Hippocampal Neuronal Density Research Articles

Signaling via the p75 neurotrophin receptor facilitates amyloid-\u03b2-induced dendritic spine pathology

Synapse and dendritic spine loss induced by amyloid-β oligomers is one of the main hallmarks of the early phases of Alzheimer’s disease (AD) and is directly correlated with the cognitive decline typical of this pathology. The p75 neurotrophin receptor (p75NTR) binds amyloid-β oligomers in the nM range. While it was shown that µM concentrations of amyloid-β mediate cell death, the role and intracellular signaling of p75NTR for dendritic spine pathology induced by sublethal concentrations of amyloid-β has not been analyzed. We describe here p75NTR as a crucial binding partner in mediating effects of soluble amyloid-β oligomers on dendritic spine density and structure in non-apoptotic hippocampal neurons. Removing or over-expressing p75NTR in neurons rescues or exacerbates the typical loss of dendritic spines and their structural alterations observed upon treatment with nM concentrations of amyloid-β oligomers. Moreover, we show that binding of amyloid-β oligomers to p75NTR activates the RhoA/ROCK signaling cascade resulting in the fast stabilization of the actin spinoskeleton. Our results describe a role for p75NTR and downstream signaling events triggered by binding of amyloid-β oligomers and causing dendritic spine pathology. These observations further our understanding of the molecular mechanisms underlying one of the main early neuropathological hallmarks of AD.

Hippocampal volume and hippocampal neuron density, number and size in schizophrenia: a systematic review and meta-analysis of postmortem studies.

Reduced hippocampal volume is a consistent finding in neuroimaging studies of individuals with schizophrenia. While these studies have the advantage of large sample sizes, they are unable to quantify the cellular basis of structural or functional changes. In contrast, postmortem studies are well suited to explore subfield and cellular alterations, but low sample sizes and subject heterogeneity impede establishment of statistically significant differences. Here we use a meta-analytic approach to synthesize the extant literature of hippocampal subfield volume and cellular composition in schizophrenia patients and healthy control subjects. Following pre-registration (PROSPERO CRD42019138280), PubMed, Web of Science, and PsycINFO were searched using the term: (schizophrenia OR schizoaffective) AND (post-mortem OR postmortem) AND hippocampus. Subjects were adult men and women with schizophrenia or schizoaffective disorder or non-psychiatric control subjects, and key outcomes, stratified by hippocampal hemisphere and subfield, were volume, neuron number, neuron density, and neuron size. A random effects meta-analysis was performed. Thirty-two studies were included (413 patients, 415 controls). In patients, volume and neuron number were significantly reduced in multiple hippocampal subfields in left, but not right hippocampus, whereas neuron density was not significantly different in any hippocampal subfield. Neuron size, averaged bilaterally, was also significantly reduced in all calculated subfields. Heterogeneity was minimal to moderate, with rare evidence of publication bias. Meta-regression of age and illness duration did not explain heterogeneity of total hippocampal volume effect sizes. These results extend neuroimaging findings of smaller hippocampal volume in schizophrenia patients and further our understanding of regional and cellular neuropathology in schizophrenia.

Erythropoietin shows gender dependent positive effects on social deficits, learning/memory impairments, neuronal loss and neuroinflammation in the lipopolysaccharide induced rat model of autism

We aimed to evaluate the effects of EPO in the lipopolysaccharide (LPS) induced rat model of autism in terms of social deficits, learning and memory impairments, as well as their neurochemical correlates.Sixteen female Sprague Dawley rats randomly distributed into two equel groups, then were caged with fertile males for mating. At the 10th day of pregnancy, 0.5 ml %0,9 NaCl saline was given to first group, 100 μg/kg LPS was given to second group to induce autism. On postnatal 21th day, forty-eight littermates were divided into four groups as; 8 male, 8 female controls, 16 male and 16 female LPS-exposed. Then, LPS groups were also divided in to two groups as saline (1 mg/kg/day) and EPO 600 U/kg/day groups, and animals were treated 45 days. At 50th day, after behavioral evaluations, brain levels of TNF-α, nerve growth factor (NGF) were measured. Histologically, hippocampal neuronal density and GFAP expression were assessed.Three-chamber sociability and social novelty test, passive avoidance learning test were revealed significant differences among the EPO and control groups. Histologically, hippocampal CA1 & CA3 regions displayed significant alterations regarding gliosis (GFAP-positive cells) and regarding frontal cortical thickness in EPO groups compare to controls. Biochemical measurements of the brain levels of TNF-α and NGF levels showed significant differences between controls and EPO groups.According to our findings EPO treatment has beneficial effects on ASD-like symptoms, learning and memory processes, neuronal loss and neuroinflammation in the LPS induced rat model of autism, with some gender differences through inflammatory and neurotrophic pathways.

