Plasticity in the Hippocampus, Neurogenesis and Drugs of Abuse

Mapping dynamic molecular changes in hippocampal subregions after traumatic brain injury through spatial proteomics

BACKGROUND

Traumatic brain injury (TBI) often results in diverse molecular responses, challenging traditional proteomic studies that measure average changes at tissue levels and fail to capture the complexity and heterogeneity of the affected tissues. Spatial proteomics offers a solution by providing insights into sub-region-specific alterations within tissues. This study focuses on the hippocampal sub-regions, analyzing proteomic expression profiles in mice at the acute (1 day) and subacute (7 days) phases of post-TBI to understand subregion-specific vulnerabilities and long-term consequences.

METHODS

Three mice brains were collected from each group, including Sham, 1-day post-TBI and 7-day post-TBI. Hippocampal subregions were extracted using Laser Microdissection (LMD) and subsequently analyzed by label-free quantitative proteomics.

RESULTS

The spatial analysis reveals region-specific protein abundance changes, highlighting the elevation of FN1, LGALS3BP, HP, and MUG-1 in the stratum moleculare (SM), suggesting potential immune cell enrichment post-TBI. Notably, established markers of chronic traumatic encephalopathy, IGHM and B2M, exhibit specific upregulation in the dentate gyrus bottom (DG2) independent of direct mechanical injury. Metabolic pathway analysis identifies disturbances in glucose and lipid metabolism, coupled with activated cholesterol synthesis pathways enriched in SM at 7-Day post-TBI and subsequently in deeper DG1 and DG2 suggesting a role in neurogenesis and the onset of recovery. Coordinated activation of neuroglia and microtubule dynamics in DG2 suggest recovery mechanisms in less affected regions. Cluster analysis revealed spatial variations post-TBI, indicative of dysregulated neuronal plasticity and neurogenesis and further predisposition to neurological disorders. TBI-induced protein upregulation (MUG-1, PZP, GFAP, TJP, STAT-1, and CD44) across hippocampal sub-regions indicates shared molecular responses and links to neurological disorders. Spatial variations were demonstrated by proteins dysregulated in both or either of the time-points exclusively in each subregion (ELAVL2, CLIC1 in PL, CD44 and MUG-1 in SM, and SHOC2, LGALS3 in DG).

CONCLUSIONS

Utilizing advanced spatial proteomics techniques, the study unveils the dynamic molecular responses in distinct hippocampal subregions post-TBI. It uncovers region-specific vulnerabilities and dysregulated neuronal processes, and potential recovery-related pathways that contribute to our understanding of TBI's neurological consequences and provides valuable insights for biomarker discovery and therapeutic targets.

Identifying candidate genes associated with hippocampal dysfunction in a hemiparkinsonian rat model by transcriptomic profiling

Parkinson's disease (PD) often results in hippocampal dysfunction, which leads to cognitive and emotional challenges and synaptic irregularities. This study attempted to assess behavioral anomalies and identify differentially expressed genes (DEGs) within the hippocampus of a hemiparkinsonian rat model to potentially uncover novel genetic candidates linked to hippocampal dysfunction. Striatal 6-hydroxydopamine (6-OHDA) infusions were performed unilaterally in the brains of adult SD rats, while dopaminergic impairments were verified in rats with 6-OHDA-lesioned striata. RNA sequencing and gene expression analysis unveiled 1018 DEGs in the ipsilateral rat hippocampus following 6-OHDA infusion: 631 genes exhibited upregulation, while 387 genes were downregulated (with FDR-adjusted p-value < 0.05 and absolute fold-change > 1.5). Gene ontology analysis of DEGs indicated that alterations in the hippocampi of 6-OHDA-lesioned rats were primarily associated with synaptic signaling, axon development, behavior, postsynaptic membrane, synaptic membrane, neurotransmitter receptor activity, and peptide receptor activity. The Kyoto Encyclopedia of Genes and Genomes analysis of DEGs demonstrated significant enrichment of the neuroactive ligand-receptor interaction, calcium signaling pathway, cAMP signaling pathway, axon guidance, and notch signaling pathway in rat hippocampi that had been subjected to striatal 6-OHDA infusion. STRING analysis confirmed a notable upregulation of eight hub genes (Notch3, Gng4, Itga3, Grin2d, Hgf, Fgf11, Htr3a, and Col6a2), along with a significant downregulation of two hub genes (Itga11 and Plp1), as validated by reverse transcription-quantitative polymerase chain reaction. This study provides a comprehensive transcriptomic profile of the hippocampi in a hemiparkinsonian rat model, thereby offering insights into the signaling pathways underlying hippocampal dysfunction.

