Enhanced excitability in the infralimbic cortex produces anxiety-like behaviors

Involvement of the serotonergic, GABAergic and glutamatergic systems of the rostral anterior cingulate cortex in the trait and state anxiety of adult male Wistar rats

Despite significant advancements to understand of the neural circuitry involved in anxiety, the neurobiology of trait anxiety remains unclear. The rostral anterior cingulate cortex (rACC) and various pathways have been implicated in its regulation, making it a key to trait anxiety. The present study aimed to investigate the role of these neurotransmitter systems in the rACC in trait anxiety. Since trait anxiety is known to modulate state anxiety, we further investigated this relationship. Specifically, in Experiment I, we used animals with high trait anxiety; in Experiment II, we used animals with low trait anxiety; and in Experiment III, we used animals with medium trait anxiety. Before each behavioral assessment, drugs that either increased or decreased serotonergic (Fluoxetine or WAY-100635), GABAergic (Muscimol or Bicuculline), and glutamatergic (NMDA or Ketamine) neurotransmission in the rACC were administered, along with their respective controls. Additionally, in Experiment IV, all animals from the previous experiments were subjected to the Elevated Plus Maze (EPM) and Hole board (HB) test and evaluated without taking into account their trait anxiety levels. The results of the present study showed that, in Exp I, the modulation of the serotonergic, GABAergic and glutamatergic systems in the rACC decreased trait anxiety in highly anxious rats, while by submitting the animals to HB, the administration of fluoxetine increased state anxiety. In Exp II, the modulation of all systems increased trait anxiety in rats with low trait anxiety, whereas, in HB, state anxiety levels were increased with the administration of NMDA. In Exp III, only the modulation of the glutamatergic system, with NMDA, increased both trait and state anxiety levels. However, none of the evaluated neurotransmitter systems altered the state anxiety modeled in the EPM. Overall, the results of the present study provide new insights into the role of the neurotransmitter systems in the rACC in the regulation of trait anxiety and state anxiety.

The Medial Prefrontal Cortex-Basolateral Amygdala Circuit Mediates Anxiety in Shank3 InsG3680 Knock-in Mice

Anxiety disorder is a major symptom of autism spectrum disorder (ASD) with a comorbidity rate of ~40%. However, the neural mechanisms of the emergence of anxiety in ASD remain unclear. In our study, we found that hyperactivity of basolateral amygdala (BLA) pyramidal neurons (PNs) in Shank3 InsG3680 knock-in (InsG3680+/+) mice is involved in the development of anxiety. Electrophysiological results also showed increased excitatory input and decreased inhibitory input in BLA PNs. Chemogenetic inhibition of the excitability of PNs in the BLA rescued the anxiety phenotype of InsG3680+/+ mice. Further study found that the diminished control of the BLA by medial prefrontal cortex (mPFC) and optogenetic activation of the mPFC-BLA pathway also had a rescue effect, which increased the feedforward inhibition of the BLA. Taken together, our results suggest that hyperactivity of the BLA and alteration of the mPFC-BLA circuitry are involved in anxiety in InsG3680+/+ mice.

Infralimbic-basolateral amygdala circuit associated with depression-like not anxiety-like behaviors induced by chronic neuropathic pain and the antidepressant effects of electroacupuncture

Chronic pain, such as neuropathic pain, can lead to anxiety, depression, and other negative emotions, thereby forming comorbidities and increasing the risk of chronic pain over time. Both the infralimbic amygdala (IL) and the basolateral amygdala (BLA) are significantly associated with negative emotions and pain, and they are known to have reciprocal connections. However, the role of IL-BLA circuit pathways in neuropathic pain-induced anxiety and depression remains unexplored. Electroacupuncture (EA) is frequently employed in the treatment of chronic pain and emotional disorders. However, The mechanism by which EA mediates its analgesic and emotion-alleviating effects via the IL-BLA circuit remains uncertain. Here, we used chemogenetic manipulation combined with behavioral tests to detect pain induced anxiety-like and depression-like behaviors. We observed that activation of the IL-BLA circuit by chemogenetic activation induced depression-like behavior of mice. Additionally, we discovered that chemogenetic activation of the IL-BLA circuit successfully prevented the beneficial effects of EA on depression-like behavior brought on by chronic pain in mice with spared nerve injury (SNI). We discovered that SNI-induced depression-like behavior could be mitigated by inhibiting the circuit, and EA had a comparable depressive-relieving effect. Furthermore, the IL-BLA circuit's activation or inhibition had no effect on the anxiety-like feelings brought on by SNI. Overall, our findings identify a specific neural circuit that selectively regulates pain-induced depression-like emotions, without affecting pain-induced anxiety-like emotions. This discovery offers a precise target for future treatments of comorbid pain and depression and provides a plausible explanation for the efficacy of EA in treating depression-like emotions associated with chronic pain.

Elevated dorsal medial prefrontal cortex to lateral habenula pathway activity mediates chronic stress-induced depressive and anxiety-like behaviors

The medial prefrontal cortex (mPFC) sends projections to numerous brain regions and is believed to play a significant role in depression and anxiety. One of the key downstream targets of the mPFC, the lateral habenula (LHb), is essential for chronic stress (CS)-induced depressive and anxiety-like behaviors. Nevertheless, whether the mPFC-LHb pathway mediates the co-occurrence of depression and anxiety and the underlying mechanism remain incompletely understood. Here, using chemogenetics, we first determined that activation of LHb-projecting mPFC neurons is essential for the development of depressive and anxiety-like behaviors induced by CS. Subsequently, we identify the extent and distribution of LHb-projecting neurons originating from the mPFC subregion. Through circuit-specific in vivo fiber photometry, we found that Ca2+ activity in dorsal mPFC (dmPFC) axon terminals within the LHb was increased during exposure to stressful and anxiety-related stimuli, highlighting the potential role of LHb-projecting dmPFC neurons in conveying stressful and anxiety-related information to the LHb. Finally, we observed that activation of both LHb-projecting dmPFC neurons and their postsynaptic counterparts in the LHb was necessary for CS-induced depressive and anxiety-like behaviors. Overall, this study provides multiple lines of evidence demonstrating that activation of the dmPFC-LHb pathway is a crucial neural circuitry for CS-induced depressive and anxiety-like behaviors.

A Prelimbic Cortex-Thalamus Circuit Bidirectionally Regulates Innate and Stress-Induced Anxiety-Like Behavior

Anxiety-related disorders respond to cognitive behavioral therapies, which involved the medial prefrontal cortex (mPFC). Previous studies have suggested that subregions of the mPFC have different and even opposite roles in regulating innate anxiety. However, the specific causal targets of their descending projections in modulating innate anxiety and stress-induced anxiety have yet to be fully elucidated. Here, we found that among the various downstream pathways of the prelimbic cortex (PL), a subregion of the mPFC, PL-mediodorsal thalamic nucleus (MD) projection, and PL-ventral tegmental area (VTA) projection exhibited antagonistic effects on anxiety-like behavior, while the PL-MD projection but not PL-VTA projection was necessary for the animal to guide anxiety-related behavior. In addition, MD-projecting PL neurons bidirectionally regulated remote but not recent fear memory retrieval. Notably, restraint stress induced high-anxiety state accompanied by strengthening the excitatory inputs onto MD-projecting PL neurons, and inhibiting PL-MD pathway rescued the stress-induced anxiety. Our findings reveal that the activity of PL-MD pathway may be an essential factor to maintain certain level of anxiety, and stress increased the excitability of this pathway, leading to inappropriate emotional expression, and suggests that targeting specific PL circuits may aid the development of therapies for the treatment of stress-related disorders.

Ketamine and fluoxetine exert similar actions on prelimbic and infralimbic responsivity to lateral septal nucleus stimulation in Wistar rats

Ketamine is a dissociative anesthetic that has been proposed to be a useful alternative in cases of a poor response to other treatments in patients with depression. Remarkably, beneficial clinical actions of ketamine are detected once its psychotropic actions disappear. Therefore, clinical actions may occur independently of dose. Most current studies focus on actions of ketamine on neurotrophic factors, but few studies have investigated actions of ketamine on neural structures for which actions of antidepressants have been previously explored. Lateral septal nucleus (LSN) stimulation reduces neural activity in the prelimbic cortex (PL) and infralimbic cortex (IL) subregions of the medial prefrontal cortex (mPFC). Fluoxetine increases inhibitory responsivity of the LSN-IL connection. In the present study, actions of an anesthetic dose of ketamine were compared with a high dose of fluoxetine on behavior and neural responsivity 24 h after drug administration. Fluoxetine reduced immobility in the forced swim test without changing locomotor activity in the open field test. Ketamine strongly decreased locomotor activity and did not produce changes in immobility. In another set of Wistar rats that received similar drug treatment regimens, the results indicated that LSN stimulation in saline-treated animals produced a long-lasting inhibitory afterdischarge in these mPFC subregions. Actions of ketamine on the LSN-mPFC connection reproduced actions of fluoxetine, consisting of accentuated inhibition of the LSN action on the mPFC. These findings suggest that independent of different actions on neurotransmission, the common final pathway of antidepressants lies in their actions on forebrain structures that are related to emotional regulation.

