European Journal of Pharmacology (v.719, #1-3)
Editorial Board (i).
Willem Hendrik Gispen – An interview by P.R. Bär (2-8).
This text is based on three long interviews in Utrecht University′s Faculty Club, and on almost 40 years of working together in the same city, the same department, the same university.
Keywords: Willem Hendrik Gispen; Interview; Rudolf Magnus Institute; Utrecht University; De Smet; Tolkien; Poetry; Bird watching; Marsman; Achterberg; FENS; Memory; Grooming; Behaviour; Utrecht; De Wied; B50; Kingfisher;
From molecule to market access: Drug regulatory science as an upcoming discipline by Christine C. Gispen-de Wied; Hubertus G.M. Leufkens (9-15).
Regulatory science as a discipline has evolved over the past years with the object to boost and promote scientific rationale behind benefit/risk and decision making by regulatory authorities. The European Medicines Agency, EMA, the Food and Drug Administration, FDA, and the Japanese Pharmaceutical and Medical Devices Agency, PMDA, highlighted in their distinct ways the importance of regulatory science as a basis of good quality assessment in their strategic plans. The Medicines Evaluation Board, MEB, states: ‘regulatory science is the science of developing and validating new standards and tools to evaluate and assess the benefit/risk of medicinal products, facilitating sound and transparent regulatory decision making’. Through analysis of regulatory frameworks itself and their effectiveness, however, regulatory science can also advance knowledge of these systems in general. The comprehensive guidance that is issued to complete an application dossier for regulatory product approval has seldomly been scrutinized for its efficiency. Since it is the task of regulatory authorities to protect and promote public health, it is understood that they take a cautious approach in regulating drugs prior to market access. In general, the authorities are among the first to be blamed if dangerous or useless drugs were allowed to the market. Yet, building a regulatory framework that is not challenged continuously in terms of deliverables for public health and cost-effectiveness, might be counterproductive in the end. Regulatory science and research can help understand how and why regulatory decisions are made, and where renewed discussions may be warranted. The MEB supports regulatory science as an R&D activity to fuel primary regulatory processes on product evaluation and vigilance, but also invests in a ‘looking into the mirror’ approach. Along the line of the drug life-cycle, publicly available data are reviewed and their regulatory impact highlighted. If made explicit, regulatory research can open the door to evidence based regulatory practice and serve the regulator's contribution to innovative drug licensing today.
Keywords: Regulatory science; Drug development; Benefit-risk assessment; Market authorization; Post-marketing surveillance;
A human rights view on access to controlled substances for medical purposes under the international drug control framework by Marie Elske C. Gispen (16-24).
The world is confronted with a major public health deficit caused by poor access to controlled essential medicines under the international drug control framework. This is affecting millions of patients on a daily basis and resulting in numerous human rights violations. The present review contextualises this deficit from a human rights perspective. Drug control efforts are informed by a twofold objective stemming from the double nature of scheduled substances: free access for medical purposes should be ensured, though non-medical use of substances such as opium should be restricted. The international drug control framework is, in theory, based on this twofold notion, however at the level of interpretation, monitoring, and implementation, a one-sided emphasis is demonstrated. By tracing a parallel between the obligations of states under the international drug control framework and those that derive from human rights law, the review shows that the two systems seem incoherent and conflicting in nature and flags the importance of cross-disciplinary research into drug control and human rights.
Keywords: Controlled substance; Drug control; Human rights; Pain treatment;
Dopamine D3 receptor as a new pharmacological target for the treatment of depression by Gian Marco Leggio; Salvatore Salomone; Claudio Bucolo; Chiara Platania; Vincenzo Micale; Filippo Caraci; Filippo Drago (25-33).