Effect of Methylene Blue and PI3K-Akt Pathway Inhibitors on the Neurovascular System after Chronic Cerebral Hypoperfusion in Rats.

Methylene blue (MB) has a protective effect on cognitive decline caused by chronic hypoperfusion, but the specific mechanism is not clear. This article aims to determine whether MB protects vascular neurons through PI3K/Akt and plays a role in improving cognitive impairment. Molecular biological methods, the hippocampal neuronal density test, the hippocampal vascular network density test, and dynamic enhanced magnetic resonance imaging (MRI) were used to detect the blood-brain barrier permeability and Evans blue leakage rate in the hippocampus. We also observed and evaluated the changes in the above results after administration of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway protein inhibitor LY294002. There were significant differences for cerebral blood flow (CBF) between the chronic cerebral hypoperfusion (CCH) + MB group (100ml/100g/min) and the CCH group (60ml/100g/min, P < 0.05). After using LY294002, the CBF of the CCH + MB + LY294002 group dropped to 82ml/100g/min. The vascular density in the CCH + MB group was 23%, which is significantly higher than that in the CCH group (15.1%) (P < 0.05). The vascular density (17.5%) in the CCH + MB + LY294002 group was significantly higher than that in the CCH group but lower than that in the CCH + MB group. Western blotting results showed that one week after intraperitoneal injection of MB, the expression of t-Akt and p-Akt in the CCH + MB group was increased after CCH, and LY294002 partially blocked this up-regulation effect (CCH + MB + LY294002 group). MB is a potential therapy for the relief of mild cognitive impairment associated with CCH, vascular dementia, and Alzheimer's disease.

Mitigation of helium irradiation-induced brain injury by microglia depletion

BackgroundCosmic radiation exposures have been found to elicit cognitive impairments involving a wide-range of underlying neuropathology including elevated oxidative stress, neural stem cell loss, and compromised neuronal architecture. Cognitive impairments have also been associated with sustained microglia activation following low dose exposure to helium ions. Space-relevant charged particles elicit neuroinflammation that persists long-term post-irradiation. Here, we investigated the potential neurocognitive benefits of microglia depletion following low dose whole body exposure to helium ions.MethodsAdult mice were administered a dietary inhibitor (PLX5622) of colony stimulating factor-1 receptor (CSF1R) to deplete microglia 2 weeks after whole body helium irradiation (4He, 30 cGy, 400 MeV/n). Cohorts of mice maintained on a normal and PLX5622 diet were tested for cognitive function using seven independent behavioral tasks, microglial activation, hippocampal neuronal morphology, spine density, and electrophysiology properties 4–6 weeks later.ResultsPLX5622 treatment caused a rapid and near complete elimination of microglia in the brain within 3 days of treatment. Irradiated animals on normal diet exhibited a range of behavioral deficits involving the medial pre-frontal cortex and hippocampus and increased microglial activation. Animals on PLX5622 diet exhibited no radiation-induced cognitive deficits, and expression of resting and activated microglia were almost completely abolished, without any effects on the oligodendrocyte progenitors, throughout the brain. While PLX5622 treatment was found to attenuate radiation-induced increases in post-synaptic density protein 95 (PSD-95) puncta and to preserve mushroom type spine densities, other morphologic features of neurons and electrophysiologic measures of intrinsic excitability were relatively unaffected.ConclusionsOur data suggest that microglia play a critical role in cosmic radiation-induced cognitive deficits in mice and, that approaches targeting microglial function are poised to provide considerable benefit to the brain exposed to charged particles.