Adolescent nicotine exposure induces long-term, sex-specific disturbances in mood and anxiety-related behavioral, neuronal and molecular phenotypes in the mesocorticolimbic system

The majority of lifetime smokers begin using nicotine during adolescence, a critical period of brain development wherein neural circuits critical for mood, affect and cognition are vulnerable to drug-related insults. Specifically, brain regions such as the medial prefrontal cortex (mPFC), the ventral tegmental area (VTA), nucleus accumbens (NAc) and hippocampus, are implicated in both nicotine dependence and pathological phenotypes linked to mood and anxiety disorders. Clinical studies report that females experience higher rates of mood/anxiety disorders and are more resistant to smoking cessation therapies, suggesting potential sex-specific responses to nicotine exposure and later-life neuropsychiatric risk. However, the potential neural and molecular mechanisms underlying such sex differences are not clear. In the present study, we compared the impacts of adolescent nicotine exposure in male vs. female rat cohorts. We performed a combination of behavioral, electrophysiological and targeted protein expression analyses along with matrix assisted laser deionization imaging (MALDI) immediately post-adolescent exposure and later in early adulthood. We report that adolescent nicotine exposure induced long-lasting anxiety/depressive-like behaviors, disrupted neuronal activity patterns in the mPFC-VTA network and molecular alterations in various neural regions linked to affect, anxiety and cognition. Remarkably, these phenotypes were only observed in males and/or were expressed in the opposite direction in females. These findings identify a series of novel, sex-selective biomarkers for adolescent nicotine-induced neuropsychiatric risk, persisting into adulthood.

Vibration-reduced anxiety-like behavior relies on ameliorating abnormalities of the somatosensory cortex and medial prefrontal cortex

Tibetan singing bowls emit low-frequency sounds and produce perceptible harmonic tones and vibrations through manual tapping. The sounds the singing bowls produce have been shown to enhance relaxation and reduce anxiety. However, the underlying mechanism remains unclear. In this study, we used chronic restraint stress or sleep deprivation to establish mouse models of anxiety that exhibit anxiety-like behaviors. We then supplied treatment with singing bowls in a bottomless cage placed on the top of a cushion. We found that unlike in humans, the combination of harmonic tones and vibrations did not improve anxiety-like behaviors in mice, while individual vibration components did. Additionally, the vibration of singing bowls increased the level of N-methyl-D-aspartate receptor 1 in the somatosensory cortex and prefrontal cortex of the mice, decreased the level of γ-aminobutyric acid A (GABA) receptor α 1 subtype, reduced the level of CaMKII in the prefrontal cortex, and increased the number of GABAergic interneurons. At the same time, electrophysiological tests showed that the vibration of singing bowls significantly reduced the abnormal low-frequency gamma oscillation peak frequency in the medial prefrontal cortex caused by stress restraint pressure and sleep deprivation. Results from this study indicate that the vibration of singing bowls can alleviate anxiety-like behaviors by reducing abnormal molecular and electrophysiological events in somatosensory and medial prefrontal cortex.

Acute manipulation of Drd1 neurons in the prefrontal cortex bidirectionally regulates anxiety and depression-like behaviors

BACKGROUND CONTEXT

The medial prefrontal cortex (mPFC) has been implicated in modulating anxiety and depression. Manipulation of Drd1 neurons in the mPFC resulted in variable neuronal activity and, consequently, strikingly different behaviors. The acute regulation of anxiety- and depression-like behaviors by Drd1 neurons, a major neuronal subtype in the mPFC, has not yet been investigated.

PURPOSE

The purpose of this study was to investigate whether acute manipulation of Drd1 neurons in the mPFC affects anxiety- and depression-like behaviors.

STUDY DESIGN

Male Drd1-Cre mice were injected with an adeno-associated virus (AAV) expressing hM3DGq or hM4DGi. Clozapine-n-oxide (CNO, 1 mg/kg, i.p.) was injected 30 min before the behavioral tests.

METHODS

Male Drd1-Cre mice were injected with AAV-Ef1α-DIO-hM4DGi-mCherry-WPRE-pA, AAV-Ef1α-DIO-hM3DGq-mCherry-WPRE-pA or AAV-Ef1α-DIO-mCherry-WPRE-pA. Three weeks later, whole-cell recordings after CNO (5 μM) were applied to the bath were used to validate the functional expression of hM4DGi and hM3DGq. Four groups of mice underwent all the behavioral tests, and after each of the tests, the mice were allowed to rest for 3-4 days. CNO (1 mg/kg) was injected intraperitoneally 30 min before the behavior test. Anxiety-like behaviors were evaluated by the open field test (OFT), the elevated plus maze test (EPMT), and the novelty-suppressed feeding test (NSFT). Depression-like behaviors were evaluated by the sucrose preference test (SPT) and force swimming test (FST). For all experiments, coronal sections of the targeted brain area were used to confirm virus expression.

RESULTS

Whole-cell recordings from brain slices demonstrated that infusions of CNO (5 µM) into mPFC slices dramatically increased the firing activity of hM3DGq-mCherry+ neurons and abolished the firing activity of hM4DGi-mCherry+ neurons. Acute chemogenetic activation of Drd1 neurons in the mPFC increased the time spent in the central area in the OFT, increased the time spent in the open arms in the EMPT, decreased the latency to bite the food in the NSFT, increased the sucrose preference in the SPT, and decreased the immobility time in the FST. Acute chemogenetic inhibition of Drd1 neurons in the mPFC decreased the time spent in the central area in the OFT, decreased the time spent in the open arms in the EMPT, increased the latency to bite the food in the NSFT, decreased the sucrose preference in the SPT, and increased the immobility time in the FST.

CONCLUSIONS

The present study showed that acute activation of Drd1 neurons in the mPFC produced rapid anxiolytic- and antidepressant-like effects, and acute inhibition had the opposite effect, revealing that Drd1 neurons in the mPFC bidirectionally regulate anxiety- and depression-like behaviors.

CLINICAL SIGNIFICANCE

The findings of the present study regarding the acute effects of stimulating Drd1 neurons in the mPFC on anxiety and depression suggest that Drd1 neurons in the mPFC are a focus for the treatment of anxiety disorders and depression.

Dorsal peduncular cortex activity modulates affective behavior and fear extinction in mice

The medial prefrontal cortex (mPFC) is critical to cognitive and emotional function and underlies many neuropsychiatric disorders, including mood, fear and anxiety disorders. In rodents, disruption of mPFC activity affects anxiety- and depression-like behavior, with specialized contributions from its subdivisions. The rodent mPFC is divided into the dorsomedial prefrontal cortex (dmPFC), spanning the anterior cingulate cortex (ACC) and dorsal prelimbic cortex (PL), and the ventromedial prefrontal cortex (vmPFC), which includes the ventral PL, infralimbic cortex (IL), and in some studies the dorsal peduncular cortex (DP) and dorsal tenia tecta (DTT). The DP/DTT have recently been implicated in the regulation of stress-induced sympathetic responses via projections to the hypothalamus. While many studies implicate the PL and IL in anxiety-, depression-like and fear behavior, the contribution of the DP/DTT to affective and emotional behavior remains unknown. Here, we used chemogenetics and optogenetics to bidirectionally modulate DP/DTT activity and examine its effects on affective behaviors, fear and stress responses in C57BL/6J mice. Acute chemogenetic activation of DP/DTT significantly increased anxiety-like behavior in the open field and elevated plus maze tests, as well as passive coping in the tail suspension test. DP/DTT activation also led to an increase in serum corticosterone levels and facilitated auditory fear extinction learning and retrieval. Activation of DP/DTT projections to the dorsomedial hypothalamus (DMH) acutely decreased freezing at baseline and during extinction learning, but did not alter affective behavior. These findings point to the DP/DTT as a new regulator of affective behavior and fear extinction in mice.

