Norepinephrine versus dopamine and their interaction in modulating synaptic function in the prefrontal cortex

From neurons to brain networks, pharmacodynamics of stimulant medication for ADHD

Stimulants represent the first line pharmacological treatment for attention-deficit/hyperactivity disorder (ADHD) and are among the most prescribed psychopharmacological treatments. Their mechanism of action at synaptic level has been extensively studied. However, it is less clear how their mechanism of action determines clinically observed benefits. To help bridge this gap, we provide a comprehensive review of stimulant effects, with an emphasis on nuclear medicine and magnetic resonance imaging (MRI) findings. There is evidence that stimulant-induced modulation of dopamine and norepinephrine neurotransmission optimizes engagement of task-related brain networks, increases perceived saliency, and reduces interference from the default mode network. An acute administration of stimulants may reduce brain alterations observed in untreated individuals in fronto-striato-parieto-cerebellar networks during tasks or at rest. Potential effects of prolonged treatment remain controversial. Overall, neuroimaging has fostered understanding on stimulant mechanism of action. However, studies are often limited by small samples, short or no follow-up, and methodological heterogeneity. Future studies should address age-related and longer-term effects, potential differences among stimulants, and predictors of treatment response.

Adolescent stress differentially modifies dopamine and norepinephrine release in the medial prefrontal cortex of adult rats

Adolescent stress (AS) has been associated with higher vulnerability to psychiatric disorders such as schizophrenia, depression, or drug dependence. Moreover, the alteration of brain catecholamine (CAT) transmission in the medial prefrontal cortex (mPFC) has been found to play a major role in the etiology of psychiatric disturbances. We investigated the effect of adolescent stress on CAT transmission in the mPFC of freely moving adult rats because of the importance of this area in the etiology of psychiatric disorders, and because CAT transmission is the target of a relevant group of drugs used in the therapy of depression and psychosis. We assessed basal dopamine (DA) and norepinephrine (NE) extracellular concentrations (output) by brain microdialysis in in the mPFC of adult rats that were exposed to chronic mild stress in adolescence. To ascertain the role of an altered release or reuptake, we stimulated DA and NE output by administering either different doses of amphetamine (0.5 and 1.0 mg / kg s.c.), which by a complex mechanism determines a dose dependent increase in the CAT output, or reboxetine (10 mg/kg i.p.), a selective NE reuptake inhibitor. The results showed the following: (i) basal DA output in AS rats was lower than in controls, while no difference in basal NE output was observed; (ii) amphetamine, dose dependently, stimulated DA and NE output to a greater extent in AS rats than in controls; (iii) reboxetine stimulated NE output to a greater extent in AS rats than in controls, while no difference in stimulated DA output was observed between the two groups. These results show that AS determines enduring effects on DA and NE transmission in the mPFC and might lead to the occurrence of psychiatric disorders or increase the vulnerability to drug addiction.

New Therapeutic Targets and Drugs for Schizophrenia Beyond Dopamine D2 Receptor Antagonists

Schizophrenia is a disease with a complex pathological mechanism that is influenced by multiple genes. The study of its pathogenesis is dominated by the dopamine hypothesis, as well as other hypotheses such as the 5-hydroxytryptamine hypothesis, glutamate hypothesis, immune-inflammatory hypothesis, gene expression abnormality hypothesis, and neurodevelopmental abnormality hypothesis. The first generation of antipsychotics was developed based on dopaminergic receptor antagonism, which blocks dopamine D2 receptors in the brain to exert antipsychotic effects. The second generation of antipsychotics acts by dual blockade of 5-hydroxytryptamine and dopamine receptors. From the third generation of antipsychotics onwards, the therapeutic targets for antipsychotic schizophrenia expanded beyond D2 receptor blockade to explore D2 receptor partial agonism and the antipsychotic effects of new targets such as D3, 5-HT1A, 5-HT7, and mGlu2/3 receptors. The main advantages of the second and third generation antipsychotics over first-generation antipsychotics are the reduction of side effects and the improvement of negative symptoms, and even though third-generation antipsychotics do not directly block D2 receptors, the modulation of the dopamine transmitter system is still an important part of their antipsychotic process. According to recent research, several receptors, including 5-hydroxytryptamine, glutamate, γ-aminobutyric acid, acetylcholine receptors and norepinephrine, play a role in the development of schizophrenia. Therefore, the focus of developing new antipsychotic drugs has shifted towards agonism or inhibition of these receptors. Specifically, the development of NMDARs stimulants, GABA receptor agonists, mGlu receptor modulators, cholinergic receptor modulators, 5-HT2C receptor agonists and alpha-2 receptor modulators has become the main direction. Animal experiments have confirmed the antipsychotic effects of these drugs, but their pharmacokinetics and clinical applicability still require further exploration. Research on alternative targets for antipsychotic drugs, beyond the dopamine D2 receptor, has expanded the potential treatment options for schizophrenia and gives an important way to address the challenge of refractory schizophrenia. This article aims to provide a comprehensive overview of the research on therapeutic targets and medications for schizophrenia, offering valuable insights for both treatment and further research in this field.

The Effects of Fluoxetine and Agomelatine on Neurocognitive Functions and Sleep in Patients with Major Depressive Disorder

Background

We aimed to evaluate the effects of 6 weeks of agomelatine versus fluoxetine treatment on cognition and sleep.

Methods

Agomelatine 25 mg/day and fluoxetine 20 mg/day were administered to major depressive disorder (MDD) patients. Assessments were conducted before the treatment and at the sixth week of treatment via psychometric measures and comprehensive neurocognitive assessments of various functions, including executive skills, attention, memory, verbal fluency, and speed of processing.

Results

They both improved the evaluated neurocognitive test scores (P < .05), except for the scores of the Digit Span Test (P > .05), but only fluoxetine significantly improved the scores of the Controlled Oral Word Association Test (P = .018). Only in relation to the subjective sleep quality part of the Pittsburgh Sleep Quality Index (P = .035) and the Trail Making Test-B (TMT-B) (P = .046) was there an important difference between the study groups, and agomelatine showed better effects than fluoxetine in these measures.

Conclusion

Both drugs improved the neurocognitive functioning in the participants. However, the better effect of agomelatine in improving the TMT-B scores suggests that it is a suitable option for MDD patients with noticeable executive disturbances.

Enhanced Risky Choice in Male Rats Elicited by the Acute Pharmacological Stressor Yohimbine Involves Prefrontal Dopamine D1 Receptor Activation

BACKGROUND

Acute stress alters risk-based decision-making; however, the underlying neural and neurochemical substrates are underexplored. Given their well-documented stress-inducing effects in humans and laboratory animals, glucocorticoids such as cortisol and corticosterone and the α2-adrenoceptor antagonist yohimbine represent potent pharmacological tools to mimic some characteristics of acute stress.

METHODS

Here, we analyzed the effects of the pharmacological stressors corticosterone and yohimbine given systemically on risk-based decision-making in male rats. Moreover, we investigated whether pharmacological stressor effects on risk-based decision-making involve dopamine D1 receptor stimulation in the dorsal prelimbic cortex (PL). We used a risk discounting task that requires choosing between a certain/small reward lever that always delivered 1 pellet and a risky/large reward lever that delivered 4 pellets with a decreasing probability across subsequent trials.

RESULTS

Systemic administration of yohimbine increased the preference for the risky/large reward lever. By contrast, systemic single administration of corticosterone did not significantly promote risky choice. Moreover, co-administration of corticosterone did not enhance the effects of yohimbine on risky choice. The data further show that the increased preference for the risky/large reward lever under systemic yohimbine was lowered by a concurrent pharmacological blockade of dopamine D1 receptors in the PL.

CONCLUSIONS

Our rodent data provide causal evidence that stimulation of PL D1 receptors may represent a neurochemical mechanism by which the acute pharmacological stressor yohimbine, and possibly nonpharmacological stressors as well, promote risky choice.

The Ability to Voluntarily Regulate Theta Band Activity Affects How Pharmacological Manipulation of the Catecholaminergic System Impacts Cognitive Control

BACKGROUND

The catecholaminergic system influences response inhibition, but the magnitude of the impact of catecholaminergic manipulation is heterogeneous. Theoretical considerations suggest that the voluntary modulability of theta band activity can explain this variance. The study aimed to investigate to what extent interindividual differences in catecholaminergic effects on response inhibition depend on voluntary theta band activity modulation.

METHODS

A total of 67 healthy adults were tested in a randomized, double-blind, cross-over study design. At each appointment, they received a single dose of methylphenidate or placebo and performed a Go/Nogo task with stimuli of varying complexity. Before the first appointment, the individual's ability to modulate theta band activity was measured. Recorded EEG data were analyzed using temporal decomposition and multivariate pattern analysis.

RESULTS

Methylphenidate effects and voluntary modulability of theta band activity showed an interactive effect on the false alarm rates of the different Nogo conditions. The multivariate pattern analysis revealed that methylphenidate effects interacted with voluntary modulability of theta band activity at a stimulus processing level, whereas during response selection methylphenidate effects interacted with the complexity of the Nogo condition.

