Abnormal neurotransmitter release underlying behavioral and cognitive disorders: toward concepts of dynamic and function-specific dysregulation

Pituitary neuroendocrine tumor: A neuropsychological comparison with intra-axial tumor

OBJECTIVE

Despite pituitary neuroendocrine tumor (PitNET) being extra-axial tumors without direct damage to brain tissue, patients with PitNET exhibit neuropsychological impairments. However, it remains unclear whether there are neuropsychological differences between PitNET and intra-axial tumors that directly destroy the brain parenchyma. This prospective study aims to clarify this distinction to inform decision-making for intracranial tumors of diverse origins.

METHODS

A total of 146 patients with PitNET, 74 patients with glioma representing intra-axial tumors, and 52 age-, sex-, and education-matched healthy controls were recruited. All patients received standard treatment and postoperative rehabilitation. Clinical data were meticulously collected, and neuropsychological tests were administered to all participants both before and 3 months after surgery.

RESULTS

Both PitNET and glioma patients experience the dual burden of cognitive and affective deficits. However, the feature of these deficits differs substantially. In PitNET patients, the deficits are relatively mild and focal, whereas in glioma patients, they are severe and extensive. Specifically, PitNET patients exhibit deficits in memory, anxiety, and negative affect. In contrast, glioma patients display deficits in executive function, attention, anxiety, positive/negative affect, and empathy. Notably, except for persistent memory deficits, the majority of neuropsychological scores declines in PitNET patients are restorable and can reach improvement within a short period after standard surgical therapy and perioperative management. Conversely, glioma patients not only fail to show improvements but also demonstrate worsening in terms of general cognition and memory postoperatively.

INTERPRETATION

As an extra-axial tumor, PitNET may exhibit distinctive cognitive and affective functioning compared to intra-axial tumors, highlighting the need for specific treatment approaches for PitNET patients.

Protective role of madecassoside from Centella asiatica against protein L-isoaspartyl methyltransferase deficiency-induced neurodegeneration

Protein L-isoaspartyl methyltransferase (PIMT/PCMT1) could repair l-isoaspartate (L-isoAsp) residues formed by deamidation of asparaginyl (Asn) residues or isomerization of aspartyl (Asp) residues in peptides and proteins during aging. Aside from abnormal accumulation of L-isoAsp, PIMT knockout (KO) mice mirrors some neuropathological hallmarks such as anxiety-like behaviors, impaired spatial memory and aberrant synaptic plasticity in the hippocampus of neurodegenerative diseases (NDs), including Alzheimer's disease (AD) and related dementias, and Parkinson's disease (PD). While some reports indicate the neuroprotective effect of madecassoside (MA) as a triterpenoid saponin component of Centella asiatica, its role against NDs-related anxiety and cognitive impairment remains unclear. Therefore, we investigated the effect of MA against anxiety-related behaviors in PIMT deficiency-induced mouse model of NDs. Results obtained from the elevated plus maze (EPM) test revealed that MA treatment alleviated anxiety-like behaviors in PIMT knockout mice. Furthermore, Real-time PCR, electroencephalogram (EEG) recordings, transmission electron microscopy analysis and ELISA were carried out to evaluate the expression of clock genes, sleep and synaptic function, respectively. The PIMT knockout mice were characterized by abnormal clock patterns, sleep disturbance and synaptic dysfunction, which could be improved by MA administration. Collectively, these findings suggest that MA exhibits neuroprotective effects associated with improved circadian rhythms sleep-wake cycle and synaptic plasticity in PIMT deficient mice, which could be translated to ameliorate anxiety-related symptoms and cognitive impairments in NDs.

Sweet basil (Ocimum basilicum) leaf and seed extracts alleviate neuronal dysfunction in aluminum chloride-induced neurotoxicity in Drosophila melanogaster Meigen model

Ocimum basilicum is an important medicinal plant and culinary herb generally known as sweet basil (SB). These plants are effective radical scavengers, that have been employed in treatment of nervous system disorders, and thus, could be beneficial for the management of neurodegenerative diseases (NDs). Current clinical treatments for NDs present several side effects, therefore, there is need to develop new treatments that can mitigate these deadly diseases. Hence, this study investigated the neuroprotective activities of SB leaf and seed in aluminum chloride (AlCl3)-induced toxicity in Drosophila melanogaster. HPLC characterization of the leaves and seeds were carried out. AlCl3-diet was used to induce neurodegeneration and treated flies received SB leaf and seed extracts-supplemented diet. Survival and locomotor performance activities/levels of oxidative biomarkers [reactive oxygen species (ROS), thiobarbituric acid reactive species (TBARS), total thiol, catalase, superoxide dismutase (SOD) and glutathione-S-transferase (GST)], enzymes linked with neurodegeneration (acetylcholinesterase (AChE) and monoamine oxidase (MAO)) were investigated. SB leaf had significantly (p < 0.05) higher polyphenol contents; gallic acid and P-coumaric acid were the most abundant polyphenol in the leaf and seed respectively. Percentage survival and locomotor rates, level/activities of total thiol, catalase, SOD and GST were significantly (p < 0.05) reduced while ROS, TBARS, AChE and MAO activities were significantly (p < 0.05) increased in AlCl3-diet-fed flies. Treatment with SB leaf and seed diet lessened these observed impairments. However, SB leaf had better neuroprotective activities that could be related to the observed higher phenolic constituents. Hence, SB leaf diet may offer improved therapeutic effect in NDs.

The effects of paranoia and dopamine on perception of cohesion and conspiracy: a pre-registered, double-blind, placebo-controlled experiment

Paranoia is a common symptom of psychotic disorders but is also present on a spectrum of severity in the general population. Although paranoia is associated with an increased tendency to perceive cohesion and conspiracy within groups, the mechanistic basis of this variation remains unclear. One potential avenue involves the brain's dopaminergic system, which is known to be altered in psychosis. In this study, we used large-N online samples to establish the association between trait paranoia and perceptions of cohesion and conspiracy. We further evaluated the role of dopamine on perceptions of cohesion and conspiracy using a double-blind, placebo-controlled laboratory experiment where participants received levodopa or a placebo control. Our results were mixed: group perceptions and perceptions of cohesion were higher among more paranoid individuals but were not altered under dopamine administration. We outline the potential reasons for these discrepancies and the broader implications for understanding paranoia in terms of dopamine dysregulation.

