Expression of GCaMP6s in the dentate gyrus induces tonic-clonic seizures.

GCaMP is a genetically encoded calcium indicator (GECI) widely used in neuroscience research. It measures intracellular Ca2+ level by fluorescence changes as it directly binds to Ca2+. In this process, the effect of this calcium buffer on the intracellular calcium signaling and cell physiology is often not taken into consideration. However, growing evidence from calcium imaging studies shows GCaMP expression under certain conditions can generate aberrant activity, such as seizures. In this study, we examined the effect of GCaMP6 expression in the dentate gyrus (DG) on epileptogenesis. We found that viral expression of GCaMP6s but not GCaMP6f in the DG induces tonic-clonic seizures several weeks after viral injection. Cell-type specific expression of GCaMP6s revealed the granule cells (GCs) as the key player in GCaMP6s-induced epilepsy. Finally, by using slice electrophysiology, we demonstrated that GCaMP6s expression increases neuronal excitability in the GCs. Together, this study highlights the ability of GCaMP6s in DG-associated epileptogenesis.

Role of folate receptor α in the partial rejuvenation of dentate gyrus cells: Improvement of cognitive function in 21-month-old aged mice.

Neuronal aging may be, in part, related to a change in DNA methylation. Thus, methyl donors, like folate and methionine, may play a role in cognitive changes associated to neuronal aging. To test the role of these metabolites, we performed stereotaxic microinjection of these molecules into the dentate gyrus (DG) of aged mice (an average age of 21 month). Folate, but not S-Adenosyl-Methionine (SAM), enhances cognition in aged mice. In the presence of folate, we observed partial rejuvenation of DG cells, characterized by the expression of juvenile genes or reorganization of extracellular matrix. Here, we have also tried to identify the mechanism independent of DNA methylation, that involve folate effects on cognition. Our analyses indicated that folate binds to folate receptor α (FRα) and, upon folate binding, FRα is transported to cell nucleus, where it is acting as transcription factor for expressing genes like SOX2 or GluN2B. In this work, we report that a FRα binding peptide also replicates the folate effect on cognition, in aged mice. Our data suggest that such effect is not sex-dependent. Thus, we propose the use of this peptide to improve cognition since it lacks of folate-mediated side effects. The use of synthetic FRα binding peptides emerge as a future strategy for the study of brain rejuvenation.

Inhibition of Granule Cell Dispersion and Seizure Development by Astrocyte Elevated Gene-1 in a Mouse Model of Temporal Lobe Epilepsy.

Although granule cell dispersion (GCD) in the hippocampus is known to be an important feature associated with epileptic seizures in temporal lobe epilepsy (TLE), the endogenous molecules that regulate GCD are largely unknown. In the present study, we have examined whether there is any change in AEG-1 expression in the hippocampus of a kainic acid (KA)-induced mouse model of TLE. In addition, we have investigated whether the modulation of astrocyte elevated gene-1 (AEG-1) expression in the dentate gyrus (DG) by intracranial injection of adeno-associated virus 1 (AAV1) influences pathological phenotypes such as GCD formation and seizure susceptibility in a KA-treated mouse. We have identified that the protein expression of AEG-1 is upregulated in the DG of a KA-induced mouse model of TLE. We further demonstrated that AEG-1 upregulation by AAV1 delivery in the DG-induced anticonvulsant activities such as the delay of seizure onset and inhibition of spontaneous recurrent seizures (SRS) through GCD suppression in the mouse model of TLE, while the inhibition of AEG-1 expression increased susceptibility to seizures. The present observations suggest that AEG-1 is a potent regulator of GCD formation and seizure development associated with TLE, and the significant induction of AEG-1 in the DG may have therapeutic potential against epilepsy.

Spine plasticity of dentate gyrus parvalbumin-positive interneurons is regulated by experience.

Experience-driven alterations in neuronal activity are followed by structural-functional modifications allowing cells to adapt to these activity changes. Structural plasticity has been observed for cortical principal cells. However, how GABAergic interneurons respond to experience-dependent network activity changes is not well understood. We show that parvalbumin-expressing interneurons (PVIs) of the dentate gyrus (DG) possess dendritic spines, which undergo behaviorally induced structural dynamics. Glutamatergic inputs at PVI spines evoke signals with high spatial compartmentalization defined by neck length. Mice experiencing novel contexts form more PVI spines with elongated necks and exhibit enhanced network and PVI activity and cFOS expression. Enhanced green fluorescent protein reconstitution across synaptic partner-mediated synapse labeling shows that experience-driven PVI spine growth boosts targeting of PVI spines over shafts by glutamatergic synapses. Our findings propose a role for PVI spine dynamics in regulating PVI excitation by their inputs, which may allow PVIs to dynamically adjust their functional integration in the DG microcircuitry in relation to network computational demands.

