 min. There was no difference in responses between Val66Met genotype and Met66Met genotype subjects. Tetanic auditory stimulation also produced late facilitation of N1-P2 AEP at 25 min, but there was no apparent effect of genetic status. This study indicates that Met66Met carriers behave like Val66Met carriers for TDCS-induced plasticity, and produce a late facilitation of MEPs. Auditory cortical plasticity was not affected by the BDNF Val66Met polymorphism. This study sheds light on the differences between auditory and motor cortical plasticity and the role of the BDNF Val66Met polymorphism.

BDNF serum levels in subjects developing or not post-traumatic stress disorder after trauma exposure

Post-traumatic stress disorder (PTSD) is a syndrome resulting from exposure to a severe traumatic event that poses threatened death or injury and produces intense fear and helplessness. The neural structures implicated in PTSD development belong to the limbic system, an important region for emotional processing. Brain-derived neurotrophic factor (BDNF) is a neurotrophin that serves as survival factor for selected populations of central nervous system (CNS) neurons and plays a role in the limbic system by regulating synaptic plasticity, memory processes and behavior. Impaired BDNF production in the brain can lead to a variety of CNS dysfunctions including symptoms associated with PTSD. However, so far fewer studies have investigated this neurotrophin in patients with PTSD. Furthermore, given the multiple role of BDNF in various CNS disorders, it cannot be excluded that traumatic events per se may influence neurotrophin levels, without a direct association to the PTSD syndrome. To elucidate these issues, in this study we analyzed BDNF serum levels in two groups of subjects: patients with trauma exposure who developed PTSD, and subjects with trauma exposure who did not develop PTSD. We found that BDNF serum levels were lower in PTSD patients as compared to related control subjects. Thus, these data suggest that BDNF might be involved in pathophysiology of PTSD and consequently therapeutic approaches aimed at restoring BDNF serum levels may be beneficial to this pathology.

Enzymatic activity of CaMKII is not required for its interaction with the glutamate receptor subunit GluN2B

Binding of the Ca²⁺/calmodulin (CaM)-dependent protein kinase II (CaMKII) to the NMDA-type glutamate receptor subunit GluN2B is an important control mechanism for the regulation of synaptic strength. CaMKII binding to GluN2B and CaMKII translocation to synapses are induced by an initial Ca²⁺/CaM stimulus, which also activates the kinase. Indeed, several mechanistically different CaMKII inhibitors [tatCN21 and KN-93 (N-[2-[[[3-(4-chlorophenyl)-2-propenyl]methylamino]methyl]phenyl]-N-(2-hydroxyethyl)-4-methoxybenzenesulphonamide)] and inactivating mutations (K42M, A302R, and T305/T306D) impair this interaction, suggesting that it requires CaMKII enzymatic activity. However, this study shows that two general kinase inhibitors, H7 [1-(5-isoquinolinylsulfonyl)-2-methylpiperazine] and staurosporine (Sta), which inhibit CaMKII activity by yet another mechanism, did not interfere with GluN2B binding in vitro or within cells. In contrast to a previous report, we found that Sta, like H7, inhibited CaMKII in an ATP-competitive manner. Nucleotide binding significantly enhances CaMKII/GluN2B binding in vitro, but the nucleotide competition by H7 or Sta did not prevent this effect and instead even mimicked it. H7 (700 µM) and Sta (2 µM) efficiently blocked enzymatic activity of CaMKII, both in vitro and within cells. However, neither H7 nor Sta prevented Ca²⁺-induced translocation of CaMKII to GluN2B in heterologous cells or to synapses in hippocampal neurons. Thus, activity of CaMKII (or of any other kinase inhibited by H7 or Sta) is not required for stimulation-induced GluN2B-binding or synaptic translocation of CaMKII, despite previous indication to the contrary. This shows that results with inhibitors and inhibiting mutants can be caused by structural effects independent from catalytic activity, and that detailed understanding of the mechanisms is required for their interpretation.

Increased neuroplasticity may protect against cardiovascular disease

Neuroplasticity refers to the capacity of the nervous system to modify its organization such that the brain can be shaped by environmental input. Individuals exhibit different degrees of neuroplasticity because of their different courses of growth. Neuroplasticity may thus play a role in individual differences in the treatment of neuropsychiatric diseases. The nervous system monitors and coordinates internal organ function. Thus neuroplasticity may also be associated with the pathogenesis and the treatment of some other diseases besides neuropsychiatric diseases. The cardiovascular system is controlled by the nervous system, mainly by the autonomic nervous system. Stress may lead to depression and cardiovascular disease (CVD). CVD is associated with depression, which is a disorder of decreased neuroplasticity. And the mechanisms of depression and CVD are related. So we conclude that decreased neuroplasticity causes the coexistence of depression with CVD, and increased neuroplasticity may be beneficial against the development of CVD. This theory provides another angle that can explain some of the reported phenomena related to CVD and neuropsychiatry and provide a potential treatment to protect against CVD.

