Hippocampal modulation of sensorimotor processes

The microgravity environment affects sensorimotor adaptation and its neural correlates

The microgravity environment results in transient changes in sensorimotor behavior upon astronauts' return to Earth; the effects on behavior inflight are less understood. We examined whether adaptation to sensory conflict is disrupted in microgravity, suggesting competition for adaptive resources. We evaluated sensorimotor adaptation pre-, in-, and post-flight, as well as functional brain changes at pre- and post-flight, in astronauts participating in International Space Station missions. Astronauts (n = 13) performed this task pre- and four times post-flight within an MRI scanner and performed the task three times in microgravity during a 6-mo mission. We collected behavioral data from Earth-bound controls (n = 13) along the same timeline. Astronauts displayed no change in adaptation from pre- to inflight or following their return to Earth. They showed greater aftereffects of adaptation inflight; controls did not. Astronauts also displayed increased brain activity from pre- to post-flight. These increases did not return to baseline levels until 90 d post-flight. This pattern of brain activity may reflect compensation, allowing astronauts to maintain pre-flight performance levels. These findings indicate that microgravity does not alter short-term visuomotor adaptation; however, it does affect de-adaptation, and post-flight sensorimotor neural activation can take up to 90 d to return to pre-flight levels.

Impact of sleep disturbance in shift workers on hippocampal volume and psychomotor speed

STUDY OBJECTIVES

Shift work interferes with circadian rhythms, affecting sleep quality and cognitive function. Poor sleep quality in shift worker (SW)s can impair psychomotor performance due to fatigue and sleepiness, increasing the risk of errors, accidents, and reduced productivity. Given the potential for atrophic changes in the hippocampus due to sleep disturbances, our study investigates how poor sleep quality correlates with hippocampal structural alterations and impacts psychomotor performance among SWs.

METHODS

We recruited 100 SWs, classifying them based on sleep quality into two groups: good sleep-SW group (n = 59) and poor sleep-SW group (n = 41). Sleep quality was assessed using both 7-day actigraphy for sleep efficiency and the Pittsburgh Sleep Quality Index. A control group of 106 non-SWs without sleep problems (non-SW group) was also included for comparison. The outcome measures were psychomotor speed and hippocampal volumes, both total and by subfield.

RESULTS

The poor sleep-SW group showed significantly smaller hippocampal volumes than both the good sleep-SW group (p < .001) and the non-SW group (p = .003). Longer shift work years correlated with greater reductions in hippocampal volume in this group (r = -0.42, p = .009), unlike in the good sleep-SW group (r = 0.08, p = .541). Furthermore, they demonstrated declines in psychomotor speed relative to the non-SW group (p = .006), which correlated with smaller hippocampal volumes (r = 0.37, p = .020).

CONCLUSIONS

SWs with poor sleep quality exhibit significant hippocampal volume reductions and psychomotor speed decline, underscoring the importance of early intervention and support for sleep issues in this population.

Investigating 7,8-Dihydroxyflavone to combat maternal immune activation effects on offspring gene expression and behaviour

Infection during pregnancy is a substantial risk factor for the unborn child to develop autism or schizophrenia later in life, and is thought to be driven by maternal immune activation (MIA). MIA can be modelled by exposing pregnant mice to Polyinosinic: polycytidylic acid (Poly-I:C), a viral mimetic that induces an immune response and recapitulates in the offspring many neurochemical features of ASD and schizophrenia, including altered BDNF-TrkB signalling and disruptions to excitatory/inhibitory balance. Therefore, we hypothesised that a BDNF mimetic, 7,8-Dihydroxyflavone (7,8-DHF), administered prophylactically to the dam may prevent the neurobehavioural sequelae of disruptions induced by MIA. Dams were treated with 7,8-DHF in the drinking water (0.08 mg/ML) from gestational day (GD) 9-20 and were exposed to Poly-I:C at GD17 (20 mg/kg, i.p.). Foetal brains were collected 6 h post Poly-I:C exposure for RT-qPCR analysis of BDNF, cytokine, GABAergic and glutamatergic gene targets. A second adult cohort were tested in a battery of behavioural tests relevant to schizophrenia and the prefrontal cortex and ventral hippocampus dissected for RT-qPCR analysis. Foetal brains exposed to Poly-I:C showed increased IL-6, but reduced expression of Ntrk2 and multiple GABAergic and glutamatergic markers. Anxiety-like behaviour was observed in adult offspring prenatally exposed to poly-I:C, which was accompanied by altered expression of Gria2 in the prefrontal cortex and Gria4 in the ventral hippocampus. While 7-8 DHF normalised the expression of some glutamatergic (Grm5) and GABAergic (Gabra1) genes in Poly-I:C exposed offspring, it also led to substantial alterations in offspring not exposed to Poly-I:C. Furthermore, mice exposed to 7,8-DHF prenatally showed increased pre-pulse inhibition and reduced working memory in adulthood. These data advance understanding of how 7,8-DHF and MIA prenatal exposure impacts genes critical to excitatory/inhibitory pathways and related behaviour.

Facial icons as indexes of emotions and intentions

Various objects and artifacts incorporate representations of faces, encompassing artworks like portraits, as well as ethnographic or industrial artifacts such as masks or humanoid robots. These representations exhibit diverse degrees of human-likeness, serving different functions and objectives. Despite these variations, they share common features, particularly facial attributes that serve as building blocks for facial expressions-an effective means of communicating emotions. To provide a unified conceptualization for this broad spectrum of face representations, we propose the term "facial icons" drawing upon Peirce's semiotic concepts. Additionally, based on these semiotic principles, we posit that facial icons function as indexes of emotions and intentions, and introduce a significant anthropological theory aligning with our proposition. Subsequently, we support our assertions by examining processes related to face and facial expression perception, as well as sensorimotor simulation processes involved in discerning others' mental states, including emotions. Our argumentation integrates cognitive and experimental evidence, reinforcing the pivotal role of facial icons in conveying mental states.

Influence of preterm birth on the association between gestational diabetes mellitus and childhood developmental vulnerability: a causal mediation analysis

BACKGROUND

Epidemiological studies examining the direct and indirect effects of gestational diabetes mellitus (GDM) on offspring early childhood developmental vulnerability are lacking. Therefore, the aims of this study were to estimate the direct and indirect effects of GDM (through preterm birth) on early childhood developmental vulnerability.

METHODS

We conducted a retrospective population-based cohort study on the association between gestational diabetes mellitus and early childhood developmental vulnerability in children born in Western Australia (WA) using maternal, infant and birth records from the Midwives Notification, Hospitalizations, Developmental Anomalies, and the Australian Early Development Census (AEDC) databases. We used two aggregated outcome measures: developmentally vulnerable on at least one AEDC domain (DV1) and developmentally vulnerable on at least two AEDC domains (DV2). Causal mediation analysis was applied to estimate the natural direct (NDE), indirect (NIE), and total (TE) effects as relative risks (RR).

RESULTS

In the whole cohort (n = 64,356), approximately 22% were classified as DV1 and 11% as DV2 on AEDC domains. Estimates of the natural direct effect suggested that children exposed to GDM were more likely to be classified as DV1 (RR = 1.20, 95% CI: 1.10-1.31) and DV2 (RR = 1.34, 95% CI: 1.19-1.50) after adjusting for potential confounders. About 6% and 4% of the effect of GDM on early childhood developmental vulnerability was mediated by preterm birth for DV1 and DV2, respectively.

CONCLUSION

Children exposed to gestational diabetes mellitus were more likely to be developmentally vulnerable in one or more AEDC domains. The biological mechanism for these associations is not well explained by mediation through preterm birth.

The impact of maternal immune activation on GABAergic interneuron development: A systematic review of rodent studies and their translational implications

Mothers exposed to infections during pregnancy disproportionally birth children who develop autism and schizophrenia, disorders associated with altered GABAergic function. The maternal immune activation (MIA) model recapitulates this risk factor, with many studies also reporting disruptions to GABAergic interneuron expression, protein, cellular density and function. However, it is unclear if there are species, sex, age, region, or GABAergic subtype specific vulnerabilities to MIA. Furthermore, to fully comprehend the impact of MIA on the GABAergic system a synthesised account of molecular, cellular, electrophysiological and behavioural findings was required. To this end we conducted a systematic review of GABAergic interneuron changes in the MIA model, focusing on the prefrontal cortex and hippocampus. We reviewed 102 articles that revealed robust changes in a number of GABAergic markers that present as gestationally-specific, region-specific and sometimes sex-specific. Disruptions to GABAergic markers coincided with distinct behavioural phenotypes, including memory, sensorimotor gating, anxiety, and sociability. Findings suggest the MIA model is a valid tool for testing novel therapeutics designed to recover GABAergic function and associated behaviour.

