Synaptic plasticity during systems memory consolidation

Promotion of structural plasticity in area V2 of visual cortex prevents against object recognition memory deficits in aging and Alzheimer's disease rodents

JOURNAL/nrgr/04.03/01300535-202408000-00038/figure1/v/2023-12-16T180322Z/r/image-tiff Memory deficit, which is often associated with aging and many psychiatric, neurological, and neurodegenerative diseases, has been a challenging issue for treatment. Up till now, all potential drug candidates have failed to produce satisfactory effects. Therefore, in the search for a solution, we found that a treatment with the gene corresponding to the RGS14414 protein in visual area V2, a brain area connected with brain circuits of the ventral stream and the medial temporal lobe, which is crucial for object recognition memory (ORM), can induce enhancement of ORM. In this study, we demonstrated that the same treatment with RGS14414 in visual area V2, which is relatively unaffected in neurodegenerative diseases such as Alzheimer's disease, produced long-lasting enhancement of ORM in young animals and prevent ORM deficits in rodent models of aging and Alzheimer's disease. Furthermore, we found that the prevention of memory deficits was mediated through the upregulation of neuronal arborization and spine density, as well as an increase in brain-derived neurotrophic factor (BDNF). A knockdown of BDNF gene in RGS14414-treated aging rats and Alzheimer's disease model mice caused complete loss in the upregulation of neuronal structural plasticity and in the prevention of ORM deficits. These findings suggest that BDNF-mediated neuronal structural plasticity in area V2 is crucial in the prevention of memory deficits in RGS14414-treated rodent models of aging and Alzheimer's disease. Therefore, our findings of RGS14414 gene-mediated activation of neuronal circuits in visual area V2 have therapeutic relevance in the treatment of memory deficits.

Serotonergic neuromodulation of synaptic plasticity

Synaptic plasticity constitutes a fundamental process in the reorganization of neural networks that underlie memory, cognition, emotional responses, and behavioral planning. At the core of this phenomenon lie Hebbian mechanisms, wherein frequent synaptic stimulation induces long-term potentiation (LTP), while less activation leads to long-term depression (LTD). The synaptic reorganization of neuronal networks is regulated by serotonin (5-HT), a neuromodulator capable of modify synaptic plasticity to appropriately respond to mental and behavioral states, such as alertness, attention, concentration, motivation, and mood. Lately, understanding the serotonergic Neuromodulation of synaptic plasticity has become imperative for unraveling its impact on cognitive, emotional, and behavioral functions. Through a comparative analysis across three main forebrain structures-the hippocampus, amygdala, and prefrontal cortex, this review discusses the actions of 5-HT on synaptic plasticity, offering insights into its role as a neuromodulator involved in emotional and cognitive functions. By distinguishing between plastic and metaplastic effects, we provide a comprehensive overview about the mechanisms of 5-HT neuromodulation of synaptic plasticity and associated functions across different brain regions.

Berberine and hesperidin prevent the memory consolidation impairment induced by pentylenetetrazole in zebrafish

This study verified the effects of the natural compounds berberine and hesperidin on seizure development and cognitive impairment triggered by pentylenetetrazole (PTZ) in zebrafish. Adult animals were submitted to a training session in the inhibitory avoidance test and, after 10 minutes, they received an intraperitoneal injection of 25, 50, or 100 mg/kg berberine or 100 or 200 mg/kg hesperidin. After 30 minutes, the animals were exposed to 7.5 mM PTZ for 10 minutes. Animals were submitted to the test session 24 h after the training session to verify their cognitive performance. Zebrafish larvae were exposed to 100 µM or 500 µM berberine or 10 µM or 50 µM hesperidin for 30 minutes. After, larvae were exposed to PTZ and had the seizure development evaluated by latency to reach the seizure stages I, II, and III. Adult zebrafish pretreated with 50 mg/kg berberine showed a longer latency to reach stage III. Zebrafish larvae pretreated with 500 µM berberine showed a longer latency to reach stages II and III. Hesperidin did not show any effect on seizure development both in larvae and adult zebrafish. Berberine and hesperidin pretreatments prevented the memory consolidation impairment provoked by PTZ-induced seizures. There were no changes in the distance traveled in adult zebrafish pretreated with berberine or hesperidin. In larval stage, berberine caused no changes in the distance traveled; however, hesperidin increased the locomotion. Our results reinforce the need for investigating new therapeutic alternatives for epilepsy and its comorbidities.

