Targeting Prefrontal Cortical Systems for Drug Development: Potential Therapies for Cognitive Disorders

Potentiation of prefrontal cortex dopamine function by the novel cognitive enhancer d-govadine

Cognitive impairment is a debilitating feature of psychiatric disorders including schizophrenia, mood disorders and substance use disorders for which there is a substantial lack of effective therapies. d-Govadine (d-GOV) is a tetrahydroprotoberberine recently shown to significantly enhance working memory and behavioural flexibility in several prefrontal cortex (PFC)-dependent rodent tasks. d-GOV potentiates dopamine (DA) efflux in the mPFC and not the nucleus accumbens, a unique pharmacology that sets it apart from many dopaminergic drugs and likely contributes to its effects on cognitive function. However, specific mechanisms involved in the preferential effects of d-GOV on mPFC DA function remain to be determined. The present study employs brain dialysis in male rats to deliver d-GOV into the mPFC or ventral tegmental area (VTA), while simultaneously sampling DA and norepinephrine (NE) efflux in the mPFC. Intra-PFC delivery or systemic administration of d-GOV preferentially potentiated medial prefrontal DA vs NE efflux. This differential effect of d-GOV on the primary catecholamines known to affect mPFC function further underscores its specificity for the mPFC DA system. Importantly, the potentiating effect of d-GOV on mPFC DA was disrupted when glutamatergic transmission was blocked in either the mPFC or the VTA. We hypothesize that d-GOV acts in the mPFC to engage the mesocortical feedback loop through which prefrontal glutamatergic projections activate a population of VTA DA neurons that specifically project back to the PFC. The activation of a PFC-VTA feedback loop to elevate PFC DA efflux without affecting mesolimbic DA release represents a novel approach to developing pro-cognitive drugs.

Frontotemporal disorders: the expansive panoply of syndromes and spectrum of etiologies

Background

Frontotemporal lobe disorders (FTD) are amongst the most common brain neurodegenerative disorders. Their relatively covert, frequently subtle presentations and diverse etiologies, pose major challenges in diagnosis and treatments. Recent studies have yielded insights that the etiology in the majority are due to environmental and sporadic causes, rather than genetic in origin.

Aims

To retrospectively examine the cognitive and behavioral impairments in the veteran population to garner the range of differing syndrome presentations and etiological subcategories with a specific focus on frontotemporal lobe disorders.

Methodology

The design is a retrospective, observational registry, case series with the collection of epidemiological, clinical, cognitive, laboratory and radiological data on people with cognitive and behavioral disorders. Inclusion criteria for entry were veterans evaluated exclusively at Orlando VA Healthcare System, neurology section, receiving a diagnosis of FTD by standard criteria, during the observation period dated from July 2016 to March 2021. Frontotemporal disorders (FTD) were delineated into five clinical 5 subtypes. Demographic, cardiovascular risk factors, cognitive, behavioral neurological, neuroimaging data and presumed etiological categories, were collected for those with a diagnosis of frontotemporal disorder.

Results

Of the 200 patients with FTD, further cognitive, behavioral neurological evaluation with standardized, metric testing was possible in 105 patients. Analysis of the etiological groups revealed significantly different younger age of the traumatic brain injury (TBI) and Gulf War Illness (GWI) veterans who also had higher Montreal Cognitive Assessment (MOCA) scores. The TBI group also had significantly more abnormalities of hypometabolism, noted on the PET brain scans. Behavioral neurological testing was notable for the findings that once a frontotemporal disorder had been diagnosed, the four different etiological groups consistently had abnormal FRSBE scores for the 3 principal frontal presentations of (i) abulia/apathy, (ii) disinhibition, and (iii) executive dysfunction as well as abnormal Frontal Behavioral Inventory (FBI) scores with no significant difference amongst the etiological groups. The most common sub-syndromes associated with frontotemporal syndromes were the Geschwind-Gastaut syndrome (GGS), Klüver-Bucy syndrome (KBS), involuntary emotional expression disorder (IEED), cerebellar cognitive affective syndrome (CCA), traumatic encephalopathy syndrome (TES) and prosopagnosia. Comparisons with the three principal frontal lobe syndrome clusters (abulia, disinhibition, executive dysfunction) revealed a significant association with abnormal disinhibition FRSBE T-scores with the GGS. The regression analysis supported the potential contribution of disinhibition behavior that related to this complex, relatively common behavioral syndrome in this series. The less common subsyndromes in particular, were notable, as they constituted the initial overriding, presenting symptoms and syndromes characterized into 16 separate conditions.

Conclusion

By deconstructing FTD into the multiple sub-syndromes and differing etiologies, this study may provide foundational insights, enabling a more targeted precision medicine approach for future studies, both in treating the sub-syndromes as well as the underlying etiological process.

Single-cell spatial transcriptome reveals cell-type organization in the macaque cortex

Elucidating the cellular organization of the cerebral cortex is critical for understanding brain structure and function. Using large-scale single-nucleus RNA sequencing and spatial transcriptomic analysis of 143 macaque cortical regions, we obtained a comprehensive atlas of 264 transcriptome-defined cortical cell types and mapped their spatial distribution across the entire cortex. We characterized the cortical layer and region preferences of glutamatergic, GABAergic, and non-neuronal cell types, as well as regional differences in cell-type composition and neighborhood complexity. Notably, we discovered a relationship between the regional distribution of various cell types and the region's hierarchical level in the visual and somatosensory systems. Cross-species comparison of transcriptomic data from human, macaque, and mouse cortices further revealed primate-specific cell types that are enriched in layer 4, with their marker genes expressed in a region-dependent manner. Our data provide a cellular and molecular basis for understanding the evolution, development, aging, and pathogenesis of the primate brain.