No Evidence for Cognitive Impairment in an Experimental Rat Model of Knee Osteoarthritis and Associated Chronic Pain

Although chronic pain states have been associated with impaired cognitive functions, including memory and cognitive flexibility, the cognitive effects of osteoarthritis (OA) pain remain to be clarified. The aim of this study was to measure cognitive function in the mono-iodoacetate (MIA) rat model of chronic OA-like knee pain. We used young adult male Lister hooded rats, which are well-suited for cognitive testing. Rats received either a unilateral knee injection of MIA (3 mg/50 µL) or saline as control. Joint pain at rest was assessed for up to 12 weeks, using weight-bearing asymmetry, and referred pain at a distal site, using determination of hindpaw withdrawal thresholds. The watermaze delayed-matching-to-place test of rapid place learning, novel object recognition memory assay, and an operant response-shift and -reversal task were used to measure memory and behavioral flexibility. Open-field locomotor activity, startle response, and prepulse inhibition were also measured for comparison. MIA-injected rats showed markedly reduced weight-bearing on the injured limb, as well as pronounced cartilage damage and synovitis, but interestingly no changes in paw withdrawal threshold. Rearing was reduced, but otherwise, locomotor activity was normal and no changes in startle and prepulse inhibition were detected. MIA-injected rats had intact watermaze delayed-matching-to-place performance, suggesting no substantial change in hippocampal function, and there were no changes in novel object recognition memory or performance on the operant task of behavioral flexibility. Our finding that OA-like pain does not alter hippocampal function, unlike other chronic pain conditions, is consistent with human neuroimaging findings. PERSPECTIVE: Young adult rats with OA-like knee pain showed no impairments in hippocampal memory function and behavioral flexibility, suggesting that OA pain impacts cognitive functions less than other chronic pain conditions. In patients, OA pain may interact with other factors (e.g., age, socio-economic factors, and medication) to impair cognition.

Daily artificial gravity is associated with greater neural efficiency during sensorimotor adaptation

Altered vestibular signaling and body unloading in microgravity results in sensory reweighting and adaptation. Microgravity effects are well-replicated in head-down tilt bed rest (HDBR). Artificial gravity (AG) is a potential countermeasure to mitigate the effects of microgravity on human physiology and performance. We examined the effectiveness of daily AG for mitigating brain and/or behavioral changes in 60 days of HDBR. One group received AG for 30 minutes daily (AG; n = 16) and a control group spent the same time in HDBR but received no AG (CTRL; n = 8). All participants performed a sensorimotor adaptation task five times during fMRI scanning: twice prior to HDBR, twice during HDBR, and once following HDBR. The AG group showed similar behavioral adaptation effects compared with the CTRLs. We identified decreased brain activation in the AG group from pre to late HDBR in the cerebellum for the task baseline portion and in the thalamus, calcarine, cuneus, premotor cortices, and superior frontal gyrus in the AG group during the early adaptation phase. The two groups also exhibited differential brain-behavior correlations. Together, these results suggest that AG may result in a reduced recruitment of brain activity for basic motor processes and sensorimotor adaptation. These effects may stem from the somatosensory and vestibular stimulation that occur with AG.

Higher hippocampal diffusivity values in welders are associated with greater R2* in the red nucleus and lower psychomotor performance

INTRODUCTION

Chronic excessive welding exposure may be related to higher metal accumulation and structural differences in different subcortical structures. We examined how welding affected brain structures and their associations with metal exposure and neurobehavioral consequences.

METHODS

Study includes 42 welders and 31 controls without a welding history. Welding-related structural differences were assessed by volume and diffusion tensor imaging (DTI) metrics in basal ganglia, red nucleus (RN), and hippocampus. Metal exposure was estimated by both exposure questionnaires and whole blood metal levels. Brain metal accumulations were estimated by R1 (for Mn) and R2* (for Fe). Neurobehavioral status was assessed by standard neuropsychological tests.

RESULTS

Compared to controls, welders displayed higher hippocampal mean (MD), axial (AD), and radial diffusivity (RD) (p's < 0.036), but similar DTI or volume in other ROIs (p's > 0.117). Welders had higher blood metal levels (p's < 0.004), higher caudate and RN R2* (p's < 0.014), and lower performance on processing/psychomotor speed, executive function, and visuospatial processing tasks (p's < 0.046). Higher caudate and RN R2* were associated with higher blood Fe and Pb (p's < 0.043), respectively. RN R2* was a significant predictor of all hippocampal diffusivity metrics (p's < 0.006). Higher hippocampal MD and RD values were associated with lower Trail Making Test-A scores (p's < 0.025). A mediation analysis of both groups revealed blood Pb indirectly affected hippocampal diffusivity via RN R2* (p's < 0.041).

DISCUSSION

Welding-related higher hippocampal diffusivity metrics may be associated with higher RN R2* and lower psychomotor speed performance. Future studies are warranted to test the role of Pb exposure in these findings.

Acoustic startle and prepulse inhibition deficits in adult monkeys with neonatal lesions of the hippocampus, amygdala and orbital frontal cortex

Sensory-motor gating, the process of filtering sensory stimuli to modulate motor responses, is impaired in many psychiatric diseases but especially schizophrenia. Sensory-motor gating assessed with the prepulse inhibition paradigm (PPI) measures startle in response to preceding acoustic stimuli. PPI studies in rodents have consistently found that neonatal hippocampal lesions impair sensory-motor gating in adult animals, but its applicability to primates has yet to be tested. The study examined acoustic startle responses and PPI in adult rhesus monkeys with neonatal lesions of the hippocampus (Neo-Hibo), amygdala (Neo-Aibo), and orbital frontal cortex areas 11 and 13 (Neo-Oasp) and with sham-operations (Neo-C). All monkeys were initially habituated to the startle apparatus and assayed for acoustic startle response curves. Subsequently, PPI was measured with the prepulse occurring at 60, 120, 240, 480, 1000 and 5000 msec prior to the pulse onset. No significant group differences in baseline startle were found. Compared to Neo-C monkeys, Neo-Hibo monkeys showed normal startle curves as well as normal PPI at short prepulse delays but prepulse facilitation (PPF) at longer prepulse intervals. Neo-Aibo monkeys displayed enhanced startle responses with only minor changes in PPI, whereas Neo-Oasp monkeys had severe dampening of startle responses and impaired PPI at shorter prepulse intervals. These results support prior evidence from rodent literature of the involvement of each of these areas in the development of the complex cortico-limbic circuit modulating sensory-motor gating and may shade light on the specific neural structures associated with deficits in PPI reported in neuropsychiatric disorders, such as schizophrenia, autism spectrum disorders, and post-traumatic disorders.

The Glycolysis Inhibitor 2-Deoxy-D-Glucose Exerts Different Neuronal Effects at Circuit and Cellular Levels, Partially Reverses Behavioral Alterations and does not Prevent NADPH Diaphorase Activity Reduction in the Intrahippocampal Kainic Acid Model of Temporal Lobe Epilepsy

Temporal lobe epilepsy is the most drug-resistant type with the highest incidence among the other focal epilepsies. Metabolic manipulations are of great interest among others, glycolysis inhibitors like 2-deoxy D-glucose (2-DG) being the most promising intervention. Here, we sought to investigate the effects of 2-DG treatment on cellular and circuit level electrophysiological properties using patch-clamp and local field potentials recordings and behavioral alterations such as depression and anxiety behaviors, and changes in nitric oxide signaling in the intrahippocampal kainic acid model. We found that epileptic animals were less anxious, more depressed, with more locomotion activity. Interestingly, by masking the effect of increased locomotor activity on the parameters of the zero-maze test, no altered anxiety behavior was noted in epileptic animals. However, 2-DG could partially reverse the behavioral changes induced by kainic acid. The findings also showed that 2-DG treatment partially suppresses cellular level alterations while failing to reverse circuit-level changes resulting from kainic acid injection. Analysis of NADPH-diaphorase positive neurons in the CA1 area of the hippocampus revealed that the number of positive neurons was significantly reduced in dorsal CA1 of the epileptic animals and 2-DG treatment did not affect the diminishing effect of kainic acid on NADPH-d+ neurons in the CA1 area. In the control group receiving 2-DG, however, an augmented NADPH-d+ cell number was noted. These data suggest that 2-DG cannot suppress epileptiform activity at the circuit-level in this model of epilepsy and therefore, may fail to control the seizures in temporal lobe epilepsy cases.

Recent advances in dopamine D2 receptor ligands in the treatment of neuropsychiatric disorders

Dopamine is a biologically active amine synthesized in the central and peripheral nervous system. This biogenic monoamine acts by activating five types of dopamine receptors (D_1-5 Rs), which belong to the G protein-coupled receptor family. Antagonists and partial agonists of D₂ Rs are used to treat schizophrenia, Parkinson's disease, depression, and anxiety. The typical pharmacophore with high D₂ R affinity comprises four main areas, namely aromatic moiety, cyclic amine, central linker and aromatic/heteroaromatic lipophilic fragment. From the literature reviewed herein, we can conclude that 4-(2,3-dichlorophenyl), 4-(2-methoxyphenyl)-, 4-(benzo[b]thiophen-4-yl)-1-substituted piperazine, and 4-(6-fluorobenzo[d]isoxazol-3-yl)piperidine moieties are critical for high D₂ R affinity. Four to six atoms chains are optimal for D₂ R affinity with 4-butoxyl as the most pronounced one. The bicyclic aromatic/heteroaromatic systems are most frequently occurring as lipophilic appendages to retain high D₂ R affinity. In this review, we provide a thorough overview of the therapeutic potential of D₂ R modulators in the treatment of the aforementioned disorders. In addition, this review summarizes current knowledge about these diseases, with a focus on the dopaminergic pathway underlying these pathologies. Major attention is paid to the structure, function, and pharmacology of novel D₂ R ligands, which have been developed in the last decade (2010-2021), and belong to the 1,4-disubstituted aromatic cyclic amine group. Due to the abundance of data, allosteric D₂ R ligands and D₂ R modulators from patents are not discussed in this review.

