Genetic deletion of P-glycoprotein alters stress responsivity and increases depression-like behavior, social withdrawal and microglial activation in the hippocampus of female mice

Interactions between ABC gene polymorphisms and processing speed in predicting depression severity

BACKGROUND

ABC family genes encode ATP-binding cassette proteins, which are involved in the transport of various substances and are associated with major depressive disorder (MDD); however, their clinical significance in MDD remains unclear. Therefore, this study aimed to investigate whether ABC family genes are associated with cognitive function, and the combined effects of genes and cognitive function on the severity of depression.

METHOD

Linear models or logistic regression models were used to investigate the associations of ABC family gene variants with clinical symptoms and cognitive function in 805 MDD patients (12-65 years old) and 1493 age-matched healthy controls (HCs). Seven single nucleotide polymorphisms (rs28401781, rs4148739, rs3747802, rs1109866, rs1109867, rs3731885, and rs3755047) of ABCB1 and ABCB6 were selected. The cognitive function was assessed by the Wisconsin Card Sorting Test (WCST), Tower of Hanoi Test (TOH), Trail Making Test (TMT), and Verbal Fluency Test (VF).

RESULTS

Significant differences in gene frequency and genotype frequency were observed at the rs1109866 (X2 = 8.22, p = 0.004; X2 = 9.82, p = 0.007) and rs1109867 (X2 = 7.35, p = 0.007; X2 = 9.15, p = 0.010) between MDD patients and HCs, even after correction. While rs28401781 (t = 2.78, p = 0.006) and rs4148739 (t = 3.08, p = 0.003) were associated with the TOH test. And both rs1109866 and rs1109867 interacted with TMT results to influence depression severity in MDD patients.

CONCLUSION

The results suggest that ABC family genes influence the severity of depression through cognitive functioning, providing possible evidence for genetic markers in MDD patients.

Contributions of associative and non-associative learning to the dynamics of defensive ethograms

Defensive behavior changes based on threat intensity, proximity, and context of exposure, and learning about danger-predicting stimuli is critical for survival. However, most Pavlovian fear conditioning paradigms focus only on freezing behavior, obscuring the contributions of associative and non-associative mechanisms to dynamic defensive responses. To thoroughly investigate defensive ethograms, we subjected male and female adult C57BL/6 J mice to a Pavlovian conditioning paradigm that paired footshock with a serial compound stimulus (SCS) consisting of distinct tone and white noise (WN) stimulus periods. To investigate how associative and non-associative mechanisms affect defensive responses, we compared this paired SCS-footshock group with four control groups that were conditioned with either pseudorandom unpaired presentations of SCS and footshock, shock only, or reversed SCS presentations with inverted tone-WN order, with paired or unpaired presentations. On day 2 of conditioning, the paired group exhibited robust freezing during the tone period with switching to explosive jumping and darting behaviors during the WN period. Comparatively, the unpaired and both reverse SCS groups expressed less tone-induced freezing and rarely showed jumping or darting during WN. Following the second day of conditioning, we observed how defensive behavior changed over two extinction sessions. During extinction, the tone-induced freezing decreased in the paired group, and mice rapidly shifted from escape jumping during WN to a combination of freezing and darting. The unpaired, unpaired reverse, and shock-only groups displayed defensive tail rattling and darting during the SCS, with minimal freezing and jumping. Interestingly, the paired reverse group did not jump to WN, and tone-evoked freezing was resistant to extinction. These findings demonstrate that non-associative factors promote some defensive responsiveness, but associative factors are required for robust cue-induced freezing and high-intensity flight expression.