Sham surgical embryo transfer affects offspring neurodevelopment and manifestation of hypertensive phenotype in ISIAH rats

ABSTRACT The study investigates how surgery during pregnancy, i.e., sham operation associated with embryo transfer, affects hypertensive phenotype in ISIAH rats genetically predisposed to hypertension. ISIAH rats born after maternal surgery at fourth day of pregnancy were compared with naturally conceived controls. Surgery during pregnancy in ISIAH rats caused acceleration of neurodevelopment in young offspring, as well as aggravating hypertension, suppressing exploratory activity, reducing hippocampal BDNF expression, and compensatory increasing of hippocampal neuronal density in adult ISIAH offspring. Maternal surgery during early pregnancy caused alterations in offspring phenotype in hypertensive ISIAH rat model.

SAT-285 TSH/TSHR Signaling Deficiency Impairs Spatial Learning and Memory

Background: Subclinical hyperthyroidism is associated with cognitive impairment, but the mechanism has remained unclear. As subclinical hyperthyroidism is characterized by significantly decreased TSH levels, this study aimed to investigate whether TSH regulates cognitive function. Methods: The correlation between TSH and cognitive impairment was investigated in a cross-sectional population study. The role of TSH/TSH receptor (TSHR) signaling in spatial learning and memory was further examined by behavior tests in Tshr-/- mice. Dendritic spine, synaptic density and structure of hippocampal CA1 pyramidal neurons were detected by Golgi’s method and electron microscopy. The mRNA and protein expression levels of learning and memory-related genes were assessed by RNA sequencing, real-time PCR, immunoblotting and immunofluorescence approaches. Results: Serum TSH level correlated negatively with cognitive impairment in the current population. Consistently, Tshr deletion in mice led to significantly compromised performance in hippocampus-dependent tasks, reduced dendritic spine density and excitatory synaptic density as well as altered synaptic structure in CA1 subfield of the hippocampus. Furthermore, the mRNA levels of learning and memory-related genes were altered, and protein levels of CREB-regulated genes were downregulated in the hippocampus of Tshr-/- mice. Conclusions: These findings reveal that TSH/TSHR signaling ablation impairs spatial learning and memory, indicating a decline in TSH level might contribute to the increased prevalence of cognitive impairment in subclinical hyperthyroidism patients.

Fingolimod Modulates Dendritic Architecture in a BDNF-Dependent Manner.

The brain-derived neurotrophic factor (BDNF) plays crucial roles in both the developing and mature brain. Moreover, alterations in BDNF levels are correlated with the cognitive impairment observed in several neurological diseases. Among the different therapeutic strategies developed to improve endogenous BDNF levels is the administration of the BDNF-inducing drug Fingolimod, an agonist of the sphingosine-1-phosphate receptor. Fingolimod treatment was shown to rescue diverse symptoms associated with several neurological conditions (i.e., Alzheimer disease, Rett syndrome). However, the cellular mechanisms through which Fingolimod mediates its BDNF-dependent therapeutic effects remain unclear. We show that Fingolimod regulates the dendritic architecture, dendritic spine density and morphology of healthy mature primary hippocampal neurons. Moreover, the application of Fingolimod upregulates the expression of activity-related proteins c-Fos and pERK1/2 in these cells. Importantly, we show that BDNF release is required for these actions of Fingolimod. As alterations in neuronal structure underlie cognitive impairment, we tested whether Fingolimod application might prevent the abnormalities in neuronal structure typical of two neurodevelopmental disorders, namely Rett syndrome and Cdk5 deficiency disorder. We found a significant rescue in the neurite architecture of developing cortical neurons from Mecp2 and Cdkl5 mutant mice. Our study provides insights into understanding the BDNF-dependent therapeutic actions of Fingolimod.

Effects of Lisinopril on Arterial Stiffness, Cerebral Blood Flow and Cortical Thickness in Hypertensive Dahl‐S Rats

