Major depressive disorder (MDD) is a debilitating disorder. Suicide attempts are 5-times higher in MDD patients than in the general population. Interestingly, not all MDD patients develop suicidal thoughts or complete suicide. Thus, it is important to study the risk factors that can distinguish suicidality among MDD patients. The present study examined if DNA methylation changes can distinguish suicidal behavior among depressed subjects. Genome-wide DNA methylation was examined in the dorsolateral prefrontal cortex of depressed suicide (MDD+S; n = 15), depressed non-suicide (MDD-S; n = 17), and nonpsychiatric control (C; n = 16) subjects using 850 K Infinium Methylation EPIC BeadChip. The significantly differentially methylated genes were used to determine the functional enrichment of genes for ontological clustering and pathway analysis. Based on the number of CpG content and their relative distribution from specific landmark regions of genes, 32,958 methylation sites were identified across 12,574 genes in C vs. MDD+/-S subjects, 30,852 methylation sites across 12,019 genes in C vs. MDD-S, 41,648 methylation sites across 13,941 genes in C vs. MDD+S, and 49,848 methylation sites across 15,015 genes in MDD-S vs. MDD+S groups. A comparison of methylation sites showed 33,129 unique methylation sites and 5451 genes in the MDD-S group compared to the MDD+S group. Functional analysis suggested oxytocin, GABA, VGFA, TNFA, and mTOR pathways associated with suicide in the MDD group. Altogether, our data show a distinct pattern of DNA methylation, the genomic distribution of differentially methylated sites, gene enrichment, and pathways in MDD suicide compared to non-suicide MDD subjects.

New combinations or alternative therapies for major depressive disorder (MDD) are necessary. Intradermal acupuncture (IA) shows promise but requires further investigation regarding its efficacy, safety, and mechanisms. Conducted across 3 centers from November 2022 to January 2024, our randomized controlled trial included 120 participants with moderate to severe MDD, divided into the selective serotonin reuptake inhibitors (SSRIs), SSRIs plus sham IA (SSRIs + SIA), and SSRIs plus active IA (SSRIs + AIA) groups. Acupuncture groups received 10 sessions over 6 weeks at Shenmen (HT7), Neiguan (PC6), Sanyinjiao (SP6) and Taichong (LR3) bilaterally, followed by a 4-week follow-up. The primary outcome was changes in Hamilton Depression Rating Scale-17 (HAMD-17) scores at week 6. Furthermore, healthy controls (HCs) and MDD patients underwent magnetic resonance imaging (MRI) scans for functional connectivity (FC) analysis. After 6 weeks of treatment, the SSRIs + AIA group showed a greater reduction in HAMD-17 score than the SSRIs + SIA group (MD, -4.9 [CI, -7.6 to -2.2], P < 0.001) and SSRIs group (MD, -5.1 [CI, -7.8 to -2.3], P < 0.001). No serious adverse events occurred. SSRIs + AIA resulted in lower incidences of palpitations (vs.SSRIs + SIA: OR, 0.1% [CI, 0.0-1.0%]; vs. SSRIs: OR, 0.1% [CI, 0.0-0.7%]; P < 0.05), somnolence (vs.SSRIs + SIA: OR, 0.1% [CI, 0.0-0.9%]; vs.SSRIs: OR, 0.1% [CI, 0.0-0.7%]; P < 0.05), and nausea (vs.SSRIs + SIA: OR, 0.1% [CI, 0.0-1.0%]; vs. SSRIs: OR, 0.1% [CI, 0.0-0.9%]; P < 0.05). MDD patients showed abnormal FCs, and IA enhanced FCs between striatum and frontal_inf_tri, and striatum and cerebellum in the MRI study. Overall, IA as adjunctive therapy provides clinical efficacy and safety for MDD, and it may exert antidepressant effects by modulating striatal FCs.