Co-exposure to lead, mercury, and cadmium induces neurobehavioral impairments in mice by interfering with dopaminergic and serotonergic neurotransmission in the striatum

Humans are exposed to lead (Pb), mercury (Hg), and cadmium (Cd) through various routes, including drinking water, and such exposure can lead to a range of toxicological effects. However, few studies have investigated the toxic effects of exposure to mixtures of metals, particularly in relation to neurotoxicity. In this study, 7-week-old male mice were exposed to Pb, Hg, and Cd individually or in combination through their drinking water for 28 days. The mice exposed to the metal mixture exhibited significantly reduced motor coordination and impaired learning and memory abilities compared to the control group and each of the single metal exposure groups, indicating a higher level of neurotoxicity of the metal mixture. The dopamine content in the striatum was significantly lower in the metal mixture exposure group than in the single metal exposure groups and the control group. Furthermore, compared to the control group, the metal mixture exposure group showed a significantly lower expression level of tyrosine hydroxylase (TH) and significantly higher expression levels of dopamine transporter (DAT), tryptophan hydroxylase 1 (TPH1), and serotonin reuptake transporter (SERT). Notably, there were no significant differences in SERT expression between the single metal exposure groups and the control group, but SERT expression was significantly higher in the metal mixture exposure group than in the single metal and control groups. These findings suggest that the key proteins involved in the synthesis and reuptake of dopamine (TH and DAT, respectively), as well as in the synthesis and reuptake of serotonin (TPH1 and SERT, respectively), play crucial roles in the neurotoxic effects associated with exposure to metal mixtures. In conclusion, this study demonstrates that simultaneous exposure to different metals can impact key enzymes involved in dopaminergic and serotonergic neurotransmission processes, leading to disruptions in dopamine and serotonin homeostasis and consequently a range of detrimental neurobehavioral effects.

Sex- and age-dependent contribution of System xc- to cognitive, sensory, and social behaviors revealed by comprehensive behavioral analyses of System xc- null mice

Background

System xc- (Sxc-) is an important heteromeric amino acid cystine/glutamate exchanger that plays a pivotal role in the CNS by importing cystine into cells while exporting glutamate. Although certain behaviors have been identified as altered in Sxc- null mutant mice, our understanding of the comprehensive impact of Sxc- on behavior remains incomplete.

Methods

To address this gap, we compared motor, sensory and social behaviors of male and female mice in mice null for Sxc- (SLC7A11sut/sut) with wildtype littermates (SLC7A11+/+) in a comprehensive and systematic manner to determine effects of genotype, sex, age, and their potential interactions.

Results

Motor performance was not affected by loss of Sxc- in both males and females, although it was impacted negatively by age. Motor learning was specifically disrupted in female mice lacking Sxc- at both 2 and 6 months of age. Further, female SLC7A11sut/sut mice at both ages exhibited impaired sociability, but normal spatial and recognition memory, as well as sensorimotor gating. Finally, pronounced open-space anxiety was displayed by female SLC7A11sut/sut when they were young. In contrast, young SLC7A11sut/sut male mice demonstrated normal sociability, delayed spatial learning, increased open-space anxiety and heightened sensitivity to noise. As they aged, anxiety and noise sensitivity abated but hyperactivity emerged.

Discussion

We find that the behavioral phenotypes of female SLC7A11sut/sut are similar to those observed in mouse models of autism spectrum disorder, while behaviors of male SLC7A11sut/sut resemble those seen in mouse models of attention deficit hyperactivity disorder. These results underscore the need for further investigation of SLC7A11 in neurodevelopment. By expanding our understanding of the potential involvement of Sxc-, we may gain additional insights into the mechanisms underlying complex neurodevelopmental conditions.

Comparison of fluorescence biosensors and whole-cell patch clamp recording in detecting ACh, NE, and 5-HT

The communication between neurons and, in some cases, between neurons and non-neuronal cells, through neurotransmission plays a crucial role in various physiological and pathological processes. Despite its importance, the neuromodulatory transmission in most tissues and organs remains poorly understood due to the limitations of current tools for direct measurement of neuromodulatory transmitters. In order to study the functional roles of neuromodulatory transmitters in animal behaviors and brain disorders, new fluorescent sensors based on bacterial periplasmic binding proteins (PBPs) and G-protein coupled receptors have been developed, but their results have not been compared to or multiplexed with traditional methods such as electrophysiological recordings. In this study, a multiplexed method was developed to measure acetylcholine (ACh), norepinephrine (NE), and serotonin (5-HT) in cultured rat hippocampal slices using simultaneous whole-cell patch clamp recordings and genetically encoded fluorescence sensor imaging. The strengths and weaknesses of each technique were compared, and the results showed that both techniques did not interfere with each other. In general, genetically encoded sensors GRAB_NE and GRAB_5HT1.₀ showed better stability compared to electrophysiological recordings in detecting NE and 5-HT, while electrophysiological recordings had faster temporal kinetics in reporting ACh. Moreover, genetically encoded sensors mainly report the presynaptic neurotransmitter release while electrophysiological recordings provide more information of the activation of downstream receptors. In sum, this study demonstrates the use of combined techniques to measure neurotransmitter dynamics and highlights the potential for future multianalyte monitoring.

Sensing and Stimulation Applications of Carbon Nanomaterials in Implantable Brain-Computer Interface

Implantable brain–computer interfaces (BCIs) are crucial tools for translating basic neuroscience concepts into clinical disease diagnosis and therapy. Among the various components of the technological chain that increases the sensing and stimulation functions of implanted BCI, the interface materials play a critical role. Carbon nanomaterials, with their superior electrical, structural, chemical, and biological capabilities, have become increasingly popular in this field. They have contributed significantly to advancing BCIs by improving the sensor signal quality of electrical and chemical signals, enhancing the impedance and stability of stimulating electrodes, and precisely modulating neural function or inhibiting inflammatory responses through drug release. This comprehensive review provides an overview of carbon nanomaterials’ contributions to the field of BCI and discusses their potential applications. The topic is broadened to include the use of such materials in the field of bioelectronic interfaces, as well as the potential challenges that may arise in future implantable BCI research and development. By exploring these issues, this review aims to provide insight into the exciting developments and opportunities that lie ahead in this rapidly evolving field.

Functional bioengineered models of the central nervous system

The functional complexity of the central nervous system (CNS) is unparalleled in living organisms. Its nested cells, circuits and networks encode memories, move bodies and generate experiences. Neural tissues can be engineered to assemble model systems that recapitulate essential features of the CNS and to investigate neurodevelopment, delineate pathophysiology, improve regeneration and accelerate drug discovery. In this Review, we discuss essential structure-function relationships of the CNS and examine materials and design considerations, including composition, scale, complexity and maturation, of cell biology-based and engineering-based CNS models. We highlight region-specific CNS models that can emulate functions of the cerebral cortex, hippocampus, spinal cord, neural-X interfaces and other regions, and investigate a range of applications for CNS models, including fundamental and clinical research. We conclude with an outlook to future possibilities of CNS models, highlighting the engineering challenges that remain to be overcome.

Neurotransmitters Regulation and Food Intake: The Role of Dietary Sources in Neurotransmission

Neurotransmitters (NTs) are biologically active chemicals, which mediate the electrochemical transmission between neurons. NTs control numerous organic functions particularly crucial for life, including movement, emotional responses, and the physical ability to feel pleasure and pain. These molecules are synthesized from simple, very common precursors. Many types of NTs have both excitatory and inhibitory effects. Neurotransmitters' imbalance can cause many diseases and disorders, such as Parkinson's disease, depression, insomnia, increased anxiety, memory loss, etc. Natural food sources containing NTs and/or their precursors would be a potential option to help maintain the balance of NTs to prevent brain and psychiatric disorders. The level of NTs could be influenced, therefore, by targeting dietary habits and nutritional regimens. The progressive implementation of nutritional approaches in clinical practice has made it necessary to infer more about some of the nutritional NTs in neuropsychiatry. However, the importance of the intake of nutritional NTs requires further understanding, since there are no prior significant studies about their bioavailability, clinical significance, and effects on nerve cells. Interventional strategies supported by evidence should be encouraged.

