Granule Cells In Mice Research Articles

Deleting Adult Neural Stem Cells Ameliorates Synaptic and Cognitive Deficits in Animal Models of Alzheimer's Disease

The development of adult neural stem cells (aNSCs) was impaired in the hippocampus of animal models of Alzheimer’s disease (AD). However, whether and how aNSCs and new neurons derived from aNSCs affect AD neuropathology is unclear. Here, we found that genetic or drug-induced ablation of aNSCs significantly ameliorated deficits of synaptic plasticity and cognitive functions in two mouse models of AD. On the other hand, whole cell recording revealed that deleting aNSCs prevented the increased inhibition in the dentate granule cells of AD mice. Furthermore, deleting aNSCs did not affect Aβ levels but prevented the calbindin depletion in the hippocampus of AD mice. Knocking down calbindin in the hippocampus abolished the effects of deleting aNSCs on synaptic and cognitive functions in AD mice. Taken together, our data suggest that deleting aNSCs improved synaptic plasticity and cognitive functions in AD mice by regulating the activity of dentate granule cells via calbindin.

Olfactory deficit is associated with mitral cell dysfunction in the olfactory bulb of P301S tau transgenic mice

Neurofibrillary tangles consisting of hyperphosphorylated tau (P-tau) are the neuropathological hallmark of Alzheimer’s disease (AD), and olfaction disorder is an early symptom of AD. However, the link between P-tau aggregation and olfaction disorder remains unclear. In this study, the expression of P-tau in the olfactory bulb (OB), particularly in the mitral cell layer (MCL), external plexiform layer (EPL), and granule cell layer (GCL), of AD patients was found to be significantly higher than that in the OB of normal aging subjects, which suggested that these layers in the OB were susceptible to P-tau. The P301S tau transgenic mice (P301S mice) exhibit AD-like features, which can be characterized by olfactory dysfunction that precedes cognitive disorder. Importantly, the excessive P-tau expression in the OB of P301S mice, particularly in MCs, was associated with MC loss at 9 months of age, and decreased MC firing activities started to be observed at 2 months of age. Our results revealed that MCs might contribute to olfactory dysfunction in P301S mice. Furthermore, we described an aberrant dendro-dendritic synaptic structure between granule cells (GCs) and MCs and abnormal gamma oscillations in the EPL of the OB, and these findings indicated that P-tau might disrupt the regulation of MCs by GCs in P301S mice starting at 5 months of age. These data showed that the reduction in the MC firing frequency at 2 months of age might not be caused by GC suppression. Based on these findings, we speculated that MCs are a putative target for the treatment of P-tau-induced early olfactory dysfunction, and thus, an exploration of the specific causes and mechanisms of MC functional changes in P301S mice is crucial.

TWIK-1/TASK-3 heterodimeric channels contribute to the neurotensin-mediated excitation of hippocampal dentate gyrus granule cells

Two-pore domain K+ (K2P) channels have been shown to modulate neuronal excitability. The physiological role of TWIK-1, the first identified K2P channel, in neuronal cells is largely unknown, and we reported previously that TWIK-1 contributes to the intrinsic excitability of dentate gyrus granule cells (DGGCs) in mice. In the present study, we investigated the coexpression of TWIK-1 and TASK-3, another K2P member, in DGGCs. Immunohistochemical staining data showed that TASK-3 proteins were highly localized in the proximal dendrites and soma of DGGCs, and this localization is similar to the expression pattern of TWIK-1. TWIK-1 was shown to associate with TASK-3 in DGGCs of mouse hippocampus and when both genes were overexpressed in COS-7 cells. shRNA-mediated gene silencing demonstrated that TWIK-1/TASK-3 heterodimeric channels displayed outwardly rectifying currents and contributed to the intrinsic excitability of DGGCs. Neurotensin–neurotensin receptor 1 (NT–NTSR1) signaling triggered the depolarization of DGGCs by inhibiting TWIK-1/TASK-3 heterodimeric channels, causing facilitated excitation of DGGCs. Taken together, our study clearly showed that TWIK-1/TASK-3 heterodimeric channels contribute to the intrinsic excitability of DGGCs and that their activities are regulated by NT–NTSR1 signaling.

