Physical, behavioral, and cognitive effects of prenatal tobacco and postnatal secondhand smoke exposure

The purpose of this review is to examine the rapidly expanding literature regarding the effects of prenatal tobacco and postnatal secondhand smoke (SHS) exposure on child health and development. Mechanisms of SHS exposure are reviewed, including critical periods during which exposure to tobacco products appears to be particularly harmful to the developing fetus and child. The biological, biochemical, and neurologic effects of the small fraction of identified components of SHS are described. Research describing these adverse effects of both in utero and childhood exposure is reviewed, including findings from both animal models and humans. The following adverse physical outcomes are discussed: sudden infant death syndrome, low birth weight, decreased head circumference, respiratory infections, otitis media, asthma, childhood cancer, hearing loss, dental caries, and the metabolic syndrome. In addition, the association between the following adverse cognitive and behavioral outcomes and such exposures is described: conduct disorder, attention-deficit/hyperactivity disorder, poor academic achievement, and cognitive impairment. The evidence supporting the adverse effects of SHS exposure is extensive yet rapidly expanding due to improving technology and increased awareness of this profound public health problem. The growing use of alternative tobacco products, such as hookahs (a.k.a. waterpipes), and the scant literature on possible effects from prenatal and secondhand smoke exposure from these products are also discussed. A review of the current knowledge of this important subject has implications for future research as well as public policy and clinical practice.

The role of microglia in diabetic retinopathy

There is growing evidence that chronic inflammation plays a role in both the development and progression of diabetic retinopathy. There is also evidence that molecules produced as a result of hyperglycemia can activate microglia. However the exact contribution of microglia, the resident immune cells of the central nervous system, to retinal tissue damage during diabetes remains unclear. Current data suggest that dysregulated microglial responses are linked to their deleterious effects in several neurological diseases associated with chronic inflammation. As inflammatory cytokines and hyperglycemia disseminate through the diabetic retina, microglia can change to an activated state, increase in number, translocate through the retina, and themselves become the producers of inflammatory and apoptotic molecules or alternatively exert anti-inflammatory effects. In addition, microglial genetic variations may account for some of the individual differences commonly seen in patient's susceptibility to diabetic retinopathy.

The nerve growth factor signaling and its potential as therapeutic target for glaucoma

Neuroprotective therapies which focus on factors leading to retinal ganglion cells (RGCs) degeneration have been drawing more and more attention. The beneficial effects of nerve growth factor (NGF) on the glaucoma have been recently suggested, but its effects on eye tissue are complex and controversial in various studies. Recent clinical trials of systemically and topically administrated NGF demonstrate that NGF is effective in treating several ocular diseases, including glaucoma. NGF has two receptors named high affinity NGF tyrosine kinase receptor TrkA and low affinity receptor p75NTR. Both receptors exist in cells in retina like RGC (expressing TrkA) and glia cells (expressing p75NTR). NGF functions by binding to TrkA or p75NTR alone or both together. The binding of NGF to TrkA alone in RGC promotes RGC's survival and proliferation through activation of TrkA and several prosurvival pathways. In contrast, the binding of NGF to p75NTR leads to apoptosis although it also promotes survival in some cases. Binding of NGF to both TrkA and p75NTR at the same time leads to survival in which p75NTR functions as a TrkA helping receptor. This review discusses the current understanding of the NGF signaling in retina and the therapeutic implications in the treatment of glaucoma.

A two-layered diffusion model traces the dynamics of information processing in the valuation-and-choice circuit of decision making

A circuit of evaluation and selection of the alternatives is considered a reliable model in neurobiology. The prominent contributions of the literature to this topic are reported. In this study, valuation and choice of a decisional process during Two-Alternative Forced-Choice (TAFC) task are represented as a two-layered network of computational cells, where information accrual and processing progress in nonlinear diffusion dynamics. The evolution of the response-to-stimulus map is thus modeled by two linked diffusive modules (2LDM) representing the neuronal populations involved in the valuation-and-decision circuit of decision making. Diffusion models are naturally appropriate for describing accumulation of evidence over the time. This allows the computation of the response times (RTs) in valuation and choice, under the hypothesis of ex-Wald distribution. A nonlinear transfer function integrates the activities of the two layers. The input-output map based on the infomax principle makes the 2LDM consistent with the reinforcement learning approach. Results from simulated likelihood time series indicate that 2LDM may account for the activity-dependent modulatory component of effective connectivity between the neuronal populations. Rhythmic fluctuations of the estimate gain functions in the delta-beta bands also support the compatibility of 2LDM with the neurobiology of DM.

Encoding and decoding in parietal cortex during sensorimotor decision-making

The lateral intraparietal area (LIP) of macaques has been asserted to play a fundamental role in sensorimotor decision-making. Here we dissect the neural code in LIP at the level of individual trial spike trains using a statistical approach based on generalized linear models. We show that LIP responses reflect a combination of temporally-overlapping task and decision-related signals. Our model accounts for the detailed statistics of LIP spike trains, and accurately predicts spike trains from task events on single trials. Moreover, we derive an optimal decoder for heterogeneous, multiplexed LIP responses that could be implemented in biologically plausible circuits. In contrast to interpretations of LIP as providing an instantaneous code for decision variables, we show that optimal decoding requires integrating LIP spikes over two timescales. These analyses provide a detailed understanding of the neural code in LIP, and a framework for studying the coding of multiplexed signals in higher brain areas.

Cocaine dependent individuals with attenuated striatal activation during reinforcement learning are more susceptible to relapse

Cocaine-dependent individuals show altered brain activation during decision making. It is unclear, however, whether these activation differences are related to relapse vulnerability. This study tested the hypothesis that brain-activation patterns during reinforcement learning are linked to relapse 1 year later in individuals entering treatment for cocaine dependence. Subjects performed a Paper-Scissors-Rock task during functional magnetic resonance imaging (fMRI). A year later, we examined whether subjects had remained abstinent (n=15) or relapsed (n=15). Although the groups did not differ on demographic characteristics, behavioral performance, or lifetime substance use, abstinent patients reported greater motivation to win than relapsed patients. The fMRI results indicated that compared with abstinent individuals, relapsed users exhibited lower activation in (1) bilateral inferior frontal gyrus and striatum during decision making more generally; and (2) bilateral middle frontal gyrus and anterior insula during reward contingency learning in particular. Moreover, whereas abstinent patients exhibited greater left middle frontal and striatal activation to wins than losses, relapsed users did not demonstrate modulation in these regions as a function of outcome valence. Thus, individuals at high risk for relapse relative to those who are able to abstain allocate fewer neural resources to action-outcome contingency formation and decision making, as well as having less motivation to win on a laboratory-based task.

