The only-child effect in the neural and behavioral signatures of trust revealed by fNIRS hyperscanning

In daily life, trust is important in interpersonal interactions. However, little is known about interpersonal brain synchronization with respect to trust; in particular, the differences between individuals with and without siblings are not clear. Therefore, this study applied functional near-infrared spectroscopy hyperscanning in a sequential reciprocal-trust task. We divided pairs of participants (strangers) into two groups according to their only-child status. The two strangers interacted with one another in an online trust game while their brain activities in the medial prefrontal cortex (mPFC) and the right temporoparietal junction (rTPJ) were measured. The behavioral results revealed that compared with the non-only-child group, the only-child group exhibited lower repayment, less reciprocation, and less cooperative decisions during the process. In addition, the brain imaging results showed that the interpersonal synchronization of the mPFC in the only-child group was significantly weaker than that in the non-only-child group. Our findings demonstrate neurobehavioral support for the only-child effect in terms of the trust by revealing that an only child shows less trust than does a non-only-child, resulting in lower inter-brain coherence.

Neuropathological and neuromorphometric abnormalities in bipolar disorder: view from the medial prefrontal cortical network

The question of whether BD is primarily a developmental disorder or a progressive, neurodegenerative disorder remains unresolved. Here, we review the morphometric postmortem and neuroimaging literature relevant to the neuropathology of bipolar disorder (BD). We focus on the medial prefrontal cortex (mPFC) network, a key system in the regulation of emotional, behavioral, endocrine, and innate immunological responses to stress. We draw four main conclusions: the mPFC is characterized by (1) a decrease in volume, (2) reductions in neuronal size, and/or changes in neuronal density, (3) reductions in glial cell density, and (4) changes in gene expression. These data suggest the presence of dendritic atrophy of neurons and the loss of oligodendroglial cells in BD, although some data additionally suggest a reduction in the cell counts of specific subpopulations of GABAergic interneurons. Based on the weight of the postmortem and neuroimaging literature discussed herein, we favor a complex hypothesis that BD primarily constitutes a developmental disorder, but that additional, progressive, histopathological processes also are associated with recurrent or chronic illness. Conceivably BD may be best conceptualized as a progressive neurodevelopmental disorder.

Chronic myocardial infarction changed the excitatory-inhibitory synaptic balance in the medial prefrontal cortex of rat

The medial prefrontal cortex is a key area for the regulation of pain and emotion. However, the functional involvement of the medial prefrontal cortex for visceral nociception, at the neuronal or synaptic level, is obscure yet. In the present study, the properties of excitatory and inhibitory synaptic transmission within the layer II/III of rat medial prefrontal cortex after chronic myocardial infarction were studied. It is found that the excitation–inhibition ratio of the medial prefrontal cortex was greatly changed, with enhanced excitation and decreased inhibition inputs to the pyramidal cells of the medial prefrontal cortex, which largely due to decreased spike firing in gamma-aminobutyric acid-ergic neurons. Behaviorally, inhibition of gamma-aminobutyric acid-ergic synaptic transmission alleviated the visceral pain and anxiety. It is thus for the first time showing that the excitation–inhibition ratio is increased in the medial prefrontal cortex after chronic myocardial infarction, which may come from the reduced intrinsic activity of gamma-aminobutyric acid-ergic neurons and is important for regulating the angina pectoris and anxiety induced by chronic myocardial infarction.

MK212, a 5-hydroxytryptamine 2C receptor agonist, reverses prepulse inhibition deficits in the medial prefrontal cortex and ventral hippocampus

Prepulse inhibition (PPI) is disrupted in many neuropsychiatric diseases. Molecules such as 5-HT_2C receptor agonists alleviate PPI deficits in rodents; however, the precise mechanisms and critical regions of the brain responsible for the reversal effect of these agonists remain inconclusive. The present study aimed to investigate the areas of the brain critical for the reversal effect of 5-HT_2C receptor agonists on PPI deficits in mice. The results showed that systemic administration of the 5-HT_2C receptor agonist MK212 did not affect normal PPI behavior, but reversed the PPI deficits induced by the N-methyl d-aspartate receptor antagonist MK801 in mice. In addition, the 5-HT_2C receptor antagonist SB242084 had no effect on PPI behavior despite MK801 treatment. Moreover, local infusion of MK212 into the medial prefrontal cortex and ventral hippocampus, excluding the nucleus accumbens or ventral tegmental area, rescued the PPI deficits induced by MK801. These data suggest that the medial prefrontal cortex and ventral hippocampus are critical brain areas responsible for the reversal of 5-HT_2C agonists on PPI deficits. The results will contribute to our current knowledge on the molecular and neural mechanisms underlying the antipsychotic effects of 5-HT_2C receptor agonists, especially the neural circuits modulated by 5-HT_2C receptor activity.