NMDA receptors mediate synaptic depression, but not spine loss in the dentate gyrus of adult amyloid Beta (A\u03b2) overexpressing mice

Amyloid beta (Aβ)-mediated synapse dysfunction and spine loss are considered to be early events in Alzheimer’s disease (AD) pathogenesis. N-methyl-D-aspartate receptors (NMDARs) have previously been suggested to play a role for Amyloid beta (Aβ) toxicity. Pharmacological block of NMDAR subunits in cultured neurons and mice suggested that NMDARs containing the GluN2B subunit are necessary for Aβ-mediated changes in synapse number and function in hippocampal neurons. Interestingly, NMDARs undergo a developmental switch from GluN2B- to GluN2A-containing receptors. This indicates different functional roles of NMDARs in young mice compared to older animals. In addition, the lack of pharmacological tools to efficiently dissect the role of NMDARs containing the different subunits complicates the interpretation of their specific role. In order to address this problem and to investigate the specific role for Aβ toxicity of the distinct NMDAR subunits in dentate gyrus granule cells of adult mice, we used conditional knockout mouse lines for the subunits GluN1, GluN2A and GluN2B. Aβ-mediated changes in synaptic function and neuronal anatomy were investigated in several-months old mice with virus-mediated overproduction of Aβ and in 1-year old 5xFAD mice. We found that all three NMDAR subunits contribute to the Aβ-mediated decrease in the number of functional synapses. However, NMDARs are not required for the spine number reduction in dentate gyrus granule cells after chronic Aβ-overproduction in 5xFAD mice. Furthermore, the amplitude of synaptic and extrasynaptic NMDAR-mediated currents was reduced in dentate gyrus granule of 5xFAD mice without changes in current kinetics, suggesting that a redistribution or change in subunit composition of NMDARs does not play a role in mediating Amyloid beta (Aβ) toxicity. Our study indicates that NMDARs are involved in AD pathogenesis by compromising synapse function but not by affecting neuron morphology.

Biphasic Modulation of NMDA Receptor Function by Metabotropic Glutamate Receptors.

A recently reported rapid potentiation of NMDA receptors by Group I metabotropic glutamate receptors (mGluRIs) via a Homer protein link is distinct from the classical, relatively slow inhibitory G-protein-associated signaling triggered by mGluRI activation. The relationship between these two mechanisms remains unknown. Here, we focused on the mGluRI-dependent modulation of NMDAR response in hippocampal dentate gyrus granule cells and cerebellar granule cells of C57BL6-J mice and found that these two contrasting mechanisms overlap competitively on the time scale from hundreds of milliseconds to seconds, with the net effect depending on the cell type. At a shorter time interval (units of millisecond), the Homer-mediated signal from mGluRIs prevails, causing upregulation of NMDAR function, in both dentate gyrus granule cells and cerebellar granule cells. Our results shed light on the possible mechanisms of anti-schizophrenia drugs that disrupt Homer-containing protein link.SIGNIFICANCE STATEMENT Here we study modulation of NMDA receptors triggered by activation of metabotropic glutamate receptors Group I via two distinct pathways: classical G-protein signaling system and newly discovered high-speed modulatory mechanism associated with Homer-protein-containing direct molecular link. We found that these two contrasting mechanisms overlap competitively on the time scale from hundreds of milliseconds to seconds, with the net effect depending on the cell type. We have also found that both crosstalk mechanisms cause significant changes in synaptic strength and plasticity. Our results resolve an apparent discrepancy between earlier studies that demonstrated contradictive effects of Homer-containing protein link disruption on NMDA receptor signaling. On top of that, our data provide a plausible explanation for unclear action mechanisms of anti-schizophrenia drugs.