CONCLUSIONS

The findings reveal that the individual's theta band modulability affects the responsiveness of an individual's catecholaminergic system to pharmacological modulation. Thus, the impact of pharmacological manipulation of the catecholaminergic system on cognitive control most likely depends on the existing ability to self-modulate relevant brain oscillatory patterns underlying the cognitive processes being targeted by pharmacological modulations.

Dopamine D2 receptors in the dorsomedial prefrontal cortex modulate social hierarchy in male mice

Social hierarchy greatly influences behavior and health. Both human and animal studies have signaled the medial prefrontal cortex (mPFC) as specifically related to social hierarchy. Dopamine D1 receptors (D1Rs) and D2 receptors (D2Rs) are abundantly expressed in the mPFC, modulating its functions. However, it is unclear how DR-expressing neurons in the mPFC regulate social hierarchy. Here, using a confrontation tube test, we found that most adult C57BL/6J male mice could establish a linear social rank after 1 week of cohabitation. Lower rank individuals showed social anxiety together with decreased serum testosterone levels. D2R expression was significantly downregulated in the dorsal part of mPFC (dmPFC) in lower rank individuals, whereas D1R expression showed no significant difference among the rank groups in the whole mPFC. Virus knockdown of D2Rs in the dmPFC led to mice being particularly prone to lose the contests in the confrontation tube test. Finally, simultaneous D2R activation in the subordinates and D2R inhibition in the dominants in a pair switched their dominant-subordinate relationship. The above results indicate that D2Rs in the dmPFC play an important role in social dominance. Our findings provide novel insights into the divergent functions of prefrontal D1Rs and D2Rs in social dominance, which may contribute to ameliorating social dysfunctions along with abnormal social hierarchy.

Noradrenergic alpha-2a Receptor Stimulation Enhances Prediction Error Signaling in Anterior Cingulate Cortex and Striatum

The noradrenergic system is implicated to support behavioral flexibility by increasing exploration during periods of uncertainty and by enhancing working memory for goal-relevant stimuli. Possible sources mediating these pro-cognitive effects are α2A adrenoceptors (α2AR) in prefrontal cortex or the anterior cingulate cortex facilitating fronto-striatal learning processes. We tested this hypothesis by selectively stimulating α2ARs using Guanfacine during feature-based attentional set shifting in nonhuman primates. We found that α2A stimulation improved learning from errors and facilitates updating the target feature of an attentional set. Neural recordings in the anterior cingulate cortex (ACC), the dorsolateral prefrontal cortex (dlPFC), and the striatum showed that α2A stimulation selectively enhanced the neural representation of negative reward prediction errors in neurons of the ACC and of positive prediction errors in the striatum, but not in dlPFC. This modulation was accompanied by enhanced encoding of the feature and location of the attended target across the fronto-striatal network. Enhanced learning was paralleled by enhanced encoding of outcomes in putative fast-spiking interneurons in the ACC, dlPFC, and striatum but not in broad spiking cells, pointing to an interneuron mediated mechanism of α2AR action. These results illustrate that α2A receptors causally support the noradrenergic enhancement of updating attention sets through an enhancement of prediction error signaling in the ACC and the striatum.

The mesocortical dopaminergic system cannot explain hyperactivity in an animal model of attention deficit hyperactivity disorder (ADHD)- Spontaneously hypertensive rats (SHR)

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) is one of the most prevalent neuropsychiatric disorders with morphological brain abnormalities. There is a growing body of evidence that abnormalities in the dopaminergic system may account for ADHD pathogenesis. However, it is not clear whether the dopaminergic system is hyper or hypoactive. To determine whether the DA neurons and/or axons deficiency might be the cause of the postulated dopaminergic hypofunction in spontaneously hypertensive rats (SHR, animal model of ADHD), this study examined the dopaminergic neurons and fibers in the brain tissues of SHRs and Wistar Kyoto rats (WKY, control animals). Here, we performed immunohistochemical tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) staining on brain sections collected on juveniles from SHR and WKY. Moreover, behavioral testing to examine the hyperactivity in the open field area was also elucidated.

RESULTS

The mesocortical dopaminergic system appears to be normal in juvenile SHR, as suggested by (i) no alteration in the area density of TH-immunoreactive (TH-ir) dopaminergic neurons in the ventral tegmental area (VTA), (ii) no alterations in the volume density of TH-ir fibers in layer I of the prelimbic (PrL) subregion of medial PFC (mPFC), (iii) no alteration in the percentage of TH-ir dopaminergic fibers in layer I of the PrL subregion of mPFC as revealed by TH and/or DBH immunoreactivity. Furthermore, the SHR showed increased locomotor activity than WKY in the open field test.

CONCLUSIONS

The demonstration of no alteration in mesocortical dopaminergic neurons and fiber in SHR raises some concern about the position of SHR as an animal model of the inattentive subtype of ADHD. However, these results strengthen this strain as an animal model of hyperactive/impulsive subtype ADHD for future studies that may elucidate the underlying mechanism mediating hyperactivity and test various treatment strategies.

Clozapine but not lithium reverses aberrant tyrosine uptake in patients with bipolar disorder

RATIONALE

Availability of the dopamine and noradrenaline precursor tyrosine is critical for normal functioning, and deficit in tyrosine transport across cell membrane and the blood-brain barrier has been reported in bipolar disorder and schizophrenia. Clozapine and lithium are two psychoactive agents used to treat psychosis, mood disorders and suicidal behavior, but their mechanism of action remains largely unknown.

OBJECTIVE

To characterize immediate and delayed differences in tyrosine uptake between healthy controls (HC) and bipolar patients (BP) and see if these differences could be normalized by either clozapine, lithium or both. A second objective was to see if clozapine and lithium have additive, antagonistic or synergistic effects in this.

METHOD

Fibroblasts from five HC and five BP were incubated for 5 min or 6 h with clozapine, lithium, or combination of both. Radioactive labelled tyrosine was used to quantify tyrosine membrane transport.

RESULTS

There was significantly reduced tyrosine uptake at baseline in BP compared to HC, a deficit that grew with increasing incubation time. Clozapine selectively increased tyrosine uptake in BP and abolished the deficit seen under baseline conditions, while lithium had no such effect. Combination treatment with clozapine and lithium was less effective than when clozapine was used alone.

CONCLUSIONS

There was significant deficit in tyrosine transport in BP compared to HC that was reversed by clozapine but not lithium. Clozapine was more effective when used alone than when added together with lithium. Potential clinical implications of this will be discussed.

Assessing attention and impulsivity in the variable stimulus duration and variable intertrial interval rodent continuous performance test schedules using noradrenaline receptor antagonists in female C57BL/6JRj mice

RATIONALE

Noradrenergic dysfunction is associated with disorders of impulsivity and inattention. The rodent continuous performance test (rCPT) quantifies changes in attention and impulsivity.

OBJECTIVE

To use NA receptor antagonists to examine the roles of NA on attention and impulsivity behaviours measured in the rCPT variable stimulus duration (vSD) and the variable intertrial interval (vITI) schedules.

METHODS

Two cohorts of 36 female C57BL/6JRj mice were examined separately in the rCPT vSD and vITI schedules. Both cohorts received antagonists of the following adrenoceptors: α1 (doxazosin, DOX: 1.0, 3.0, 10.0 mg/kg), α2 (yohimbine, YOH: 0.1, 0.3, 1.0 mg/kg), and β1/2 (propranolol, PRO: 1.0, 3.0, 10.0 mg/kg) in consecutive balanced Latin square designs with flanking reference measurements. The antagonists were subsequently examined for effects on locomotor activity.

RESULTS

DOX showed similar effects in both schedules, improving discriminability and accuracy, and reducing responding and impulsivity, and DOX also reduced locomotor activity. YOH showed prominent effects in the vSD schedule to increase responding and impulsivity, while impairing discriminability and accuracy. YOH did not affect locomotor activity. PRO increased responding and impulsivity, decreased accuracy, but did not affect discriminability or locomotor activity.

CONCLUSION

Antagonism of α2 or β1/2 adrenoceptors caused similar increases in responding and impulsivity and worsened attentional performance, while α1 adrenoceptor antagonism showed the opposite effects. Our results suggest that endogenous NA exerts bidirectional control of most behaviours in the rCPT. The parallel vSD and vITI studies showed a substantial overlap in effects, but also some differences that indicate differing sensitivity towards noradrenergic manipulations.