Mechanisms of synaptic transmission dysregulation in the prefrontal cortex: pathophysiological implications

The prefrontal cortex (PFC) serves as the chief executive officer of the brain, controlling the highest level cognitive and emotional processes. Its local circuits among glutamatergic principal neurons and GABAergic interneurons, as well as its long-range connections with other brain regions, have been functionally linked to specific behaviors, ranging from working memory to reward seeking. The efficacy of synaptic signaling in the PFC network is profundedly influenced by monoaminergic inputs via the activation of dopamine, adrenergic, or serotonin receptors. Stress hormones and neuropeptides also exert complex effects on the synaptic structure and function of PFC neurons. Dysregulation of PFC synaptic transmission is strongly linked to social deficits, affective disturbance, and memory loss in brain disorders, including autism, schizophrenia, depression, and Alzheimer's disease. Critical neural circuits, biological pathways, and molecular players that go awry in these mental illnesses have been revealed by integrated electrophysiological, optogenetic, biochemical, and transcriptomic studies of PFC. Novel epigenetic mechanism-based strategies are proposed as potential avenues of therapeutic intervention for PFC-involved diseases. This review provides an overview of PFC network organization and synaptic modulation, as well as the mechanisms linking PFC dysfunction to the pathophysiology of neurodevelopmental, neuropsychiatric, and neurodegenerative diseases. Insights from the preclinical studies offer the potential for discovering new medical treatments for human patients with these brain disorders.

Differential brain ADRA2A and ADRA2C gene expression and epigenetic regulation in schizophrenia. Effect of antipsychotic drug treatment

Postsynaptic α_2A-adrenoceptor density is enhanced in the dorsolateral prefrontal cortex (DLPFC) of antipsychotic-treated schizophrenia subjects. This alteration might be due to transcriptional activation, and could be regulated by epigenetic mechanisms such as histone posttranslational modifications (PTMs). The aim of this study was to evaluate ADRA2A and ADRA2C gene expression (codifying for α₂-adrenoceptor subtypes), and permissive and repressive histone PTMs at gene promoter regions in the DLPFC of subjects with schizophrenia and matched controls (n = 24 pairs). We studied the effect of antipsychotic (AP) treatment in AP-free (n = 12) and AP-treated (n = 12) subgroups of schizophrenia subjects and in rats acutely and chronically treated with typical and atypical antipsychotics. ADRA2A mRNA expression was selectively upregulated in AP-treated schizophrenia subjects (+93%) whereas ADRA2C mRNA expression was upregulated in all schizophrenia subjects (+53%) regardless of antipsychotic treatment. Acute and chronic clozapine treatment in rats did not alter brain cortex Adra2a mRNA expression but increased Adra2c mRNA expression. Both ADRA2A and ADRA2C promoter regions showed epigenetic modification by histone methylation and acetylation in human DLPFC. The upregulation of ADRA2A expression in AP-treated schizophrenia subjects might be related to observed bivalent chromatin at ADRA2A promoter region in schizophrenia (depicted by increased permissive H3K4me3 and repressive H3K27me3) and could be triggered by the enhanced H4K16ac at ADRA2A promoter. In conclusion, epigenetic predisposition differentially modulated ADRA2A and ADRA2C mRNA expression in DLPFC of schizophrenia subjects.

Monoaminergic Genetic Variants, Prefrontal Cortex-Amygdala Circuit, and Emotional Symptoms in Children With ADHD: Exploration Based on the Gene-Brain-Behavior Relationship

Objective: This study aimed to explore the association between monoaminergic genetic variants and emotional lability (EL) symptoms in children with ADHD. In addition, genetic effects on prefrontal cortex (PFC)-amygdala functional connectivity (FC) were investigated. Method: Children with ADHD and controls were genotyped for five monoaminergic genetic variants and were evaluated for EL symptoms. Imaging genetic exploration was conducted with previously reported aberrant PFC-amygdala resting-state functional connectivities (RSFCs) as target features. Results: A genotypic effect on EL symptoms was only found for NET1-rs3785143, indicating higher EL symptoms in TT genotype carriers than in C-allele carriers. Imaging genetic analyses indicated a marginal effect of NET1-rs3785143 on ADHD-altered FC between the superficial amygdala (SFA) and middle frontal gyrus (MFG). Mediation analysis suggested potential effects of NET1-rs3785143 via RSFC (SFA-MFG) on EL. Conclusion:NET1 variants might participate in the pathogenesis of EL in children with ADHD by influencing the function of the PFC-amygdala circuit.

Long term effects of early life stress on HPA circuit in rodent models

Adaptation to environmental challenges represents a critical process for survival, requiring the complex integration of information derived from both external cues and internal signals regarding current conditions and previous experiences. The Hypothalamic-pituitary-adrenal axis plays a central role in this process inducing the activation of a neuroendocrine signaling cascade that affects the delicate balance of activity and cross-talk between areas that are involved in sensorial, emotional, and cognitive processing such as the hippocampus, amygdala, Prefrontal Cortex, Ventral Tegmental Area, and dorsal raphe. Early life stress, especially early critical experiences with caregivers, influences the functional and structural organization of these areas, affects these processes in a long-lasting manner and may result in long-term maladaptive and psychopathological outcomes, depending on the complex interaction between genetic and environmental factors. This review summarizes the results of studies that have modeled this early postnatal stress in rodents during the first 2 postnatal weeks, focusing on the long-term effects on molecular and structural alteration in brain areas involved in Hypothalamic-pituitary-adrenal axis function. Moreover, a brief investigation of epigenetic mechanisms and specific genetic targets mediating the long-term effects of these early environmental manipulations and at the basis of differential neurobiological and behavioral effects during adulthood is provided.

A narrative review of pharmacologic approaches to symptom management of pediatric patients diagnosed with anti-NMDA receptor encephalitis

Anti-N-Methyl-D-Aspartate Receptor Encephalitis (ANMDARE) is one of the most common autoimmune encephalitis in the pediatric population. Patients with ANMDARE initially present with a prodrome of neuropsychiatric symptoms followed by progressively worsening seizures, agitation, and movement disorders. Complications can include problems such as aggression, insomnia, catatonia, and autonomic instability. Due to the complexity of this disease process, symptom management can be complex and may lead to significant polypharmacy. The goal of this review is to educate clinicians about the challenges of managing this disorder and providing guidance in symptom management.

