Increase in polysialyltransferase gene expression following LTP in adult rat dentate gyrus

Psychopharmacological Approaches for Neural Plasticity and Neurogenesis in Major Depressive Disorders

Major depressive disorder (MDD) is a mental health disorder associated with cognitive impairment, dysregulated appetite, fatigue, insomnia or hypersomnia, and severe mood changes that significantly impact the ability of the affected individual to perform day-to-day tasks, leading to suicide in the worst-case scenario. As MDD is becoming more prevalent, affecting roughly 300 million individuals worldwide, its treatment has become a major point of interest. Antidepressants acting as selective serotonin reuptake inhibitors (SSRIs) are currently used as the first line of treatment for MDD. Other antidepressants currently used for the treatment of MDD include the serotonin and norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants (TCAs), and monoamine oxidase inhibitors (MAOIs). However, although effective in alleviating symptoms of MDD, most antidepressants require weeks or even months of regular administration prior to eliciting a rational clinical effect. Owing to the strong evidence showing a relationship between neural plasticity, neurogenesis, and MDD, researchers have also looked at the possibility of using treatment modalities that target these processes in an attempt to improve clinical outcome. The overarching aim of this chapter is to highlight the role of neural plasticity and neurogenesis in the pathophysiology of MDD and discuss the most recently studied treatment strategies that target these processes by presenting supporting evidence from both animal and human studies.

Neural glycomics: the sweet side of nervous system functions

The success of investigations on the structure and function of the genome (genomics) has been paralleled by an equally awesome progress in the analysis of protein structure and function (proteomics). We propose that the investigation of carbohydrate structures that go beyond a cell's metabolism is a rapidly developing frontier in our expanding knowledge on the structure and function of carbohydrates (glycomics). No other functional system appears to be suited as well as the nervous system to study the functions of glycans, which had been originally characterized outside the nervous system. In this review, we describe the multiple studies on the functions of LewisX, the human natural killer cell antigen-1 (HNK-1), as well as oligomannosidic and sialic (neuraminic) acids. We attempt to show the sophistication of these structures in ontogenetic development, synaptic function and plasticity, and recovery from trauma, with a view on neurodegeneration and possibilities to ameliorate deterioration. In view of clinical applications, we emphasize the need for glycomimetic small organic compounds which surpass the usefulness of natural glycans in that they are metabolically more stable, more parsimonious to synthesize or isolate, and more advantageous for therapy, since many of them pass the blood brain barrier and are drug-approved for treatments other than those in the nervous system, thus allowing a more ready access for application in neurological diseases. We describe the isolation of such mimetic compounds using not only Western NIH, but also traditional Chinese medical libraries. With this review, we hope to deepen the interests in this exciting field.

The Role of Cell Adhesion Molecule Genes Regulating Neuroplasticity in Addiction

A variety of genetic approaches, including twin studies, linkage studies, and candidate gene studies, has established a firm genetic basis for addiction. However, there has been difficulty identifying the precise genes that underlie addiction liability using these approaches. This situation became especially clear in genome-wide association studies (GWAS) of addiction. Moreover, the results of GWAS brought into clarity many of the shortcomings of those early genetic approaches. GWAS studies stripped away those preconceived notions, examining genes that would not previously have been considered in the study of addiction, consequently creating a shift in our understanding. Most importantly, those studies implicated a class of genes that had not previously been considered in the study of addiction genetics: cell adhesion molecules (CAMs). Considering the well-documented evidence supporting a role for various CAMs in synaptic plasticity, axonal growth, and regeneration, it is not surprising that allelic variation in CAM genes might also play a role in addiction liability. This review focuses on the role of various cell adhesion molecules in neuroplasticity that might contribute to addictive processes and emphasizes the importance of ongoing research on CAM genes that have been implicated in addiction by GWAS.

Neural Cell Adhesion Molecules of the Immunoglobulin Superfamily Regulate Synapse Formation, Maintenance, and Function

Immunoglobulin superfamily adhesion molecules are among the most abundant proteins in vertebrate and invertebrate nervous systems. Prominent family members are the neural cell adhesion molecules NCAM and L1, which were the first to be shown to be essential not only in development but also in synaptic function and as key regulators of synapse formation, synaptic activity, plasticity, and synaptic vesicle recycling at distinct developmental and activity stages. In addition to interacting with each other, adhesion molecules interact with ion channels and cytokine and neurotransmitter receptors. Mutations in their genes are linked to neurological disorders associated with abnormal development and synaptic functioning. This review presents an overview of recent studies on these molecules and their crucial impact on neurological disorders.

Expression of polysialyltransferases (STX and PST) in adult rat olfactory bulb after an olfactory associative discrimination task

Neuronal plasticity and neurogenesis occur in the adult hippocampus and in other brain structures such as the olfactory bulb and often involve the neural cell adhesion molecule NCAM. During an olfactory associative discrimination learning task, NCAM polysialylation triggers neuronal plasticity in the adult hippocampus. The PST enzyme likely modulates this polysialylation, but not STX, a second sialyltransferase. How the two polysialyltransferases are involved in the adult olfactory bulb remains unknown. We addressed this question by investigating the effect of olfactory associative learning on plasticity and neurogenesis. After a hippocampo-dependent olfactory associative task learning, we measured the expression of both PST and STX polysialyltransferases in the olfactory bulbs of adult rats using quantitative PCR. In parallel, immunohistochemistry was used to evaluate both NCAM polysialylation level and newly-born cells, with or without learning. After learning, no changes were observed neither in the expression level of PST and NCAM polysialylation, nor in STX gene expression level and newly-born cells number in the olfactory bulb.