The olfactory bulb coordinates the ventral hippocampus-medial prefrontal cortex circuit during spatial working memory performance

Neural oscillations synchronize the activity of brain regions during cognitive functions, such as spatial working memory. Olfactory bulb (OB) oscillations are ubiquitous rhythms that can modulate neocortical and limbic regions. However, the functional connectivity between the OB and areas contributing to spatial working memory, such as the ventral hippocampus (vHPC) and medial prefrontal cortex (mPFC), is less understood. Hence, we investigated functional interaction between OB and the vHPC-mPFC circuit during the spatial working memory performance in rats. To this end, we analyzed the simultaneously recorded local field potentials from OB, vHPC, and mPFC when rats explored the Y-maze and compared the brain activities of correct trials vs. wrong trials. We found that coupling between the vHPC and mPFC was augmented during correct trials. The enhanced coherence of OB activity with the vHPC-mPFC circuit at delta (< 4 Hz) and gamma (50-80 Hz) ranges were observed during correct trials. The cross-frequency analysis revealed that the OB delta phase increased the mPFC gamma power within corrected trials, indicating a modulatory role of OB oscillations on mPFC activity during correct trials. Moreover, the correlation between OB oscillations and the vHPC-mPFC circuit was increased at the delta range during correct trials, exhibiting enhanced synchronized activity of these regions during the cognitive task. We demonstrated a functional engagement of OB connectivity with the vHPC-mPFC circuit during spatial working memory task performance.

Effects of subanesthetic ketamine and (2R,6R) hydroxynorketamine on working memory and synaptic transmission in the nucleus reuniens in mice

RATIONALE

Acute cognitive impairment and abuse potential of ketamine incentivizes the search for alternatives to ketamine for clinical management of treatment-resistant depression. Recently, (2R,6R) hydroxynorketamine ((2R,6R)-HNK), a metabolite of ketamine, has shown promise due to its reported lack of ketamine-like reinforcing properties. Nonetheless, the effect of (2R,6R)-HNK on cognition has not been reported.

METHOD

Adult male mice were placed in a Y-maze to measure spatial working memory (SWM) 24 h after treatment with either a single or repeated subanesthetic dose of (2R,6R)-HNK or ketamine. To determine the effect of the drug regimens on synaptic mechanisms in neural circuits deemed critical for SWM, we conducted patch-clamp electrophysiological recordings from neurons in the midline thalamic nucleus reuniens (RE) in response to optogenetic stimulation of medial prefrontal cortex (mPFC) inputs in acutely prepared brain slices.

RESULTS

Single or repeated treatment with a 10 mg/kg dose of either drug did not impact performance in a Y-maze. However, single administration of a ½-log higher dose (32 mg/kg) of ketamine significantly reduced SWM. The same dose of (2R,6R)-HNK did not produce SWM deficits. Interestingly, repeated administration of either drugs at the 32 mg/kg had no effect on SWM performances. Concomitant to these effects on SWM, only single injection of 32 mg/kg of ketamine was found to increase the mPFC-driven action potential firing activity in the RE neurons. Conversely, both single and repeated administration of the 32 mg/kg dose of (2R,6R)-HNK but not ketamine, increased the input resistance of the RE neurons.

CONCLUSION

Our results indicate that acute treatment of ketamine at 32 mg/kg increases mPFC-driven firing activity of RE neurons, and this contributes to the ketamine-mediated cognitive deficit. Secondly, sub-chronic treatment with the same dose of ketamine likely induces tolerance. Although single or repeated administration of the 32 mg/kg dose of (2R,6R)-HNK can alter intrinsic properties of RE neurons, this dose does not produce cognitive deficit or changes in synaptic mechanism in the RE.