A substantial proportion of depressed patients do not respond to current antidepressant drug therapies. So far, antidepressant drugs have been developed based on the “monoaminergic hypothesis” of depression, which considers a synaptic deficiency in 5-hydroxytryptamine (5-HT; serotonin) or noradrenaline as main cause. More recently, the dopaminergic system has been implicated in the efficacy of some antidepressants, such as desipramine, amineptine, nomifensine. Dysfunction of dopaminergic neurotransmission within the mesolimbic system may contribute to anhedonia, loss of motivation and psychomotor retardation in severe depressive disorders. Dopamine D3 receptor subtype is located both pre- and postsynaptically in brain areas regulating motivation and reward-related behavior and has been implicated in depression-like behaviors. Activity of mesolimbic dopamine neurons in the reward circuit is a key determinant of behavioral susceptibility/resilience to chronic stress, which plays a central role in the pathogenesis of depression. Dopamine D3 receptor expression and function are both down-regulated in stress and depression, and these changes are reversed by antidepressant treatments, suggesting that enhanced dopaminergic neurotransmission mediated by dopamine D3 receptor participates in adaptive changes related to antidepressant activity. Of note, brain derived neurotrophic factor (BDNF) controls the expression of the dopamine D3 receptor in some brain areas and BDNF induction by antidepressant treatments is related to their behavioral activity. A number of experimental drugs in pre-clinical or clinical development, including aripiprazole and cariprazine, may act as antidepressants because of their partial agonist activity at dopamine D3 receptors. These preclinical and clinical data are discussed in the present review.
Keywords: Depression; Dopamine D3 receptor; Brain-derived neurotrophic factor; Partial agonist; Treatment-resistant depression; Aripiprazole;
Hippocampal calcium dysregulation at the nexus of diabetes and brain aging by Olivier Thibault; Katie L. Anderson; Chris DeMoll; Lawrence D. Brewer; Philip W. Landfield; Nada M. Porter (34-43).
Recently it has become clear that conditions of insulin resistance/metabolic syndrome, obesity and diabetes, are linked with moderate cognitive impairment in normal aging and elevated risk of Alzheimer's disease. It appears that a common feature of these conditions is impaired insulin signaling, affecting the brain as well as peripheral target tissues. A number of studies have documented that insulin directly affects brain processes and that reduced insulin signaling results in impaired learning and memory. Several studies have also shown that diabetes induces Ca2+ dysregulation in neurons. Because brain aging is associated with substantial Ca2+ dyshomeostasis, it has been proposed that impaired insulin signaling exacerbates or accelerates aging-related Ca2+ dyshomeostasis. However, there have been few studies examining insulin interactions with Ca2+ regulation in aging animals. We have been testing predictions of the Ca2+ dysregulation/diabetes/brain aging hypothesis and have found that insulin and insulin-sensitizers (thiazolidinediones) target several hippocampal Ca2+-related processes affected by aging. The drugs appear able to reduce the age-dependent increase in Ca2+ transients and the Ca2+ -sensitive afterhyperpolarization. Thus, while additional testing is needed, the results to date are consistent with the view that strategies that enhance insulin signaling can counteract the effect of aging on Ca2+ dysregulation.
Keywords: Afterhyperpolarization; Thiazolidinediones; Cognition; Imaging; Aging; Learning;
The interplay between rapid and slow corticosteroid actions in brain by Marian Joëls; Natasha Pasricha; Henk Karst (44-52).
Stress causes the release of many transmitters and hormones, including corticosteroids. These molecules enter the brain and exert their effects through the mineralo- and glucocorticoid receptor. The former receptor plays an important role in neuronal stability. However, it also mediates rapid non-genomic corticosteroid effects that in synergy with other stress mediators activate limbic cells and promote behavioral choices allowing the organism to quickly respond to the imminent danger. Glucocorticoid receptors primarily mediate slow genomic effects, for instance in the hippocampus and prefrontal cortex, which are thought to contribute to contextual and higher cognitive aspects of behavioral performance several hours after stress. Rapid and slow effects interact and collectively contribute to successful behavioral adaptation. Long-term disturbances in the release pattern of corticosteroid hormones and in the responsiveness of their receptors give rise to structural and functional changes in neuronal properties which may contribute to the expression of psychopathology.
Keywords: Corticosterone; Hippocampus; Amygdala; Genomic; Non-genomic; Adrenalectomy; Chronic stress;
Functional profile of the binary brain corticosteroid receptor system: Mediating, multitasking, coordinating, integrating by E.R. de Kloet (53-62).