Enhanced NMDA receptor pathway and glutamate transmission in the hippocampal dentate gyrus mediate the spatial learning and memory impairment of obese rats.

Obesity has been linked with the impairment of spatial memory and synaptic plasticity but the molecular mechanisms remained unidentified. Since glutamatergic transmission and NMDA receptor neural pathways in hippocampal dentate gyrus (DG) are essential in the learning and memory, we aimed to investigate glutamate (Glu) and NMDA receptor signaling of DG in spatial learning and memory in diet-induced obesity (DIO) rats. Spatial learning and memory were assessed via Morris water maze (MWM) test on control (Ctr) and DIO rats. Extracellular concentration of Glu in the DG was determined using in vivo microdialysis and HPLC. The protein expressions of NMDA receptor subunit 2B (NR2B), brain-derived neurotrophic factor (BDNF), the activation of calcium/calmodulin-dependent kinase II (CaMKII) and cAMP-response-element-binding protein (CREB) in the DG were observed by western blot. Spatial learning and memory were impaired in DIO rats compared to those of Ctr. NR2B expression was increased, while BDNF expression and CaMKII and CREB activation were decreased in DG of DIO rats. Extracellular concentration of Glu was increased in Ctr on the 3rd and 4th days of the MWM test, but significant further increment was observed in DIO rats. Microinjection of an NMDA antagonist (MK-801) into the DG reversed spatial learning and memory impairment. Such effects were accompanied by greater BDNF expression and CaMKII/CREB activation in the DG of DIO rats. In conclusion, the enhancement of Glu-NMDA receptor transmission in the hippocampal DG contributes to the impairment of spatial learning and memory in DIO rats, maybe via the modulation of CaMKII-CREB-BDNF signaling pathway.

Blocking the dopaminergic receptors within the hippocampal dentate gyrus reduced analgesic responses induced by restraint stress in the formalin test.

Previous studies have shown that various receptors, including dopamine receptors, are expressed in the hippocampal dentate gyrus (DG). Besides, indicatively, dopamine receptors play an essential role in the modulation of pain perception. On the other hand, stressful experiences can produce analgesia, termed stress-induced analgesia (SIA). The current study examined the probable role of dopamine receptors within the DG in antinociception induced by restraint stress (RS). Ninety-seven male albino Wistar rats were unilaterally implanted with a cannula in the DG. Animals received intra-DG microinjections of SCH23390 or Sulpiride (0.25, 1, and 4 µg/rat) as D1-and D2-like dopamine receptor antagonists, respectively, five minutes before RS. Ten minutes after the end of the induction of RS for three hours, 50 µl 2.5% formalin was injected subcutaneously into the plantar surface of the hind paw to induce persistent inflammatory pain. Pain scores were evaluated at 5-minute intervals for 60 minutes. These findings showed that; exposure to RS for three hours produced SIA in both phases of the formalin test, while this RS-induced analgesia was attenuated in the early and late phases of the formalin test by intra-DG microinjection of SCH23390 and Sulpiride. The results of the present study suggested that both D1- and D2-like dopamine receptors in the DG have a considerable role in the induced analgesia by RS.

Acetylated oligopeptide and N-acetylcysteine protect against iron overload-induced dentate gyrus hippocampal degeneration through upregulation of Nestin and Nrf2/HO-1 and downregulation of MMP-9/TIMP-1 and GFAP.