Aberrant hippocampus and amygdala morphology associated with cognitive deficits in schizophrenia

Background

Working memory deficits are thought to be a primary disturbance in schizophrenia. We aimed to identify differences in morphology of the hippocampus and amygdala in patients with schizophrenia compared with healthy controls (HCs), and in patients who were either neuropsychologically near normal (NPNN) or neuropsychologically impaired (NPI). Morphological disturbances in the same subfields of the hippocampus and amygdala, but of greater magnitude in those with NPI, would strengthen evidence for the centrality of these limbic regions and working memory deficits in the pathogenesis of schizophrenia.

Methods

We acquired anatomical MRIs in 69 patients with schizophrenia (18 NPNN, 46 NPI) and 63 age-matched HC participants. We compared groups in hippocampus and amygdala surface morphologies and correlated morphological measures with clinical symptoms and working memory scores.

Results

Schizophrenia was associated with inward deformations of the head and tail of the hippocampus, protrusion of the hippocampal body, and widespread inward deformations of the amygdala. In the same regions where we detected the effects of schizophrenia, morphological measures correlated positively with the severity of symptoms and inversely with working memory performance. Patients with NPI displayed a similar pattern of anatomical abnormality compared to patients with NPNN.

Conclusion

Our findings indicate that anatomical abnormalities of the hippocampus relate to working memory performance and clinical symptoms in persons with schizophrenia. Moreover, NPNN and NPI patients may lie on a continuum of severity, both in terms of working memory abilities and altered brain structure, with NPI patients being more severe than NPNN patients in both domains.

Df(h22q11)/+ mouse model exhibits reduced binding levels of GABAA receptors and structural and functional dysregulation in the inhibitory and excitatory networks of hippocampus

The 22q11.2 hemizygous deletion confers high risk for multiple neurodevelopmental disorders. Inhibitory signaling, largely regulated through GABA_A receptors, is suggested to serve a multitude of brain functions that are disrupted in the 22q11.2 deletion syndrome. We investigated the putative deficit of GABA_A receptors and the potential substrates contributing to the inhibitory and excitatory dysregulations in hippocampal networks of the Df(h22q11)/+ mouse model of the 22q11.2 hemizygous deletion. The Df(h22q11)/+ mice exhibited impairments in several hippocampus-related functional domains, represented by impaired spatial memory and sensory gating functions. Autoradiography using the [³H]muscimol tracer revealed a significant reduction in GABA_A receptor binding in the CA1 and CA3 subregions, together with a loss of GAD67⁺ interneurons in CA1 of Df(h22q11)/+ mice. Furthermore, electrophysiology recordings exhibited significantly higher neuronal activity in CA3, in response to the GABA_A receptor antagonist, bicuculline, as compared with wild type mice. Density and volume of dendritic spines in pyramidal neurons were reduced and Sholl analysis also showed a reduction in the complexity of basal dendritic tree in CA1 and CA3 subregions of Df(h22q11)/+ mice. Overall, our findings demonstrate that hemizygous deletion in the 22q11.2 locus leads to dysregulations in the inhibitory circuits, involving reduced binding levels of GABA_A receptors, in addition to functional and structural modulations of the excitatory networks of hippocampus.

Morphological Biomarkers in the Amygdala and Hippocampus of Children and Adults at High Familial Risk for Depression

Major Depressive Disorder (MDD) is highly familial, and the hippocampus and amygdala are important in the pathophysiology of MDD. Whether morphological markers of risk for familial depression are present in the hippocampus or amygdala is unknown. We imaged the brains of 148 individuals, aged 6 to 54 years, who were members of a three-generation family cohort study and who were at either high or low familial risk for MDD. We compared surface morphological features of the hippocampus and amygdala across risk groups and assessed their associations with depression severity. High- compared with low-risk individuals had inward deformations of the head of both hippocampi and the medial surface of the left amygdala. The hippocampus findings persisted in analyses that included only those participants who had never had MDD, suggesting that these are true endophenotypic biomarkers for familial MDD. Posterior extension of the inward deformations was associated with more severe depressive symptoms, suggesting that a greater spatial extent of this biomarker may contribute to the transition from risk to the overt expression of symptoms. Significant associations of these biomarkers with corresponding biomarkers for cortical thickness suggest that these markers are components of a distributed cortico-limbic network of familial vulnerability to MDD.

Sleep as a window on the sensorimotor foundations of the developing hippocampus

The hippocampal formation plays established roles in learning, memory, and related cognitive functions. Recent findings also suggest that the hippocampus integrates sensory feedback from self-generated movements to modulate ongoing motor responses in a changing environment. Such findings support the view of Bland and Oddie (Behavioural Brain Research, 2001, 127, 119-136) that the hippocampus is a site of sensorimotor integration. In further support of this view, we review neurophysiological evidence in developing rats that hippocampal function is built on a sensorimotor foundation and that this foundation is especially evident early in development. Moreover, at those ages when the hippocampus is first establishing functional connectivity with distant sensory and motor structures, that connectivity is preferentially expressed during periods of active (or REM) sleep. These findings reinforce the notion that sleep, as the predominant state of early infancy, provides a critical context for sensorimotor development, including development of the hippocampus and its associated network.

Longitudinal hippocampal circuit change differentiates persistence and remission of pediatric posttraumatic stress disorder

BACKGROUND

Previous studies have identified functional brain abnormalities in pediatric posttraumatic stress disorder (pPTSD) suggesting altered frontoparietal-subcortical function during emotion processing. However, little is known about how the brain functionally changes over time in recovery versus the persistence of pPTSD.

METHODS

This longitudinal study recruited 23 youth with PTSD and 28 typically developing (TD) youth (ages: 8.07-17.99). Within the PTSD group, nine remitted by the 1-year follow-up (Remit) while the remaining 14 persisted (PTSD). At each visit, youth completed an emotional processing task in which they viewed threat and neutral images during functional magnetic resonance imaging (fMRI). Voxelwise activation analyses using linear mixed-effects regression were conducted using a group (TD, Remit, PTSD) by time (baseline, follow-up) by valence (threat, neutral) design. Based on activation findings, a subsequent analysis of hippocampal functional connectivity was performed using a similar model.

RESULTS

PTSD youth showed significantly increasing hippocampal activation to threatening images compared to TD youth, while the Remit group showed more similar patterns to TD youth. Subsequent hippocampal functional connectivity analyses reveal the Remit group showed increasing functional connectivity between the hippocampus and visual cortex (V4) while viewing threat stimuli.

CONCLUSIONS

These findings represent one of the first preliminary reports of functional brain substrates of persistence and remission in pPTSD. Notably, increased hippocampal activation to threat and decreased connectivity in the hippocampal-V4 network over time may contribute to persistence in pPTSD. These findings suggest potential biomarkers that could be utilized to advance the treatment of pediatric PTSD.

Altered Functional Connectivity of the Orbital Cortex and Striatum Associated with Catalepsy Induced by Dopamine D1 and D2 Antagonists

The dopamine system plays an important role in regulating many brain functions, including the motor function. The blockade of dopamine receptors results in a serious motor dysfunction, such as catalepsy and Parkinsonism. However, the neuronal mechanism underlying the drug-induced motor dysfunction is not well understood. Here, we examine brain-wide activation patterns in Fos-enhanced green fluorescent protein reporter mice that exhibit cataleptic behavior induced by SCH39166, a dopamine D1-like receptor antagonist, and raclopride, a dopamine D2-like receptor antagonist. Support vector classifications showed that the orbital cortex (ORB) and striatum including the caudoputamen (CP) and nucleus accumbens (ACB), prominently contribute to the discrimination between brains of the vehicle-treated and both SCH39166- and raclopride-treated mice. Interregional correlations indicated that the increased functional connectivity of functional networks, including the ORB, CP, and ACB, is the common mechanism underlying SCH39166- and raclopride-induced cataleptic behavior. Moreover, the distinct mechanisms in the SCH39166- and raclopride-induced cataleptic behaviors are the decreased functional connectivity between three areas above and the cortical amygdala, and between three areas above and the anterior cingulate cortex, respectively. Thus, the alterations of functional connectivity in diverse brain regions, including the ORB, provide new insights on the mechanism underlying drug-induced movement disorders.