Prelimbic and infralimbic responsivity to amygdala input is modified by gonadal hormones in parallel to low anxiety-like behavior in ovariectomized rats

Gonadal hormones may influence sexual activity by reducing anxiety. The basolateral amygdala (BLA) and prelimbic (PL) and infralimbic (IL) cortical regions comprise a loop that is related to fear, anxiety, and social behavior. In female ovariectomized rats, actions of estradiol, progesterone, and sequential estradiol and progesterone administration were explored in the open field test (OFT) and plus maze test (PMT) to evaluate signs of anxiety-like behavior. The three hormonal treatments reduced indicators of anxiety in the PMT but did not influence behavior in the OFT. In the same behaviorally tested rats under urethane anesthesia, single-unit extracellular recordings were obtained from the PL and IL during electrical stimulation of the BLA. The analysis of 250 ms peristimulus histograms showed that BLA stimulation produced two kinds of response. A small group of neurons increased their firing rate after BLA stimulation. Most neurons exhibited a reduction of spiking. Neurons that increased their firing rate after BLA stimulation did not show any difference with the hormonal treatments. In neurons that were inhibited by BLA stimulation, estradiol reduced the neuronal firing rate in the PL and IL, and progesterone alone and the sequential administration of estradiol followed by progesterone administration 24 h later (priming) increased the firing rate during the 240 ms before BLA stimulation. Analyses of responsivity of the PL and IL during electrical stimulation of the BLA indicated that estradiol, progesterone, and estradiol followed by progesterone administration 24 h later (priming) reduced inhibitory actions of the BLA on the PL but not IL. In the BLA-IL connection, progesterone exacerbated the inhibitory response. These findings indicate that anxiolytic actions of estradiol, progesterone, and estradiol followed by progesterone administration 24 h later (priming) correspond to lower BLA-PL responsivity. Actions of progesterone on BLA-IL responsivity appear to contribute to sexual activity by interacting with other forebrain structures that are also related to sexual receptivity.

Projection-Targeted Photopharmacology Reveals Distinct Anxiolytic Roles for Presynaptic mGluR2 in Prefrontal- and Insula-Amygdala Synapses

Dissecting how membrane receptors regulate neural circuit function is critical for deciphering basic principles of neuromodulation and mechanisms of therapeutic drug action. Classical pharmacological and genetic approaches are not well-equipped to untangle the roles of specific receptor populations, especially in long-range projections which coordinate communication between brain regions. Here we use viral tracing, electrophysiological, optogenetic, and photopharmacological approaches to determine how presynaptic metabotropic glutamate receptor 2 (mGluR2) activation in the basolateral amygdala (BLA) alters anxiety-related behavior. We find that mGluR2-expressing neurons from the ventromedial prefrontal cortex (vmPFC) and posterior insular cortex (pIC) preferentially target distinct cell types and subregions of the BLA to regulate different forms of avoidant behavior. Using projection-specific photopharmacological activation, we find that mGluR2-mediated presynaptic inhibition of vmPFC-BLA, but not pIC-BLA, connections can produce long-lasting decreases in spatial avoidance. In contrast, presynaptic inhibition of pIC-BLA connections decreased social avoidance, novelty-induced hypophagia, and increased exploratory behavior without impairing working memory, establishing this projection as a novel target for the treatment of anxiety disorders. Overall, this work reveals new aspects of BLA neuromodulation with therapeutic implications while establishing a powerful approach for optical mapping of drug action via photopharmacology.

A neuronal coping mechanism linking stress-induced anxiety to motivation for reward

Stress coping involves innate and active motivational behaviors that reduce anxiety under stressful situations. However, the neuronal bases directly linking stress, anxiety, and motivation are largely unknown. Here, we show that acute stressors activate mouse GABAergic neurons in the interpeduncular nucleus (IPN). Stress-coping behavior including self-grooming and reward behavior including sucrose consumption inherently reduced IPN GABAergic neuron activity. Optogenetic silencing of IPN GABAergic neuron activation during acute stress episodes mimicked coping strategies and alleviated anxiety-like behavior. In a mouse model of stress-enhanced motivation for sucrose seeking, photoinhibition of IPN GABAergic neurons reduced stress-induced motivation for sucrose, whereas photoactivation of IPN GABAergic neurons or excitatory inputs from medial habenula potentiated sucrose seeking. Single-cell sequencing, fiber photometry, and optogenetic experiments revealed that stress-activated IPN GABAergic neurons that drive motivated sucrose seeking express somatostatin. Together, these data suggest that stress induces innate behaviors and motivates reward seeking to oppose IPN neuronal activation as an anxiolytic stress-coping mechanism.

Maternal separation modifies spontaneous synaptic activity in the infralimbic cortex of stress-resilient male rats

Glutamate and GABA signaling systems are necessary to maintain proper function of the central nervous system through excitation/inhibition (E/I) balance. Alteration of this balance in the medial prefrontal cortex (mPFC), as an effect of early-life stress, may lead to the development of anxiety and depressive disorders. Few studies exist in the infralimbic division of the mPFC to understand the effect of early-life stress at different ages, which is the purpose of the present work. Newborn Sprague Dawley male rats were subjected to maternal separation (MS) for two weeks. First, tests measuring anxiety- and depression-like behaviors were performed on adolescent and adult rats subjected to MS (MS-rats). Then, to establish a relationship with behavioral results, electrophysiological recordings were performed in neurons of the infralimbic cortex in acute brain slices of infant, adolescent, and adult rats. In the behavioral tests, there were no significant differences in MS-rats compared to control rats at any age. Moreover, MS had no effect on the passive membrane properties nor neuronal excitability in the infralimbic cortex, whereas spontaneous synaptic activity in infralimbic neurons was altered. The frequency of spontaneous glutamatergic synaptic events increased in infant MS-rats, whereas in adolescent MS-rats both the frequency and the amplitude of spontaneous GABAergic events increased without any effect on glutamatergic synaptic responses. In adult MS-rats, these two parameters decreased in spontaneous GABAergic synaptic events, whereas only the frequency of glutamatergic events decreased. These data suggest that rats subjected to MS did not exhibit behavioral changes and presented an age-dependent E/I imbalance in the infralimbic cortex, possibly due to differential changes in neurotransmitter release and/or receptor expression.

Activation of mediodorsal thalamic dopamine receptors inhibited nicotine-induced anxiety in rats: A possible role of corticolimbic NMDA neurotransmission and BDNF expression

The present study aimed to evaluate the functional interaction between the dopaminergic and glutamatergic systems of the mediodorsal thalamus (MD), the ventral hippocampus (VH), and the prefrontal cortex (PFC) in nicotine-induced anxiogenic-like behaviors. Brain-derived neurotrophic factor (BDNF) level changes were measured in the targeted brain areas following the drug treatments. The percentage of time spent in the open arm (% OAT) and open arm entry (% OAE) were calculated in the elevated plus maze (EPM) to measure anxiety-related behaviors in adult male Wistar rats. Systemic administration of nicotine at a dose of 0.5 mg/kg induced an anxiogenic-like response associated with decreased BDNF levels in the hippocampus and the PFC. Intra-MD microinjection of apomorphine (0.1-0.3 μg/rat) induced an anxiogenic-like response, while apomorphine inhibited nicotine-induced anxiogenic-like behaviors associated with increased hippocampal and PFC BDNF expression levels. Interestingly, the blockade of the VH or the PFC NMDA receptors via the microinjection of D-AP5 (0.3-0.5 μg/rat) into the targeted sites reversed the inhibitory effect of apomorphine (0.5 μg/rat, intra-MD) on the nicotine response and led to the decrease of BDNF levels in the hippocampus and the PFC. Also, the microinjection of a higher dose of D-AP5 (0.5 μg/rat, intra-PFC) alone produced an anxiogenic effect. These findings suggest that the functional interaction between the MD dopaminergic D1/D2-like and the VH/PFC glutamatergic NMDA receptors may be partially involved in the anxiogenic-like effects of nicotine, likely via the alteration of BDNF levels in the hippocampus and the PFC.