Orienting of attention: Then and now

It is nearly 35 years since I gave the 7th Sir Frederick Bartlett lecture at Oxford University. This was published as a paper entitled "Orienting of attention in the quarterly journal". The topic was then primarily in psychology, but now equally often in neuroscience. This paper summarizes the background of the reaction time methods used in the original paper and findings that emerged later on the sensory consequences of orienting, mainly in the visual system. It then discusses the brain network that is the source of the sensory amplification and other brain networks that are involved in attention. Next, it reviews studies of the development of attentional networks in early life. Finally, it indicates how the new tools available to explore the human brain can lead to further progress.

Functions of the human frontoparietal attention network: Evidence from neuroimaging

Human frontoparietal cortex has long been implicated as a source of attentional control. However, the mechanistic underpinnings of these control functions have remained elusive due to limitations of neuroimaging techniques that rely on anatomical landmarks to localize patterns of activation. The recent advent of topographic mapping via functional magnetic resonance imaging (fMRI) has allowed the reliable parcellation of the network into 18 independent subregions in individual subjects, thereby offering unprecedented opportunities to address a wide range of empirical questions as to how mechanisms of control operate. Here, we review the human neuroimaging literature that has begun to explore space-based, feature-based, object-based and category-based attentional control within the context of topographically defined frontoparietal cortex.

Inhibition of phosphodiesterase 2 reverses impaired cognition and neuronal remodeling caused by chronic stress

Chronic stress and neuronal vulnerability have recently been recognized as factors contributing to cognitive disorders. One way to modify neuronal vulnerability is through mediation of phosphodiesterase 2 (PDE2), an enzyme that exerts its action on cognitive processes via the control of intracellular second messengers, cGMP and, to a lesser extent, cAMP. This study explored the effects of a PDE2 inhibitor, Bay 60-7550, on stress-induced learning and memory dysfunction in terms of its ramification on behavioral, morphologic, and molecular changes. Bay 60-7550 reversed stress-induced cognitive impairment in the Morris water maze, novel object recognition, and location tasks (object recognition test and/or object location test), effects prevented by treatment with 7-NI, a selective inhibitor of neuronal nitric oxide synthase; MK801, a glutamate receptor (NMDAR) inhibitor; myr-AIP, a CaMKII inhibitor; and KT5823, a protein kinase G inhibitor. Bay 60-7550 also ameliorated stress-induced structural remodeling in the CA1 of the hippocampus, leading to increases in dendritic branching, length, and spine density. However, the neuroplasticity initiated by Bay 60-7550 was not seen in the presence of 7-NI, MK801, myr-AIP, or KT5823. PDE2 inhibition reduced stress-induced extracellular-regulated protein kinase activation and attenuated stress-induced decreases in transcription factors (e.g., Elk-1, TORC1, and CREB phosphorylation) and plasticity-related proteins (e.g., Egr-1 and brain-derived neurotrophic factor). Pretreatment with inhibitors of NMDA, CaMKII, neuronal nitric oxide synthase, and protein kinase G (or protein kinase A) blocked the effects of Bay 60-7550 on cGMP or cAMP signaling. These findings indicate that the effect of PDE2 inhibition on stress-induced memory impairment is potentially mediated via modulation of neuroplasticity-related NMDAR-CaMKII-cGMP/cAMP signaling.

Reduced cortical thickness in veterans exposed to early life trauma

Studies have shown that early life trauma may influence neural development and increase the risk of developing psychological disorders in adulthood. We used magnetic resonance imaging to examine the impact of early life trauma on the relationship between current posttraumatic stress disorder (PTSD) symptoms and cortical thickness/subcortical volumes in a sample of deployed personnel from Operation Enduring Freedom/Operation Iraqi Freedom. A group of 108 service members enrolled in the Translational Research Center for Traumatic Brain Injury and Stress Disorders (TRACTS) were divided into those with interpersonal early life trauma (EL-Trauma+) and Control (without interpersonal early life trauma) groups based on the Traumatic Life Events Questionnaire. PTSD symptoms were assessed using the Clinician-Administered PTSD Scale. Cortical thickness and subcortical volumes were analyzed using the FreeSurfer image analysis package. Thickness of the paracentral and posterior cingulate regions was positively associated with PTSD severity in the EL-Trauma+ group and negatively in the Control group. In the EL-Trauma+ group, both the right amygdala and the left hippocampus were positively associated with PTSD severity. This study illustrates a possible influence of early life trauma on the vulnerability of specific brain regions to stress. Changes in neural morphometry may provide information about the emergence and maintenance of symptoms in individuals with PTSD.

Age-related changes in the intrinsic functional connectivity of the human ventral vs. dorsal striatum from childhood to middle age

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Striatal resting state iFC in 106 healthy individuals ranging from 9 to 44 years.

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Findings cohere with a dorsal–ventral functional dissociation of the striatum.

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Ventral striatal (VS) iFC with insula and anterior cingulate decreased with age.

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Dorsal striatal (DS) iFC with posterior cingulate increased with age.

The striatum codes motivated behavior. Delineating age-related differences within striatal circuitry can provide insights into neural mechanisms underlying ontogenic behavioral changes and vulnerabilities to mental disorders. To this end, a dual ventral/dorsal model of striatal function was examined using resting state intrinsic functional connectivity (iFC) imaging in 106 healthy individuals, ages 9–44. Broadly, the dorsal striatum (DS) is connected to prefrontal and parietal cortices and contributes to cognitive processes; the ventral striatum (VS) is connected to medial orbitofrontal and anterior cingulate cortices, and contributes to affective valuation and motivation. Findings revealed patterns of age-related changes that differed between VS and DS iFCs. We found an age-related increase in DS iFC with posterior cingulate cortex (pCC) that stabilized after the mid-twenties, but a decrease in VS iFC with anterior insula (aIns) and dorsal anterior cingulate cortex (dACC) that persisted into mid-adulthood. These distinct developmental trajectories of VS vs. DS iFC might underlie adolescents’ unique behavioral patterns and vulnerabilities to psychopathology, and also speaks to changes in motivational networks that extend well past 25 years old.