Targeted deletion of HYBID (hyaluronan binding protein involved in hyaluronan depolymerization/ KIAA1199/CEMIP) decreases dendritic spine density in the dentate gyrus through hyaluronan accumulation

HYBID (hyaluronan binding protein involved in hyaluronan [HA] depolymerization, KIAA1199/CEMIP) is a key player in HA depolymerization of the skin fibroblasts, arthritic synovial fibroblasts, and brain. Our previous study demonstrated that Hybid knock-out (KO) mice showed spatial memorial impairment, which is accompanied by the accumulation of high molecular weight HA in the hippocampus. However, the mechanism underlying cognitive impairment by Hybid deficiency remains unclear. In the present study, we examined the HA distribution patterns in the brains of wild-type (WT) and Hybid KO mice by HA staining using HA binding protein, and found that in Hybid KO mice, HA is accumulated and doublecortin-positive immature neurons are significantly decreased in the dentate gyrus of the hippocampus, where Hybid mRNA is highly expressed in WT mice. The Golgi-Cox staining demonstrated that the dendritic spine density is significantly decreased in the dentate gyrus granule cells in Hybid KO mice. These results suggest that Hybid-mediated HA degradation is critical for the synaptic formation process by contributing to cognitive functions, such as learning and memory, in the mouse brain.

The Low-Threshold Calcium Channel Cav3.2 Mediates Burst Firing of Mature Dentate Granule Cells.

Mature granule cells are poorly excitable neurons that were recently shown to fire action potentials, preferentially in bursts. It is believed that the particularly pronounced short-term facilitation of mossy fiber synapses makes granule cell bursting a very effective means of properly transferring information to CA3. However, the mechanism underlying the unique bursting behavior of mature granule cells is currently unknown. Here, we show that Cav3.2 T-type channels at the axon initial segment are responsible for burst firing of mature granule cells in rats and mice. Accordingly, Cav3.2 knockout mice fire tonic spikes and exhibit impaired bursting, synaptic plasticity and dentate-to-CA3 communication. The data show that Cav3.2 channels are strong modulators of bursting and can be considered a critical molecular switch that enables effective information transfer from mature granule cells to the CA3 pyramids.

Meis1 Coordinates Cerebellar Granule Cell Development by Regulating Pax6 Transcription, BMP Signaling and Atoh1 Degradation.

Cerebellar granule cell precursors (GCPs) and granule cells (GCs) represent good models to study neuronal development. Here, we report that the transcription factor myeloid ectopic viral integration site 1 homolog (Meis1) plays pivotal roles in the regulation of mouse GC development. We found that Meis1 is expressed in GC lineage cells and astrocytes in the cerebellum during development. Targeted disruption of the Meis1 gene specifically in the GC lineage resulted in smaller cerebella with disorganized lobules. Knock-down/knock-out (KO) experiments for Meis1 and in vitro assays showed that Meis1 binds to an upstream sequence of Pax6 to enhance its transcription in GCPs/GCs and also suggested that the Meis1-Pax6 cascade regulates morphology of GCPs/GCs during development. In the conditional KO (cKO) cerebella, many Atoh1-positive GCPs were observed ectopically in the inner external granule layer (EGL) and a similar phenomenon was observed in cultured cerebellar slices treated with a bone morphogenic protein (BMP) inhibitor. Furthermore, expression of Smad proteins and Smad phosphorylation were severely reduced in the cKO cerebella and Meis1-knock-down GCPs cerebella. Reduction of phosphorylated Smad was also observed in cerebellar slices electroporated with a Pax6 knock-down vector. Because it is known that BMP signaling induces Atoh1 degradation in GCPs, these findings suggest that the Meis1-Pax6 pathway increases the expression of Smad proteins to upregulate BMP signaling, leading to degradation of Atoh1 in the inner EGL, which contributes to differentiation from GCPs to GCs. Therefore, this work reveals crucial functions of Meis1 in GC development and gives insights into the general understanding of the molecular machinery underlying neural differentiation from neural progenitors.SIGNIFICANCE STATEMENT We report that myeloid ectopic viral integration site 1 homolog (Meis1) plays pivotal roles in the regulation of mouse granule cell (GC) development. Here, we show Meis1 is expressed in GC precursors (GCPs) and GCs during development. Our knock-down and conditional knock-out (cKO) experiments and in vitro assays revealed that Meis1 is required for proper cerebellar structure formation and for Pax6 transcription in GCPs and GCs. The Meis1-Pax6 cascade regulates the morphology of GCs. In the cKO cerebella, Smad proteins and bone morphogenic protein (BMP) signaling are severely reduced and Atoh1-expressing GCPs are ectopically detected in the inner external granule layer. These findings suggest that Meis1 regulates degradation of Atoh1 via BMP signaling, contributing to GC differentiation in the inner EGL, and should provide understanding into GC development.