Chronic stress induces neural dysfunctions and risks mental illnesses. Clinical and preclinical studies have established the roles of brain regions underlying emotional and cognitive functions in stress and depression. However, neural pathways to perceive sensory stimuli as stress to cause behavioral disturbance remain unknown. Using whole-brain imaging of Arc-dVenus neuronal response reporter mice and machine learning analysis, here we unbiasedly demonstrated different patterns of contribution of widely distributed brain regions to neural responses to acute and chronic social defeat stress (SDS). Among these brain regions, multiple sensory cortices, especially the piriform (olfactory) cortex, primarily contributed to classifying neural responses to chronic SDS. Indeed, SDS-induced activation of the piriform cortex was augmented with repetition of SDS, accompanied by impaired odor discrimination. Axonal tracing and chemogenetic manipulation showed that excitatory neurons in the piriform cortex directly project to the lateral septum and activate it in response to chronic SDS, thereby inducing behavioral disturbance. These results pave the way for identifying a spatially defined sequence of neural consequences of stress and the roles of sensory pathways in perceiving chronic stress in mental illness pathology.

Use of one addictive drug typically influences the behavioral response to other drugs, either administered at the same time or a subsequent time point. The nature of the drugs being used, as well as the timing and dosing, also influence how these drugs interact. Here, we tested the effects of adolescent THC exposure on the development of morphine-induced behavioral adaptations following repeated morphine exposure during adulthood. We found that adolescent THC administration paradoxically prevented the development of anxiety-related behaviors that emerge during a forced abstinence period following morphine administration but facilitated reinstatement of morphine CPP. Following forced abstinence, we then mapped the whole-brain response to a moderate dose of morphine and found that adolescent THC administration led to an overall increase in brain-wide neuronal activity and increased the functional connectivity between frontal cortical regions and the ventral tegmental area. Last, we show using rabies virus-based circuit mapping that adolescent THC exposure triggers a long-lasting elevation in connectivity from the frontal cortex regions onto ventral tegmental dopamine cells. Our study adds to the rich literature on the interaction between drugs, including THC and opioids, and provides potential neural substates by which adolescent THC exposure influences responses to morphine later in life.

Brain alterations associated with illness severity in schizophrenia remain poorly understood. Establishing linkages between imaging biomarkers and symptom expression may enhance mechanistic understanding of acute psychotic illness. Constructing models using MRI and clinical features together to maximize model validity may be particularly useful for these purposes. A multi-task deep learning model for standard case/control recognition incorporated with psychosis symptom severity regression was constructed with anatomic MRI collected from 286 patients with drug-naïve first-episode schizophrenia and 330 healthy controls from two datasets, and validated with an independent dataset including 40 first-episode schizophrenia. To evaluate the contribution of regression to the case/control recognition, a single-task classification model was constructed. Performance of unprocessed anatomical images and of predefined imaging features obtained using voxel-based morphometry (VBM) and surface-based morphometry (SBM), were examined and compared. Brain regions contributing to the symptom severity regression and illness identification were identified. Models developed with unprocessed images achieved greater group separation than either VBM or SBM measurements, differentiating schizophrenia patients from healthy controls with a balanced accuracy of 83.0% with sensitivity = 76.1% and specificity = 89.0%. The multi-task model also showed superior performance to single-task classification model without considering clinical symptoms. These findings showed high replication in the site-split validation and external validation analyses. Measurements in parietal, occipital and medial frontal cortex and bilateral cerebellum had the greatest contribution to the multi-task model. Incorporating illness severity regression in pattern recognition algorithms, our study developed an MRI-based model that was of high diagnostic value in acutely ill schizophrenia patients, highlighting clinical relevance of the model.

Serotonin (5-hydroxytryptamine, 5-HT) is a powerful modulator of neuronal activity within the central nervous system and dysfunctions of the serotonergic system have been linked to several neuropsychiatric disorders such as major depressive disorders or schizophrenia. The anterior cingulate cortex (aCC) plays an important role in cognitive capture of stimuli and valence processing and it is densely innervated by serotonergic fibers from the nucleus raphe. In order to understand how pathophysiological 5-HT signalling can lead to neuropsychiatric diseases, it is important to understand the physiological actions of 5-HT on cortical circuits. Therefore, we combined electrophysiological recordings with pharmacology and immunocytochemistry to investigate the effects of 5-HT on Somatostatin-positive interneurons (SOM-INs) and compared these to supragranular pyramidal cells (PCs). This comparison allowed us to identify common and contrasting effects of 5-HT on SOM-INs and PCs of the aCC resulting in a specific modulation of the excitation-to-inhibition balance in PCs but not in SOM-INs.

