Molecular Brain最新文献

The vast majority of gene mutations and/or gene knockouts result in either no observable changes, or significant deficits in molecular, cellular, or organismal function. However, in a small number of cases, mutant animal models display enhancements in specific behaviors such as learning and memory. To date, most gene deletions shown to enhance cognitive ability generally affect a limited number of pathways such as NMDA receptor- and translation-dependent plasticity, or GABA receptor- and potassium channel-mediated inhibition. While endolysosomal trafficking of AMPA receptors is a critical mediator of synaptic plasticity, mutations in genes that affect AMPAR trafficking either have no effect or are deleterious for synaptic plasticity, learning and memory. NSG2 is one of the three-member family of Neuron-specific genes (NSG1-3), which have been shown to regulate endolysosomal trafficking of a number of proteins critical for neuronal function, including AMPAR subunits (GluA1-2). Based on these findings and the largely universal expression throughout mammalian brain, we predicted that genetic knockout of NSG2 would result in significant impairments across multiple behavioral modalities including motor, affective, and learning/memory paradigms. However, in the current study we show that loss of NSG2 had highly selective effects on associative learning and memory, leaving motor and affective behaviors intact. For instance, NSG2 KO animals performed equivalent to wild-type C57Bl/6n mice on rotarod and Catwalk motor tasks, and did not display alterations in anxiety-like behavior on open field and elevated zero maze tasks. However, NSG2 KO animals demonstrated enhanced recall in the Morris water maze, accelerated reversal learning in a touch-screen task, and accelerated acquisition and enhanced recall on a Trace Fear Conditioning task. Together, these data point to a specific involvement of NSG2 on multiple types of associative learning, and expand the repertoire of pathways that can be targeted for cognitive enhancement.

Rapid adaptation to novel environments is crucial for survival, and this ability is impaired in many neuropsychiatric disorders. Understanding neural adaptation to novelty exposure therefore has therapeutic implications. Here, I found that novelty induces time-dependent theta (4-12Hz) oscillatory dynamics in brain circuits including the medial prefrontal cortex (mPFC), ventral hippocampus (vHPC), and ventral tegmental area (VTA), but not dorsal hippocampus (dHPC), as mice adapt to a novel environment. Local field potential (LFP) recordings were performed while mice were freely behaving in a novel or a familiar arena for 10 min. Initially, mice exhibited increased exploratory behavior upon exposure to novelty, which gradually decreased to levels observed in mice exposed to the familiar arena. Over the same time course, the mPFC, vHPC, and VTA displayed progressively increasing theta power through novelty exposure. Additionally, theta coherence and theta phase synchrony measures demonstrated that novelty weakened the connectivity between these areas, which then gradually strengthened to the level observed in the familiar group. Conversely, mice exposed to the familiar arena showed steady and consistent behavior as well as theta dynamics in all areas. Treatment with a dopamine D1-receptor (D1R) antagonist in the vHPC disrupted neurophysiological adaptation to novelty specifically in the vHPC-mPFC and vHPC-VTA circuits, without affecting behavior. Thus, novelty induces distinct theta dynamics that are not readily dictated by behavior in the mPFC, vHPC, and VTA circuits, a process mediated by D1Rs in the vHPC. The observed time-dependent circuit dynamics in the key learning and memory circuit would provide new insights for treating neuropsychiatric disorders that often show impaired novelty processing.

Trace and delay auditory fear conditioning involve different memory association strategies based on working memory involvement; however, their differences in long-term processing through sleep and extinction training remain unclear. While females often exhibit more persistent fear, complicating psychiatric treatment, most studies have primarily focused on how sleep affects initial recall in male mice. We investigated the three-way interaction between tests (trace vs. delay), sleep states, and sex during initial recall, extinction, and post-extinction remote recall. A six-hour post-conditioning sleep deprivation (SD) did not affect freezing behavior during the following day's extinction training of delay fear memory. However, during post-extinction remote recall of delay fear memory, SD prevented spontaneous recovery in males and reduced persistent freezing in females. In contrast, SD rapidly facilitated extinction of trace fear memory. In summary, SD enhances extinction both in the short-term and long-term, depending on the conditioning protocol. These findings highlight the importance of long-term assessments to explore interactions among emotional memory, sleep, and sex differences, with implications for individualized mechanisms underlying post-traumatic stress disorder (PTSD) and its treatments.