Iron accumulation in the brain causes oxidative stress, blood-brain barrier (BBB) breakdown, and neurodegeneration. We examined the preventive effects of acetylated oligopeptides (AOP) from whey protein on iron-induced hippocampal damage compared to N-acetyl cysteine (NAC). This 5-week study used 40 male albino rats. At the start, all rats received 150 mg/kg/day of oral NAC for a week. The 40 animals were then randomly divided into four groups: Group I (control) received a normal diet; Group II (iron overload) received 60 mg/kg/day intraperitoneal iron dextran 5 days a week for 4 weeks; Group III (NAC group) received 150 mg/kg/day NAC and iron dextran; and Group IV (AOP group) received 150 mg/kg/day AOP and iron dextran. Enzyme-linked immunosorbent assay, spectrophotometry, and qRT-PCR were used to measure MMP-9, tissue inhibitor metalloproteinase-1 (TIMP-1), MDA, reduced glutathione (GSH) levels, and nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) gene expression. Histopathological and immunohistochemical detection of nestin, claudin, caspase, and GFAP was also done. MMP-9, TIMP-1, MDA, caspase, and GFAP rose in the iron overload group, while GSH, Nrf2, HO-1, nestin, and claudin decreased. The NAC and AOP administrations improved iron overload-induced biochemical and histological alterations. We found that AOP and NAC can protect the brain hippocampus from iron overload, improve BBB disruption, and provide neuroprotection with mostly no significant difference from healthy controls.

Hyperthyroidism-Induced Upregulation of Neurodegeneration-Related Gene Expression in Metaplasticity-Induced Hippocampus.

INTRODUCTION: Thyroid hormones, which produce critical changes in our bodies even when their physiological levels alter slightly, are crucial hormones that influence gene transcription. Neuronal plasticity, on the other hand, requires both the activation of local proteins as well as protein translation and transcription in response to external signals. So far, no study has examined metaplastic long-term potentiation (LTP) and related gene expression levels in a hyperthyroid experimental model. METHODS: The Wistar male rats were administered 0.2 mg/kg/day of l-thyroxine for 21 days to induce hyperthyroidism. Perforant path was primed with 1-Hz low-frequency stimuli (LFS) for 900 s to investigate metaplasticity responses. The LFS was followed by high-frequency stimuli (HFS, 100 Hz) after 5 min. Excitatory postsynaptic potential (EPSP) slope and population spike (PS) amplitude were recorded from the granule cell layer of the dentate gyrus. The mRNA levels of genes related to neurodegeneration (Gsk-3ß, Cdk5, Akt1, Mapt, p35, Capn1, Bace1, and Psen2) were measured using the RT-PCR method for the stimulated hippocampus. RESULTS: Similar to euthyroid rats, hyperthyroid animals had a lower EPSP slope and PS after LFS. Depression of EPSP prevented subsequently induced EPSP-LTP, although HFS was able to elicit PS-LTP despite depression of PS amplitude in both groups. Despite similarities in metaplastic LTP responses, these electrophysiological findings were accompanied by increased Akt, Bace1, Cdk5, and p35-mRNA expressions and decreased Gsk-3ß mRNA expression in hyperthyroid rats' hippocampus. CONCLUSION: These data support the view that in thyroid hormone excess, the mechanism that keeps synaptic efficacy within a dynamic range occurs concurrently with increased mRNA expression of neurodegeneration-related genes. Our study encourages further examination of the increased risk of neurodegenerative disease in hyperthyroidism.

The effects of induced type I diabetes on developmental regulation of GDNF, NRTN, and NCAM proteins in the dentate gyrus of male rat offspring.

BACKGROUND: Maternal diabetes during pregnancy can affect the neurological development of offspring. Glial cell-derived neurotrophic factor (GDNF), neurturin (NRTN), and neural cell adhesion molecules (NCAM) are three important proteins for brain development. Therefore, this study aimed to investigate the impacts of the mentioned neurotrophic factors in the hippocampal dentate gyrus (DG) of rat offspring born to diabetic mothers. METHODS: Wistar female rats were randomly allocated into diabetic (STZ-D) [(45 mg/kg BW, STZ (Streptozotocin), i.p)], diabetic + NPH insulin (STZ-INS) [(4-6 unit/kg/day SC)], and control groups. The animals in all groups were mated by non-diabetic male rats. Two weeks after birth, male pups from each group were sacrificed and then protein contents of GDNF, NRTN, and NCAM were evaluated using immunohistochemistry. RESULTS: The study found that the expression of GDNF and NRTN in the hippocampus of diabetic rat offspring was significantly higher compared to the diabetic+ insulin and control groups, respectively (P < 0.01, P < 0.001). Additionally, the expression of NCAM was significantly higher in the diabetic group the diabetic+ insulin and control groups (P < 0.01, P < 0.001). CONCLUSIONS: The results of the study revealed that diabetes during pregnancy significantly impacts the distribution pattern of GDNF, NRTN, and NCAM in the hippocampus of rat neonates.