Unraveling the Role of the Blood-Brain Barrier in the Pathophysiology of Depression: Recent Advances and Future Perspectives

Depression is a highly prevalent psychological disorder characterized by persistent dysphoria, psychomotor retardation, insomnia, anhedonia, suicidal ideation, and a remarkable decrease in overall well-being. Despite the prevalence of accessible antidepressant therapies, many individuals do not achieve substantial improvement. Understanding the multifactorial pathophysiology and the heterogeneous nature of the disorder could lead the way toward better outcomes. Recent findings have elucidated the substantial impact of compromised blood-brain barrier (BBB) integrity on the manifestation of depression. BBB functions as an indispensable defense mechanism, tightly overseeing the transport of molecules from the periphery to preserve the integrity of the brain parenchyma. The dysfunction of the BBB has been implicated in a multitude of neurological disorders, and its disruption and consequent brain alterations could potentially serve as important factors in the pathogenesis and progression of depression. In this review, we extensively examine the pathophysiological relevance of the BBB and delve into the specific modifications of its components that underlie the complexities of depression. A particular focus has been placed on examining the effects of peripheral inflammation on the BBB in depression and elucidating the intricate interactions between the gut, BBB, and brain. Furthermore, this review encompasses significant updates on the assessment of BBB integrity and permeability, providing a comprehensive overview of the topic. Finally, we outline the therapeutic relevance and strategies based on BBB in depression, including COVID-19-associated BBB disruption and neuropsychiatric implications. Understanding the comprehensive pathogenic cascade of depression is crucial for shaping the trajectory of future research endeavors.

Contributions of associative and non-associative learning to the dynamics of defensive ethograms

Defensive behavior changes based on threat intensity, proximity, and context of exposure, and learning about danger-predicting stimuli is critical for survival. However, most Pavlovian fear conditioning paradigms focus only on freezing behavior, obscuring the contributions of associative and non-associative mechanisms to dynamic defensive responses. To thoroughly investigate defensive ethograms, we subjected male and female adult C57BL/6J mice to a Pavlovian conditioning paradigm that paired footshock with a serial compound stimulus (SCS) consisting of distinct tone and white noise (WN) stimulus periods. To investigate how associative and non-associative mechanisms affect defensive responses, we compared this paired SCS-footshock group with four control groups that were conditioned with either pseudorandom unpaired presentations of SCS and footshock, shock only, or reversed SCS presentations with inverted tone--WN order, with paired or unpaired presentations. On day 2 of conditioning, the paired group exhibited robust freezing during the tone period with switching to explosive jumping and darting behaviors during the WN period. Comparatively, the unpaired and both reverse SCS groups expressed less tone-induced freezing and rarely showed jumping or darting during WN. Following the second day of conditioning, we observed how defensive behavior changed over two extinction sessions. During extinction, the tone-induced freezing decreased in the paired group and mice rapidly shifted from escape jumping during WN to a combination of freezing and darting. The unpaired, unpaired reverse, and shock-only groups displayed defensive tail rattling and darting during the SCS, with minimal freezing and jumping. Interestingly, the paired reverse group did not jump to WN, and tone-evoked freezing was resistant to extinction. These findings demonstrate that non-associative factors promote some defensive responsiveness, but associative factors are required for robust cue-induced freezing and high-intensity flight expression.

P-Glycoprotein Exacerbates Brain Injury Following Experimental Cerebral Ischemia by Promoting Proinflammatory Microglia Activation

Microglia are activated following cerebral ischemic insult. P-glycoprotein (P-gp) is an efflux transporter on microvascular endothelial cells and upregulated after cerebral ischemia. This study evaluated the effects and possible mechanisms of P-gp on microglial polarization/activation in mice after ischemic stroke. P-gp-specific siRNA and adeno-associated virus (p-AAV) were used to silence and overexpress P-gp, respectively. Middle cerebral artery occlusion/reperfusion (MCAO/R) and oxygen-glucose deprivation/reoxygenation (OGD/R) were performed in mice and cerebral microvascular endothelial cells (bEnd.3) in vitro, respectively. OGD/R-injured bEnd.3 cells were cocultured with mouse microglial cells (BV2) in Transwell. Influences on acute ischemic stroke outcome, the expression of inflammatory cytokines, and chemokines and chemokines receptors, microglial polarization, glucocorticoid receptor (GR) nuclear translocation, and GR-mediated mRNA decay (GMD) activation were evaluated via reverse transcription real-time polymerase chain reaction, western blot, or immunofluorescence. Silencing P-gp markedly alleviated experimental ischemia injury as indicated by reduced cerebral infarct size, improved neurological deficits, and reduced the expression of interleukin-6 (IL-6) and IL-12 expression. Silencing P-gp also mitigated proinflammatory microglial polarization and the expression of C-C motif chemokine ligand 2 (CCL2) and its receptor CCR2 expression, whereas promoted anti-inflammatory microglia polarization. Additionally, P-gp silencing promoted GR nuclear translocation and the expression of GMD relative proteins in endothelial cells. Conversely, overexpressing P-gp via p-AAV transfection offset all these effects. Furthermore, silencing endothelial GR counteracted all effects mediated by silencing or overexpressing P-gp. Elevated P-gp expression aggravated inflammatory response and brain damage after ischemic stroke by augmenting proinflammatory microglial polarization in association with increased endothelial CCL2 release due to GMD inhibition by P-gp.