Study objectivesCentral arterial stiffness (CAS), associated with hypertension, is likely underlies the stiffening of cerebral arterial wall resulting in cerebral hypoperfusion, neuronal density loss and cognitive decline. We previously found associations between pulse wave velocity (PWV), a marker of CAS, and hippocampal cerebral blood flow (CBF) and neuronal density in 6‐mo old hypertensive Dahl salt‐sensitive (Dahl‐S) rats. This study examined the effect of ACE inhibitor, Lisinopril, on cardiovascular and brain parameters in hypertensive Dahl‐S rats.MethodsMale Dahl‐S rats (n=32) were fed with a normal salt diet (0.5% NaCl) for a duration of study. Systolic blood pressure (SBP), PWV (by echocardiography); hippocampal N‐acetyl aspartate (NAA) concentration, hippocampal CBF were measured at 6‐mo of age (baseline) and after 3‐mo and 6‐mo of Lisinopril (15mg/kg body weight/day in drinking water; n=14) or control (n=18) treatment. NAA was measured using proton spectroscopy in a 7T Bruker Biospec MRI scanner; CBF was measured using continuous arterial spin labeling (CASL) in the coronal slice with the largest hippocampal area; cortical thickness (CT) analysis was done using a T2 weighted RARE 3D image (n=12). Advanced Normalization Tools (ANTs) were used for the CT estimation. T‐test and 2‐way ANOVA linear mix effect model analyses were performed in R, EXCEL and MATLAB. Data presented as mean±SE.ResultsAt 6‐mo of age, the Dahl‐S rats developed advanced hypertension vs. 3‐mo (SBP: 164±4 vs. 141±3 mmHg; P&lt;0.01, t‐test). SBP of non‐treated (NT) animals was steadily high at all time points while treated animals exhibited a decrease in SBP at 9‐mo vs. 6‐mo of age. SBP remained low from 9‐mo to 12‐mo of age (Fig. 1a). In treated animals, PWV decreased at all timepoints after 6‐mo of age. For NT animals, PWV remained steady from 6‐mo to 9‐mo but increases from 9‐mo to12‐mo of age (Fig. 1b). Hippocampal CBF of NT animals decreased in a downwards trend but remain stabilized in the treated group across timepoints (Fig. 1c). Likewise, the hippocampal NAA, among treated animals remained stabilized, while in NT animals this parameter fluctuated with an eventual downwards trend (Fig. 1d). The mean difference maps of the CT for the NT and treated rats are similar except for the regions denoted by the red arrows when comparing treated to NT (Fig. 2a–b). The occipital region showed cortical thickening (blue) and parietal region showed cortical thinning (yellow). The P value maps show that those regions of significant thickening and thinning are greater in the treated vs. NT rats (Fig. 2c–d).ConclusionThe posterior cerebral artery is a dominant source of perfusion to the hippocampus and the occipital lobe; thus, our findings suggest a coherent pattern through which CAS can affect the cerebral arteries in hypertensive Dahl‐S rats. Lisinopril treatment decrease CAS and improve regional CBF and neuronal density. Therefore, CAS may be a therapeutic target for vascular dementia.Support or Funding InformationThe work was supported by the Intramural Research Program of the National Institute on Aging of the National Institutes of Health.Longitudinal changes in cardiovascular parameters in Lisinopril treated Dahl‐S rats. Systolic blood pressure SBP (a), pulse wave velocity PWV (b), hippocampal CBF (c), and NAA (d) in Lisinopril treated (T) and nontreated (NT) rats. By 2‐way ANOVA Linear Mixed Effects: *p &lt; 0.001 vs. age‐matched treated rats; #p &lt; 0.03 vs. 6‐mo, ## p &lt;0.001 vs. 6‐mo; by paired T‐test (c, d): * p = 0.07 vs. 6‐mo; # p = 0.06 vs. 9‐mo NT.Figure 1Mean Differences in Cortical Thickness and their p value maps (6‐mo subtracted by 12‐mo). Mean difference between age 6‐mo and 12‐mo of (a) nontreated animals and (b) lisinopril treated animals. Blue indicates regions of thickening. Yellow indicated regions of thinning. Occipital and parietal regions indicated by the red arrows. P value map of nontreated animals (c) and lisinopril treated animals (d). All insignificant p values &gt; 0.05 were revalued as 0.05 for visualization purposes.Figure 2

Acute Pannexin 1 Blockade Mitigates Early Synaptic Plasticity Defects in a Mouse Model of Alzheimer's Disease.