Impact of acute psychosocial stress on attentional control in humans. A study of evoked potentials and pupillary response

Psychosocial stress has increased considerably in our modern lifestyle, affecting global mental health. Deficits in attentional control are cardinal features of stress disorders and pathological anxiety. Studies suggest that changes in the locus coeruleus-norepinephrine system could underlie the effects of stress on top-down attentional control. However, the impact of psychosocial stress on attentional processes and its underlying neural mechanisms are poorly understood. This study aims to investigate the effect of psychosocial stress on attentional processing and brain signatures. Evoked potentials and pupillary activity related to the oddball auditory paradigm were recorded before and after applying the Montreal Imaging Stress Task (MIST). Electrocardiogram (ECG), salivary cortisol, and subjective anxiety/stress levels were measured at different experimental periods. The control group experienced the same physical and cognitive effort but without the psychosocial stress component. The results showed that stressed subjects exhibited decreased P3a and P3b amplitude, pupil phasic response, and correct responses. On the other hand, they displayed an increase in Mismatch Negativity (MMN). N1 amplitude after MIST only decreased in the control group. We found that differences in P3b amplitude between the first and second oddball were significantly correlated with pupillary dilation and salivary cortisol levels. Our results suggest that under social-evaluative threat, basal activity of the coeruleus-norepinephrine system increases, enhancing alertness and decreasing voluntary attentional resources for the cognitive task. These findings contribute to understanding the neurobiological basis of attentional changes in pathologies associated with chronic psychosocial stress.

Anxiety and depression: A top-down, bottom-up model of circuit function

A functional interplay of bottom-up and top-down processing allows an individual to appropriately respond to the dynamic environment around them. These processing modalities can be represented as attractor states using a dynamical systems model of the brain. The transition probability to move from one attractor state to another is dependent on the stability, depth, neuromodulatory tone, and tonic changes in plasticity. However, how does the relationship between these states change in disease states, such as anxiety or depression? We describe bottom-up and top-down processing from Marr's computational-algorithmic-implementation perspective to understand depressive and anxious disease states. We illustrate examples of bottom-up processing as basolateral amygdala signaling and projections and top-down processing as medial prefrontal cortex internal signaling and projections. Understanding these internal processing dynamics can help us better model the multifaceted elements of anxiety and depression.

Motor and Cognitive Modulation of a Single Session of Transcutaneous Auricular Vagus Nerve Stimulation in Post Stroke Patients: A Pilot Study

Objective: The aim of the present study is to explore whether a single session of transcutaneous Vagus Nerve Stimulation (tVNS) can enhance the ipsilesional, and contralesional upper limb motor functions as well as cognitive functions in stroke patients. The effects of the stimulation were evaluated through two different tasks: the box and blocks test (BB), indexing manual dexterity, and the Go/No-go task, a visuomotor paradigm used to assess both motor readiness and response inhibition. Tests were administered without tVNS, during tVNS and during sham tVNS. Results: The BB showed a statistical difference for both contralesional side (p = 0.05) between Basal-Real condition (p = 0.042) and ipsilesional side (p = 0.001) between Basal-Real (p = 0.008) and for Real-Sham (p = 0.005). Any statistical difference was found for the mean latencies in the three conditions of the Go/No-go test. Conclusion: A single session of tVNS seems to improve upper limb motor functions but not cognitive functions in post-stroke patients, despite a positive trend was detected.

A multiple-step screening protocol to identify norepinephrine and dopamine reuptake inhibitors for depression

Depression severely impairs the health of people all over the world. Cognitive dysfunction due to depression has resulted in a severe economic burden to family and society induced by the reduction of social functioning of patients. Norepinephrine-dopamine reuptake inhibitors (NDRIs) targeted with the human norepinephrine transporter (hNET) and distributed with the human dopamine transporter (hDAT) simultaneously treat depression and improve cognitive function, and they effectively prevent sexual dysfunction and other side effects. Because many patients continue to poorly respond to NDRIs, it is urgent to discover novel NDRI antidepressants that do not interfere with cognitive function. The aim of this work was to selectively identify novel NDRI candidates acting against hNET and hDAT from large compound libraries by a comprehensive strategy integrating support vector machine (SVM) models, ADMET, molecular docking, in vitro binding assays, molecular dynamics simulation, and binding energy calculation. First, 6522 compounds that do not inhibit the human serotonin transporter (hSERT) were obtained by SVM models of hNET, hDAT, and non-target hSERT with similarity analyses from compound libraries. ADMET and molecular docking were then used to identify compounds that could potently bind to the hNET and hDAT with satisfactory ADMET, and 4 compounds were successfully identified. According to their docking scores and ADMET information, 3719810 was advanced for profiling by in vitro assays as a novel NDRI lead compound due to its strongest druggability and balancing activities. Encouragingly, 3719810 performed comparative activities on two targets, with Ki values of 7.32 μM for hNET and 5.23 μM for hDAT. To obtain candidates with additional activities and balance the activities of 2 targets, 5 analogs were optimized, and 2 novel scaffold compounds were successively designed. By assessment of molecular docking, molecular dynamics simulations, and binding energy calculations, 5 compounds were validated as NDRI candidates with high activities, and 4 of them performed acceptable balancing activities acting on hNET and hDAT. This work supplied promising novel NDRIs for treatment of depression with cognitive dysfunction or other related neurodegenerative disorders, and also provided a strategy for highly efficient and cost-effective identification of inhibitors for dual targets with homologous non-targets.

Noradrenergic Modulation of Learned and Innate Behaviors in Dopamine Transporter Knockout Rats by Guanfacine

Investigation of the precise mechanisms of attention deficit and hyperactivity disorder (ADHD) and other dopamine-associated conditions is crucial for the development of new treatment approaches. In this study, we assessed the effects of repeated and acute administration of α2A-adrenoceptor agonist guanfacine on innate and learned forms of behavior of dopamine transporter knockout (DAT-KO) rats to evaluate the possible noradrenergic modulation of behavioral deficits. DAT-KO and wild type rats were trained in the Hebb-Williams maze to perform spatial working memory tasks. Innate behavior was evaluated via pre pulse inhibition (PPI). Brain activity of the prefrontal cortex and the striatum was assessed. Repeated administration of GF improved the spatial working memory task fulfillment and PPI in DAT-KO rats, and led to specific changes in the power spectra and coherence of brain activity. Our data indicate that both repeated and acute treatment with a non-stimulant noradrenergic drug lead to improvements in the behavior of DAT-KO rats. This study further supports the role of the intricate balance of norepinephrine and dopamine in the regulation of attention. The observed compensatory effect of guanfacine on the behavior of hyperdopaminergic rats may be used in the development of combined treatments to support the dopamine-norepinephrine balance.

Long-term memory, synaptic plasticity and dopamine in rodent medial prefrontal cortex: Role in executive functions

Mnemonic functions, supporting rodent behavior in complex tasks, include both long-term and (short-term) working memory components. While working memory is thought to rely on persistent activity states in an active neural network, long-term memory and synaptic plasticity contribute to the formation of the underlying synaptic structure, determining the range of possible states. Whereas, the implication of working memory in executive functions, mediated by the prefrontal cortex (PFC) in primates and rodents, has been extensively studied, the contribution of long-term memory component to these tasks received little attention. This review summarizes available experimental data and theoretical work concerning cellular mechanisms of synaptic plasticity in the medial region of rodent PFC and the link between plasticity, memory and behavior in PFC-dependent tasks. A special attention is devoted to unique properties of dopaminergic modulation of prefrontal synaptic plasticity and its contribution to executive functions.

Catecholaminergic and cholinergic neuromodulation in autism spectrum disorder: A comparison to attention-deficit hyperactivity disorder

Autism spectrum disorder (ASD) is a heterogeneous neurodevelopmental disorder characterized by social impairments and restricted, repetitive behaviors. Treatment of ASD is notoriously difficult and might benefit from identification of underlying mechanisms that overlap with those disturbed in other developmental disorders, for which treatment options are more obvious. One example of the latter is attention-deficit hyperactivity disorder (ADHD), given the efficacy of especially stimulants in treatment of ADHD. Deficiencies in catecholaminergic systems [dopamine (DA), norepinephrine (NE)] in ADHD are obvious targets for stimulant treatment. Recent findings suggest that dysfunction in catecholaminergic systems may also be a factor in at least a subgroup of ASD. In this review we scrutinize the evidence for catecholaminergic mechanisms underlying ASD symptoms, and also include in this analysis a third classic ascending arousing system, the acetylcholinergic (ACh) network. We complement this with a comprehensive review of DA-, NE-, and ACh-targeted interventions in ASD, and an exploratory search for potential treatment-response predictors (biomarkers) in ASD, genetically or otherwise. Based on this review and analysis we propose that (1) stimulant treatment may be a viable option for an ASD subcategory, possibly defined by genetic subtyping; (2) cerebellar dysfunction is pronounced for a relatively small ADHD subgroup but much more common in ASD and in both cases may point toward NE- or ACh-directed intervention; (3) deficiency of the cortical salience network is sizable in subgroups of both disorders, and biomarkers such as eye blink rate and pupillometric data may predict the efficacy of targeting this underlying deficiency via DA, NE, or ACh in both ASD and ADHD.