P-glycoprotein and cancer: what do we currently know?

Acquired resistance during cancer treatment is unfortunately a frequent event. There are several reasons for this, including the ability of the ATP-binding cassette transporters (ABC transporters), which are integral membrane proteins, to export chemotherapeutic molecules from the interior of the tumor cells. One important member of this family is the protein known as Permeability Glycoprotein (P-Glycoprotein, P-gp or ABCB1). Its clinical relevance relies mainly on the fact that the inhibition of P-gp and other ABC transporters could result in the reversal of the multidrug resistance (MDR) phenotype in some patients. Recently, other roles apart from being a key player in MDR, have emerged for P-gp. Therefore, this review discusses the relationship between P-gp and MDR, in addition to the possible role of this protein as a biomarker in cancer.

Sex-specific transcriptomic and epitranscriptomic signatures of PTSD-like fear acquisition

Our understanding of the molecular pathology of posttraumatic stress disorder (PTSD) is evolving due to advances in sequencing technologies. With the recent emergence of Oxford Nanopore direct RNA-seq (dRNA-seq), it is now also possible to interrogate diverse RNA modifications, collectively known as the “epitranscriptome.”. Here, we present our analyses of the male and female mouse amygdala transcriptome and epitranscriptome, obtained using parallel Illumina RNA-seq and Oxford Nanopore dRNA-seq, associated with the acquisition of PTSD-like fear induced by Pavlovian cued-fear conditioning. We report significant sex-specific differences in the amygdala transcriptional response during fear acquisition and a range of shared and dimorphic epitranscriptomic signatures. Differential RNA modifications are enriched among mRNA transcripts associated with neurotransmitter regulation and mitochondrial function, many of which have been previously implicated in PTSD. Very few differentially modified transcripts are also differentially expressed, suggesting an influential, expression-independent role for epitranscriptional regulation in PTSD-like fear acquisition.

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PTSD-like trauma has sexually dimorphic effects on the amygdala transcriptome

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Most RNA modifications identified adhere to the known patterns associated with m6A

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There was enrichment of RNA modifications in neurological/PTSD-related genes

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There was little overlap between transcriptomic and epitranscriptomic signatures

The Cannabis Constituent Cannabigerol Does Not Disrupt Fear Memory Processes or Stress-Induced Anxiety in Mice

Introduction: Medicinal cannabis has proliferated around the world and there is increasing interest in the therapeutic potential of individual plant-derived cannabinoids (phytocannabinoids). Preclinical evidence suggests the phytocannabinoid cannabigerol (CBG) could be useful in treating brain disorders, including stress and anxiety-related disorders. In this study, we aimed to explore whether CBG disrupts various contextually conditioned fear memory processes and trauma-induced anxiety-related behavior in a mouse model of post-traumatic stress disorder (PTSD). Materials and Methods: All mice underwent contextual fear conditioning. CBG was administered between 1 and 60 mg/kg intraperitoneally (i.p.). We first assessed the effects of repeated CBG exposure on long-term fear memories. We also examined whether acute CBG affected various fear memory processes, namely expression, acquisition, consolidation, and reconsolidation of conditioned fear. Finally, the effect of acute CBG administration on stress-induced anxiety in the light/dark test was assessed. Results: Repeated CBG exposure did not affect long-term conditioned fear that was observed 24 days after the conditioning session. Moreover, acute CBG administration did not influence the acquisition, consolidation, reconsolidation, or expression of contextually conditioned fear. Acute CBG treatment also did not affect stress-induced anxiety-related behaviors in the light/dark test. Conclusions: CBG was ineffective in disrupting long-term fear memories, various conditioned fear memory processes, or stress-induced anxiety-related behavior in mice. These preclinical data suggest CBG may have limited scope in the treatment of PTSD and stress-related anxiety.