Spinophilin expression in postmortem prefrontal cortex of schizophrenic subjects: Effects of antipsychotic treatment

Schizophrenia has been associated with alterations in neurotransmission and synaptic dysfunction. Spinophilin is a multifunctional scaffold protein that modulates excitatory synaptic transmission and dendritic spine morphology. Spinophilin can also directly interact with and regulate several receptors for neurotransmitters, such as dopamine D₂ receptors, which play a role in the pathophysiology of schizophrenia and are targets of antipsychotics. Several studies have thus suggested an implication of spinophilin in schizophrenia. In the present study spinophilin protein expression was determined by western blot in the postmortem dorsolateral prefrontal cortex of 24 subjects with schizophrenia (12 antipsychotic-free and 12 antipsychotic-treated subjects) and 24 matched controls. Experiments were performed in synaptosomal membranes (SPM) and in postsynaptic density fractions (PSD). As previously reported, two specific bands for this protein were observed: an upper 120-130 kDa band and a lower 80-95 kDa band. The spinophilin lower band showed a significant decrease in schizophrenia subjects compared to matched controls, both in SPM and PSD fractions (-15%, p = 0.007 and -15%, p = 0.039, respectively). When schizophrenia subjects were divided by the presence or absence of antipsychotics in blood at death, the lower band showed a significant decrease in antipsychotic-treated schizophrenia subjects (-24%, p = 0.003 for SPM and -26%, p = 0.014 for PSD), but not in antipsychotic-free subjects, compared to their matched controls. These results suggest that antipsychotics could produce alterations in spinophilin expression that do not seem to be related to schizophrenia per se. These changes may underlie some of the side effects of antipsychotics.

Nimodipine improves cortical efficiency during working memory in healthy subjects

The L-type calcium channel gene, CACNA1C, is a validated risk gene for schizophrenia and the target of calcium channel blockers. Carriers of the risk-associated genotype (rs1006737 A allele) have increased frontal cortical activity during working memory and higher CACNA1C mRNA expression in the prefrontal cortex. The aim of this study was to determine how the brain-penetrant calcium channel blocker, nimodipine, changes brain activity during working memory and other cognitive and emotional processes. We conducted a double-blind randomized cross-over pharmacoMRI study of a single 60 mg dose of oral nimodipine solution and matching placebo in healthy men, prospectively genotyped for rs1006737. With performance unchanged, nimodipine significantly decreased frontal cortical activity by 39.1% and parietal cortical activity by 42.8% during the N-back task (2-back > 0-back contrast; P_FWE < 0.05; n = 28). Higher peripheral nimodipine concentrations were correlated with a greater decrease in activation in the frontal cortex. Carriers of the risk-associated allele, A (n = 14), had a greater decrease in frontal cortical activation during working memory compared to non-risk allele carriers. No differences in brain activation were found between nimodipine and placebo for other tasks. Future studies should be conducted to test if the decreased cortical brain activity after nimodipine is associated with improved working memory performance in patients with schizophrenia, particularly those who carry the risk-associated genotype. Furthermore, changes in cortical activity during working memory may be a useful biomarker in future trials of L-type calcium channel blockers.

Opportunities and limitations of genetically modified nonhuman primate models for neuroscience research

The recently developed new genome-editing technologies, such as the CRISPR/Cas system, have opened the door for generating genetically modified nonhuman primate (NHP) models for basic neuroscience and brain disorders research. The complex circuit formation and experience-dependent refinement of the human brain are very difficult to model in vitro, and thus require use of in vivo whole-animal models. For many neurodevelopmental and psychiatric disorders, abnormal circuit formation and refinement might be at the center of their pathophysiology. Importantly, many of the critical circuits and regional cell populations implicated in higher human cognitive function and in many psychiatric disorders are not present in lower mammalian brains, while these analogous areas are replicated in NHP brains. Indeed, neuropsychiatric disorders represent a tremendous health and economic burden globally. The emerging field of genetically modified NHP models has the potential to transform our study of higher brain function and dramatically facilitate the development of effective treatment for human brain disorders. In this paper, we discuss the importance of developing such models, the infrastructure and training needed to maximize the impact of such models, and ethical standards required for using these models.

Impact of childhood adversity on network reconfiguration dynamics during working memory in hypogonadal women

Many women with no history of cognitive difficulties experience executive dysfunction during menopause. Significant adversity during childhood negatively impacts executive function into adulthood and may be an indicator of women at risk of a mid-life cognitive decline. Previous studies have indicated that alterations in functional network connectivity underlie these negative effects of childhood adversity. There is growing evidence that functional brain networks are not static during executive tasks; instead, such networks reconfigure over time. Optimal dynamics are necessary for efficient executive function; while too little reconfiguration is insufficient for peak performance, too much reconfiguration (supra-optimal reconfiguration) is also maladaptive and associated with poorer performance. Here we examined the impact of adverse childhood experiences (ACEs) on network flexibility, a measure of dynamic reconfiguration, during a letter n-back task within three networks that support executive function: frontoparietal, salience, and default mode networks. Several animal and human subject studies have suggested that childhood adversity exerts lasting effects on executive function via serotonergic mechanisms. Tryptophan depletion (TD) was used to examine whether serotonin function drives ACE effects on network flexibility. We hypothesized that ACE would be associated with higher flexibility (supra-optimal flexibility) and that TD would further increase this measure. Forty women underwent functional imaging at two time points in this double-blind, placebo controlled, crossover study. Participants also completed the Penn Conditional Exclusion Test, a task assessing abstraction and mental flexibility. The effects of ACE and TD were evaluated using generalized estimating equations. ACE was associated with higher flexibility across networks (frontoparietal β = 0.00748, D = 2.79, p = 0.005; salience β = 0.00679, D = 3.02, p = 0.003; and default mode β = 0.00910, D = 3.53, p = 0.0004). While there was no interaction between ACE and TD, active TD increased network flexibility in both ACE groups in comparison to sham depletion (frontoparietal β = 0.00489, D = 2.15, p = 0.03; salience β = 0.00393, D = 1.91, p = 0.06; default mode β = 0.00334, D = 1.73, p = 0.08). These results suggest that childhood adversity has lasting impacts on dynamic reconfiguration of functional brain networks supporting executive function and that decreasing serotonin levels may exacerbate these effects.