The effects of morphine treatment on the NCAM and its signaling in the MLDS of rats

Prolonged exposure to opiates induces a constellation of neuroadaptations, especially in the mesolimbic dopamine system (MLDS), which leads to alteration in the function of motivational circuitry. The neural cell adhesion molecule (NCAM) mediates cell-cell interactions and plays an important role in processes associated with neural plasticity. Moreover, it has been shown that NCAM were related to risk of alcoholism in human populations. Here, coimmunoprecipitation and western blotting were used to investigate whether morphine treatment induced alteration of the expression of NCAM or its signaling level in MLDS. The rats receiving escalating dose of morphine treatment were divided into three groups: morphine 1d, 3d and 5d group, which were injected subcutaneously with morphine hydrochloride for 1 day, 3 days and 5 days, respectively. Twelve hours after the last injection, animals were sacrificed and the tissues of ventral tegmental area (VTA), prefrontal cortex (PFC) and nucleus accumbens (NAc) were punched out to examine the expression of NCAM or its signaling level. The results showed that morphine treatment had no significant effect on the expression of NCAM, but downregulated the phosphorylation of NCAM-associated focal adhesion kinase (FAK) in the VTA and PFC of rats. In the NAc of rats, however, the expression of NCAM and its signaling were not altered significantly by morphine treatment. These results indicated that the downregulation of NCAM signaling in the VTA and PFC might be involved in the formation of morphine addiction.

The neural plasticity theory of depression: assessing the roles of adult neurogenesis and PSA-NCAM within the hippocampus

Depression is a devastating and prevalent disease, with profound effects on neural structure and function; however the etiology and neuropathology of depression remain poorly understood. Though antidepressant drugs exist, they are not ideal, as only a segment of patients are effectively treated, therapeutic onset is delayed, and the exact mechanism of these drugs remains to be elucidated. Several theories of depression do exist, including modulation of monoaminergic neurotransmission, alterations in neurotrophic factors, and the upregulation of adult hippocampal neurogenesis, and are briefly mentioned in the review. However none of these theories sufficiently explains the pathology and treatment of depression unto itself. Recently, neural plasticity theories of depression have postulated that multiple aspects of brain plasticity, beyond neurogenesis, may bridge the prevailing theories. The term “neural plasticity” encompasses an array of mechanisms, from the birth, survival, migration, and integration of new neurons to neurite outgrowth, synaptogenesis, and the modulation of mature synapses. This review critically assesses the role of adult hippocampal neurogenesis and the cell adhesion molecule, PSA-NCAM (which is known to be involved in many facets of neural plasticity), in depression and antidepressant treatment.

NCAM function in the adult brain: lessons from mimetic peptides and therapeutic potential

Neural cell adhesion molecules (NCAMs) are complexes of transmembranal proteins critical for cell-cell interactions. Initially recognized as key players in the orchestration of developmental processes involving cell migration, cell survival, axon guidance, and synaptic targeting, they have been shown to retain these functions in the mature adult brain, in relation to plastic processes and cognitive abilities. NCAMs are able to interact among themselves (homophilic binding) as well as with other molecules (heterophilic binding). Furthermore, they are the sole molecule of the central nervous system undergoing polysialylation. Most interestingly polysialylated and non-polysialylated NCAMs display opposite properties. The precise contributions each of these characteristics brings in the regulations of synaptic and cellular plasticity in relation to cognitive processes in the adult brain are not yet fully understood. With the aim of deciphering the specific involvement of each interaction, recent developments led to the generation of NCAM mimetic peptides that recapitulate identified binding properties of NCAM. The present review focuses on the information such advances have provided in the understanding of NCAM contribution to cognitive function.

PSA-NCAM: synaptic functions mediated by its interactions with proteoglycans and glutamate receptors

Dynamic regulation of glycosylation of the neural cell adhesion molecule (NCAM) by an unusual large negatively charged polysialic acid (PSA) is the major prerequisite for correct formation of brain circuitries during development and for normal synaptic plasticity, learning and memory in the adult. Traditionally, PSA is viewed as a de-adhesive highly hydrated molecule, which interferes with cell adhesion and promotes cellular/synaptic dynamics by steric hindrance. Analysis of synaptic functions of PSA-NCAM highlighted additional features of this molecule. First, PSA promotes interaction of NCAM with heparan sulfate proteoglycans and thus stimulates synaptogenesis. Second, PSA-NCAM modulates glutamate receptors: it restrains activity of extrasynaptic GluN2B-containing NMDA receptors and facilitates activity of a subset of AMPA receptors. Perturbation in polysialylation and/or NCAM expression in mouse models recapitulates many symptoms of human brain disorders such as schizophrenia, depression, anxiety and Alzheimer's disease.