Neural signatures of the interaction between the 5-HTTLPR genotype and stressful life events in healthy women

A change in neural connectivity of brain structures implicated in the memory of negative life events has been hypothesized to explain the enhancement of memory encoding during the processing of negative stimuli in depressed patients. Here, we investigated the effects of the interaction between negative life events and the 5-HTTLPR genotype - a polymorphism of the serotonin transporter gene - on the functional and structural connectivity of the hippocampal area in 34 healthy women. All participants were genotyped for the presence of the 5-HTTLPR short variant and for the A/G single-nucleotide polymorphism; they underwent clinical assessment including structured diagnostic interviews to exclude the presence of psychiatric disorders and to assess the presence of stressful life events. Resting state functional magnetic resonance imaging and diffusion tensor imaging scans were performed. We found significant interactions between stressful events and the 5-HTTLPR genotype in both the functional connectivity of the parahippocampus with the posterior cingulate cortex and the structural connectivity between the hippocampus and both the amygdala and the putamen. In addition, we found several genotype-related differences in the relationship between functional/structural connectivity of the hippocampal area and the ability to update expectations or stress-related phenotypes, such as anxiety symptoms. If confirmed by future studies, these mechanisms may clarify the role of the 5HTTLPR genotype as a risk factor for depression, in interaction with negative events.

The Effects of 12 Weeks Regular Aerobic Exercise on Brain-derived Neurotrophic Factor and Inflammatory Factors in Juvenile Obesity and Type 2 Diabetes Mellitus

[Purpose] The purpose of this study was to investigate the effects of 12 weeks regular aerobic exercise on brain-derived neurotrophic factor (BDNF) and inflammatory factors in juvenile obesity and type 2 diabetes mellitus (T2DM). Obesity and T2DM, typically common among adults, have recently become more prevalent in the Korean juvenile population, affecting not only their lipid profiles and oxidant stress levels, but also their BDNF and inflammatory factor levels. [Subjects] This study enrolled 26 juveniles (boys = 15, girls = 9) who were assigned to a control group (CG, n = 11), obesity group (OG, n = 8), or T2DM group (TG, n = 7). [Methods] The outcome of a 40–60-minute aerobic exercise session that took place three times per week for 12 weeks at a maximum oxygen intake (VO_2max) of 50~60% was investigated. [Results] The exercise resulted in a significant reduction in the resting serum BDNF and TrkB levels (baseline) among juveniles in the OG and TG as compared to those in the CG. Additionally, the 12 weeks of regular aerobic exercise led to significant reductions in body weight, body fat percentage, and body mass index in the OG and a significant increase of VO_2max in the OG and TG. However, no significant differences in serum NGF or inflammatory factors were found among the three groups. There was a significant increase in resting serum BDNF levels following the 12 weeks regular exercise only in the OG. [Conclusion] While 12 weeks of regular aerobic exercise had a positive effect on body composition, and increased BDNF levels of juveniles in the OG, it did not affect the inflammatory factor levels and had no effect on the TG.

Effects of repetitive transcranial magnetic stimulation on recovery of function after spinal cord injury

A major goal of rehabilitation strategies after spinal cord injury (SCI) is to enhance the recovery of function. One possible avenue to achieve this goal is to strengthen the efficacy of the residual neuronal pathways. Noninvasive repetitive transcranial magnetic stimulation (rTMS) has been used in patients with motor disorders as a tool to modulate activity of corticospinal, cortical, and subcortical pathways to promote functional recovery. This article reviews a series of studies published during the last decade that used rTMS in the acute and chronic stages of paraplegia and tetraplegia in humans with complete and incomplete SCI. In the studies, rTMS has been applied over the arm and leg representations of the primary motor cortex to target 3 main consequences of SCI: sensory and motor function impairments, spasticity, and neuropathic pain. Although some studies demonstrated that consecutive sessions of rTMS improve aspects of particular functions, other studies did not show similar effects. We discuss how rTMS parameters and postinjury reorganization in the corticospinal tract, motor cortical, and spinal cord circuits might be critical factors in understanding the advantages and disadvantages of using rTMS in patients with SCI. The available data highlight the limited information on the use of rTMS after SCI and the need to further understand the pathophysiology of neuronal structures affected by rTMS to maximize the potential beneficial effects of this technique in humans with SCI.

Development of thalamocortical connectivity during infancy and its cognitive correlations

Although commonly viewed as a sensory information relay center, the thalamus has been increasingly recognized as an essential node in various higher-order cognitive circuits, and the underlying thalamocortical interaction mechanism has attracted increasing scientific interest. However, the development of thalamocortical connections and how such development relates to cognitive processes during the earliest stages of life remain largely unknown. Leveraging a large human pediatric sample (N = 143) with longitudinal resting-state fMRI scans and cognitive data collected during the first 2 years of life, we aimed to characterize the age-dependent development of thalamocortical connectivity patterns by examining the functional relationship between the thalamus and nine cortical functional networks and determine the correlation between thalamocortical connectivity and cognitive performance at ages 1 and 2 years. Our results revealed that the thalamus-sensorimotor and thalamus-salience connectivity networks were already present in neonates, whereas the thalamus-medial visual and thalamus-default mode network connectivity emerged later, at 1 year of age. More importantly, brain-behavior analyses based on the Mullen Early Learning Composite Score and visual-spatial working memory performance measured at 1 and 2 years of age highlighted significant correlations with the thalamus-salience network connectivity. These results provide new insights into the understudied early functional brain development process and shed light on the behavioral importance of the emerging thalamocortical connectivity during infancy.

Prion protein and aging

The cellular prion protein (PrP^C) has been widely investigated ever since its conformational isoform, the prion (or PrP^Sc), was identified as the etiological agent of prion disorders. The high homology shared by the PrP^C-encoding gene among mammals, its high turnover rate and expression in every tissue strongly suggest that PrP^C may possess key physiological functions. Therefore, defining PrP^C roles, properties and fate in the physiology of mammalian cells would be fundamental to understand its pathological involvement in prion diseases. Since the incidence of these neurodegenerative disorders is enhanced in aging, understanding PrP^C functions in this life phase may be of crucial importance. Indeed, a large body of evidence suggests that PrP^C plays a neuroprotective and antioxidant role. Moreover, it has been suggested that PrP^C is involved in Alzheimer disease, another neurodegenerative pathology that develops predominantly in the aging population. In prion diseases, PrP^C function is likely lost upon protein aggregation occurring in the course of the disease. Additionally, the aging process may alter PrP^C biochemical properties, thus influencing its propensity to convert into PrP^Sc. Both phenomena may contribute to the disease development and progression. In Alzheimer disease, PrP^C has a controversial role because its presence seems to mediate β-amyloid toxicity, while its down-regulation correlates with neuronal death. The role of PrP^C in aging has been investigated from different perspectives, often leading to contrasting results. The putative protein functions in aging have been studied in relation to memory, behavior and myelin maintenance. In aging mice, PrP^C changes in subcellular localization and post-translational modifications have been explored in an attempt to relate them to different protein roles and propensity to convert into PrP^Sc. Here we provide an overview of the most relevant studies attempting to delineate PrP^C functions and fate in aging.