Angelman syndrome (AS) is a rare genetic neurodevelopmental disorder with profoundly debilitating symptoms with no FDA-approved cure or therapeutic. Brain-derived neurotrophic factor (BDNF), and its receptor tropomyosin receptor kinase B (TrkB), have a well-established role as regulators of synaptic plasticity, dendritic outgrowth and spine formation. Previously, we reported that the association of postsynaptic density protein 95 (PSD-95) with TrkB is critical for intact BDNF signaling in the AS mouse model, as illustrated by attenuated PLCγ and PI3K signaling and intact MAPK pathway signaling. These data suggest that drugs tailored to enhance the TrkB-PSD-95 interaction may provide a novel approach for the treatment of AS and a variety of neurodevelopmental disorders (NDDs). To evaluate this critical interaction, we synthesized a class of high-affinity PSD-95 ligands that bind specifically to the PDZ3 domain of PSD-95, denoted as Syn3 peptidomimetic ligands. We evaluated Syn3 and its analog D-Syn3 (engineered using dextrorotary (D)-amino acids) in vivo using the Ube3a exon 2 deletion mouse model of AS. Following systemic administration of Syn3 and D-Syn3, we demonstrate improvement in the seizure domain of AS. Learning and memory using the novel object recognition assay also illustrated improved cognition following Syn3 and D-Syn3, along with restored long-term potentiation. A pharmacokinetic analysis of D-Syn3 demonstrates that it crosses the blood-brain barrier (BBB), and the brain influx rate is in the range of CNS therapeutics. Finally, D-Syn3 treated mice showed a partial rescue in motor learning. Neither Syn3 nor D-Syn3 improved gross exploratory locomotion deficits, nor gait impairments that have been well documented in the AS rodent models. These findings highlight the need for further investigation of this compound class as a potential therapeutic for AS and other genetic NDDs.

Medicinal cannabis is being used worldwide and there is increasing use of novel cannabis products in the community. Cannabis contains the major cannabinoids, Δ-tetrahydrocannabinol (Δ-THC) and cannabidiol (CBD), but also an array of minor cannabinoids that have undergone much less pharmacological characterization. Cannabinol (CBN) is a minor cannabinoid used in the community in "isolate' products and is claimed to have pro-sleep effects comparable to conventional sleep medications. However, no study has yet examined whether it impacts sleep architecture using objective sleep measures. The effects of CBN on sleep in rats using polysomnography were therefore examined. CBN increased total sleep time, although there was evidence of biphasic effects with initial sleep suppression before a dramatic increase in sleep. CBN increased both non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. The magnitude of the effect of CBN on NREM was comparable to the sleep aid zolpidem, although, unlike CBN, zolpidem did not influence REM sleep. Following CBN dosing, 11-hydroxy-CBN, a primary metabolite of CBN surprisingly attained equivalently high brain concentrations to CBN. 11-hydroxy-CBN was active at cannabinoid CB receptors with comparable potency and efficacy to Δ-THC, however, CBN had much lower activity. We then discovered that the metabolite 11-hydroxy-CBN also influenced sleep architecture, albeit with some subtle differences from CBN itself. This study shows CBN affects sleep using objective sleep measures and suggests an active metabolite may contribute to its hypnotic action.