Prefrontal modulation of anxiety through a lens of noradrenergic signaling

Anxiety disorders are the most common class of mental illness in the U.S., affecting 40 million individuals annually. Anxiety is an adaptive response to a stressful or unpredictable life event. Though evolutionarily thought to aid in survival, excess intensity or duration of anxiogenic response can lead to a plethora of adverse symptoms and cognitive dysfunction. A wealth of data has implicated the medial prefrontal cortex (mPFC) in the regulation of anxiety. Norepinephrine (NE) is a crucial neuromodulator of arousal and vigilance believed to be responsible for many of the symptoms of anxiety disorders. NE is synthesized in the locus coeruleus (LC), which sends major noradrenergic inputs to the mPFC. Given the unique properties of LC-mPFC connections and the heterogeneous subpopulation of prefrontal neurons known to be involved in regulating anxiety-like behaviors, NE likely modulates PFC function in a cell-type and circuit-specific manner. In working memory and stress response, NE follows an inverted-U model, where an overly high or low release of NE is associated with sub-optimal neural functioning. In contrast, based on current literature review of the individual contributions of NE and the PFC in anxiety disorders, we propose a model of NE level- and adrenergic receptor-dependent, circuit-specific NE-PFC modulation of anxiety disorders. Further, the advent of new techniques to measure NE in the PFC with unprecedented spatial and temporal resolution will significantly help us understand how NE modulates PFC function in anxiety disorders.

Astrocytic MicroRNAs and Transcription Factors in Alzheimer's Disease and Therapeutic Interventions

Astrocytes are important for maintaining cholesterol metabolism, glutamate uptake, and neurotransmission. Indeed, inflammatory processes and neurodegeneration contribute to the altered morphology, gene expression, and function of astrocytes. Astrocytes, in collaboration with numerous microRNAs, regulate brain cholesterol levels as well as glutamatergic and inflammatory signaling, all of which contribute to general brain homeostasis. Neural electrical activity, synaptic plasticity processes, learning, and memory are dependent on the astrocyte-neuron crosstalk. Here, we review the involvement of astrocytic microRNAs that potentially regulate cholesterol metabolism, glutamate uptake, and inflammation in Alzheimer's disease (AD). The interaction between astrocytic microRNAs and long non-coding RNA and transcription factors specific to astrocytes also contributes to the pathogenesis of AD. Thus, astrocytic microRNAs arise as a promising target, as AD conditions are a worldwide public health problem. This review examines novel therapeutic strategies to target astrocyte dysfunction in AD, such as lipid nanodiscs, engineered G protein-coupled receptors, extracellular vesicles, and nanoparticles.

Effects of Atomoxetine on Motor and Cognitive Behaviors and Brain Electrophysiological Activity of Dopamine Transporter Knockout Rats

Changes in dopaminergic and noradrenergic transmission are considered to be the underlying cause of attention deficit and hyperactivity disorder (ADHD). Atomoxetine (ATX) is a selective norepinephrine transporter (NET) inhibitor that is currently used for ADHD treatment. In this study, we aimed to evaluate the effect of atomoxetine on the behavior and brain activity of dopamine transporter knockout (DAT-KO) rats, which are characterized by an ADHD-like behavioral phenotype. Prepulse inhibition (PPI) was assessed in DAT-KO and wild type rats after saline and ATX injections, as well as behavioral parameters in the Hebb-Williams maze and power spectra and coherence of electrophysiological activity. DAT-KO rats demonstrated a pronounced behavioral and electrophysiological phenotype, characterized by hyperactivity, increased number of errors in the maze, repetitive behaviors and disrupted PPI, changes in cortical and striatal power spectra and interareal coherence. Atomoxetine significantly improved PPI and decreased repetitive behaviors in DAT-KO rats and influenced behavior of wild-type rats. ATX also led to significant changes in power spectra and coherence of DAT-KO and wild type rats. Assessment of noradrenergic modulation effects in DAT-KO provides insight into the intricate interplay of monoaminergic systems, although further research is still required to fully understand the complexity of this interaction.

Blunt dopamine transmission due to decreased GDNF in the PFC evokes cognitive impairment in Parkinson's disease

Studies have found that the absence of glial cell line-derived neurotrophic factor may be the primary risk factor for Parkinson's disease. However, there have not been any studies conducted on the potential relationship between glial cell line-derived neurotrophic factor and cognitive performance in Parkinson's disease. We first performed a retrospective case-control study at the Affiliated Hospital of Xuzhou Medical University between September 2018 and January 2020 and found that a decreased serum level of glial cell line-derived neurotrophic factor was a risk factor for cognitive disorders in patients with Parkinson's disease. We then established a mouse model of Parkinson's disease induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and analyzed the potential relationships among glial cell line-derived neurotrophic factor in the prefrontal cortex, dopamine transmission, and cognitive function. Our results showed that decreased glial cell line-derived neurotrophic factor in the prefrontal cortex weakened dopamine release and transmission by upregulating the presynaptic membrane expression of the dopamine transporter, which led to the loss and primitivization of dendritic spines of pyramidal neurons and cognitive impairment. In addition, magnetic resonance imaging data showed that the long-term lack of glial cell line-derived neurotrophic factor reduced the connectivity between the prefrontal cortex and other brain regions, and exogenous glial cell line-derived neurotrophic factor significantly improved this connectivity. These findings suggested that decreased glial cell line-derived neurotrophic factor in the prefrontal cortex leads to neuroplastic degeneration at the level of synaptic connections and circuits, which results in cognitive impairment in patients with Parkinson's disease.

Communicative roots of complex sociality and cognition: neuropsychological mechanisms underpinning the processing of social information

Primate social bonds are described as being especially complex in their nature, and primates have unusually large brains for their body size compared to other mammals. Communication in primates has attracted considerable attention because of the important role it plays in social bonding. It has been proposed that differentiated social relationships are cognitively complex because primates need to continuously update their knowledge about different types of social bonds. Therefore, primates infer whether an opportunity for social interaction is rewarding (valuable to individual goals) based on their knowledge of the social relationships of the interactants. However, exposure to distraction and stress has detrimental effects on the dopaminergic system, suggesting that understanding social relationships as rewarding is affected in these conditions. This paper proposes that complex communication evolved to augment the capacity to form social relationships during stress through flexibly modifying intentionality in communication (audience checking, response waiting and elaboration). Intentional communication may upregulate dopamine dynamics to allow recognition that an interaction is rewarding during stress. By examining these associations between complexity of communication and stress, we provide new insights into the cognitive skills involved in forming social bonds in primates and the evolution of communication systems in both primates and humans. This article is part of the theme issue 'Cognition, communication and social bonds in primates'.

Cognitive science theory-driven pharmacology elucidates the neurobiological basis of perception-motor integration

An efficient integration of sensory and motor processes is crucial to goal-directed behavior. Despite this high relevance, and although cognitive theories provide clear conceptual frameworks, the neurobiological basis of these processes remains insufficiently understood. In a double-blind, randomized placebo-controlled pharmacological study, we examine the relevance of catecholamines for perception-motor integration processes. Using EEG data, we perform an in-depth analysis of the underlying neurophysiological mechanisms, focusing on sensorimotor integration processes during response inhibition. We show that the catecholaminergic system affects sensorimotor integration during response inhibition by modulating the stability of the representational content. Importantly, catecholamine levels do not affect the stability of all aspects of information processing during sensorimotor integration, but rather-as suggested by cognitive theory-of specific codes in the neurophysiological signal. Particularly fronto-parietal cortical regions are associated with the identified mechanisms. The study shows how cognitive science theory-driven pharmacology can shed light on the neurobiological basis of perception-motor integration and how catecholamines affect specific information codes relevant to cognitive control.

The Neurobiological Links between Stress and Traumatic Brain Injury: A Review of Research to Date

Neurological dysfunctions commonly occur after mild or moderate traumatic brain injury (TBI). Although most TBI patients recover from such a dysfunction in a short period of time, some present with persistent neurological deficits. Stress is a potential factor that is involved in recovery from neurological dysfunction after TBI. However, there has been limited research on the effects and mechanisms of stress on neurological dysfunctions due to TBI. In this review, we first investigate the effects of TBI and stress on neurological dysfunctions and different brain regions, such as the prefrontal cortex, hippocampus, amygdala, and hypothalamus. We then explore the neurobiological links and mechanisms between stress and TBI. Finally, we summarize the findings related to stress biomarkers and probe the possible diagnostic and therapeutic significance of stress combined with mild or moderate TBI.