Epigenetic drugs and psychedelics as emerging therapies for alcohol use disorder: insights from preclinical studies

Alcohol use disorder (AUD) is a public health issue that affects millions of people worldwide leading to physical, mental and socio-economic consequences. While current treatments for AUD have provided relief to individuals, their effectiveness on the long term is often limited, leaving a number of affected individuals without sustainable solutions. In this review, we aim to explore two emerging approaches for AUD: psychedelics and epigenetic drugs (i.e., epidrugs). By examining preclinical studies, different animal species and procedures, we delve into the potential benefits of each of these treatments in terms of addictive behaviors (alcohol drinking and seeking, motivation to drink alcohol and prevention of relapse). Because psychedelics and epidrugs may share common and complementary mechanisms of action, there is an exciting opportunity for exploring synergies between these approaches and their parallel effectiveness in treating AUD and the diverse associated psychiatric conditions.

Agomelatine improves memory and learning impairments in a rat model of LPS-induced neurotoxicity by modulating the ERK/SorLA/BDNF/TrkB pathway

The mutual interplay between neuroinflammation, synaptic plasticity, and autophagy has piqued researchers' interest, particularly when it comes to linking their impact and relationship to cognitive deficits. Being able to reduce inflammation and apoptosis, melatonin has shown to have positive neuroprotective effects; that is why we thought to check the possible role of agomelatine (AGO) as a promising candidate that could have a positive impact on cognitive deficits. In the current study, AGO (40 mg/kg/day, p.o., 7 days) successfully ameliorated the cognitive and learning disabilities caused by lipopolysaccharide (LPS) in rats (250 μg/kg/day, i.p., 7 days). This positive impact was supported by improved histopathological findings and improved spatial memory as assessed using Morris water maze. AGO showed a strong ability to control BACE1 activity and to rein in the hippocampal amyloid beta (Aβ) deposition. Also, it improved neuronal survival, neuroplasticity, and neurogenesis by boosting BDNF levels and promoting its advantageous effects and by reinforcing the pTrkB expression. In addition, it upregulated the pre- and postsynaptic neuroplasticity biomarkers resembled in synapsin I, synaptophysin, and PSD-95. Furthermore, AGO showed a modulatory action on Sortilin-related receptor with A-type repeats (SorLA) pathway and adjusted autophagy. It is noteworthy that all of these actions were abolished by administering PD98059 a MEK/ERK pathway inhibitor (0.3 mg/kg/day, i.p., 7 days). In conclusion, AGO administration significantly improves memory and learning disabilities associated with LPS administration by modulating the ERK/SorLA/BDNF/TrkB signaling pathway parallel to its capacity to adjust the autophagic process.

Receive, Retain and Retrieve: Psychological and Neurobiological Perspectives on Memory Retrieval

Memory and learning are interdependent processes that involve encoding, storage, and retrieval. Especially memory retrieval is a fundamental cognitive ability to recall memory traces and update stored memory with new information. For effective memory retrieval and learning, the memory must be stabilized from short-term memory to long-term memory. Hence, it is necessary to understand the process of memory retention and retrieval that enhances the process of learning. Though previous cognitive neuroscience research has focused on memory acquisition and storage, the neurobiological mechanisms underlying memory retrieval and its role in learning are less understood. Therefore, this article offers the viewpoint that memory retrieval is essential for selecting, reactivating, stabilizing, and storing information in long-term memory. In arguing how memories are retrieved, consolidated, transmitted, and strengthened for the long term, the article will examine the psychological and neurobiological aspects of memory and learning with synaptic plasticity, long-term potentiation, genetic transcription, and theta oscillation in the brain.

The cognitive impact of light: illuminating ipRGC circuit mechanisms

Ever-present in our environments, light entrains circadian rhythms over long timescales, influencing daily activity patterns, health and performance. Increasing evidence indicates that light also acts independently of the circadian system to directly impact physiology and behaviour, including cognition. Exposure to light stimulates brain areas involved in cognition and appears to improve a broad range of cognitive functions. However, the extent of these effects and their mechanisms are unknown. Intrinsically photosensitive retinal ganglion cells (ipRGCs) have emerged as the primary conduit through which light impacts non-image-forming behaviours and are a prime candidate for mediating the direct effects of light on cognition. Here, we review the current state of understanding of these effects in humans and mice, and the tools available to uncover circuit-level and photoreceptor-specific mechanisms. We also address current barriers to progress in this area. Current and future efforts to unravel the circuits through which light influences cognitive functions may inform the tailoring of lighting landscapes to optimize health and cognitive function.

Metal-Oxide Heterojunction: From Material Process to Neuromorphic Applications

As technologies like the Internet, artificial intelligence, and big data evolve at a rapid pace, computer architecture is transitioning from compute-intensive to memory-intensive. However, traditional von Neumann architectures encounter bottlenecks in addressing modern computational challenges. The emulation of the behaviors of a synapse at the device level by ionic/electronic devices has shown promising potential in future neural-inspired and compact artificial intelligence systems. To address these issues, this review thoroughly investigates the recent progress in metal-oxide heterostructures for neuromorphic applications. These heterostructures not only offer low power consumption and high stability but also possess optimized electrical characteristics via interface engineering. The paper first outlines various synthesis methods for metal oxides and then summarizes the neuromorphic devices using these materials and their heterostructures. More importantly, we review the emerging multifunctional applications, including neuromorphic vision, touch, and pain systems. Finally, we summarize the future prospects of neuromorphic devices with metal-oxide heterostructures and list the current challenges while offering potential solutions. This review provides insights into the design and construction of metal-oxide devices and their applications for neuromorphic systems.

