Coherence and congruency mediate medial temporal and medial prefrontal activity during event construction

The precise roles of the hippocampus (HPC) and medial prefrontal cortex (mPFC) in initially constructing imagined events remains unclear. HPC activity during imagination may be modulated by mnemonic load, given its role in working memory for complex materials, and/or by the semantic relatedness (i.e. congruency) between items and their context. MPFC activation may track with congruency or mnemonic load, given the role of ventral mPFC in schema processing and the dorsal mPFC in working memory for social information. Sixteen healthy adults (M age = 22.3) underwent an event construction task, wherein participants were provided with a context and item words and imagined an event, forming as many inter-item associations as possible among the items. The stimuli varied by set size and by normatively-defined congruence (normative congruency) to explore their effects on HPC and mPFC activity and functional connectivity. We observed HPC connectivity during event construction in general, whereas dorsal mPFC connectivity occurred during imagining only at higher set sizes. Moreover, anterior hippocampal activity correlated positively with increasing coherence between items during imagining, suggesting that the anterior HPC is sensitive to the relational demands of constructing a novel event. Parahippocampal, hippocampal, temporal pole, and mPFC activity tracked only with individual differences in subjective ratings of congruency of imagined events, which may contribute to construction by retrieving existing schema-related information. Collectively, these findings provide new insights into the factors that modulate HPC and mPFC activity when constructing mental simulations.

Effects of stress on the corticolimbic system: implications for chronic pain

Stress has multifaceted effects on pain. On the one hand, it is a powerful inhibitor of nociception and inflammation; on the other hand, it contributes to enhanced pathological states including the establishment and continuation of chronic pain. These seemingly paradoxical effects can be better understood by investigating how stress-induced plasticity in particular brain circuitry contributes to the chronic pain state. This review presents the rationale and evidence for the interactions between stress and pain, emphasizing underlying mechanisms and putting forth the hypothesis that stress partly mediates the deleterious effects of pain on the corticolimbic system. First, a general description of the corticolimbic circuitry predisposing and amplifying chronic pain will be discussed, followed by an overview of the neurotoxic effects of stress hormones on this circuitry. Recent studies show that the resulting perturbations to these brain circuits have significant consequences both for chronic pain and for general regulation of the stress response, primarily through feedback mechanisms controlling the hypothalamic-pituitary-adrenal axis. This overlap in effected circuitry provides a key point of comparison between stress and pain, and the similarities between the plasticity induced by chronic pain and chronic stress will be examined here. Chronic pain patients have been shown to exhibit maladaptive stress responses in general and in response to pain; the cause of this response and its consequence on pain severity will then be reviewed. Finally, factors that have been shown to lead to resilience or vulnerability for chronic pain and maladaptive stress responses will be summarized.

Distinct regulation pattern of Egr-1, BDNF and Arc during morphine-withdrawal conditioned place aversion paradigm: Role of glucocorticoids

Negative affective aspects of opiate abstinence contribute to the persistence of substance abuse. Importantly, interconnected brain areas involved in aversive motivational processes, such as the ventral tegmental area (VTA) and medial prefrontal cortex (mPFC), become activated when animals are confined to withdrawal-paired environments. In the present study, place aversion was elicited in sham and adrenalectomized (ADX) animals by conditioned naloxone-precipitated drug withdrawal following exposure to chronic morphine. qPCR was employed to detect the expression of brain derived neurotrophic factor (Bdnf) and the immediate early genes (IEG) early growth response 1 (Egr-1) and activity-regulated cytoskeletal-associated protein (Arc) mRNAs in the VTA and mPFC at different time points of the conditioned place aversion (CPA) paradigm: after the conditioning phase and after the test phase. Sham + morphine rats exhibited robust CPA, which was impaired in ADX + morphine animals. Egr-1 and Arc were induced in the VTA and mPFC after morphine-withdrawal conditioning phase. Furthermore, Bdnf expression was enhanced in the VTA during the test phase. Bdnf induction seemed to be glucocorticoid-dependent, given that was correlated with HPA axis function and was not observed in morphine-dependent ADX animals. In addition, BDNF regulation and function was opposite in the VTA and mPFC during aversive-withdrawal memory retrieval. Our results suggest that IEGs and BDNF in these brain regions may play key roles in mediating the negative motivational component of opiate withdrawal.

Frontal hypoactivation and alterations in the reward-system during humor processing in patients with schizophrenia spectrum disorders

Humor is a ubiquitous human ability with important implications for both social and emotional functioning. Patients with neuropsychiatric disorders, such as schizophrenia, experience difficulties in the comprehension and appreciation of humor. However, the specific neural mechanisms underlying these deficits are unknown. In the current study, we sought to elucidate the neural correlates of humor processing in patients with schizophrenia spectrum disorders (SSD). Functional Magnetic Resonance Imaging (fMRI) was used in thirty-one patients with SSD and a control group, performing a humor processing paradigm. Both regional brain activation and parametric modulation of brain responses via subjective funniness ratings were collected during the scanning procedure. On a neural level, large overlaps in fronto-temporal brain activation was found in both groups. However, patients compared to healthy control subjects showed attenuated responses in frontal brain regions, including the anterior cingulate cortex, medial prefrontal cortex (mPFC), superior frontal gyrus and middle frontal gyrus, as well as in the striatum (i.e. caudate nucleus, putamen). Furthermore, parametric modulation of subjective funniness ratings resulted in attenuated responses in the mPFC, bilateral insula, and left hippocampus. Analysis of functional connectivity revealed alterations in mPFC-caudate nucleus coupling in patients with SSD, which might reflect impairments in reward-related processing. Notably, alterations in mPFC-caudate nucleus coupling in patients were significantly associated to subjective funniness ratings. Our results extend previous findings demonstrating the relevance of frontal hypoactivation for humor processing impairments in patients with SSD and first point towards alterations in humor appreciation processes.

An fMRI study of decision-making under sunk costs in gambling disorder

The sunk cost effect is the tendency to continue an investment, or take an action, even though it has higher future costs than benefits, if costs of time, money, or effort were previously incurred. This type of decision bias is pervasive in real life and has been studied in various disciplines. Previous studies and clinical observations suggest that decision-making under sunk costs is altered in gambling disorder (GD). However, the neural mechanisms of decision-making under sunk costs in GD remain largely unknown, and so is their association with the clinical characteristics of this patient group. Here, by combining functional magnetic resonance imaging and the task that demonstrated a clear example of the sunk cost effect, we investigated the neural correlates during decision-making under sunk costs in GD. We found no significant differences in the strength of the sunk cost effect between the GD and healthy control (HC) groups. However, the strength of the sunk cost effect in patients with GD showed a significant negative correlation with abstinence period and a marginally significant positive correlation with the duration of illness. We also found a reduction in the neural activation in the dorsal medial prefrontal cortex during decision-making under sunk costs for the GD group compared with the HC group. Furthermore, in patients with GD, the levels of activation in this area negatively correlated with the duration of illness. These findings have important clinical implications. This study will contribute to a better understanding of the mechanisms underlying altered decision-making abilities in GD.

Differential fear conditioning generates prefrontal neural ensembles of safety signals

Fear discrimination is critical for survival, while fear generalization is effective for avoiding dangerous situations. Overgeneralized fear is a typical symptom of anxiety disorders, including generalized anxiety disorder and posttraumatic stress disorder (PTSD). Previous research demonstrated that fear discrimination learning is mediated by prefrontal mechanisms. While the prelimbic (PL) and infralimbic (IL) subdivisions of the medial prefrontal cortex (mPFC) are recognized for their excitatory and inhibitory effects on the fear circuit, respectively, the mechanisms driving fear discrimination are unidentified. To obtain insight into the mechanisms underlying context-specific fear discrimination, we investigated prefrontal neuronal ensembles representing distinct experiences associated with learning to disambiguate between dangerous and similar, but not identical, harmless stimuli. Here, we show distinct quantitative activation differences in response to conditioned and generalized fear experiences, as well as modulation of the neuronal ensembles associated with successful acquisition of context-safety contingencies. These findings suggest that prefrontal neuronal ensembles patterns code functional context-danger and context-safety relationships. The PL subdivision of the mPFC monitors context-danger associations to conditioned fear, whereas differential conditioning sparks additional ensembles associated with the inhibition of generalized fear in both the PL and IL subdivisions of the mPFC. Our data suggest that fear discrimination learning is associated with the modulation of prefrontal subpopulations in a subregion- and experience-specific fashion, and the learning of appropriate responses to conditioned and initially generalized fear experiences is driven by gradual updating and rebalancing of the prefrontal memory representations.