Enhanced AMPAR-dependent synaptic transmission by S-nitrosylation in the vmPFC contributes to chronic inflammatory pain-induced persistent anxiety in mice

Chronic pain patients often have anxiety disorders, and some of them suffer from anxiety even after analgesic administration. In this study, we investigated the role of AMPAR-mediated synaptic transmission in the ventromedial prefrontal cortex (vmPFC) in chronic pain-induced persistent anxiety in mice and explored potential drug targets. Chronic inflammatory pain was induced in mice by bilateral injection of complete Freund's adjuvant (CFA) into the planta of the hind paws; anxiety-like behaviours were assessed with behavioural tests; S-nitrosylation and AMPAR-mediated synaptic transmission were examined using biochemical assays and electrophysiological recordings, respectively. We found that CFA induced persistent upregulation of AMPAR membrane expression and function in the vmPFC of anxious mice but not in the vmPFC of non-anxious mice. The anxious mice exhibited higher S-nitrosylation of stargazin (an AMPAR-interacting protein) in the vmPFC. Inhibition of S-nitrosylation by bilaterally infusing an exogenous stargazin (C302S) mutant into the vmPFC rescued the surface expression of GluA1 and AMPAR-mediated synaptic transmission as well as the anxiety-like behaviours in CFA-injected mice, even after ibuprofen treatment. Moreover, administration of ZL006, a small molecular inhibitor disrupting the interaction of nNOS and PSD-95 (20 mg·kg-1·d-1, for 5 days, i.p.), significantly reduced nitric oxide production and S-nitrosylation of AMPAR-interacting proteins in the vmPFC, resulting in anxiolytic-like effects in anxious mice after ibuprofen treatment. We conclude that S-nitrosylation is necessary for AMPAR trafficking and function in the vmPFC under chronic inflammatory pain-induced persistent anxiety conditions, and nNOS-PSD-95 inhibitors could be potential anxiolytics specific for chronic inflammatory pain-induced persistent anxiety after analgesic treatment.

Corticosteroid treatment attenuates anxiety and mPFC-amygdala circuit dysfunction in allergic asthma

AIMS

Allergic asthma is associated with anxiety-related behaviors, leading to poor quality of life. Previous studies mainly described the neuropathophysiology of asthma-induced anxiety. However, the effects of corticosteroids, the most common anti-inflammatory agents for asthma treatment, on the neurophysiological foundations of allergic asthma-induced anxiety are unexplored.

MAIN METHODS

Here, we evaluated lung and brain inflammation as well as anxiety in an animal model of allergic asthma pretreated with inhaled fluticasone propionate. Furthermore, to define the neurophysiological bases of these conditions, we studied the medial prefrontal cortex (mPFC)-amygdala circuit, which is previously shown to accompany asthma-induced anxiety.

KEY FINDINGS

Our data showed that allergen induces anxiety, mPFC and amygdala inflammation, as well as disruptions in the local and long-range oscillatory activities within the mPFC-amygdala circuit. Interestingly, we observed a roughly consistent trend of changes with inhaled fluticasone pretreatment. Namely, the asthma-induced behavioral, inflammatory, and neurophysiological changes were partly, but not totally, prevented by inhaled fluticasone pretreatment.

SIGNIFICANCE

We suggest that early treatment of asthmatic patients with inhaled corticosteroids improves mPFC-amygdala circuit function by attenuating neuroinflammation leading to reduced anxiety. These findings could lead clinical guidelines of asthma to consider the neuropsychiatric disorders of patients in treatment recommendations.

Insulin and fluoxetine produce opposite actions on lateral septal nucleus-infralimbic region connection responsivity

Some diabetes patients develop depression, the main treatment for which is antidepressants. Pharmacological interactions between insulin and antidepressants (e.g., fluoxetine) are controversial in the literature. Some authors reported hypoglycemic actions of fluoxetine, whereas others reported antidepressant-like actions. In healthy rats, insulin produces an antidespair-like action in rats through an increase in locomotor and exploratory activity, but differences in actions of insulin and fluoxetine on neuronal activity are unknown. The present study evaluated Wistar healthy rats that were treated with saline, insulin, fluoxetine, or fluoxetine + insulin for 3 days (short-term) or 21 days (long-term). The model consisted of electrical stimulation of the lateral septal nucleus (LSN) while we performed single-unit extracellular response recordings in the prelimbic cortex (PL) and infralimbic cortex (IL) subregions of the medial prefrontal cortex (mPFC). Stimulation of the LSN produced an initial brief excitatory paucisynaptic response and then a long-lasting inhibitory afterdischarge in the PL and IL. Treatment with saline and fluoxetine, but not insulin, minimally affected the paucisynaptic response. Differences were found in LSN-IL responsivity. The inhibitory afterdischarge was clearly enhanced in the long-term fluoxetine group but not by insulin alone or fluoxetine + insulin. These findings suggest that insulin produces some actions that are opposite to fluoxetine on LSN-mPFC connection responsivity, with no synergistic actions between the actions of insulin and fluoxetine.

Agarwood essential oil inhalation exerts antianxiety and antidepressant effects via the regulation of Glu/GABA system homeostasis

Depression and anxiety are common diseases that endanger the physical and mental health of individuals. Agarwood incense inhalation has been used as a traditional Chinese medicine for relaxation and to improve sleep for centuries. In a previous study by the authors it was demonstrated that agarwood essential oil (AEO) injection exerted anxiolytic and antidepressant effects. Therefore the present study further investigated the anxiolytic and antidepressant effects of AEO inhalation on anxiolytic mice induced by M-chlorophenylpiperazine and depressive mice induced by chronic unpredictable mild stress. The results demonstrated that AEO exerted a significant anxiolytic effect, whereby autonomous movements were inhibited during the light dark exploration test and open field test. Furthermore, the tail suspension test and the forced swimming test demonstrated that AEO also exerted an antidepressant effect, whereby the immobility times were decreased. Moreover, AEO was determined to increase the levels of 5-hydroxytryptamine, γ-aminobutyric acid (GABA) A receptor (GABA_A) and glutamate (Glu) in anxiolytic mice and inhibit the levels of GABA_A and Glu in depressive mice. Further investigations into how AEO affected the Glu/GABA system demonstrated that AEO markedly increased the protein expression levels of GABA transaminase (GABAT), glutamate metabotropic receptor 5 (GRM5), glutamate ionotropic receptor AMPA type subunit 1 (GluR1) and vesicular glutamate transporter 1 (VGluT1). Furthermore, AEO reduced the expression levels of GABAT, glutamate ionotropic receptor NMDA type subunit 2B and GRM5, and enhanced the expression levels of GluR1 and VGluT1. These results demonstrated that AEO potentially possesses antianxiety and antidepressant properties. The present study determined that the mechanism was related to the regulation of Glu/GABA neurotransmitter system homeostasis.

Modularity and neuronal heterogeneity: Two properties that influence in vitro neuropharmacological experiments

Introduction

The goal of this work is to prove the relevance of the experimental model (in vitro neuronal networks in this study) when drug-delivery testing is performed.

Methods

We used dissociated cortical and hippocampal neurons coupled to Micro-Electrode Arrays (MEAs) arranged in different configurations characterized by modularity (i.e., the presence of interconnected sub-networks) and heterogeneity (i.e., the co-existence of neurons coming from brain districts). We delivered increasing concentrations of bicuculline (BIC), a neuromodulator acting on the GABAergic system, and we extracted the IC₅₀ values (i.e., the effective concentration yielding a reduction in the response by 50%) of the mean firing rate for each configuration.

Results

We found significant lower values of the IC₅₀ computed for modular cortical-hippocampal ensembles than isolated cortical or hippocampal ones.

Discussion

Although tested with a specific neuromodulator, this work aims at proving the relevance of ad hoc experimental models to perform neuropharmacological experiments to avoid errors of overestimation/underestimation leading to biased information in the characterization of the effects of a drug on neuronal networks.

The ventromedial prefrontal cortex and emotion regulation: lost in translation?

Neuroimaging studies implicate the ventromedial prefrontal cortex (vmPFC) in a wide range of emotional and cognitive functions, and changes in activity within vmPFC have been linked to the aetiology and successful treatment of depression. However, this is a large, structurally heterogeneous region and the extent to which this structural heterogeneity reflects functional heterogeneity remains unclear. Causal studies in animals should help address this question but attempts to map findings from vmPFC studies in rodents onto human imaging studies highlight cross-species discrepancies between structural homology and functional analogy. Bridging this gap, recent studies in marmosets - a species of new world monkey in which the overall organization of vmPFC is more like humans than that of rodents - have revealed that over-activation of the caudal subcallosal region of vmPFC, area 25, but not neighbouring area 32, heightens reactivity to negatively valenced stimuli whilst blunting responsivity to positively valenced stimuli. These co-occurring states resemble those seen in depressed patients, which are associated with increased activity in caudal subcallosal regions. In contrast, only reward blunting but not heightening of threat reactivity is seen following over-activation of the structurally homologous region in rodents. To further advance understanding of the role of vmPFC in the aetiology and treatment of depression, future work should focus on the behaviourally specific networks by which vmPFC regions have their effects, together with characterization of cross-species similarities and differences in function.