Mouse maternal odontogenic infection with Porphyromonas gingivalis induces cognitive decline in offspring

Introduction

Porphyromonas gingivalis (P. gingivalis), a major periodontal pathogen, causes intrauterine infection/inflammation. Offspring exposed to intrauterine infection/inflammation have an increased risk of neurological disorders, regardless of gestational age. However, the relationship between maternal periodontitis and offspring functional/histological changes in the brain has not yet been elucidated.

Methods

In this study, we used a gestational mouse model to investigate the effects of maternal odontogenic infection of P. gingivalis on offspring behavior and brain tissue.

Results

The step-through passive avoidance test showed that the latency of the acquisition trial was significantly shorter in the P. gingivalis group (p < 0.05), but no difference in spontaneous motor/exploratory parameters by open-field test. P. gingivalis was diffusely distributed throughout the brain, especially in the hippocampus. In the hippocampus and amygdala, the numbers of neuron cells and cyclic adenosine monophosphate response element binding protein-positive cells were significantly reduced (p < 0.05), whereas the number of ionized calcium binding adapter protein 1-positive microglia was significantly increased (p < 0.05). In the hippocampus, the number of glial fibrillary acidic protein-positive astrocytes was also significantly increased (p < 0.05).

Discussion

The offspring of P. gingivalis-infected mothers have reduced cognitive function. Neurodegeneration/neuroinflammation in the hippocampus and amygdala may be caused by P. gingivalis infection, which is maternally transmitted. The importance of eliminating maternal P. gingivalis-odontogenic infection before or during gestation in maintenance healthy brain function in offspring should be addressed in near future.

CBD enhances the cognitive score of adolescent rats prenatally exposed to THC and fine-tunes relevant effectors of hippocampal plasticity

Introduction: An altered neurodevelopmental trajectory associated with prenatal exposure to ∆-9-tetrahydrocannabinol (THC) leads to aberrant cognitive processing through a perturbation in the effectors of hippocampal plasticity in the juvenile offspring. As adolescence presents a unique window of opportunity for "brain reprogramming", we aimed at assessing the role of the non-psychoactive phytocannabinoid cannabidiol (CBD) as a rescue strategy to temper prenatal THC-induced harm. Methods: To this aim, Wistar rats prenatally exposed to THC (2 mg/kg s.c.) or vehicle (gestational days 5-20) were tested for specific indexes of spatial and configural memory in the reinforcement-motivated Can test and in the aversion-driven Barnes maze test during adolescence. Markers of hippocampal excitatory plasticity and endocannabinoid signaling-NMDAR subunits NR1 and 2A-, mGluR5-, and their respective scaffold proteins PSD95- and Homer 1-; CB1R- and the neuromodulatory protein HINT1 mRNA levels were evaluated. CBD (40 mg/kg i.p.) was administered to the adolescent offspring before the cognitive tasks. Results: The present results show that prenatal THC impairs hippocampal memory functions and the underlying synaptic plasticity; CBD is able to mitigate cognitive impairment in both reinforcement- and aversion-related tasks and the neuroadaptation of hippocampal excitatory synapses and CB1R-related signaling. Discussion: While this research shows CBD potential in dampening prenatal THC-induced consequences, we point out the urgency to curb cannabis use during pregnancy in order to avoid detrimental bio-behavioral outcomes in the offspring.

Trait representation of embodied cognition in dancers pivoting on the extended mirror neuron system: a resting-state fMRI study

Introduction

Dance is an art form that integrates the body and mind through movement. Dancers develop exceptional physical and mental abilities that involve various neurocognitive processes linked to embodied cognition. We propose that dancers' primary trait representation is movement-actuated and relies on the extended mirror neuron system (eMNS).

Methods

A total of 29 dancers and 28 non-dancer controls were recruited. A hierarchical approach of intra-regional and inter-regional functional connectivity (FC) analysis was adopted to probe trait-like neurodynamics within and between regions in the eMNS during rest. Correlation analyses were employed to examine the associations between dance training, creativity, and the FC within and between different brain regions.

Results

Within the eMNS, dancers exhibited increased intra-regional FC in various brain regions compared to non-dancers. These regions include the left inferior frontal gyrus, left ventral premotor cortex, left anterior insula, left posterior cerebellum (crus II), and bilateral basal ganglia (putamen and globus pallidus). Dancers also exhibited greater intrinsic inter-regional FC between the cerebellum and the core/limbic mirror areas within the eMNS. In dancers, there was a negative correlation observed between practice intensity and the intrinsic FC within the eMNS involving the cerebellum and basal ganglia. Additionally, FCs from the basal ganglia to the dorsolateral prefrontal cortex were found to be negatively correlated with originality in dancers.