Letting the little light of mind shine: Advances and future directions in neurochemical detection

Synaptic transmission via neurochemical release is the fundamental process that integrates and relays encoded information in the brain to regulate physiological function, cognition, and emotion. To unravel the biochemical, biophysical, and computational mechanisms of signal processing, one needs to precisely measure the neurochemical release dynamics with molecular and cell-type specificity and high resolution. Here we reviewed the development of analytical, electrochemical, and fluorescence imaging approaches to detect neurotransmitter and neuromodulator release. We discussed the advantages and practicality in implementation of each technology for ease-of-use, flexibility for multimodal studies, and challenges for future optimization. We hope this review will provide a versatile guide for tool engineering and applications for recording neurochemical release.

Pushing the frontiers: tools for monitoring neurotransmitters and neuromodulators

Neurotransmitters and neuromodulators have a wide range of key roles throughout the nervous system. However, their dynamics in both health and disease have been challenging to assess, owing to the lack of in vivo tools to track them with high spatiotemporal resolution. Thus, developing a platform that enables minimally invasive, large-scale and long-term monitoring of neurotransmitters and neuromodulators with high sensitivity, high molecular specificity and high spatiotemporal resolution has been essential. Here, we review the methods available for monitoring the dynamics of neurotransmitters and neuromodulators. Following a brief summary of non-genetically encoded methods, we focus on recent developments in genetically encoded fluorescent indicators, highlighting how these novel indicators have facilitated advances in our understanding of the functional roles of neurotransmitters and neuromodulators in the nervous system. These studies present a promising outlook for the future development and use of tools to monitor neurotransmitters and neuromodulators.

Role of BDNF/ProBDNF Imbalance in Postoperative Cognitive Dysfunction by Modulating Synaptic Plasticity in Aged Mice

Postoperative cognitive dysfunction (POCD) is a disturbing neurological complication in patients undergoing anesthesia and surgical procedures. Brain-derived neurotrophic factor (BDNF) and its precursor proBDNF binding to their corresponding receptors tyrosine kinase (TrkB) and p75 neurotrophin receptor (p75NTR) exert quite an opposite biological function in neuron survival and synaptic function. This study aimed to demonstrate the critical role of the BDNF/proBDNF ratio in modulating synaptic plasticity, which further leads to anesthesia-/surgery-induced POCD. It also showed that the exogenous BDNF or p75NTR inhibitor could ameliorate cognitive dysfunction. In detail, 16-month-old C57BL/6 mice were subjected to a stabilized tibial fracture surgery with isoflurane anesthesia to establish the POCD animal model. The mice were then microinjected with either p75NTR inhibitor or exogenous BDNF into the dorsal hippocampus. Behavioral experiments were performed by open field and fear conditioning tests (FCTs). Western blotting was also used to measure the expression levels of BDNF, proBDNF, TrkB, p-TrkB, p75NTR, and synapse proteins. Golgi staining and electrophysiology were applied to evaluate the neuronal synaptic plasticity. Here, we demonstrated that anesthesia/surgery induced a reduction of BDNF/proBDNF, which negatively regulates the synaptic function in hippocampus, subsequently leading to cognitive impairment in aged mice. P75NTR inhibitor and exogenous BDNF could attenuate cognitive deficits by rescuing the dendritic spine loss and long-term potentiation (LTP) via altering the BDNF/proBDNF ratio. This study unveiled that the BDNF/proBDNF ratio in the hippocampus played a key role in anesthesia-/surgery-induced POCD. Thereby, tuning the ratio of BDNF/proBDNF is supposed to be a promising therapeutic target for POCD.

Reaching into the toolbox: Stem cell models to study neuropsychiatric disorders

Recent advances in genetics, molecular biology, and stem cell biology have accelerated our understanding of neuropsychiatric disorders, like autism spectrum disorder (ASD), major depressive disorder (MDD), bipolar disorder (BD), and schizophrenia (SZ). This progress highlights the incredible complexity of both the human brain and mental illnesses from the biochemical to the cellular level. Contributing to the complexity of neuropsychiatric disorders are their polygenic nature, cellular and brain region interconnectivity, and dysregulation of human-specific neurodevelopmental processes. Here, we discuss available tools, including CRISPR-Cas9, and the applications of these tools to develop cell-based two-dimensional (2D) models and 3D brain organoid models that better represent and unravel the intricacies of neuropsychiatric disorder pathophysiology.

The Transcriptome and Methylome of the Developing and Aging Brain and Their Relations to Gliomas and Psychological Disorders

Mutually linked expression and methylation dynamics in the brain govern genome regulation over the whole lifetime with an impact on cognition, psychological disorders, and cancer. We performed a joint study of gene expression and DNA methylation of brain tissue originating from the human prefrontal cortex of individuals across the lifespan to describe changes in cellular programs and their regulation by epigenetic mechanisms. The analysis considers previous knowledge in terms of functional gene signatures and chromatin states derived from independent studies, aging profiles of a battery of chromatin modifying enzymes, and data of gliomas and neuropsychological disorders for a holistic view on the development and aging of the brain. Expression and methylation changes from babies to elderly adults decompose into different modes associated with the serial activation of (brain) developmental, learning, metabolic and inflammatory functions, where methylation in gene promoters mostly represses transcription. Expression of genes encoding methylome modifying enzymes is very diverse reflecting complex regulations during lifetime which also associates with the marked remodeling of chromatin between permissive and restrictive states. Data of brain cancer and psychotic disorders reveal footprints of pathophysiologies related to brain development and aging. Comparison of aging brains with gliomas supports the view that glioblastoma-like and astrocytoma-like tumors exhibit higher cellular plasticity activated in the developing healthy brain while oligodendrogliomas have a more stable differentiation hierarchy more resembling the aged brain. The balance and specific shifts between volatile and stable and between more irreversible and more plastic epigenomic networks govern the development and aging of healthy and diseased brain.

Mechanisms of Neurotoxicity Associated with Exposure to the Herbicide Atrazine

Atrazine is an herbicide commonly used on crops to prevent broadleaf weeds. Atrazine is an endocrine-disrupting chemical mainly targeting the neuroendocrine system and associated axes, especially as a reproductive toxicant through attenuation of the luteinizing hormone (LH). Current regulatory levels for chronic exposure are based on no observed adverse effect levels (NOAELs) of these LH alterations in rodent studies. Atrazine has also been studied for its effects on the central nervous system and neurotransmission. The European Union (EU) recognized the health risks of atrazine exposure as a public health concern with no way to contain contamination of drinking water. As such, the EU banned atrazine use in 2003. The United States recently reapproved atrazine's use in the fall of 2020. Research has shown that there is a wide array of adverse health effects that are seen across multiple models, exposure times, and exposure periods leading to dysfunction in many different systems in the body with most pointing to a neuroendocrine target of toxicity. There is evidence of crosstalk between systems that can be affected by atrazine exposure, causing widespread dysfunction and leading to changes in behavior even with no direct link to the hypothalamus. The hypothetical mechanism of toxicity of atrazine endocrine disruption and neurotoxicity can therefore be described as a web of pathways that are influenced through changes occurring in each and their multiple feedback loops with further research needed to refine NOAELs for neurotoxic outcomes.