Age-related alterations in functional connectivity along the longitudinal axis of the hippocampus and its subfields

Hippocampal circuit alterations that differentially affect hippocampal subfields are associated with age-related memory decline. Additionally, functional organization along the longitudinal axis of the hippocampus has revealed distinctions between anterior and posterior (A-P) connectivity. Here, we examined the functional connectivity (FC) differences between young and older adults at high-resolution within the medial temporal lobe network (entorhinal, perirhinal, and parahippocampal cortices), allowing us to explore how hippocampal subfield connectivity across the longitudinal axis of the hippocampus changes with age. Overall, we found reliably greater connectivity for younger adults than older adults between the hippocampus and parahippocampal cortex (PHC) and perirhinal cortex (PRC). This drop in functional connectivity was more pronounced in the anterior regions of the hippocampus than the posterior ones, consistent for each of the hippocampal subfields. Further, intra-hippocampal connectivity also reflected an age-related decrease in functional connectivity within the anterior hippocampus in older adults that was offset by an increase in posterior hippocampal functional connectivity. Interestingly, the anterior-posterior dysfunction in older adults between hippocampus and PHC was predictive of lure discrimination performance on the Mnemonic similarity task (MST), suggesting a role in memory performance. While age-related dysfunction within the hippocampal subfields has been well-documented, these results suggest that the age-related dysfunction in hippocampal connectivity across the longitudinal axis may also contribute significantly to memory decline in older adults.

A Probiotic Mixture Induces Anxiolytic- and Antidepressive-Like Effects in Fischer and Maternally Deprived Long Evans Rats

A role of the gut microbiota in psychiatric disorders is supported by a growing body of literature. The effects of a probiotic mixture of four bacterial strains were studied in two models of anxiety and depression, naturally stress-sensitive Fischer rats and Long Evans rats subjected to maternal deprivation. Rats chronically received either the probiotic mixture (1.10⁹ CFU/day) or the vehicle. Anxiety- and depressive-like behaviors were evaluated in several tests. Brain monoamine levels and gut RNA expression of tight junction proteins (Tjp) and inflammatory markers were quantified. The gut microbiota was analyzed in feces by 16S rRNA gene sequencing. Untargeted metabolite analysis reflecting primary metabolism was performed in the cecal content and in serum. Fischer rats treated with the probiotic mixture manifested a decrease in anxiety-like behaviors, in the immobility time in the forced swimming test, as well as in levels of dopamine and its major metabolites, and those of serotonin metabolites in the hippocampus and striatum. In maternally deprived Long Evans rats treated with the probiotic mixture, the number of entries into the central area in the open-field test was increased, reflecting an anxiolytic effect. The probiotic mixture increased Tjp1 and decreased Ifnγ mRNA levels in the ileum of maternally deprived rats. In both models, probiotic supplementation changed the proportions of several Operational Taxonomic Units (OTU) in the gut microbiota, and the levels of certain cecal and serum metabolites were correlated with behavioral changes. Chronic administration of the tested probiotic mixture can therefore beneficially affect anxiety- and depressive-like behaviors in rats, possibly owing to changes in the levels of certain metabolites, such as 21-deoxycortisol, and changes in brain monoamines.

Maternal Immune Activation Affects Hippocampal Excitatory and Inhibitory Synaptic Transmission in Offspring From an Early Developmental Period to Adulthood

One of the risk factors for schizophrenia is maternal infection. We have previously shown that Polyriboinosinic-polyribocytidylic acid (poly I:C) induced maternal immune activation in mice caused histological changes in the hippocampal CA1 area of offspring during the developmental period and impaired sensorimotor gating in offspring during adulthood, resulting in behavioral changes. However, it remains unclear how maternal immune activation functionally impacts the hippocampal neuronal activity of offspring. We studied the effect of prenatal poly I:C treatment on synaptic transmission of hippocampal CA1 pyramidal cells in postnatal and adult offspring. Treatment with poly I:C diminished excitatory and enhanced inhibitory (GABAergic) synaptic transmission on pyramidal cells in adult offspring. During the early developmental period, we still observed that treatment with poly I:C decreased excitatory synaptic transmission and potentially increased GABAergic synaptic transmission, which was uncovered under a condition of high extracellular potassium-activated neurons. In conclusion, we demonstrate that maternal immune activation decreased excitatory and increased inhibitory synaptic transmission on hippocampal pyramidal cells from an early developmental period to adulthood, which could result in net inhibition in conjunction with poor functional organization and integration of hippocampal circuits.

Decrease of Rab11 prevents the correct dendritic arborization, synaptic plasticity and spatial memory formation

Emerging evidence shows that Rab11 recycling endosomes (REs Rab11) are essential for several neuronal processes, including the proper functioning of growth cones, synapse architecture regulation and neuronal migration. However, several aspects of REs Rab11 remain unclear, such as its sub-cellular distribution across neuronal development, contribution to dendritic tree organization and its consequences in memory formation. In this work we show a spatio-temporal correlation between the endogenous localization of REs Rab11 and developmental stage of neurons. Furthermore, Rab11-suppressed neurons showed an increase on dendritic branching (without altering total dendritic length) and misdistribution of dendritic proteins in cultured neurons. In addition, suppression of Rab11 in adult rat brains in vivo (by expressing shRab11 through lentiviral infection), showed a decrease on both the sensitivity to induce long-term potentiation and hippocampal-dependent memory acquisition. Taken together, our results suggest that REs Rab11 expression is required for a proper dendritic architecture and branching, controlling key aspects of synaptic plasticity and spatial memory formation.

Prepulse inhibition of the acoustic startle reflex and P50 gating in aging and alzheimer's disease

Inhibition plays a crucial role in many functional domains, such as cognition, emotion, and actions. Studies on cognitive aging demonstrate changes in inhibitory mechanisms are age- and pathology-related. Prepulse inhibition (PPI) is the suppression of an acoustic startle reflex (ASR) to an intense stimulus when a weak prepulse stimulus precedes the startle stimulus. A reduction of PPI is thought to reflect dysfunction of sensorimotor gating which normally suppresses excessive behavioral responses to disruptive stimuli. Both human and rodent studies show age-dependent alterations of PPI of the ASR that are further compromised in Alzheimer's disease (AD). The auditory P50 gating, an index of repetition suppression, also is characterized as a putative electrophysiological biomarker of prodromal AD. This review provides the latest evidence of age- and AD-associated impairment of sensorimotor gating based upon both human and rodent studies, as well as the AD-related disruption of P50 gating in humans. It begins with a concise review of neural networks underlying PPI regulation. Then, evidence of age- and AD-related dysfunction of both PPI and P50 gating is discussed. The attentional/ emotional aspects of sensorimotor gating and the neurotransmitter mechanisms underpinning PPI and P50 gating are also reviewed. The review ends with conclusions and research directions.

Chronic alcohol-induced liver injury correlates with memory deficits: Role for neuroinflammation

Alcohol use disorder (AUD) affects over 15 million adults over age 18 in the United States, with estimated costs of 220 billion dollars annually - mainly due to poor quality of life and lost productivity, which in turn is intricately linked to cognitive dysfunction. AUD-induced neuroinflammation in the brain, notably the hippocampus, is likely to contribute to cognitive impairments. The neuroinflammatory mechanisms mediating the impact of chronic alcohol on the central nervous system, specifically cognition, require further study. We hypothesized that chronic alcohol consumption impairs memory and increases the inflammatory cytokines TNFα, IL6, MCP1, and IL1β in the hippocampus and prefrontal cortex regions in the brain. Using the chronic-binge Gao-NIAAA alcohol mouse model of liver disease, representative of the drinking pattern common to human alcoholics, we investigated behavioral and neuroinflammatory parameters. Our data show that chronic alcohol intake elevated peripheral and brain alcohol levels, induced serum alanine aminotransferase (ALT, a marker of liver injury), impaired memory and sensorimotor coordination, and increased inflammatory gene expression in the hippocampus and prefrontal cortex. Interestingly, serum ALT and hippocampal IL6 correlated with memory impairment, suggesting an intrinsic relationship between neuroinflammation, cognitive decline, and liver disease. Overall, our results point to a likely liver-brain functional partnership and suggest that future strategies to alleviate hepatic and/or neuroinflammatory impacts of chronic AUD may result in improved cognitive outcomes.