Immature morphological properties in subcellular-scale structures in the dentate gyrus of Schnurri-2 knockout mice: a model for schizophrenia and intellectual disability

Accumulating evidence suggests that subcellular-scale structures such as dendritic spine and mitochondria may be involved in the pathogenesis/pathophysiology of schizophrenia and intellectual disability. Previously, we proposed mice lacking Schnurri-2 (Shn2; also called major histocompatibility complex [MHC]-binding protein 2 [MBP-2], or human immunodeficiency virus type I enhancer binding protein 2 [HIVEP2]) as a schizophrenia and intellectual disability model with mild chronic inflammation. In the mutants’ brains, there are increases in C4b and C1q genes, which are considered to mediate synapse elimination during postnatal development. However, morphological properties of subcellular-scale structures such as dendritic spine in Shn2 knockout (KO) mice remain unknown. In this study, we conducted three-dimensional morphological analyses in subcellular-scale structures in dentate gyrus granule cells of Shn2 KO mice by serial block-face scanning electron microscopy. Shn2 KO mice showed immature dendritic spine morphology characterized by increases in spine length and decreases in spine diameter. There was a non-significant tendency toward decrease in spine density of Shn2 KO mice over wild-type mice, and spine volume was indistinguishable between genotypes. Shn2 KO mice exhibited a significant reduction in GluR1 expression and a nominally significant decrease in SV2 expression, while PSD95 expression had a non-significant tendency to decrease in Shn2 KO mice. There were significant decreases in dendrite diameter, nuclear volume, and the number of constricted mitochondria in the mutants. Additionally, neuronal density was elevated in Shn2 KO mice. These results suggest that Shn2 KO mice serve as a unique tool for investigating morphological abnormalities of subcellular-scale structures in schizophrenia, intellectual disability, and its related disorders.

High Plasticity of New Granule Cells in the Aging Hippocampus

During aging, the brain undergoes changes that impair cognitive capacity and circuit plasticity, including a marked decrease in production of adult-born hippocampal neurons. It is unclear whether development and integration of those new neurons are also affected by age. Here, we show that adult-born granule cells (GCs) in aging mice are scarce and exhibit slow development, but they display aremarkable potential for structural plasticity. Retrovirally labeled 3-week-old GCs in middle-aged micewere small, underdeveloped, and disconnected. Neuronal development and integration were accelerated by voluntary exercise or environmental enrichment. Similar effects were observed via knockdown of Lrig1, an endogenous negative modulator of neurotrophin receptors. Consistently, blocking neurotrophin signaling by Lrig1 overexpression abolished thepositive effects of exercise. These results demonstrate an unparalleled degree of plasticity in the aging brain mediated by neurotrophins, whereby new GCs remain immature until becoming rapidly recruited to the network by activity.

Decreased Glial GABA and Tonic Inhibition in Cerebellum of Mouse Model for Attention-Deficit/Hyperactivity Disorder (ADHD).

About 5~12% of school-aged children suffer from the Attention-Deficit/Hyperactivity Disorder (ADHD). However, the core mechanism of ADHD remains unclear. G protein-coupled receptor kinase-interacting protein-1 (GIT1) has recently been reported to be associated with ADHD in human and the genetic deletion of GIT1 result in ADHD-like behaviors in mice. Mice lacking GIT1 shows a shift in neuronal excitation/inhibition (E/I) balance. However, the pricise mechanism for E/I imbalance and the role of neuron-glia interaction in GIT1 knockout (KO) mice have not been studied. Especially, a possible contribution of glial GABA and tonic inhibition mediated by astrocytic GABA release in the mouse model for ADHD remains unexplored. Therefore, we investigated the changes in the amount of GABA and degree of tonic inhibition in GIT1 KO mice. We observed a decreased glial GABA intensity in GIT1 KO mice compared to wild type (WT) mice and an attenuation of tonic current from cerebellar granule cells in GIT1 KO mice. Our study identifies the previously unknown mechanism of reduced astrocytic GABA and tonic inhibition in GIT1 lacking mice as a potential cause of hyperactivity disorder.