Uncoupling nNOS-PSD-95 in mPFC inhibits morphine priming-induced reinstatement after extinction training

Extremely high relapse rate is the dramatic challenge of drug abuse at present. Environmental cues play an important role in relapse of drug abuse. However, the specific mechanism underlying relapse remains unclear. Using morphine conditioned place preference (CPP) model, we show that association of neuronal nitric oxide synthase (nNOS) with postsynaptic density-95 (PSD-95) plays a significant role in morphine priming-induced reinstatement. The nNOS-PSD-95 coupling and c-Fos expression in the medial prefrontal cortex (mPFC) was significantly increased after extinction of morphine CPP. Dissociation of nNOS-PSD-95 in the mPFC by ZL006 inhibited the reinstatement of morphine CPP induced by a priming dose of morphine. Significantly reduced phosphorylation of cAMP-response element binding protein (CREB) in the mPFC was observed in the mice exposed to morphine after the extinction training. Uncoupling nNOS-PSD-95 reversed the morphine-induced CREB dysfunction. Moreover, effects of ZL006 on the reinstatement of morphine CPP and CREB activation depended on nNOS-PSD-95 target. Together, our findings suggest that nNOS-PSD-95 in the mPFC contributes to reinstatement of morphine CPP, possibly through CREB dysfunction, offering a potential target to prevent relapse of drug abuse.

Prefrontal mRNA expression of long and short isoforms of D2 dopamine receptor: Possible role in delayed learning deficit caused by early life interleukin-1β treatment

Long (D2L) and short (D2S) isoform of the D2 dopamine receptor are believed to play different roles in behavioral regulation. However, little is known about differential regulation of these isoforms mRNA expression during the process of learning in physiological and pathological states. In this study, we have investigated the combined effect of training in active avoidance (AA) paradigm and chronic early life treatment with pro-inflammatory cytokine interleukin (IL)-1β (1μg/kg i.p., P15-21) on D2S and D2L dopamine receptor mRNA expression in the medial prefrontal cortex (mPFC) of adult rats. We have shown differential regulation of D2 short and long mRNA isoform expression in the mPFC. There was no effect of AA-training on D2S mRNA expression, while D2L mRNA was downregulated in AA-trained control (intact and saline-treated) animals, and this effect was not observed in rats treated with IL-1β. D2S mRNA expression level negatively correlated with learning ability within control (saline-treated and intact) groups but not in IL-1β-treated animals. Thus, prefrontal expression of distinct D2 dopamine receptor splice variants is supposed to be implicated in cognitive decline caused by early life immune challenge.

The antidepressant-like effect of resolvin E1 in repeated prednisolone-induced depression model mice

Resolvin E1 (RvE1) is an anti-inflammatory lipid mediator derived from eicosapentaenoic acid. We previously demonstrated that intracerebroventricular (i.c.v.) and intra-medial prefrontal cortex (mPFC) infusions of RvE1 produce antidepressant-like effects in a lipopolysaccharide-induced depression mouse model. To further confirm the antidepressant-like effect of RvE1, the present study examined whether RvE1 ameliorated depression-like behavior induced by repeated injections of prednisolone (PSL), a synthetic glucocorticoid, in male ICR mice. We first ascertained whether repeated subcutaneous treatment with PSL (50 mg/kg, once a day) affected locomotor activity and anxiety-like behavior in the open field test (OFT; after a 5-day PSL treatment) and induced depression-like behavior in the tail suspension test (TST; after a 6-day PSL treatment) and forced swim test (FST; after a 7-day PSL treatment). Repeated PSL injections significantly increased immobility in the FST, which was not ameliorated by acute desipramine treatment (30 mg/kg, i.p.), but not in the TST, without affecting locomotor activity and anxiety-like behavior in the OFT. Subsequently, we investigated the therapeutic effects of i.c.v. (1 ng) and intra-mPFC (50 pg/side) infusions of RvE1 in the repeated PSL-induced depression mouse model using the OFT and FST after 5- and 6-day PSL treatments, respectively. The repeated PSL-induced increase in immobility in the FST was significantly attenuated by both i.c.v. and intra-mPFC infusions of RvE1 without affecting the locomotor activity and anxiety-like behavior. In addition, a single i.c.v. infusion of RvE1 immediately before the first or fourth injection of PSL also attenuated PSL-induced depression-like behavior in the FST, suggesting the preventive effect of RvE1. These results indicate that RvE1 produces antidepressant-like effects in a mouse model of repeated PSL-induced depression.