Regulation of cocaine seeking behavior by locus coeruleus noradrenergic activity in the ventral tegmental area is time- and contingency-dependent

Substance use disorder is linked to impairments in the ventral tegmental area (VTA) dopamine (DA) reward system. Noradrenergic (NA) inputs from locus coeruleus (LC) into VTA have been shown to modulate VTA neuronal activity, and are implicated in psychostimulant effects. Phasic LC activity controls time- and context-sensitive processes: decision making, cognitive flexibility, motivation and attention. However, it is not yet known how such temporally-distinct LC activity contributes to cocaine seeking. In a previous study we demonstrated that pharmacological inhibition of NA signaling in VTA specifically attenuates cocaine-seeking. Here, we used virally-delivered opsins to target LC neurons for inhibition or excitation, delivered onto afferents in VTA of male rats seeking cocaine under extinction conditions. Optogenetic stimulation or inhibition was delivered in distinct conditions: upon active lever press, contingently with discreet cues; or non-contingently, i.e., throughout the cocaine seeking session. Non-contingent inhibition of LC noradrenergic terminals in VTA attenuated cocaine seeking under extinction conditions. In contrast, contingent inhibition increased, while contingent stimulation reduced cocaine seeking. These findings were specific for cocaine, but not natural reward (food) seeking. Our results show that NA release in VTA drives behavior depending on timing and contingency between stimuli – context, discreet conditioned cues and reinforcer availability. We show that, depending on those factors, noradrenergic signaling in VTA has opposing roles, either driving CS-induced drug seeking, or contributing to behavioral flexibility and thus extinction.

Excessive folic acid intake combined with undernutrition during gestation alters offspring behavior and brain monoamine profiles

Dietary folic acid augmentation during gestation reduces neurodevelopmental disorder risk in offspring; however, it is still unclear if excessive maternal folic acid intake can impair brain function in offspring. We examined if excessive folic acid intake throughout gestation altered the behavior of male offspring under poor nutrition during early gestation (E5.5-E11.5). Dams were divided into four groups: control (CON, 2 mg folic acid/kg of food), excessive folic acid fortification (FF, 10 mg folic acid/kg of food), undernutrition (UN, 40% food reduction from E5.5-E11.5), and excessive folic acid fortification plus undernutrition (UN-FF). Excess maternal folic acid fortification induced hyperactivity in the open-field and lower anxiety-like behavior in the elevated plus maze at 9 weeks of age. These behavioral changes were accompanied by reduced dopamine in the prefrontal cortex (PFC), norepinephrine in the amygdala, and 5-hydroxytryptamine (5-HT) in the dorsal midbrain (DM), PFC, and amygdala where 5-HT neurons project from the DM. Furthermore, canonical discriminant analysis, including dopamine and DOPAC concentrations in the PFC, norepinephrine concentrations in the PFC, amygdala, and pons, and 5-HT and 5-HIAA concentrations in the amygdala and DM, correctly classified 73.5% of the offspring in CON, FF, UN, and UN-FF groups. The first discriminant function mainly classified groups based on nutritional status, whereas the second function mainly classified groups based on folic acid intake. Our study suggests that combined transformations of brain monoamine profiles by maternal undernutrition and excess folic acid intake is involved in the behavioral alteration of offsprings.

“The Wandering Nerve Linking Heart and Mind” – The Complementary Role of Transcutaneous Vagus Nerve Stimulation in Modulating Neuro-Cardiovascular and Cognitive Performance

The vagus nerve is the longest nerve in the human body, providing afferent information about visceral sensation, integrity and somatic sensations to the CNS via brainstem nuclei to subcortical and cortical structures. Its efferent arm influences GI motility and secretion, cardiac ionotropy, chonotropy and heart rate variability, blood pressure responses, bronchoconstriction and modulates gag and cough responses via palatine and pharyngeal innervation. Vagus nerve stimulation has been utilized as a successful treatment for intractable epilepsy and treatment-resistant depression, and new non-invasive transcutaneous (t-VNS) devices offer equivalent therapeutic potential as invasive devices without the surgical risks. t-VNS offers exciting potential as a therapeutic intervention in cognitive decline and aging populations, classically affected by reduced cerebral perfusion by modulating both limbic and frontal cortical structures, regulating cerebral perfusion and improving parasympathetic modulation of the cardiovascular system. In this narrative review we summarize the research to date investigating the cognitive effects of VNS therapy, and its effects on neurocardiovascular stability.

Altered Arginine/Nitric Oxide Pathway in Children Diagnosed Attention Deficit Hyperactivity Disorder, and the Effect of 10 Weeks Methylphenidate Treatment

Objective

In this study, we investigated the levels of arginine, nitric oxide (NO), asymmetric dimethylarginine (ADMA), and adrenomedullin that are presumed to play a role in attention deficit hyperactivity disorder (ADHD) etiology, and to compare the findings with healthy controls.

Methods

Thirty ADHD patients and thirty healthy control subjects aged 6−12 years were included in the study. Sociodemographic data form, Schedule for Affective Disorders and Schizophrenia for School Age Children-Present and Lifetime Version; Conners’ Parent/Teacher Rating Scale-Revised Long Form; Children’s Depression Inventory; and The State-Trait Anxiety Inventory for Children were applied to all cases. All participants included in the study were evaluated in terms of their serum arginine, NO, ADMA, and adrenomedullin levels. Subsequently, methylphenidate treatment was started in ADHD patients and blood parameters were tested again in the tenth week of treatment.

Results

At the start of the study, arginine and ADMA levels were significantly higher and NO and adrenomedullin levels were significantly lower in the ADHD group compared to the control group. Post-treatment arginine and ADMA levels were found to be significantly lower than in the pre-treatment period. There were no significant differences in NO and adrenomedullin levels before and after treatment. There was no correlation between scale scores and blood parameters.

Conclusion

These variations in the blood parameters of the ADHD group seem to be worth further investigation. Studies to be conducted with larger sample groups after longer-term treatment may provide new information about the alterations in neurobiological processes related to ADHD etiology and treatment.

Neural Control of Action Selection Among Innate Behaviors

Nervous systems must not only generate specific adaptive behaviors, such as reproduction, aggression, feeding, and sleep, but also select a single behavior for execution at any given time, depending on both internal states and external environmental conditions. Despite their tremendous biological importance, the neural mechanisms of action selection remain poorly understood. In the past decade, studies in the model animal Drosophila melanogaster have demonstrated valuable neural mechanisms underlying action selection of innate behaviors. In this review, we summarize circuit mechanisms with a particular focus on a small number of sexually dimorphic neurons in controlling action selection among sex, fight, feeding, and sleep behaviors in both sexes of flies. We also discuss potentially conserved circuit configurations and neuromodulation of action selection in both the fly and mouse models, aiming to provide insights into action selection and the sexually dimorphic prioritization of innate behaviors.

Psychostimulant use and clinical outcome of repetitive transcranial magnetic stimulation treatment of major depressive disorder

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) is an effective treatment for major depressive disorder (MDD). Psychostimulant medication use may be associated with improved rTMS outcomes, but a detailed understanding of these relationships is lacking.

METHODS

We compared MDD subjects taking psychostimulants (n = 37) with those not taking one of these medications (n = 53) during a course of 30 rTMS treatments. Changes in the 30-item Inventory of Depressive Symptomatology Self Report (IDS-SR30) subscale scores were examined at treatment 30. We also subdivided subjects into three categories based on drug mechanism and looked at IDS-SR30 total score after treatments 10, 20, and 30.

RESULTS

Subjects taking psychostimulants had a significantly greater overall clinical improvement than those not taking these medications at treatment 30. The psychostimulant group also improved significantly more than the control group in "sleep" and "mood/cognition," but not "anxiety/arousal" IDS-SR30 subscales. No differences were detected among individual drug categories, which may reflect the limited sample size for individual medications. There was a negative dose-response relationship for the lisdexamfetamine/dextroamphetamine group, in which lower doses were associated with better clinical outcome.

CONCLUSIONS

Psychostimulant medications may enhance clinical efficacy of rTMS for MDD by preferentially impacting specific symptom domains. For some psychostimulants, these effects may be dose-dependent. Prospective clinical trials are needed to guide psychostimulant augmentation of brain stimulation therapies.

Signaler's Vasotocin Alters the Relationship between the Responder's Forebrain Catecholamines and Communication Behavior in Lizards (Anolis carolinensis)

Dynamic fluctuations in the distribution of catecholamines across the brain modulate the responsiveness of vertebrates to social stimuli. Previous work demonstrates that green anoles (Anolis carolinensis) increase chemosensory behavior in response to males treated with exogenous arginine vasotocin (AVT), but the neurochemical mechanisms underlying this behavioral shift remains unclear. Since central catecholamine systems, including dopamine, rapidly activate in response to social stimuli, we tested whether exogenous AVT in signalers (stimulus animals) impacts catecholamine concentrations in the forebrain (where olfactory and visual information are integrated and processed) of untreated lizard responders. We also tested whether AVT influences the relationship between forebrain catecholamine concentrations and communication behavior in untreated receivers. We measured global catecholamine (dopamine = DA, epinephrine = Epi, and norepinephrine = NE) concentrations in the forebrain of untreated responders using high-performance liquid chromatography-mass spectrometry following either a 30-min social interaction with a stimulus male or a period of social isolation. Stimulus males were injected with exogenous AVT or vehicle saline (SAL). We found that global DA, but not Epi or NE, concentrations were elevated in lizards responding to SAL-males relative to isolated lizards. Lizards interacting with AVT-males had DA, Epi and NE concentrations that were not significantly different from SAL or isolated groups. For behavior, we found a significant effect of social treatment (AVT vs. SAL) on the relationships between (1) DA concentrations and the motivation to perform a chemical display (latency to tongue flick) and (2) Epi concentrations and time spent displaying mostly green body coloration. We also found a significant negative correlation between DA concentrations and the latency to perform a visual display but found no effect of social treatment on this relationship. These data suggest that catecholamine concentrations in the forebrain of untreated responders are associated with chemical and visual communication in lizards and that signaler AVT alters this relationship for some, but not all, aspects of social communication.