Online stimulus optimization rapidly reveals multidimensional selectivity in auditory cortical neurons

Neurons in sensory brain regions shape our perception of the surrounding environment through two parallel operations: decomposition and integration. For example, auditory neurons decompose sounds by separately encoding their frequency, temporal modulation, intensity, and spatial location. Neurons also integrate across these various features to support a unified perceptual gestalt of an auditory object. At higher levels of a sensory pathway, neurons may select for a restricted region of feature space defined by the intersection of multiple, independent stimulus dimensions. To further characterize how auditory cortical neurons decompose and integrate multiple facets of an isolated sound, we developed an automated procedure that manipulated five fundamental acoustic properties in real time based on single-unit feedback in awake mice. Within several minutes, the online approach converged on regions of the multidimensional stimulus manifold that reliably drove neurons at significantly higher rates than predefined stimuli. Optimized stimuli were cross-validated against pure tone receptive fields and spectrotemporal receptive field estimates in the inferior colliculus and primary auditory cortex. We observed, from midbrain to cortex, increases in both level invariance and frequency selectivity, which may underlie equivalent sparseness of responses in the two areas. We found that onset and steady-state spike rates increased proportionately as the stimulus was tailored to the multidimensional receptive field. By separately evaluating the amount of leverage each sound feature exerted on the overall firing rate, these findings reveal interdependencies between stimulus features as well as hierarchical shifts in selectivity and invariance that may go unnoticed with traditional approaches.

Loss of GluN2A-containing NMDA receptors impairs extra-dimensional set-shifting

Glutamate neurotransmission via the N-methyl-D-aspartate receptor (NMDAR) is thought to mediate the synaptic plasticity underlying learning and memory formation. There is increasing evidence that deficits in NMDAR function are involved in the pathophysiology of cognitive dysfunction seen in neuropsychiatric disorders and addiction. NMDAR subunits confer different physiological properties to the receptor, interact with distinct intracellular postsynaptic scaffolding and signaling molecules, and are differentially expressed during development. Despite these known differences, the relative contribution of individual subunit composition to synaptic plasticity and learning is not fully elucidated. We have previously shown that constitutive deletion of GluN2A subunit in the mouse impairs discrimination and re-learning phase of reversal when exemplars are complex picture stimuli, but spares acquisition and extinction of non-discriminative visually cued instrumental response. To investigate the role of GluN2A containing NMDARs in executive control, we tested GluN2A knockout (GluN2A(KO) ), heterozygous (GluN2A(HET) ) and wild-type (WT) littermates on an attentional set-shifting task using species-specific stimulus dimensions. To further explore the nature of deficits in this model, mice were tested on a visual discrimination reversal paradigm using simplified rotational stimuli. GluN2A(KO) were not impaired on discrimination or reversal problems when tactile or olfactory stimuli were used, or when visual stimuli were sufficiently easy to discriminate. GluN2A(KO) showed a specific and significant impairment in ventromedial prefrontal cortex-mediated set-shifting. Together these results support a role for GluN2A containing NMDAR in modulating executive control that can be masked by overlapping deficits in attentional processes during high task demands.

Astrocyte glutamine synthetase: pivotal in health and disease

The multifunctional properties of astrocytes signify their importance in brain physiology and neurological function. In addition to defining the brain architecture, astrocytes are primary elements of brain ion, pH and neurotransmitter homoeostasis. GS (glutamine synthetase), which catalyses the ATP-dependent condensation of ammonia and glutamate to form glutamine, is an enzyme particularly found in astrocytes. GS plays a pivotal role in glutamate and glutamine homoeostasis, orchestrating astrocyte glutamate uptake/release and the glutamate-glutamine cycle. Furthermore, astrocytes bear the brunt of clearing ammonia in the brain, preventing neurotoxicity. The present review depicts the central function of astrocytes, concentrating on the importance of GS in glutamate/glutamine metabolism and ammonia detoxification in health and disease.

Fluctuations in oscillation frequency control spike timing and coordinate neural networks

Neuroscience research spans multiple spatiotemporal scales, from subsecond dynamics of individual neurons to the slow coordination of billions of neurons during resting state and sleep. Here it is shown that a single functional principle-temporal fluctuations in oscillation peak frequency ("frequency sliding")-can be used as a common analysis approach to bridge multiple scales within neuroscience. Frequency sliding is demonstrated in simulated neural networks and in human EEG data during a visual task. Simulations of biophysically detailed neuron models show that frequency sliding modulates spike threshold and timing variability, as well as coincidence detection. Finally, human resting-state EEG data demonstrate that frequency sliding occurs endogenously and can be used to identify large-scale networks. Frequency sliding appears to be a general principle that regulates brain function on multiple spatial and temporal scales, from modulating spike timing in individual neurons to coordinating large-scale brain networks during cognition and resting state.

MeCP2 repression of G9a in regulation of pain and morphine reward

Opioids are commonly used for pain relief, but their strong rewarding effects drive opioid misuse and abuse. How pain affects the liability of opioid abuse is unknown at present. In this study, we identified an epigenetic regulating cascade activated by both pain and the opioid morphine. Both persistent pain and repeated morphine upregulated the transcriptional regulator MeCP2 in mouse central nucleus of the amygdala (CeA). Chromatin immunoprecipitation analysis revealed that MeCP2 bound to and repressed the transcriptional repressor histone dimethyltransferase G9a, reducing G9a-catalyzed repressive mark H3K9me2 in CeA. Repression of G9a activity increased expression of brain-derived neurotrophic factor (BDNF). Behaviorally, persistent inflammatory pain increased the sensitivity to acquiring morphine-induced, reward-related behavior of conditioned place preference in mice. Local viral vector-mediated MeCP2 overexpression, Cre-induced G9a knockdown, and CeA application of BDNF mimicked, whereas MeCP2 knockdown inhibited, the pain effect. These results suggest that MeCP2 directly represses G9a as a shared mechanism in central amygdala for regulation of emotional responses to pain and opioid reward, and for their behavioral interaction.