Selective changes in moral judgment by noninvasive brain stimulation of the medial prefrontal cortex

Multiple cortical networks intervene in moral judgment, among which the dorsolateral prefrontal cortex (DLPFC) and the medial prefrontal structures (medial PFC) emerged as two major territories, which have been traditionally attributed, respectively, to cognitive control and affective reactions. However, some recent theoretical and empirical accounts disputed this dualistic approach to moral evaluation. In the present study, to further assess the functional contribution of the medial PFC in moral judgment, we modulated its cortical excitability by means of transcranial direct current stimulation (tDCS) and tracked the change in response to different types of moral dilemmas, including switch-like and footbridge-like moral dilemmas, with and without personal involvement. One hundred participants (50 males) completed a questionnaire to assess the baseline levels of deontology. Next, participants were randomly assigned to receive anodal, sham, or cathodal tDCS over the medial prefrontal structures and then were asked to address a series of dilemmas. The results showed that participants who received anodal stimulation over the medial PFC provided more utilitarian responses to switch-like (but not footbridge-like) dilemmas than those who received cathodal tDCS. We also found that neurostimulation modulated the influence that deontology has on moral choices. Specifically, in the anodal tDCS group, participants' decisions were less likely to be influenced by their baseline levels of deontology compared with the sham or cathodal groups. Overall, our results seem to refute a functional role of the medial prefrontal structures purely restricted to affective reactions for moral dilemmas, providing new insights on the functional contribution of the medial PFC in moral judgment.

Effects of repeated cocaine administration on dopamine D1 receptor modulation of mesocorticolimbic GABA and glutamate transmission

Repeated cocaine exposure alters medial prefrontal cortex (mPFC) function to allow for enhanced excitatory transmission to the nucleus accumbens and ventral tegmental area (VTA). Previous studies have demonstrated changes in receptor function in the mPFC in animals repeatedly exposed to cocaine that produced increased excitatory output. The present report tested the hypothesis that daily injections of cocaine would enhance D1 receptor responsiveness by infusing the D1 receptor agonist SKF 38393 into the mPFC and monitoring glutamate and/or GABA release in the mPFC, nucleus accumbens and VTA of saline- and cocaine-pretreated animals using in vivo microdialysis. The data demonstrated that intra-mPFC SKF 38393 reduced GABA and glutamate levels in the mPFC in control animals. Intra-mPFC SKF 38393 had no effect on glutamate levels in animals 1 day after daily cocaine treatments, increased mPFC glutamate at 7 days of withdrawal and reverted to decreasing glutamate at 30 days of withdrawal. SKF 38393 induced reduction in mPFC GABA is lost at 7 and 30 days of withdrawal. Intra-mPFC SKF 38393 did not alter glutamate levels in the nucleus accumbens or VTA of control animals. Infusion of SKF 38393 into the mPFC of animals previously exposed to cocaine increased and reduced glutamate release in the nucleus accumbens after 7 and 30 days of withdrawal, respectively and increased glutamate levels in the VTA 7 and 30 days after daily cocaine injections. The data suggest that repeated cocaine exposure alters D1 receptor function in the mPFC that could contribute to enhanced behavioral responses that occur following repeated cocaine.

Increased training compensates for OX1R blockage-impairment of spatial memory and c-Fos expression in different cortical and subcortical areas

It has been suggested that the orexin system modulates learning and memory-related processes. However, the possible influence that training could have on the effect of the blockade of orexin-A selective receptor (OX1R) on a spatial memory task has not been explored. Therefore, the present study attempts to compare the effects of OX1R antagonist SB-334867 infusion on spatial memory in two different conditions in the Morris Water Maze (MWM). This experiment evaluated the animals' performance in weak training (2 trials per session) vs strong training (6 trials per session) protocols in a spatial version of the MWM. We found that in the 2-trial condition the post-training SB-334867 infusion had a negative effect on consolidation as well as on the retention and reversal learning of the task 72 h later. This effect was not apparent in the 6-trial condition. In addition, while the strong training groups showed a general increase in c-Fos expression in several brain areas of the hippocampal-thalamic-cortical circuit, SB-334867 administration had the opposite effect in areas that have been previously reported to have a high density of OX1R. Specifically, the SB-infused group in the 2-trial condition showed a decrease in c-Fos immunoreactivity in the dentate gyrus, granular retrosplenial and prelimbic cortices, and centrolateral thalamic nucleus. This was not observed for subjects in the 6-trial condition. The activation of these areas could constitute a neuroanatomical substrate involved in the compensatory mechanisms of training upon SB-334867 impairing effects on a MWM spatial task.

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.

Neural Mechanisms Linking Emotion with Cardiovascular Disease

PURPOSE OF REVIEW

The present review discusses brain circuits that are engaged by negative emotions and possibly linked to cardiovascular disease risk. It describes recent human brain imaging studies that relate activity in these brain circuits to emotional processes, peripheral physiology, preclinical pathophysiology, as well as clinical outcomes.

RECENT FINDINGS

Negative emotions and the regulation of negative emotions reliably engage several brain regions that cross-sectional and longitudinal brain imaging studies have associated with CVD risk markers and outcomes. These brain regions include the amygdala, anterior cingulate cortex, medial prefrontal cortex, and insula. Other studies have applied advanced statistical techniques to characterize multivariate patterns of brain activity and brain connectivity that associate with negative emotion and CVD-relevant peripheral physiology. Brain imaging studies on emotion and cardiovascular disease risk are expanding our understanding of the brain-body bases of psychosocial and behavioral risk for cardiovascular disease.

Intranasal cerebrolysin improves cognitive function and structural synaptic plasticity in photothrombotic mouse model of medial prefrontal cortex ischemia

Medial prefrontal cortex (mPFC) ischemia affects post-stroke cognitive outcomes. We aimed to investigate the effects of different doses and routes of cerebrolysin (CBL) on the structural synaptic plasticity and cognitive function after mPFC ischemia in mice. Thence, CBL (1, 2.5 ml/kg/i.p./daily) or (1 ml/kg/i.n./daily), were administrated in photothrombotic mouse model of mPFC ischemia for two weeks. Episodic and spatial memories were assessed by the What-Where-Which (WWWhich) and Barnes tasks. Growth-associated protein 43 (GAP-43), postsynaptic density-95 (PSD-95), and synaptophysin (SYN) levels were measured in the lesioned area using western blot analysis. Dendritic arbors, spine densities, and morphology were assessed via Golgi-Cox staining. Treatment with 2.5 ml/kg/i.p. and 1 ml/kg/i.n. doses attenuated mPFC ischemia-induced episodic and spatial memories impairment. Results showed an obvious increase in the GAP-43, PSD-95 and SYN levels and improvement in the structural synaptic indexes in lesioned area induced by the same doses and routes of CBL. In conclusion, we found that specific doses/routes of CBL have positive effects on the structural synaptic plasticity and cognitive outcomes after mPFC ischemia.

Hemispheric mPFC asymmetry in decision making under ambiguity and risk: An fNIRS study

The Iowa Gambling Task (IGT) is a commonly used task for testing decision-making under ambiguity (the early stage) and risk (the late stage). However, differences between the temporal dynamic signals underlying these two types of decision-making as well as the hemispheric specificity of decision making during the IGT remain unknown. The present study sought to address this gap by focusing on the medial prefrontal cortex (mPFC), which plays an important role in decision-making across life domains. We used functional near-infrared spectroscopy (fNIRS) with high spatial and temporal resolution and measured oxy-hemoglobin concentration within the mPFC in 25 healthy participants who performed the IGT. Results showed that there are different activations of the right and left hemispheres of the mPFC during the different stages of IGT and types of decisions. This implies that the left and right mPFC can have different patterns of involvement in decision making, at least in IGT decisions, including making good (low risk) and bad (high risk) choices, under ambiguity and under risk conditions.