Discussion

Our results highlight the proficient communication within the cortical-subcortical hierarchy of the eMNS in dancers, linked to the automaticity and cognitive-motor interactions acquired through training. Altered functional couplings in the eMNS can be regarded as a unique neural signature specific to virtuoso dancers, which might predispose them for skilled dancing performance, perception, and creation.

Glucocorticoids Orchestrate Adult Hippocampal Plasticity: Growth Points and Translational Aspects

The review analyzes modern concepts about the control of various mechanisms of the hippocampal neuroplasticity in adult mammals and humans by glucocorticoids. Glucocorticoid hormones ensure the coordinated functioning of key components and mechanisms of hippocampal plasticity: neurogenesis, glutamatergic neurotransmission, microglia and astrocytes, systems of neurotrophic factors, neuroinflammation, proteases, metabolic hormones, neurosteroids. Regulatory mechanisms are diverse; along with the direct action of glucocorticoids through their receptors, there are conciliated glucocorticoid-dependent effects, as well as numerous interactions between various systems and components. Despite the fact that many connections in this complex regulatory scheme have not yet been established, the study of the factors and mechanisms considered in the work forms growth points in the field of glucocorticoid-regulated processes in the brain and primarily in the hippocampus. These studies are fundamentally important for the translation into the clinic and the potential treatment/prevention of common diseases of the emotional and cognitive spheres and respective comorbid conditions.

Muscarinic Cholinergic Receptor Antagonism Impairs Spatial Memory Retrieval and Minimizes Retrieval-Induced Alterations in Matrix Metalloproteinase-9

Cholinergic dysfunction in the hippocampus causes memory impairment, and degradation of the forebrain cholinergic system has been implicated in several neurological disorders. One such disorder, Alzheimer's Disease (AD) is associated with the abnormal expression of various proteins including matrix metalloproteinase-9 (MMP-9), an enzyme known to regulate hippocampus-dependent memory. Memory involves several stages including acquisition, consolidation, and retrieval, but the neurobiological correlates of retrieval have been studied much less than other stages of memory. We sought to investigate the potential relationship between cholinergic signaling and hippocampal MMP-9 expression and the involvement of each in spatial memory retrieval. We trained rats in the water maze until the task was well-learned, then, seven days later, we allowed some to retrieve the memory after an intracerebroventricular injection of scopolamine or vehicle. Western blot analysis of hippocampal tissue shows elevated levels of a truncated form of MMP-9 associated with spatial memory retrieval. Additionally, our results indicate that centrally administered scopolamine both impairs spatial memory retrieval and prevents retrieval-induced elevations in MMP-9. These findings provide evidence for a potential link between cholinergic dysregulation and abnormal MMP-9 levels seen in the brains of AD patients. An important, yet unresolved question is whether MMP-9 serves to support memory retrieval itself or if it is involved in maintaining the ongoing stability of a retrieved memory.

Compensatory cognition in neurological diseases and aging: A review of animal and human studies

Specialized individual circuits in the brain are recruited for specific functions. Interestingly, multiple neural circuitries continuously compete with each other to acquire the specialized function. However, the dominant among them compete and become the central neural network for that particular function. For example, the hippocampal principal neural circuitries are the dominant networks among many which are involved in learning processes. But, in the event of damage to the principal circuitry, many times, less dominant networks compensate for the primary network. This review highlights the psychopathologies of functional loss and the aspects of functional recuperation in the absence of the hippocampus.

Exploiting volume electron microscopy to investigate structural plasticity and stability of the postsynaptic compartment of central synapses

Volume reconstruction from electron microscopy datasets is a tool increasingly used to study the ultrastructure of the synapse in the broader context of neuronal network and brain organization. Fine modifications of synapse structure, such as activity-dependent dendritic spine enlargement and changes in the size and shape of the postsynaptic density, occur upon maturation and plasticity. The lack of structural plasticity or the inability to stabilize potentiated synapses are associated with synaptic and neuronal functional impairment. Mapping these rearrangements with the high resolution of electron microscopy proved to be essential in order to establish precise correlations between the geometry of synapses and their functional states. In this review we discuss recent discoveries on the substructure of the postsynaptic compartment of central excitatory synapses and how those are correlated with functional states of the neuronal network. The added value of volume electron microscopy analyses with respect to conventional transmission electron microscopy studies is highlighted considering that some limitations of volume-based methods imposed several adjustments to describe the geometry of this synaptic compartment and new parameters-that are good indicators of synapses strength and activity-have been introduced.