Study of locomotion response and development in zebrafish (Danio rerio) embryos and larvae exposed to enniatin A, enniatin B, and beauvericin

Mycotoxins are secondary metabolites produced by a variety of fungi that contaminate food and feed resources, and are capable of inducing a wide range of toxicity. Here, we studied the developmental and behavioral toxicity in zebrafish (Danio rerio) embryos and larvae exposed to three mycotoxins: beauvericin (BEA), Enniatin A (ENN A), and Ennitain B (ENN B). Zebrafish embryos were collected after fertilization, treated individually from 1 to 6 dpf with BEA at 8, 16, 32 and, 64 μM and for both enniatins at 3.12, 6.25, 12.5 and, 25 μM. Mixture of mycotoxins were assayed as follows: i) for BEA + ENN A and BEA + ENN B at [32 + 12.5] μM and [16 + 6.25] μM; ii) for ENN A + ENN B at [12.5 + 12.5] μM and [6.25 + 6.25] μM and, iii) for BEA + ENN A + ENN B at [32 + 12.5 + 12.5] μM and [16 + 6.25 + 6.25] μM. Response was collected after a white light-flash intermittent coming on for 5 s during 2 h with a imaging platform. Outcomes measured were: time to death, response to light, and circadian rhythm. This last outcome was measured in a plate where embryos had evolved in natural intervals of light and dark until day 7 or in a plate maintained in darkness. Images of all stages and evolution were collected. Results indicated that mycotoxins induced toxicity at the concentrations tested. All exposed zebrafish induced developmental defects, specifically hatching time and motion activity. After exposure, fish showed enhanced baseline activity but they lost their responsiveness to light.

Paternal exposure to excessive methionine altered behavior and neurochemical activities in zebrafish offspring

An increase in plasma L-methionine (Met) levels, even if transitory, can cause important toxicological alterations in the affected individuals. Met is essential in the regulation of epigenetic mechanisms and its influence on the subsequent generation has been investigated. However, few studies have explored the influence of a temporary increase in Met levels in parents on their offspring. This study evaluated the behavioral and neurochemical effects of parental exposure to high Met concentration (3 mM) in zebrafish offspring. Adult zebrafish were exposed to Met for 7 days, maintained for additional 7 days in tanks that contained only water, and then used for breeding. The offspring obtained from these fish (F1) were tested in this study. During the early stages of offspring development, morphology, heart rate, survival, locomotion, and anxiety-like behavior were assessed. When these animals reached the adult stage, locomotion, anxiety, aggression, social interaction, memory, oxidative stress, and levels of amino acids and neurotransmitters were analyzed. F1 larvae Met group presented an increase in the distance and mean speed when compared to the control group. F1 adult Met group showed decreased anxiety-like behavior and locomotion. An increase in reactive oxygen species was also observed in the F1 adult Met group whereas lipid peroxidation and antioxidant enzymes did not change when compared to the control group. Dopamine, serotonin, glutamate, and glutathione levels were increased in the F1 adult Met group. Taken together, our data show that even a transient increase in Met in parents can cause behavioral and neurochemical changes in the offspring, promoting transgenerational effects.

Agitation and Dementia: Prevention and Treatment Strategies in Acute and Chronic Conditions

Agitation is a behavioral syndrome characterized by increased, often undirected, motor activity, restlessness, aggressiveness, and emotional distress. According to several observations, agitation prevalence ranges from 30 to 50% in Alzheimer's disease, 30% in dementia with Lewy bodies, 40% in frontotemporal dementia, and 40% in vascular dementia (VaD). With an overall prevalence of about 30%, agitation is the third most common neuropsychiatric symptoms (NPS) in dementia, after apathy and depression, and it is even more frequent (80%) in residents of nursing homes. The pathophysiological mechanism underlying agitation is represented by a frontal lobe dysfunction, mostly involving the anterior cingulate cortex (ACC) and the orbitofrontal cortex (OFC), respectively, meaningful in selecting the salient stimuli and subsequent decision-making and behavioral reactions. Furthermore, increased sensitivity to noradrenergic signaling has been observed, possibly due to a frontal lobe up-regulation of adrenergic receptors, as a reaction to the depletion of noradrenergic neurons within the locus coeruleus (LC). Indeed, LC neurons mainly project toward the OFC and ACC. These observations may explain the abnormal reactivity to weak stimuli and the global arousal found in many patients who have dementia. Furthermore, agitation can be precipitated by several factors, e.g., the sunset or low lighted environments as in the sundown syndrome, hospitalization, the admission to nursing residencies, or changes in pharmacological regimens. In recent days, the global pandemic has increased agitation incidence among dementia patients and generated higher distress levels in patients and caregivers. Hence, given the increasing presence of this condition and its related burden on society and the health system, the present point of view aims at providing an extensive guide to facilitate the identification, prevention, and management of acute and chronic agitation in dementia patients.

Behavioral and Metabolome Differences between C57BL/6 and DBA/2 Mouse Strains: Implications for Their Use as Models for Depression- and Anxiety-Like Phenotypes

Mouse models are widely used to study behavioral phenotypes related to neuropsychiatric disorders. However, different mouse strains vary in their inherent behavioral and molecular characteristics, which needs to be taken into account depending on the nature of the study. Here, we performed a detailed behavioral and molecular comparison of C57BL/6 (B6) and DBA/2 (DBA) mice, two inbred strains commonly used in neuropsychiatric research. We analyzed anxiety-related and depression-like traits, quantified hippocampal and plasma metabolite profiles, and assessed total antioxidant capacity (ΤAC). B6 mice exhibit increased depression-like and decreased anxiety-related behavior compared to DBA mice. Metabolite level differences indicate alterations in amino acid, nucleotide and mitochondrial metabolism that are accompanied by a decreased TAC in B6 compared to DBA mice. Our data reveal multiple behavioral and molecular differences between B6 and DBA mouse strains, which should be considered in the experimental design for phenotype, pharmacological and mechanistic studies relevant for neuropsychiatric disorders.

Contributions of animal models of cognitive disorders to neuropsychopharmacology

Cognitive disorders and symptoms are key features of many mental and neurological diseases, with a large spectrum of impaired domains. Because of their possible evolution and detrimental functioning impact, they are a major pharmacological target for both symptomatic and disease-modifier drugs, while few cognitive enhancers have been marketed with an insufficient efficiency. It explains the need to model these cognitive disorders beyond the modelization of mental or neurological diseases themselves. According to the experimental strategy used to induce cognitive impairment, three categories of models have been identified: neurotransmission-driven models; pathophysiology-driven models; environment-driven models. These three categories of models reflect different levels of integration of endogenous and exogenous mechanisms underlying cognitive disorders in humans. Their comprehensive knowledge and illustration of their pharmacological modulation could help to propose a renewing strategy of drug development in central nervous system (CNS) field at a time when the academic and industrial invest seems to be declining despite the medical and social burden of brain diseases.