Fluctuation of lysosomal protein degradation in neural stem cells of the postnatal mouse brain.

Lysosomes are intracellular organelles responsible for degrading diverse macromolecules delivered from several pathways, including the endo-lysosomal and autophagic pathways. Recent reports have suggested that lysosomes are essential for regulating neural stem cells in developing, adult and aged brains. However, the activity of these lysosomes has yet to be monitored in these brain tissues. Here, we report the development of a new probe to measure lysosomal protein degradation in brain tissue by immunostaining. Our results indicate that lysosomal protein degradation fluctuates in neural stem cells of the hippocampal dentate gyrus, depending on age and brain disorders. Neural stem cells increase their lysosomal activity during hippocampal development in the dentate gyrus, but aging and aging-related disease reduce lysosomal activity. In addition, physical exercise increases lysosomal activity in neural stem cells and astrocytes in the dentate gyrus. We therefore propose that three different stages of lysosomal activity exist: the state of increase during development, the stable state during adulthood and the state of reduction due to damage caused by either age or disease.

SIRT6 Improves Hippocampal Neurogenesis Following Prolonged Sleep Deprivation Through Modulating Energy Metabolism in Developing rats.

OBJECTIVE: Prolonged sleep deprivation is known to have detrimental effects on the hippocampus during development or in adulthood. Furthermore, it is well-established that sleep deprivation disrupts energy metabolism broadly. SIRT6 is a critical regulator of energy metabolism in both central and peripheral tissues. This study aims to investigate the role of SIRT6 in modulating hippocampal neurogenesis following sleep deprivation during development, and elucidate the underlying mechanism. METHODS: Male Sprague-Dawley rats, aged three weeks, were subjected to 2 weeks of sleep deprivation using the modified multiple platform method. Metabolomic profiling was carried out using the liquid chromatography-electrospray ionization-tandem mass spectrometry (LC‒ESI‒MS/MS). To investigate the role of SIRT6 in energy metabolism, the rats were administered with either the SIRT6-specific inhibitor, OSS128167, or SIRT6-overexpressing adeno-associated virus (AAV). Hippocampal neurogenesis was assessed by immunostaining with markers for neural stem cells (SOX2), immature neurons [doublecortin (DCX)] and newborn cells (BrdU). Sparse labeling of adult neurons was used to determine the density of dendritic spines in the dentate gyrus (DG). The Y-maze and novel object recognition (NOR) tests were performed to evaluate the spatial and recognition memory. SIRT6 expression was examined using immunofluorescence and western blotting (WB). The inhibition of SIRT6 was confirmed by assessing the acetylation of histone 3 lysine 9 (aceH3K9), a well-known substrate of SIRT6, through WB. RESULTS: Sleep deprivation for a period of two weeks leads to inhibited hippocampal neurogenesis, reduced density of dendritic spines in the DG, and impaired memory, accompanied by decreased SIRT6 expression and disrupted energy metabolism. Similar to sleep deprivation, administration of OSS128167 significantly decreased energy metabolism, leading to reduced neurogenesis and memory dysfunction. Notably, the abnormal hippocampal energy metabolism, neurogenetic pathological changes and memory dysfunction caused by sleep deprivation were alleviated by SIRT6 overexpression in the DG. CONCLUSION: Our results suggest that SIRT6 plays a critical role in maintaining energy metabolism homeostasis in the hippocampus after sleep deprivation, promoting hippocampal neurogenesis and enhancing memory during development.

The integrative role of orexin-1 and orexin-2 receptors within the hippocampal dentate gyrus in the modulation of the stress-induced antinociception in the formalin pain test in the rat.

The stressful experiences, by triggering a cascade of hormonal and neural changes, can produce antinociception commonly referred to as stress-induced antinociception (SIA). Orexin neuropeptides have an essential role in stress responses and pain modulation. The dentate gyrus receives orexinergic projections and has been shown to be involved in pain processing. The current study investigated the possible role of orexin-1 and orexin-2 receptors (OX1r and OX2r, respectively) within the dentate gyrus in SIA in a rat model of formalin-induced pain behavior in one hind paw. Male Wistar rats weighing 230-250 g underwent stereotaxic surgery and a cannula was implanted in their brains, above the dentate gyrus region. Either SB334867 or TCS OX2 29 (OX1r and OX2r antagonists, respectively) was microinjected into the dentate gyrus region at a range of doses at 1, 3, 10, and 30 nmol (control group received DMSO 12% as vehicle), 5 min before the forced swim stress (FSS) exposure. The formalin test was performed to assess pain-related behaviors. The results indicated that FSS exposure relieves pain-related behavior in the early and late phases of the formalin test. Blockade of intra-dentate gyrus OX1 or OX2 receptors reduced the antinociceptive responses induced by FSS in the formalin test, with more impact during the late phase. Our findings support the potential role of intra-dentate gyrus orexin receptors as target sites of orexin neurons in painful and stressful situations. Therefore, understanding the exact mechanisms of SIA and the role of the orexinergic system in this phenomenon can lead to identifying the strategies to guide future research and offer a new approach to discovering new pain therapeutic agents.