Synaptic loss induced by soluble oligomeric forms of the amyloid β peptide (sAβos) is one of the earliest events in Alzheimer’s disease (AD) and is thought to be the major cause of the cognitive deficits. These abnormalities rely on defects in synaptic plasticity, a series of events manifested as activity-dependent modifications in synaptic structure and function. It has been reported that pannexin 1 (Panx1), a nonselective channel implicated in cell communication and intracellular signaling, modulates the induction of excitatory synaptic plasticity under physiological contexts and contributes to neuronal death under inflammatory conditions. Here, we decided to study the involvement of Panx1 in functional and structural defects observed in excitatory synapses of the amyloid precursor protein (APP)/presenilin 1 (PS1) transgenic (Tg) mice, an animal model of AD. We found an age-dependent increase in the Panx1 expression that correlates with increased Aβ levels in hippocampal tissue from Tg mice. Congruently, we also observed an exacerbated Panx1 activity upon basal conditions and in response to glutamate receptor activation. The acute inhibition of Panx1 activity with the drug probenecid (PBN) did not change neurodegenerative parameters such as amyloid deposition or astrogliosis, but it significantly reduced excitatory synaptic defects in the AD model by normalizing long-term potentiation (LTP) and depression and improving dendritic arborization and spine density in hippocampal neurons of the Tg mice. These results suggest a major contribution of Panx1 in the early mechanisms leading to the synaptopathy in AD. Indeed, PBN induced a reduction in the activation of p38 mitogen-activated protein kinase (MAPK), a kinase widely implicated in the early neurotoxic signaling in AD. Our data strongly suggest that an enhanced expression and activation of Panx1 channels contribute to the Aβ-induced cascades leading to synaptic dysfunction in AD.

The Complement Regulator Susd4 Influences Nervous-System Function and Neuronal Morphology in Mice.

SummaryThe SUSD4 (Sushi domain-containing protein 4) gene encodes a complement inhibitor that is frequently deleted in 1q41q42 microdeletion syndrome, a multisystem congenital disorder that includes neurodevelopmental abnormalities. To understand SUSD4's role in the mammalian nervous system, we analyzed Susd4 knockout (KO) mice. Susd4 KO mice exhibited significant defects in motor performance and significantly higher levels of anxiety-like behaviors. Susd4 KO brain had abnormal “hairy” basket cells surrounding Purkinje neurons within the cerebellum and significantly reduced dendritic spine density in hippocampal pyramidal neurons. Neurons and oligodendrocyte lineage cells of wild-type mice were found to express Susd4 mRNA. Protein expression of the complement component C1q was increased in the brains of Susd4 KO mice. Our data indicate that SUSD4 plays an important role in neuronal functions, possibly via the complement pathway, and that SUSD4 deletion may contribute to the nervous system abnormalities in patients with 1q41q42 deletions.

Protective Effect of Curcumin on the Density of Hippocampal Dark Neurons in Mice Model of Aging Induced by D-Galactose: A Histopathological Study

Background: Curcumin is the most active ingredient in turmeric root of Curcuma longa of the Zingiberaceae family and has a potent antioxidant activity. This study aimed at investigating the effects of curcumin with various doses on the density of dark neurons in the hippocampus of induced D-galactose aging mice model. This experimental study was conducted on 40 adult male BALB/c mice.&#x0D; Materials and Methods: We randomly divided animals into 5 groups: D-galactose, control, and curcumin 1, curcumin 2, and curcumin 3 groups. D-galactose (300 mg/kg) was intraperitoneally injected into the D galactose group for 6 weeks. D-galactose and doses of 25, 50, and 100 mg of curcumin were administrated, respectively, to the curcumin groups 1-3 every day for 14 days. After 6 weeks, the mice’s brains were stained with toluidine blue after tissue passage. Then, the mean dark neuron volume density in each unit of the tissue was assessed using stereological formulas. The obtained data were analyzed by Aanlysis of Variance (ANOVA) in SPSS.&#x0D; Results: Compared with the control group, the average number of dark neurons in the hippocampus significantly increased following the administration of D-galactose (P=0.001). The average dark neurons frequency in the hippocampus significantly decreased in the 50 and 100 mg/kg curcumin-treated groups (P=0.001 for both) compared to that of the D-galactose treated animals.&#x0D; Conclusion: The results of this study showed that treatment with 100 mg/kg of curcumin reduced the number of dark neurons in the hippocampus of the aging mice. It seems that curcumin decreases dark neurons via the reduction of apoptosis. Also, curcumin is a powerful antioxidant and affects the level of antioxidant status in the brain.