Emerging evidence suggests that the enhanced activity of lateral habenula (LHb) is involved in depressive disorders. This abnormal potentiation of LHb neurons was shown to originate from presynaptic alterations; however, the mechanisms underlying this presynaptic enhancement and physiological consequences are yet to be elucidated. Previously, we reported that presynaptic transmission in the LHb is temporally rhythmic, showing greater activity in the afternoon than in the morning. Here, we used a learned helpless rodent model of depression to show that exposure to a stressor or incubation with the stress hormone, corticosterone, abolished the presynaptic temporal variation in the LHb. In addition, selective inhibition of mitogen-activated protein kinase (MAPK) kinase (MAPKK, MEK) activity in the LHb restored the presynaptic alteration even after stress exposure. Moreover, we observed a slight increase in phosphorylated synapsin I after stress exposure. Finally, we found that a blockade of MAPK signaling before stress exposure successfully prevented the depression-like behaviors, including behavioral despair and helplessness, in an acute learned helpless animal model of depression. Our study delineates the cellular and molecular mechanisms responsible for the abnormal presynaptic enhancement of the LHb in depression, which may mediate depressive behaviors.

Although chronic cannabis use during adolescence can alter brain function and impair complex behavioral processes, it is unclear whether such deficits persist into adulthood. Using a coordinated awake neuroimaging and behavioral approach in nonhuman primates, we addressed this issue by examining the impact of chronic adolescent exposure to Δ-tetrahydrocannabinol (THC) on brain functional connectivity and motivational processes during early adulthood. Female and male squirrel monkeys (n = 23) were treated daily for 6 months during adolescence with vehicle or either a low (0.32 mg/kg) or high dose (3.2 mg/kg) of THC. Regional homogeneity and seed-to-whole-brain functional connectivity were analyzed prior to, during, and following discontinuation of chronic treatment to examine changes in regions implicated in reward processing. Subsequently, motivation and reward sensitivity in these subjects, now young adults, were evaluated in economic demand studies by determining the relationship between escalating response requirements and consumption of differing magnitudes of a palatable food reinforcer. Results show that adolescent THC exposure led to persistent alterations in mOFC, caudate, and ventral striatum whole-brain connectivity. Moreover, subjects treated with vehicle during adolescence displayed an orderly and expected inverse relationship between reward magnitude and demand elasticity, whereas THC-treated subjects exhibited dosage-dependent disorder in reward sensitivity and motivational deficits. Changes in neural circuitry (local connectivity in ventral striatum and whole brain connectivity in mOFC) and economic demand were correlated with indices of reward sensitivity in vehicle- but not THC-treated subjects. Taken together, these data indicate that chronic adolescent THC exposure produced long-lasting neurocognitive abnormalities in reward processing.

The neurocircuitry mechanisms underlying recall of traumatic memories remain unclear. This study investigated whether traumatic memory recall engages neurocircuitry representations that mirror activity patterns engaged during generalized threat stimulus processing in Post Traumatic Stress Disorder (PTSD). Multivariate pattern analysis was used to train 3 decoders. A "trauma" decoder was trained on fMRI patterns during idiographic trauma versus neutral narratives in a sample of 73 adult women with PTSD. A separate cohort of 125 adult participants completed a reward and threat learning task, from which "shock" and "reward loss" decoders were trained on neural patterns during threat or reward outcome delivery, respectively. These decoders were then cross-tested on the alternative datasets, allowing analyses of the degree to which traumatic memory recall engaged neurocircuitry representations that overlap with more general aversive stimuli. Decoders were trained and tested in four networks related to salience processing as well bilateral amygdala and hippocampal masks. The shock decoder trained in a midcingulate / posterior insula network demonstrated elevated predictions for shock during traumatic versus neutral memory recall. Similarly, the trauma decoder made elevated predictions about trauma recall during shock versus no shock delivery across multiple networks related to salience processing. There was no overlap between reward loss decoder predictions and trauma memory recall or vice versa. PTSD participants with elevated re-experiencing symptoms demonstrated the highest engagement of shock activity patterns during trauma memory recall. These results suggest that trauma memory recall engages neurocircuitry representations that overlap with threat, specifically painful, stimulus delivery.