Impacted spike frequency adaptation associated with reduction of KCNQ2/3 exacerbates seizure activity in temporal lobe epilepsy.

Numerous epilepsy-related genes have been identified in recent decades by unbiased genome-wide screens. However, the available druggable targets for temporal lobe epilepsy (TLE) remain limited. Furthermore, a substantial pool of candidate genes potentially applicable to TLE therapy awaits further validation. In this study, we reveal the significant role of KCNQ2 and KCNQ3, two M-type potassium channel genes, in the onset of seizures in TLE. Our investigation began with a quantitative analysis of two publicly available TLE patient databases to establish a correlation between seizure onset and the downregulated expression of KCNQ2/3. We then replicated these pathological changes in a pilocarpine seizure mouse model and observed a decrease in spike frequency adaptation due to the affected M-currents in dentate gyrus granule neurons. In addition, we performed a small-scale simulation of the dentate gyrus network and confirmed that the impaired spike frequency adaptation of granule cells facilitated epileptiform activity throughout the network. This, in turn, resulted in prolonged seizure duration and reduced interictal intervals. Our findings shed light on an underlying mechanism contributing to ictogenesis in the TLE hippocampus and suggest a promising target for the development of antiepileptic drugs.

Orexin receptors in the hippocampal dentate gyrus modulated the restraint stress-induced analgesia in the animal model of chronic pain.

Previous studies have shown that stressful stimuli induced an adaptive response of reduced nociception, known as stress-induced analgesia (SIA). Since orexin neuropeptides are involved in pain modulation, and orexin neurons, primarily located in the lateral hypothalamus (LH), project to various hippocampal regions, such as the dentate gyrus (DG), the current study aimed to examine the role of orexin receptors within the DG region in the restraint SIA in the animal model of chronic pain. One hundred-thirty adult male Wistar rats (230-250 g) were unilaterally implanted with a cannula above the DG region. Animals were given SB334867 or TCS OX2 29 (1, 3, 10, and 30 nmol, 0.5 µl/rat) into the DG region as orexin-1 receptor (OX1r) and orexin-2 receptor (OX2r) antagonists, respectively, five min before exposure to a 3-hour restraint stress (RS) period. Animals were then undergone the formalin test to assess pain-related behaviors as the animal model of chronic pain. The results showed that RS produces an analgesic response during the early and late phases of the formalin test. However, intra-DG microinjection of OX1r and OX2r antagonists attenuated the restraint SIA. OX2r antagonist was more potent than OX1r antagonist in the early phase of the formalin test, while OX1r antagonist was little more effective in the late phase. Predominantly, it could be concluded that the orexinergic system in the DG region might act as a potential endogenous pain control system and a novel target for treating stress-related disorders.

Voluntary exercise during puberty promotes spatial memory and hippocampal DG/CA3 synaptic transmission in mice.

Physical exercise has been shown to have an impact on memory and hippocampal function across different age groups. Nevertheless, the influence and mechanisms underlying how voluntary exercise during puberty affects memory are still inadequately comprehended. This research aims to examine the impacts of self-initiated physical activity throughout adolescence on spatial memory. Developing mice were exposed to a 4-wk voluntary wheel running exercise protocol, commencing at the age of 30 d. After engaging in voluntary wheel running exercise during development, there was an enhancement in spatial memory. Moreover, hippocampal dentate gyrus and CA3 neurons rather than CA1 neurons exhibited an increase in the miniature excitatory postsynaptic currents and miniature inhibitory postsynaptic currents. In addition, there was an increase in the expression of NR2A/NR2B subunits of N-methyl-D-aspartate receptors and α1GABAA subunit of gamma-aminobutyric acid type A receptors, as well as dendritic spine density, specifically within dentate gyrus and CA3 regions rather than CA1 region. The findings suggest that voluntary exercise during development can enhance spatial memory in mice by increasing synapse numbers and improving synaptic transmission in hippocampal dentate gyrus and CA3 regions, but not in CA1 region. This study sheds light on the neural mechanisms underlying how early-life exercise improves cognitive function.