Lead acetate- induced neurodegenerative changes in the dorsolateral prefrontal cortex of mice: the role of Vitexin

This study was aimed at investigating the neuroprotective effect of Vitexin against lead (Pb) induced neurodegenerative changes in the dorsolateral prefrontal cortex (DLPFC) and working memory in mice. Thirty-two adolescent male albino mice were divided into four groups (n=8). Control group received 0.2 mL of normal saline; Pb group received 100 mg/kg of Pb acetate for 14 days, Vitexin group received 1mg/kg of Vitexin for 14 days, and Pb+Vitexin group received 100 mg/kg of Pb acetate and 1 mgkg of Vitexin for 14 days. Barnes maze test and novel object recognition test were done to ascertain working memory. Histoarchitectural assessment of DLPFC was done with haematoxylin and eosin (H&E), cresyl fast violet and congo red stains. Furthermore, cell count and other morphometric measurements were done. There was significant decline in working memory in the Pb group, but a combination of Pb+Vitexin improved the working memory. Vitexin significantly reduced neuronal death and chromatolysis caused by Pb. Amyloid aggregation was not observed in any of the groups. This study has shown that concurrent administration of Vitexin and Pb will significantly reduce neurodegeneration and improve working memory. However, Pb treatment or Pb+Vitexin treatment does not have any effect on intercellular distance, neuronal length and the cross-sectional area of neurons in layer III of DLPFC.

Muscarinic M1 Receptors Modulate Working Memory Performance and Activity via KCNQ Potassium Channels in the Primate Prefrontal Cortex

Working memory relies on the dorsolateral prefrontal cortex (dlPFC), where microcircuits of pyramidal neurons enable persistent firing in the absence of sensory input, maintaining information through recurrent excitation. This activity relies on acetylcholine, although the molecular mechanisms for this dependence are not thoroughly understood. This study investigated the role of muscarinic M1 receptors (M1Rs) in the dlPFC using iontophoresis coupled with single-unit recordings from aging monkeys with naturally occurring cholinergic depletion. We found that M1R stimulation produced an inverted-U dose response on cell firing and behavioral performance when given systemically to aged monkeys. Immunoelectron microscopy localized KCNQ isoforms (Kv7.2, Kv7.3, and Kv7.5) on layer III dendrites and spines, similar to M1Rs. Iontophoretic manipulation of KCNQ channels altered cell firing and reversed the effects of M1R compounds, suggesting that KCNQ channels are one mechanism for M1R actions in the dlPFC. These results indicate that M1Rs may be an appropriate target to treat cognitive disorders with cholinergic alterations.

KCNH2-3.1 mediates aberrant complement activation and impaired hippocampal-medial prefrontal circuitry associated with working memory deficits

Increased expression of the 3.1 isoform of the KCNH2 potassium channel has been associated with cognitive dysfunction and with schizophrenia, yet little is known about the underlying pathophysiological mechanisms. Here, by using in vivo wireless local field potential recordings during working memory processing, in vitro brain slice whole-cell patching recordings and in vivo stereotaxic hippocampal injection of AAV-encoded expression, we identified specific and delayed disruption of hippocampal-mPFC synaptic transmission and functional connectivity associated with reductions of SERPING1, CFH, and CD74 in the KCNH2-3.1 overexpression transgenic mice. The differentially expressed genes in mice are enriched in neurons and microglia, and reduced expression of these genes dysregulates the complement cascade, which has been previously linked to synaptic plasticity. We find that knockdown of these genes in primary neuronal-microglial cocultures from KCNH2-3.1 mice impairs synapse formation, and replenishing reduced CFH gene expression rescues KCNH2-3.1-induced impaired synaptogenesis. Translating to humans, we find analogous dysfunctional interactions between hippocampus and prefrontal cortex in coupling of the fMRI blood oxygen level-dependent (BOLD) signal during working memory in healthy subjects carrying alleles associated with increased KCNH2-3.1 expression in brain. Our data uncover a previously unrecognized role of the truncated KCNH2-3.1 potassium channel in mediating complement activation, which may explain its association with altered hippocampal-prefrontal connectivity and synaptic function. These results provide a potential molecular link between increased KCNH2-3.1 expression, synapse alterations, and hippocampal-prefrontal circuit abnormalities implicated in schizophrenia.

Dopamine and Gambling Disorder: Prospects for Personalized Treatment

Purpose of Review

To address variation in the severity of gambling disorder, this review evaluates the contribution of mesocorticolimbic dopamine neurons to potential behavioral endophenotypes, the influence of individual differences in the dopamine system on gambling and related behaviors, and the possible role for dopaminergic medications in the treatment of gambling disorder.

Recent Findings

Newer work has suggested that dopaminergic dysfunction can lead to increased reward anticipation and a greater sensitivity to uncertainty, which in turn may drive addictive gambling behaviors. In addition, increased impulsivity, a well-recognized risk factor for gambling disorder, has been linked to dopaminergic dysfunction. More recently, emerging evidence has suggested that dopaminergic medications can influence the discounting of delayed rewards.

Summary

Dopaminergic drugs that increase the salience of long-term over short-term goals may ameliorate symptoms of impulsive individuals with gambling disorder. More broadly, improved understanding of intermediate behavioral and other phenotypes with a defined neurobiological substrate may allow for personalized treatment of gambling disorder and other psychiatric conditions.

A novel dopamine D1 receptor agonist excites delay-dependent working memory-related neuronal firing in primate dorsolateral prefrontal cortex

Decades of research have emphasized the importance of dopamine (DA) D1 receptor (D1R) mechanisms to dorsolateral prefrontal cortex (dlPFC) working memory function, and the hope that D1R agonists could be used to treat cognitive disorders. However, existing D1R agonists all have had high affinity for D1R, and engage β-arrestin signaling, and these agonists have suppressed task-related neuronal firing. The current study provides the first physiological characterization of a novel D1R agonist, PF-3628, with low affinity for D1R -more similar to endogenous DA actions- as well as little engagement of β-arrestin signaling. PF-3628 was applied by iontophoresis directly onto dlPFC neurons in aged rhesus monkeys performing a delay-dependent working memory task. Aged monkeys have naturally-occurring loss of DA, and naturally-occurring reductions in dlPFC neuronal firing and working memory performance. We found the first evidence of excitatory actions of a D1R agonist on dlPFC task-related firing, and this PF-3628 beneficial response was blocked by co-application of a D1R antagonist. These D1R actions likely occur on pyramidal cells, based on previous immunoelectron microscopic studies showing expression of D1R on layer III spines, and current microarray experiments showing that D1R are four times more prevalent in pyramidal cells than in parvalbumin-containing interneurons laser-captured from layer III of the human dlPFC. These results encourage the translation of D1R mechanisms from monkey to human, with the hope PF-3628 and related, novel D1R agonists will be more appropriate for enhancing dlPFC cognitive functions in patients with mental disorders.