Serotonin2B receptors in the rat dorsal raphe nucleus exert a GABA-mediated tonic inhibitory control on serotonin neurons

The central serotonin_2B receptor (5-HT_2BR) is a well-established modulator of dopamine (DA) neuron activity in the rodent brain. Recent studies in rats have shown that the effect of 5-HT_2BR antagonists on accumbal and medial prefrontal cortex (mPFC) DA outflow results from a primary action in the dorsal raphe nucleus (DRN), where they activate 5-HT neurons innervating the mPFC. Although the mechanisms underlying this interaction remain largely unknown, data in the literature suggest the involvement of DRN GABAergic interneurons in the control of 5-HT activity. The present study examined this hypothesis using in vivo (intracerebral microdialysis) and in vitro (immunohistochemistry coupled to reverse transcription-polymerase chain reaction) experimental approaches in rats. Intraperitoneal (0.16 mg/kg) or intra-DRN (1 μM) administration of the selective 5-HT_2BR antagonist RS 127445 increased 5-HT outflow in both the DRN and the mPFC, these effects being prevented by the intra-DRN perfusion of the GABA_A antagonist bicuculline (100 μM), as well as by the subcutaneous (0.16 mg/kg) or the intra-DRN (0.1 μM) administration of the selective 5-HT_1AR antagonist WAY 100635. The increase in DRN 5-HT outflow induced by the intra-DRN administration of the selective 5-HT reuptake inhibitor citalopram (0.1 μM) was potentiated by the intra-DRN administration (0.5 μM) of RS 127445 only in the absence of bicuculline perfusion. Finally, in vitro experiments revealed the presence of the 5-HT_2BR mRNA on DRN GABAergic interneurons. Altogether, these results show that, in the rat DRN, 5-HT_2BRs are located on GABAergic interneurons, and exert a tonic inhibitory control on 5-HT neurons innervating the mPFC.

Classic Hallucinogens and Mystical Experiences: Phenomenology and Neural Correlates

This chapter begins with a brief review of descriptions and definitions of mystical-type experiences and the historical connection between classic hallucinogens and mystical experiences. The chapter then explores the empirical literature on experiences with classic hallucinogens in which claims about mystical or religious experiences have been made. A psychometrically validated questionnaire is described for the reliable measurement of mystical-type experiences occasioned by classic hallucinogens. Controlled laboratory studies show that under double-blind conditions that provide significant controls for expectancy bias, psilocybin can occasion complete mystical experiences in the majority of people studied. These effects are dose-dependent, specific to psilocybin compared to placebo or a psychoactive control substance, and have enduring impact on the moods, attitudes, and behaviors of participants as assessed by self-report of participants and ratings by community observers. Other studies suggest that enduring personal meaning in healthy volunteers and therapeutic outcomes in patients, including reduction and cessation of substance abuse behaviors and reduction of anxiety and depression in patients with a life-threatening cancer diagnosis, are related to the occurrence of mystical experiences during drug sessions. The final sections of the chapter draw parallels in human neuroscience research between the neural bases of experiences with classic hallucinogens and the neural bases of meditative practices for which claims of mystical-type experience are sometimes made. From these parallels, a functional neural model of mystical experience is proposed, based on changes in the default mode network of the brain that have been observed after the administration of classic hallucinogens and during meditation practices for which mystical-type claims have been made.

Dopamine D1 receptor in the medial prefrontal cortex mediates anxiety-like behaviors induced by blocking glutamatergic activity of the ventral hippocampus in rats

The medial prefrontal cortex (mPFC) receives direct and indirect projections from the ventral hippocampus (VH) and plays an important role in the regulation of anxiety. However, the effect of the mPFC dopamine D₁ receptor on anxiety-like behaviors induced by inhibition of glutamatergic activity in the VH has not been described. Here, we examined the effects of SKF38393, a selective dopamine D₁ receptor agonist, on anxiety-like behaviors induced by NMDA receptor inhibition in the VH and neuron firing activity of mPFC. Injection of MK-801 (6 μg/0.5 μl) into the VH produced anxiety-like behaviors in the elevated plus maze and open field tests, increased the firing activity of pyramidal neurons in the mPFC, and decreased the level of dopamine in the mPFC. Injection of SKF38393 (0.5 μg/0.5 μl) into the mPFC produced anxiolytic effects, and normalized the hyperactive firing activity of mPFC pyramidal neurons induced by MK-801, whereas in both normal and anxiety-like rats caused by MK-801, injection of SKF38393 into the mPFC decreased the firing activity of mPFC interneurons but did not affect the dopamine content in the mPFC. The present data demonstrate that decreased D₁ receptor activation in the mPFC may mediate anxiety-like behaviors induced by inhibition of glutamatergic activity in the VH. The balance of D₁ receptor activity between pyramidal neurons and interneurons is a crucial factor in maintaining normal conditions, and inhibitory glutamatergic activity in the VH induces hyperactivity of mPFC pyramidal neurons through decreases in dopamine release and in the amount of D₁ receptor activation on mPFC pyramidal neurons, which may be a critical factor for anxiety disorders.

Pathway-Specific Alterations of Cortico-Amygdala Transmission in an Arthritis Pain Model

Medial prefrontal cortex (mPFC) and amygdala are closely interconnected brain areas that play a key role in cognitive-affective aspects of pain through their reciprocal interactions. Clinical and preclinical evidence suggests that dysfunctions in the mPFC-amygdala circuitry underlie pain-related cognitive-affective deficits. However, synaptic mechanisms of pain-related changes in these long-range pathways are largely unknown. Here we used optogenetics and brain slice physiology to analyze synaptic transmission in different types of amygdala neurons driven by inputs from infralimbic (IL) and prelimbic (PL) subdivisions of the mPFC. We found that IL inputs evoked stronger synaptic inhibition of neurons in the latero-capsular division of the central nucleus (CeLC) of the amygdala than PL inputs, and this inhibition was impaired in an arthritis pain model. Furthermore, inhibition-excitation ratio in basolateral amygdala neurons was increased in the pain model in the IL pathway but not in the PL pathway. These results suggest that IL rather than PL controls CeLC activity, and that changes in this acute pain model occur predominantly in the IL-amygdala pathway.

Central serotonin modulates neural responses to virtual violent actions in emotion regulation networks

Disruptions in the cortico-limbic emotion regulation networks have been linked to depression, anxiety, impulsivity, and aggression. Altered transmission of the central nervous serotonin (5-HT) contributes to dysfunctions in the cognitive control of emotions. To date, studies relating to pharmaco-fMRI challenging of the 5-HT system have focused on emotion processing for facial expressions. We investigated effects of a single-dose selective 5-HT reuptake inhibitor (escitalopram) on emotion regulation during virtual violence. For this purpose, 38 male participants played a violent video game during fMRI scanning. The SSRI reduced neural responses to violent actions in right-hemispheric inferior frontal gyrus and medial prefrontal cortex encompassing the anterior cingulate cortex (ACC), but not to non-violent actions. Within the ACC, the drug effect differentiated areas with high inhibitory 5-HT1A receptor density (subgenual s25) from those with a lower density (pregenual p32, p24). This finding links functional responses during virtual violent actions with 5-HT neurotransmission in emotion regulation networks, underpinning the ecological validity of the 5-HT model in aggressive behavior. Available 5-HT receptor density data suggest that this SSRI effect is only observable when inhibitory and excitatory 5-HT receptors are balanced. The observed early functional changes may impact patient groups receiving SSRI treatment.

Trait and state anxiety is marked by increased working memory-related parietal BOLD signal

Anxiety is associated with compromised cognitive control functions, such as working memory. State and trait anxiety within the non-clinical population can be utilised to investigate potential neural markers for anxiety, which may help to elucidate potential prevention and intervention methods. Thirty-two healthy adults (20 female, 12 male), aged between 30 and 65 years, performed a 2-back task whilst fMRI BOLD signal was acquired using a 3T scanner. Mean BOLD signal was obtained in cognitive control network regions of interest of: left and right dorsolateral prefrontal cortex (DLPFC) and posterior parietal lobe (PPL), and medial prefrontal cortex (MPFC). State and trait anxiety levels were recorded. Higher overall anxiety was moderately associated with more left and right PPL BOLD signal; there was a weak relationship between anxiety and left DLPFC BOLD signal. MPFC BOLD signal and trait anxiety were moderately associated with overall 2-back task performance. These findings suggest that non-clinical anxiety affects the recruitment of cortical resources during working memory, but that anxiety does not impair performance during a 2-back task.