Ketamine contributes to the alteration of Ca2+ transient evoked by behavioral tests in the prelimbic area of mPFC: A study on chronic CORT-induced depressive mice

Recent studies have showed that ketamine is a rapid and efficient antidepressant, but the mechanism of its antidepressant effect is not fully clear. It is still lack of the research investigating the relation between depressive-like behaviors and neuronal activities in specific brain area after administration of ketamine in vivo. Medial prefrontal cortex (mPFC) involved in the pathogenesis of depression. As a result of effective assessments after behavioral test, most studies lack of direct evidence of the relation between efficacy and the activity of specific brain area. Therefore, we used fiber photometry to explore the alteration of Ca²⁺ transient in the prelimbic (PrL) area of mPFC during behavioral tests in freely moving mice. Our results showed that the chronic corticosterone (CORT) protocol induced depressive-like behaviors. Administration of ketamine reversed these effects. The activation of Ca²⁺ transients was associated with some behaviors during behavioral tests. Struggling, rearing and exploring evoked strong Ca²⁺ transients, but moving and grooming did not. The Ca²⁺ transients amplitude reductions of struggling, rearing and exploring induced by CORT were reversed by ketamine. The results indicated that ketamine ameliorated depressive-like behaviors via mediating neural activation in PrL.

The role of the mPFC in the social influence of majority and expert opinion

Individual attitudes and preferences are easily affected by social information. In a world where information sharing and dissemination are extremely convenient, social influence has played a greater role than in any previous era. Previous studies have suggested that the medial prefrontal cortex (mPFC) participates in mediating the tendency towards social conformity. However, the specific role of this brain area is still unknown, and it is not clear whether various types of external information influences share a mechanism. In this research, we aimed to use transcranial direct current stimulation (tDCS) to further explore the role of the mPFC in human conformity behaviour. In our experiment, the subjects received the majority opinion/expert opinion, and conformity behaviour was measured by the subject's tendency to follow this information after receiving the social information. Our research found that when social information conveys the majority opinion, cathodal stimulation of the mPFC significantly enhances the subject's consistency tendency. When social information conveys an expert opinion, stimulation of the mPFC has no significant effect on the conformity tendency of subjects. The results suggest that the mPFC plays an inhibitory role in regulating the social conformity tendency and that the activated neural circuits may vary with source when dealing with social influences.

Left medial orbitofrontal cortex volume correlates with skydive-elicited euphoric experience

The medial orbitofrontal cortex has been linked to the experience of positive affect. Greater medial orbitofrontal cortex volume is associated with greater expression of positive affect and reduced medial orbital frontal cortex volume is associated with blunted positive affect. However, little is known about the experience of euphoria, or extreme joy, and how this state may relate to variability in medial orbitofrontal cortex structure. To test the hypothesis that variability in euphoric experience correlates with the volume of the medial orbitofrontal cortex, we measured individuals' (N = 31) level of self-reported euphoria in response to a highly anticipated first time skydive and measured orbitofrontal cortical volumes with structural magnetic resonance imaging. Skydiving elicited a large increase in self-reported euphoria. Participants' euphoric experience was predicted by the volume of their left medial orbitofrontal cortex such that, the greater the volume, the greater the euphoria. Further analyses indicated that the left medial orbitofrontal cortex and amygdalo-hippocampal complex independently explain variability in euphoric experience and that medial orbitofrontal cortex volume, in conjunction with other structures within the mOFC-centered corticolimbic circuit, can be used to predict individuals' euphoric experience.

Subcallosal Cingulate Structural Connectivity Differs in Responders and Nonresponders to Electroconvulsive Therapy

BACKGROUND

Subcallosal cingulate (SCC) activity is associated with treatment response in major depressive disorder (MDD). Using electroconvulsive therapy (ECT) as a treatment model in this exploratory study, we addressed whether pretreatment SCC structural connectivity with corticolimbic-striatal circuitry relates to therapeutic outcome and whether these connectivity patterns change with treatment.

METHODS

Diffusion magnetic resonance imaging scans were acquired in 43 patients with MDD (mean [SD] age = 41 [13] years; men/women: 18/25) before and within 1 week of completing an ECT index series and in 31 healthy control subjects scanned twice (mean [SD] age = 38 [11] years; men/women: 17/18). Probabilistic tractography from subject-specific anatomically defined SCC seed regions to the ventral striatum (VS), anterior cingulate cortex (ACC), and bilateral medial prefrontal cortex (mPFC) was used to estimate structural connectivity in the target network.