Differential α2A- and α2C-adrenoceptor protein expression in presynaptic and postsynaptic density fractions of postmortem human prefrontal cortex

BACKGROUND

Three different α₂-adrenoceptor (α₂-AR) subtypes have been described. The α_2A-AR and α_2C-AR subtypes are highly expressed in the human prefrontal cortex, where they modulate neurotransmission. However, due to the lack of subtype-selective ligands, the physiological relevance of both subtypes has not been fully resolved.

AIMS

In this context, the aim of the present study was to characterize the protein expression of both α₂-AR subtypes, in different synaptic fractions of postmortem human prefrontal cortex.

METHODS

A subcellular fractionation of the samples was performed and the protein expression of α_2A- and α_2C-ARs was measured in presynaptic membranes and postsynaptic density fractions by Western blot.

RESULTS

The results revealed that the α_2A-AR subtype is mainly located postsynaptically (95±3%) whereas the remaining 5±3% is in the presynapse. Conversely, the α_2C-AR subtype showed a similar distribution between pre- and postsynaptic membranes, with a slightly higher percentage present in the presynapse (60±2% vs. 40±2%).

CONCLUSIONS

These findings could explain some contradictory effects reported for α₂-AR agonists and antagonists in the human prefrontal cortex. Furthermore, the present data could contribute to elucidating the therapeutic potential of selectively targeting α_2A- or α_2C-AR subtypes.

Enhancing the Utility of Preclinical Research in Neuropsychiatry Drug Development

Most large pharmaceutical companies have downscaled or closed their clinical neuroscience research programs in response to the low clinical success rate for drugs that showed tremendous promise in animal experiments intended to model psychiatric pathophysiology. These failures have raised serious concerns about the role of preclinical research in the identification and evaluation of new pharmacotherapies for psychiatry. In the absence of a comprehensive understanding of the neurobiology of psychiatric disorders, the task of developing "animal models" seems elusive. The purpose of this review is to highlight emerging strategies to enhance the utility of preclinical research in the drug development process. We address this issue by reviewing how advances in neuroscience, coupled with new conceptual approaches, have recently revolutionized the way we can diagnose and treat common psychiatric conditions. We discuss the implications of these new tools for modeling psychiatric conditions in animals and advocate for the use of systematic reviews of preclinical work as a prerequisite for conducting psychiatric clinical trials. We believe that work in animals is essential for elucidating human psychopathology and that improving the predictive validity of animal models is necessary for developing more effective interventions for mental illness.

Neuromodulation and a Reconceptualization of Autism Spectrum Disorders: Using the Locus Coeruleus Functioning as an Exemplar

The Autism Spectrum Disorders (ASD) are a heterogeneous group of developmental disorders. Although, ASD can be reliably diagnosed, the etiology, pathophysiology, and treatment targets remain poorly characterized. While there are many atypical findings in anatomy, genetics, connectivity, and other biologic parameters, there remains no discreet hypothesis to explain the core signs as well as the very frequent comorbidities. Due to this, designing targets for treatments can only be done by assuming each symptom is a result of a discreet abnormality which is likely not the case. Neuronal circuity remains a major focus of research but rarely taking into account the functioning of the brain is highly dependent on various systems, including the neuromodulatory substances originating in the midbrain. A hypothesis is presented which explores the possibility of explaining many of the symptoms found in ASD in terms of inefficient neuromodulation using the functioning of the locus coeruleus and norepinephrine (LC/NE) as exemplars. The basic science of LC/NE is reviewed. Several functions found to be impaired in ASD including learning, attention, sensory processing, emotional regulation, autonomic functioning, adaptive and repetitive behaviors, sleep, language acquisition, initiation, and prompt dependency are examined in terms of the functioning of the LC/NE system. Suggestions about possible treatment directions are explored.

QuilliChew extended-release chewable tablets for the treatment of ADHD in patients ages 6 years old and above

INTRODUCTION

Attention-deficit/hyperactivity disorder (ADHD) is a common neurobehavioral disorder affecting as many as 6.4 million children and adolescents in the United States. Since amphetamine (AMPH) and methylphenidate (MPH) were found to be effective more than 60 years ago, numerous formulations of these compounds have been developed. New preparations have focused on convenience, with extended-release (ER) drugs allowing once-daily dosing. Multiple ER formulations do not require patients to swallow a tablet or capsule. Recent ER preparations include liquids, oral disintegrating tablets, and chewable tablets. Several new formulations use ion exchange technology containing both immediate-release and ER components. Areas covered: Quillichew ER^TM (MPH-ERCT) is an ER methylphenidate designed to be chewed before swallowing. The technology and pharmacokinetics, along with efficacy and safety data, are presented. Expert opinion: Extensive safety and efficacy data exist for MPH. ER formulations can be distinguished by preparation (tablet, capsule, liquid) and onset and duration of effect, but efficacy is similar for all ER MPH products. Each formulation has attributes, such as ease of titration, portability, and taste, that make it more acceptable for certain patients. Because AMPH and MPH are so effective, current technology research is focused on improving safety, convenience, and onset and duration of effect.

Prospective memory impairment following whole brain radiotherapy in patients with metastatic brain cancer

OBJECTIVE

To investigate the prospective memory (PM) impairment following whole brain radiotherapy (WBRT) in cancer patients with brain metastases.

METHOD

Eighty-one patients with metastatic brain cancer, agreeing to undergo WBRT, were enrolled and subjected to a battery of cognitive neuropsychological tests, including the mini-mental state examination (MMSE), verbal fluency test (VFT), digit span test (DST), and event-based and time-based prospective memory (EBPM and TBPM) tasks, before and after radiotherapy.