This contribution is focused on the action of the naturally occurring corticosteroids, cortisol and corticosterone, which are secreted from the adrenals in hourly pulses and after stress with the goal to maintain resilience and health. To achieve this goal the action of the corticosteroids displays an impressive diversity, because it is cell-specific and context-dependent in coordinating the individual's response to changing environments. These diverse actions of corticosterone are mediated by mineralocorticoid- and glucocorticoid-receptors that operate as a binary system in concert with neurotransmitter and neuropeptide signals to activate and inhibit stress reactions, respectively. Classically MR and GR are gene transcription factors, but recently these receptors appear to mediate also rapid non-genomic actions on excitatory neurotransmission suggesting that they integrate functions over time. Hence the balance of receptor-mediated actions is crucial for homeostasis. This balanced function of mineralo- and glucocorticoid-receptors can be altered epigenetically by a history of traumatic (early) life events and the experience of repeated stressors as well as by predisposing genetic variants in signaling pathways of these receptors. One of these variants, mineralocorticoid receptor haplotype 2, is associated with dispositional optimism in appraisal of environmental challenges. Imbalance in receptor-mediated corticosterone actions was found to leave a genomic signature highlighting the role of master switches such as cAMP response element-binding protein and mammalian target of rapamycin to compromise health, and to promote vulnerability to disease. Diabetic encephalopathy is a pathology of imbalanced corticosterone action, which can be corrected in its pre-stage by a brief treatment with the antiglucocorticoid mifepristone.
Keywords: Stress; Depression; Diabetes; Brain; Behavior; Glucocorticoids; Genome;
Contactins in the neurobiology of autism by Amila Zuko; Kristel T.E. Kleijer; Asami Oguro-Ando; Martien J.H. Kas; Emma van Daalen; Bert van der Zwaag; J. Peter H. Burbach (63-74).
Autism is a disease of brain plasticity. Inspiring work of Willem Hendrik Gispen on neuronal plasticity has stimulated us to investigate gene defects in autism and the consequences for brain development. The central process in the pathogenesis of autism is local dendritic mRNA translation which is dependent on axodendritic communication. Hence, most autism-related gene products (i) are part of the protein synthesis machinery itself, (ii) are components of the mTOR signal transduction pathway, or (iii) shape synaptic activity and plasticity. Accordingly, prototype drugs have been recognized that interfere with these pathways. The contactin (CNTN) family of Ig cell adhesion molecules (IgCAMs) harbours at least three members that have genetically been implicated in autism: CNTN4, CNTN5, and CNTN6. In this chapter we review the genetic and neurobiological data underpinning their role in normal and abnormal development of brain systems, and the consequences for behavior. Although data on each of these CNTNs are far from complete, we tentatively conclude that these three contactins play roles in brain development in a critical phase of establishing brain systems and their plasticity. They modulate neuronal activities, such as neurite outgrowth, synaptogenesis, survival, guidance of projections and terminal branching of axons in forming neural circuits. Current research on these CNTNs concentrate on the neurobiological mechanism of their developmental functions. A future task will be to establish if proposed pharmacological strategies to counteract ASD-related symptomes can also be applied to reversal of phenotypes caused by genetic defects in these CNTN genes.
Keywords: Autism spectrum disorder; Contactins; Neurobiology; Behavior; Cell adhesion molecules; Dendrites; Synapse;
Modulation of NMDA receptor at the synapse: Promising therapeutic interventions in disorders of the nervous system by Manuela Mellone; Fabrizio Gardoni (75-83).
There is general agreement that excessive activation of N-methyl-D-aspartate (NMDA) receptors plays a key role in mediating at least some aspects of synaptic dysfunction in several central nervous system disorders. On this view, in the last decades, research focused on the discovery of different compounds able to reduce NMDA receptor activity, such as classical and/or subunit-specific antagonists. However, the increasing body of knowledge on specific signaling pathways downstream NMDA receptors led to the identification of new pharmacological targets for NMDA receptor-related pathological conditions. Moreover, besides over-activation, several studies indicated that also abnormal NMDA receptor trafficking, resulting in the modification of the receptor subunit composition at the synapse, has a major role in the pathogenesis of several brain disorders. For this reason, the discovery of the molecular mechanisms regulating the abundance of synaptic versus extra-synaptic NMDA receptors as well as the activation of the specific signaling pathways downstream the different NMDA receptor subtypes is needed for the development of novel therapeutic approaches for NMDA receptor-dependent synaptic dysfunction.
Keywords: N-methyl-D-aspartate receptor; Post-synaptic density; Trafficking; Central nervous system disorders; Cell-permeable peptides; Preclinical studies;
Trafficking in neurons: Searching for new targets for Alzheimer's disease future therapies by Stefano Musardo; Claudia Saraceno; Silvia Pelucchi; Elena Marcello (84-106).