Inter-trial priming does not affect attentional priority in asymmetric visual search

Visual search is considerably speeded when the target's characteristics remain constant across successive selections. Here, we investigated whether such inter-trial priming increases the target's attentional priority, by examining whether target repetition reduces search efficiency during serial search. As the study of inter-trial priming requires the target and distractors to exchange roles unpredictably, it has mostly been confined to singleton searches, which typically yield efficient search. We therefore resorted to two singleton searches known to yield relatively inefficient performance, that is, searches in which the target does not pop out. Participants searched for a veridical angry face among neutral ones or vice-versa, either upright or inverted (Experiment 1) or for a Q among Os or vice-versa (Experiment 2). In both experiments, we found substantial intertrial priming that did not improve search efficiency. In addition, intertrial priming was asymmetric and occurred only when the more salient target repeated. We conclude that intertrial priming does not modulate attentional priority allocation and that it occurs in asymmetric search only when the target is characterized by an additional feature that is consciously perceived.

On social neuroscience methodologies and their applicability to group processes and intergroup relations

Group processes and intergroup relations are one of the most important topics examined by social psychologists. Recent advancements in social neuroscience methodologies provide valuable insight into these processes by allowing researchers to examine different psychological phenomena via neural processes that instantiate them while individuals interact with ingroup and outgroup members. This includes responses that occur outside conscious awareness or are deemed undesirable to overtly express. The purpose of this review is to provide an overview of the different social neuroscience methodologies that afford these possibilities. Specifically, functional magnetic resonance imaging (fMRI), electroencephalography (EEG), functional near infrared spectroscopy (fNIRS), transcranial magnetic stimulation (TMS), and genetic approaches will be discussed. Each section includes a discussion of what the methodology is and how it is used to assess neural function. A secondary goal of the review is to highlight recent studies that have utilized the aforementioned tools to better understand intergroup processes and interactions. Throughout, advantages and limitations of each approach are discussed, particularly with respect to the study of group processes and intergroup relations.

Syncrip/hnRNP Q influences synaptic transmission and regulates BMP signaling at the Drosophila neuromuscular synapse

Synaptic plasticity involves the modulation of synaptic connections in response to neuronal activity via multiple pathways. One mechanism modulates synaptic transmission by retrograde signals from the post-synapse that influence the probability of vesicle release in the pre-synapse. Despite its importance, very few factors required for the expression of retrograde signals, and proper synaptic transmission, have been identified. Here, we identify the conserved RNA binding protein Syncrip as a new factor that modulates the efficiency of vesicle release from the motoneuron and is required for correct synapse structure. We show that syncrip is required genetically and its protein product is detected only in the muscle and not in the motoneuron itself. This unexpected non-autonomy is at least partly explained by the fact that Syncrip modulates retrograde BMP signals from the muscle back to the motoneuron. We show that Syncrip influences the levels of the Bone Morphogenic Protein ligand Glass Bottom Boat from the post-synapse and regulates the pre-synapse. Our results highlight the RNA-binding protein Syncrip as a novel regulator of synaptic output. Given its known role in regulating translation, we propose that Syncrip is important for maintaining a balance between the strength of presynaptic vesicle release and postsynaptic translation.

Robustness as a non-localizable relational phenomenon

A current challenge in neuroscience, systems and theoretical biology is to understand what properties allow organisms to exhibit and sustain behaviours despite perturbations (behavioural robustness). Indeed, there are still significant theoretical difficulties in this endeavour due to the context-dependent nature of the problem. Contrary to the common view of biological robustness as a phenomenon that emerges internally, this article discusses the hypothesis that behavioural robustness is rooted in dynamical processes that distribute between internal controls, the organism body and the environment. This review highlights the varied perspectives and how they have led to the current focus on robustness as a relational phenomenon. A new perspective is proposed in which robustness is better understood in the context of agent-environment dynamical couplings, in which such couplings are not always the full determinants of robustness. The challenges and limitations of the proposed approach are identified.

Down-regulation of 5-HT1B and 5-HT1D receptors inhibits proliferation, clonogenicity and invasion of human pancreatic cancer cells

Pancreatic ductal adenocarcinoma is characterized by extensive local tumor invasion, metastasis and early systemic dissemination. The vast majority of pancreatic cancer (PaCa) patients already have metastatic complications at the time of diagnosis, and the death rate of this lethal type of cancer has increased over the past decades. Thus, efforts at identifying novel molecularly targeted therapies are priorities. Recent studies have suggested that serotonin (5-HT) contributes to the tumor growth in a variety of cancers including prostate, colon, bladder and liver cancer. However, there is lack of evidence about the impact of 5-HT receptors on promoting pancreatic cancer. Having considered the role of 5-HT-1 receptors, especially 5-HT_1B and 5-HT_1D subtypes in different types of malignancies, the aim of this study was to investigate the role of 5-HT_1B and 5-HT_1D receptors in PaCa growth and progression and analyze their potential as cytotoxic targets. We found that knockdown of 5-HT_1B and 5-HT_1D receptors expression, using specific small interfering RNA (siRNA), induced significant inhibition of proliferation and clonogenicity of PaCa cells. Also, it significantly suppressed PaCa cells invasion and reduced the activity of uPAR/MMP-2 signaling and Integrin/Src/Fak-mediated signaling, as integral tumor cell pathways associated with invasion, migration, adhesion, and proliferation. Moreover, targeting 5-HT_1B and 5-HT_1D receptors down-regulates zinc finger ZEB1 and Snail proteins, the hallmarks transcription factors regulating epithelial-mesenchymal transition (EMT), concomitantly with up-regulating of claudin-1 and E-Cadherin. In conclusion, our data suggests that 5-HT_1B– and 5-HT_1D–mediated signaling play an important role in the regulation of the proliferative and invasive phenotype of PaCa. It also highlights the therapeutic potential of targeting of 5-HT_1B/1D receptors in the treatment of PaCa, and opens a new avenue for biomarkers identification, and valuable new therapeutic targets for managing pancreatic cancer.

Amplification of Tau fibrils from minute quantities of seeds

The propagation of Tau pathology in Alzheimer’s disease (AD) is thought to proceed through templated conversion of Tau protein into fibrils and cell-to-cell transfer of elongation-competent seeds. To investigate the efficiency of Tau conversion, we adapted the protein misfolding cyclic amplification assay used for the conversion of prions. Utilizing heparin as a cofactor and employing repetitive cycles of shearing and growth, synthetic Tau fibrils and Tau fibrils in AD brain extract are progressively amplified. Concurrently, self-nucleation is suppressed. The results highlight breakage-induced replication of Tau fibrils as a potential facilitator of disease spread.