Neuroprotective potential of hydroethanolic hull extract of Juglans regia L. on isoprenaline induced oxidative damage in brain of Wistar rats

The study was aimed at assessing isoprenaline (ISO) induced oxidative damage in brain of Wistar rats and its protection by hydroethanolic hull extract of Juglans regia. Administration of ISO significantly increases catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR), malondialdehyde (MDA) and advanced oxidation protein product (AOPP) levels and significantly reduced activities of antioxidant status (TAS), total thiols (TTH), acetylcholinesterase (AChE), arylesterase (AE), and glutathione peroxidase (GPx) in rat brain. Histopathologically, neuronal degeneration, spongiosis and gliosis were seen in cerebral cortex after ISO administration. Pretreatment with hull extract restored TAS, TTH, AChE, CAT and SOD values. Additionally, significant reductions were noted in levels of MDA, AOPP, and severity of histomorphological changes in cerebral cortex following hull extract treatment. Altered antioxidant biomarkers along with histopathological changes indicate oxidative injury in rat brain following ISO administration. Repeated administration of J. regia hull extract demonstrating presence of neuroprotective properties against ISO induced oxidative damage in rat brain.

Attenuating Cholinergic Transmission Increases the Number of Satellite Cells and Preserves Muscle Mass in Old Age

In addition to driving contraction of skeletal muscles, acetylcholine (ACh) acts as an anti-synaptogenic agent at neuromuscular junctions (NMJs). Previous studies suggest that aging is accompanied by increases in cholinergic activity at the NMJ, which may play a role in neuromuscular degeneration. In this study, we hypothesized that moderately and chronically reducing ACh could attenuate the deleterious effects of aging on NMJs and skeletal muscles. To test this hypothesis, we analyzed NMJs and muscle fibers from heterozygous transgenic mice with reduced expression of the vesicular ACh transporter (VAChT; VKD^Het), which present with approximately 30% less synaptic ACh compared to control mice. Because ACh is constitutively decreased in VKD^Het, we first analyzed developing NMJs and muscle fibers. We found no obvious morphological or molecular differences between NMJs and muscle fibers of VKD^Het and control mice during development. In contrast, we found that moderately reducing ACh has various effects on adult NMJs and muscle fibers. VKD^Het mice have significantly larger NMJs and muscle fibers compared to age-matched control mice. They also present with reduced expression of the pro-atrophy gene, Foxo1, and have more satellite cells in skeletal muscles. These molecular and cellular features may partially explain the increased size of NMJs and muscle fibers. Thus, moderately reducing ACh may be a therapeutic strategy to prevent the loss of skeletal muscle mass that occurs with advancing age.

The role of oxidative stress in anxiety disorder: cause or consequence?

Anxiety disorders are the most common mental illness in the USA affecting 18% of the population. The cause(s) of anxiety disorders is/are not completely clear, and research in the neurobiology of anxiety at the molecular level is still rather limited. Although mounting clinical and preclinical evidence now indicates that oxidative stress may be a major component of anxiety pathology, whether oxidative stress is the cause or consequence remains elusive. Studies conducted over the past few years suggest that anxiety disorders may be characterised by lowered antioxidant defences and increased oxidative damage to proteins, lipids, and nucleic acids. In particular, oxidative modifications to proteins have actually been proposed as a potential factor in the onset and progression of several psychiatric disorders, including anxiety and depressive disorders. Oxidised proteins are normally degraded by the proteasome proteolytic complex in the cell cytoplasm, nucleus, and endoplasmic reticulum. The Lon protease performs a similar protective function inside mitochondria. Impairment of the proteasome and/or the Lon protease results in the accumulation of toxic oxidised proteins in the brain, which can cause severe neuronal trauma. Recent evidence points to possible proteolytic dysfunction and accumulation of damaged, oxidised proteins as factors that may determine the appearance and severity of psychotic symptoms in mood disorders. Thus, critical interactions between oxidative stress, proteasome, and the Lon protease may provide keys to the molecular mechanisms involved in emotional regulation, and may also be of great help in designing and screening novel anxiolytics and antidepressants.

Altered release and uptake of gamma-aminobutyric acid in the cerebellum of dystrophin-deficient mice

Dystrophin deficiency caused by mutations of the related gene leads to muscle wasting in Duchenne muscular dystrophy (DMD). Some patients with DMD also present with intellectual disability and various degrees of neurological disorders, which have been related to a decreased number of postsynaptic gamma-aminobutyric acid type A receptors (GABA_ARs) in the hippocampus (HPC) and cerebellum (CBL). The aim of this study was to examine the relevance of dystrophin in the presynaptic GABAergic function in brain regions in which this protein is normally abundant. [³H]-GABA release, induced by nicotinic receptor (nAChR) activation or K⁺ depolarization, and [³H]-GABA uptake were determined using synaptosomes extracted from the cortex (CTX), HPC, and CBL of littermate control and mdx mice. Superfusion of the synaptosomes with nicotine or high K⁺ solutions led to a concentration-dependent and Ca²⁺-dependent [³H]-GABA release in control and mdx synaptosomes. [³H]-GABA release induced by 10 μM nicotine in mdx CBL synaptosomes was 47% less than that in control mice. K⁺-induced [³H]-GABA release did not differ between control and mdx synaptosomes. α7-containing and β2-containing nAChRs were involved in nicotine-induced [³H]-GABA release in control and mdx synaptosomes. Kinetic analysis of [³H]-GABA uptake in mdx CBL synaptosomes showed a reduced (50%) half-maximal uptake time (t_1/2) and increased (44%) rate of [³H]-GABA uptake (V_max) compared to controls. The apparent transporter affinity (K_m) for GABA was not altered. Our findings show that dystrophin deficiency in mdx mice is associated with significant changes in the release and uptake of GABA in the CBL. These presynaptic alterations may be related to the reported decrease in postsynaptic GABA_AR in the same brain region. The results indicate possible dysfunction of GABAergic synapses associated with dystrophin deficiency in the CBL, which may contribute to the cognitive and neurobehavioral disorders in mdx mice and patients with DMD.

Absence of Claudin 11 in CNS Myelin Perturbs Behavior and Neurotransmitter Levels in Mice

Neuronal origins of behavioral disorders have been examined for decades to construct frameworks for understanding psychiatric diseases and developing useful therapeutic strategies with clinical application. Despite abundant anecdotal evidence for white matter etiologies, including altered tractography in neuroimaging and diminished oligodendrocyte-specific gene expression in autopsy studies, mechanistic data demonstrating that dysfunctional myelin sheaths can cause behavioral deficits and perturb neurotransmitter biochemistry have not been forthcoming. At least in part, this impasse stems from difficulties in identifying model systems free of degenerative pathology to enable unambiguous assessment of neuron biology and behavior in a background of myelin dysfunction. Herein we examine myelin mutant mice lacking expression of the Claudin11 gene in oligodendrocytes and characterize two behavioral endophenotypes: perturbed auditory processing and reduced anxiety/avoidance. Importantly, these behaviors are associated with increased transmission time along myelinated fibers as well as glutamate and GABA neurotransmitter imbalances in auditory brainstem and amygdala, in the absence of neurodegeneration. Thus, our findings broaden the etiology of neuropsychiatric disease to include dysfunctional myelin, and identify a preclinical model for the development of novel disease-modifying therapies.