The role of orexin receptors within the CA1 area in the acquisition and expression of methamphetamine place preference

Treatment of Methamphetamine (METH) use disorder has become a crucial public health issue. The orexin system manipulation has provided promising evidence to attenuate addictive-like behaviors. This study explored the role of the orexin 1 receptor and orexin 2 receptor (OX1R and OX2R) in the CA1 area of the hippocampal formation in the acquisition and expression of METH-induced place preference. Animals were subjected to bilateral administration of different dosages (1, 3, 10, and 30 nmol/0.5 μl DMSO per side) of a selective OX1R antagonist, SB334867, or selective OX2R antagonist, TCS OX2 29 into the CA1 area throughout the conditioning phase or once on the post-conditioning phase in separate control and experimental groups. Behavioral data revealed that both OX1R (10 nmol; P < 0.01 and 30 nmol; P < 0.001) and OX2R (10 nmol; P < 0.05 and 30 nmol; P < 0.001) antagonism during the conditioning phase could block the formation of METH place preference dose-dependently. In addition, intra-CA1 microinjection of SB334867 on the post-conditioning phase attenuated the expression of METH place preference in a dose-dependent manner (3 nmol; P < 0.05, 10 nmol; P < 0.01 and 30 nmol; P < 0.001) whereas intra-CA1 administration of TCS OX2 29 only at the highest dosage (30 nmol) declined the expression of METH place preference (P < 0.01). It was also indicated that the suppressive effects of orexin receptor blockade on the METH-seeking behavior in the CA1 area were anatomically specific to this area. These findings support the possibility of targeting the orexin system to develop novel and successful pharmacological options for the treatment of METH dependence.

Perinatal compromise affects development, form, and function of the hippocampus part one; clinical studies

The hippocampus is a neuron-rich specialised brain structure that plays a central role in the regulation of emotions, learning and memory, cognition, spatial navigation, and motivational processes. In human fetal development, hippocampal neurogenesis is principally complete by mid-gestation, with subsequent maturation comprising dendritogenesis and synaptogenesis in the third trimester of pregnancy and infancy. Dendritogenesis and synaptogenesis underpin connectivity. Hippocampal development is exquisitely sensitive to perturbations during pregnancy and at birth. Clinical investigations demonstrate that preterm birth, fetal growth restriction (FGR), and acute hypoxic-ischaemic encephalopathy (HIE) are common perinatal complications that alter hippocampal development. In turn, deficits in hippocampal development and structure mediate a range of neurodevelopmental disorders, including cognitive and learning problems, autism, and Attention-Deficit/Hyperactivity Disorder (ADHD). In this review, we summarise the developmental profile of the hippocampus during fetal and neonatal life and examine the hippocampal deficits observed following common human pregnancy complications. IMPACT: The review provides a comprehensive summary of the developmental profile of the hippocampus in normal fetal and neonatal life. We address a significant knowledge gap in paediatric research by providing a comprehensive summary of the relationship between pregnancy complications and subsequent hippocampal damage, shedding new light on this critical aspect of early neurodevelopment.

Protective effects of alpha-lipoic acid on anxiety-like behavior, memory and prevention of hippocampal oxidative stress in methamphetamine-treated rats

RATIONALE

Alpha-lipoic acid is an essential cofactor for aerobic metabolism and acts as a potent antioxidant in the body. It has been shown that acute exposure to methamphetamine induces oxidative stress, which is responsible for severe cognitive deficits in animals. The hippocampus plays a crucial role in the processing of memory and anxiety-like behavior.