Neural mapping of guilt: a quantitative meta-analysis of functional imaging studies

Guilt is a self-conscious emotion associated with the negative appraisal of one's behavior. In recent years, several neuroimaging studies have investigated the neural correlates of guilt, but no meta-analyses have yet identified the most robust activation patterns. A systematic review of literature found 16 functional magnetic resonance imaging studies with whole-brain analyses meeting the inclusion criteria, for a total of 325 participants and 135 foci of activation. A meta-analysis was then conducted using activation likelihood estimation. Additionally, Meta-Analytic Connectivity Modeling (MACM) analysis was conducted to investigate the functional connectivity of significant clusters. The analysis revealed 12 significant clusters of brain activation (voxel-based FDR-corrected p < 0.05) located in the prefrontal, temporal and parietal regions, mainly in the left hemisphere. Only the left dorsal cingulate cluster survived stringent FWE correction (voxel-based p < 0.05). Secondary analyses (voxel-based FDR-corrected p < 0.05) on the 7 studies contrasting guilt with another emotional condition showed an association with clusters in the left precuneus, the anterior cingulate, the left medial frontal gyrus, the right superior frontal gyrus and the left superior temporal gyrus. MACM demonstrated that regions associated with guilt are highly interconnected. Our analysis identified a distributed neural network of left-lateralized regions associated with guilt. While voxel-based FDR-corrected results should be considered exploratory, the dorsal cingulate was robustly associated with guilt. We speculate that this network integrates cognitive and emotional processes involved in the experience of guilt, including self-representation, theory of mind, conflict monitoring and moral values. Limitations of our meta-analyses comprise the small sample size and the heterogeneity of included studies, and concerns about naturalistic validity.

The synthetic cannabinoid 5F-AMB changes the balance between excitation and inhibition of layer V pyramidal neurons in the mouse medial prefrontal cortex

RATIONALE

5F-AMB is one of the synthetic cannabinoids (SCs) designed to potentiate the ability to activate cannabinoid 1 (CB1) receptors and is abused worldwide. Although inhalation of 5F-AMB elicits serious adverse effects including impaired memory and consciousness, it is not known whether and how 5F-AMB affects the activity of pyramidal neurons in the medial prefrontal cortex (mPFC), a brain region associated with higher functions such as memory and cognition.

OBJECTIVES

In the present study, we examined the effects of 5F-AMB on mPFC layer V (L5) pyramidal neurons using in vitro whole-cell patch-clamp recordings.

RESULTS

Bath application of 5F-AMB attenuated the frequency but not the amplitude of spontaneous excitatory and inhibitory postsynaptic currents (sEPSCs and sIPSCs). The attenuating effects of 5F-AMB were abolished by the CB1 receptor antagonist AM251. 5F-AMB also attenuated the frequency of miniature EPSCs and IPSCs recorded in the presence of tetrodotoxin. Moreover, the extent of attenuating effects of 5F-AMB on stimulus-evoked EPSCs was significantly larger than that on evoked IPSCs.

CONCLUSIONS

These findings suggest that 5F-AMB attenuates both excitatory and inhibitory transmission in mPFC L5 pyramidal neurons via the activation of CB1 receptors located in presynaptic terminals. Further, the net impact of 5F-AMB on L5 pyramidal neurons is inhibition due to the change in balance between excitation and inhibition. This inhibitory effect might at least partly contribute to the expression of the adverse effects induced by 5F-AMB inhalation.

Increasing Brain-Derived Neurotrophic Factor (BDNF) in medial prefrontal cortex selectively reduces excessive drinking in ethanol dependent mice

The neurotrophin Brain-Derived Neurotrophic Factor (BDNF) has been implicated in a number of neuropsychiatric disorders, including alcohol use disorder. Studies have shown that BDNF activity in cortical regions, such as the medial prefrontal cortex (mPFC) mediates various ethanol-related behaviors. We previously reported a significant down-regulation in Bdnf mRNA in mPFC following chronic ethanol exposure compared to control mice. The present study was conducted to extend these findings by examining whether chronic ethanol treatment reduces BDNF protein expression in mPFC and whether reversing this deficit via direct injection of BDNF or viral-mediated overexpression of BDNF in mPFC alters voluntary ethanol consumption in dependent and nondependent mice. Repeated cycles of chronic intermittent ethanol (CIE) exposure was employed to model ethanol dependence, which produces robust escalation of ethanol intake. Results indicated that CIE treatment significantly increased ethanol intake and this was accompanied by a significant decrease in BDNF protein in mPFC that lasted at least 72 h after CIE exposure. In a separate study, once dependence-related increased drinking was established, bilateral infusion of BDNF (0, 0.25, 0.50 μg) into mPFC significantly decreased ethanol intake in a dose-related manner in dependent mice but did not affect moderate drinking in nondependent mice. In a third study, viral-mediated overexpression of BDNF in mPFC prevented escalation of drinking in dependent mice but did not alter intake in nondependent mice. Collectively, these results provide evidence that adaptations in cortical (mPFC) BDNF activity resulting from chronic ethanol exposure play a role in mediating excessive ethanol drinking associated with dependence.

Inactivation of prelimbic and infralimbic cortex respectively affects minimally-trained and extensively-trained goal-directed actions

Several studies have examined a role for the prelimbic cortex (PL) and infralimbic cortex (IL) in free operant behavior. The general conclusion has been that PL controls goal-directed actions (instrumental behaviors that are sensitive to reinforcer devaluation) whereas IL controls habits (instrumental behaviors that are not sensitive to reinforcer devaluation). To further examine the involvement of these regions in the expression of instrumental behavior, we first implanted male rats with bilateral guide cannulae into their PL, then trained two responses to produce a sucrose pellet reinforcer, R1 and R2, each in a distinct context. R1 received extensive training and R2 received minimal training. Rats then received lithium chloride injections either paired or unpaired with sucrose pellets in both contexts until paired rats rejected all pellets. Following acquisition, in Experiment 1, rats received either an infusion of saline or baclofen/muscimol into the PL and were tested (in extinction) on both R1 and R2. In vehicle controls, both responses were goal-directed actions, as indicated by their sensitivity to reinforcer devaluation. PL inactivation decreased expression of the minimally-trained action without affecting expression of the extensively-trained action. Experiment 2 utilized the same experimental design but with IL inactivation at test. The extensively-trained response was again a goal-directed action. However, now expression of the extensively-trained goal-directed action was suppressed by IL inactivation. The overall pattern of results suggests that the PL is involved in expression of minimally trained goal-directed behavior while the IL is involved in expression of extensively trained goal-directed behavior. This implies that the PL does not control all types of actions and the IL can control some types of actions. These results expand upon the traditional view that the PL controls action while the IL controls habit.

Contributions of medial prefrontal cortex to decision making involving risk of punishment

The prefrontal cortex (PFC) plays an important role in several forms of cost-benefit decision making. Its contributions to decision making under risk of explicit punishment, however, are not well understood. A rat model was used to investigate the role of the medial PFC (mPFC) and its monoaminergic innervation in a Risky Decision-making Task (RDT), in which rats chose between a small, "safe" food reward and a large, "risky" food reward accompanied by varying probabilities of mild footshock punishment. Inactivation of mPFC increased choice of the large, risky reward when the punishment probability increased across the session ("ascending RDT"), but decreased choice of the large, risky reward when the punishment probability decreased across the session ("descending RDT"). In contrast, enhancement of monoamine availability via intra-mPFC amphetamine reduced choice of the large, risky reward only in the descending RDT. Systemic administration of amphetamine reduced choice of the large, risky reward in both the ascending and descending RDT; however, this reduction was not attenuated by concurrent mPFC inactivation, indicating that mPFC is not a critical locus of amphetamine's effects on risk taking. These findings suggest that mPFC plays an important role in adapting choice behavior in response to shifting risk contingencies, but not necessarily in risk-taking behavior per se.

Neural Correlates of Compulsive Alcohol Seeking in Heavy Drinkers

BACKGROUND

Compulsive alcohol use, the tendency to continue alcohol seeking and taking despite negative consequences, is a hallmark of alcohol use disorder. Preclinical rodent studies have suggested a role for the medial prefrontal cortex, anterior insula, and nucleus accumbens in compulsive alcohol seeking. It is presently unknown whether these findings translate to humans. We used a novel functional magnetic resonance imaging paradigm and tested the hypothesis that heavy drinkers would compulsively seek alcohol despite the risk of an aversive consequence, and that this behavior would be associated with the activity of frontostriatal circuitry.

METHODS

Non-treatment-seeking heavy and light drinkers (n = 21 per group) completed a functional magnetic resonance imaging paradigm in which they could earn alcohol or food points at various threat levels (i.e., various probabilities of incurring an aversive consequence). Brain function was evaluated when individuals had the opportunity to earn reward points at the risk of an aversive consequence, an electric shock on the wrist.

RESULTS

Compared with light drinkers, heavy drinkers attempted to earn more aversion-paired alcohol points. Frontostriatal circuitry, including the medial prefrontal cortex, anterior insula, and striatum, was more active in this group when viewing threat-predictive alcohol cues. Heavy drinkers had increased connectivity between the anterior insula and the nucleus accumbens. Greater connectivity was associated with more attempts to earn aversion-paired alcohol points and self-reported compulsive alcohol use scores.