Cognitive Characterization of Schizophrenia Risk Variants Involved in Synaptic Transmission: Evidence of CACNA1C's Role in Working Memory

With >100 common variants associated with schizophrenia risk, establishing their biological significance is a priority. We sought to establish cognitive effects of risk variants at loci implicated in synaptic transmission by (1) identifying GWAS schizophrenia variants whose associated gene function is related to synaptic transmission, and (2) testing for association between these and measures of neurocognitive function. We selected variants, reported in the largest GWAS to date, associated with genes involved in synaptic transmission. Associations between genotype and cognitive test score were analyzed in a discovery sample (988 Irish participants, including 798 with psychosis), and replication samples (528 UK patients with schizophrenia/schizoaffective disorder; 921 German participants including 362 patients with schizophrenia). Three loci showed significant associations with neuropsychological performance in the discovery samples. This included an association between the rs2007044 (risk allele G) within CACNA1C and poorer working memory performance (increased errors B (95% CI)=0.635-4.535, p=0.012), an effect driven mainly by the psychosis groups. In an fMRI analysis of working memory performance (n=84 healthy participants, a subset of the discovery sample), we further found evidence that the same CACNA1C allele was associated with decreased functional connectivity between the right dorsolateral prefrontal cortex and right superior occipital gyrus/cuneus and anterior cingulate cortex. In conclusion, these data provide evidence to suggest that the CACNA1C risk variant rs2007044 is associated with poorer memory function that may result from risk carriers' difficulty with top-down initiated responses caused by dysconnectivity between the right DLPFC and several cortical regions.

Instrumentation for electrochemical performance characterization of neural electrodes

In an effort to determine the chronic stability, sensitivity, and thus the potential viability of various neurochemical recording electrode designs and compositions, we have developed a custom device called the Voltammetry Instrument for Neurochemical Applications (VINA). Here, we describe the design of the VINA and initial testing of its functionality for prototype neurochemical sensing electrodes. The VINA consists of multiple electrode fixtures, a flowing electrolyte bath, associated reservoirs, peristaltic pump, voltage waveform generator, data acquisition hardware, and system software written in National Instrument's LabVIEW. The operation of VINA was demonstrated on a set of boron-doped diamond neurochemical recording electrodes, which were subjected to an applied waveform for a period of eighteen days. Each electrode's cyclic voltammograms (CVs) were recorded, and sensitivity calibration to dopamine (DA) was performed. Results showed an initial decline with subsequent stabilization in the CV current measured during the voltammetric sweep, corresponding closely with changes in electrode sensitivity to DA. The VINA has demonstrated itself as a useful tool for the characterization of electrode stability and chronic electrochemical performance.

Disruption of Ninjurin1 Leads to Repetitive and Anxiety-Like Behaviors in Mice

Over the last few decades, molecular neurobiology has uncovered many genes whose deficiency in mice results in behavioral traits associated with human neuropsychiatric disorders such as autism, obsessive-compulsive disorder (OCD), and schizophrenia. However, the etiology of these common diseases remains enigmatic with the potential involvement of a battery of genes. Here, we report abnormal behavioral phenotypes of mice deficient in a cell adhesion molecule Ninjurin 1 (Ninj1), which are relevant to repetitive and anxiety behaviors of neuropsychiatric disorders. Ninj1 knockout (KO) mice exhibit compulsive grooming-induced hair loss and self-made lesions as well as increased anxiety-like behaviors. Histological analysis reveals that Ninj1 is predominantly expressed in cortico-thalamic circuits, and neuron-specific Ninj1 conditional KO mice manifest aberrant phenotypes similar to the global Ninj1 KO mice. Notably, the brains of Ninj1 KO mice display altered synaptic transmission in thalamic neurons as well as a reduced number of functional synapses. Moreover, the disruption of Ninj1 leads to glutamatergic abnormalities, including increased ionotropic glutamate receptors but reduced glutamate levels. Furthermore, chronic treatment with fluoxetine, a drug reportedly ameliorates compulsive behaviors in mice, prevents progression of hair loss and alleviates the compulsive grooming and anxiety-like behavior of Ninj1 KO mice. Collectively, our results suggest that Ninj1 could be involved in neuropsychiatric disorders associated with impairments of repetitive and anxiety behaviors.

Zebrafish Get Connected: Investigating Neurotransmission Targets and Alterations in Chemical Toxicity

Neurotransmission is the basis of neuronal communication and is critical for normal brain development, behavior, learning, and memory. Exposure to drugs and chemicals can alter neurotransmission, often through unknown pathways and mechanisms. The zebrafish (Danio rerio) model system is increasingly being used to study the brain and chemical neurotoxicity. In this review, the major neurotransmitter systems, including glutamate, GABA, dopamine, norepinephrine, serotonin, acetylcholine, histamine, and glutamate are surveyed and pathways of synthesis, transport, metabolism, and action are examined. Differences between human and zebrafish neurochemical pathways are highlighted. We also review techniques for evaluating neurological function, including the measurement of neurotransmitter levels, assessment of gene expression through transcriptomic analysis, and the recording of neurobehavior. Finally examples of chemical toxicity studies evaluating alterations in neurotransmitter systems in the zebrafish model are reviewed.

Oral administration of potassium bromate induces neurobehavioral changes, alters cerebral neurotransmitters level and impairs brain tissue of swiss mice

Background

Potassium bromate (KBrO₃) is widely used as a food additive and is a major water disinfection by-product. The present study reports the side effects of KBrO₃ administration on the brain functions and behaviour of albino mice.

Methods

Animals were divided into three groups: control, low dose KBrO₃ (100 mg/kg/day) and high dose KBrO₃ (200 mg/kg/day) groups.

Results

Administration of KBrO₃ led to a significant change in the body weight in the animals of the high dose group in the first, second and the last weeks while water consumption was not significantly changed. Neurobehavioral changes and a reduced Neurotransmitters levels were observed in both KBrO₃ groups of mice. Also, the brain level of reduced glutathione (GSH) in KBrO₃ receiving animals was decreased. Histological studies favoured these biochemical results showing extensive damage in the histological sections of brain of KBrO₃-treated animals.

Conclusions

These results show that KBrO₃ has serious damaging effects on the central nervous system and therefore, its use should be avoided.

A Diamond-Based Electrode for Detection of Neurochemicals in the Human Brain

Deep brain stimulation (DBS), a surgical technique to treat certain neurologic and psychiatric conditions, relies on pre-determined stimulation parameters in an open-loop configuration. The major advancement in DBS devices is a closed-loop system that uses neurophysiologic feedback to dynamically adjust stimulation frequency and amplitude. Stimulation-driven neurochemical release can be measured by fast-scan cyclic voltammetry (FSCV), but existing FSCV electrodes rely on carbon fiber, which degrades quickly during use and is therefore unsuitable for chronic neurochemical recording. To address this issue, we developed durable, synthetic boron-doped diamond-based electrodes capable of measuring neurochemical release in humans. Compared to carbon fiber electrodes, they were more than two orders-of-magnitude more physically-robust and demonstrated longevity in vitro without deterioration. Applied for the first time in humans, diamond electrode recordings from thalamic targets in patients (n = 4) undergoing DBS for tremor produced signals consistent with adenosine release at a sensitivity comparable to carbon fiber electrodes. (Clinical trials # NCT01705301).