OBJECTIVES

In this study, preventive effect of the alpha-lipoic acid on memory impairment in methamphetamine-induced neurotoxicity was investigated.

METHODS

Wistar male rats (200-220 g) were allocated to five groups (seven rats in each group): (1) saline + saline, (2) saline + vehicle (sunflower oil as alpha-lipoic acid solvent), (3) methamphetamine + vehicle, (4) methamphetamine + alpha-lipoic acid 10 mg/kg, and (5) methamphetamine + alpha-lipoic acid 40 mg/kg. Rats received intraperitoneal methamphetamine repeatedly (2 × 20 mg/kg, 2 h interval). Alpha-lipoic acid was injected 30 min, 24 h, and 48 h after the last injection of methamphetamine. The passive avoidance test and open field were used for evaluation of memory retrieval and anxiety, respectively. After behavioral test, rats were anesthetized, their brains were extracted, and after preparing hippocampal homogenates, malondialdehyde (MDA) level, catalase, and superoxide dismutase (SOD) activities were evaluated.

RESULTS

Statistical analysis showed that injection of saline or sunflower oil had no significant effect on anxiety, memory, or oxidative stress markers. Methamphetamine induced memory impairment, increased anxiety-like behavior and MDA level, but it reduced catalase and SOD activity. Treatment with alpha-lipoic acid decreased MDA, increased catalase and SOD activity, and also prevented memory impairment and anxiety-like behavior. Our results showed that alpha-lipoic acid protected the hippocampus from oxidative stress by elevating SOD and CAT activities and reduced memory impairment following acute methamphetamine injection. These findings suggest that alpha-lipoic acid may have a protective effect against the adverse effects of methamphetamine exposure on the hippocampus. Therefore, the current data indicated that ALA can reduce oxidative stress predominantly by its antioxidant property.

Prolonged Zaleplon Treatment Increases the Expression of Proteins Involved in GABAergic and Glutamatergic Signaling in the Rat Hippocampus

Zaleplon is a positive allosteric modulator of the γ-aminobutyric acid (GABA)A receptor approved for the short-term treatment of insomnia. Previous publications on zaleplon have not addressed the proteins involved in its mechanism of action but have mostly referred to behavioral or pharmacological studies. Since both GABAergic and glutamatergic signaling have been shown to regulate wakefulness and sleep, we examined the effects of prolonged zaleplon treatment (0.625 mg/kg for 5 days) on these systems in the hippocampus of male Wistar rats. Western blot and immunohistochemical analyses showed that the upregulated components of GABAergic signaling (glutamate decarboxylase, vesicular GABA transporter, GABA, and α1 subunit of the GABAA receptor) were accompanied by increased protein levels in the glutamatergic system (vesicular glutamate transporter 1 and NR1, NR2A, and NR2B subunits of N-methyl-d-aspartate receptor). Our results, showing that zaleplon enhances GABA neurotransmission in the hippocampus, were not surprising. However, we found that treatment also increased glutamatergic signaling. This could be the result of the downregulation of adenosine A1 receptors, important modulators of the glutamatergic system. Further studies are needed to investigate the effects of the zaleplon-induced increase in hippocampal glutamatergic neurotransmission and the possible involvement of the adenosine system in zaleplon's mechanism of action.

Association between gaming disorder and regional homogeneity in highly involved male adult gamers: A pilot resting-state fMRI study

BACKGROUND

Gaming behavior can induce cerebral changes that may be related to the neurobiological features of gaming disorder (GD). Additionally, individuals with higher levels of depression or impulsivity are more likely to experience GD. Therefore, the present pilot study explored potential neurobiological correlates of GD in the context of depression and impulsivity, after accounting for video gaming behavior.

METHODS

Using resting-state functional magnetic resonance imaging (fMRI), a cross-sectional study was conducted with 35 highly involved male adult gamers to examine potential associations between GD severity and regional homogeneity (ReHo) in the entire brain. A mediation model was used to test the role of ReHo in the possible links between depression/impulsivity and GD severity.