Tailoring of P-glycoprotein for effective transportation of actives across blood-brain-barrier

P-Glycoprotein serves as a gatekeeper in the blood-brain-barrier wherein, it shows a vital part in the elimination of xenobiotics, drugs, foreign molecules etc. and guards the central nervous system from infections and external toxic molecules by functioning as an efflux transporter. It plays an essential role in various brain-related conditions like Parkinsonism, Alzheimer's disease, depression, cancer, etc. and terminates the entry of therapeutic agents across blood-brain-barrier which remains a significant challenge serving as major hindrance in pharmacotherapy of disease. The physiological structure and topology of P-glycoprotein and its relation with blood-brain-barrier and central nervous system gives an idea for targeting nanocarriers across the barrier into brain. This review article provides an overview of current understanding of the nanoformulations-based P-gp trafficking strategies like nanocarriers, stem cell therapy, drugs, substrates, polymeric materials, chemical compounds as well as naturally occurring active constituents for improving drug transport in brain across blood-brain-barrier and contributing in effective nanotherapeutic development for treatment of CNS disorders.

Adolescent behavioral abnormalities in a Scn1a+/- mouse model of Dravet syndrome

Dravet syndrome is an intractable pediatric epilepsy associated with SCN1A mutations. In addition to having a large seizure burden and a reduced lifespan, patients with Dravet syndrome also exhibit delays in reaching normal developmental milestones in attentional, emotional, and cognitive function. These developmental delays manifest in autistic-like social withdrawal and compulsive behavior. Additionally, cognitive impairments including deficits in sensorimotor processing and memory function are present. Several mouse models utilizing heterozygous deletion of Scn1a (Scn1a^+/- mice) have been generated that recapitulate many aspects of Dravet syndrome. Studies in these mouse models of Dravet syndrome have characterized behavioral phenotypes in adult mice. In the present study, we characterized the behavioral phenotype of Scn1a^+/- mice generated by targeted deletion of Scn1a exon 1 (Scn1a^tm1Kea) during adolescence. Identifying behavioral deficits in adolescent mice would more closely model the early onset of attentional, emotional, and cognitive delays observed in patients with Dravet syndrome. The behaviors of adolescent Scn1a^+/- and wildtype (WT) mice were compared across several behavioral domains. We assessed motor function (open-field test), sociability and social recognition memory (three-chambered social preference and social interaction tests), memory function (novel object recognition, Barnes maze, fear conditioning paradigm), anxiety-related behavior (elevated plus maze and open-field thigmotaxis), startle reflex and sensorimotor gating (prepulse inhibition of startle (PPI) tests), and repetitive compulsive behavior (marble burying test). Adolescent Scn1a^+/- mice exhibited normal locomotor activity, marble burying behavior, sociability, and sensorimotor gating. However, adolescent Scn1a^+/- mice displayed increased anxiety-related thigmotactic behavior, atypical fear expression, blunted acoustic startle responses, and impaired social recognition and spatial memory. Our results show that Scn1a^+/- mice display various behavioral impairments during adolescence, which provides a foundation for testing early intervention therapies targeting developmental delays modeled in Dravet syndrome mice.