Up to 45% of patients surviving from transient global cerebral ischemia (GCI) after cardiac arrest develop post-global cerebral ischemia depression (PGCID), but how to treat PGCID is clinically unknown. Here we find that cannabinoid type-1 receptor (CBR) antagonists, CBR knockout and endocannabinoid (eCB) synthesis inhibition block acute stress-induced PGCID. Application of acute stress to GCI mice increases CBR activity from ventromedial prefrontal cortical (vmPFC) terminals synapsing with the basolateral amygdala (BLA) neurons, indicating the involvement of increased vmPFC-BLA synaptic eCB signaling in PGCID induction. This idea is supported by findings that optogenetic activation of CBRs in vmPFC-BLA projections mimics stress effects to induce PGCID, which is blocked by knock-down of eCB biosynthesis enzyme genes in vmPFC-BLA synapses. Interestingly, GCI mice show decreased mRNA expression of eCB degradation enzymes in vmPFCs without significant changes on mRNA expression of eCB biosynthesis and degradation enzymes in BLA cells. Thus, over-expression of eCB degradation enzymes in vmPFC cells innervating BLA neurons or activation of vmPFC-BLA projections blocks stress effects to induce PGCID. Our findings suggest that decreased eCB degradation and subsequent stress-increased eCB signaling in vmPFC-BLA circuits participate in the mechanism of PGCID, which can be treated clinically by eCB signaling interference systemically or in vmPFC-BLA circuits.

Studies using acute or subchronic pharmacological inhibition of phosphodiesterase 2 A (PDE2A) have led to its proposal as a target for treatment of cognitive deficits associated with neuropsychiatric and neurodegenerative disease. However, the impact of continuous inhibition of PDE2A on memory is unknown. Moreover, the neuroanatomical regions mediating memory enhancement have not been categorically identified. To address these open questions, we studied knockout mice and hippocampus restricted manipulations. Pde2a heterozygous knockout mice are viable with no gross histological abnormalities. The mice exhibit enhanced spatial and object recognition memory that is independent of anxiolytic effects and is paralleled by increased density of dendritic mushroom and thin spines in hippocampal CA3 and dentate gyrus in adult mice. In CA1, subtle alterations in spine density were seen, while theta-burst LTP and paired-pulse facilitation were normal. Spatial memory enhancement persists in aged Pde2a heterozygous knockout mice, and to our surprise these mice live significantly longer than wild-type littermate controls. In summary, we provide evidence that life-long reduction of PDE2A expression promotes spine formation and maturation, exerts beneficial effects on memory, and increases lifespan.

Previous studies indicated that ASD-related olfactory dysfunctions are rooted in the piriform cortex. However, the direct evidence supporting a causal link between the dysfunction of the piriform cortex and olfactory disorders in ASD is limited. In the present study, we explored the role of anterior piriform cortex (aPC) in ASD-related olfactory disorders by specifically ablating Fmr1, a leading known monogenic cause for ASD, in the pyramidal neurons. Our data demonstrated that the targeted deletion of Fmr1 in aPC pyramidal neurons was sufficient to induce deficits in olfactory detection. In vivo and in vitro electrophysiological recordings showed that the deletion of Fmr1 increased the activity of pyramidal neurons, exhibiting an enhanced excitatory response and a reduced inhibitory response upon odor stimulation. Furthermore, specific deletion of Fmr1 enhanced the power of beta oscillations during odor stimuli, meanwhile, disturbed excitatory and inhibitory synaptic transmission. The abnormal morphology of pyramidal neurons induced by the deletion of Fmr1 may be responsible for the impaired aPC neuronal function. These findings suggest that dysfunction of the aPC may play a role in olfactory impairments observed in ASD models related to Fmr1 deficiency.