RESULTS

Individuals with greater GD severity showed increased ReHo in the right Heschl's gyrus and decreased ReHo in the right hippocampus (rHip). Furthermore, depression and impulsivity were negatively correlated with ReHo in the rHip, respectively. More importantly, ReHo in the rHip was found to mediate the associations between depression/impulsivity and GD.

CONCLUSIONS

These preliminary findings suggest that GD severity is related to ReHo in brain regions associated with learning/memory/mood and auditory function. Higher levels of depression or impulsivity may potentiate GD through the functional activity of the hippocampus. Our findings advance our understanding of the neurobiological differences behind GD symptoms in highly involved gamers.

Association between physical activity measured by accelerometry and cognitive function in older adults: a systematic review

OBJECTIVE

To analyze studies that investigated the association between physical activity assessed by accelerometry and cognitive function in older people.

METHODS

A systematic review was carried out in four electronic databases (PubMed, Web of Science, Scopus, and SportsDiscus).

RESULTS

In total, 195 records were identified. Fifty-two studies were selected for a full evaluation; 23 were selected according to the inclusion criteria adopted and divided into four chapters (characteristics of the studies, the association between physical activity level and cognitive function decline, effects of physical activity in reducing the chances of cognitive function decline and effects of physical activity on brain plasticity. The cross-sectional studies had an average score of 7 points, and the cohort studies obtained 10 points, indicating the high quality of the selected studies. Seven studies indicated an association between Moderate to vigorous physical activities (MVPA) and cognitive function, two specifically indicated a reduction in the chances of cognitive function decline according to the interquartile of MVPA, and three studies indicated improvements in MVPA in brain plasticity.

CONCLUSION

Measured by accelerometry, seems to be favorably associated with important outcomes in cognitive function assessed through questionnaires, imaging analyses, and biochemical markers with older adults.

Addictive drugs modify neurogenesis, synaptogenesis and synaptic plasticity to impair memory formation through neurotransmitter imbalances and signaling dysfunction

Drug abuse changes neurophysiological functions at multiple cellular and molecular levels in the addicted brain. Well-supported scientific evidence suggests that drugs negatively affect memory formation, decision-making and inhibition, and emotional and cognitive behaviors. The mesocorticolimbic brain regions are involved in reward-related learning and habitual drug-seeking/taking behaviors to develop physiological and psychological dependence on the drugs. This review highlights the importance of specific drug-induced chemical imbalances resulting in memory impairment through various neurotransmitter receptor-mediated signaling pathways. The mesocorticolimbic modifications in the expression levels of brain-derived neurotrophic factor (BDNF) and the cAMP-response element binding protein (CREB) impair reward-related memory formation following drug abuse. The contributions of protein kinases and microRNAs (miRNAs), along with the transcriptional and epigenetic regulation have also been considered in memory impairment underlying drug addiction. Overall, we integrate the research on various types of drug-induced memory impairment in distinguished brain regions and provide a comprehensive review with clinical implications addressing the upcoming studies.

Connectome-based predictive modeling of smoking severity using individualized structural covariance network in smokers

Introduction

Abnormal interactions among distributed brain systems are implicated in the mechanisms of nicotine addiction. However, the relationship between the structural covariance network, a measure of brain connectivity, and smoking severity remains unclear. To fill this gap, this study aimed to investigate the relationship between structural covariance network and smoking severity in smokers.

Methods

A total of 101 male smokers and 51 male non-smokers were recruited, and they underwent a T1-weighted anatomical image scan. First, an individualized structural covariance network was derived via a jackknife-bias estimation procedure for each participant. Then, a data-driven machine learning method called connectome-based predictive modeling (CPM) was conducted to infer smoking severity measured with Fagerström Test for Nicotine Dependence (FTND) scores using an individualized structural covariance network. The performance of CPM was evaluated using the leave-one-out cross-validation and a permutation testing.

Results

As a result, CPM identified the smoking severity-related structural covariance network, as indicated by a significant correlation between predicted and actual FTND scores (r = 0.23, permutation p = 0.020). Identified networks comprised of edges mainly located between the subcortical-cerebellum network and networks including the frontoparietal default model and motor and visual networks.