Modified constraint-induced movement therapy alters synaptic plasticity of rat contralateral hippocampus following middle cerebral artery occlusion

Modified constraint-induced movement therapy is an effective treatment for neurological and motor impairments in patients with stroke by increasing the use of their affected limb and limiting the contralateral limb. However, the molecular mechanism underlying its efficacy remains unclear. In this study, a middle cerebral artery occlusion (MCAO) rat model was produced by the suture method. Rats received modified constraint-induced movement therapy 1 hour a day for 14 consecutive days, starting from the 7^th day after middle cerebral artery occlusion. Day 1 of treatment lasted for 10 minutes at 2 r/min, day 2 for 20 minutes at 2 r/min, and from day 3 onward for 20 minutes at 4 r/min. CatWalk gait analysis, adhesive removal test, and Y-maze test were used to investigate motor function, sensory function as well as cognitive function in rodent animals from the 1^st day before MCAO to the 21^st day after MCAO. On the 21^st day after MCAO, the neurotransmitter receptor-related genes from both contralateral and ipsilateral hippocampi were tested by micro-array and then verified by western blot assay. The glutamate related receptor was shown by transmission electron microscopy and the glutamate content was determined by high-performance liquid chromatography. The results of behavior tests showed that modified constraint-induced movement therapy promoted motor and sensory functional recovery in the middle cerebral artery-occluded rats, but had no effect on cognitive function. The modified constraint-induced movement therapy upregulated the expression of glutamate ionotropic receptor AMPA type subunit 3 (Gria3) in the hippocampus and downregulated the expression of the beta3-adrenergic receptor gene Adrb3 and arginine vasopressin receptor 1A, Avpr1a in the middle cerebral artery-occluded rats. In the ipsilateral hippocampus, only Adra2a was downregulated, and there was no significant change in Gria3. Transmission electron microscopy revealed a denser distribution the more distribution of postsynaptic glutamate receptor 2/3, which is an α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor, within 240 nm of the postsynaptic density in the contralateral cornu ammonis 3 region. The size and distribution of the synaptic vesicles within 100 nm of the presynaptic active zone were unchanged. Western blot analysis showed that modified constraint-induced movement therapy also increased the expression of glutamate receptor 2/3 and brain-derived neurotrophic factor in the hippocampus of rats with middle cerebral artery occlusion, but had no effect on Synapsin I levels. Besides, we also found modified constraint-induced movement therapy effectively reduced glutamate content in the contralateral hippocampus. This study demonstrated that modified constraint-induced movement therapy is an effective rehabilitation therapy in middle cerebral artery-occluded rats, and suggests that these positive effects occur via the upregulation of the postsynaptic membrane α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor expression. This study was approved by the Institutional Animal Care and Use Committee of Fudan University, China (approval No. 201802173S) on March 3, 2018.

Reduced Acoustic Startle Response and Prepulse Inhibition in the Tg4-42 Model of Alzheimer's Disease

Sensorimotor deficits have been described in several neuropsychiatric disorders including Alzheimer’s disease. The aim of the present study was to evaluate possible sensorimotor gating deficits in the Tg4-42 mouse model of Alzheimer’s disease using the prepulse inhibition task (PPI). Previous studies indicated that the hippocampus is essentially involved in the regulation of PPI. We analyzed 7-month-old homozygous Tg4-42 mice as mice at this age display severe neuron loss especially in the CA1 region of the hippocampus. Our results revealed a reduced startle response and PPI in Tg4-42 mice. The observed deficits in startle response and PPI are likely due to altered sensory processing abilities rather than hearing deficits as Tg4-42 displayed intact hearing in the fear conditioning task. The present study demonstrates for the first time that sensorimotor gating is impaired in Tg4-42 mice. Analyzing startle response as well as the PPI may offer valuable measurements to assess the efficacy of therapeutic strategies in the future in this Alzheimer’s disease model.

Parvalbumin-positive GABAergic interneurons deficit in the hippocampus in Gunn rats: A possible hyperbilirubinemia-induced animal model of schizophrenia

A reduction of GABAergic markers in postmortem tissue is consistently found in schizophrenia. Importantly, these alterations in GABAergic neurons are not global, which means they are more prevalent among distinct subclasses of interneurons, including those that express the calcium binding protein parvalbumin. A decreased expression of parvalbumin in the hippocampus is a consistent observation not only in postmortem human schizophrenia patients, but also in a diverse number of rodent models of the disease. Meanwhile, previously we reported that the congenital hyperbilirubinemia model rats (Gunn rats), which is a mutant of the Wistar strain, showed behavioral abnormalities, for instance, hyperlocomotor activity, deficits of prepulse inhibition, inappropriate social interaction, impaired recognition memory similar with several rodent models of schizophrenia. Several animal studies linked the importance of palvalbumin in relation to abnormal hippocampal activity and schizophrenia-like behavior. Here, we show that parvalbumin positive cell density was significantly lower in the CA1, CA3 and the total hippocampus of Gunn rats (congenital hyperbilirubinemia model rats) compared to Wistar control rats. The correlations between serum UCB levels and loss of PV expression in the hippocampus were also detected. The decreases in the PV-expression in the hippocampus might suggest an association of the behavioral abnormalities as schizophrenia-like behaviors of Gunn rats, compared to the Wistar control rats.

Distinct Time-Course of Alterations of Groups I and II Metabotropic Glutamate Receptor and GABAergic Receptor Expression Along the Dorsoventral Hippocampal Axis in an Animal Model of Psychosis

Psychosis is a clinical state that encompasses a range of abnormal conditions, including distortions in sensory information processing and the resultant delusional thinking, emotional discordance and cognitive impairments. Upon developing this condition, the rate at which cognitive and behavioral deteriorations progress steadily increases suggesting an active contribution of the first psychotic event to the progression of structural and functional abnormalities and disease establishment in diagnosed patients. Changes in GABAergic and glutamatergic function, or expression, in the hippocampus have been proposed as a key factor in the pathophysiology of psychosis. However, little is known as to the time-point of onset of putative changes, to what extent they are progressive, and their relation to disease stabilization. Here, we characterized the expression and distribution patterns of groups I and II metabotropic glutamate (mGlu) receptors and GABA receptors 1 week and 3 months after systemic treatment with an N-methyl-D-aspartate receptor (NMDAR) antagonist (MK801) that is used to model a psychosis-like state in adult rats. We found an early alteration in the expression of mGlu1, mGlu2/3, and GABA_B receptors across the hippocampal dorsoventral and transverse axes. This expanded to include an up-regulation of mGlu5 levels across the entire CA1 region and a reduction in GABA_B expression, as well as GAD67-positive interneurons particularly in the dorsal hippocampus that appeared 3 months after treatment. Our findings indicate that a reduction of excitability may occur in the hippocampus soon after first-episode psychosis. This changes, over time, into increased excitability. These hippocampus-specific alterations are likely to contribute to the pathophysiology and stabilization of psychosis.

Cyclohexane Inhalation Produces Long-Lasting Alterations in the Hippocampal Integrity and Reward-Seeking Behavior in the Adult Mouse

Cyclohexane (CHX) is an organic solvent commonly used as a drug-of-abuse. This drug increases the oxidative stress and glial reactivity in the hippocampus, which suggests that this brain region is vulnerable to CHX effects. This study aimed to establish the behavioral changes and the pathological alterations that occur in the Cornu Ammonis 3 (CA3) and Dentate Gyrus (DG) after a long-lasting exposure to CHX. We exposed CD1 mice to a recreational-like dose of CHX (~ 30,000 ppm) for 30 days and explored its consequences in motor skills, reward-seeking behavior, and the CA3 and DG hippocampal subfields. Twenty-four hours after the last administration of CHX, we found a significant decrease in the number of c-Fos+ cells in the hippocampal CA3 and DG regions. This event coincided with an increased in NMDAR1 expression and apoptotic cells in the CA3 region. At day 13th without CHX, we found a persistent reduction in the number of c-Fos+ and TUNEL+ cells in DG. At both time points, the CHX-exposed mice showed a strong overexpression of neuropeptide Y (NPY) in the CA3 stratum lucidum and the hippocampal hilus. In parallel, we used an operant-based task to assess motor performance and operant conditioning learning. The behavioral analysis indicated that CHX did not modify the acquisition of operant conditioning tasks, but affected some motor skills and increased the reward-seeking behavior. Altogether, this evidence reveals that CHX exposure provokes long-lasting changes in the hippocampal subfields, induces motor impairments and increases the motivation-guided behavior. These findings can help understand the deleterious effect of CHX into the adult hippocampus and unveil its potential to trigger addiction-like behaviors.

Formation of a morphine-conditioned place preference does not change the size of evoked potentials in the ventral hippocampus-nucleus accumbens projection

In opioid addiction, cues and contexts associated with drug reward can be powerful triggers for drug craving and relapse. The synapses linking ventral hippocampal outputs to medium spiny neurons of the accumbens may be key sites for the formation and storage of associations between place or context and reward, both drug-related and natural. To assess this, we implanted rats with electrodes in the accumbens shell to record synaptic potentials evoked by electrical stimulation of the ventral hippocampus, as well as continuous local-field-potential activity. Rats then underwent morphine-induced (10 mg/kg) conditioned-place-preference training, followed by extinction. Morphine caused an acute increase in the slope and amplitude of accumbens evoked responses, but no long-term changes were evident after conditioning or extinction of the place preference, suggesting that the formation of this type of memory does not lead to a net change in synaptic strength in the ventral hippocampal output to the accumbens. However, analysis of the local field potential revealed a marked sensitization of theta- and high-gamma-frequency activity with repeated morphine administration. This phenomenon may be linked to the behavioral changes—such as psychomotor sensitization and the development of drug craving—that are associated with chronic use of addictive drugs.