CONCLUSIONS

Higher activation of frontostriatal circuitry in heavy drinkers may contribute to compulsive alcohol seeking. Treatments that disrupt this circuitry may result in a decrease in compulsive alcohol use.

Effect of electrical stimulation of the infralimbic and prelimbic cortices on anxiolytic-like behavior of rats during the elevated plus-maze test, with particular reference to multiunit recording of the behavior-associated neural activity

Fear and anxiety affect the activities of daily living and require concerted management, such as coping strategies, to preserve quality of life. The infralimbic (IL) and prelimbic (PL) medial prefrontal cortices have been implicated in the regulation of fear- and anxiety-like behavior, but their roles in overcoming fear- and anxiety-like behavior remain unknown. We investigated the anxiolytic-like effects of electrical stimulation of the IL and PL cortices in rats during the elevated plus-maze test. IL stimulation led to a significantly higher percentage of time spent and entries in the open arms, whereas PL stimulation did not have any significant behavioral effects. Subsequently, we recorded multiunit activity from the IL and PL cortices in rats using a wireless telemetry device, to determine whether activation of the IL occurs when rats enter the open arms in the elevated plus-maze test. The firing rate of IL neurons increased 1-3 s prior to entry from the closed arm to the open arm, whereas there were no corresponding changes in the firing rate of PL neurons. Taken together, the present findings suggest that the IL plays a key role in exerting active action to overcome anxiety-like behavior.

Effects of transcranial direct current stimulation for treating depression: A modeling study

BACKGROUND

Transcranial direct current stimulation (tDCS) above the left dorsolateral prefrontal cortex (lDLPFC) has been widely used to improve symptoms of major depressive disorder (MDD). However, the effects of different stimulation protocols in the entire frontal lobe have not been investigated in a large sample including patient data.

METHODS

We used 38 head models created from structural magnetic resonance imaging data of 19 healthy adults and 19 MDD patients and applied computational modeling to simulate the spatial distribution of tDCS-induced electric fields (EFs) in 20 frontal regions. We evaluated effects of seven bipolar and two multi-electrode 4 × 1 tDCS protocols.

RESULTS

For bipolar montages, EFs were of comparable strength in the lDLPFC and in the medial prefrontal cortex (MPFC). Depending on stimulation parameters, EF cortical maps varied to a considerable degree, but were found to be similar in controls and patients. 4 × 1 montages produced more localized, albeit weaker effects.

LIMITATIONS

White matter anisotropy was not modeled. The relationship between EF strength and clinical response to tDCS could not be evaluated.

CONCLUSIONS

In addition to lDLPFC stimulation, excitability changes in the MPFC should also be considered as a potential mechanism underlying clinical efficacy of bipolar montages. MDD-associated anatomical variations are not likely to substantially influence current flow. Individual modeling of tDCS protocols can substantially improve cortical targeting. We make recommendations for future research to explicitly test the contribution of lDLPFC vs. MPFC stimulation to therapeutic outcomes of tDCS in this disorder.

Chronic traffic noise stress accelerates brain impairment and cognitive decline in mice

Although traffic noise exposure is a well-known environmental pollutant whose negative health effect has been discussed in different aspects of the human life, only a few animal studies have tackled this issue as a cohort study, which is not feasible to be addressed in human studies. In addition to the deleterious impact of the daytime noise on well-being, chronic nocturnal noise can also disturb sleep and affects physical and mental health, but to date, little research has examined the neurobiological effects of light/dark cycles of traffic noise exposure. We investigated the effects of light/dark cycles and sex on the impact of chronic traffic noise exposure on mouse brain structure-function. The mice were randomly assigned to either one of two stress conditions or a control condition. Animals were exposed to traffic noise on either the light-cycle (LC) or dark-cycle (DC) for 30 days. Traffic noise exposure caused the hypothalamic-pituitary-adrenal (HPA) axis hyperactivity, anxiety-like behavior, impairments in learning and memory, dysfunction in balance and motor coordination, and a reduction in variety of brain measures including a brain volume, medial prefrontal cortex (mPFC) area, cortical thickness, hippocampal volume, amygdala area, and the neural density in mPFC and dentate gyrus. All behavioral and brain measures revealed adverse effects of the chronic noise stress irrespective of the LC/DC exposure or sex. Our findings were a re-emphasis on the significance of noise prevention and mitigation strategies for public health.

Representation of actions and outcomes in medial prefrontal cortex during delayed conditional decision-making: Population analyses of single neuron activity

Background

To respond adaptively in a dynamic environment, it is important for organisms to utilise information about recent events to decide between response options.

Methods

To examine the role of medial prefrontal cortex in adaptive decision-making, we recorded single neuron activity in rats performing a dynamic delayed non-matching to position task.

Results

We recorded activity from 1335 isolated neurons, 458 (34%) with criterion event-related activity, of which 431 (94%) exhibited 1 of 10 distinct excitatory response types: five at different times relative to delivery (or lack) of reinforcement following sample and choice responses and five correlated with movements or lever press actions that occurred multiple times in each trial. Normalised population averages revealed a precisely timed cascade of population responses representing the temporal organisation behavioural events that constitute delayed non-matching to position trials. Firing field analyses identified a subset of neurons with restricted spatial fields: responding to the conjunction of a behavioural event with a specific location. Anatomical analyses showed considerable overlap in the distribution of different response types in medial prefrontal cortex with a significant trend for dorsal areas to contain more neurons with action-related activity and ventral areas more responses related to action outcomes.

Conclusion

These results indicate that medial prefrontal cortex contains discrete populations of neurons that represent the temporal organisation of actions and outcomes during delayed non-matching to position trials. They support the hypothesis that medial prefrontal cortex promotes flexible control of complex behaviours by action-outcome contingencies.

Medial prefrontal cortex TRPV1 and CB1 receptors modulate cardiac baroreflex activity by regulating the NMDA receptor/nitric oxide pathway

The ventral medial prefrontal cortex (vMPFC) facilitates the cardiac baroreflex response through N-methyl-D-aspartate (NMDA) receptor activation and nitric oxide (NO) formation by neuronal NO synthase (nNOS) and soluble guanylate cyclase (sGC) triggering. Glutamatergic transmission is modulated by the cannabinoid receptor type 1 (CB₁) and transient receptor potential vanilloid type 1 (TRPV₁) receptors, which may inhibit or stimulate glutamate release in the brain, respectively. Interestingly, vMPFC CB₁ receptors decrease cardiac baroreflex responses, while TRPV₁ channels facilitate them. Therefore, the hypothesis of the present study is that the vMPFC NMDA/NO pathway is regulated by both CB₁ and TRPV₁ receptors in the modulation of cardiac baroreflex activity. In order to test this assumption, we used male Wistar rats that had stainless steel guide cannulae bilaterally implanted in the vMPFC. Subsequently, a catheter was inserted into the femoral artery, for cardiovascular recordings, and into the femoral vein for assessing baroreflex activation. The increase in tachycardic and bradycardic responses observed after the microinjection of a CB₁ receptors antagonist into the vMPFC was prevented by an NMDA antagonist as well as by the nNOS and sGC inhibition. NO extracellular scavenging also abolished these responses. These same pharmacological manipulations inhibited cardiac reflex enhancement induced by TRPV₁ agonist injection into the area. Based on these results, we conclude that vMPFC CB₁ and TRPV₁ receptors inhibit or facilitate the cardiac baroreflex activity by stimulating or blocking the NMDA activation and NO synthesis.

Binge ethanol effects on prefrontal cortex neurons, spatial working memory and task-induced neuronal activation in male and female rats

Excessive alcohol intake is associated with a multitude of health risks, especially for women. Recent studies in animal models indicate that the female brain is more negatively affected by alcohol, compared to the male brain. Among other regions, excessive alcohol consumption damages the frontal cortex, an area important for many functions and decision making of daily life. The objective of the present study was to determine whether the medial prefrontal cortex (mPFC) in female rats is selectively vulnerable to alcohol-induced damage. In humans, loss of prefrontal grey matter resulting from heavy alcohol consumption has been documented, however this volume loss is not necessarily due to a decrease in the number of neurons. We therefore quantified both number and nuclear volume of mPFC neurons following binge alcohol, as well as performance and neuronal activation during a prefrontal-dependent behavioral task. Adult male and female Long-Evans rats were assigned to binge or control groups and exposed to ethanol using a well-established 4-day model of alcohol-induced neurodegeneration. Both males and females had significantly smaller average neuronal nuclei volumes than their respective control groups immediately following alcohol binge, but neither sex showed a decrease in neuron number. Binged rats of both sexes initially showed spatial working memory deficits. Although they eventually achieved control performance, binged rats of both sexes showed increased c-Fos labeling in the mPFC during rewarded alternation, suggesting decreased neural efficiency. Overall, our results substantiate prior evidence indicating that the frontal cortex is vulnerable to alcohol, but also indicate that sex-specific vulnerability to alcohol may be brain region-dependent.