Gene-environment interactions in human health: case studies and strategies for developing new paradigms and research methodologies

THE SYNERGISTIC EFFECTS OF GENES AND THE ENVIRONMENT ON HEALTH ARE EXPLORED IN THREE CASE STUDIES: adult lactase persistence, autism spectrum disorders, and the metabolic syndrome, providing examples of the interactive complexities underlying these phenotypes. Since the phenotypes are the initial targets of evolutionary processes, understanding the specific environmental contexts of the genetic, epigenetic, and environmental changes associated with these phenotypes is essential in predicting their health implications. Robust databases must be developed on the local scale to deconstruct both the population substructure and the unique components of the environment that stimulate geographically specific changes in gene expression patterns. To produce these databases and make valid predictions, new, locally focused, and information-dense models are needed that incorporate data on evolutionary ecology, environmental complexity, local geographic patterns of gene expression, and population substructure.

Involvement of the superior temporal cortex in action execution and action observation

The role of the superior temporal sulcus (STs) in action execution and action observation remains unsettled. In an attempt to shed more light on the matter, we used the quantitative method of (14)C-deoxyglucose to reveal changes in activity, in the cortex of STs and adjacent inferior and superior temporal convexities of monkeys, elicited by reaching-to-grasp in the light or in the dark and by observation of the same action executed by an external agent. We found that observation of reaching-to-grasp activated the components of the superior temporal polysensory area [STP; including temporo-parieto-occipital association area (TPO), PGa, and IPa], the motion complex [including medial superior temporal area (MST), fundus of superior temporal area (FST), and dorsal and ventral parts of the middle temporal area (MTd and MTv, respectively)], and area TS2. A significant part of most of these activations was associated with observation of the goal-directed action, and a smaller part with the perception of arm-motion. Execution of reaching-to-grasp in the light-activated areas TS2, STP partially and marginally, and MT compared with the fixation but not to the arm-motion control. Consequently, MT-activation is associated with the arm-motion and not with the purposeful action. Finally, reaching-to-grasp in complete darkness activated all components of the motion complex. Conclusively, lack of visibility of our own actions involves the motion complex, whereas observation of others' actions engages area STP and the motion complex. Our previous and present findings together suggest that sensory effects are interweaved with motor commands in integrated action codes, and observation of an action or its execution in complete darkness triggers the retrieval of the visual representation of the action.

Mutations in cytoplasmic dynein and its regulators cause malformations of cortical development and neurodegenerative diseases

Neurons are highly specialized for the processing and transmission of electrical signals and use cytoskeleton-based motor proteins to transport different vesicles and cellular materials. Abnormalities in intracellular transport are thought to be a critical factor in the degeneration and death of neurons in both the central and peripheral nervous systems. Several recent studies describe disruptive mutations in the minus-end-directed microtubule motor cytoplasmic dynein that are directly linked to human motor neuropathies, such as SMA (spinal muscular atrophy) and axonal CMT (Charcot-Marie-Tooth) disease or malformations of cortical development, including lissencephaly, pachygyria and polymicrogyria. In addition, genetic defects associated with these and other neurological disorders have been found in multifunctional adaptors that regulate dynein function, including the dynactin subunit p150(Glued), BICD2 (Bicaudal D2), Lis-1 (lissencephaly 1) and NDE1 (nuclear distribution protein E). In the present paper we provide an overview of the disease-causing mutations in dynein motors and regulatory proteins that lead to a broad phenotypic spectrum extending from peripheral neuropathies to cerebral malformations.

Convergence in reflex pathways from multiple cutaneous nerves innervating the foot depends upon the number of rhythmically active limbs during locomotion

Neural output from the locomotor system for each arm and leg influences the spinal motoneuronal pools directly and indirectly through interneuronal (IN) reflex networks. While well documented in other species, less is known about the functions and features of convergence in common IN reflex system from cutaneous afferents innervating different foot regions during remote arm and leg movement in humans. The purpose of the present study was to use spatial facilitation to examine possible convergence in common reflex pathways during rhythmic locomotor limb movements. Cutaneous reflexes were evoked in ipsilateral tibialis anterior muscle by stimulating (in random order) the sural nerve (SUR), the distal tibial nerve (TIB), and combined simultaneous stimulation of both nerves (TIB&SUR). Reflexes were evoked while participants performed rhythmic stepping and arm swinging movement with both arms and the leg contralateral to stimulation (ARM&LEG), with just arm movement (ARM) and with just contralateral leg movement (LEG). Stimulation intensities were just below threshold for evoking early latency (<80 ms to peak) reflexes. For each stimulus condition, rectified EMG signals were averaged while participants held static contractions in the stationary (stimulated) leg. During ARM&LEG movement, amplitudes of cutaneous reflexes evoked by combined TIB&SUR stimulation were significantly larger than simple mathematical summation of the amplitudes evoked by SUR or TIB alone. Interestingly, this extra facilitation seen during combined nerve stimulation was significantly reduced when performing ARM or LEG compared to ARM&LEG. We conclude that locomotor rhythmic limb movement induces excitation of common IN reflex pathways from cutaneous afferents innervating different foot regions. Importantly, activity in this pathway is most facilitated during ARM&LEG movement. These results suggest that transmission in IN reflex pathways is weighted according to the number of limbs directly engaged in human locomotor activity and underscores the importance of arm swing to support neuronal excitability in leg muscles.

Serotonergic modulation of post-synaptic inhibition and locomotor alternating pattern in the spinal cord

The central pattern generators (CPGs) for locomotion, located in the lumbar spinal cord, are functional at birth in the rat. Their maturation occurs during the last few days preceding birth, a period during which the first projections from the brainstem start to reach the lumbar enlargement of the spinal cord. Locomotor burst activity in the mature intact spinal cord alternates between flexor and extensor motoneurons through reciprocal inhibition and between left and right sides through commisural inhibitory interneurons. By contrast, all motor bursts are in phase in the fetus. The alternating pattern disappears after neonatal spinal cord transection which suppresses supraspinal influences upon the locomotor networks. This article will review the role of serotonin (5-HT), in particular 5-HT₂ receptors, in shaping the alternating pattern. For instance, pharmacological activation of these receptors restores the left-right alternation after injury. Experiments aimed at either reducing the endogenous level of serotonin in the spinal cord or blocking the activation of 5-HT₂ receptors. We then describe recent evidence that the action of 5-HT₂ receptors is mediated, at least in part, through a modulation of chloride homeostasis. The postsynaptic action of GABA and glycine depends on the intracellular concentration of chloride ions which is regulated by a protein in the plasma membrane, the K⁺-Cl⁻ cotransporter (KCC2) extruding both K⁺ and Cl⁻ ions. Absence or reduction of KCC2 expression leads to a depolarizing action of GABA and glycine and a marked reduction in the strength of postsynaptic inhibition. This latter situation is observed early during development and in several pathological conditions, such as after spinal cord injury, thereby causing spasticity and chronic pain. It was recently shown that specific activation of 5-HT_2A receptors is able to up-regulate KCC2, restore endogenous inhibition and reduce spasticity.