Know thy SEFL: Fear sensitization and its relevance to stressor-related disorders

Extreme stress can cause long-lasting changes in affective behavior manifesting in conditions such as post-traumatic stress disorder (PTSD). Understanding the biological mechanisms that govern trauma-induced behavioral dysregulation requires reliable and rigorous pre-clinical models that recapitulate multiple facets of this complex disease. For decades, Pavlovian fear conditioning has been a dominant paradigm for studying the effects of trauma through an associative learning framework. However, severe stress also causes long-lasting nonassociative fear sensitization, which is often overlooked in Pavlovian fear conditioning studies. This paper synthesizes recent research on the stress-enhanced fear learning (SEFL) paradigm, a valuable rodent model that can dissociate associative and nonassociative effects of stress. We discuss evidence that the SEFL paradigm produces nonassociative fear sensitization that is distinguishable from Pavlovian fear conditioning. We also discuss key biological variables, such as age and sex, neural circuit mechanisms, and crucial gaps in knowledge. We argue that nonassociative fear sensitization deserves more attention within current PTSD models and that SEFL provides a valuable complement to Pavlovian conditioning research on trauma-related pathology.

Prefrontal cortex is necessary for long-term social recognition memory in mice

The prefrontal cortex (PFC) plays critical roles in social cognition and emotional regulation in humans and rodents; however, its involvement in social recognition memory in mice remains unclear. Here, we examined the roles of the PFC in short-term and long-term social recognition memory, social motivation, and anxiety-related behavior in C57BL/6J male mice. Sham control and PFC-lesioned mice underwent four different behavioral tests. In the social recognition test, composed of three daily trials over 3 consecutive days, the control mice spent less time investigating the juvenile stimulus mouse both within each day and across days. By contrast, while social investigation behavior in PFC-lesioned mice decreased across the three trials within each day, it did not decrease over the 3-day testing period. These results indicate that the PFC has an important role in long-term, but not short-term, social recognition memory. The control and PFC-lesioned mice exhibited similar social motivation in the three-chamber test - both groups preferred the juvenile mouse to the empty cylinder and did not prefer the adult mouse. In addition, the PFC lesion had no impact on anxiety-related behavior or general activity in the light-dark transition test or the open field test. Our findings demonstrate that the PFC is essential for long-term social recognition memory and that it plays a critical role in higher-order social cognition.

β2-Adrenoceptors in the Medial Prefrontal Cortex Excitatory Neurons Regulate Anxiety-like Behavior in Mice

The medial prefrontal cortex (mPFC) and β-adrenoceptors (βARs) have been implicated in modulating anxiety-like behavior. However, the specific contributions of the β2-AR subtype in mPFC in anxiety are still unclear. To address this issue, we used optogenetic and microRNA-based (miRNA) silencing to dissect the role of β2-AR in mPFC in anxiety-like behavior. On the one hand, we use a chimeric rhodopsin/β2-AR (Opto-β2-AR) with in vivo optogenetic techniques to selectively activate β2-adrenergic signaling in excitatory neurons of the mPFC. We found that opto-activation of β2-AR is sufficient to induce anxiety-like behavior and reduce social interaction. On the other hand, we utilize the miRNA silencing technique to specifically knock down the β2-AR in mPFC excitatory neurons. We found that the β2-AR knock down induces anxiolytic-like behavior and promotes social interaction compared to the control group. These data suggest that β2-AR signaling in the mPFC has a critical role in anxiety-like states. These findings suggest that inhibiting of β2-AR signaling in the mPFC may be an effective treatment of anxiety disorders.

Multisensory Integration: Is Medial Prefrontal Cortex Signaling Relevant for the Treatment of Higher-Order Visual Dysfunctions?

In the mammalian brain, information processing in sensory modalities and global mechanisms of multisensory integration facilitate perception. Emerging experimental evidence suggests that the contribution of multisensory integration to sensory perception is far more complex than previously expected. Here we revise how associative areas such as the prefrontal cortex, which receive and integrate inputs from diverse sensory modalities, can affect information processing in unisensory systems via processes of down-stream signaling. We focus our attention on the influence of the medial prefrontal cortex on the processing of information in the visual system and whether this phenomenon can be clinically used to treat higher-order visual dysfunctions. We propose that non-invasive and multisensory stimulation strategies such as environmental enrichment and/or attention-related tasks could be of clinical relevance to fight cerebral visual impairment.

Daily Optogenetic Stimulation of the Left Infralimbic Cortex Reverses Extinction Impairments in Male Rats Exposed to Single Prolonged Stress

Post-traumatic stress disorder (PTSD) is associated with decreased activity in the prefrontal cortex. PTSD-like pathophysiology and behaviors have been observed in rodents exposed to a single prolonged stress (SPS) procedure. When animals are left alone for 7 days after SPS treatment, they show increased anxiety-like behavior and impaired extinction of conditioned fear, and reduced activity in the prefrontal cortex. Here, we tested the hypothesis that daily optogenetic stimulation of the infralimbic region (IL) of the medial prefrontal cortex (mPFC) during the 7 days after SPS would reverse SPS effects on anxiety and fear extinction. Male Sprague-Dawley rats underwent SPS and then received daily optogenetic stimulation (20 Hz, 2 s trains, every 10 s for 15 min/day) of glutamatergic neurons of the left or right IL for seven days. After this incubation period, rats were tested in the elevated plus-maze (EPM). Twenty-four hours after the EPM test, rats underwent auditory fear conditioning (AFC), extinction training and a retention test. SPS increased anxiety-like behavior in the EPM task and produced a profound impairment in extinction of AFC. Optogenetic stimulation of the left IL, but not right, during the 7-day incubation period reversed the extinction impairment. Optogenetic stimulation did not reverse the increased anxiety-like behavior, suggesting that the extinction effects are not due to a treatment-induced reduction in anxiety. Results indicate that increased activity of the left IL after traumatic experiences can prevent development of extinction impairments. These findings suggest that non-invasive brain stimulation may be a useful tool for preventing maladaptive responses to trauma.

Loss of liver X receptor β in astrocytes leads to anxiety-like behaviors via regulating synaptic transmission in the medial prefrontal cortex in mice

Astrocytes are integral components of synaptic transmission, and their dysfunction leads to neuropsychiatric disorders such as anxiety and depression. Liver X receptor β (LXRβ) is expressed in astrocytes, and LXRβ global knockout mice shows impaired synaptic formation. In order to define the role of LXRβ in astrocytes, we used a conditional Cre-loxP system to specifically remove LXRβ from astrocytes. We found that this deletion caused anxiety-like but not depressive-like behaviors in adult male mice. This behavioral phenotype could be completely reproduced by selective deletion of LXRβ in astrocytes in the medial prefrontal cortex (mPFC). Pyramidal neurons in layer V of mPFC are involved in mood behaviors. We found that there was an increased spontaneous excitatory synaptic transmission in layer V pyramidal neurons of the mPFC of these mice. This was concurrent with increased dendritic complexity, despite normal appearance and number of dendritic spines. In addition, gene ontology analysis of RNA sequencing revealed that deletion of astrocytic LXRβ led to the enrichment of the process of synaptic transmission in mPFC. Finally, we also confirmed that renormalized excitatory synaptic transmission in layer V pyramidal neurons alleviated the anxiety in mice with astrocytic LXRβ deletion in mPFC. Together, our findings reveal that astrocytic LXRβ in mPFC is critical in the regulation of synaptic transmission, and this provides a potential new target for treatment of anxiety-like behavior.

Effects of psychogenic stress on some peripheral and central inflammatory markers in rats with the different level of excitability of the nervous system

Patients with post-stress pathologies display the signs of inflammation in the peripheral blood as well as in the brain. The mechanisms of such post-stress neuroimmune changes, their contribution to the behavior, the relationship of the intensity of inflammation with genetically determined features have not been clarified. The goal of this work was to evaluate the dynamics of post-stress inflammation in the blood and hippocampus of rats which differ in level of excitability of the nervous system. Rats of two strains (high/low excitability threshold) were subjected to stress according to the K. Hecht protocol and their behavior, neutrophil:lymphocyte ratio and the number of Iba+ cells in the hippocampus were analysed 24 hours, 7 and 24 days after stress exposure. Highly excitable animals show an increase in anxiety-like behavior, in the number of neutrophils compared to lymphocytes as well as in the number of Iba1+ cells in CA1, CA3 and DG areas of the hippocampus in response to stress. Thus, hereditary high excitability of the nervous system is a possible risk factor for the development of post-stress pathologies.