RESULTS

The patients with metastatic brain cancer after WBRT exhibited a significant decrease in the MMSE, DST, VFT, and EBPM scores (t = 6.258, 10.192, 5.361, -5.892, P < 0.01), but nonsignificant decrease in the TBPM scores (t = -1.172, P > 0.05).

CONCLUSION

There is significant EBPM impairment in cancer patients with brain metastases after WBRT, whereas that in the TBPM remained relatively unaffected. The result suggests that EBPM impairment may be as an early cognitive impairment marker in patients with BM who undergo WBRT.

Glutamate and norepinephrine interaction: Relevance to higher cognitive operations and psychopathology

Mather and colleagues present an impressive interdisciplinary model of arousal-induced norepinephrine release and its role in selectively enhancing/inhibiting perception, attention, and memory consolidation. This model will require empirical investigation to test its validity and generalizability beyond classic norepinephrine circuits because it simplifies extremely complex and heterogeneous actions including norepinephrine mechanisms related to higher cognitive circuits and psychopathology.

Unique Molecular Regulation of Higher-Order Prefrontal Cortical Circuits: Insights into the Neurobiology of Schizophrenia

Schizophrenia is associated with core deficits in cognitive abilities and impaired functioning of the newly evolved prefrontal association cortex (PFC). In particular, neuropathological studies of schizophrenia have found selective atrophy of the pyramidal cell microcircuits in deep layer III of the dorsolateral PFC (dlPFC) and compensatory weakening of related GABAergic interneurons. Studies in monkeys have shown that recurrent excitation in these layer III microcircuits generates the precisely patterned, persistent firing needed for working memory and abstract thought. Importantly, excitatory synapses on layer III spines are uniquely regulated at the molecular level in ways that may render them particularly vulnerable to genetic and/or environmental insults. Glutamate actions are remarkably dependent on cholinergic stimulation, and there are inherent mechanisms to rapidly weaken connectivity, e.g. during stress. In particular, feedforward cyclic adenosine monophosphate (cAMP)-calcium signaling rapidly weakens network connectivity and neuronal firing by opening nearby potassium channels. Many mechanisms that regulate this process are altered in schizophrenia and/or associated with genetic insults. Current data suggest that there are "dual hits" to layer III dlPFC circuits: initial insults to connectivity during the perinatal period due to genetic errors and/or inflammatory insults that predispose the cortex to atrophy, followed by a second wave of cortical loss during adolescence, e.g. driven by stress, at the descent into illness. The unique molecular regulation of layer III circuits may provide a nexus where inflammation disinhibits the neuronal response to stress. Understanding these mechanisms may help to illuminate dlPFC susceptibility in schizophrenia and provide insights for novel therapeutic targets.

Cell Type- and Layer-Specific Muscarinic Potentiation of Excitatory Synaptic Drive onto Parvalbumin Neurons in Mouse Prefrontal Cortex

Cholinergic neuromodulation is thought to shape network activity in the PFC, and thus PFC-dependent cognitive functions. ACh may modulate the activity of parvalbumin-positive (PV+) neurons, which critically regulate cortical network function. However, the mechanisms of cholinergic regulation of PV+ neuron activity, and particularly of the basket cell (BC) versus chandelier cell (ChC) subtypes, are unclear. Using patch clamp recordings in acute slices, we examined the effects of the ACh receptor (AChR) agonist carbachol on the excitatory synaptic drive onto BCs or ChCs in layers 2 to 6 of mouse PFC. Carbachol increased the frequency and amplitude of spontaneous EPSCs (sEPSCs) recorded from PV+ BCs in layers 3-6, but not in BCs from layer 2. Moreover, carbachol did not change the sEPSCs in ChCs, which were located exclusively in layer 2. The potentiation of sEPSCs in layers 3-6 BCs was prevented by the Na+ channel blocker tetrodotoxin and was abolished by the M1-selective muscarinic AChR antagonist pirenzepine. Thus, carbachol potentiates the activity-dependent excitatory drive onto PV+ neurons via M1-muscarinic AChR activation in a cell type- and layer-specific manner. In current clamp recordings with synaptic transmission blocked, carbachol directly evoked firing in deep layer pyramidal neurons (PNs). In contrast, carbachol elicited deep layer BC firing indirectly, via glutamate-mediated synaptic drive. Our data suggest that ACh powerfully regulates PFC microcircuit function by facilitating the firing of PNs that synaptically recruit deep layer PV+ BC activity, possibly shaping the patterns of network activity that contribute to cognitive function.

Evolution in Neuromodulation-The Differential Roles of Acetylcholine in Higher Order Association vs. Primary Visual Cortices

This review contrasts the neuromodulatory influences of acetylcholine (ACh) on the relatively conserved primary visual cortex (V1), compared to the newly evolved dorsolateral prefrontal association cortex (dlPFC). ACh is critical both for proper circuit development and organization, and for optimal functioning of mature systems in both cortical regions. ACh acts through both nicotinic and muscarinic receptors, which show very different expression profiles in V1 vs. dlPFC, and differing effects on neuronal firing. Cholinergic effects mediate attentional influences in V1, enhancing representation of incoming sensory stimuli. In dlPFC ACh plays a permissive role for network communication. ACh receptor expression and ACh actions in higher visual areas have an intermediate profile between V1 and dlPFC. This changing role of ACh modulation across association cortices may help to illuminate the particular susceptibility of PFC in cognitive disorders, and provide therapeutic targets to strengthen cognition.

Perturbed Developmental Serotonin Signaling Affects Prefrontal Catecholaminergic Innervation and Cortical Integrity

Proper development of the medial prefrontal cortex (mPFC), crucial for correct cognitive functioning, requires projections from, among others, the serotonergic (5-HT) and catecholaminergic systems, but it is unclear how these systems influence each other during development. Here, we describe the parallel development of the 5-HT and catecholaminergic prefrontal projection systems in rat and demonstrate a close engagement of both systems in the proximity of Cajal-Retzius cells. We further show that in the absence of the 5-HT transporter (5-HTT), not only the developing 5-HT but also the catecholaminergic system, including their projections towards the mPFC, are affected. In addition, the layer identity of the mPFC neurons and reelin-positive interneuron number and integration are altered in the absence of the 5-HTT. Together, our data demonstrate a functional interplay between the developing mPFC 5-HT and catecholaminergic systems, and call for a holistic approach in studying neurotransmitter systems-specific developmental consequences for adult behavior, to eventually allow the design of better treatment strategies for neuropsychiatric disorders.