Temporal lobe epilepsy (TLE) is the most common form of medically-intractable epilepsy. Subicular hyperexcitability is frequently observed with TLE, presumably caused by impaired inhibition of local excitatory neurons. Here, we evaluated the effectiveness of silencing subicular pyramidal neurons to treat a rodent model of TLE. First, we generated a chronic TLE mouse model via initial intrahippocampal kainic acid (IHKA) injection. In the chronic state after first IHKA injection, behavioral seizures and histological abnormalities were reliably observed. We then injected an adeno-associated viral (AAV) vector carrying an inhibitory chemogenetic element, hM4D_i, directly into the subiculum. Eight weeks after the first IHKA injection, acute seizures were induced by giving a second dose of kainic acid (KA), which mimicked generalized tonic-clonic seizures. Herein, precise control over generalized tonic-clonic seizure onset was achieved via this two-step process. We found that chemogenetic suppression of subicular pyramidal neurons had a robust anti-epileptogenesis effect in this acute-chronic model of TLE. These data confirm a crucial role of the subiculum in the propagation of hippocampal seizures and highlight the potential for using subicular chemogenetic manipulation to treat generalized tonic-clonic seizures.

Sorting spikes from extracellular recordings, obtained by sensing neuronal activity around an electrode tip, is essential for unravelling the complexities of neural coding and its implications across diverse neuroscientific disciplines. However, the presence of overlapping spikes, originating from neurons firing simultaneously or within a short delay, has been overlooked because of the difficulty in identifying individual neurons due to the lack of ground truth. In this study, we propose a method to identify overlapping spikes in extracellular recordings and to recover hidden spikes by decomposing them. We initially estimate spike waveform templates through a series of steps, including discriminative subspace learning and the isolation forest algorithm. By leveraging these estimated templates, we generate synthetic spikes and train a classifier using their feature components to identify overlapping spikes from observed spike data. The identified overlapping spikes are then decomposed into individual hidden spikes using a particle swarm optimization. Results from the testing of the proposed approach, using the simulation dataset we generated, demonstrated that employing synthetic spikes in the overlapping spike classifier accurately identifies overlapping spikes among the detected ones (the maximum F1 score of 0.88). Additionally, the approach can infer the synchronization between hidden spikes by decomposing the overlapped spikes and reallocating them into distinct clusters. This study advances spike sorting by accurately identifying overlapping spikes, providing a more precise tool for neural activity analysis.

The histaminergic system plays a key role in modulating learning and memory, wakefulness, and energy balance. Histamine H₃ receptors constitutively inhibit the synthesis and release of histamine and other neurotransmitters. Therefore, H₃ receptor inverse agonists/antagonists increase the synthesis and release of these neurotransmitters, enhancing cognitive functions, including memory consolidation and retrieval. Spontaneous neural activity across the cerebral cortex is essential for cognitive function, including memory consolidation. Abnormal spontaneous activity has, in fact, been associated with cognitive dysfunctions and psychiatric disorders. Given the cognitive improvement achieved with the use of H₃ receptor inverse agonists/antagonists, we examined the effects of two inverse agonists/antagonists - thioperamide and pitolisant - on spontaneous cortical activity, using in vivo wide-field Ca²⁺ imaging. Changes in cortical activity, across multiple cortical regions and in inter-regional connectivity, from pre- to post-administration were evaluated using a linear support vector machine decoder. Thioperamide and pitolisant both modified the amplitude distribution of calcium events across multiple cortical regions, including a reduction in the frequency of low-amplitude calcium events in the somatosensory cortex. Graph theory analysis revealed increases in centrality measures in the somatosensory cortex with the use of both thioperamide and pitolisant, indicative of their importance in the organization of cortical networks. These findings indicate that H₃ receptor inverse agonists/antagonists influence intra-regional cortical activity and inter-regional synchronization of activity in the cerebral cortex during the resting state.

Depression, a prevalent neuropsychiatric disorder, involves the dysregulation of neurotransmitters such as dopamine (DA). The restoration of DA balance is a pivotal therapeutic target for this condition. Recent studies have indicated that both antidepressant medications and non-pharmacological treatments, such as transcutaneous auricular vagus nerve stimulation (taVNS), can promote recovery from depressive symptoms. Despite the promise of taVNS as a non-invasive depression therapy, its precise mechanism remains unclear. We hypothesized that taVNS exerts antidepressant effects by modulating the DAergic system. To investigate this, we conducted experiments demonstrating that taVNS in anesthetized mice reduced depressive-like behaviors. However, this effect was abolished when DA neurons in the ventral tegmental area (VTA^DA) were inhibited. Additionally, taVNS in anesthetized mice enhanced VTA^DA activity, providing further evidence to support its antidepressant effects. Overall, our findings suggest that taVNS alleviates depression by augmenting VTA^DA activity, thereby contributing to a more comprehensive understanding of its therapeutic mechanisms.