Ketogenic diet sensitizes glucose control of hippocampal excitability

A high-fat low-carbohydrate ketogenic diet (KD) is an effective treatment for refractory epilepsy, yet myriad metabolic effects in vivo have not been reconciled clearly with neuronal effects. A KD limits blood glucose and produces ketone bodies from β-oxidation of lipids. Studies have explored changes in ketone bodies and/or glucose in the effects of the KD, and glucose is increasingly implicated in neurological conditions. To examine the interaction between altered glucose and the neural effects of a KD, we fed rats and mice a KD and restricted glucose in vitro while examining the seizure-prone CA3 region of acute hippocampal slices. Slices from KD-fed animals were sensitive to small physiological changes in glucose, and showed reduced excitability and seizure propensity. Similar to clinical observations, reduced excitability depended on maintaining reduced glucose. Enhanced glucose sensitivity and reduced excitability were absent in slices obtained from KD-fed mice lacking adenosine A₁ receptors (A₁Rs); in slices from normal animals effects of the KD could be reversed with blockers of pannexin-1 channels, A₁Rs, or K_ATP channels. Overall, these studies reveal that a KD sensitizes glucose-based regulation of excitability via purinergic mechanisms in the hippocampus and thus link key metabolic and direct neural effects of the KD.

NMDA and AMPA receptors: development and status epilepticus

Glutamate is the main excitatory neurotransmitter in the brain and ionotropic glutamate receptors mediate the majority of excitatory neurotransmission (Dingeldine et al. 1999). The high level of glutamatergic excitation allows the neonatal brain (the 2(nd) postnatal week in rat) to develop quickly but it also makes it highly prone to age-specific seizures that can cause lifelong neurological and cognitive disability (Haut et al. 2004). There are three types of ionotropic glutamate receptors (ligand-gated ion channels) named according to their prototypic agonists: N-methyl-D-aspartate (NMDA), 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl) propanoic acid (AMPA) and kainate (KA). During early stages of postnatal development glutamate receptors of NMDA and AMPA type undergo intensive functional changes owing to modifications in their subunit composition (Carter et al. 1988, Watanabe et al. 1992, Monyer et al. 1994, Wenzel et al. 1997, Sun et al. 1998, Lilliu et al. 2001, Kumar et al. 2002, Matsuda et al. 2002, Wee et al. 2008, Henson et al. 2010, Pachernegg et al. 2012, Paoletti et al. 2013). Participation and role of these receptors in mechanisms of seizures and epilepsy became one of the main targets of intensive investigation (De Sarro et al. 2005, Di Maio et al. 2012, Rektor 2013). LiCl/Pilocarpine (LiCl/Pilo) induced status epilepticus is a model of severe seizures resulting in development temporal lobe epilepsy (TLE). This review will consider developmental changes and contribution of NMDA and AMPA receptors in LiCl/Pilo model of status epilepticus in immature rats.

Transcellular chaperone signaling: an organismal strategy for integrated cell stress responses

The ability of each cell within a metazoan to adapt to and survive environmental and physiological stress requires cellular stress-response mechanisms, such as the heat shock response (HSR). Recent advances reveal that cellular proteostasis and stress responses in metazoans are regulated by multiple layers of intercellular communication. This ensures that an imbalance of proteostasis that occurs within any single tissue 'at risk' is protected by a compensatory activation of a stress response in adjacent tissues that confers a community protective response. While each cell expresses the machinery for heat shock (HS) gene expression, the HSR is regulated cell non-autonomously in multicellular organisms, by neuronal signaling to the somatic tissues, and by transcellular chaperone signaling between somatic tissues and from somatic tissues to neurons. These cell non-autonomous processes ensure that the organismal HSR is orchestrated across multiple tissues and that transmission of stress signals between tissues can also override the neuronal control to reset cell- and tissue-specific proteostasis. Here, we discuss emerging concepts and insights into the complex cell non-autonomous mechanisms that control stress responses in metazoans and highlight the importance of intercellular communication for proteostasis maintenance in multicellular organisms.

Neurons in the nucleus tractus solitarius mediate the acupuncture analgesia in visceral pain rats

The study investigated the role of nucleus tractus solitarius (NTS) neurons in electroacupuncture (EA) analgesia in colorectal distension (CRD) rats. NTS neurons responding to both CRD test and EA conditioning stimulations were considered somato-visceral convergent neurons. The neuronal activities evoked by graded CRD showed multiple firing patterns indicating multisynaptic connections. Some of the CRD excitatory neurons were inhibited by EA and vice versa. There was no discrepancy among different acupoints in inducing the changes of unit discharges. Conclusively, EA could regulate CRD related neurons in the NTS through polysynaptic cross-talk mechanism, which mediates EA analgesia on visceral pain in anesthetized rats.

Evidence for functional diversity between the voltage-gated proton channel Hv1 and its closest related protein HVRP1

The Hv1 channel and voltage-sensitive phosphatases share with voltage-gated sodium, potassium, and calcium channels the ability to detect changes in membrane potential through voltage-sensing domains (VSDs). However, they lack the pore domain typical of these other channels. Na_V, K_V, and Ca_V proteins can be found in neurons and muscles, where they play important roles in electrical excitability. In contrast, VSD-containing proteins lacking a pore domain are found in non-excitable cells and are not involved in neuronal signaling. Here, we report the identification of HVRP1, a protein related to the Hv1 channel (from which the name Hv1 Related Protein 1 is derived), which we find to be expressed primarily in the central nervous system, and particularly in the cerebellum. Within the cerebellar tissue, HVRP1 is specifically expressed in granule neurons, as determined by in situ hybridization and immunohistochemistry. Analysis of subcellular distribution via electron microscopy and immunogold labeling reveals that the protein localizes on the post-synaptic side of contacts between glutamatergic mossy fibers and the granule cells. We also find that, despite the similarities in amino acid sequence and structural organization between Hv1 and HVRP1, the two proteins have distinct functional properties. The high conservation of HVRP1 in vertebrates and its cellular and subcellular localizations suggest an important function in the nervous system.

The singer and the song: the neuromechanics of avian sound production

Song is crucial to songbirds for establishing territories and signaling genetic quality and an important driver in speciation. Songbirds also have become a widely used experimental model system to study the neural basis of vocal learning, a form of imitation learning with strong parallels to human speech learning. While there is a strong focus on central processing of song production, we still have limited insights into the functional output of the motor neural circuits. This review focuses on recent developments in motor control, biomechanics and feedback mechanisms of sound production in songbirds.