Nicotinamide attenuates the decrease in dendritic spine density in hippocampal primary neurons from 5xFAD mice, an Alzheimer\u2019s disease animal model

Alzheimer’s disease (AD) is the most common neurodegenerative disease characterized by memory loss and the presence of amyloid plaques and neurofibrillary tangles in the patients’ brains. In this study, we investigated the alterations in metabolite profiles of the hippocampal tissues from 6, 8, and 12 month-old wild-type (WT) and 5xfamiliar AD (5xFAD) mice, an AD mouse model harboring 5 early-onset familiar AD mutations, which shows memory loss from approximately 5 months of age, by exploiting the untargeted metabolomics profiling. We found that nicotinamide and adenosine monophosphate levels have been significantly decreased while lysophosphatidylcholine (LysoPC) (16:0), LysoPC (18:0), and lysophosphatidylethanolamine (LysoPE) (16:0) levels have been significantly increased in the hippocampi from 5xFAD mice at 8 months or 12 months of age, compared to those from age-matched wild-type mice. In the present study, we focused on the role of nicotinamide and examined if replenishment of nicotinamide exerts attenuating effects on the reduction in dendritic spine density in hippocampal primary neurons from 5xFAD mice. Treatment with nicotinamide attenuated the deficits in spine density in the hippocampal primary neurons derived from 5xFAD mice, indicating a potential role of nicotinamide in the pathogenesis of AD. Taken together, these findings suggest that the decreased hippocampal nicotinamide level could be linked with AD pathogenesis and be a useful therapeutic target for AD.

The endocannabinoid system regulates the moderate exercise-induced enhancement of learning and memory in mice.

Exercise has been reported to enhance cognitive functions via mechanism(s) yet to be fully understood. The endogenous cannabinoid system (ECS) is involved in regulating cognitive function, including learning and memory. This system may also be involved in enhancing learning and memory after exercise. The objective of this study is to explore whether and how ECS participates in the enhancement of learning and memory after exercise. In this study, a treadmill exercise training model was established. Wild-type C57BL/6J mice and those deficient in the cannabinoid receptor 1 (CB1R) coding gene, Cnr1, specifically in the glutamatergic neurons, γ-aminobutyric acid (GABA) neurons or glial cells were randomly grouped for 4 weeks' moderate treadmill exercise. The Morris water maze was used to evaluate the spatial learning and memory abilities of mice in each group. The expression of brain-derived neurotrophic factor (BDNF) and CB1R in hippocampus was detected by western blot. The dendritic spine density of pyramidal cells in the hippocampal CA1 region was analyzed by quantitative Golgi staining. This study consisted of eight single-factor inter-subject designs, and each batch of experiments was divided into two groups. Corresponding experimental items and data analysis were carried out according to the experimental objectives. CB1R antagonist administration or CB1R knockout in glutamatergic neurons eliminated the effect of exercise on learning and memory, and counteracted exercise-elicited upregulation of BDNF in the hippocampus; CB1R-specific knockout on GABAergic neurons and glial cells did not affect the moderate exercise-induced enhancement of learning and memory. In addition, the results of Golgi staining showed that exercise increased dendritic spine density in hippocampal neurons, which was abolished by specific CB1R depletion in glutamatergic neurons. The ECS, particularly CB1R signaling in glutamatergic neurons, mediates the enhancement of learning and memory by exercise, which involves increased BDNF production and dendritic spine density.

Treatment with gut bifidobacteria improves hippocampal plasticity and cognitive behavior in adult healthy rats

At the present time, gut microbiota inspires great interest in the field of neuroscience as a function of its role in normal physiology and involvement in brain function. This aspect suggests a specific gut-brain pathway, mainly modulated by gut microbiota activity. Among the multiple actions controlled by microbiota at the brain level, neuronal plasticity and cognitive function represent two of the most interesting aspects of this cross-talk communication. We address the possible action of two-months implementation of gut Bifidobacteria using a mixture of three different strains (B-MIX) on hippocampal plasticity and related cognitive behavior in adult healthy Sprague Dawley rats. B-MIX treatment increases the hippocampal BDNF with a parallel gain in dendritic spines’ density of hippocampal CA1 pyramidal neurons. Electrophysiological experiments revealed a significant increment of HFS-induced LTP formation on the CA1 hippocampal region in B-MIX treated rats. All these effects are accompanied by a better cognitive performance observed in B-MIX treated animals with no impairments in locomotion activity. Therefore, in adult rats, the treatment with different strains of bifidobacteria is able to markedly enhance neuronal plasticity and the CNS function influencing cognitive behavior, an effect that may suggest a potential therapeutic treatment in brain diseases associated with cognitive functions.