Decreased surface expression of the δ subunit of the GABAA receptor contributes to reduced tonic inhibition in dentate granule cells in a mouse model of fragile X syndrome

While numerous changes in the GABA system have been identified in models of Fragile X Syndrome (FXS), alterations in subunits of the GABAA receptors (GABAARs) that mediate tonic inhibition are particularly intriguing. Considering the key role of tonic inhibition in controlling neuronal excitability, reduced tonic inhibition could contribute to FXS-associated disorders such as hyperactivity, hypersensitivity, and increased seizure susceptibility. The current study has focused on the expression and function of the δ subunit of the GABAAR, a major subunit involved in tonic inhibition, in granule cells of the dentate gyrus in the Fmr1 knockout (KO) mouse model of FXS. Electrophysiological studies of dentate granule cells revealed a marked, nearly four-fold, decrease in tonic inhibition in the Fmr1 KO mice, as well as reduced effects of two δ subunit-preferring pharmacological agents, THIP and DS2, supporting the suggestion that δ subunit-containing GABAARs are compromised in the Fmr1 KO mice. Immunohistochemistry demonstrated a small but statistically significant decrease in δ subunit labeling in the molecular layer of the dentate gyrus in Fmr1 KO mice compared to wildtype (WT) littermates. The discrepancy between the large deficits in GABA-mediated tonic inhibition in granule cells in the Fmr1 KO mice and only modest reductions in immunolabeling of the δ subunit led to studies of surface expression of the δ subunit. Cross-linking experiments followed by Western blot analysis demonstrated a small, non-significant decrease in total δ subunit protein in the hippocampus of Fmr1 KO mice, but a four-fold decrease in surface expression of the δ subunit in these mice. No significant changes were observed in total or surface expression of the α4 subunit protein, a major partner of the δ subunit in the forebrain. Postembedding immunogold labeling for the δ subunit demonstrated a large, three-fold, decrease in the number of symmetric synapses with immunolabeling at perisynaptic locations in Fmr1 KO mice. While α4 immunogold particles were also reduced at perisynaptic locations in the Fmr1 KO mice, the labeling was increased at synaptic sites. Together these findings suggest that, in the dentate gyrus, altered surface expression of the δ subunit, rather than a decrease in δ subunit expression alone, could be limiting δ subunit-mediated tonic inhibition in this model of FXS. Finding ways to increase surface expression of the δ subunit of the GABAAR could be a novel approach to treatment of hyperexcitability-related alterations in FXS.

Cerebellar perineuronal nets in cocaine-induced pavlovian memory: Site matters

One of the key mechanisms for the stabilization of synaptic changes near the end of critical periods for experience-dependent plasticity is the formation of specific lattice extracellular matrix structures called perineuronal nets (PNNs). The formation of drug memories depends on local circuits in the cerebellum, but it is unclear to what extent it may also relate to changes in their PNN. Here, we investigated changes in the PNNs of the cerebellum following cocaine-induced preference conditioning. The formation of cocaine-related preference memories increased expression of PNN-related proteins surrounding Golgi inhibitory interneurons as well as that of cFos in granule cells at the apex of the cerebellar cortex. In contrast, the expression of PNNs surrounding projection neurons in the medial deep cerebellar nucleus (DCN) was reduced in all cocaine-treated groups, independently of whether animals expressed a preference for cocaine-related cues. Discriminant function analysis confirmed that stronger PNNs in Golgi neurons and higher cFos levels in granule cells of the apex might be considered as the cerebellar hallmarks of cocaine-induced preference conditioning. Blocking the output of cerebellar granule cells in α6Cre-Cacna1a mutant mice prevented re-acquisition, but not acquisition, of cocaine-induced preference conditioning. Interestingly, this impairment in consolidation was selectively accompanied by a reduction in the expression of PNN proteins around Golgi cells. Our data suggest that PNNs surrounding Golgi interneurons play a role in consolidating drug-related memories.