Discussion

These results identified smoking severity-related structural covariance networks and provided a new insight into the neural underpinnings of smoking severity.

Changes in synaptic markers after administration of ketamine or psychedelics: a systematic scoping review

Background

Ketamine and psychedelics have abuse liability. They can also induce "transformative experiences" where individuals experience enhanced states of awareness. This enhanced awareness can lead to changes in preexisting behavioral patterns which could be beneficial in the treatment of substance use disorders (SUDs). Preclinical and clinical studies suggest that ketamine and psychedelics may alter markers associated with synaptic density, and that these changes may underlie effects such as sensitization, conditioned place preference, drug self-administration, and verbal memory performance. In this scoping review, we examined studies that measured synaptic markers in animals and humans after exposure to ketamine and/or psychedelics.

Methods

A systematic search was conducted following PRISMA guidelines, through PubMed, EBSCO, Scopus, and Web of Science, based on a published protocol (Open Science Framework, DOI: 10.17605/OSF.IO/43FQ9). Both in vivo and in vitro studies were included. Studies on the following synaptic markers were included: dendritic structural changes, PSD-95, synapsin-1, synaptophysin-1, synaptotagmin-1, and SV2A.

Results

Eighty-four studies were included in the final analyses. Seventy-one studies examined synaptic markers following ketamine treatment, nine examined psychedelics, and four examined both. Psychedelics included psilocybin/psilocin, lysergic acid diethylamide, N,N-dimethyltryptamine, 2,5-dimethoxy-4-iodoamphetamine, and ibogaine/noribogaine. Mixed findings regarding synaptic changes in the hippocampus and prefrontal cortex (PFC) have been reported when ketamine was administered in a single dose under basal conditions. Similar mixed findings were seen under basal conditions in studies that used repeated administration of ketamine. However, studies that examined animals during stressful conditions found that a single dose of ketamine counteracted stress-related reductions in synaptic markers in the hippocampus and PFC. Repeated administration of ketamine also counteracted stress effects in the hippocampus. Psychedelics generally increased synaptic markers, but results were more consistently positive for certain agents.

Conclusion

Ketamine and psychedelics can increase synaptic markers under certain conditions. Heterogeneous findings may relate to methodological differences, agents administered (or different formulations of the same agent), sex, and type of markers. Future studies could address seemingly mixed results by using meta-analytical approaches or study designs that more fully consider individual differences.

The blockade of orexin receptors within the dentate gyrus of the hippocampus attenuated methamphetamine-induced reward learning during conditioning place preference

Orexins and orexinergic receptors have been shown to play a critical role in reward processing and drug addiction. Previous studies showed that the orexinergic system in the dentate gyrus (DG) region of the hippocampus affects the conditioning (acquisition) and post-conditioning (expression) phases of morphine-induced conditioned place preference (CPP). The action of each orexin receptor within the DG during conditioning and expression phases for methamphetamine (METH)-induced CPP remains unclear. The present study aimed to determine the role of orexin-1 and -2 receptors in the hippocampal DG in METH CPP acquisition and expression. During the 5-day conditioning phase, rats received an intra-DG microinjection of SB334867, a selective orexin-1 receptor (OX1R) antagonist, or TCS OX2-29, a selective orexin-2 receptor (OX2R) antagonist, before injection of METH (1 mg/kg; sc). In different sets of animals on the expression day, rats received each antagonist before the CPP test. The results showed that SB334867 (3, 10, and 30 nmol) and TCS OX2-29 (3, 10, and 30 nmol) significantly decreased the acquisition of METH CPP during the conditioning phase. Furthermore, administration of SB 334867 (10 and 30 nmol) and TCS OX2-29 (3 and 10 nmol) on the post-conditioning day significantly reduced METH-induced CPP expression. The results also indicated that orexin receptors play a more critical role in the conditioning phase than in the expression phase. In summary, the orexin receptors in the DG play a crucial role in drug learning and memory and are essential for METH reward acquisition and expression.