Is major depression a cognitive disorder?

This is a review of cognitive abilities in major depression, which is associated with attention problems, memory deficit and wide impairment in executive functions. Depressed patients show two major cognitive biases: excessive processing of negatively valenced emotional stimuli; and increased self-focus. Both of these biases help to facilitate the integration of negative self-related information in depressed patients and to maintain their negative mood. Brain imaging studies suggest that this cognitive impairment is characterized by abnormal cooperation between the cognitive and limbic networks involved in cognitive control and self-referential processing. In general, depression is a disorder of multiple networks with emotional, cognitive and emotional symptoms. Among these symptoms, cognition is a major determinant of functional and social outcomes.

Downregulation of 5-hydroxytryptamine7 receptor in the medial prefrontal cortex ameliorates impulsive actions in animal models of schizophrenia

R mRNA in the mPFC was significantly decreased to 5-Hydroxytryptamine₇ (5-HT₇) receptors in the medial prefrontal cortex (mPFC) play a critical role in complex cognitive impairment in schizophrenia. The mouse model of schizophrenia was established through the neonatal administration of phencyclidine (nPCP). Recombinant adeno-associated virus-mediated gene knockdown was used to investigate the role of mPFC 5-HT₇ receptor in the schizophrenia-like symptoms in mice. Under baseline conditions in the 5-choice serial reaction time task (5-CSRTT), nPCP produced a significant attentional impairment that was exacerbated when mice were tested under LITI. Premature and perseverative responding in nPCP mice were both increased, thus suggesting deficits in inhibitory response control. The deficits in attentional performance and premature responding of nPCP mice were improved or fully rescued by 5-HT₇ receptor downregulation under heavy perceptual load. Downregulation of the 5-HT₇ receptor in the mPFC ameliorated spatial working memory and had no effects on nPCP-induced impairments in recognition memory and MA-induced hyperlocomotion. These results suggest that 5-HT₇ receptor is involved in the cognitive outcomes of schizophrenia-like symptoms similar to humans. Downregulation of the 5-HT₇ receptor in the mPFC exert complex effects in a mouse model of schizophrenia and may be of benefit in treating schizophrenia-related impulsive actions.

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.

Interaction of basolateral amygdala, ventral hippocampus and medial prefrontal cortex regulates the consolidation and extinction of social fear

Background

Following a social defeat, the balanced establishment and extinction of aversive information is a beneficial strategy for individual survival. Abnormal establishment or extinction is implicated in the development of mental disorders. This study investigated the time course of the establishment and extinction of aversive information from acute social defeat and the temporal responsiveness of the basolateral amygdala (BLA), ventral hippocampus (vHIP) and medial prefrontal cortex (mPFC) in this process.

Methods

Mouse models of acute social defeat were established by using the resident–intruder paradigm. To evaluate the engram of social defeat, the intruder mice were placed into the novel context at designated time to test the social behavior. Furthermore, responses of BLA, vHIP and mPFC were investigated by analyzing the expression of immediate early genes, such as zif268, arc, and c-fos.

Results

The results showed after an aggressive attack, aversive memory was maintained for approximately 7 days before gradually diminishing. The establishment and maintenance of aversive stimulation were consistently accompanied by BLA activity. By contrast, vHIP and mPFC response was inhibited from this process. Additionally, injecting muscimol (Mus), a GABA receptor agonist, into the BLA alleviated the freezing behavior and social fear and avoidance. Simultaneously, Mus treatment decreased the zif268 and arc expression in BLA, but it increased their expression in vHIP.

Conclusion

Our data support and extend earlier findings that implicate BLA, vHIP and mPFC in social defeat. The time courses of the establishment and extinction of social defeat are particularly consistent with the contrasting BLA and vHIP responses involved in this process.

Electronic supplementary material

The online version of this article (10.1186/s12993-018-0139-6) contains supplementary material, which is available to authorized users.

Transcranial direct current stimulation of the medial prefrontal cortex modulates the propensity to help in costly helping behavior

Social decision-making engages traditional decision-making processes (e.g. valuation), as well as social cognition processes (e.g. inferring the affective and mental states of another person). Neuroimaging and neuro-stimulation studies have suggested the involvement of the medial prefrontal cortex (mPFC) in a variety of social decision-making tasks. Yet no study has investigated the effect of the cortical excitability of mPFC in the decision-making of costly helping behavior. Here, we used tDCS to demonstrate the causal relationship between the cortical excitability of mPFC and costly helping decision-making. Subjects assigned to the anodal, cathodal and sham groups were required to decide whether they would like to cost their own money to relieve another subject (a confederate actually) from painful electrical shocks with a certain probability of success. Results showed that the subjects receiving anodal stimulation acted more prosaically than the subjects receiving cathodal stimulation. And this effect was only significant when the probability of success was high. We proposed that tDCS induced modulation of the cortical excitability, targeting the mPFC, can affect the prosocial propensity in costly helping behavior, and the possible underlying mechanisms were discussed.

Deep brain stimulation and fluoxetine exert different long-term changes in the serotonergic system

Both selective serotonin reuptake inhibitors (SSRIs) and ventromedial prefrontal cortex (vmPFC) deep brain stimulation (DBS) modulate serotonergic activity. We compared the acute (1 day) and long-term (12 days) effects of vmPFC stimulation and fluoxetine on serotonin (5-HT) release and receptor expression in rats. Samples to measure serotonin levels were collected from the hippocampus using microdialysis. Serotonin transporter (SERT), 5-HT_1A and 5-HT_1B mRNA were measured using in situ hybridization. [³H]8-OH-DPAT and [¹²⁵I]cyanopindolol autoradiography were used to measure 5-HT_1A and 5-HT_1B binding. Our results show that after fluoxetine injections serotonin levels were approximately 150% higher than at baseline. Twelve days later, pre-injection 5-HT extracellular concentration was substantially higher than on day 1. In contrast, serotonin levels following DBS were only 50% higher than at baseline. While pre-stimulation 5-HT on day 12 was significantly higher than on treatment day 1, no stimulation-induced 5-HT peak was recorded. SERT expression in the dorsal raphe was increased after acute fluoxetine and decreased following a single day of DBS. Neither fluoxetine nor DBS administered acutely substantially changed 5-HT_1A or 5-HT_1B binding. Chronic fluoxetine treatment, however, was associated with a decrease in [³H]8-OH-DPAT prefrontal cortex and hippocampus expression. In contrast, chronic DBS induced a significant increase in [¹²⁵I]cyanopindolol binding in the prefrontal cortex, globus pallidus, substantia nigra and raphe nuclei. mRNA expression of 5-HT_1A and 5-HT_1B in raphe nuclei was not altered by either treatment. These results suggest that fluoxetine and DBS modulate activity of the serotonergic system but likely exert their effects through different mechanisms.

Hippocampal network oscillations as mediators of behavioural metaplasticity: Insights from emotional learning

Behavioural metaplasticity is evident in experience-dependent changes of network activity patterns in neuronal circuits that connect the hippocampus, amygdala and medial prefrontal cortex. These limbic regions are key structures of a brain-wide neural network that translates emotionally salient events into persistent and vivid memories. Communication in this network by-and-large depends on behavioural state-dependent rhythmic network activity patterns that are typically generated and/or relayed via the hippocampus. In fact, specific hippocampal network oscillations have been implicated to the acquisition, consolidation and retrieval, as well as the reconsolidation and extinction of emotional memories. The hippocampal circuits that contribute to these network activities, at the same time, are subject to both Hebbian and non-Hebbian forms of plasticity during memory formation. Further, it has become evident that adaptive changes in the hippocampus-dependent network activity patterns provide an important means of adjusting synaptic plasticity. We here summarise our current knowledge on how these processes in the hippocampus in interaction with amygdala and medial prefrontal cortex mediate the formation and persistence of emotional memories.