RESULTS

SCC-mPFC connectivity was lower in responders (>50% symptom improvement) than nonresponders both before (p < .014) (difference 37%-96% left and right hemispheres) and after (p = .023) (difference 100% right hemisphere) treatment. SCC-mPFC connectivity in responders was also decreased compared with control subjects both at baseline (p = .012) and after ECT (p = .006), whereas nonresponders had SCC-right mPFC connectivity similar to that of control subjects. Subjects with MDD also showed decreased SCC-ACC connectivity compared with control subjects (baseline: p < .003, after ECT: p = .001), although SCC-ACC connectivity did not distinguish responders from nonresponders. Bilateral SCC-VS connectivity decreased (11%) with ECT (p = .021) regardless of treatment response.

CONCLUSIONS

While SCC-ACC connectivity may be a hallmark of MDD compared with control subjects, lower pretreatment SCC-mPFC connectivity in ECT responders (compared with nonresponders and control subjects) suggests that connectivity in this pathway may serve as a potential biomarker of therapeutic outcome and be relevant for treatment selection.

A comparative neuroimaging perspective of olfaction and higher-order olfactory processing: on health and disease

Olfactory dysfunction is often the earliest indicator of disease in a range of neurological and psychiatric disorders. One tempting working hypothesis is that pathological changes in the peripheral olfactory system where the body is exposed to many adverse environmental stressors may have a causal role for the brain alteration. Whether and how the peripheral pathology spreads to more central brain regions may be effectively studied in rodent models, and there is successful precedence in experimental models for Parkinson's disease. It is of interest to study whether a similar mechanism may underlie the pathology of psychiatric illnesses, such as schizophrenia. However, direct comparison between rodent models and humans includes challenges under light of comparative neuroanatomy and experimental methodologies used in these two distinct species. We believe that neuroimaging modality that has been the main methodology of human brain studies may be a useful viewpoint to address and fill the knowledge gap between rodents and humans in this scientific question. Accordingly, in the present review article, we focus on brain imaging studies associated with olfaction in healthy humans and patients with neurological and psychiatric disorders, and if available those in rodents. We organize this review article at three levels: 1) olfactory bulb (OB) and peripheral structures of the olfactory system, 2) primary olfactory cortical and subcortical regions, and 3) associated higher-order cortical regions. This research area is still underdeveloped, and we acknowledge that further validation with independent cohorts may be needed for many studies presented here, in particular those with human subjects. Nevertheless, whether and how peripheral olfactory disturbance impacts brain function is becoming even a hotter topic in the ongoing COVID-19 pandemic, given the risk of long-term changes of mental status associated with olfactory infection of SARS-CoV-2. Together, in this review article, we introduce this underdeveloped but important research area focusing on its implications in neurological and psychiatric disorders, with several pioneered publications.

Circuit-wide proteomics profiling reveals brain region-specific protein signatures in the male WKY rats with endogenous depression

BACKGROUND

Although the Wistar Kyoto (WKY) rat has been consistently recognized as an animal model with endogenous depression, the exact molecular mechanisms underlying its genetic susceptibility to depression remain undetermined.

METHODS

Compared with the Wistar rats, the depression-like behaviors of the male WKY ones were evaluated by both the sucrose preference test and forced swimming test. Golgi staining analysis was conducted to access the dendritic morphology. TMT-labelled quantitative proteomics analyses were respectively performed in the medial prefrontal cortex (mPFC), nucleus accumbens (NAc), and hippocampus (Hip), followed by KEGG enrichment-based clustering analysis, Venn diagram analysis, and Pearson correlation analysis.

RESULTS

The WKY strain showed significant differences in both the depression-like behaviors and synaptic plasticity. Moreover, the WKY model displayed markedly distinct differentially-expressed protein (DEP) profiles, with minor differences between the WKY subgroups. A cerebral regional commonality and specificity were evident in the signaling pathways enriched in the WKY model, and a total of 15 brain region-specific DEPs were identified to closely correlate with the depression-like phenotypes (in the mPFC: Lrrc8d, Dcun1d2, and Mtnd5; in the NAc: Ccdc154, Sec14l2, Kif2a, LOC680322, Me1, Mknk1, and Ret7; in the Hip: Sec14l2, Serpinf2, LOC103694855, Fam13c, and Loxl1). Data were available via ProteomeXchange with identifier PXD029079.

LIMITATIONS

Female WKY rats are not included, and the roles of these candidate DEPs in depression remain further elucidation.

CONCLUSION

The present study further evidences the brain region-specific protein signatures in the male WKY model with endogenous depression, providing novel insights into the pathogenesis of depression in males.