Distinct projections from the infralimbic cortex exert opposing effects in modulating anxiety and fear

Anxiety-related disorders can be treated by cognitive therapies and transcranial magnetic stimulation, which involve the medial prefrontal cortex (mPFC). Subregions of the mPFC have been implicated in mediating different and even opposite roles in anxiety-related behaviors. However, precise causal targets of these top-down connections among diverse possibilities have not been established. Here, we show that the lateral septum (LS) and the central nucleus of the amygdala (CeA) represent 2 direct targets of the infralimbic cortex (IL), a subregion of the mPFC that modulates anxiety and fear. Two projections were unexpectedly found to exert opposite effects on the anxious state and learned freezing: the IL-LS projection promoted anxiety-related behaviors and fear-related freezing, whereas the IL-CeA projection exerted anxiolytic and fear-releasing effects for the same features. Furthermore, selective inhibition of corresponding circuit elements showed opposing behavioral effects compared with excitation. Notably, the IL-CeA projection implemented top-down control of the stress-induced high-anxiety state. These results suggest that distinct IL outputs exert opposite effects in modulating anxiety and fear and that modulating the excitability of these projections with distinct strategies may be beneficial for the treatment of anxiety disorders.

Medial prefrontal cortex encoding of stress and anxiety

The prefrontal cortex (PFC) is involved in adaptive control of behavior and optimizing action selection. When an organism is experiencing an aversive event, such as a sustained state of anxiety or an overt experience of fear or stress, the mechanisms that govern PFC regulation of action selection may be critical for survival. A large body of literature has shown that acute aversive states influence the activity of PFC neurons and the release of neurotransmitters in this region. These states also result in long-term neurobiological changes in the PFC and expression of PFC-dependent motivated behaviors. The mechanism for how these changes lead to modifying action selection is only recently beginning to emerge. Here, we review animal and human studies into the neural mechanisms which may mediate the adaptive changes in the PFC that emerge during negative affective states. We then highlight recent advances in approaches for understanding how anxiety influences action selection and related cortical processes. We conclude by proposing that PFC neurons selectively influence action encoding during conditions where actions toward obtaining a reward or avoiding harm are executed under a fog of fear and anxiety.

The Paraventricular Nucleus of the Thalamus as an Integrating and Relay Node in the Brain Anxiety Network

The brain anxiety network is composed of a number of interconnected cortical regions that detect threats and execute appropriate defensive responses via projections to the shell of the nucleus accumbens (NAcSh), dorsolateral region of the bed nucleus of the stria terminalis (BSTDL) and lateral region of the central nucleus of the amygdala (CeL). The paraventricular nucleus of the thalamus (PVT) is anatomically positioned to integrate threat- and arousal-related signals from cortex and hypothalamus and then relay these signals to neural circuits in the NAcSh, BSTDL, and CeL that mediate defensive responses. This review describes the anatomical connections of the PVT that support the view that the PVT may be a critical node in the brain anxiety network. Experimental findings are reviewed showing that the arousal peptides orexins (hypocretins) act at the PVT to promote avoidance of potential threats especially following exposure of rats to a single episode of footshocks. Recent anatomical and experimental findings are discussed which show that neurons in the PVT provide divergent projections to subcortical regions that mediate defensive behaviors and that the projection to the NAcSh is critical for the enhanced social avoidance displayed in rats exposed to footshocks. A theoretical model is proposed for how the PVT integrates cortical and hypothalamic signals to modulate the behavioral responses associated with anxiety and other challenging situations.

Long-Term Decreases in the Expression of Calcineurin and GABAA Receptors Induced by Early Maternal Separation Are Associated with Increased Anxiety-Like Behavior in Adult Male Rats

INTRODUCTION

Early life stress is a well-described risk factor of anxiety disorders in adulthood. Dysfunction in GABA/glutamate receptors and their functional regulator, calcineurin, is linked to anxiety disorders. Here, we investigated the effect of early life stress, such as repeated maternal separation (MS; 3 h per day from postnatal day [P] 2 to 11), on changes in the expression of calcineurin as well as the ionotropic glutamatergic and GABAergic receptors including α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), N-methyl-D-aspartate (NMDA) and GABAA receptors in the hippocampus and prefrontal cortex (PFC) of adolescent (P35) and adult (P62) male Wistar rats and their correlations with anxiety-like behavior in adulthood.

METHODS

The protein levels were assessed by Western blot analysis. Anxiety-like behavior was measured in the elevated plus maze (EPM) and open field (OF) tests.

RESULTS

MS induced a regional transient decrease of glutamate receptors expression at P35, with decreased NMDA and AMPA receptor levels, respectively, in the hippocampus and PFC, suggesting a possible decrease in excitatory synaptic strength. In contrast to glutamate receptors, MS had long-lasting influence on GABAA receptor and calcineurin levels, with reduced expression of GABAA receptor and calcineurin in both brain regions at P35 that continued into adulthood. These results were accompanied by increased anxiety behavior in adulthood, shown by lower percentage of number of total entries and time spent in the open arms of the EPM, and by lower time spent and number of entries in the OF central area.

CONCLUSIONS

Together, our study suggests that GABAA receptors via calcineurin-dependent signaling pathways may play an important role in the expression of stress-induced anxiety-like behavior.

Differential effects of GABAA receptor activation in the prelimbic and orbitofrontal cortices on anxiety

RATIONALE

The development of effective anxiety treatments has been hindered by limited understanding of the neurobiological mechanisms involved in anxiety regulation. Whilst gamma-aminobutyric acid (GABA) neurotransmission in the prefrontal cortex (PFC) is one mechanism consistently implicated in anxiety regulation, PFC subregions may contribute uniquely.

OBJECTIVES

The present study examined the effects of inactivating the PFC subregions of the prelimbic cortex (PrL) or orbitofrontal cortex (OFC) through GABA_A receptor (GABA_AR) activation, on anxiety behaviours in male Wistar rats.

METHODS

Sixty-six male Wistar rats were surgically implanted with bilateral cannulae into the PrL (n = 33) or the OFC (n = 33). Rats then received a microinjection of either the GABA_A receptor agonist muscimol or vehicle prior to each experiment, conducted 1 week apart. Measures of anxiety were examined using the elevated plus maze (EPM) and the emergence test (ET). The effect on locomotor activity (baseline or methamphetamine-induced) was also tested.

RESULTS

Differential effects of brain region inactivation on anxiety-like behaviour were shown by measures in the EPM and ET; muscimol infused into the PrL-reduced anxiety-like behaviour, yet had no significant effect when infused into the OFC, compared with control treated rats. No effects on locomotor activity at baseline or following methamphetamine treatment were found.

CONCLUSIONS

This study highlights that activation of GABA_ARs specifically within the PrL, but not OFC, reduces anxiety behaviours in male rats. This suggests that activity of the PrL plays a more important role than the OFC in the neurobiological mechanisms of unconditioned anxiety and should be targeted for future therapies.

The anxiolytic effect of perampanel and possible mechanisms mediating its anxiolytic effect in mice

AIMS

The aim of this study is to investigate the anxiolytic activity of perampanel, a non-competitive antagonist of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-type glutamate receptors, which is approved for partial-onset seizures in patients with epilepsy, and its mechanism of action.

MAIN METHODS

The anxiolytic activity of perampanel at the doses of 0.25, 0.5, 1, 2, and 4 mg/kg intraperitoneally (i.p.) was investigated in mice using elevated plus-maze, hole-board, and open-field tests. The findings were compared to the anxiolytic activity of gamma-aminobutyric acid type A benzodiazepine (GABA_A/BZ) receptor allosteric modulator diazepam (1 mg/kg, i.p.) and AMPA antagonist GYKI-53655 (5 mg/kg, i.p.). The mechanisms of action of perampanel were evaluated by pre-treatment with GABA_A/BZ receptor antagonist flumazenil (3 mg/kg, i.p.), serotonin 5-hydroxytryptamine 1A (5-HT_1A) antagonist WAY-100635 (1 mg/kg, i.p.), and α₂-adrenoreceptor antagonist yohimbine (5 mg/kg, i.p.).

KEY FINDINGS

In the elevated plus-maze and open-field tests, perampanel at the dose of 0.5 mg/kg, and in the hole-board test, at the doses of 0.25, 0.5, and 1 mg/kg demonstrated an anxiolytic effect without altering the locomotor activity. The effect of perampanel was comparable to the effect of diazepam. Stimulation of GABA_A/BZ and α₂-adrenergic receptors contributed to the anxiolytic effect of perampanel, since significant antagonisms were determined in various behavioral parameters by the antagonist pre-treatments.