Neurogranin regulates sensorimotor gating through cortico-striatal circuitry

Glutamate dysregulation is known to contribute to many psychiatric disorders including schizophrenia. Aberrant cortico-striatal activity and therefore glutamate levels might be relevant to this disease characterized by reduced prepulse inhibition (PPI), however, the molecular and behavioral mechanism of the pathophysiology of schizophrenia remains unclear. The focus of this study was to contribute to the current understanding of the glutamate and neurogranin (Ng) pathway, in relation to the cortico-striatal pathology of schizophrenia using a mouse model. A variant of the Ng gene has been detected in people with schizophrenia, implicating maladaptation of cortical glutamate signaling and sensorimotor gating. To test Ng-mediated PPI regulation in the mouse model, we utilized Ng null mice, viral-mediated Ng expression, and genetics approaches. Our results demonstrate that lack of Ng in mice decreases PPI. Ng over-expression in the prefrontal cortex (PFC) increases PPI, while Ng expression in either the nucleus accumbens (NAc) or hippocampus induces no change in PPI. Using optogenetics and chemogenetics, we identified that cortico-striatal activation is involved in PPI regulation. Finally, pharmacological regulation of Ng using glutamate receptor inhibitors demonstrated altered PPI between genotypes. In this study, we have investigated the impact of Ng expression on sensorimotor gating. This study contributes to a better understanding of the glutamatergic theory of schizophrenia, opening novel therapeutic avenues that may lead to glutamatergic treatments to ameliorate the symptoms of schizophrenia.

Infusions of scopolamine in dorsal hippocampus reduce anticipatory responding in an appetitive trace conditioning procedure

INTRODUCTION

Trace conditioning is impaired by lesions to dorsal hippocampus, as well as by treatment with the muscarinic acetylcholine antagonist scopolamine. However, the role of muscarinic receptors within hippocampus has received little attention.

METHODS

The present study examined the effects of intra-hippocampal infusion of scopolamine (30 µg/side) in an appetitive (2 vs. 10 s) trace conditioning procedure using sucrose pellets as the unconditioned stimulus (US). Locomotor activity (LMA) was examined in a different apparatus.

RESULTS

Intra-hippocampal scopolamine reduced responding to the 2 s trace conditioned stimulus (CS). Intra-hippocampal scopolamine similarly depressed responding within the inter-stimulus interval (ISI) at both 2 and 10 s trace intervals, but there was no such effect in the inter-trial interval. There was also some overall reduction in responding when the US was delivered; significant at the 10 s but not at the 2 s trace interval. A similar pattern of results to that seen in response to the CS during acquisition was shown drug-free (in the 5 s post-CS) in the extinction tests of conditioned responding. LMA was increased under scopolamine.

CONCLUSIONS

The results suggest that nonspecific changes in activity or motivation to respond for the US cannot explain the reduction in trace conditioning as measured by reduced CS responding and in the ISI. Rather, the findings of the present study point to the importance of associative aspects of the task in determining its sensitivity to the effects of scopolamine, suggesting that muscarinic receptors in the hippocampus are important modulators of short-term working memory.

Hippocampal deficits in neurodevelopmental disorders

Neurodevelopmental disorders result from impaired development or maturation of the central nervous system. Both genetic and environmental factors can contribute to the pathogenesis of these disorders; however, the exact causes are frequently complex and unclear. Individuals with neurodevelopmental disorders may have deficits with diverse manifestations, including challenges with sensory function, motor function, learning, memory, executive function, emotion, anxiety, and social ability. Although these functions are mediated by multiple brain regions, many of them are dependent on the hippocampus. Extensive research supports important roles of the mammalian hippocampus in learning and cognition. In addition, with its high levels of activity-dependent synaptic plasticity and lifelong neurogenesis, the hippocampus is sensitive to experience and exposure and susceptible to disease and injury. In this review, we first summarize hippocampal deficits seen in several human neurodevelopmental disorders, and then discuss hippocampal impairment including hippocampus-dependent behavioral deficits found in animal models of these neurodevelopmental disorders.

Medial septum modulates hippocampal gamma activity and prepulse inhibition in an N-methyl-d-aspartate receptor antagonist model of schizophrenia

We reviewed the participation of the septohippocampal system in an animal model of schizophrenia that was acutely induced by systemic injection of an N-methyl-d-aspartate (NMDA) receptor antagonist such as phencyclidine, MK-801 and ketamine. The NMDA receptor antagonist-induced model of schizophrenia is characterized by behavioral and electrophysiological disruptions, including a decrease in prepulse inhibition of the acoustic startle response (PPI), hyperlocomotion, decrease in gating of hippocampal auditory evoked potentials and robust increase in hippocampal gamma (30-100Hz) oscillations. Similar disruptions were also induced by a single electrographic seizure in the hippocampus. The behavioral and electrophysiological disruptions induced by an NMDA receptor antagonist can be reduced by inactivation or lesion of GABAergic neurons in the medial septum, deep brain stimulation of the medial septum or nucleus accumbens, or positive modulation of GABA_B receptors. Our results suggest a close association between high-amplitude hippocampal gamma oscillations and psychosis-relevant behaviors including PPI loss, behavioral hyperactivity and loss in auditory gating. Abnormal electrophysiology suggests a disruption of somatic and apical dendritic inhibition in the hippocampus, resulting in distorted sensory integration, and impaired cognitive and memory processing. The hippocampus is suggested to be a hub in a brain network that participates in psychosis-relevant behaviors, through its direct projection to the nucleus accumbens, or through indirect connections via the entorhinal, cingulate and prefrontal cortices.

Hippocampal Neural Disinhibition Causes Attentional and Memory Deficits

Subconvulsive hippocampal neural disinhibition, that is reduced GABAergic inhibition, has been implicated in neuropsychiatric disorders characterized by attentional and memory deficits, including schizophrenia and age-related cognitive decline. Considering that neural disinhibition may disrupt both intra-hippocampal processing and processing in hippocampal projection sites, we hypothesized that hippocampal disinhibition disrupts hippocampus-dependent memory performance and, based on strong hippocampo-prefrontal connectivity, also prefrontal-dependent attention. In support of this hypothesis, we report that acute hippocampal disinhibition by microinfusion of the GABA-A receptor antagonist picrotoxin in rats impaired hippocampus-dependent everyday-type rapid place learning performance on the watermaze delayed-matching-to-place test and prefrontal-dependent attentional performance on the 5-choice-serial-reaction-time test, which does not normally require the hippocampus. For comparison, we also examined psychosis-related sensorimotor effects, using startle/prepulse inhibition (PPI) and locomotor testing. Hippocampal picrotoxin moderately increased locomotion and slightly reduced startle reactivity, without affecting PPI. In vivo electrophysiological recordings in the vicinity of the infusion site showed that picrotoxin mainly enhanced burst firing of hippocampal neurons. In conclusion, hippocampal neural disinhibition disrupts hippocampus-dependent memory performance and also manifests through deficits in not normally hippocampus-dependent attentional performance. These behavioral deficits may reflect a disrupted control of burst firing, which may disrupt hippocampal processing and cause aberrant drive to hippocampal projection sites.

Early intervention of tau pathology prevents behavioral changes in the rTg4510 mouse model of tauopathy

Although tau pathology, behavioral deficits, and neuronal loss are observed in patients with tauopathies, the relationship between these endpoints has not been clearly established. Here we found that rTg4510 mice, which overexpress human mutant tau in the forebrain, develop progressive age-dependent increases in locomotor activity (LMA), which correlates with neurofibrillary tangle (NFT) pathology, hyperphosphorylated tau levels, and brain atrophy. To further clarify the relationship between these endpoints, we treated the rTg4510 mice with either doxycycline to reduce mutant tau expression or an O-GlcNAcase inhibitor Thiamet G, which has been shown to ameliorate tau pathology in animal models. We found that both doxycycline and Thiamet G treatments starting at 2 months of age prevented the progression of hyperactivity, slowed brain atrophy, and reduced brain hyperphosphorylated tau. In contrast, initiating doxycycline treatment at 4 months reduced neither brain hyperphosphorylated tau nor hyperactivity, further confirming the relationship between these measures. Collectively, our results demonstrate a unique behavioral phenotype in the rTg4510 mouse model of tauopathy that strongly correlates with disease progression, and that early interventions which reduce tau pathology ameliorate the progression of the locomotor dysfunction. These findings suggest that better understanding the relationship between locomotor deficits and tau pathology in the rTg4510 model may improve our understanding of the mechanisms underlying behavioral disturbances in patients with tauopathies.

Mature Hippocampal Neurons Require LIS1 for Synaptic Integrity: Implications for Cognition

BACKGROUND

Platelet-activating factor acetylhydrolase 1B1 (LIS1), a critical mediator of neuronal migration in developing brain, is expressed throughout life. However, relatively little is known about LIS1 function in the mature brain. We previously demonstrated that LIS1 involvement in the formation and turnover of synaptic protrusions and synapses of young brain after neuronal migration is complete. Here we examine the requirement for LIS1 to maintain hippocampal circuit function in adulthood.

METHODS

Effects of conditional Lis1 inactivation in excitatory pyramidal neurons, starting in juvenile mouse brain, were probed using high-resolution approaches combining mouse genetics, designer receptor exclusively activated by designer drug technology to specifically manipulate CA1 pyramidal neuron excitatory activity, electrophysiology, hippocampus-selective behavioral testing, and magnetic resonance imaging tractography to examine the connectivity of LIS1-deficient neurons.