The kynurenine pathway as a therapeutic target in cognitive and neurodegenerative disorders

Understanding the neurochemical basis for cognitive function is one of the major goals of neuroscience, with a potential impact on the diagnosis, prevention and treatment of a range of psychiatric and neurological disorders. In this review, the focus will be on a biochemical pathway that remains under-recognized in its implications for brain function, even though it can be responsible for moderating the activity of two neurotransmitters fundamentally involved in cognition - glutamate and acetylcholine. Since this pathway - the kynurenine pathway of tryptophan metabolism - is induced by immunological activation and stress, it also stands in a unique position to mediate the effects of environmental factors on cognition and behaviour. Targeting the pathway for new drug development could, therefore, be of value not only for the treatment of existing psychiatric conditions, but also for preventing the development of cognitive disorders in response to environmental pressures.

The redistribution of Drosophila vesicular monoamine transporter mutants from synaptic vesicles to large dense-core vesicles impairs amine-dependent behaviors

Monoamine neurotransmitters are stored in both synaptic vesicles (SVs), which are required for release at the synapse, and large dense-core vesicles (LDCVs), which mediate extrasynaptic release. The contributions of each type of vesicular release to specific behaviors are not known. To address this issue, we generated mutations in the C-terminal trafficking domain of the Drosophila vesicular monoamine transporter (DVMAT), which is required for the vesicular storage of monoamines in both SVs and LDCVs. Deletion of the terminal 23 aa (DVMAT-Δ3) reduced the rate of endocytosis and localization of DVMAT to SVs, but supported localization to LDCVs. An alanine substitution mutation in a tyrosine-based motif (DVMAT-Y600A) also reduced sorting to SVs and showed an endocytic deficit specific to aminergic nerve terminals. Redistribution of DVMAT-Y600A from SV to LDCV fractions was also enhanced in aminergic neurons. To determine how these changes might affect behavior, we expressed DVMAT-Δ3 and DVMAT-Y600A in a dVMAT null genetic background that lacks endogenous dVMAT activity. When expressed ubiquitously, DVMAT-Δ3 showed a specific deficit in female fertility, whereas DVMAT-Y600A rescued behavior similarly to DVMAT-wt. In contrast, when expressed more specifically in octopaminergic neurons, both DVMAT-Δ3 and DVMAT-Y600A failed to rescue female fertility, and DVMAT-Y600A showed deficits in larval locomotion. DVMAT-Y600A also showed more severe dominant effects than either DVMAT-wt or DVMAT-Δ3. We propose that these behavioral deficits result from the redistribution of DVMAT from SVs to LDCVs. By extension, our data suggest that the balance of amine release from SVs versus that from LDCVs is critical for the function of some aminergic circuits.

Altered acetylcholine release in the hippocampus of dystrophin-deficient mice

Mild cognitive impairments have been described in one-third of patients with Duchenne muscle dystrophy (DMD). DMD is characterized by progressive and irreversible muscle degeneration caused by mutations in the dystrophin gene and lack of the protein expression. Previously, we have reported altered concentrations of α7- and β2-containing nicotinic acetylcholine receptors (nAChRs) in hippocampal membranes of dystrophic (mdx) mice. This suggests that alterations in the central cholinergic synapses are associated with dystrophin deficiency. In this study, we examined the release of acetylcholine (ACh) and the level of the vesicular ACh transporter (VAChT) using synaptosomes isolated from brain regions that normally have a high density of dystrophin (cortex, hippocampus and cerebellum), in control and mdx mice at 4 and 12months of age. ACh release evoked by nicotinic stimulation or K(+) depolarization was measured as the tritium outflow from superfused synaptosomes preloaded with [(3)H]-choline. The results showed that the evoked tritium release was Ca(2+)-dependent and mostly formed by [(3)H]-ACh. β2-containing nAChRs were involved in agonist-evoked [(3)H]-ACh release in control and mdx preparations. In hippocampal synaptosomes from 12-month-old mdx mice, nAChR-evoked [(3)H]-ACh release increased by 57% compared to age-matched controls. Moreover, there was a 98% increase in [(3)H]-ACh release compared to 4-month-old mdx mice. [(3)H]-ACh release evoked by K(+) depolarization was not altered, while the VAChT protein level was decreased (19%) compared to that of age-matched controls. In cortical and cerebellar preparations, there was no difference in nAChR-evoked [(3)H]-ACh release and VAChT levels between mdx and age-matched control groups. Our previous findings and the presynaptic alterations observed in the hippocampi of 12-month-old mdx mice indicate possible dysfunction of nicotinic cholinergic synapses associated with dystrophin deficiency. These changes may contribute to the cognitive and behavioral abnormalities described in dystrophic mice and patients with DMD.

Perforin- and granulysin-mediated cytotoxicity and interleukin 15 play roles in neurocognitive impairment in patients with acute lymphoblastic leukaemia

Acute lymphoblastic leukaemia (ALL) is an aggressive disease. The course of disease is regulated by pro-inflammatory agents, and malignant cell infiltration of tissues plays a deleterious role in disease progression, greatly impacting quality of life, especially in the cognitive domains. Our hypothesis is that significant serum concentrations of interleukin 15 (IL-15) are responsible for higher expression of adhesion molecules on endothelial cells of blood-brain barrier (BBB) which allow leukaemia cells and/or normal lymphocytes the infiltration into the brain. In brain tissue these cells could be stimulated to release perforin and granulysin causing induction of apoptosis in brain cells that are involved in complex neural signalling mediated by neurotransmitters, and consequent fine cognitive impairment. Such changes could be detected early, even before notable clinical psycho-neurological or radiological changes in patients with ALL. To evaluate this hypothesis we propose measuring cognitive function using Complex Reactiometer Drenovac (CRD) scores in patients with ALL. The expression of different adhesion molecules on BBB as well as presence and distribution of different lymphocytes in brain tissue will be analyzed. We will then correlate CRD scores with levels of IL-15 and the percentages of T cells, natural killer T cells, and natural killer cells expressing perforin and/or granulysin proteins. CRD is a scientifically recognised and highly sensitive psychometric laboratory test based on the complex chronometric mathematical measuring of speed of reaction to various stimuli. It provides an objective assessment of cognitive functions from the most complex mental activities to the simplest reaction reflexes. Early recognition of cognitive dysfunction might be important when selecting the most appropriate chemotherapy and/or radiotherapy regimens, and could allow for the implementation of preventive measures against further deterioration in cognitive function and quality of life in patients with ALL.