Neurosteroids reverse tonic inhibitory deficits in Fragile X syndrome mouse model

Fragile X syndrome (FXS) is the most common form of inherited intellectual disability. In addition, there is increased incidence of anxiety, sleep irregularities, and seizure activity. The underlying cause of FXS is a loss of the fragile X mental retardation protein (FMRP) which has been shown to participate in the biosynthesis of δ subunits. Studies from both FXS patients and animal models have revealed reduced expression levels of GABAAR α4 and δ subunits with a reduced efficacy of tonic inhibition. Neurosteroids (NS) are known allosteric modulators of GABAAR channel function but recent studies from our laboratory have revealed that NS also exert persistent effects on the efficacy of tonic inhibition by increasing the PKC‐mediated phosphorylation of the α4 subunit which increases the membrane expression and boosts tonic inhibition. We have used a combination of biochemical and electrophysiological methods to assess alterations in GABAergic signaling in the hippocampus of FMRP knock‐out mouse (Fmr1 KO), a widely validated model of the human syndrome.Our preliminary studies demonstrate that Fmr1 KO mice at p21 have a decrease in phosphorylation of S443 in the α4 subunit compared to WT and an increase in the phosphorylation of β3 subunits at the S408/409 site compared to WT. We have previously showed that phosphorylation of these residues changes the trafficking of the subunits so the changes observed in Fmr1 KO mice would predictably have consequences for trafficking of these essential inhibitory subunits. However, at p48–72 Fmr1 KO mice did not exhibit any deficits in GABAAR expression levels or phosphorylation demonstrating a critical developmental deficit in GABAAR expression. We noted that there was a significant decrease in tonic inhibition in dentate gyrus granule cells in p21 Fmr1 KO mice compared to WT. A 10 min exposure to 1μM THDOC followed by 330 min wash induced a >3 fold increase in tonic current in Fmr1 KO animals which was prevented with PKC inhibition. Using a perforated multi‐electrode array we have observed in horizontal cortical‐hippocampal slices seizure like events (SLE) propagating through the dentate gyrus and into the CA3 and CA1 regions of the hippocampus of Fmr1 KO mice but in WT mice SLEs did not propagate through the dentate gyrus. We predict the increase neuronal excitability seen in Fmr1 KO mice is due to the deficits in tonic inhibition.We have observed that THDOC treatment effectively reversed tonic current deficits in Fmr1 KO mice. Future studies will focus on ameliorating behavioral deficits in Fmr1 KO mice with synthetic neuroactive steroids that display improved pharmacokinetic properties.Support or Funding InformationThis work was supported by grants from the National Institutes of Health (NIH)‐National Institute of Alcoholism and Alcohol Abuse grant AA017938 (P.A.D), NIH‐National Institute of Mental Health grant, MH097446, and DOD, AR140209 (PAD & SJM), NIH‐National Institute of Neurological Disorders and Stroke grant NS051195, NS056359, NS081735, NS080064, NS087662 (SJM), the Simons Foundation #206026 (S.J.M.).

Loss of protohaem IX farnesyltransferase in mature dentate granule cells impairs short-term facilitation at mossy fibre to CA3 pyramidal cell synapses.

Key points Neurodegenerative disorders can exhibit dysfunctional mitochondrial respiratory chain complex IV activity.Conditional deletion of cytochrome c oxidase, the terminal enzyme in the respiratory electron transport chain of mitochondria, from hippocampal dentate granule cells in mice does not affect low‐frequency dentate to CA3 glutamatergic synaptic transmission.High‐frequency dentate to CA3 glutamatergic synaptic transmission and feedforward inhibition are significantly attenuated in cytochrome c oxidase‐deficient mice.Intact presynaptic mitochondrial function is critical for the short‐term dynamics of mossy fibre to CA3 synaptic function. Neurodegenerative disorders are characterized by peripheral and central symptoms including cognitive impairments which have been associated with reduced mitochondrial function, in particular mitochondrial respiratory chain complex IV or cytochrome c oxidase activity. In the present study we conditionally removed a key component of complex IV, protohaem IX farnesyltransferase encoded by the COX10 gene, in granule cells of the adult dentate gyrus. Utilizing whole‐cell patch‐clamp recordings from morphologically identified CA3 pyramidal cells from control and complex IV‐deficient mice, we found that reduced mitochondrial function did not result in overt deficits in basal glutamatergic synaptic transmission at the mossy‐fibre synapse because the amplitude, input–output relationship and 50 ms paired‐pulse facilitation were unchanged following COX10 removal from dentate granule cells. However, trains of stimuli given at high frequency (> 20 Hz) resulted in dramatic reductions in short‐term facilitation and, at the highest frequencies (> 50 Hz), also reduced paired‐pulse facilitation, suggesting a requirement for adequate mitochondrial function to maintain glutamate release during physiologically relevant activity patterns. Interestingly, local inhibition was reduced, suggesting the effect observed was not restricted to synapses with CA3 pyramidal cells via large mossy‐fibre boutons, but rather to all synapses formed by dentate granule cells. Therefore, presynaptic mitochondrial function is critical for the short‐term dynamics of synapse function, which may contribute to the cognitive deficits observed in pathological mitochondrial dysfunction.