RESULTS

We found progressive excitatory and inhibitory postsynaptic dysfunction as soon as 10 days after conditional inactivation of Lis1 targeting CA1 pyramidal neurons. Surprisingly, by postnatal day 60 it also caused CA1 histological disorganization, with a selective decline in parvalbumin-expressing interneurons and further reduction in inhibitory neurotransmission. Accompanying these changes were behavioral and cognitive deficits that could be rescued by either designer receptor exclusively activated by designer drug-directed specific increases in CA1 excitatory transmission or pharmacological enhancement of gamma-aminobutyric acid transmission. Lagging behind electrophysiological changes was a progressive, selective decline in neural connectivity, affecting hippocampal efferent pathways documented by magnetic resonance imaging tractography.

CONCLUSIONS

LIS1 supports synaptic function and plasticity of mature CA1 neurons. Postjuvenile loss of LIS1 disrupts the structure and cellular composition of the hippocampus, its connectivity with other brain regions, and cognition dependent on hippocampal circuits.

A Role for Phosphodiesterase 11A (PDE11A) in the Formation of Social Memories and the Stabilization of Mood

The most recently discovered 3',5'-cyclic nucleotide phosphodiesterase family is the Phosphodiesterase 11 (PDE11) family, which is encoded by a single gene PDE11A. PDE11A is a dual-specific PDE, breaking down both cAMP and cGMP. There are four PDE11A splice variants (PDE11A1-4) with distinct tissue expression profiles and unique N-terminal regulatory regions, suggesting that each isoform could be individually targeted with a small molecule or biologic. PDE11A4 is the PDE11A isoform expressed in brain and is found in the hippocampal formation of humans and rodents. Studies in rodents show that PDE11A4 mRNA expression in brain is, in fact, restricted to the hippocampal formation (CA1, possibly CA2, subiculum, and the adjacently connected amygdalohippocampal area). Within the hippocampal formation of rodents, PDE11A4 protein is expressed in neurons but not astrocytes, with a distribution across nuclear, cytoplasmic, and membrane compartments. This subcellular localization of PDE11A4 is altered in response to social experience in mouse, and in vitro studies show the compartmentalization of PDE11A4 is controlled, at least in part, by homodimerization and N-terminal phosphorylation. PDE11A4 expression dramatically increases in the hippocampus with age in the rodent hippocampus, from early postnatal life to late aging, suggesting PDE11A4 function may evolve across the lifespan. Interestingly, PDE11A4 protein shows a three to tenfold enrichment in the rodent ventral hippocampal formation (VHIPP; a.k.a. anterior in primates) versus dorsal hippocampal formation (DHIPP). Consistent with this enrichment in VHIPP, studies in knockout mice show that PDE11A regulates the formation of social memories and the stabilization of mood and is a critical mechanism by which social experience feeds back to modify the brain and subsequent social behaviors. PDE11A4 likely controls behavior by regulating hippocampal glutamatergic, oxytocin, and cytokine signaling, as well as protein translation. Given its unique tissue distribution and relatively selective effects on behavior, PDE11A may represent a novel therapeutic target for neuropsychiatric, neurodevelopmental, or age-related disorders. Therapeutically targeting PDE11A4 may be a way to selectively restore aberrant cyclic nucleotide signaling in the hippocampal formation while leaving the rest of the brain and periphery untouched, thus, relieving deficits while avoiding unwanted side effects.

Common Pathophysiology in Multiple Mouse Models of Pitt-Hopkins Syndrome

Mutations or deletions of the transcription factor TCF4 are linked to Pitt-Hopkins syndrome (PTHS) and schizophrenia, suggesting that the precise pathogenic mutations dictate cellular, synaptic, and behavioral consequences. Here, we generated two novel mouse models of PTHS, one that mimics the most common pathogenic TCF4 point mutation (human R580W, mouse R579W) and one that deletes three pathogenic arginines, and explored phenotypes of these lines alongside models of pan-cellular or CNS-specific heterozygous Tcf4 disruption. We used mice of both sexes to show that impaired Tcf4 function results in consistent microcephaly, hyperactivity, reduced anxiety, and deficient spatial learning. All four PTHS mouse models demonstrated exaggerated hippocampal long-term potentiation (LTP), consistent with deficits in hippocampus-mediated behaviors. We further examined R579W mutant mice and mice with pan-cellular Tcf4 heterozygosity and found that they exhibited hippocampal NMDA receptor hyperfunction, which likely drives the enhanced LTP. Together, our data pinpoint convergent neurobiological features in PTHS mouse models and provide a foundation for preclinical studies and a rationale for testing whether NMDAR antagonists might be used to treat PTHS.SIGNIFICANCE STATEMENT Pitt-Hopkins syndrome (PTHS) is a rare neurodevelopmental disorder associated with TCF4 mutations/deletions. Despite this genetic insight, there is a need to identify the function of TCF4 in the brain. Toward this goal, we developed two mouse lines, including one harboring the most prevalent pathogenic point mutation, and compared them with two existing models that conditionally delete Tcf4 Our data identify a set of overlapping phenotypes that may serve as outcome measures for preclinical studies of PTHS treatments. We also discovered penetrant enhanced synaptic plasticity across mouse models that may be linked to increased NMDA receptor function. These data reveal convergent neurobiological characteristics of PTHS mouse models and support the further investigation of NMDA receptor antagonists as a possible PTHS treatment.

Involvement of posterior cingulate cortex in ketamine-induced psychosis relevant behaviors in rats

The involvement of posterior cingulate cortex (PCC) on ketamine-induced psychosis relevant behaviors was investigated in rats. Bilateral infusion of muscimol, a GABA_A receptor agonist, into the PCC significantly antagonized ketamine-induced deficit in prepulse inhibition of a startle reflex (PPI), deficit in gating of hippocampal auditory evoked potentials, and behavioral hyperlocomotion in a dose dependent manner. Local infusion of ketamine directly into the PCC also induced a PPI deficit. Systemic injection of ketamine (3mg/kg,s.c.) induced an increase in power of electrographic activity in the gamma band (30-100Hz) in both the PCC and the hippocampus; peak theta (4-10Hz) power was not significantly altered, but peak theta frequency was increased by ketamine. In order to exclude volume conduction from the hippocampus to PCC, inactivation of the hippocampus was made by local infusion of muscimol into the hippocampus prior to ketamine administration. Muscimol in the hippocampus effectively blocked ketamine-induced increase of gamma power in the hippocampus but not in the PCC, suggesting independent generation of gamma waves in PCC and hippocampus. It is suggested that the PCC is part of the brain network mediating ketamine-induced psychosis related behaviors.

Core-Cross-Linked Nanoparticles Reduce Neuroinflammation and Improve Outcome in a Mouse Model of Traumatic Brain Injury

Traumatic brain injury (TBI) is the leading cause of death and disability in children and young adults, yet there are currently no treatments available that prevent the secondary spread of damage beyond the initial insult. The chronic progression of this secondary injury is in part caused by the release of reactive oxygen species (ROS) into surrounding normal brain. Thus, treatments that can enter the brain and reduce the spread of ROS should improve outcome from TBI. Here a highly versatile, reproducible, and scalable method to synthesize core-cross-linked nanoparticles (NPs) from polysorbate 80 (PS80) using a combination of thiol-ene and thiol-Michael chemistry is described. The resultant NPs consist of a ROS-reactive thioether cross-linked core stabilized in aqueous solution by hydroxy-functional oligoethylene oxide segments. These NPs show narrow molecular weight distributions and have a high proportion of thioether units that reduce local levels of ROS. In a controlled cortical impact mouse model of TBI, the NPs are able to rapidly accumulate and be retained in damaged brain as visualized through fluorescence imaging, reduce neuroinflammation and the secondary spread of injury as determined through magnetic resonance imaging and histopathology, and improve functional outcome as determined through behavioral analyses. Our findings provide strong evidence that these NPs may, upon further development and testing, provide a useful strategy to help improve the outcome of patients following a TBI.

IgSF21 promotes differentiation of inhibitory synapses via binding to neurexin2α

Coordinated development of excitatory and inhibitory synapses is essential for higher brain function, and impairment in this development is associated with neuropsychiatric disorders. In contrast to the large body of accumulated evidence regarding excitatory synapse development, little is known about synaptic adhesion and organization mechanisms underlying inhibitory synapse development. Through unbiased expression screens and proteomics, we identified immunoglobulin superfamily member 21 (IgSF21) as a neurexin2α-interacting membrane protein that selectively induces inhibitory presynaptic differentiation. IgSF21 localizes postsynaptically and recruits axonal neurexin2α in a trans-interaction manner. Deleting IgSF21 in mice impairs inhibitory presynaptic organization, especially in the hippocampal CA1 stratum radiatum, and also diminishes GABA-mediated synaptic transmission in hippocampal CA1 neurons without affecting their excitatory synapses. Finally, mice lacking IgSF21 show a sensorimotor gating deficit. These findings suggest that IgSF21 selectively regulates inhibitory presynaptic differentiation through interacting with presynaptic neurexin2α and plays a crucial role in synaptic inhibition in the brain.