Molecular and cellular mechanisms of antidepressant action

A long-standing theory is that brain monoamine signalling is critically involved in the mechanisms of antidepressant drug treatment. Theories on the nature of these mechanisms commenced with ideas developed in the 1960s that the drugs act simply by increasing monoamine availability in the synapse. However, this thinking has advanced remarkably in the last decade to concepts which position that antidepressant drug action on monoamine signalling is just the starting point for a complex sequence of neuroadaptive molecular and cellular changes that bring about the therapeutic effect. These changes include activation of one or more programmes of gene expression that leads to the strengthening of synaptic efficacy and connectivity, and even switching neural networks into a more immature developmental state. It is thought that through this increase in plasticity, key neural circuits within the limbic system are more easily remodelled by incoming emotionally relevant stimuli. This article attempts to bring together previous and current knowledge of antidepressant drug action on monoamine signalling at molecular and cellular levels, and introduces current thinking that these changes interact with neuropsychological processes ultimately to elevate mood.

An epigenetic framework for neurodevelopmental disorders: from pathogenesis to potential therapy

Neurodevelopmental disorders (NDDs) are characterized by aberrant and delayed early-life development of the brain, leading to deficits in language, cognition, motor behaviour and other functional domains, often accompanied by somatic symptoms. Environmental factors like perinatal infection, malnutrition and trauma can increase the risk of the heterogeneous, multifactorial and polygenic disorders, autism and schizophrenia. Conversely, discrete genetic anomalies are involved in Down, Rett and Fragile X syndromes, tuberous sclerosis and neurofibromatosis, the less familiar Phelan-McDermid, Sotos, Kleefstra, Coffin-Lowry and "ATRX" syndromes, and the disorders of imprinting, Angelman and Prader-Willi syndromes. NDDs have been termed "synaptopathies" in reference to structural and functional disturbance of synaptic plasticity, several involve abnormal Ras-Kinase signalling ("rasopathies"), and many are characterized by disrupted cerebral connectivity and an imbalance between excitatory and inhibitory transmission. However, at a different level of integration, NDDs are accompanied by aberrant "epigenetic" regulation of processes critical for normal and orderly development of the brain. Epigenetics refers to potentially-heritable (by mitosis and/or meiosis) mechanisms controlling gene expression without changes in DNA sequence. In certain NDDs, prototypical epigenetic processes of DNA methylation and covalent histone marking are impacted. Conversely, others involve anomalies in chromatin-modelling, mRNA splicing/editing, mRNA translation, ribosome biogenesis and/or the regulatory actions of small nucleolar RNAs and micro-RNAs. Since epigenetic mechanisms are modifiable, this raises the hope of novel therapy, though questions remain concerning efficacy and safety. The above issues are critically surveyed in this review, which advocates a broad-based epigenetic framework for understanding and ultimately treating a diverse assemblage of NDDs ("epigenopathies") lying at the interface of genetic, developmental and environmental processes. This article is part of the Special Issue entitled 'Neurodevelopmental Disorders'.

Role of presynaptic metabotropic glutamate receptors in the induction of long-term synaptic plasticity of vesicular release

While postsynaptic ionotropic and metabotropic glutamate receptors have received the lions share of attention in studies of long-term activity-dependent synaptic plasticity, it is becoming clear that presynaptic metabotropic glutamate receptors play critical roles in both short-term and long-term plasticity of vesicular transmitter release, and that they act both at the level of voltage-dependent calcium channels and directly on proteins of the vesicular release machinery. Activation of G protein-coupled receptors can transiently inhibit vesicular release through the release of Gβγ which binds to both voltage-dependent calcium channels to reduce calcium influx, and directly to the C-terminus region of the SNARE protein SNAP-25. Our recent work has revealed that the binding of Gβγ to SNAP-25 is necessary, but not sufficient, to elicit long-term depression (LTD) of vesicular glutamate release, and that the concomitant release of Gα(i) and the second messenger nitric oxide are also necessary steps in the presynaptic LTD cascade. Here, we review the current state of knowledge of the molecular steps mediating short-term and long-term plasticity of vesicular release at glutamatergic synapses, and the many gaps that remain to be addressed. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.