Ginsenoside Rg1 improves fertility and reduces ovarian pathological damages in premature ovarian failure model of mice.

This study aims to investigate the effect as well as mechanism of ginsenoside Rg1 (Rg1) on premature ovarian failure (POF) induced by d-galactose (d-gal) in mice. C57BL/6 female mice were divided into four groups randomly, which were the saline group, the d-gal group, the d-gal + Rg1 group, and the Rg1 group. Body weight was recorded. Overall ovarian function including estrous cycles, sex hormone secretion, ovarian follicle development, and ovarian morphology was analyzed by H&E staining and ELISA. Effect of Rg1 on aging was determined by analyzing the activities of oxidation-associated biomarkers, pro-inflammatory cytokine secretion, expression of senescence-associated proteins, and fertility. Compared with the d-gal group, in Rg1 + d-gal group, body weight was increased significantly, estrous cycle block was released, and fertility and the morphology of ovaries were restored. And, Rg1 treatment after d-gal administration significantly reduced senescence-associated protein expression, increased the activity of total superoxide dismutase and glutathione peroxidase from bovine erythrocyte, and induced higher follicle stimulating hormone receptor protein expression. Additionally, the expression levels of malondialdehyde, interleukin-1β, tumor necrosis factor-α, and interleukin-6 were significantly decreased. Together, Rg1 improves mouse fertility and reduces ovarian pathological damage in d-gal-induced POF model possibly through enhancing anti-inflammatory and antioxidant capacities and reducing expression of senescence signal pathway proteins. Impact statement Ginsenoside Rg1 (Rg1) is a kind of natural estrogen and it has antioxidation and antiaging effects. However, whether Rg1 has effects on premature ovarian failure (POF) is still not clear. In this study, aging model induced by d-galactose was used to mimic POF. The effect and possible mechanism of Rg1 on ovary aging was investigated. We found that Rg1 treatment up-regulated the expression of follicle stimulating hormone receptor and down-regulated senescence-associated protein expression in granule cells of POF mice. Particularly, Rg1 improved fertility ability and reduced ovarian pathological damages by its antioxidative and anti-inflammation capacity. Thus, Rg1 enhances the antiaging ability of ovary and fertility ability of POF mice through enhancing the anti-inflammatory and antioxidant capacities of ovary.

GABAergic hyperinnervation of dentate granule cells in the Ts65Dn mouse model of down syndrome: Exploring the role of App.

It has been suggested that increased GABAergic innervation in the hippocampus plays a significant role in cognitive dysfunction in Down syndrome (DS). Bolstering this notion, are studies linking hyper-innervation of the dentate gyrus (DG) by GABAergic terminals to failure in LTP induction in the Ts65Dn mouse model of DS. Here, we used extensive morphometrical methods to assess the status of GABAergic interneurons in the DG of young and old Ts65Dn mice and their 2N controls. We detected an age-dependent increase in GABAergic innervation of dentate granule cells (DGCs) in Ts65Dn mice. The primary source of GABAergic terminals to DGCs somata is basket cells (BCs). For this reason, we assessed the status of these cells and found a significant increase in the number of BCs in Ts65Dn mice compared with controls. Then we aimed to identify the gene/s whose overexpression could be linked to increased number of BCs in Ts65Dn and found that deleting the third copy of App gene in Ts65Dn mice led to normalization of the number of BCs in these mice. Our data suggest that App overexpression plays a major role in the pathophysiology of GABAergic hyperinnervation of the DG in Ts65Dn mice. © 2016 Wiley Periodicals, Inc.

A Subtype of Olfactory Bulb Interneurons Is Required for Odor Detection and Discrimination Behaviors.