SIGNIFICANCE

AMPA antagonism is believed to provide the determined anxiolytic activity of perampanel. Increased GABAergic tonus induced by AMPA receptor antagonism along with other systems, especially the noradrenergic system, might be involved in the anxiolytic activity.

The cornucopia of central disinhibition pain - An evaluation of past and novel concepts

Central disinhibition (CD), as applied to pain, decreases thresholds of endogenous systems. This provokes onset of spontaneous or evoked pain in an individual beyond the ability of the nervous system to inhibit pain resulting from a disease or tissue damage. The original CD concept as proposed by Craig entails a shift from the lateral pain pathway (i.e. discriminative pain processing) towards the medial pain pathway (i.e. emotional pain processing), within an otherwise neurophysiological intact environment. In this review, the original CD concept as proposed by Craig is extended by the primary "nociceptive pathway damage - CD" concept and the secondary "central pathway set point - CD". Thereby, the original concept may be transferred into anatomical and psychological non-functional conditions. We provide examples for either primary or secondary CD concepts within different clinical etiologies as well as present surrogate models, which directly mimic the underlying pathophysiology (A-fiber block) or modulate the CD pathway excitability (thermal grill). The thermal grill has especially shown promising advancements, which may be useful to examine CD pathway activation in the future. Therefore, within this topical review, a systematic review on the thermal grill illusion is intended to stimulate future research. Finally, the authors review different mechanism-based treatment approaches to combat CD pain.

Activation of LXRβ Signaling in the Amygdala Confers Anxiolytic Effects Through Rebalancing Excitatory and Inhibitory Neurotransmission upon Acute Stress

The balance of major excitatory (glutamate, Glu) and inhibitory (γ-aminobutyric acid, GABA), named as E/I neurotransmission, is critical for proper information processing. Anxiety-like responses upon stress are accompanied by abnormal alterations in the formation and function of synapses, resulting in the imbalance of E/I neurotransmission in the amygdala. Liver X receptors (LXRs), including LXRα and LXRβ isoforms, are nuclear receptors responsible for regulating central nervous system (CNS) functions besides maintaining metabolic homeostasis. However, little is known about the contribution of LXRs in E/I balance in regulating anxiety-related behaviors induced by stress. In this study, we found stress-induced anxiety led to the expression reduction of LXRβ not LXRα in mice amygdala. GW3965, a dual agonist for both LXRα and LXRβ, alleviated anxiety-like behaviors of stressed mice through activation of LXRβ, confirmed by the knockdown of LXRβ mediated by lentiviral shRNAs in the basolateral amygdala (BLA). This was paralleled by correcting the disequilibrium of E/I neurotransmission in the stressed BLA. Importantly, GW3965 exerted anxiolytic effects by correcting the promoted amplitude and frequency of miniature excitatory postsynaptic current (mEPSC), and augmenting the decreased that of miniature inhibitory postsynaptic current (mIPSC) in the stressed BLA. This suggests that stress-induced anxiety-like behaviors can largely be ascribed to the deficit of LXRβ signaling in E/I neurotransmission in BLA. These findings highlight the deficiency of LXRβ signaling in the amygdala linked to anxiety disorder, and LXRβ activation may represent a potential novel target for anxiety treatment with an alteration in synaptic transmission in the amygdala.

Autistic-like behaviours and associated brain structural plasticity are modulated by oxytocin in maternally separated rats

BACKGROUND

Early psycho-social experiences influence the developing brain and possible onset of various neurodevelopmental disorders, such as Autism Spectrum Disorder (ASD). ASD is characterized by a variety of brain abnormalities, including alteration of oxytocin receptors in the brain. Recently, early life adverse experiences, such as maternal separation (MS), have been shown to constitute risk factors for ASD in preclinical studies. Therefore, the main aims of the current study were to i) explore the association between onset of autistic-like behaviours and molecular/structural changes in the brain following MS, and ii) evaluate the possible beneficial effects of oxytocin treatment on the same parameters.

METHOD AND MATERIAL

Male rats were exposed to the maternal separation from post-natal day (PND) 1 to PND14. After weaning, daily injections of oxytocin (1 mg/kg, ip) were administered (PND 22-30), followed by examination of autism-related behaviours at adolescence (PND 42-50). Brain structural plasticity was examined using stereological methods, and the plasma level of brain derived neurotrophic factor (BDNF) was analysed using ELISA.

RESULTS

We found that maternal separation induced autistic-like behaviours, which was associated with increase in the hippocampal CA1 stratum radiatum (CA1.SR) volume. In addition, we observed increase in the infralimbic brain region volume and in the number of the pyramidal neurons in the same brain region. Maternal separation significantly increased the plasma BDNF levels. Treatment with oxytocin improved autistic like behaviours, normalized the number of neurons and the volume of the infralimbic region as well as the plasma BDNF level (p < 0.05).

CONCLUSION

Maternal separation induced autistic-like behaviours, brain structural impairment together with plasma BDNF level abnormality, which could be improved by oxytocin treatment.

nNOS-expressing neurons in the vmPFC transform pPVT-derived chronic pain signals into anxiety behaviors

Anxiety is common in patients suffering from chronic pain. Here, we report anxiety-like behaviors in mouse models of chronic pain and reveal that nNOS-expressing neurons in ventromedial prefrontal cortex (vmPFC) are essential for pain-induced anxiety but not algesia, using optogenetic and chemogenetic strategies. Additionally, we determined that excitatory projections from the posterior subregion of paraventricular thalamic nucleus (pPVT) provide a neuronal input that drives the activation of vmPFC nNOS-expressing neurons in our chronic pain models. Our results suggest that the pain signal becomes an anxiety signal after activation of vmPFC nNOS-expressing neurons, which causes subsequent release of nitric oxide (NO). Finally, we show that the downstream molecular mechanisms of NO likely involve enhanced glutamate transmission in vmPFC CaMKIIα-expressing neurons through S-nitrosylation-induced AMPAR trafficking. Overall, our data suggest that pPVT excitatory neurons drive chronic pain-induced anxiety through activation of vmPFC nNOS-expressing neurons, resulting in NO-mediated AMPAR trafficking in vmPFC pyramidal neurons.

Chronic pain usually induces anxiety. Here, the authors report that vmPFC nNOS-expressing neurons are activated by excitatory inputs from pPVT during chronic pain and subsequently induce anxiety-like behaviors in mice through promoting AMPAR trafficking.

Prelimbic and Infralimbic Prefrontal Regulation of Active and Inhibitory Avoidance and Reward-Seeking

Flexible initiation or suppression of actions to avoid aversive events is crucial for survival. The prelimbic (PL) and infralimbic (IL) regions of the medial prefrontal cortex (mPFC) have been implicated in different aspects of avoidance and reward-seeking, but their respective contribution in instigating versus suppressing actions in aversive contexts remains to be clarified. We examined mPFC involvement in different forms of avoidance in rats well trained on different cued lever-press avoidance tasks. Active/inhibitory avoidance required flexible discrimination between auditory cues signaling foot-shock could be avoided by making or withholding instrumental responses. On a simpler active avoidance task, a single cue signaled when a lever press would avoid shock. PL inactivation disrupted active but not inhibitory avoidance on the discriminative task while having no effect on single-cued avoidance. In comparison, IL inactivation broadly impaired active and inhibitory avoidance. Conversely, on a cued appetitive go/no-go task, both IL and PL inactivation impaired inhibitory but not active reward-seeking, the latter effect being diametrically opposite to that observed on the avoidance task. These findings highlight the complex manner in which different mPFC regions aid in initiating or inhibiting actions in the service of avoiding aversive outcomes or obtaining rewarding ones. IL facilitates active avoidance but suppress inappropriate actions in appetitive and aversive contexts. In contrast, contextual valence plays a critical role in how the PL is recruited in initiating or suppressing actions, which may relate to the degree of cognitive control required to flexibly negotiate response or motivational conflicts and override prepotent behaviors.SIGNIFICANCE STATEMENT Choosing to make or withhold actions in a context-appropriate manner to avoid aversive events or obtain other goals is a critical survival skill. Different medial prefrontal cortex (mPFC) regions have been implicated in certain aspects of avoidance, but their contributions to instigating or suppressing actions remains to be clarified. Here, we show that the dorsal, prelimbic (PL) region of the medial PFC aids active avoidance in situations requiring flexible mitigation of response conflicts, but also aids in withholding responses to obtain rewards. In comparison the ventral infralimbic (IL) cortex plays a broader role in active and inhibitory avoidance as well as suppressing actions to obtain rewards. These findings provide insight into mechanisms underlying normal and maladaptive avoidance behaviors and response inhibition.