The Role of Orexin-1 Receptors Within the Hippocampal CA1 Area in the Extinction and Reinstatement of Methamphetamine-Seeking Behaviors

Psychostimulant addiction is a chronic brain disorder with high relapse rates, requiring new therapeutic strategies. The orexin system is highly implicated in processing reward and addiction through connections with critical areas such as the hippocampus. This study investigated the role of orexin-1 receptors (OX1R) within the CA1 subregion of the hippocampus in the extinction and reinstatement of the methamphetamine-induced conditioned place preference. After cannulae implantation, recovery, and establishing the methamphetamine place preference, 98 male Wistar rats received different doses of bilateral intra-CA1 selective OX1R antagonist, SB334867 (1, 3, 10, and 30 nmol/0.5 μl DMSO per side) during the 10-day extinction period (daily) or after extinction phase, just on the reinstatement day (single dose) in separate experimental and control groups. The findings indicated that bilateral microinjection of SB334867 into the CA1 area during the extinction period could significantly reduce the extinction latency and maintenance of rewarding aspects of methamphetamine dose-dependently (3, 10, and 30 nmol). In another set of experiments, a single dose of bilateral intra-CA1 SB334867 administration on the reinstatement phase prevented the methamphetamine-induced reinstatement of drug-seeking behaviors at the high doses (10, and 30 nmol). The present study provided more evidence for the implication of hippocampal OX1R in the maintenance of rewarding and reinforcing properties of methamphetamine and its role in the relapse of methamphetamine-seeking behavior. Further investigations on the role of the orexin system, including the orexin-2 receptors in treating addiction, are needed to introduce its antagonists as effective therapeutic options for psychostimulant addiction.

Hippocampal neurogenesis promotes effortful responding but does not regulate effort-based choice

A fundamental trait of depression is low motivation. Hippocampal neurogenesis has been associated with motivational deficits but detailed evidence on how it regulates human-relevant behavioral traits is still missing. We used the hGFAP-TK rat model to deplete actively dividing neural stem cells in the rat hippocampus. Use of the effort-discounting operant task allowed us to identify specific and detailed deficits in motivation behavior. In this task, rats are given a choice between small and large food rewards, where 2-20 lever presses are required to obtain the large reward (four sugar pellets) versus one press to receive the smaller reward (two sugar pellets). We found that depleting adult neurogenesis did not affect effort-based choice or general motivation to complete the task. However, lack of adult neurogenesis reduced the pressing rate and thus increased time to complete the required presses to obtain a reward. In summary, the present study finds that adult hippocampal neurogenesis specifically reduces response vigor to obtain rewards and thus deepens our understanding in how neurogenesis shapes depression.

Digital Addiction and Sleep

In 2020, the World Health Organization formally recognized addiction to digital technology (connected devices) as a worldwide problem, where excessive online activity and internet use lead to inability to manage time, energy, and attention during daytime and produce disturbed sleep patterns or insomnia during nighttime. Recent studies have shown that the problem has increased in magnitude worldwide during the COVID-19 pandemic. The extent to which dysfunctional sleep is a consequence of altered motivation, memory function, mood, diet, and other lifestyle variables or results from excess of blue-light exposure when looking at digital device screens for long hours at day and night is one of many still unresolved questions. This article offers a narrative overview of some of the most recent literature on this topic. The analysis provided offers a conceptual basis for understanding digital addiction as one of the major reasons why people, and adolescents in particular, sleep less and less well in the digital age. It discusses definitions as well as mechanistic model accounts in context. Digital addiction is identified as functionally equivalent to all addictions, characterized by the compulsive, habitual, and uncontrolled use of digital devices and an excessively repeated engagement in a particular online behavior. Once the urge to be online has become uncontrollable, it is always accompanied by severe sleep loss, emotional distress, depression, and memory dysfunction. In extreme cases, it may lead to suicide. The syndrome has been linked to the known chronic effects of all drugs, producing disturbances in cellular and molecular mechanisms of the GABAergic and glutamatergic neurotransmitter systems. Dopamine and serotonin synaptic plasticity, essential for impulse control, memory, and sleep function, are measurably altered. The full spectrum of behavioral symptoms in digital addicts include eating disorders and withdrawal from outdoor and social life. Evidence pointing towards dysfunctional melatonin and vitamin D metabolism in digital addicts should be taken into account for carving out perspectives for treatment. The conclusions offer a holistic account for digital addiction, where sleep deficit is one of the key factors.