Ketamine exerts neurotoxic effects on the offspring of pregnant rats via the Wnt/β-catenin pathway.

Ketamine is an anesthetic and analgesic drug widely used in clinical anesthesia. To ensure the safety of anesthesia, it is necessary to study its side effects. Pregnancy is a key period for the development and growth of offspring. During this period, the proliferation and differentiation of brain cells and the synaptic formation are easily affected by external stimuli. Therefore, the aim of this study was to evaluate the effect of ketamine. Ketamine anesthesia was administered to rats in the second trimester of pregnancy, and two behavioral tests were performed, including contextual and cued fear conditioning test (CFC) and Morris water maze (MWM). At the end of the behavioral test, Nissl and Golgi staining were used to detect the dendrite density of hippocampal neurons to reveal the effect of maternal ketamine anesthesia on the hippocampus of offspring. Key proteins and their downstream transcription factors in Wnt/β-catenin signaling pathway from the embryonic development to the adulthood were studied. Our results showed that rats receiving maternal ketamine suffered from nerve injury. The density of hippocampal nerves and dendritic spine changed. Some genes related to Wnt/β-catenin pathway and Tcf/Lef were downregulated. In conclusion, maternal anesthesia with ketamine in the second trimester of pregnancy can lead to cognitive memory impairment and neurotoxicity in the hippocampus of offspring through Wnt/ β-catenin signaling pathway.

A Conserved Tyrosine Residue in Slitrk3 Carboxyl-Terminus Is Critical for GABAergic Synapse Development

Single-passing transmembrane protein, Slitrk3 (Slit and Trk-like family member 3, ST3), is a synaptic cell adhesion molecule highly expressed at inhibitory synapses. Recent studies have shown that ST3, through its extracellular domain, selectively regulates inhibitory synapse development via the trans-synaptic interaction with presynaptic cell adhesion molecule, receptor protein tyrosine phosphatase δ (PTPδ) and the cis-interaction with postsynaptic cell adhesion molecule, Neuroligin 2 (NL2). However, little is known about the physiological function of ST3 intracellular, carboxyl (C)-terminal region. Here we report that in heterologous cells, ST3 C-terminus is not required for ST3 homo-dimerization and trafficking to the cell surface. In contrast, in hippocampal neurons, ST3 C-terminus, more specifically, the conserved tyrosine Y969 (in mice), is critical for GABAergic synapse development. Indeed, overexpression of ST3 Y969A mutant markedly reduced the gephyrin puncta density and GABAergic transmission in hippocampal neurons. In addition, single-cell genetic deletion of ST3 strongly impaired GABAergic transmission. Importantly, wild-type (WT) ST3, but not the ST3 Y969A mutant, could fully rescue GABAergic transmission deficits in neurons lacking endogenous ST3, confirming a critical role of Y969 in the regulation of inhibitory synapses. Taken together, our data identify a single critical residue in ST3 C-terminus that is important for GABAergic synapse development and function.

Loss of Bardet-Biedl syndrome proteins causes synaptic aberrations in principal neurons.

Bardet-Biedl syndrome (BBS), a ciliopathy, is a rare genetic condition characterised by retinal degeneration, obesity, kidney failure, and cognitive impairment. In spite of progress made in our general understanding of BBS aetiology, the molecular and cellular mechanisms underlying cognitive impairment in BBS remain elusive. Here, we report that the loss of BBS proteins causes synaptic dysfunction in principal neurons, providing a possible explanation for the cognitive impairment phenotype observed in BBS patients. Using synaptosomal proteomics and immunocytochemistry, we demonstrate the presence of Bbs proteins in the postsynaptic density (PSD) of hippocampal neurons. Loss of Bbs results in a significant reduction of dendritic spines in principal neurons of Bbs mouse models. Furthermore, we show that spine deficiency correlates with events that destabilise spine architecture, such as impaired spine membrane receptor signalling, known to be involved in the maintenance of dendritic spines. Our findings suggest a role for BBS proteins in dendritic spine homeostasis that may be linked to the cognitive phenotype observed in BBS.