Neural circuits that undergo reorganization by newborn interneurons in the olfactory bulb (OB) are necessary for odor detection and discrimination, olfactory memory, and innate olfactory responses, including predator avoidance and sexual behaviors. The OB possesses many interneurons, including various types of granule cells (GCs); however, the contribution that each type of interneuron makes to olfactory behavioral control remains unknown. Here, we investigated the in vivo functional role of oncofetal trophoblast glycoprotein 5T4, a regulator for dendritic arborization of 5T4-expressing GCs (5T4 GCs), the level of which is reduced in the OB of 5T4 knock-out (KO) mice. Electrophysiological recordings with acute OB slices indicated that external tufted cells (ETCs) can be divided into two types, bursting and nonbursting. Optogenetic stimulation of 5T4 GCs revealed their connection to both bursting and nonbursting ETCs, as well as to mitral cells (MCs). Interestingly, nonbursting ETCs received fewer inhibitory inputs from GCs in 5T4 KO mice than from those in wild-type (WT) mice, whereas bursting ETCs and MCs received similar inputs in both mice. Furthermore, 5T4 GCs received significantly fewer excitatory inputs in 5T4 KO mice. Remarkably, in olfactory behavior tests, 5T4 KO mice had higher odor detection thresholds than the WT, as well as defects in odor discrimination learning. Therefore, the loss of 5T4 attenuates inhibitory inputs from 5T4 GCs to nonbursting ETCs and excitatory inputs to 5T4 GCs, contributing to disturbances in olfactory behavior. Our novel findings suggest that, among the various types of OB interneurons, the 5T4 GC subtype is required for odor detection and discrimination behaviors. Neuronal circuits in the brain include glutamatergic principal neurons and GABAergic interneurons. Although the latter is a minority cell type, they are vital for normal brain function because they regulate the activity of principal neurons. If interneuron function is impaired, brain function may be damaged, leading to behavior disorder. The olfactory bulb (OB) possesses various types of interneurons, including granule cells (GCs); however, the contribution that each type of interneuron makes to the control of olfactory behavior remains unknown. Here, we analyzed electrophysiologically and behaviorally the function of oncofetal trophoblast glycoprotein 5T4, a regulator for dendritic branching in OB GCs. We found that, among the various types of OB interneuron, the 5T4 GC subtype is required for odor detection and odor discrimination behaviors.

Adult microbiota-deficient mice have distinct dendritic morphological changes: differential effects in the amygdala and hippocampus.

Increasing evidence implicates the microbiota in the regulation of brain and behaviour. Germ‐free mice (GF; microbiota deficient from birth) exhibit altered stress hormone signalling and anxiety‐like behaviours as well as deficits in social cognition. Although the mechanisms underlying the ability of the gut microbiota to influence stress responsivity and behaviour remain unknown, many lines of evidence point to the amygdala and hippocampus as likely targets. Thus, the aim of this study was to determine if the volume and dendritic morphology of the amygdala and hippocampus differ in GF versus conventionally colonized (CC) mice. Volumetric estimates revealed significant amygdalar and hippocampal expansion in GF compared to CC mice. We also studied the effect of GF status on the level of single neurons in the basolateral amygdala (BLA) and ventral hippocampus. In the BLA, the aspiny interneurons and pyramidal neurons of GF mice exhibited dendritic hypertrophy. The BLA pyramidal neurons of GF mice had more thin, stubby and mushroom spines. In contrast, the ventral hippocampal pyramidal neurons of GF mice were shorter, less branched and had less stubby and mushroom spines. When compared to controls, dentate granule cells of GF mice were less branched but did not differ in spine density. These findings suggest that the microbiota is required for the normal gross morphology and ultrastructure of the amygdala and hippocampus and that this neural remodelling may contribute to the maladaptive stress responsivity and behavioural profile observed in GF mice.

PM366. Three-dimensional analysis of morphological changes in dendritic spines and mitochondria in dentate gyrus granule cells in Schnurri-2 knockout mice, an animal model for schizophrenia

PM366. Three-dimensional analysis of morphological changes in dendritic spines and mitochondria in dentate gyrus granule cells in Schnurri-2 knockout mice, an animal model for schizophrenia