Alzheimer's disease (AD) is the most common cause of dementia and no cure is available at the moment. As the disease progresses, patients become increasingly dependent, needing constant supervision and care. Prevention or delay of AD onset is among the most urgent moral, social, economic and scientific imperatives in industrialized countries. A better understanding of the pathogenic mechanisms leading to the disease and the consequent identification of new pharmacological targets are now a need. One of the most prominent molecular events occurring in AD patients’ brains is the deposition of a peptide named amyloid-β (Aβ). Aβ derives from the concerted action of β-secretase, which mediates the amyloid precursor protein (APP) shedding at Aβ N-terminus, and γ-secretase, responsible for APP C-terminal stub cleavage. The production of Aβ can be prevented by the cleavage of ADAM10 on APP. In regard of AD pathogenesis, it is notable that neurons are the cell type affected in AD and that APP and the secretases are all integral transmembrane proteins, and so they are dynamically sorted in neurons. Therefore, neuronal sorting mechanisms responsible for APP and the secretases colocalization in the same membranous compartment play important roles in the regulation of Aβ production. In light of these considerations, this review provides an overview on the actual knowledge of the trafficking mechanisms involved in the regulation of APP and secretases localization, paying particular attention to the specific neuronal setting.
Keywords: Alzheimer's disease; Amyloid β; Amyloid precursor protein; Secretase;
Glutamatergic receptors at developing synapses: The role of GluN3A-containing NMDA receptors and GluA2-lacking AMPA receptors by Tifei Yuan; Camilla Bellone (107-111).
During brain development excitatory synapses exhibit significant changes in their postsynaptic receptors and activated signaling pathways. Calcium represents the most crucial signaling factor in synaptic transmission and plasticity. Therefore developmental changes in calcium-permeable channels on the membrane contribute significantly to the modulation of neurotransmission at excitatory synapses. The present review focuses on two types of “non-canonical” glutamate receptors in terms of calcium permeability: GluN3A-containing NMDA receptors (calcium-impermeable) and GluA2-lacking AMPA receptors (calcium permeable). The involvement of these receptors during development and their potential function in synaptic plasticity are discussed. The synaptic incorporation of these receptors would alter calcium permeability, and therefore the threshold/direction of further plastic changes. We believe that characterizing the dynamics of non-canonical glutamate receptors during development could provide insight into how these receptors are recruited or removed in pathological conditions.
Keywords: AMPA receptor; NMDA receptor; Synaptic plasticity; Postnatal development;
Mutations of the synapse genes and intellectual disability syndromes by Chiara Verpelli; Caterina Montani; Cinzia Vicidomini; Christopher Heise; Carlo Sala (112-116).
Intellectual disability syndromes have been found associated to numerous mutated genes that code for proteins functionally involved in synapse formation, the regulation of dendritic spine morphology, the regulation of the synaptic cytoskeleton or the synthesis and degradation of specific synapse proteins. These studies have strongly demonstrated that even mild alterations in synapse morphology and function give rise to mild or severe alteration in intellectual abilities. Interestingly, pharmacological agents that are able to counteract these morphological and functional synaptic anomalies can also improve the symptoms of some of these conditions. This review is summarizing recent discoveries on the functions of some of the genes responsible for intellectual disability syndromes connected with synapse dysfunctions.
Keywords: Intellectual disability; Brain synapses; Dendritic spine; Autism;
Resident adult neural stem cells in Parkinson′s disease—The brain′s own repair system? by Simone A. van den Berge; Miriam E. van Strien; Elly M. Hol (117-127).
One important pathological process in the brain of Parkinson disease (PD) patients is the degeneration of the dopaminergic neurons in the substantia nigra, which leads to a decline in striatal dopamine levels and motor dysfunction. A major clinical problem is that this degenerative process currently cannot be stopped or reversed. Expectations from the restorative capacity of neural stem cells (NSCs) are high, as these cells can potentially replace the degenerating neurons. The discovery of the presence of NSCs in the adult human brain has instigated research into the potential of these cells as a resource to promote brain repair in neurodegenerative diseases. Neural stem and progenitor cells reside in the subventricular zone (SVZ), which is closely situated to the striatum, which is affected in PD. Therefore, restoring the dopamine levels in the striatum of PD patients through stimulating endogenous NSCs in the nearby SVZ to migrate into the striatum and differentiate into dopaminergic neurons might thus be an attractive future therapeutic approach. We will review the reported changes in NSCs in the SVZ of PD animal models and PD patients, which are due to a lack of striatal dopamine. Furthermore, we will summarise the reports that describe efforts to stimulate NSCs to replace dopaminergic cells in the SN and restore striatal dopamine levels. In our opinion, mobilizing the endogenous SVZ NSCs to replenish striatal dopamine is an attractive approach to alleviate the motor symptoms in PD patients, without the ethical and immunological challenges of transplantation of NSCs and foetal brain tissue.