The reinforcing effects of ethanol within the prelimbic cortex and ethanol drinking: Involvement of local dopamine D2 receptor-mediated neurotransmission

Previous studies have identified important mesolimbic regions in supporting the reinforcing effects of ethanol. However, the involvement of the medial prefrontal cortex (mPFC), another key region within the mesocorticolimbic system, in ethanol reinforcement has been understudied. The objective of the current study was to examine the role of the prelimbic (PL) cortex sub-region of the mPFC in ethanol reinforcement and drinking. Intracranial self-administration was used to examine the reinforcing effects of ethanol within the PL cortex. Quantitative microdialysis was used to measure basal extracellular DA concentrations and clearance in the PL cortex following chronic ethanol drinking. In addition, the involvement of dopamine (DA) D2 receptors within the PL cortex on the reinforcing effects of ethanol and ethanol drinking was determined. Ethanol was dose-dependent self-administered into the PL cortex, with significantly more infusions elicited by 100-200 mg% ethanol than vehicle. Co-infusion of the D2 receptor antagonist sulpiride significantly reduced ethanol self-administration. Chronic ethanol drinking significantly elevated basal extracellular DA concentrations without altering DA clearance. Microinjection of sulpiride into the PL cortex selectively reduced ethanol, but not saccharine, drinking. These results indicate that the PL cortex supported the reinforcing effects of ethanol, and that ethanol drinking enhanced basal DA neurotransmission within the PL cortex. In addition, D2 receptor antagonism within the PL cortex reduced ethanol self-administration and drinking. Collectively, these findings revealed important DA mechanisms within the PL cortex in mediating ethanol reinforcement and drinking.

FTY720 (Fingolimod), a modulator of sphingosine-1-phosphate receptors, increases baseline hypothalamic-pituitary adrenal axis activity and alters behaviors relevant to affect and anxiety

FTY720 (fingolimod) is an analog of sphingosine, a ubiquitous sphingolipid. Phosphorylated FTY720 (FTY720-P) non-selectively binds to sphingosine-1-phosphate receptors (S1PRs) and regulates multiple cellular processes including cell proliferation, inflammation, and vascular remodeling. We recently demonstrated that S1PR3 expression in the medial prefrontal cortex (mPFC) of rats promotes stress resilience and that S1PR3 expression in blood may serve as a biomarker for PTSD. Here we investigate the effects of FTY720 in regulating the stress response. We found that single and repeated intraperitoneal injections of FTY720 increased baseline plasma adrenocorticotropic hormone (ACTH) and corticosterone concentrations. FTY720 reduced social anxiety- and despair-like behavior as assessed by increased social interaction time and reduced time spent immobile in the Porsolt forced swim test. In blood, FTY720 administration reduced lymphocyte and reticulocyte counts, but raised erythrocyte counts. FTY720 also reduced mRNA of angiopoietin 1, endothelin 1, plasminogen, TgfB2, Pdgfa, and Mmp2 in the medial prefrontal cortex, suggesting that FTY720 reduced vascular remodeling. The antidepressant-like and anxiolytic-like effects of FTY720 may be attributed to reduced vascular remodeling as increased stress-induced blood vessel density in the brain contributes to behavior associated with vulnerability in rats. Together, these results demonstrate that FTY720 regulates baseline HPA axis activity but reduces social anxiety and despair, providing further evidence that S1PRs are important and novel regulators of stress-related functions.

Corticosterone level and central dopaminergic activity involved in agile and exploratory behaviours in formosan wood mice (Apodemus semotus)

The native Formosan wood mouse (Apodemus semotus) is the dominant rodent in Taiwan. In their natural environment, Formosan wood mice exhibit high locomotor activity, including searching and exploratory behaviours, which is observed similarly in the laboratory environment. How the behavioural responses of Formosan wood mice exhibit in elevated plus maze and marble burying tests remains unclear. How corticosterone levels and central dopaminergic activities are related to the behaviours in these tests is also unclear. This study compared the behaviours of Formosan wood mice with that of C57BL/6J mice using the elevated plus maze and marble burying tests, and measured the corticosterone levels and central dopaminergic activities. Formosan wood mice showed greater locomotor and exploratory activity than the C57BL/6J mice. Similarly, the marble burying and rearing numbers were higher for Formosan wood mice. High locomotor and exploratory behaviours were strongly correlated with corticosterone levels after acute mild restraint stress in Formosan wood mice. The anxiolytic, diazepam, reduced the high exploratory activity, corticosterone levels and central dopaminergic activities. The high locomotor and exploratory behaviours of Formosan wood mice are related to the corticosterone levels and central dopaminergic activities. These data may explain Formosan wood mice dominance in the intermediate altitude of Taiwan.