Neuronal IGF-1 overexpression restores hippocampal newborn cell survival and recent CFC memory consolidation in Cav1.3 knock-out mice.

Insulin-like growth factor-1 (IGF-1) exogenously supplied in the brain was shown to enhance the survival of hippocampal dentate gyrus (DG) newborn cells and some cognitive functions of mice. This study aims to test whether IGF-1 requires Cav1.3 activity critically while enhancing newborn cell survival and cognitive functions. We used Cav1.3 KO mice, where both DG newborn cell survival and the recent (1 day) single-trial contextual fear conditioning (CFC) memory consolidation were impaired. To supply IGF-1, we overexpressed (OX) IGF-1 in DG mature neurons by injecting an adeno-associated virus (AAV-IGF-1-mCherry) into the hippocampal areas of Cav1.3 KO mice. Our results, first, confirmed the enhanced expression of IGF-1 in the DG granule cell layer by immunohistochemistry. Next, we found this IGF-1 OX resulted in fully restoring both the survival rate of DCX (+) newborn cells and the recent single-trial CFC memory formation in Cav1.3 KO mice. Our results show that IGF-1 can enhance the survival of DG immature newborn cells and the recent CFC memory formation in a Cav1.3 channel-independent manner in vivo, suggesting activation of complementary pathways including the Cav1.2 channel. The result will help the application of adult newborn cell-based therapy improve the cognitive functions of neurological disorders.

Knockout of NMDARs in CA1 and dentate gyrus fails to impair temporal control of conditioned behavior in mice.

The hippocampus has been implicated in temporal learning. Plasticity within the hippocampus requires NMDA receptor-dependent glutamatergic neurotransmission. We tested the prediction that hippocampal NMDA receptors are required for learning about time by testing mice that lack postembryonal NMDARs in the CA1 and dentate gyrus (DG) hippocampal subfields on three different appetitive temporal learning procedures. The conditional knockout mice (Grin1ΔDCA1 ) showed normal sensitivity to cue duration, responding at a higher level to a short duration cue than compared to a long duration cue. Knockout mice also showed normal precision and accuracy of response timing in the peak procedure in which reinforcement occurred after 10 s delay within a 30 s cue presentation. Mice were tested on the matching of response rates to reinforcement rates on instrumental conditioning with two levers reinforced on a concurrent variable interval schedule. Pressing on one lever was reinforced at a higher rate than the other lever. Grin1ΔDGCA1 mice showed normal sensitivity to the relative reinforcement rates of the levers. In contrast to the lack of effect of hippocampal NMDAR deletion on measures of temporal sensitivity, Grin1ΔDGCA1 mice showed increased baseline measures of magazine activity and lever pressing. Furthermore, reversal learning was enhanced when the reward contingencies were switched in the lever pressing task, but this was true only for mice trained with a large difference between relative reinforcement rates between the levers. The results failed to demonstrate a role for NMDARs in excitatory CA1 and DG neurons in learning about temporal information.

Electroacupuncture promotes neurogenesis in the dentate gyrus and improves pattern separation in an early Alzheimer's disease mouse model.