Keywords: Dopaminergic neurons; Neural stem cells; Parkinson′s disease; Subventricular zone; Neurogenesis;
Optical imaging of structural and functional synaptic plasticity in vivo by Anthony Holtmaat; Jerome Randall; Michele Cane (128-136).
The adult brain has long been viewed as a collection of neuronal networks that maintain a fixed configuration of synaptic connections. Brain plasticity and learning was thought to depend exclusively on changes in the gain and offset of these connections. Over the last 50 years, molecular and cellular studies of neuroplasticity have altered this view. Brain plasticity is now viewed as a continuum of structural changes that could vary from long-range axon growth to the twitching of dendritic spines and synaptic receptor composition dynamics. Plasticity proteins similar to those that drive neuronal development may underpin brain plasticity, and consequently could regulate adaptations to new experiences and learning. In vivo imaging has confirmed that neuronal plasticity in the adult brain involves subtle structural changes at synaptic connections, including synapse formation and pruning. Synaptic structural changes are associated with experience-dependent plasticity, learning, brain traumas and neurodegeneration. Owing to the expanding toolbox of in vivo imaging we have come to the brink of understanding the causal relationship between structural synaptic network dynamics and functional brain plasticity. This review summarizes the technical developments in the imaging of laboratory animals' brains in vivo and the insights they have provided into the mechanisms of brain plasticity and learning.
Keywords: Neuronal plasticity; 2-Photon laser scanning microscopy; In vivo imaging; Synaptogenesis; Dendritic spine; Axonal bouton; Structural plasticity;
Hypothalamic plasticity of neuropeptide Y is lacking in brain-type creatine kinase double knockout mice with defective thermoregulation by Catharina E.E.M. Van der Zee (137-144).
The neural substrate of adaptive thermoregulation in mice lacking both brain-type creatine kinase isoforms is further investigated. The cytosolic brain-type creatine kinase (CK-B) and mitochondrial ubiquitous creatine kinase (UbCKmit) are expressed in neural cells throughout the central and peripheral nervous system, where they have an important role in cellular energy homeostasis. Several integral functions appear altered when creatine kinases are absent in the brain (Jost et al., 2002; Streijger et al., 2004, 2005), which has been explained by inefficient neuronal transmission. The CK‐‐/‐‐ double knockout mice demonstrate every morning a body temperature drop of ∼1.0 °C, and they have impaired thermogenesis, as revealed by severe hypothermia upon cold exposure. This defective thermoregulation is not associated with abnormal food intake, decreased locomotive activity, or increased torpor sensitivity. Although white and brown adipose tissue fat pads are diminished in CK‐‐/‐‐ mice, intravenous norepinephrine infusion results in a normal brown adipose tissue response with increasing core body temperatures, indicating that the sympathetic innervation functions correctly (Streijger et al., 2009). This study revealed c-fos changes following a cold challenge, and that neuropeptide Y levels were decreased in the paraventricular nucleus of wildtype, but not CK‐‐/‐‐, mice. A reduction in hypothalamic neuropeptide Y is coupled to increased uncoupling protein 1 expression in brown adipose tissue, resulting in thermogenesis. In CK‐‐/‐‐ mice the neuropeptide Y levels did not change. This lack of hypothalamic plasticity of neuropeptide Y might be the result of inefficient neuronal transmission or can be explained by the previous observation of reduced circulating levels of leptin in CK‐‐/‐‐ mice.
Keywords: Brain-type creatine kinase; Mitochondrial ubiquitous creatine kinase; Neuropeptide Y immunoreactivity; C-fos immunoreactivity; Paraventricular nucleus; Leptin; Brown adipose tissue thermogenesis;
Gene therapy approaches to enhance regeneration of the injured peripheral nerve by Fred de Winter; Stefan Hoyng; Martijn Tannemaat; Ruben Eggers; Matthew Mason; Martijn Malessy; Joost Verhaagen (145-152).