Peripheral neuropathic pain poses a significant global health challenge. Current drugs for peripheral neuropathic pain often fall short in efficacy or come with severe side effects, emphasizing the critical need for the development of highly effective and well-tolerated alternatives. Sophoricoside (SOP) is a nature product-derived isoflavone that possesses various pharmacological effects on inflammatory and neuropathy diseases. Here, in this study, analgesic effect was investigated by intrathecally administration of SOP/vehicle to spared nerve injury (SNI) or paclitaxel-induced peripheral neuropathic pain (PINP) rodent models, and mechanical allodynia was measured in Von Frey tests. Ipsilateral L4-L6 dorsal root ganglia (DRG) were used for protein expression. In silico molecular docking analysis was applied for assessing compound-target binding affinity. Primary cultured DRG neurons were utilized to investigate SOP's effect on veratridine-triggered nociceptor activities and its selective inhibition of voltage-gated sodium channels subtype 1.6 (NaV1.6). The results showed SOP treatment alleviated mechanical allodynia in SNI and PINP rodent models (paw withdrawal threshold after 1 h of injection: SNI-vehicle: 1.385 ± 0.338 g; SNI-SOP: 9.963 ± 2.029 g, P < 0.001; PINP-vehicle: 5.040 ± 0.985 g; PINP-SOP: 8.287 ± 3.812 g, P = 0.004). SOP presented effects on both inhibiting veratridine-triggered nociceptor activities (oscillatory population: vehicle: 39.9 ± 7.3%; SOP: 30.7 ± 9.8%, P = 0.021) and selectively blocking NaV1.6 in DRG sensory neurons. Molecular docking analysis indicated direct binding between SOP and NaV1.6, leading to its endocytosis in DRG Sensory Neurons. In conclusion, SOP alleviated nociceptive allodynia induced by peripheral nerve injury via selectively blocking of NaV1.6 in DRG nociceptive neurons. we highlight its potential as an analgesic and elucidate its mechanism involving NaV1.6 endocytosis. This research opens avenues for exploring the analgesic effects of SOP and its potential impact on neuropathic pain therapy.

Epilepsy often presents with severe emotional comorbidities including anxiety and abnormal fear responses which impose a significant burden on, and reduce, quality of life in people living with the disease. Our lab has recently shown that kindled seizures lead to changes in emotional processing resulting from the downregulation of anandamide signalling within the amygdala. Phytocannabinoids derived from the Cannabis sativa plant have attracted a lot of interest as a new class of drugs with potential anticonvulsant effects. Among the wide number of compounds occurring in Cannabis sativa, Δ9- tetrahydrocannabinol (THC), the one responsible for its main psychoactive effects, and the nonpsychoactive cannabidiol (CBD) have been extensively examined under pre-clinical and clinical contexts to control seizures, however, neither have been assessed in the context of the management of emotional comorbidities associated with seizure activity. We used two behavioural procedures to assess anxiety- and fear-like responding in adult male Long-Evans rats: elevated plus maze and auditory fear conditioning. In agreement with previous reports, we found seizure-induced increases in anxiety- and fear-like responding. These effects were reversed by either CBD (vaporized) or THC (oral). We also found that antagonism of serotonin 1 A receptors prior to CBD exposure prevented its protective effects. Phytocannabinoids offer a novel and reliable opportunity to treat seizure induced comorbid emotional alterations.

The co-chaperone FKBP51, encoded by FKBP5 gene, is recognized as a psychiatric risk factor for anxiety and depressive disorders due to its crucial role in the stress response. Another key modulator in stress response regulation is the corticotropin releasing hormone (CRH), which is co-expressed with FKBP51 in many stress-relevant brain-regions and cell-types. Together, they intricately influence the balance of the hypothalamic-pituitary-adrenal (HPA) axis, one of the primary stress response systems. Previous research underscores the potential moderating effects these genes have on the regulation of the stressful life events towards the vulnerability of major depressive disorder (MDD). However, the specific function of FKBP51 in CRH-expressing neurons remains largely unexplored. Here, through deep behavioral phenotyping, we reveal heightened stress effects in mice lacking FKBP51 in CRH co-expressing neurons (CRH), particularly evident in social contexts. Our findings highlight the importance of considering cell-type specificity and context in comprehending stress responses and advocate for the utilization of machine-learning-driven phenotyping of mouse models. By elucidating these intricacies, we lay down the groundwork for personalized interventions aimed at enhancing stress resilience and individual well-being.