Two meta-analyses of the association between atopic diseases and core symptoms of attention deficit hyperactivity disorder

Studies in the field of neuroscience and psychology have hypothesized that a causal association exists between atopic diseases and attention-deficit/hyperactivity disorder (ADHD). Previous systematic reviews and meta-analyses have reported a higher risk of ADHD in children with atopic diseases; however, the relationship between ADHD symptoms and atopic diseases remains unclear. We systematically reviewed observational cross-sectional and longitudinal studies to investigate the relationship between atopic diseases and ADHD symptom severity (hyperactivity/impulsivity and inattention). The majority of studies showed a statistically significant association between atopic diseases and both ADHD symptoms, with substantial heterogeneity in the outcome of hyperactivity/impulsivity. Remarkably decreased heterogeneity and statistical significance were observed in the second meta-analysis of ADHD-related behavior symptoms in atopic patients without ADHD. Our study indicated that atopic diseases not only associated with ADHD but also ADHD symptoms severity. This association was even observed in children with subthreshold ADHD, indicating that atopic diseases may play a role in the spectrum of ADHD symptom severity. Trial registration: This study was registered on PROSPERO (registration ID: CRD42020213219).

Cell-Based Ambient Venturi Autosampling and Matrix-Assisted Laser Desorption Ionization Mass Spectrometric Imaging of Secretory Products

A cell-based ambient Venturi autosampling device was established for the monitoring of dynamic cell secretions in response to chemical stimulations in real time with temporal resolution on the order of a second. Detection of secretory products of cells and screening of bioactive compounds are primarily performed on an ambient autosampling probe and matrix-assisted laser desorption ionization (MALDI) mass spectrometry. It takes advantage of the Venturi effect in which the fluid flowing through an inlet capillary tube is automatically fed into a parallel array of multiple outlet capillaries. Cells are incubated inside the inlet capillary tube that is connected with either a syringe pump or liquid chromatography (LC) for the transfer of single compounds or mixtures, respectively. Secretory products were continuously pushed into the outlet capillaries and then spotted into a compressed thin film of the matrix material 9-aminoacridine for MALDI mass spectrometric imaging. In physiological pH, without the use of high voltages and without the use of chemical derivatizations, this platform can be applied to the direct assay of neurotransmitters or other secretory products released from cells in response to the stimulation of individual compounds or LC-separated eluates of natural mixtures. It provides a new way to identify bioactive compounds with a detection limit down to 0.04 fmol/pixel.

Neuronal Circuits Associated with Fear Memory: Potential Therapeutic Targets for Posttraumatic Stress Disorder

Posttraumatic stress disorder (PTSD) is a psychiatric disorder that is associated with long-lasting memories of traumatic experiences. Extinction and discrimination of fear memory have become therapeutic targets for PTSD. Newly developed optogenetics and advanced in vivo imaging techniques have provided unprecedented spatiotemporal tools to characterize the activity, connectivity, and functionality of specific cell types in complicated neuronal circuits. The use of such tools has offered mechanistic insights into the exquisite organization of the circuitry underlying the extinction and discrimination of fear memory. This review focuses on the acquisition of more detailed, comprehensive, and integrated neural circuits to understand how the brain regulates the extinction and discrimination of fear memory. A future challenge is to translate these researches into effective therapeutic treatment for PTSD from the perspective of precise regulation of the neural circuits associated with the extinction and discrimination of fear memories.

Distinct Roles for Prefrontal Dopamine D1 and D2 Neurons in Social Hierarchy

Neuronal activity in the prefrontal cortex (PFC) controls dominance hierarchies in groups of animals. Dopamine (DA) strongly modulates PFC activity mainly through D1 receptors (D1Rs) and D2 receptors (D2Rs). Still, it is unclear how these two subpopulations of DA receptor-expressing neurons in the PFC regulate social dominance hierarchy. Here, we demonstrate distinct roles for prefrontal D1R- and D2R-expressing neurons in establishing social hierarchy, with D1R⁺ neurons determining dominance and D2R⁺ neurons for subordinate. Ex vivo whole-cell recordings revealed that the dominant status of male mice correlates with rectifying AMPAR transmission and stronger excitatory synaptic strength onto D1R⁺ neurons in PFC pyramidal neurons. In contrast, the submissive status is associated with higher neuronal excitability in D2R⁺ neurons. Moreover, simultaneous manipulations of synaptic efficacy of D1R⁺ neurons in dominant male mice and neuronal excitability of D2R⁺ neurons of their male subordinates switch their dominant-subordinate relationship. These results reveal that prefrontal D1R⁺ and D2R⁺ neurons have distinct but synergistic functions in the dominance hierarchy, and DA-mediated regulation of synaptic strengths acts as a powerful behavioral determinant of intermale social rank.SIGNIFICANCE STATEMENT Dominance hierarchy exists widely among animals who confront social conflict. Studies have indicated that social status largely relies on the neuronal activity in the PFC, but how dopamine influences social hierarchy via subpopulation of prefrontal neurons is still elusive. Here, we explore the cell type-specific role of dopamine receptor-expressing prefrontal neurons in the dominance-subordinate relationship. We found that the synaptic strength of D1 receptor-expressing neurons determines the dominant status, whereas hyperactive D2-expressing neurons are associated with the subordinate status. These findings highlight how social conflicts recruit distinct cortical microcircuits to drive different behaviors and reveal how D1- and D2-receptor enriched neurocircuits in the PFC establish a social hierarchy.

Reduced prefrontal cortex and sympathetic nervous system activity correlate with fatigue after aHSCT

Long-term fatigue and cognitive dysfunction affects 35% of allogeneic haematopoietic stem cell transplantation (aHSCT) survivors, suggesting a dysfunctional prefrontal cortex. In this study, we assessed prefrontal cortex and sympathetic nervous system activity in aHSCT patients with fatigue (n = 12), non-fatigued patients (n = 12) and healthy controls (n = 27). Measurement of near-infrared spectroscopy and electrodermal activity was carried out at rest and during cognitive performance (Stroop, verbal fluency and emotion regulation tasks). Prefrontal cortex and sympathetic nervous system activity were also analyzed in response to dopamine and noradrenaline increase after a single dose of methylphenidate. Baseline cognitive performance was similar in the two patient groups. However, after methylphenidate, only non-fatigued patients improved in Stroop accuracy and had better verbal fluency task performance compared to the fatigued group. Task-related activation of prefrontal cortex in fatigued patients was lower compared to non-fatigued patients during all cognitive tests, both before and after methylphenidate administration. During the Stroop task, reaction time, prefrontal cortex activation, and sympathetic nervous system activity were all lower in fatigued patients compared to healthy controls, but similar in non-fatigued patients and healthy controls.Reduced prefrontal cortex activity and sympathetic arousal suggests novel treatment targets to improve fatigue after aHSCT.

Effects of Lisdexamfetamine, a Prodrug of D-Amphetamine, on Locomotion, Spatial Cognitive Processing and Neurochemical Profiles in Rats: A Comparison With Immediate-Release Amphetamine

D-amphetamine has been used to enhance cognitive performance over the last few decades. Due to the rapid absorption after administration, d-amphetamine shows narrow effective window and severe abuse potential. Lisdexamfetamine, a prodrug of d-amphetamine, reduces the magnitude of plasma d-amphetamine concentration and prolongs the action duration when compared with immediate-release d-amphetamine at equimolar doses. However, the differences of these two drugs, which produce distinct pharmacokinetic characteristics, in cognition improvement still unclear. In present study, we compared the effects of d-amphetamine (i.p) and lisdexamfetamine (p.o) at equimolar doses (0.2, 0.5, 1.5, 4.5, and 13.5 mg/kg of d-amphetamine base) on locomotion, spatial working memory and recognition memory in rats. Given the crucial involvement of dopamine neurotransmitter system within the medial prefrontal cortex (mPFC) in cognitive processing, microdialysis was conducted to profile the difference in neurochemical characteristics between the two drugs. In our results, d-amphetamine ranges from 0.5 to 1.5 mg/kg significantly increased locomotor activity. However, d-amphetamine ranges from 0.2 to 13.5 mg/kg failed to improve spatial working memory and recognition memory in Y-maze-based spontaneous alternation and two-trial delayed alternation tasks of rats, respectively. In contrast, lisdexamfetamine with 4.5 mg/kg significantly increased the locomotion and improved both spatial working and recognition memory. Further, microdialysis showed that lisdexamfetamine induced lower magnitude and longer duration of extracellular dopamine increase than that of d-amphetamine. These results suggest that lisdexamfetamine was more effective than d-amphetamine in improving spatial cognitive performance, which was attributed to the steady and lasting dopamine release pattern within the mPFC.