Transcriptome Analysis of the Mouse Medial Prefrontal Cortex in a Chronic Constriction Injury Model

The medial prefrontal cortex (mPFC) is critical for both the sensory and emotional/cognitive components of pain. However, the underlying mechanism remains largely unknown. Here, we examined changes in the transcriptomic profiles in the mPFC of mice with chronic pain using RNA sequencing (RNA-seq) technology. A mouse model of peripheral neuropathic pain was established via chronic constriction injury (CCI) of the sciatic nerve. CCI mice developed sustained mechanical allodynia and thermal hyperalgesia, as well as cognitive impairment four weeks after surgery. RNA-seq was conducted 4 weeks after CCI surgery. Compared with contral group, RNA-seq identified a total 309 and 222 differentially expressed genes (DEGs) in the ipsilateral and contralateral mPFC of CCI model mice, respectively. GO analysis indicated that the functions of these genes were mainly enriched in immune- and inflammation-related processes such as interferon-gamma production and cytokine secretion. KEGG analysis further showed the enrichment of genes involved in the neuroactive ligand-receptor interaction signaling pathway and Parkinson disease pathway that have been reported to be importantly involved in chronic neuralgia and cognitive dysfunction. Our study may provide insights into the possible mechanisms underlying neuropathic pain and pain-related comorbidities.

Medial prefrontal and occipito-temporal activity at encoding determines enhanced recognition of threatening faces after 1.5 years

Studies demonstrated that faces with threatening emotional expressions are better remembered than non-threatening faces. However, whether this memory advantage persists over years and which neural systems underlie such an effect remains unknown. Here, we employed an individual difference approach to examine whether the neural activity during incidental encoding was associated with differential recognition of faces with emotional expressions (angry, fearful, happy, sad and neutral) after a retention interval of > 1.5 years (N = 89). Behaviorally, we found a better recognition for threatening (angry, fearful) versus non-threatening (happy and neutral) faces after a delay of > 1.5 years, which was driven by forgetting of non-threatening faces compared with immediate recognition after encoding. Multivariate principal component analysis (PCA) on the behavioral responses further confirmed the discriminative recognition performance between threatening and non-threatening faces. A voxel-wise whole-brain analysis on the concomitantly acquired functional magnetic resonance imaging (fMRI) data during incidental encoding revealed that neural activity in bilateral inferior occipital gyrus (IOG) and ventromedial prefrontal/orbitofrontal cortex (vmPFC/OFC) was associated with the individual differences in the discriminative emotional face recognition performance measured by an innovative behavioral pattern similarity analysis (BPSA). The left fusiform face area (FFA) was additionally determined using a regionally focused analysis. Overall, the present study provides evidence that threatening facial expressions lead to persistent face recognition over periods of > 1.5 years, and that differential encoding-related activity in the medial prefrontal cortex and occipito-temporal cortex may underlie this effect.

Is value-based choice repetition susceptible to medial frontal transcranial direct current stimulation (tDCS)? A preregistered study

In value-based decision making, people have to weigh different options based on their subjective value. This process, however, also is influenced by choice biases, such as choice repetition: in a series of choices, people are more likely to repeat their decision than to switch to a different choice. Previously, it was shown that transcranial direct current stimulation (tDCS) can affect such choice biases. We applied tDCS over the medial prefrontal cortex to investigate whether tDCS can alter choice repetition in value-based decision making. In a preregistered study, we applied anodal, cathodal, and sham tDCS stimulation to 52 participants. While we found robust choice repetition effects, we did not find support for an effect of tDCS stimulation. We discuss these findings within the larger scope of the tDCS literature and highlight the potential roles of interindividual variability and current density strength.