Peripheral nerve injury in humans often leads to incomplete functional recovery. In this review we discuss the potential for gene therapy to be used as a strategy alongside surgical repair techniques for the study of peripheral nerve regeneration in rodent models and with a view to its eventual use for the promotion of successful regeneration in the clinic. Gene therapy can be defined as the introduction of a foreign, therapeutic gene into living cells in order to treat a disease. The first attempts to express a foreign gene in peripheral neurons date back more than 25 years. The vectors used at that time were imperfect—mainly because they contained viral genes that were expressed in the target cells and elicited an immunological response. Fortunately significant progress has been made: today adeno-associated viral vectors can be produced completely free of viral genes and Phase I and II clinical studies have shown that these vectors are well tolerated. The technology for gene delivery has reached a state of readiness for clinical translation in many fields of neurology, including peripheral nerve repair. The current range of potential therapeutic genes for the repair of the traumatized peripheral nerve has also grown over the years and now includes neurotrophic factors with specificities for various subtypes of peripheral neurons, cell adhesion and extracellular matrix molecules and transcription factors. This review for this Festschrift, published to celebrate the 70th birthday of Willem Hendrik Gispen, contains many “footprints” from the time the senior author (JV) worked with Willem Hendrik, first as a student intern, then as a Ph.D. student (1983–1987) and later as a postdoctoral fellow (1989–1993). The preface of this article highlights personal memories of a time that will never come back.
Keywords: Peripheral nerve; Gene therapy; Adeno-associated viral vector; Lentiviral vector;
Sweet memories: 20 years of progress in research on cognitive functioning in diabetes by Geert Jan Biessels (153-160).
This paper appears in a special issue of the European Journal of Pharmacology that commemorates the retirement of Professor Willem Hendrik Gispen as distinguished professor of Utrecht University and as editor of the European Journal of Pharmacology. The paper provides an overview of a research line on the impact of diabetes on cognition that we started together 20 years ago, and that continues to this day. I will report how we more or less stumbled upon this topic, that was understudied, but proved to be of definite clinical relevance. I will discuss how we tried to establish animal models, how developments from clinical and experimental studies from around the world led us to reconsider our concepts, and how findings from research on diabetic neuropathy, insulin signaling in the brain, Alzheimer′s disease and dementia, and vascular disease and stroke converged and helped to create new ideas and refute others. This voyage has not ended yet, because the ultimate goal is to offer patients with diabetes treatment that can protect them against accelerated cognitive decline. Although this could take another 20 years, the research from Willem Hendrik and his group brought us an important step in the right direction.
Keywords: Diabetes mellitus; Dementia; Magnetic resonance imaging; Brain; Alzheimer′s disease; Cognitive dysfunction;
Diabetes mellitus- and ageing-induced changes in the capacity for long-term depression and long-term potentiation inductions: Toward a unified mechanism by Alain Artola (161-169).
Long-lasting type 1 and type 2 diabetes mellitus (DM) are both associated with impaired cognitive function in humans. Animal models of DM have confirmed the detrimental effect of high blood glucose levels on learning and memory. What are the neural correlates of such impaired cognition? It is widely, although not universally, believed that long-lasting increase and decrease in synaptic strength, known as long-term potentiation (LTP) and depression (LTD), provide an important key to understanding the cellular and molecular mechanisms by which memories are formed and stored. The majority of animal studies that examined the effect of DM on LTD and LTP used the streptozotocin (STZ) rodent model of type 1 DM, with the exception of a few that used genetic models of type 2 DM. Studies in STZ-DM rodents show that cellular processes underlying synapse strengthening or weakening are not altered. Rather, the capacity for LTP induction is reduced whereas that for LTD induction is enhanced. The mechanisms underlying DM-related changes in LTD and LTP inductions are still unknown. However, that the levels of effective postsynaptic depolarization for LTD and LTP inductions are concomitantly shifted in opposite directions put constraints on them. Moreover, that DM-, metaplasticity-, stress- and ageing-related changes in LTD and LTP inductions exhibit the very same phenomenology suggests that they might involve common mechanisms. Dissecting out the mechanisms responsible for DM-related changes in the capacity for LTD and LTP inductions is helping to improve treatment of impaired cognitive function in DM patients.