Modulation of Spatial Memory Deficit and Hyperactivity in Dopamine Transporter Knockout Rats via α2A-Adrenoceptors

Attention deficit hyperactivity disorder (ADHD) is manifested by a specific set of behavioral deficits such as hyperactivity, impulsivity, and inattention. The dopamine neurotransmitter system is postulated to be involved in the pathogenesis of ADHD. Guanfacine, a selective α2A-adrenoceptor agonist, is prescribed for ADHD treatment. ADHD also is known to be associated with impairment of multiple aspects of cognition, including spatial memory, however, it remains unclear how modulation of the norepinephrine system can affect these deficits. Hyperdopaminergic dopamine transporter knockout (DAT-KO) rats are a valuable model for investigating ADHD. The DAT-KO rats are hyperactive and deficient in spatial working memory. This work aimed to evaluate the effects of noradrenergic drugs on the fulfillment of spatial cognitive tasks by DAT-KO rats. The rats were tested in the Hebb - Williams maze during training and following noradrenergic drugs administration. The efficiency of spatial orientation was assessed as to how fast the animal finds an optimal way to the goal box. Testing in a new maze configuration allowed us to evaluate the effects of drug administration after the acquisition of the task rules. The behavioral variables such as the distance traveled, the time to reach the goal box, and the time spent in the error zones were analyzed. It has been observed that α2A-adrenoceptor agonist Guanfacine (0.25 mg/kg) had only a minimal inhibitory effect on hyperactivity of DAT-KO rats in the maze but significantly ameliorated their perseverative pattern of activity and reduced the time spent in the error zones. In contrast, α2A-adrenoceptor antagonist Yohimbine, at the dose of 1 mg/kg, increased the distance traveled by DAT-KO rats and elevated the number of perseverative reactions and the time spent in the error zones. Guanfacine caused minimal effects in wild-type rats, while Yohimbine altered several parameters reflecting a detrimental effect on the performance in the maze. These data indicate that modulation of α2A-adrenoceptor activity potently affects both dopamine-dependent hyperactivity and cognitive dysfunctions. Similar mechanisms may be involved in the beneficial effects of Guanfacine on cognitive deficits in ADHD patients. This study further supports the translational potential of DAT-KO rats for testing new pharmacological drugs.

Deficient neurotransmitter systems and synaptic function in frontotemporal lobar degeneration-Insights into disease mechanisms and current therapeutic approaches

Frontotemporal lobar degeneration (FTLD) comprises a heterogenous group of fatal neurodegenerative diseases and, to date, no validated diagnostic or prognostic biomarkers or effective disease-modifying therapies exist for the different clinical or genetic subtypes of FTLD. Current treatment strategies rely on the off-label use of medications for symptomatic treatment. Changes in several neurotransmitter systems including the glutamatergic, GABAergic, dopaminergic, and serotonergic systems have been reported in FTLD spectrum disease patients. Many FTLD-related clinical and neuropsychiatric symptoms such as aggressive and compulsive behaviour, agitation, as well as altered eating habits and hyperorality can be explained by disturbances in these neurotransmitter systems, suggesting that their targeting might possibly offer new therapeutic options for treating patients with FTLD. This review summarizes the present knowledge on neurotransmitter system deficits and synaptic dysfunction in model systems and patients harbouring the most common genetic causes of FTLD, the hexanucleotide repeat expansion in C9orf72 and mutations in the granulin (GRN) and microtubule-associated protein tau (MAPT) genes. We also describe the current pharmacological treatment options for FLTD that target different neurotransmitter systems.

Behavioral and neurochemical interactions of the tricyclic antidepressant drug desipramine with L-DOPA in 6-OHDA-lesioned rats. Implications for motor and psychiatric functions in Parkinson's disease

RATIONALE

The pharmacological effects of antidepressants in modulating noradrenergic transmission as compared to serotonergic transmission in a rat model of Parkinson's disease under chronic L-DOPA therapy are insufficiently explored.

OBJECTIVES

The aim of the present study was to investigate the effect of the tricyclic antidepressant desipramine administered chronically alone or jointly with L-DOPA, on motor behavior and monoamine metabolism in selected brain structures of rats with the unilateral 6-OHDA lesion.

METHODS

The antiparkinsonian activities of L-DOPA and desipramine were assessed behaviorally using a rotation test and biochemically based on changes in the tissue concentrations of noradrenaline, dopamine and serotonin and their metabolites, evaluated separately for the ipsi- and contralateral motor (striatum, substantia nigra) and limbic (prefrontal cortex, hippocampus) structures of rat brain by HPLC method.

RESULTS

Desipramine administered alone did not induce rotational behavior, but in combination with L-DOPA, it increased the number of contralateral rotations more strongly than L-DOPA alone. Both L-DOPA and desipramine + L-DOPA significantly increased DA levels in the ipsilateral striatum, substantia nigra, prefrontal cortex and the ipsi- and contralateral hippocampus. The combined treatment also significantly increased noradrenaline content in the ipsi- and contralateral striatum, while L-DOPA alone decreased serotonin level on both sides of the hippocampus.

CONCLUSIONS

The performed analysis of the level of monoamines and their metabolites in the selected brain structures suggests that co-modulation of noradrenergic and dopaminergic transmission in Parkinson's disease by the combined therapy with desipramine + L-DOPA may have some positive implications for motor and psychiatric functions but further research is needed to exclude potential negative effects.

GSK3β Activity in Reward Circuit Functioning and Addiction

Glycogen synthase kinase-3β (GSK3β), primarily described as a regulator of glycogen metabolism, is a molecular hub linking numerous signaling pathways and regulates many cellular processes like cytoskeletal rearrangement, cell migration, apoptosis, and proliferation. In neurons, the kinase is engaged in molecular events related to the strengthening and weakening of synapses, which is a subcellular manifestation of neuroplasticity. Dysregulation of GSK3β activity has been reported in many neuropsychiatric conditions, like schizophrenia, major depressive disorder, bipolar disorder, and Alzheimer’s disease. In this review, we describe the kinase action in reward circuit-related structures in health and disease. The effect of pharmaceuticals used in the treatment of addiction in the context of GSK3β activity is also discussed.

A novel red fluorescence dopamine biosensor selectively detects dopamine in the presence of norepinephrine in vitro

Dopamine (DA) and norepinephrine (NE) are pivotal neuromodulators that regulate a broad range of brain functions, often in concert. Despite their physiological importance, untangling the relationship between DA and NE in the fine control of output function is currently challenging, primarily due to a lack of techniques to allow the observation of spatiotemporal dynamics with sufficiently high selectivity. Although genetically encoded fluorescent biosensors have been developed to detect DA, their poor selectivity prevents distinguishing DA from NE. Here, we report the development of a red fluorescent genetically encoded GPCR (G protein-coupled receptor)-activation reporter for DA termed 'R-GenGAR-DA'. More specifically, a circular permutated red fluorescent protein (cpmApple) was replaced by the third intracellular loop of human DA receptor D1 (DRD1) followed by the screening of mutants within the linkers between DRD1 and cpmApple. We developed two variants: R-GenGAR-DA1.1, which brightened following DA stimulation, and R-GenGAR-DA1.2, which dimmed. R-GenGAR-DA1.2 demonstrated a reasonable dynamic range (ΔF/F0 = - 43%), DA affinity (EC50 = 0.92 µM) and high selectivity for DA over NE (66-fold) in HeLa cells. Taking advantage of the high selectivity of R-GenGAR-DA1.2, we monitored DA in presence of NE using dual-color fluorescence live imaging, combined with the green-NE biosensor GRABNE1m, which has high selectivity for NE over DA (> 350-fold) in HeLa cells and hippocampal neurons grown from primary culture. Thus, this is a first step toward the multiplex imaging of these neurotransmitters in, for example, freely moving animals, which will provide new opportunities to advance our understanding of the high spatiotemporal dynamics of DA and NE in normal and abnormal brain function.

Fluid intelligence and the locus coeruleus-norepinephrine system

The last decade has seen significant progress identifying genetic and brain differences related to intelligence. However, there remain considerable gaps in our understanding of how cognitive mechanisms that underpin intelligence map onto various brain functions. In this article, we argue that the locus coeruleus-norepinephrine system is essential for understanding the biological basis of intelligence. We review evidence suggesting that the locus coeruleus-norepinephrine system plays a central role at all levels of brain function, from metabolic processes to the organization of large-scale brain networks. We connect this evidence with our executive attention view of working-memory capacity and fluid intelligence and present analyses on baseline pupil size, an indicator of locus coeruleus activity. Using a latent variable approach, our analyses showed that a common executive attention factor predicted baseline pupil size. Additionally, the executive attention function of disengagement--not maintenance--uniquely predicted baseline pupil size. These findings suggest that the ability to control attention may be important for understanding how cognitive mechanisms of fluid intelligence map onto the locus coeruleus-norepinephrine system. We discuss how further research is needed to better understand the relationships between fluid intelligence, the locus coeruleus-norepinephrine system, and functionally organized brain networks.