Low levels of muscarinic M1 receptor-positive neurons in cortical layers III and V in Brodmann areas 9 and 17 from individuals with schizophrenia

BACKGROUND

Results of neuroimaging and postmortem studies suggest that people with schizophrenia may have lower levels of muscarinic M1 receptors (CHRM1) in the cortex, but not in the hippocampus or thalamus. Here, we use a novel immunohistochemical approach to better understand the likely cause of these low receptor levels.

METHODS

We determined the distribution and number of CHRM1-positive (CHRM1+) neurons in the cortex, medial dorsal nucleus of the thalamus and regions of the hippocampus from controls (n = 12, 12 and 5, respectively) and people with schizophrenia (n = 24, 24 and 13, respectively).

RESULTS

Compared with controls, levels of CHRM1+ neurons in people with schizophrenia were lower on pyramidal cells in layer III of Brodmann areas 9 (-44%) and 17 (-45%), and in layer V in Brodmann areas 9 (-45%) and 17 (-62%). We found no significant differences in the number of CHRM1+ neurons in the medial dorsal nucleus of the thalamus or in the hippocampus.

LIMITATIONS

Although diagnostic cohort sizes were typical for this type of study, they were relatively small. As well, people with schizophrenia were treated with antipsychotic drugs before death.

CONCLUSION

The loss of CHRM1+ pyramidal cells in the cortex of people with schizophrenia may underpin derangements in the cholinergic regulation of GABAergic activity in cortical layer III and in cortical/subcortical communication via pyramidal cells in layer V.

Prefronto-cortical dopamine D1 receptor sensitivity can critically influence working memory maintenance during delayed response tasks

The dopamine (DA) hypothesis of cognitive deficits suggests that too low or too high extracellular DA concentration in the prefrontal cortex (PFC) can severely impair the working memory (WM) maintenance during delay period. Thus, there exists only an optimal range of DA where the sustained-firing activity, the neural correlate of WM maintenance, in the cortex possesses optimal firing frequency as well as robustness against noisy distractions. Empirical evidences demonstrate changes even in the D1 receptor (D1R)-sensitivity to extracellular DA, collectively manifested through D1R density and DA-binding affinity, in the PFC under neuropsychiatric conditions such as ageing and schizophrenia. However, the impact of alterations in the cortical D1R-sensitivity on WM maintenance has yet remained poorly addressed. Using a quantitative neural mass model of the prefronto-mesoprefrontal system, the present study reveals that higher D1R-sensitivity may not only effectuate shrunk optimal DA range but also shift of the range to lower concentrations. Moreover, higher sensitivity may significantly reduce the WM-robustness even within the optimal DA range and exacerbates the decline at abnormal DA levels. These findings project important clinical implications, such as dosage precision and variability of DA-correcting drugs across patients, and failure in acquiring healthy WM maintenance even under drug-controlled normal cortical DA levels.

Enteral Guanfacine to Treat Severe Anxiety and Agitation Complicating Critical Care After Cardiac Surgery

This article is the first reported case describing the off-label use of enteral immediate-release guanfacine, a long-acting α-2 adrenergic agonist most commonly used in the treatment of attention-deficit hyperactivity disorder, for sedation in a patient with severe anxiety and agitation limiting mechanical ventilation weaning several days after cardiac surgery. In this case, after several days of unsuccessful attempts to control his agitation and anxiety with conventional therapies, guanfacine therapy was initiated, and the patient was rapidly weaned from all other sedatives and mechanical ventilation shortly thereafter. The patient was weaned from guanfacine therapy without evidence of bradycardia, hypotension, or rebound syndrome. Enteral guanfacine therapy should be further studied as a potentially useful and cost-effective sedative therapy for patients with severe anxiety and/or agitation in the intensive care unit following cardiac and thoracic surgical procedures.

Advances in Drug Discovery and Development in Geriatric Psychiatry

PURPOSE OF REVIEW

This article reviews recent advances in drug discovery and development for geriatric psychiatry. Drug discovery for disorders of the central nervous system is a long and challenging process, with a high attrition rate from the preclinical stages through to marketing a compound. Developing drugs for geriatric neuropsychiatric conditions presents additional challenges, due to the complexity of the symptoms, comorbid diagnoses, and the variability of the population. Despite there being limited success over the past two decades, a number of new approaches have identified potential targets for preclinical development and ultimately clinical testing.

RECENT FINDINGS

Recent approaches have tried to address specific mechanisms that relate to the disease progression. These approaches include combining a number of ligands into to multi-target compounds, or targeting specific types of cells such as protein kinases or myeloid cells. In addition, the increased use of induced pluripotent stem cell cultures has enabled new compounds to be tested on disease-specific tissues, increasing the success rate of the lead compounds going through the preclinical stages. New pharmacological agents designed with advanced screening techniques and the shift towards systems pharmacology is changing the landscape of drug discovery in geriatric psychiatry. There is potential for these new agents to produce targeted effects in the framework of disorders that have long been untreatable.

The Role of Working Memory for Cognitive Control in Anorexia Nervosa versus Substance Use Disorder

Prefrontal cortex executive functions, such as working memory (WM) interact with limbic processes to foster impulse control. Such an interaction is referred to in a growing body of publications by terms such as cognitive control, cognitive inhibition, affect regulation, self-regulation, top-down control, and cognitive–emotion interaction. The rising trend of research into cognitive control of impulsivity, using various related terms reflects the importance of research into impulse control, as failure to employ cognitions optimally may eventually result in mental disorder. Against this background, we take a novel approach using an impulse control spectrum model – where anorexia nervosa (AN) and substance use disorder (SUD) are at opposite extremes – to examine the role of WM for cognitive control. With this aim, we first summarize WM processes in the healthy brain in order to frame a systematic review of the neuropsychological, neural and genetic findings of AN and SUD. In our systematic review of WM/cognitive control, we found n = 15 studies of AN with a total of n = 582 AN and n = 365 HC participants; and n = 93 studies of SUD with n = 9106 SUD and n = 3028 HC participants. In particular, we consider how WM load/capacity may support the neural process of excessive epistemic foraging (cognitive sampling of the environment to test predictions about the world) in AN that reduces distraction from salient stimuli. We also consider the link between WM and cognitive control in people with SUD who are prone to ‘jumping to conclusions’ and reduced epistemic foraging. Finally, in light of our review, we consider WM training as a novel research tool and an adjunct to enhance treatment that improves cognitive control of impulsivity.