Keywords: Long-term potentiation; Long-term depression; Metaplasticity; Diabetes mellitus; Stress; Ageing;
Insulin, cognition, and dementia by Brenna Cholerton; Laura D. Baker; Suzanne Craft (170-179).
Cognitive disorders of aging represent a serious threat to the social and economic welfare of current society. It is now widely recognized that pathology related to such conditions, particularly Alzheimer's disease, likely begins years or decades prior to the onset of clinical dementia symptoms. This revelation has led researchers to consider candidate mechanisms precipitating the cascade of neuropathological events that eventually lead to clinical Alzheimer's disease. Insulin, a hormone with potent effects in the brain, has recently received a great deal of attention for its potential beneficial and protective role in cognitive function. Insulin resistance, which refers to the reduced sensitivity of target tissues to the favorable effects of insulin, is related to multiple chronic conditions known to impact cognition and increase dementia risk. With insulin resistance-associated conditions reaching epidemic proportions, the prevalence of Alzheimer's disease and other cognitive disorders will continue to rise exponentially. Fortunately, these chronic insulin-related conditions are amenable to pharmacological intervention. As a result, novel therapeutic strategies that focus on increasing insulin sensitivity in the brain may be an important target for protecting or treating cognitive decline. The following review will highlight our current understanding of the role of insulin in brain, potential mechanisms underlying the link between insulin resistance and dementia, and current experimental therapeutic strategies aimed at improving cognitive function via modifying the brain's insulin sensitivity.
Keywords: Alzheimer's disease; Insulin; Cognition; Diabetes; Aging;
Pathogenesis of diabetic neuropathy: Focus on neurovascular mechanisms by P. Sytze Van Dam; Mary A. Cotter; Bert Bravenboer; Norman E. Cameron (180-186).
Neuropathies of the peripheral and autonomic nervous systems affect up to half of all people with diabetes, and are major risk factors for foot ulceration and amputation. The aetiology is multifactorial: metabolic changes in diabetes may directly affect neural tissue, but importantly, neurodegenerative changes are precipitated by compromised nerve vascular supply. Experiments in animal models of diabetic neuropathy suggest that similar metabolic sequelae affect neurons and vasa nervorum endothelium. These include elevated polyol pathway activity, oxidative stress, the formation of advanced glycation and lipoxidation end products, and various pro-inflammatory changes such as elevated protein kinase C, nuclear factor κB and p38 mitogen activated protein kinase signalling. These mechanisms do not work in isolation but strongly interact in a mutually facilitatory fashion. Nitrosative stress and the induction of the enzyme poly (ADP-ribose) polymerase form one important link between physiological stressors such as reactive oxygen species and the pro-inflammatory mechanisms. Recently, evidence points to endoplasmic stress and the unfolded protein response as forming another crucial link. This review focuses on the aetiopathogenesis of neurovascular changes in diabetic neuropathy, elucidated in animal studies, and on putative therapeutic targets the majority of which have yet to be tested for efficacy in clinical trials.
Keywords: Diabetic neuropathy; Blood flow; Oxidative stress; Advanced glycation; Inflammation; Endoplasmic reticulum stress;
Repeated agouti related peptide (83–132) injections inhibit cocaine-induced locomotor sensitisation, but not via the nucleus accumbens by Edwin Alserda; Roger A.H. Adan; Geert M.J. Ramakers (187-191).
Drug addiction is a chronic relapsing brain disease for which many of the underlying neuronal mechanisms are yet to be unravelled. There seems to be an interaction between the melanocortin system and drugs of abuse. For instance, infusion of the melanocortin MC4 receptor antagonist SHU9119 (Ac-Nle-cyclo(-Asp-His-d-2-Nal-Arg-Trp-Lys)-NH2) into the nucleus accumbens results in conditioned place avoidance, reduces the amount of lever presses for cocaine and blocks development of cocaine-induced locomotor sensitisation.The aim of this study is to determine whether the induction of locomotor sensitisation to repeated cocaine is inhibited by the melanocortin MC4 receptor inverse agonist Agouti Related Peptide (AgRP83–132).Rats were sensitised to daily cocaine injections for 5 consecutive days and 30 min prior to every daily cocaine injection, rats received an intracerebroventricular (i.c.v.) or intra nucleus accumbens injection with AgRP(83–132) or saline, to determine whether we could inhibit cocaine-induced locomotor sensitisation. We show that i.c.v. injections of AgRP(83–132) inhibit cocaine-induced locomotor sensitisation. This effect is not regulated via the nucleus accumbens, since injecting the melanocortin receptor inverse agonist AgRP(83–132) directly into the nucleus accumbens was unable to inhibit the cocaine-induced locomotor sensitisation. This implicates that the nucleus accumbens is an unlikely site to inhibit the induction of locomotor sensitisation via the melanocortin MC4 receptor. This is in contrast to other studies that show an effect of the melanocortin MC4 receptor antagonist SHU9119 on locomotor sensitisation when injected into the nucleus accumbens.