P2X7 receptor knockout mice display less aggressive biting behaviour correlating with increased brain activation in the piriform cortex

P2X₇ receptors are implicated in the pathophysiology of psychiatric conditions such as depression and bipolar disorder. P2X₇ receptors regulate the release of pro-inflammatory cytokines from microglia, and gain-of-function P2X₇ mutations may contribute to the neuroinflammation found in affective disorders. However, the role of this receptor in mediating other mental health conditions and aberrant behaviours requires further examination. The current study we investigated the effects of germline genetic deletion of P2xr7 on social and marble burying behaviours in mice throughout the critical adolescent developmental period. Marble burying behaviour is thought to provide a mouse model of obsessive-compulsive disorder (OCD). We also characterised the effects of P2rx7 deletion on aggressive attack behaviour in adult mice and subsequently quantifieded microglial cell densities and c-Fos expression, a marker of neuronal activation. P2rx7 knockout mice displayed reduced OCD-related marble burying behaviour which was most pronounced in late adolescence/early adulthood. P2rx7 knockout mice also exhibited reduced aggressive attack behaviours in adulthood in the resident-intruder test. Reduced aggression in P2xr7 knockout mice did not coincide with changes to microglial cell densities, however c-Fos expression was elevated in the piriform cortex of P2rx7 knockout mice compared to wildtype mice. This study suggests that the P2X₇ receptor might serve as a novel target for serenic or anti-OCD therapeutics.

Deactivation of ATP-Binding Cassette Transporters ABCB1 and ABCC1 Does Not Influence Post-ischemic Neurological Deficits, Secondary Neurodegeneration and Neurogenesis, but Induces Subtle Microglial Morphological Changes

ATP-binding cassette (ABC) transporters prevent the access of pharmacological compounds to the ischemic brain, thereby impeding the efficacy of stroke therapies. ABC transporters can be deactivated by selective inhibitors, which potently increase the brain accumulation of drugs. Concerns have been raised that long-term ABC transporter deactivation may promote neuronal degeneration and, under conditions of ischemic stroke, compromise neurological recovery. To elucidate this issue, we exposed male C57BL/6 mice to transient intraluminal middle cerebral artery occlusion (MCAO) and examined the effects of the selective ABCB1 inhibitor tariquidar (8 mg/kg/day) or ABCC1 inhibitor MK-571 (10 mg/kg/day), which were administered alone or in combination with each other over up to 28 days, on neurological recovery and brain injury. Mice were sacrificed after 14, 28, or 56 days. The Clark score, RotaRod, tight rope, and open field tests revealed reproducible motor-coordination deficits in mice exposed to intraluminal MCAO, which were not influenced by ABCB1, ABCC1, or combined ABCB1 and ABCC1 deactivation. Brain volume, striatum volume, and corpus callosum thickness were not altered by ABCB1, ABCC1 or ABCB1, and ABCC1 inhibitors. Similarly, neuronal survival and reactive astrogliosis, evaluated by NeuN and GFAP immunohistochemistry in the ischemic striatum, were unchanged. Iba1 immunohistochemistry revealed no changes of the overall density of activated microglia in the ischemic striatum of ABC transporter inhibitor treated mice, but subtle changes of microglial morphology, that is, reduced microglial cell volume by ABCB1 deactivation after 14 and 28 days and reduced microglial ramification by ABCB1, ABCC1 and combined ABCB1 and ABCC1 deactivation after 56 days. Endogenous neurogenesis, assessed by BrdU incorporation analysis, was not influenced by ABCB1, ABCC1 or combined ABCB1 and ABCC1 deactivation. Taken together, this study could not detect any exacerbation of neurological deficits or brain injury after long-term ABC transporter deactivation in this preclinical stroke model.