In response to restrictions on electroconvulsive therapy (ECT) access during COVID-19, we designed a trial to assess the clinical outcomes service impacts, employing an extended course of accelerated intermittent theta burst stimulation (aiTBS), in patients with moderate to severe depression in need of ECT. This open label clinical trial was comprised of 3 phases: (i) an acute phase, where iTBS treatments were administered 8 times daily, for up to 10 days; (ii) a tapering phase of 2 treatment days per week for 2 weeks, followed by 1 treatment day per week for 2 weeks; and (iii) a symptom-based relapse prevention phase, whereby treatments were scheduled based on symptom re-emergence, for up to 6 months. Of the 155 patients who completed the acute phase of the study, the remission rate was 16.1%. The mean reduction from baseline on the HRSD-24 was 29.4% (p < 0.001) and the response rate was 25.2%. Of the 110 patients who completed the tapering phase, the mean reduction from baseline was 42.6% (p < 0.001) and response and remission rates were 49.6% and 34.8%, respectively. Of the 61 patients who were eligible for the relapse prevention phase, 43 completed, with a mean reduction from baseline of 60.1% (p < 0.001); 7 patients relapsed during this phase. This study demonstrated that an extended aiTBS protocol safely led to meaningful clinical outcomes in patients with severe depression, who otherwise would have received ECT, and thus reduced pressure on ECT services during the pandemic. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT04384965 ( https://clinicaltrials.gov/study/NCT04384965?term=NCT04384965&rank=1 ).

Cognitive flexibility and working memory are important executive functions mediated by the prefrontal cortex and can be impaired by circadian rhythm disturbances such as chronic jet lag (CJL) or shift work. In the present study, we used mice to investigate whether (1) simulated CJL impairs cognitive flexibility, (2) the orexin system is involved in such impairment, and (3) nasal administration of orexin A is able to reverse CJL-induced deficits in cognitive flexibility and working memory. Mice were exposed to either standard light-dark conditions or simulated CJL consisting of series of advance time shifts. Experiment (1) investigated the effects of a mild CJL protocol on cognitive flexibility using the attentional set shifting task. Experiment (2) used a stronger CJL protocol and examined CJL effects on the orexin system utilizing c-Fos and orexin immunohistochemistry. Experiment (3) tested whether nasal orexin application can rescue CJL-induced deficits in cognitive flexibility and working memory, the latter by measuring spontaneous alternation in the Y-maze. The present data show that CJL (1) impairs cognitive flexibility and (2) reduces the activity of orexin neurons in the lateral hypothalamus. (3) Nasal administration of orexin A rescued CJL-induced deficits in working memory and cognitive flexibility. These findings suggest that executive function impairments by circadian rhythm disturbances such as CJL are caused by dysregulation of orexinergic input to the prefrontal cortex. Compensation of decreased orexinergic input by nasal administration of orexin A could be a potential therapy for CJL- or shift work-induced human deficits in executive functions.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide widely distributed in the brain including the hypothalamic paraventricular nucleus (PVN) implying a regulatory role in stress function. Recent evidence indicates that one of the main targets of PACAP within the PVN are corticotropin-releasing factor (CRF) neurons, which are key regulators of the hypothalamic-pituitary-adrenal (HPA) axis. However, the neural correlates that mediate PACAP effects on stress function are not fully understood. In the present study, we characterized the neuronal mechanism by which PACAP regulates neuroendocrine and behavioral stress responses in rats. We found that intracerebroventricular administration of PACAP increased the swim stress-induced c-Fos expression in distinct brain areas of the stress and anxiety circuitry including the parvocellular part of the PVN and changed behavioral stress coping during forced swimming to a more passive coping style (i.e., indicated by increased floating and reduced struggling behavior). Subsequently, PACAP administration directly into the PVN mimicked these behavioral effects and potentiated the plasma ACTH response to forced swim stress suggesting an excitatory role of PACAP on HPA stress axis reactivity. In addition, immunohistochemical analysis revealed a considerable portion of stress-activated CRF neurons in the medial parvocellular part of the PVN that co-localized PAC1 receptors suggesting that PACAP-induced effects on stress function are likely mediated directly by activation of CRF neurons in the PVN. Thus, these findings suggest that the PVN may represent one of the key areas where PACAP regulates the neuroendocrine and behavioral stress response.