Respiratory regulation & interactions with neuro-cognitive circuitry

It is increasingly being recognized that active control of breathing - a key aspect of ancient Vedic meditative practices, can relieve stress and anxiety and improve cognition. However, the underlying mechanisms of respiratory modulation of neurophysiology are just beginning to be elucidated. Research shows that brainstem circuits involved in the motor control of respiration receive input from and can directly modulate activity in subcortical circuits, affecting emotion and arousal. Meanwhile, brain regions involved in the sensory aspects of respiration, such as the olfactory bulb, are like-wise linked with wide-spread brain oscillations; and perturbing olfactory bulb activity can significantly affect both mood and cognition. Thus, via both motor and sensory pathways, there are clear mechanisms by which brain activity is entrained to the respiratory cycle. Here, we review evidence gathered across multiple species demonstrating the links between respiration, entrainment of brain activity and functional relevance for affecting mood and cognition. We also discuss further linkages with cardiac rhythms, and the potential translational implications for biorhythm monitoring and regulation in neuropsychiatric disorders.

Allergen-induced anxiety-like behavior is associated with disruption of medial prefrontal cortex - amygdala circuit

Anxiety is prevalent in asthma, and is associated with disease severity and poor quality of life. However, no study to date provides direct experimental evidence for the effect of allergic inflammation on the structure and function of medial prefrontal cortex (mPFC) and amygdala, which are essential regions for modulating anxiety and its behavioral expression. We assessed the impact of ovalbumin (OVA)-induced allergic inflammation on the appearance of anxiety-like behavior, mPFC and amygdala volumes using MRI, and the mPFC-amygdala circuit activity in sensitized rats. Our findings exhibited that the OVA challenge in sensitized rats induced anxiety-like behavior, and led to more activated microglia and astrocytes in the mPFC and amygdala. We also found a negative correlation between anxiety-like behavior and amygdala volume. Moreover, OVA challenge in sensitized rats was associated with increases in mPFC and amygdala activity, elevation of amygdala delta-gamma coupling, and the enhancement of functional connectivity within mPFC-amygdala circuit – accompanied by an inverted direction of information transferred from the amygdala to the mPFC. We indicated that disrupting the dynamic interactions of the mPFC-amygdala circuit may contribute to the induction of anxiety-related behaviors with asthma. These findings could provide new insight to clarify the underlying mechanisms of allergic inflammation-induced psychiatric disorders related to asthma.

Prefrontal Regulation of Threat-Elicited Behaviors: A Pathway to Translation

Regions of the prefrontal and cingulate cortices play important roles in the regulation of behaviors elicited by threat. Dissecting out their differential involvement will greatly increase our understanding of the varied etiology of symptoms of anxiety. I review evidence for altered activity within the major divisions of the prefrontal cortex, including orbitofrontal, ventrolateral, dorsolateral, and ventromedial sectors, along with the anterior cingulate cortex in patients with clinical anxiety. This review is integrated with a discussion of current knowledge about the causal role of these different prefrontal and cingulate regions in threat-elicited behaviors from experimental studies in rodents and monkeys. I highlight commonalities and inconsistencies between species and discuss the current state of our translational success in relating findings across species. Finally, I identify key issues that, if addressed, may improve that success in the future.

Selecting an Appropriate Animal Model of Depression

Depression has become one of the most severe psychiatric disorders and endangers the health of living beings all over the world. In order to explore the molecular mechanism that underlies depression, different kinds of animal models of depression are used in laboratory experiments. However, a credible and reasonable animal model that is capable of imitating the pathologic mechanism of depression in mankind has yet to be found, resulting in a barrier to further investigation of depression. Nevertheless, it is possible to explain the pathologic mechanism of depression to a great extent by a rational modeling method and behavioral testing. This review aims to provide a reference for researchers by comparing the advantages and disadvantages of some common animal depression models.

Distraction of olfactory bulb-medial prefrontal cortex circuit may induce anxiety-like behavior in allergic rhinitis

Allergic rhinitis is a chronic inflammatory disease of the upper respiratory tract, which is associated with high incidence of anxiety symptom. There is evidence that medial prefrontal cortex modulates anxiety-related behaviors and receives projections from olfactory bulb. Since olfactory dysfunction has been reported in allergic rhinitis, we aimed to evaluate anxiety-like behavior and oscillations of olfactory bulb-medial prefrontal cortex circuit in an animal model of allergic rhinitis. The number of open arm entries in elevated zero maze was significantly reduced in sensitized rats exposed to intranasal ovalbumin compared to the control group, which was indicating the enhancement of anxiety-like behavior in allergic rhinitis animals. Analysis of local field potentials in olfactory bulb and medial prefrontal cortex during immobility and exploration state showed that anxiety-like behavior induced by allergic rhinitis was in association with increased activity of medial prefrontal cortex and enhancement of olfactory bulb-medial prefrontal cortex coupling in delta and theta bands. Moreover, in allergic rhinitis animals, theta strongly coordinates local gamma activity in olfactory bulb and medial prefrontal cortex, which means to have a strong local theta/gamma coupling. We suggested that disruption of olfactory bulb-medial prefrontal cortex circuit due to allergic reactions might have a governing role for inducing anxiety-like behavior in the allergic rhinitis experimental model.

Medial prefrontal cortex in neurological diseases

The medial prefrontal cortex (mPFC) is a crucial cortical region that integrates information from numerous cortical and subcortical areas and converges updated information to output structures. It plays essential roles in the cognitive process, regulation of emotion, motivation, and sociability. Dysfunction of the mPFC has been found in various neurological and psychiatric disorders, such as depression, anxiety disorders, schizophrenia, autism spectrum disorders, Alzheimer's disease, Parkinson's disease, and addiction. In the present review, we summarize the preclinical and clinical studies to illustrate the role of the mPFC in these neurological diseases.

A Focus on the Functions of Area 25

Subcallosal area 25 is one of the least understood regions of the anterior cingulate cortex, but activity in this area is emerging as a crucial correlate of mood and affective disorder symptomatology. The cortical and subcortical connectivity of area 25 suggests it may act as an interface between the bioregulatory and emotional states that are aberrant in disorders such as depression. However, evidence for such a role is limited because of uncertainty over the functional homologue of area 25 in rodents, which hinders cross-species translation. This emphasizes the need for causal manipulations in monkeys in which area 25, and the prefrontal and cingulate regions in which it is embedded, resemble those of humans more than rodents. In this review, we consider physiological and behavioral evidence from non-pathological and pathological studies in humans and from manipulations of area 25 in monkeys and its putative homologue, the infralimbic cortex (IL), in rodents. We highlight the similarities between area 25 function in monkeys and IL function in rodents with respect to the regulation of reward-driven responses, but also the apparent inconsistencies in the regulation of threat responses, not only between the rodent and monkey literatures, but also within the rodent literature. Overall, we provide evidence for a causal role of area 25 in both the enhanced negative affect and decreased positive affect that is characteristic of affective disorders, and the cardiovascular and endocrine perturbations that accompany these mood changes. We end with a brief consideration of how future studies should be tailored to best translate these findings into the clinic.

Bisphenol-A exposure induced neurotoxicity in glutamatergic neurons derived from human embryonic stem cells

Bisphenol-A (BPA) is a lipophilic, organic, synthetic compound that has been used as an additive in polycarbonate plastics manufacturing since 1957. Studies have shown that BPA interferes with the development and functions of the brain, but little is known about the effects of BPA on human glutamatergic neurons (hGNs) at the molecular and cellular levels. We investigated the impact of chronic exposure to BPA to hGNs derived from human embryonic stem cells (hESCs). The results showed that chronic exposure of different concentrations of BPA (0, 0.1, 1.0 and 10 μM) to hGNs for 14 days reduced neurite outgrowth in a concentration-dependent manner. Using presynaptic protein synaptophysin and postsynaptic protein PSD-95 antibodies, immunofluorescence staining and western blotting results indicated that BPA exposure altered the morphology of dendritic spines and increased synaptophysin and PSD-95 expression. Furthermore, BPA exposure at concentrations higher than 1.0 μM resulted in the increase of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) expression and deterioration of dendritic spines. In addition, our results suggested that these BPA mediated neurotoxicity effects were due to an increased production of reactive nitrogen species (RNS) and reactive oxygen species (ROS) via increased nitric oxide synthase (iNOS), neuronal nitric oxide synthase (nNOS), 3-nitrotyrosine expression and Ca²⁺ influx. These results imply that hESC-based neuronal differentiation is an excellent cellular model to examine BPA-induced neurotoxicity on human neurons at the cellular and molecular level.