Microglial cell hyper-ramification and neuronal dendritic spine loss in the hippocampus and medial prefrontal cortex in a mouse model of PTSD

Few animal models exist that successfully reproduce several core associative and non-associative behaviours relevant to post-traumatic stress disorder (PTSD), such as long-lasting fear reactions, hyperarousal, and subtle attentional and cognitive dysfunction. As such, these models may lack the face validity required to adequately model pathophysiological features of PTSD such as CNS grey matter loss and neuroinflammation. Here we aimed to investigate in a mouse model of PTSD whether contextual fear conditioning associated with a relatively high intensity footshock exposure induces loss of neuronal dendritic spines in various corticolimbic brain regions, as their regression may help explain grey matter reductions in PTSD patients. Further, we aimed to observe whether these changes were accompanied by alterations in microglial cell number and morphology, and increased expression of complement factors implicated in the mediation of microglial cell-mediated engulfment of dendritic spines. Adult male C57Bl6J mice were exposed to a single electric footshock and subsequently underwent phenotyping of various PTSD-relevant behaviours in the short (day 2-4) and longer-term (day 29-31). 32 days post-exposure the brains of these animals were subjected to Golgi staining of dendritic spines, microglial cell Iba-1 immunohistochemistry and immunofluorescent staining of the complement factors C1q and C4. Shock exposure promoted a lasting contextual fear response, decreased locomotor activity, exaggerated acoustic startle responses indicative of hyperarousal, and a short-term facilitation of sensorimotor gating function. The shock triggered loss of dendritic spines on pyramidal neurons was accompanied by increased microglial cell number and complexity in the medial prefrontal cortex and dorsal hippocampus, but not in the amygdala. Shock also increased expression of C1q in the pyramidal layer of the CA1 region of the hippocampus but not in other brain regions. The present study further elaborates on the face and construct validity of a mouse model of PTSD and provides a good foundation to explore potential molecular interactions between microglia and dendritic spines.

Neuregulin 1 Deficiency Modulates Adolescent Stress-Induced Dendritic Spine Loss in a Brain Region-Specific Manner and Increases Complement 4 Expression in the Hippocampus

One neuropathological feature of schizophrenia is a diminished number of dendritic spines in the prefrontal cortex and hippocampus. The neuregulin 1 (Nrg1) system is involved in the plasticity of dendritic spines, and chronic stress decreases dendritic spine densities in the prefrontal cortex and hippocampus. Here, we aimed to assess whether Nrg1 deficiency confers vulnerability to the effects of adolescent stress on dendritic spine plasticity. We also assessed other schizophrenia-relevant neurobiological changes such as microglial cell activation, loss of parvalbumin (PV) interneurons, and induction of complement factor 4 (C4). Adolescent male wild-type (WT) and Nrg1 heterozygous mice were subjected to chronic restraint stress before their brains underwent Golgi impregnation or immunofluorescent staining of PV interneurons, microglial cells, and C4. Stress in WT mice promoted dendritic spine loss and microglial cell activation in the prefrontal cortex and the hippocampus. However, Nrg1 deficiency rendered mice resilient to stress-induced dendritic spine loss in the infralimbic cortex and the CA3 region of the hippocampus without affecting stress-induced microglial cell activation in these brain regions. Nrg1 deficiency and adolescent stress combined to trigger increased dendritic spine densities in the prelimbic cortex. In the hippocampal CA1 region, Nrg1 deficiency accentuated stress-induced dendritic spine loss. Nrg1 deficiency increased C4 protein and decreased C4 mRNA expression in the hippocampus, and the number of PV interneurons in the basolateral amygdala. This study demonstrates that Nrg1 modulates the impact of stress on the adolescent brain in a region-specific manner. It also provides first evidence of a link between Nrg1 and C4 systems in the hippocampus.

PI3K/Akt/NF-κB signaling pathway regulates behaviors in adolescent female rats following with neonatal maternal deprivation and chronic mild stress