Morphological and functional evidence of increased excitatory signaling in the prelimbic cortex during ethanol withdrawal

Excessive alcohol consumption in humans induces deficits in decision making and emotional processing, which indicates a dysfunction of the prefrontal cortex (PFC). The present study aimed to determine the impact of chronic intermittent ethanol (CIE) inhalation on mouse medial PFC pyramidal neurons. Data were collected 6-8 days into withdrawal from 7 weeks of CIE exposure, a time point when mice exhibit behavioral symptoms of withdrawal. We found that spine maturity in prelimbic (PL) layer 2/3 neurons was increased, while dendritic spines in PL layer 5 neurons or infralimbic (IL) neurons were not affected. Corroborating these morphological observations, CIE enhanced glutamatergic transmission in PL layer 2/3 pyramidal neurons, but not IL layer 2/3 neurons. Contrary to our predictions, these cellular alterations were associated with improved, rather than impaired, performance in reversal learning and strategy switching tasks in the Barnes maze at an earlier stage of chronic ethanol exposure (5-7 days withdrawal from 3 to 4 weeks of CIE), which could result from the anxiety-like behavior associated with ethanol withdrawal. Altogether, this study adds to a growing body of literature indicating that glutamatergic activity in the PFC is upregulated following chronic ethanol exposure, and identifies PL layer 2/3 pyramidal neurons as a sensitive target of synaptic remodeling. It also indicates that the Barnes maze is not suitable to detect deficits in cognitive flexibility in CIE-withdrawn mice.

Strategic neuronal encoding in medial prefrontal cortex of spatial working memory in the T-maze

Strategic neuronal encoding in the medial prefrontal cortex (mPFC) of the rat was correlated with spatial working memory (sWM) assessed by behavior in the T-maze. Neurons increased their firing rate around choice, with the increase largely occurring before choice as a prospective encode of behavior. This could be classified as sensitive-to-spatial information or sensitive-to-choice outcome. The sensitivity-to-spatial choice was defined by distinct firing rate changes before left- or right-choice. The percentage of left-choice sensitive neurons was not different from the percentage of right-choice sensitive neurons. There was also location-related neuronal activity in which neurons fired at distinct rates when rats were in a left- or right-location. More neurons were sensitive to left-location, as most of them were recorded from rats preferring to enter the right-location. The sensitivity to outcome was defined by a distinct firing rate around correct or error choice. Significantly more neurons were sensitive to error outcome, and, among these, more preferred to encode prospectively, increasing firing in advance of an error outcome. Similar to single neuron activity, the mPFC enhanced its neuronal network as measured by the oscillation of local field potential. The maximum power of oscillation was around choice, and occurred slightly earlier before error versus before correct outcome. Thus, sWM modulation in the mPFC includes not only spatial, but also outcome-related inputs, and neuronal ensembles monitor behavioral outcome to make strategic adjustments ensuring successful task performance.

Adverse childhood experiences are associated with self-regulation and the magnitude of the error-related negativity difference

Trauma and stress, like that which occurs as a result of adverse childhood experiences (ACEs), can change brain structure and function, especially in medial prefrontal and hippocampal areas, and can impact self-regulatory skill. The error-related negativity (ERN) is a medial frontal negative event-related potential (ERP) component that is more negative when a participant makes an erroneous versus correct response. We investigated the association of ACEs to adolescents' ERN and self-regulation. Forty-three 12-15 year olds performed a flanker task while EEG data were recorded. We found an interaction between trial type (correct vs incorrect) and group (low, medium and high trauma groups) on the ERN. The high-trauma group showed a larger Error-Correct difference than the low- and medium-trauma groups. This appeared as trend correlations between overall trauma exposure as a continuous variable and ERN-related variables. Trauma exposure was associated with reduced self-regulatory capacity, and accounting for self-regulation decreased the associations between trauma and the ERN, suggestive of a protective effect for self-regulation.

Resolvin E1/E2 ameliorate lipopolysaccharide-induced depression-like behaviors via ChemR23

RATIONALE

Resolvins are bioactive lipid mediators that are generated from docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). We recently demonstrated that the DHA-derived resolvins D1 and D2 exert antidepressant effects. However, whether the EPA-derived resolvins E1 (RvE1) and E2 (RvE2) produce antidepressant effects is not clear.

OBJECTIVES

We examined the antidepressant effects of RvE1/RvE2 in a murine lipopolysaccharide (LPS)-induced depression model using the tail suspension and forced swim tests. RvE1/RvE2 reportedly possesses both chemerin receptor ChemR23 agonistic activity and leukotriene B₄ receptor BLT1 antagonistic activity. Therefore, we investigated the receptor involved in its antidepressant effects. We also examined the roles of the mammalian target of rapamycin complex 1 (mTORC1) in the antidepressant effect of RvE1 as well as the effects of RvE1 infusions into the medial prefrontal cortex (mPFC) and hippocampal dentate gyrus (DG) on LPS-induced depression-like behaviors.

RESULTS

Intracerebroventricular infusions of RvE1 (1 ng)/RvE2 (10 ng) produced significant antidepressant effects. An intracerebroventricular infusion of chemerin (500 ng), but not U75302 (a BLT1 antagonist; 10 or 50 ng), produced antidepressant effects. Intraperitoneal rapamycin (an mTORC1 inhibitor; 10 mg/kg) blocked the antidepressant effect of intracerebroventricular RvE1. Bilateral intra-mPFC and intra-DG infusions of RvE1 (50 pg/side) exerted antidepressant effects.

CONCLUSIONS

The results of this study demonstrate that (1) RvE1/RvE2 produce antidepressant effects likely via ChemR23, (2) mTORC1 signaling mediates the antidepressant effect of RvE1, and (3) mPFC and DG are the key brain regions involved in these actions. RvE1/RvE2 and their receptors may be promising targets for the development of novel antidepressants.

Neural activity during traumatic film viewing is linked to endogenous estradiol and hormonal contraception

Women are at higher risk for Posttraumatic Stress Disorder (PTSD) and recent research has highlighted a modulating role of female sex hormones for cognitive and emotional processes potentially underlying PTSD symptoms. However, studies combining fMRI recordings of brain activity during trauma film viewing with assessment of female sex hormones are missing. The trauma film paradigm - a widely used experimental analogue for trauma exposure - confronts healthy participants with traumatic film clips and thus allows studying peritraumatic processing under laboratory conditions. Following this paradigm, the current fMRI study examined the role of endogenous estradiol and synthetic sex hormones for the neural processing of traumatic (i.e., depicting interpersonal violence) vs. neutral films in 53 healthy women (mean age 22.3 years; 23 using hormonal contraception, HC). As predicted, traumatic films strongly activated areas of the fear processing network, such as amygdala, insula, and dorsal anterior cingulate cortex. Estradiol levels in women not using HC were positively correlated with ventromedial prefrontal activity. Furthermore, women using HC as compared to women without HC demonstrated heightened insula and dorsal anterior cingulate cortex activity during traumatic film viewing. These experimental results highlight the effects of both gonadal hormone status and HC intake on peritraumatic processing in neural regions relevant for emotion generation and regulation that have been found to be abnormal in PTSD.

Differential expression of the immediate early genes c-Fos, Arc, Egr-1, and Npas4 during long-term memory formation in the context preexposure facilitation effect (CPFE)

The context preexposure facilitation effect (CPFE) is a contextual fear conditioning paradigm in which learning about the context, acquiring the context-shock association, and retrieving/expressing contextual fear are temporally dissociated into three distinct phases (context preexposure, immediate-shock training, and retention). The current study examined changes in the expression of plasticity-associated immediate early genes (IEGs) during context and contextual fear memory formation on the preexposure and training days of the CPFE, respectively. Using adolescent Long-Evans rats, preexposure and training day expression of the IEGs c-Fos, Arc, Egr-1, and Npas4 in the medial prefrontal cortex (mPFC), dorsal hippocampus (dHPC), and basolateral amygdala (BLA) was analyzed using qPCR as an extension of previous studies from our lab examining Egr-1 via in situ hybridization (Asok, Schreiber, Jablonski, Rosen, & Stanton, 2013; Schreiber, Asok, Jablonski, Rosen, & Stanton, 2014). In Expt. 1, context preexposure induced expression of c-Fos, Arc, Egr-1 and Npas4 significantly above that of home-cage (HC) controls in all three regions. In Expt. 2, immediate-shock was followed by a post-shock freezing test, resulting in increased mPFC c-Fos expression in a group preexposed to the training context but not a control group preexposed to an alternate context, indicating expression related to associative learning. This was not seen with other IEGs in mPFC or with any IEG in dHPC or BLA. Finally, when the post-shock freezing test was omitted in Expt. 3, training-related increases were observed in prefrontal c-Fos, Arc, Egr-1, and Npas4, hippocampal c-Fos, and amygdalar Egr-1 expression. These results indicate that context exposure in a post-shock freezing test re-engages IEG expression that may obscure associatively-induced expression during contextual fear conditioning. Additionally, these studies suggest a key role for long-term synaptic plasticity in the mPFC in supporting the CPFE.