BACKGROUND: Impaired pattern separation occurs in the early stage of Alzheimer's disease (AD), and hippocampal dentate gyrus (DG) neurogenesis participates in pattern separation. Here, we investigated whether spatial memory discrimination impairment can be improved by promoting the hippocampal DG granule cell neogenesis-mediated pattern separation in the early stage of AD by electroacupuncture (EA). METHODS: Five familial AD mutations (5 × FAD) mice received EA treatment at Baihui and Shenting points for 4 weeks. During EA, mice were intraperitoneally injected with BrdU (50 mg/kg) twice a day. rAAV containing Wnt5a shRNA was injected into the bilateral DG region, and the viral efficiency was evaluated by detecting Wnt5a mRNA levels. Cognitive behavior tests were conducted to assess the impact of EA treatment on cognitive function. The hippocampal DG area Aß deposition level was detected by immunohistochemistry after the intervention; The number of BrdU+/CaR+ cells and the gene expression level of calretinin (CaR) and prospero homeobox 1(Prox1) in the DG area of the hippocampus was detected to assess neurogenesis by immunofluorescence and western blotting after the intervention; The gene expression levels of FZD2, Wnt5a, DVL2, p-DVL2, CaMKII, and p-CaMKII in the Wnt signaling pathway were detected by Western blotting after the intervention. RESULTS: Cognitive behavioral tests showed that 5 × FAD mice had impaired pattern separation (P < 0.001), which could be improved by EA (P < 0.01). Immunofluorescence and Western blot showed that the expression of Wnt5a in the hippocampus was decreased (P < 0.001), and the neurogenesis in the DG was impaired (P < 0.001) in 5 × FAD mice. EA could increase the expression level of Wnt5a (P < 0.05) and promote the neurogenesis of immature granule cells (P < 0.05) and the development of neuronal dendritic spines (P < 0.05). Interference of Wnt5a expression aggravated the damage of neurogenesis (P < 0.05), weakened the memory discrimination ability (P < 0.05), and inhibited the beneficial effect of EA (P < 0.05) in AD mice. The expression level of Wnt pathway related proteins such as FZD2, DVL2, p-DVL2, CAMKII, p-CAMKII increased after EA, but the effect of EA was inhibited after Wnt5a was knocked down. In addition, EA could reduce the deposition of Aß plaques in the DG without any impact on Wnt5a. CONCLUSION: EA can promote hippocampal DG immature granule cell neogenesis-mediated pattern separation to improve spatial memory discrimination impairment by regulating Wnt5a in 5 × FAD mice.

Dopamine D2 receptors in hilar mossy cells regulate excitatory transmission and hippocampal function.

Hilar mossy cells (MCs) are principal excitatory neurons of the dentate gyrus (DG) that play critical roles in hippocampal function and have been implicated in brain disorders such as anxiety and epilepsy. However, the mechanisms by which MCs contribute to DG function and disease are poorly understood. A defining feature of MCs is the promoter activity of the dopamine D2 receptor (D2R) gene (Drd2), and previous work indicates a key role for dopaminergic signaling in the DG. Additionally, the involvement of D2R signaling in cognition and neuropsychiatric conditions is well known. Surprisingly, though, the function of MC D2Rs remains largely unexplored. In this study, we show that selective and conditional removal of Drd2 from MCs of adult mice impaired spatial memory, promoted anxiety-like behavior, and was proconvulsant. To determine the subcellular expression of D2Rs in MCs, we used a D2R knockin mouse which revealed that D2Rs are enriched in the inner molecular layer of the DG, where MCs establish synaptic contacts with granule cells (GCs). D2R activation by exogenous and endogenous dopamine reduced MC to dentate GC synaptic transmission, most likely by a presynaptic mechanism. In contrast, exogenous dopamine had no significant impact on MC excitatory inputs and passive and active properties. Our findings support that MC D2Rs are essential for proper DG function by reducing MC excitatory drive onto GCs. Lastly, impairment of MC D2R signaling could promote anxiety and epilepsy, therefore highlighting a potential therapeutic target.

Synaptic plasticity at the dentate gyrus granule cell to somatostatin-expressing interneuron synapses supports object location memory.

Somatostatin-expressing interneurons (SOMIs) in the mouse dentate gyrus (DG) receive feedforward excitation from granule cell (GC) mossy fiber (MF) synapses and provide feedback lateral inhibition onto GC dendrites to support environment representation in the DG network. Although this microcircuitry has been implicated in memory formation, little is known about activity-dependent plastic changes at MF-SOMI synapses and their influence on behavior. Here, we report that the metabotropic glutamate receptor 1α (mGluR1α) is required for the induction of associative long-term potentiation (LTP) at MF-SOMI synapses. Pharmacological block of mGluR1α, but not mGluR5, prevented synaptic weight changes. LTP at MF-SOMI synapses was postsynaptically induced, required increased intracellular Ca2+, involved G-protein-mediated and Ca2+-dependent (extracellular signal-regulated kinase) ERK1/2 pathways, and the activation of NMDA receptors. Specific knockdown of mGluR1α in DG-SOMIs by small hairpin RNA expression prevented MF-SOMI LTP, reduced SOMI recruitment, and impaired object location memory. Thus, postsynaptic mGluR1α-mediated MF-plasticity at SOMI input synapses critically supports DG-dependent mnemonic functions.