Recessive loss-of-function mutations in the mitochondrial enzyme Glutamate Pyruvate Transaminase 2 (GPT2) cause intellectual disability in children. Given this cognitive disorder, and because glutamate metabolism is tightly regulated to sustain excitatory neurotransmission, here we investigate the role of GPT2 in synaptic function. GPT2 catalyzes a reversible reaction interconverting glutamate and pyruvate with alanine and alpha-ketoglutarate, a TCA cycle intermediate; thereby, GPT2 may play an important role in linking mitochondrial tricarboxylic acid (TCA) cycle with synaptic transmission. In mouse brain, we find that GPT2 is enriched in mitochondria of synaptosomes (isolated synaptic terminals). Loss of Gpt2 in mouse appears to lead to reprogramming of glutamate and glutamine metabolism, and to decreased glutamatergic synaptic transmission. Whole-cell patch-clamp recordings in pyramidal neurons of CA1 hippocampal slices from Gpt2-null mice reveal decreased excitatory post-synaptic currents (mEPSCs) without changes in mEPSC frequency, or importantly, changes in inhibitory post-synaptic currents (mIPSCs). Additional evidence of defective glutamate release included reduced levels of glutamate released from Gpt2-null synaptosomes measured biochemically. Glutamate release from synaptosomes was rescued to wild-type levels by alpha-ketoglutarate supplementation. Additionally, we observed evidence of altered metabolism in isolated Gpt2-null synaptosomes: decreased TCA cycle intermediates, and increased glutamate dehydrogenase activity. Notably, alterations in the TCA cycle and the glutamine pool were alleviated by alpha-ketoglutarate supplementation. In conclusion, our data support a model whereby GPT2 mitochondrial activity may contribute to glutamate availability in pre-synaptic terminals, thereby highlighting potential interactions between pre-synaptic mitochondrial metabolism and synaptic transmission.

Brain-derived neurotrophic factor (BDNF) is known for its potent prosurvival effect. Despite successfully replicating this effect in various clinical and pre-clinical models, the complete characterization of the molecular mechanisms underlying its neuroprotective action remains incomplete. Emerging research suggests a vital role for A-kinase anchoring proteins (AKAPs) as central nodal points orchestrating BDNF-dependent signaling. Among the over 50 identified AKAPs, AKAP6 has recently gained special attention due to its involvement in the neurotrophin-mediated survival of injured retinal ganglion cells (RGCs). However, the mechanisms by which AKAP6 responds to pro-survival BDNF signaling remain unknown. In this study, we shown that AKAP6 plays a crucial role in regulating BDNF-mediated NFAT transcriptional activity in neuronal survival by anchoring protein phosphatase calcineurin (CaN) and nuclear factor of activated T cells (NFATc4). Furthermore, we demonstrate that disrupting the anchoring of CaN diminishes the pro-survival effect of BDNF. Lastly, through experiments with NFATc4-/- mice, we provide evidence that NFATc4 acts downstream to BDNF's neuroprotection in vivo. These findings could offer valuable insights for developing neuroprotective strategies aimed at preserving injured neurons from degeneration and promoting their regeneration.

Neuroinflammation is a significant contributor to the pathology of glaucoma. Targeting key-mediators in this process is a realistic option to slow disease progression. Galectin-3 is a β-galactoside binding lectin that has been associated with inflammation in both systemic and central nervous system diseases. Elevated Galectin-3 has recently been detected in multiple animal models of glaucoma and inhibiting Galectin-3 using an intravitreal injection of TD139 (a Galectin-3 small molecule inhibitor) is neuroprotective. We queried whether this neuroprotective effect was translatable to another animal model and species. TD139 was intravitreally injected, in a rat ocular hypertensive model of glaucoma, 3 days after the induction of ocular hypertension (at peak intraocular pressure). Retinal ganglion cell survival and glial morphological markers were quantified. The degeneration of retinal ganglion cells was prevented by TD139 injection, but gross glial markers remained unaffected. These data confirm that the intravitreal injection of TD139 is neuroprotective in a rat ocular hypertensive model of glaucoma, while suggesting that the inhibition of Galectin-3 is not sufficient to alter the gross inflammatory outcome.