Neural Plasticity and Memory: Is Memory Encoded in Hydrogen Bonding Patterns?

Current models of memory storage recognize posttranslational modification vital for short-term and mRNA translation for long-lasting information storage. However, at the molecular level things are quite vague. A comprehensive review of the molecular basis of short and long-lasting synaptic plasticity literature leads us to propose that the hydrogen bonding pattern at the molecular level may be a permissive, vital step of memory storage. Therefore, we propose that the pattern of hydrogen bonding network of biomolecules (glycoproteins and/or DNA template, for instance) at the synapse is the critical edifying mechanism essential for short- and long-term memories. A novel aspect of this model is that nonrandom impulsive (or unplanned) synaptic activity functions as a synchronized positive-feedback rehearsal mechanism by revising the configurations of the hydrogen bonding network by tweaking the earlier tailored hydrogen bonds. This process may also maintain the elasticity of the related synapses involved in memory storage, a characteristic needed for such networks to alter intricacy and revise endlessly. The primary purpose of this review is to stimulate the efforts to elaborate the mechanism of neuronal connectivity both at molecular and chemical levels.

Electrophysiological correlates of motor sequence learning

Background

The Error-related negativity (ERN) is a component of the event-related brain potentials elicited by error commission. The ERN is thought to reflect cognitive control processes aiming to improve performance. As previous studies showed a modulation of the ERN amplitude throughout the execution of a learning task, this study aims to follow the ERN amplitude changes from early to late learning blocks in relation with concomitant motor sequence learning using a serial reaction time (SRT) task. Twenty-two healthy participants completed a SRT task during which continuous EEG activity was recorded. The SRT task consists of series of stimulus-response pairs and involves motor learning of a repeating sequence. Learning was computed as the difference in mean response time between the last sequence block and the last random blocks that immediately follows it (sequence-specific learning). Event-related potentials were analysed to measure ERN amplitude elicited by error commission.

Results

Mean ERN amplitude difference between the first four learning blocks and the last four learning blocks of the SRT task correlated significantly with motor sequence learning as well as with overall response time improvement, such that those participants whose ERN amplitude most increased through learning blocks were also those who exhibited most SRT task improvements. In contrast, neither sequence-specific learning nor overall response time improvement across learning blocks were found to be related to averaged ERN amplitude from all learning blocks.

Conclusion

Findings from the present study suggest that the ERN amplitude changes from early to late learning blocks occurring over the course of the SRT task, as opposed to the averaged ERN amplitude from all learning blocks, is more closely associated with learning of a motor sequence. These findings propose an improved electrophysiological marker to index change in cognitive control efficiency during motor sequence learning.

Visual learning alters the spontaneous activity of the resting human brain: an fNIRS study

Resting-state functional connectivity (RSFC) has been widely used to investigate spontaneous brain activity that exhibits correlated fluctuations. RSFC has been found to be changed along the developmental course and after learning. Here, we investigated whether and how visual learning modified the resting oxygenated hemoglobin (HbO) functional brain connectivity by using functional near-infrared spectroscopy (fNIRS). We demonstrate that after five days of training on an orientation discrimination task constrained to the right visual field, resting HbO functional connectivity and directed mutual interaction between high-level visual cortex and frontal/central areas involved in the top-down control were significantly modified. Moreover, these changes, which correlated with the degree of perceptual learning, were not limited to the trained left visual cortex. We conclude that the resting oxygenated hemoglobin functional connectivity could be used as a predictor of visual learning, supporting the involvement of high-level visual cortex and the involvement of frontal/central cortex during visual perceptual learning.

T-type calcium channels promote predictive homeostasis of input-output relations in thalamocortical neurons of lateral geniculate nucleus

A general theory views the function of all neurons as prediction, and one component of this theory is that of “predictive homeostasis” or “prediction error.” It is well established that sensory systems adapt so that neuronal output maintains sensitivity to sensory input, in accord with information theory. Predictive homeostasis applies the same principle at the cellular level, where the challenge is to maintain membrane excitability at the optimal homeostatic level so that spike generation is maximally sensitive to small gradations in synaptic drive. Negative feedback is a hallmark of homeostatic mechanisms, as exemplified by depolarization-activated potassium channels. In contrast, T-type calcium channels exhibit positive feedback that appears at odds with the theory. In thalamocortical neurons of lateral geniculate nucleus (LGN), T-type channels are capable of causing bursts of spikes with an all-or-none character in response to excitation from a hyperpolarized potential. This “burst mode” would partially uncouple visual input from spike output and reduce the information spikes convey about gradations in visual input. However, past observations of T-type-driven bursts may have resulted from unnaturally high membrane excitability. Here we have mimicked within rat brain slices the patterns of synaptic conductance that occur naturally during vision. In support of the theory of predictive homeostasis, we found that T-type channels restored excitability toward its homeostatic level during periods of hyperpolarization. Thus, activation of T-type channels allowed two retinal input spikes to cause one output spike on average, and we observed almost no instances in which output count exceeded input count (a “burst”). T-type calcium channels therefore help to maintain a single optimal mode of transmission rather than creating a second mode. More fundamentally our results support the general theory, which seeks to predict the properties of a neuron's ion channels and synapses given knowledge of natural patterns of synaptic input.

Notch3 is necessary for neuronal differentiation and maturation in the adult spinal cord

Notch receptors are key regulators of nervous system development and promoters of neural stem cells renewal and proliferation. Defects in the expression of Notch genes result in severe, often lethal developmental abnormalities. Notch3 is generally thought to have a similar proliferative, anti-differentiation and gliogenic role to Notch1. However, in some cases, Notch3 has an opposite, pro-differentiation effect. Here, we show that Notch3 segregates from Notch1 and is transiently expressed in adult rat and mouse spinal cord neuron precursors and immature neurons. This suggests that during the differentiation of adult neural progenitor cells, Notch signalling may follow a modified version of the classical lateral inhibition model, involving the segregation of individual Notch receptors. Notch3 knockout mice, otherwise neurologically normal, are characterized by a reduced number of mature inhibitory interneurons and an increased number of highly excitable immature neurons in spinal cord laminae I–II. As a result, these mice have permanently lower nociceptive thresholds, similar to chronic pain. These results suggest that defective neuronal differentiation, for example as a result of reduced Notch3 expression or activation, may underlie human cases of intractable chronic pain, such as fibromyalgia and neuropathic pain.