Keywords: Cocaine; AgRP; Locomotor sensitisation; Nucleus accumbens;
Melanocortin MC4 receptor-mediated feeding and grooming in rodents by Joram D. Mul; Berry M. Spruijt; Jan H. Brakkee; Roger A.H. Adan (192-201).
Decades ago it was recognized that the pharmacological profile of melanocortin ligands that stimulated grooming behavior in rats was strikingly similar to that of Xenopus laevis melanophore pigment dispersion. After cloning of the melanocortin MC1 receptor, expressed in melanocytes, and the melanocortin MC4 receptor, expressed mainly in brain, the pharmacological profiles of these receptors appeared to be very similar and it was demonstrated that these receptors mediate melanocortin-induced pigmentation and grooming respectively. Grooming is a low priority behavior that is concerned with care of body surface. Activation of central melanocortin MC4 receptors is also associated with meal termination, and continued postprandial stimulation of melanocortin MC4 receptors may stimulate natural postprandial grooming behavior as part of the behavioral satiety sequence. Indeed, melanocortins fail to suppress food intake or induce grooming behavior in melanocortin MC4 receptor-deficient rats. This review will focus on how melanocortins affect grooming behavior through the melanocortin MC4 receptor, and how melanocortin MC4 receptors mediate feeding behavior. This review also illustrates how melanocortins were the most likely candidates to mediate grooming and feeding based on the natural behaviors they induced.
Keywords: Melanocortin MC4 receptor; MC4R; MSH; ACTH; Grooming; Food intake; Body weight;
“Are melanocortin receptors constitutively active in vivo?” by Anthony P. Coll (202-207).
Constitutive activity is defined as ligand-independent activity, resulting in the production of a second messenger, even in the absence of an agonist. There has been widespread acceptance of the concept of G-protein-coupled receptor constitutive activity, with this activity specifically blocked by inverse agonists, a particular class of ligands often previously characterised as merely antagonists. The melanocortin receptors are highly unusual because their physiological activity is mediated not by a single ligand but by a number of endogenous peptide ligands, with the ability to exhibit agonist, antagonist or potentially inverse agonist behaviour. It remains more contentious to what extent the demonstrable constitutive activity of melanocortin receptors, particularly those expressed within the central nervous system, has in (patho)physiological processes. This review examines evidence from animal and laboratory based studies, focussing particularly upon peripherally expressed melanocortin-1 receptors and centrally expressed melanocortin-4 receptors, to consider how recent insights into both receptor structure itself and the molecules know to play a role in melanocortin signalling continue to shape our understanding of melanocortin biology.
Keywords: G protein coupled receptor; POMC; Melanocortin; Pigmentation; Energy homeostasis;
The role of melanocortins and Neuropeptide Y in food reward by R. Pandit; S.E. la Fleur; R.A.H. Adan (208-214).
The Neuropeptide Y and the melanocortin peptides are two well-described hypothalamic feeding peptides regulating energy balance. Predominantly expressed within the arcuate nucleus, these neurons project to different brain areas and modulate various aspects of feeding. Hedonic feeding, where one overindulges in palatable food consumption beyond one′s nutritional necessities, is one such aspect regulated by NPY/melanocortin signaling. Research suggests that NPY/melanocortin regulate hedonic aspects of feeding through its projections to the brain reward circuitry (ventral tegmental area, lateral hypothalamus, nucleus accumbens etc.), however, exact target areas have not yet been identified. The current work explores literature to provide a mechanistic explanation for the effects of these peptides on food reward.
Keywords: Neuropeptide Y; Melanocortin; Food-reward; Motivation;