Cholinergic control over attention in rats prone to attribute incentive salience to reward cues

Some rats [sign-trackers (STs)] are especially prone to attribute incentive salience to reward cues, relative to others [goal-trackers (GTs)]. Thus, reward cues are more likely to promote maladaptive reward-seeking behavior in STs than GTs. Here, we asked whether STs and GTs differ on another trait that can contribute to poor restraint over behavior evoked by reward cues. We report that, relative to GTs, STs have poor control over attentional performance, due in part to insufficient cholinergic stimulation of cortical circuitry. We found that, relative to GTs, STs showed poor performance on a sustained attention task (SAT). Furthermore, their performance fluctuated rapidly between periods of good to near-chance performance. This finding was reproduced using a separate cohort of rats. As demonstrated earlier, performance on the SAT was associated with increases in extracellular levels of cortical acetylcholine (ACh); however, SAT performance-associated increases in ACh levels were significantly attenuated in STs relative to GTs. Consistent with the view that the modulatory effects of ACh involve stimulation of α4β2* nicotinic ACh receptors (nAChRs), systemic administration of the partial nAChR agonist ABT-089 improved SAT performance in STs and abolished the difference between SAT-associated ACh levels in STs and GTs. Neither the nonselective nAChR agonist nicotine nor the psychostimulant amphetamine improved SAT performance. These findings suggest that individuals who have a propensity to attribute high-incentive salience to reward cues also exhibit relatively poor attentional control. A combination of these traits may render individuals especially vulnerable to disorders, such as obesity and addiction.

A linear model for estimation of neurotransmitter response profiles from dynamic PET data

The parametric ntPET model (p-ntPET) estimates the kinetics of neurotransmitter release from dynamic PET data with receptor-ligand radiotracers. Here we introduce a linearization (lp-ntPET) that is computationally efficient and can be applied to single scan data. lp-ntPET employs a non-invasive reference region input function and extends the LSRRM of Alpert et al. (2003) using basis functions to characterize the time course of neurotransmitter activation. In simulation studies, the temporal precision of neurotransmitter profiles estimated by lp-ntPET was similar to that of p-ntPET (standard deviation ~3 min for responses early in the scan) while computation time was reduced by several orders of magnitude. Violations of model assumptions such as activation-induced changes in regional blood flow or specific binding in the reference tissue have negligible effects on lp-ntPET performance. Application of the lp-ntPET method is demonstrated on [11C]raclopride data acquired in rats receiving methamphetamine, which yielded estimated response functions that were in good agreement with simultaneous microdialysis measurements of extracellular dopamine concentration. These results demonstrate that lp-ntPET is a computationally efficient, linear variant of ntPET that can be applied to PET data from single or multiple scan designs to estimate the time course of neurotransmitter activation.

DRUG FOCUS: S 18986: A positive allosteric modulator of AMPA-type glutamate receptors pharmacological profile of a novel cognitive enhancer

Alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) type glutamate receptors are critical for synaptic plasticity and induction of long-term potentiation (LTP), considered as one of the synaptic mechanisms underlying learning and memory. Positive allosteric modulators of AMPA receptors could provide a therapeutic approach to the treatment of cognitive disorders resulting from aging and/or neurodegenerative diseases, such as Alzheimer disease (AD). Several AMPA potentiators have been described in the last decade, but for the moment their clinical efficacy has not been demonstrated due to the complexity of the target, AMPA receptors, and the difficulty in studying cognition in animals and humans. A better understanding of the mechanism of action of this type of drug remains an important issue, if knowledge of these compounds is to be increased and if this novel therapeutic approach is to be an interesting research area. Among the AMPA potentiators, S 18986 is emerging as a new selective positive allosteric modulator of AMPA-type glutamate receptors. S 18986, as with other positive AMPA receptor modulators, increased induction and maintenance of LTP in the hippocampus as well as the expression of brain-derived neurotrophic factor (BDNF) both in vitro and in vivo. Its cognitive-enhancing properties have been demonstrated in various behavioral models (procedural, spatial, "episodic," working, and relational/declarative memory) in young-adult and aged rodents. It is interesting to note that memory-enhancing effects appeared more robust in middle-aged animals compared with aged ones and in "episodic" and spatial memory tasks. From these results, S 18986 is expected to treat memory deficits associated with early cerebral aging and neurological diseases in elderly people.

Modes and models of forebrain cholinergic neuromodulation of cognition

As indicated by the profound cognitive impairments caused by cholinergic receptor antagonists, cholinergic neurotransmission has a vital role in cognitive function, specifically attention and memory encoding. Abnormally regulated cholinergic neurotransmission has been hypothesized to contribute to the cognitive symptoms of neuropsychiatric disorders. Loss of cholinergic neurons enhances the severity of the symptoms of dementia. Cholinergic receptor agonists and acetylcholinesterase inhibitors have been investigated for the treatment of cognitive dysfunction. Evidence from experiments using new techniques for measuring rapid changes in cholinergic neurotransmission provides a novel perspective on the cholinergic regulation of cognitive processes. This evidence indicates that changes in cholinergic modulation on a timescale of seconds is triggered by sensory input cues and serves to facilitate cue detection and attentional performance. Furthermore, the evidence indicates cholinergic induction of evoked intrinsic, persistent spiking mechanisms for active maintenance of sensory input, and planned responses. Models have been developed to describe the neuronal mechanisms underlying the transient modulation of cortical target circuits by cholinergic activity. These models postulate specific locations and roles of nicotinic and muscarinic acetylcholine receptors and that cholinergic neurotransmission is controlled in part by (cortical) target circuits. The available evidence and these models point to new principles governing the development of the next generation of cholinergic treatments for cognitive disorders.

Cholinergic contributions to the cognitive symptoms of schizophrenia and the viability of cholinergic treatments

Effective treatment of the cognitive symptoms of schizophrenia has remained an elusive goal. Despite the intense focus on treatments acting at or via cholinergic mechanisms, little remains known about the dynamic cholinergic abnormalities that contribute to the manifestation of the cognitive symptoms in patients. Evidence from basic neuroscientific and psychopharmacological investigations assists in proposing detailed cholinergic mechanisms and treatment targets for enhancement of attentional performance. Dynamic, cognitive performance-dependent abnormalities in cholinergic activity have been observed in animal models of the disorder and serve to further refine such proposals. Finally, the potential usefulness of individual groups of cholinergic drugs and important issues concerning the interactions between pro-cholinergic and antipsychotic treatments are addressed. The limited evidence available from patient studies and animal models indicates pressing research needs in order to guide the development of cholinergic treatments of the cognitive symptoms of schizophrenia.

What is remembered? Role of attention on the encoding and retrieval of hippocampal representations

The hippocampus is critically involved in storing explicit memory such as memory for space. A defining feature of explicit memory storage is that it requires attention both for encoding and retrieval. Whereas, a great deal is now known about the mechanisms of storage, the mechanisms whereby attention modulates the encoding and retrieval of space and other hippocampus-dependent memory representations are not known. In this review we discuss recent studies, including our own, which show on the cellular level that attention is critical for the stabilization of spatial and reward-associated odour representations. Our findings support the view that in the hippocampus attention selects the reference frame for task-relevant information. This mechanism is in part mediated by dopamine acting through D1/D5 receptors and involves an increase in neuronal synchronization in the gamma band frequency. We propose that synchronous activity leads to enhancements in synaptic strength that mediate the stabilization of hippocampal representations.