Intranasal Insulin Ameliorates Cerebral Hypometabolism, Neuronal Loss, and Astrogliosis in Streptozotocin-Induced Alzheimer's Rat Model

Intracerebroventricular injection of streptozotocin (ICV-STZ) in rodents leads to cognitive impairments and several pathological changes like Alzheimer's disease (AD). However, there is hardly any research about the effect of ICV-STZ on regional cerebral glucose metabolism in rodents. Previous studies have demonstrated that intranasal insulin improves cognition in AD patients. However, the underlying mechanism remains elusive. Here, we treated the ICV-STZ rats with daily intranasal delivery of insulin (2 U/day) for 6 consecutive weeks, then monitored ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) uptake using a high-resolution small-animal positron emission tomography (microPET) and studied the expression of neuronal nuclei (NeuN) and glial fibrillary acidic protein (GFAP) using immunohistochemical staining. We observed that ¹⁸F-FDG uptake decreased significantly at the prefrontal cortex, cingulate cortex, striatum, hippocampus, and entorhinal cortex in ICV-STZ rats as compared with the control rats. Intranasal insulin restores the cerebral glucose metabolism in prefrontal and cingulate cortex and attenuates astroglia activation and neuronal loss in the hippocampus of ICV-STZ rats. These findings provide the mechanistic basis for treating AD patients with intranasal insulin.

HCN Channel Targets for Novel Antidepressant Treatment

Major depressive disorder (MDD) is a chronic and potentially life threatening illness that carries a staggering global burden. Characterized by depressed mood, MDD is often difficult to diagnose and treat owing to heterogeneity of syndrome and complex etiology. Contemporary antidepressant treatments are based on improved monoamine-based formulations from serendipitous discoveries made > 60 years ago. Novel antidepressant treatments are necessary, as roughly half of patients using available antidepressants do not see long-term remission of depressive symptoms. Current development of treatment options focuses on generating efficacious antidepressants, identifying depression-related neural substrates, and better understanding the pathophysiological mechanisms of depression. Recent insight into the brain's mesocorticolimbic circuitry from animal models of depression underscores the importance of ionic mechanisms in neuronal homeostasis and dysregulation, and substantial evidence highlights a potential role for ion channels in mediating depression-related excitability changes. In particular, hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are essential regulators of neuronal excitability. In this review, we describe seminal research on HCN channels in the prefrontal cortex and hippocampus in stress and depression-related behaviors, and highlight substantial evidence within the ventral tegmental area supporting the development of novel therapeutics targeting HCN channels in MDD. We argue that methods targeting the activity of reward-related brain areas have significant potential as superior treatments for depression.

Impaired Tuning of Neural Ensembles and the Pathophysiology of Schizophrenia: A Translational and Computational Neuroscience Perspective

The functional optimization of neural ensembles is central to human higher cognitive functions. When the functions through which neural activity is tuned fail to develop or break down, symptoms and cognitive impairments arise. This review considers ways in which disturbances in the balance of excitation and inhibition might develop and be expressed in cortical networks in association with schizophrenia. This presentation is framed within a developmental perspective that begins with disturbances in glutamate synaptic development in utero. It considers developmental correlates and consequences, including compensatory mechanisms that increase intrinsic excitability or reduce inhibitory tone. It also considers the possibility that these homeostatic increases in excitability have potential negative functional and structural consequences. These negative functional consequences of disinhibition may include reduced working memory-related cortical activity associated with the downslope of the "inverted-U" input-output curve, impaired spatial tuning of neural activity and impaired sparse coding of information, and deficits in the temporal tuning of neural activity and its implication for neural codes. The review concludes by considering the functional significance of noisy activity for neural network function. The presentation draws on computational neuroscience and pharmacologic and genetic studies in animals and humans, particularly those involving N-methyl-D-aspartate glutamate receptor antagonists, to illustrate principles of network regulation that give rise to features of neural dysfunction associated with schizophrenia. While this presentation focuses on schizophrenia, the general principles outlined in the review may have broad implications for considering disturbances in the regulation of neural ensembles in psychiatric disorders.

Role of Prefrontal Persistent Activity in Working Memory

The prefrontal cortex is activated during working memory, as evidenced by fMRI results in human studies and neurophysiological recordings in animal models. Persistent activity during the delay period of working memory tasks, after the offset of stimuli that subjects are required to remember, has traditionally been thought of as the neural correlate of working memory. In the last few years several findings have cast doubt on the role of this activity. By some accounts, activity in other brain areas, such as the primary visual and posterior parietal cortex, is a better predictor of information maintained in visual working memory and working memory performance; dynamic patterns of activity may convey information without requiring persistent activity at all; and prefrontal neurons may be ill-suited to represent non-spatial information about the features and identity of remembered stimuli. Alternative interpretations about the role of the prefrontal cortex have thus been suggested, such as that it provides a top-down control of information represented in other brain areas, rather than maintaining a working memory trace itself. Here we review evidence for and against the role of prefrontal persistent activity, with a focus on visual neurophysiology. We show that persistent activity predicts behavioral parameters precisely in working memory tasks. We illustrate that prefrontal cortex represents features of stimuli other than their spatial location, and that this information is largely absent from early cortical areas during working memory. We examine memory models not dependent on persistent activity, and conclude that each of those models could mediate only a limited range of memory-dependent behaviors. We review activity decoded from brain areas other than the prefrontal cortex during working memory and demonstrate that these areas alone cannot mediate working memory maintenance, particularly in the presence of distractors. We finally discuss the discrepancy between BOLD activation and spiking activity findings, and point out that fMRI methods do not currently have the spatial resolution necessary to decode information within the prefrontal cortex, which is likely organized at the micrometer scale. Therefore, we make the case that prefrontal persistent activity is both necessary and sufficient for the maintenance of information in working memory.