The early-life aversive experiences are associated with the increased risk for adolescent neuropsychiatric disorders and neuroinflammation. So, we used neonatal maternal deprivation (NMD) and chronic mild stress (CMS) to build adolescent depression model and investigate the role of microglia activation, PI3K/Akt/NF-κB pathway in female rats. Pups in NMD group were separated from mothers for 3 h each day from postnatal day (PND) 2 to PND 21 and rats in CMS group were subjected to one mild stressor each day from PND 22 to PND 42. Sucrose preference test (SPT), open field test (OFT), novel objective recognition test (NORT), Elevated-plus maze (EPM), marble burying test (MBT) and forced swimming test (FST) were performed from PND 42 to PND 50. Iba-1, pPI3K/PI3K, pAkt/Akt, and NF-κB expressions in the prefrontal cortex (PFC) and hippocampus (HIP) were detected by Western-Blot. Contents of IL-6, IL-1β and TNF-α were detected by ELISA method. It was found NMD + CMS increased the immobility time, buried marble number, inflammatory cytokines release and reduced the sucrose consumption ratio, time ratio and distance ratio in open arm, crossing times, rearing times. Furthermore, it decreased the discrimination ratio (DR) and discrimination index (DI) in T₂ phase. NMD + CMS upregulated the expression of Iba-1, pPI3K/PI3K, pacts/Akt, and NF-κB in PFC and HIP. NMD or CMS solely didn't affect all these behaviors in rats. Sertraline treatment reversed these changes after NMD + CMS. In view of our findings we propose the NMD + CMS procedure as a potentially useful animal model to analyze developmental emotional behaviors and cognitive dysfunction in adolescent female rats, which may be related with microglial activation and PI3k/Akt/NF-κB pathway upregulation.

Blood-brain barrier regulation in psychiatric disorders

The blood-brain barrier (BBB) is a dynamic interface between the peripheral blood supply and the cerebral parenchyma, controlling the transport of material to and from the brain. Tight junctions between the endothelial cells of the cerebral microvasculature limit the passage of large, negatively charged molecules via paracellular diffusion whereas transcellular transportation across the endothelial cell is controlled by a number of mechanisms including transporter proteins, endocytosis, and diffusion. Here, we review the evidence that perturbation of these processes may underlie the development of psychiatric disorders including schizophrenia, autism spectrum disorder (ASD), and affective disorders. Increased permeability of the BBB appears to be a common factor in these disorders, leading to increased infiltration of peripheral material into the brain culminating in neuroinflammation and oxidative stress. However, although there is no common mechanism underpinning BBB dysfunction even within each particular disorder, the tight junction protein claudin-5 may be a clinically relevant target given that both clinical and pre-clinical research has linked it to schizophrenia, ASD, and depression. Additionally, we discuss the clinical significance of the BBB in diagnosis (genetic markers, dynamic contrast-enhanced-magnetic resonance imaging, and blood biomarkers) and in treatment (drug delivery).

Hippocampal interleukin-1 mediates stress-enhanced fear learning: A potential role for astrocyte-derived interleukin-1β

Post-traumatic stress disorder (PTSD) is associated with immune dysregulation. We have previously shown that severe stress exposure in a preclinical animal model of the disorder, stress-enhanced fear learning (SEFL), is associated with an increase in hippocampal interleukin-1β (IL-1β) and that blocking central IL-1 after the severe stress prevents the development of SEFL. Here, we tested whether blocking hippocampal IL-1 signaling is sufficient to prevent enhanced fear learning and identified the cellular source of stress-induced IL-1β in this region. Experiment 1 tested whether intra-dorsal hippocampal (DH) infusions of interleukin-1 receptor antagonist (IL-1RA, 1.25µg per hemisphere) 24 and 48h after stress exposure prevents the development of enhanced fear learning. Experiment 2 used triple fluorescence immunohistochemistry to examine hippocampal alterations in IL-1β, glial fibrillary acidic protein (GFAP), an astrocyte-specific marker, and ionized calcium binding adaptor molecule -1 (Iba-1), a microglial-specific marker, 48h after exposure to the severe stressor of the SEFL paradigm. Intra-DH IL-1RA prevented SEFL and stress-induced IL-1β was primarily colocalized with astrocytes in the hippocampus. Further, hippocampal GFAP immunoreactivity was not altered, whereas hippocampal Iba-1 immunoreactivity was significantly attenuated following severe stress. These data suggest that hippocampal IL-1 signaling is critical to the development of SEFL and that astrocytes are a predominant source of stress-induced IL-1β.