Spatial and temporal changes in the PGE2 EP2 receptor in mice hippocampi during postnatal development and its relationship with cyclooxygenase-2

Objective(s):

Prostaglandin E2 E-prostanoid 2 receptor (PGE2 EP2), downstream of cyclooxygenase-2 (COX-2), plays an important role in inflammatory responses, but there are some reports about synaptic functions of COX-2 and PGE2 EP2 in the hippocampus.

Materials and Methods:

C57BL/6J mice were sacrificed at postnatal days (P) 1, 7, 14, 28, and 56 for immunohistochemical staining for EP2 and doublecortin as well as western blot for EP2. In addition, COX-2 knockout and its wild-type mice were euthanized for immunohistochemical staining for EP2.

Results:

EP2 immunoreactivity was observed in the majority of the cells in the dentate gyrus at P1 and P7, while at P14, it was detected in the outer granule cell layer and was confined to its subgranular zone at P28 and P56. EP2 protein levels in the hippocampal homogenates were also highest at P7 and lowest at P56. EP2 immunoreactivity was partially colocalized, with doublecortin (DCX)-immunoreactive neuroblasts appearing in the mid-zone of the granule cell layer at P14 and in the subgranular zone of the dentate gyrus at P28. Co-localization of EP2 and DCX was significantly decreased in the dentate gyrus in the P28 group compared with that in the P14 group. In COX-2 knockout mice, EP2 immunoreactivity was significantly decreased in the hippocampal CA1 region (P=0.000165) and dentate gyrus (P=0.00898).

Conclusion:

EP2 decreases with age, which is expressed in DCX-immunoreactive neuroblasts in the dentate gyrus. This suggests that EP2 is closely linked to structural lamination and adult neurogenesis in the dentate gyrus.

Human Three-Finger Protein Lypd6 Is a Negative Modulator of the Cholinergic System in the Brain

Lypd6 is a GPI-tethered protein from the Ly-6/uPAR family expressed in the brain. Lypd6 enhances the Wnt/β-catenin signaling, although its action on nicotinic acetylcholine receptors (nAChRs) have been also proposed. To investigate a cholinergic activity of Lypd6, we studied a recombinant water-soluble variant of the human protein (ws-Lypd6) containing isolated “three-finger” LU-domain. Experiments at different nAChR subtypes expressed in Xenopus oocytes revealed the negative allosteric modulatory activity of ws-Lypd6. Ws-Lypd6 inhibited ACh-evoked currents at α3β4- and α7-nAChRs with IC₅₀ of ∼35 and 10 μM, respectively, and the maximal amplitude of inhibition of 30–50%. EC₅₀ of ACh at α3β4-nAChRs (∼30 μM) was not changed in the presence of 35 μM ws-Lypd6, while the maximal amplitude of ACh-evoked current was reduced by ∼20%. Ws-Lypd6 did not elicit currents through nAChRs in the absence of ACh. Application of 1 μM ws-Lypd6 significantly inhibited (up to ∼28%) choline-evoked current at α7-nAChRs in rat hippocampal slices. Similar to snake neurotoxin α-bungarotoxin, ws-Lypd6 suppressed the long-term potentiation (LTP) in mouse hippocampal slices. Colocalization of endogenous GPI-tethered Lypd6 with α3β4- and α7-nAChRs was detected in primary cortical and hippocampal neurons. Ws-Lypd6 interaction with the extracellular domain of α7-nAChR was modeled using the ensemble protein-protein docking protocol. The interaction of all three Lypd6 loops (“fingers”) with the entrance to the orthosteric ligand-binding site and the loop C of the primary receptor subunit was predicted. The results obtained allow us to consider Lypd6 as the endogenous negative modulator involved in the regulation of the cholinergic system in the brain.