Molecular mechanisms regulating the development of inhibitory synapses are poorly understood. Here the authors show that IgSF21 interacts with neurexin2α to induce presynaptic differentiation of inhibitory synapses, and that mice lacking IgSF21 exhibit deficits in inhibitory synaptic transmission.

Differential effects of neonatal SSRI treatments on hypoxia-induced behavioral changes in male and female offspring

Prenatal hypoxia induced by transient intrauterine ischemia is a serious clinical problem, and at present, effective treatments are lacking. Currently, it is unknown how prenatal hypoxia affects behaviors in adulthood. Therefore, we developed a mouse model that mimics prenatal hypoxia in humans using uterine artery occlusion in late gestation. We examined whether prenatal hypoxia induces behavioral changes in adult male and female offspring by conducting a series of behavioral tests. In adulthood, longer immobility was observed in the forced swim test in males, whereas females showed decreased inhibition in the prepulse inhibition test. We then investigated the effects of two different selective serotonin reuptake inhibitors (SSRIs), fluoxetine (FLX) and escitalopram (ESC), on these behavioral changes. These drugs affect the neurodevelopmental process and have long-term neurological consequences. FLX treatment from postnatal day 3 (P3) to P21 ameliorated the behavioral changes in both male and female mice. In comparison, ESC treatment ameliorated the behavioral changes only in female mice. Neurochemical analysis revealed that dopamine was increased in the female hippocampus, but not in males. Thus, neonatal SSRI treatment decreases dopamine levels in the hippocampus in females selectively. Our findings suggest that prenatal hypoxia is a risk factor for behavioral abnormalities in adulthood, and that neonatal SSRI treatment might have clinical potential for alleviating these long-term behavioral deficits.

Role of the anterior cingulate cortex in the retrieval of novel object recognition memory after a long delay

Previous in vivo electrophysiological studies suggest that the anterior cingulate cortex (ACgx) is an important substrate of novel object recognition (NOR) memory. However, intervention studies are needed to confirm this conclusion and permanent lesion studies cannot distinguish effects on encoding and retrieval. The interval between encoding and retrieval tests may also be a critical determinant of the role of the ACgx. The current series of experiments used micro-infusion of the GABA_A receptor agonist, muscimol, into ACgx to reversibly inactivate the area and distinguish its role in encoding and retrieval. ACgx infusions of muscimol, before encoding did not alter NOR assessed after a delay of 20 min or 24 h. However, when infused into the ACgx before retrieval muscimol impaired NOR assessed after a delay of 24 h, but not after a 20-min retention test. Together these findings suggest that the ACgx plays a time-dependent role in the retrieval, but not the encoding, of NOR memory, neuronal activation being required for the retrieval of remote (24 h old), but not recent (20 min old) visual memory.

Cognitive deficits caused by prefrontal cortical and hippocampal neural disinhibition

We review recent evidence concerning the significance of inhibitory GABA transmission and of neural disinhibition, that is, deficient GABA transmission, within the prefrontal cortex and the hippocampus, for clinically relevant cognitive functions. Both regions support important cognitive functions, including attention and memory, and their dysfunction has been implicated in cognitive deficits characterizing neuropsychiatric disorders. GABAergic inhibition shapes cortico-hippocampal neural activity, and, recently, prefrontal and hippocampal neural disinhibition has emerged as a pathophysiological feature of major neuropsychiatric disorders, especially schizophrenia and age-related cognitive decline. Regional neural disinhibition, disrupting spatio-temporal control of neural activity and causing aberrant drive of projections, may disrupt processing within the disinhibited region and efferent regions. Recent studies in rats showed that prefrontal and hippocampal neural disinhibition (by local GABA antagonist microinfusion) dysregulates burst firing, which has been associated with important aspects of neural information processing. Using translational tests of clinically relevant cognitive functions, these studies showed that prefrontal and hippocampal neural disinhibition disrupts regional cognitive functions (including prefrontal attention and hippocampal memory function). Moreover, hippocampal neural disinhibition disrupted attentional performance, which does not require the hippocampus but requires prefrontal-striatal circuits modulated by the hippocampus. However, some prefrontal and hippocampal functions (including inhibitory response control) are spared by regional disinhibition. We consider conceptual implications of these findings, regarding the distinct relationships of distinct cognitive functions to prefrontal and hippocampal GABA tone and neural activity. Moreover, the findings support the proposition that prefrontal and hippocampal neural disinhibition contributes to clinically relevant cognitive deficits, and we consider pharmacological strategies for ameliorating cognitive deficits by rebalancing disinhibition-induced aberrant neural activity. Linked Articles This article is part of a themed section on Pharmacology of Cognition: a Panacea for Neuropsychiatric Disease? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.19/issuetoc.

Ventral, but not dorsal, hippocampus inactivation impairs reward memory expression and retrieval in contexts defined by proximal cues

The hippocampus (HPC) has been widely implicated in the contextual control of appetitive and aversive conditioning. However, whole hippocampal lesions do not invariably impair all forms of contextual processing, as in the case of complex biconditional context discrimination, leading to contention over the exact nature of the contribution of the HPC in contextual processing. Moreover, the increasingly well-established functional dissociation between the dorsal (dHPC) and ventral (vHPC) subregions of the HPC has been largely overlooked in the existing literature on hippocampal-based contextual memory processing in appetitively motivated tasks. Thus, the present study sought to investigate the individual roles of the dHPC and the vHPC in contextual biconditional discrimination (CBD) performance and memory retrieval. To this end, we examined the effects of transient post-acquisition pharmacological inactivation (using a combination of GABA_A and GABA_B receptor agonists muscimol and baclofen) of functionally distinct subregions of the HPC (CA1/CA3 subfields of the dHPC and vHPC) on CBD memory retrieval. Additional behavioral assays including novelty preference, light-dark box and locomotor activity test were also performed to confirm that the respective sites of inactivation were functionally silent. We observed robust deficits in CBD performance and memory retrieval following inactivation of the vHPC, but not the dHPC. Our data provides novel insight into the differential roles of the ventral and dorsal HPC in reward contextual processing, under conditions in which the context is defined by proximal cues.

Changes in Neuronal Oscillations Accompany the Loss of Hippocampal LTP that Occurs in an Animal Model of Psychosis

The first-episode of psychosis is followed by a transient time-window of ca. 60 days during which therapeutic interventions have a higher likelihood of being effective than interventions that are started with a greater latency. This suggests that, in the immediate time-period after first-episode psychosis, functional changes occur in the brain that render it increasingly resistant to intervention. The precise mechanistic nature of these changes is unclear, but at the cognitive level, sensory and hippocampus-based dysfunctions become increasingly manifest. In an animal model of first-episode psychosis that comprises acute treatment of rats with the irreversible N-methyl-D-aspartate receptor (NMDAR)-antagonist, MK801, acute but also chronic deficits in long-term potentiation (LTP) and spatial memory occur. Neuronal oscillations, especially in the form of information transfer through θ and γ frequency oscillations are an intrinsic component of normal information processing in the hippocampus. Changes in θ-γ coupling and power are known to accompany deficits in hippocampal plasticity. Here, we examined whether changes in δ, θ, α, β and γ oscillations, or θ-γ coupling accompany the chronic loss of LTP that is observed in the MK801-animal model of psychosis. One and 4 weeks after acute systemic treatment of adult rats with MK801, a potent loss of hippocampal in vivo LTP was evident compared to vehicle-treated controls. Overall, the typical pattern of θ-γ oscillations that are characteristic for the successful induction of LTP was altered. In particular, θ-power was lower and an uncoupling of θ-γ oscillations was evident in MK801-treated rats. The alterations in network oscillations that accompany LTP deficits in this animal model may comprise a mechanism through which disturbances in sensory information processing and hippocampal function occur in psychosis. These data suggest that the hippocampus is likely to comprise a very early locus of functional change after instigation of a first-episode psychosis-like state in rodents.

Sex differences in psychotomimetic-induced behaviours in rats

Animal model studies using equal numbers of males and females are sparse in psychiatry research. Given the marked sex differences observed in psychiatric disorders, such as schizophrenia, using both males and females in research studies is an important requirement. Thus the aim of this study was to examine sex differences in psychotomimetic-induced behavioural deficits relevant to psychosis. We therefore compared the acute effect of amphetamine or phencyclidine on locomotor activity and prepulse inhibition in adult male and female Sprague-Dawley rats. The results of this study were that: (1) amphetamine-induced distance travelled was greater in female rats than in male rats, (2) phencyclidine-induced locomotor hyperactivity was similar in male and female rats; (3) there were no sex differences in amphetamine- or phencyclidine-induced disruption of prepulse inhibition; (4) male rats had an increased startle response after amphetamine. These findings suggest that sensitivity to amphetamine, but not phencyclidine, differs between male and female rats, and that this sex difference is selective to locomotor hyperactivity and startle, but not prepulse inhibition. This study used two widely-used, validated preclinical assays relevant to psychosis; the results of this study have implications for psychiatry research, particularly for disorders where marked sex differences in onset and symptomology are observed.