An Oppositional Tolerance Account for Potential Cognitive Deficits Caused by the Discontinuation of Antidepressant Drugs

Depression is the leading cause of disability worldwide, making antidepressant drugs the most used psychiatric drugs in the USA. Withdrawal effects and rebound symptoms frequently occur after the reduction and/or discontinuation of these drugs. Although these phenomena have been investigated with respect to the clinical symptomatology, no studies have systematically investigated the effects of withdrawal/rebound on general cognition. We present a novel framework based on the idea of allostatic adaptation, which allows to predict how different antidepressants likely impair different cognitive processes as a result of withdrawal and rebound effects. This framework relies on the assumptions that the type of cognitive impairments evoked by an antidepressant is determined by the targeted neurotransmitter systems, while the severity of deficits depends on its half-life. Our model predicts that the severity of detrimental cognitive withdrawal and rebound effects increases with a shorter half-life of the discontinued antidepressant drug. It further proposes drug-specific effects: antidepressants mainly targeting serotonin should primarily impair aversive and emotional processing, those targeting norepinephrine should impair the processing of alerting signals, those targeting dopamine should impair motivational processes and reward processing, and those targeting acetylcholine should impair spatial learning and memory. We hope that this framework will motivate further research to better understand and explain cognitive changes as a consequence of antidepressant discontinuation.

Neuromodulation of Hippocampal-Prefrontal Cortical Synaptic Plasticity and Functional Connectivity: Implications for Neuropsychiatric Disorders

The hippocampus-prefrontal cortex (HPC-PFC) pathway plays a fundamental role in executive and emotional functions. Neurophysiological studies have begun to unveil the dynamics of HPC-PFC interaction in both immediate demands and long-term adaptations. Disruptions in HPC-PFC functional connectivity can contribute to neuropsychiatric symptoms observed in mental illnesses and neurological conditions, such as schizophrenia, depression, anxiety disorders, and Alzheimer's disease. Given the role in functional and dysfunctional physiology, it is crucial to understand the mechanisms that modulate the dynamics of HPC-PFC communication. Two of the main mechanisms that regulate HPC-PFC interactions are synaptic plasticity and modulatory neurotransmission. Synaptic plasticity can be investigated inducing long-term potentiation or long-term depression, while spontaneous functional connectivity can be inferred by statistical dependencies between the local field potentials of both regions. In turn, several neurotransmitters, such as acetylcholine, dopamine, serotonin, noradrenaline, and endocannabinoids, can regulate the fine-tuning of HPC-PFC connectivity. Despite experimental evidence, the effects of neuromodulation on HPC-PFC neuronal dynamics from cellular to behavioral levels are not fully understood. The current literature lacks a review that focuses on the main neurotransmitter interactions with HPC-PFC activity. Here we reviewed studies showing the effects of the main neurotransmitter systems in long- and short-term HPC-PFC synaptic plasticity. We also looked for the neuromodulatory effects on HPC-PFC oscillatory coordination. Finally, we review the implications of HPC-PFC disruption in synaptic plasticity and functional connectivity on cognition and neuropsychiatric disorders. The comprehensive overview of these impairments could help better understand the role of neuromodulation in HPC-PFC communication and generate insights into the etiology and physiopathology of clinical conditions.

Microglia regulation of synaptic plasticity and learning and memory

Microglia are the resident macrophages of the central nervous system. Microglia possess varied morphologies and functions. Under normal physiological conditions, microglia mainly exist in a resting state and constantly monitor their microenvironment and survey neuronal and synaptic activity. Through the C1q, C3 and CR3 “Eat Me” and CD47 and SIRPα “Don’t Eat Me” complement pathways, as well as other pathways such as CX3CR1 signaling, resting microglia regulate synaptic pruning, a process crucial for the promotion of synapse formation and the regulation of neuronal activity and synaptic plasticity. By mediating synaptic pruning, resting microglia play an important role in the regulation of experience-dependent plasticity in the barrel cortex and visual cortex after whisker removal or monocular deprivation, and also in the regulation of learning and memory, including the modulation of memory strength, forgetfulness, and memory quality. As a response to brain injury, infection or neuroinflammation, microglia become activated and increase in number. Activated microglia change to an amoeboid shape, migrate to sites of inflammation and secrete proteins such as cytokines, chemokines and reactive oxygen species. These molecules released by microglia can lead to synaptic plasticity and learning and memory deficits associated with aging, Alzheimer’s disease, traumatic brain injury, HIV-associated neurocognitive disorder, and other neurological or mental disorders such as autism, depression and post-traumatic stress disorder. With a focus mainly on recently published literature, here we reviewed the studies investigating the role of resting microglia in synaptic plasticity and learning and memory, as well as how activated microglia modulate disease-related plasticity and learning and memory deficits. By summarizing the function of microglia in these processes, we aim to provide an overview of microglia regulation of synaptic plasticity and learning and memory, and to discuss the possibility of microglia manipulation as a therapeutic to ameliorate cognitive deficits associated with aging, Alzheimer’s disease, traumatic brain injury, HIV-associated neurocognitive disorder, and mental disorders.

Oleanolic Acid Attenuates Morphine Withdrawal Symptoms in Rodents: Association with Regulation of Dopamine Function

Introduction

Oleanolic acid (OA) has been shown to be useful for the treatment of mental disorders.

Methods

In this study, we investigated the effects of OA in animal models of spontaneous withdrawal and naloxone-precipitated withdrawal and evaluated the effects of OA on the acquisition, extinction, and reinstatement of morphine-induced conditioned place preference (CPP).

Results

OA significantly improved symptoms of withdrawal, and significantly reduced the acquisition and reinstatement of morphine-induced conditioned place preference. Moreover, OA significantly reduced the serum content of 5-hydroxy tryptamine (5-HT) and dopamine (DA) in a dose-dependent manner, and reduced norepinephrine (NE) and 5-HT content in the frontal cortex (PFC), while significantly increasing endorphin content in rats. OA also significantly reduced serum DA content in mice.

Conclusion

These results indicate that OA can improve the withdrawal symptoms of rats and mice by regulating the DA system and suggest that OA may be useful in treatment of morphine addiction.

Visual Hallucinations and the Role of Medications in Parkinson's Disease: Triggers, Pathophysiology, and Management

Visual hallucinations, which are part of the syndrome of Parkinson's disease (PD) psychosis, affect patients' quality of life and increase the likelihood of residential aged-care placement. The association between visual hallucinations and dopaminergic and other medications that are necessary for the symptomatic management of motor and other symptoms of PD is a common clinical dilemma. While dopaminergic medications have long been associated with PD psychosis, a clear causal link has not been established, and other neurotransmitter systems, particularly noradrenaline, serotonin, and acetylcholine, are implicated and important. A diverse range of demographic and disease-related risk factors, some being modifiable, highlight the complexity of potential underlying pathophysiological processes but also broaden practical options for prevention and treatment that can be multifaceted and individualized. The investigators reviewed the clinical features and epidemiology of visual hallucinations and PD, explored the pathological evidence for dysfunction of multiple neurotransmitter systems that may be relevant to these phenomena, and addressed the potential of medications commonly used in PD to either trigger or treat these symptoms.

Sex differences in noradrenergic modulation of attention and impulsivity in rats

RATIONALE

Noradrenaline (NE) is closely related to attentive performance and impulsive control. However, the potential sex differences regarding attention and impulsivity under the noradrenergic modulation have been largely neglected. Therefore, our study aimed to investigate whether male and female rats exhibit differential responses to NE-related drugs during the five-choice serial reaction time task (5CSRT).

METHODS

Male and female rats were trained in 5CSRT and administered with different NE drugs after obtaining stable baseline performance: atipamezole, a highly selective α2 receptor antagonist; prazosin, an α1 receptor antagonist; and atomoxetine, a selective NE reuptake inhibitor. Later, prazosin was selected to co-administration with atomoxetine.

RESULTS

Male and female rats exhibited equal learning speed, and no significant baseline differences were found as measured by the 5CSRT. Atomoxetine decreased premature responses in both sexes, but the extent of this reduction was different, with the reduction greater in males. Besides, atomoxetine (1.8 mg/kg) increased the error of omissions in females. The high dose of prazosin (0.5 mg/kg) decreased the accuracy only in male rats, but this was ameliorated by the co-administration with atomoxetine.

CONCLUSIONS

Atomoxetine showed significant improvement in impulsivity, but atomoxetine had less beneficial effects on impulsive control in females than in males, and it even impaired attentional performance in female rats. The α1 receptors were mainly responsible for NE drug-related sex differences in attention rather than impulsivity. The results obtained in this study indicate that the sex differences exist in both attention and impulsivity by the modulation of noradrenaline and raise the concern to improve sex-specific treatments.