P: 74 Cholestasis Decreases Dendritic Spine Density in a Rat Hippocampal Organotypic Culture

BACKGROUND: Executive functioning impairment in children with cholestatic liver disease is increasingly recognized. Injury to developing neuronal networks could be an underlying mechanism. Given that the CSF of rat pups following bile duct ligation is highly concentrated in ammonia, murocholic and taurocholic acids, we hypothesized that cholestasis may significantly alter density of synaptic contacts onto pyramidal neurons, known to be essential in the development of executive functioning. METHODS: Transverse hippocampal organotypic slice (400 µm thick) were harvested from 6–7-day-old Wistar rats. They were maintained for 15 days in a CO2-incubator (33°C). pc-DNA3.1-EGFP plasmid biolistic transfection was performed 7 days after harvesting. 3 days following transfection, control medium or experimental medium containing 100 µM α-murocholic-acid, 200 µM taurocholic-acid and 2.5 mM ammonium was added to the culture (day 0 of exposure, MIX condition). Confocal microscopy using imageJ was used for to manually count CA1 pyramidal neuron dendritic spines as proxies for excitatory synapses. Static analysis quantified dendritic spines density each day. Dynamic analysis quantified dendritic spines turnover (loss and neo-formation) for each 24 h time-window. Statistical analysis was conducted using PRISM software for multiple t-test or mixed-effect ANOVA. RESULTS: Static analysis showed a biphasic profile in MIX condition. During early phase (first 3 days of exposure), we observed &gt;50% decrease in dendritic spine density compared to control (cf Figure 1, P &lt; 0.001). On days 3 to 4), spine density recovered to reach control value. Dynamic analysis showed 15% loss in dendritic spines stability during the early phase of exposure to MIX condition, compared to controls, with comparable low rates of spine turnover. During the late phase of MIX exposure, spine turnover increased significantly in favor of spine neo-formation: spine neo-formation was 10 times higher (0.280 vs 0.023 spines.µm-1, P = 0.033) than controls, while spine loss was 6 times higher in neurons exposed to MIX (0.154 vs 0.026 spines.µm-1, P = 0.0026) than controls. CONCLUSIONS: We demonstrate here that mimicking cholestasis ex vivo leads to a biphasic response in spine density of rat hippocampal CA1 pyramidal neurons. Spine density decreases during the first 3-days of exposure to a mix of bile acids and ammonium chloride-owing to decreased in spine stability. This is followed by increased spine turnover with spine neo-formation in excess of spine loss, yielding a final spine density similar to control animals. Whether these new spines are functionally equivalent to controls remains to be determined.

Validation of a Psychosocial Chronic Stress Model in the Pig Using a Multidisciplinary Approach at the Gut-Brain and Behavior Levels.

Psychological chronic stress is an important risk factor for major depressive disorder, of which consequences have been widely studied in rodent models. This work aimed at describing a pig model of chronic stress based on social isolation, environmental impoverishment and unpredictability. Three groups of animals of both sexes were constituted. Two were exposed to the psychosocial stressors while receiving (SF, n = 12) or not (SC, n = 22) the antidepressant fluoxetine, and a third group (NSC, n = 22) remained unstressed. Animals were observed in home pens and during dedicated tests to assess resignation and anxiety-like behaviors. Brain structure and function were evaluated via proton MRS and fMRI. Hippocampal molecular biology and immunodetection of cellular proliferation (Ki67+) and neuron maturation (DCX+) in the dentate gyrus were also performed. Salivary cortisol, fecal short-chain fatty acids (SCFAs), and various plasmatic and intestinal biomarkers were analyzed. Compared to NSC, SC animals showed more resignation (p = 0.019) and had a higher level of salivary cortisol (p = 0.020). SC brain responses to stimulation by a novel odor were lower, similarly to their hippocampal neuronal density (p = 0.015), cellular proliferation (p = 0.030), and hippocampal levels of BDNF and 5-HT1AR (p = 0.056 and p = 0.007, respectively). However, the number of DCX+ cells was higher in the ventral dentate gyrus in this group (p = 0.025). In addition, HOMA-IR was also higher (p < 0.001) and microbiota fermentation activity was lower (SCFAs, SC/NSC: p < 0.01) in SC animals. Fluoxetine partially or totally reversed several of these effects. Exposure to psychosocial stressors in the pig model induced effects consistent with the human and rodent literature, including resignation behavior and alterations of the HPA axis and hippocampus. This model opens the way to innovative translational research exploring the mechanisms of chronic stress and testing intervention strategies with good face validity related to human.