PET neuroimaging reveals upregulation of dopamine D2 receptor contributes to amygdaloid dysfunction in rat acute restraint stress model

Acute stress relates to high prevalence of anxiety, depression or even sudden death. Although dopaminergic system in amygdala-medial prefrontal cortex (mPFC) circuit is hyper-responsive to stress-induced anxiety, the mechanisms that control anxiety still remains unanswered. Here, the acute restraint stress model(ARS) was established to develop anxiety-like behavior. The D2-dopamine receptor (D2R) availability in amygdala and mPFC was assessed using [¹⁸F]-fallypride positron emission tomography(PET) and immunohistochemical assay. We revealed that ARS paradigm was successfully established, as evidenced by elevated plus-maze test(EPM) and increased corticosterone release. Moreover, PET imaging displayed elevated D2R availability in the amygdala and mPFC in ARS as compared to that in the naives. PET imaging combined with immunohistochemical assay confirmed that amygdaloid D2R was significantly implicated in stress-induced anxiety. Our findings delivered valuable insights into neuromechanism of amygdaloid D2R underlying stress-induced anxiety and might have important implications for developing therapeutics for anxiety by targeting amygdaloid D2R.

Extended operant training increases infralimbic and prelimbic cortex Fos regardless of fear conditioning experience

Extended fear training can lead to initially low fear expression that grows over time, termed fear incubation. Conversely, a single fear conditioning session typically results in high fear initially that is sustained over time. Fear expression decreases across extended training, suggesting that a fear extinction-like process might be responsible for low fear observed soon after training. Because of the prominent role medial prefrontal cortex (mPFC) plays in fear conditioning and extinction, we decided to examine Fos expression resulting from a cued fear retrieval test to gain insight into possible mechanisms involved in extended training fear incubation. Male Long-Evans rats received 1 or 10 days of tone-shock pairings or tone-only exposure (while lever-pressing for food). Two days after the end of fear training, rats received a cued fear test, with perfusions timed to visualize Fos expression during test. As expected, the limited fear conditioning group exhibited higher fear in the test than any of the other groups (as measured with conditioned suppression of lever-pressing). Interestingly, we found that extended training animals (whether they received tone-shock pairings or tone-only exposure) expressed higher levels of Fos in both prelimbic and infralimbic cortices than limited training animals. There was no association between fear expression and mPFC Fos expression. These results suggest we may have visualized Fos expression related to operant overtraining rather than conditioned fear related processes. Further research is needed to determine the neurobiological basis of extended training fear incubation and to determine processes represented by the pattern of Fos expression we observed.

Local and distributed cortical markers of effort expenditure during sustained goal pursuit

The adaptive adjustment of behavior in pursuit of desired goals is critical for survival. To accomplish this complex feat, individuals must weigh the potential benefits of a given action against time, energy, and resource costs. Here, we examine brain responses associated with willingness to exert physical effort during the sustained pursuit of desired goals. Our analyses reveal a distributed pattern of brain activity in aspects of ventral medial prefrontal cortex that tracks with trial-level variability in effort expenditure. Indicating the brain represents echoes of effort at the point of feedback, whole-brain searchlights identified signals reflecting past effort expenditure in medial and lateral prefrontal cortices, encompassing broad swaths of frontoparietal and dorsal attention networks. These data have important implications for our understanding of how the brain's valuation mechanisms contend with the complexity of real-world dynamic environments with relevance for the study of behavior across health and disease.

The NMDAR modulator NYX-2925 alleviates neuropathic pain via a Src-dependent mechanism in the mPFC

Previous studies have shown that oral administration of the NMDAR modulator NYX-2925 alleviates pain in several animal models of neuropathic pain and this appears to be through mPFC, but not spinal, mediated mechanisms. While much is known about the impact of neuropathic pain on NMDAR-mediated signaling in the spinal cord, limited studies have focused on the brain. In the current study, we assess signaling changes associated with NMDAR-mediated plasticity in the mPFC and the impact of NYX-2925 administration on the normalization of these signaling changes. We found a decrease in activated Src levels in the mPFC of animals with chronic constriction injury (CCI) of the sciatic nerve. While Src mediated activation of NMDARs was also decreased in CCI animals, the main NMDAR phosphorylation site of CAMKII was not affected. This is in opposition to what has been found in the spinal cord, where both Src and CAMKII activation are increased. Oral administration of NYX-2925 restored levels of activated Src and Src phosphorylation sites on GluN2A and GluN2B in the mPFC, with no effect on activated CAMKII levels. The analgesic effect of NYX-2925 appears dependent on this restoration of Src activation in the mPFC, as co-administering Src activation inhibitors prevented the NYX-2925 analgesic effect. Overall, these data suggest that NMDAR-mediated signaling plays a key role in neuropathic pain, albeit in different directions in the spinal cord vs. the mPFC. Furthermore, the analgesic effect of NYX-2925 appears to involve a restoration of NMDAR-mediated signaling in the mPFC.