Differential response of hippocampal and prefrontal oscillations to systemic LPS application

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1 mg/kg LPS i.p. injection robustly suppresses theta frequency in hippocampus.

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LPS administration augments delta frequency in hippocampus but not mPFC.

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LPS injection triggers hippocampal spike-wave discharges.

The early electrophysiological phenomena linked to systemic inflammation are largely underexplored. We developed here local field analyses to detect prodromal oscillatory abnormalities. We identified early band-specific patterns in local field potential recorded from freely-moving rats injected intraperitoneally with lipopolysaccharide (LPS, 1 mg/kg). Theta frequency was significantly reduced and this effect was not related to the decreased locomotion of the animal. Furthermore, LPS-induced alterations show a region-specific response when compared between the hippocampal region and medial prefrontal cortex. Delta mean frequency increased in the hippocampal region but not in the prefrontal cortex. We explored also the hypothesis that systemic inflammation increases the propensity of abnormally synchronized brain activity. Our data indicate that the LPS-evoked alteration of delta and theta frequency parameters reflects the formation of abnormal synchronization in similar frequency ranges. The onset of abnormal brain activity was indicated by spike-wave discharges in the range of 1–10 Hz with three main frequency domains. Importantly, the occurrence of spike-wave discharges was observed in the hippocampus but not in the cortex. In summary, the hippocampal theta rhythm is an accurate indicator of the oscillatory changes evoked by LPS application. The findings offer clear patterns of altered brain function that will facilitate mechanistic investigations of brain dysfunction and delirium occurring during sepsis.

Memory retrieval in addiction: a role for miR-105-mediated regulation of D1 receptors in mPFC neurons projecting to the basolateral amygdala

Background

Drug addiction is a chronic brain disorder characterized by the compulsive use of drugs. The study of chronic morphine-induced adaptation in the brain and its functional significance is of importance to understand the mechanism of morphine addiction. Previous studies have found a number of chronic morphine-induced adaptive changes at molecular levels in the brain. A study from our lab showed that chronic morphine-induced increases in the expression of D1 receptors at presynaptic terminals coming from other structures to the basolateral amygdala (BLA) played an important role in environmental cue-induced retrieval of morphine withdrawal memory. However, the neurocircuitry where the increased D1 receptors are located and how chronic morphine increases D1 receptor expression in specific neurocircuits remain to be elucidated.

Results

Our results show that chronic morphine induces a persistent increase in D1 receptor expression in glutamatergic terminals of projection neurons from the medial prefrontal cortex (mPFC) to the BLA, but has no influence on D1 receptor expression in projection neurons from the hippocampus or the thalamus to the BLA. This adaptation to chronic morphine is mediated by reduced expression of miR-105 in the mPFC, which results in enhanced D1 receptor expression in glutamatergic terminals of projection neurons from the mPFC to the BLA. Ex vivo optogenetic experiments show that a chronic morphine-induced increase in D1 receptor expression in glutamatergic terminals of projection neurons from the mPFC to the BLA results in sensitization of the effect of D1 receptor agonist on presynaptic glutamate release. mPFC to BLA projection neurons are activated by withdrawal-associated environmental cues in morphine-withdrawal rats, and overexpression of miR-105 in the mPFC leads to reduced D1 receptor induction in response to chronic morphine in glutamatergic terminals of the projection neurons from the mPFC to the BLA, and a reduction in place aversion conditioned by morphine withdrawal.

Conclusions

These results suggest that chronic morphine use induces a persistent increase in D1 receptors in glutamatergic terminals of projection neurons from the mPFC to the BLA via downregulation of miR-105 in the mPFC, and that these adaptive changes contribute to environmental cue-induced retrieval of morphine withdrawal memory.

Electronic supplementary material

The online version of this article (doi:10.1186/s12915-017-0467-2) contains supplementary material, which is available to authorized users.

Adolescent cocaine exposure induces prolonged synaptic modifications in medial prefrontal cortex of adult rats

Substance used during adolescent period increases the risk of psychiatric disorders in later life, but the underlying neural mechanisms remain unclear. We hypothesize that synaptic remodeling and changes of homeostasis in the medial prefrontal cortex (mPFC) following adolescent cocaine exposure may last for a long time, and these modifications may contribute to behavioral deficiencies in adulthood. To address this hypothesis, rats were exposed to cocaine hydrochloride from postnatal day 28 (P28) to P42. When reared to adulthood, rats were subjected to behavioral tests. On P75 and P76, cocaine-experienced rats exhibited increased locomotive and anxiety-like behaviors, as well as impaired non-selective attention. In the cocaine-experienced rats, both levels of synapse-related proteins (synapsin I and PSD-95) and density of synapse and dendrite spine in mPFC were significantly decreased when compared to controls. Unexpected, the expression of molecules related to oxidative stress, inflammation and apoptosis showed no significant changes in mPFC following adolescent cocaine exposure. These findings suggested that adolescent exposure to cocaine induce long-term modification on synapses in mPFC, which might contribute to long-term behavioral outcomes in adulthood.

Resting state connectivity mediates the relationship between collectivism and social cognition

Humans are intrinsically social beings and it is natural that self-processing is associated with social cognition. The degree to which the self is perceived as a part of social environment is modulated by cultural stereotypes, such as collectivism and individualism. Here, we tested the hypothesis that individuals who endorse collectivist values would spontaneously think more about their relationships with other people and this association would be mediated by connectivity between the medial prefrontal cortex (MPFC) and the rest of the brain. Connectivity was evaluated based on resting state EEG data using the recently developed methods, which combine beamformer spatial filtering with seed based connectivity estimation. The formal mediation analysis revealed that collectivism is associated with an enhanced connectivity of MPFC with a set of cortical regions that are frequently co-activated in moral reasoning, empathy, and theory of mind tasks and with diminished connectivity with the precuneus\posterior cingulate cortex, which is involved in self-centered cognition. The relationship between collectivism and social cognition was mediated by MPFC connectivity with the left middle temporal gyrus implying that in participants with collectivistic attitude, thinking about relationships with other people may be associated with semantic memory retrieval and reasoning on moral issues and others' intentions.

Pannexin-1 channel dysfunction in the medial prefrontal cortex mediates depressive-like behaviors induced by chronic social defeat stress and administration of mefloquine in mice

Mefloquine (MFQ) is widely used for the treatment of malaria clinically. Apart from antimalarial effect, psychiatric side effects such as depression and anxiety of MFQ have been reported. Interestingly, MFQ is also known as a broad-spectrum pannexin-1 (Panx1) inhibitor. Panx1 is a new gap junction channel in the brain which mediates efflux of adenosine triphosphate (ATP). Although exogenous ATP has been known to produce a potential antidepressant-like effect, little is known about the role of Panx1 in pathophysiology of depression, especially the depression induced by administration of MFQ. Here, we used the chronic social defeat stress (CSDS) model and found a decrease in the expression and function of Panx1 in the medial prefrontal cortex (mPFC) of susceptible mice. Furthermore, pharmacological blockade of Panx1 in the mPFC with carbenoxolone (CBX) (100 mM) or ¹⁰Panx (100 μM) was sufficient to induce depressive-like behaviors and increase vulnerability to stress in mice, which were prevented by preconditioning with ATP (25 μM). Finally, systemic and intral-mPFC injection of MFQ both inhibited the activity of Panx1 and induced depressive-like and anxiety behaviors in mice with sub-threshold social defeat stress. Indeed, the behavioral abnormalities induced by MFQ were prevented by preconditioning with ATP in the mPFC. In conclusion, our study demonstrates a role of the Panx1 channel in chronic stress and MFQ-induced depressive-like and anxiety behaviors, which may provide a novel molecular mechanism for psychiatric side effects of MFQ.

GABAergic interneurons: The orchestra or the conductor in fear learning and memory?

Fear conditioning is a form of associative learning that is fundamental to survival and involves potentiation of activity in excitatory projection neurons (PNs). Current models stipulate that the mechanisms underlying this process involve plasticity of PN synapses, which exhibit strengthening in response to fear conditioning. However, excitatory PNs are extensively modulated by a diverse array of GABAergic interneurons whose contributions to acquisition, storage, and expression of fear memory remain poorly understood. Here we review emerging evidence that genetically-defined interneurons play important subtype-specific roles in processing of fear-related stimuli and that these dynamics shape PN firing through both inhibition and disinhibition. Furthermore, interneurons exhibit structural, molecular, and electrophysiological evidence of fear learning-induced synaptic plasticity. These studies warrant discarding the notion of interneurons as passive bystanders in long-term memory.