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The Journal of Biological Chemistry May 2024Extracellular secretion is an essential mechanism for α-synuclein (α-syn) proteostasis. Although it was reported that neuronal activity affects α-syn secretion, the...
Extracellular secretion is an essential mechanism for α-synuclein (α-syn) proteostasis. Although it was reported that neuronal activity affects α-syn secretion, the underlying mechanisms remain unclear. Here, we investigated the autophagic processes that regulate the physiological release of α-syn in mouse primary cortical neurons and SH-SY5Y cells. Stimulating neuronal activity with glutamate or depolarization with high KCl enhanced α-syn secretion. This glutamate-induced α-syn secretion was blocked by a mixture of NMDA receptor antagonist AP5 and AMPA receptor antagonist NBQX, as well as by cytosolic Ca chelator BAPTA-AM. Additionally, mTOR inhibitor rapamycin increased α-syn and p62/SQSTM1 (p62) secretion, and this effect of rapamycin was reduced in primary cortical neurons deficient in the autophagy regulator beclin 1 (derived from BECN1 mice). Glutamate-induced α-syn and p62 secretion was suppressed by knockdown of ATG5, which is required for autophagosome formation. Glutamate increased LC3-II generation and decreased intracellular p62 levels, and the increase in LC3-II levels was blocked by BAPTA-AM. Moreover, glutamate promoted co-localization of α-syn with LC3-positive puncta, but not with LAMP1-positive structures in the neuronal somas. Glutamate-induced α-syn and p62 secretion was also reduced by knockdown of RAB8A, which is required for autophagosome fusion with the plasma membrane. Collectively, these findings suggest that stimulating neuronal activity mediates autophagic α-syn secretion in a cytosolic Ca-dependent manner, and autophagosomes may participate in autophagic secretion by functioning as α-syn carriers.
PubMed: 38815862
DOI: 10.1016/j.jbc.2024.107419 -
Psychiatrike = Psychiatriki May 2024Esketamine is a non-selective, competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor in the brain. Through NMDA receptor antagonism, esketamine causes a...
Esketamine is a non-selective, competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor in the brain. Through NMDA receptor antagonism, esketamine causes a transient increase in glutamate release, leading to increases in neurotrophic signaling and restoration of synaptic function in brain regions involved in mood regulation and emotional behavior. Several randomized clinical trials have shown its effectiveness in reducing the symptoms of depression in some people, despite its short-term side effects that include mainly disorientation, dizziness, nausea, and increased blood pressure. In 2019, the United States Food and Drug Administration (FDA) as well as the European Medicines Agency approved the use of esketamine nasal spray in combination with an oral antidepressant for treatment-resistant depression in adults. Our study aimed to evaluate the effectiveness of this new therapeutic proposal in a case series of five Greek patients with treatment- resistant depression. Intranasal esketamine was administered under medical supervision in combination with an oral antidepressant. Depressive symptoms were evaluated at three time points (baseline, end of treatment, and one-year post-treatment) using the Montgomery-Åsberg Depression Rating Scale (MADRS), the Patient Health Questionnaire (PHQ-9), the CGI Clinical Global Impression Scale, and the Perceived Deficits Questionnaire for Depression (PDQ-D). Possible side effects were assessed using the Richmond Suppression Agitation Scale (RASS), the Sheehan Disability Scale (SDS), the CADSS Disruptive States Scale, and a predefined list of adverse events (AEs) and serious adverse events (SAEs). Patients followed an individualized treatment plan for seven to twelve months depending on the achievement of an adequate response. Statistical analysis of the results revealed a significant improvement (p<0.05) on all scales used. All participants maintained their level of improvement at follow-up after twelve months. Adverse effects were found to be mild and tolerable. It is worth noting that significant side effects were reported only by the two patients with comorbid personality disorder. The results, despite limited to a small sample, indicate the positive effect of esketamine on the stable reduction of depressive symptoms among patients with resistant depression, even after the completion of treatment.
PubMed: 38814267
DOI: 10.22365/jpsych.2024.006 -
Frontiers in Molecular Neuroscience 2024Dm9 neurons in have been proposed as functional homologs of horizontal cells in the outer retina of vertebrates. Here we combine genetic dissection of neuronal circuit...
Dm9 neurons in have been proposed as functional homologs of horizontal cells in the outer retina of vertebrates. Here we combine genetic dissection of neuronal circuit function, two-photon calcium imaging in Dm9 and inner photoreceptors, and immunohistochemical analysis to reveal novel insights into the functional role of Dm9 in early visual processing. Our experiments show that Dm9 receive input from all four types of inner photoreceptor R7p, R7y, R8p, and R8y. Histamine released from all types R7/R8 directly inhibits Dm9 via the histamine receptor Ort, and outweighs simultaneous histamine-independent excitation of Dm9 by UV-sensitive R7. Dm9 in turn provides inhibitory feedback to all R7/R8, which is sufficient for color-opponent processing in R7 but not R8. Color opponent processing in R8 requires additional synaptic inhibition by R7 of the same ommatidium via axo-axonal synapses and the second histamine receptor HisCl1. Notably, optogenetic inhibition of Dm9 prohibits color opponent processing in all types of R7/R8 and decreases intracellular calcium in photoreceptor terminals. The latter likely results from reduced release of excitatory glutamate from Dm9 and shifts overall photoreceptor sensitivity toward higher light intensities. In summary, our results underscore a key role of Dm9 in color opponent processing in and suggest a second role of Dm9 in regulating light adaptation in inner photoreceptors. These novel findings on Dm9 are indeed reminiscent of the versatile functions of horizontal cells in the vertebrate retina.
PubMed: 38813436
DOI: 10.3389/fnmol.2024.1347540 -
Frontiers in Cellular Neuroscience 2024Intracellular Ca-signaling in astrocytes is instrumental for their brain "housekeeping" role and astroglial control of synaptic plasticity. An important source for...
Intracellular Ca-signaling in astrocytes is instrumental for their brain "housekeeping" role and astroglial control of synaptic plasticity. An important source for elevating the cytosolic Ca level in astrocytes is a release from endoplasmic reticulum which can be triggered via two fundamental pathways: IP3 receptors and calcium-induced calcium release (CICR) mediated by Ca-sensitive ryanodine receptors (RyRs). While the physiological role for glial IP3 became a focus of intensive research and debate, ryanodine receptors received much less attention. We explored the role for ryanodine receptors in the modulation of cytosolic Ca-signaling in the cortical and hippocampal astrocytes, astrocyte-neuron communication and astroglia modulation of synaptic plasticity. Our data show that RyR-mediated Ca-induced Ca-release from ER brings substantial contribution into signaling in the functional microdomains hippocampal and neocortical astrocytes. Furthermore, RyR-mediated CICR activated the release of ATP and glutamate from hippocampal and neocortical astrocytes which, in turn, elicited transient purinergic and tonic glutamatergic currents in the neighboring pyramidal neurons. The CICR-facilitated release of ATP and glutamate was inhibited after intracellular perfusion of astrocytes with ryanodine and BAPTA and in the transgenic dnSNARE mice with impaired astroglial exocytosis. We also found out that RyR-mediated amplification of astrocytic Ca-signaling enhanced the long-term synaptic potentiation in the hippocampus and neocortex of aged mice. Combined, our data demonstrate that ryanodine receptors are essential for astrocytic Ca-signaling and efficient astrocyte-neuron communications. The RyR-mediated CICR contributes to astrocytic control of synaptic plasticity and can underlie, at least partially, neuroprotective and cognitive effects of caffein.
PubMed: 38812795
DOI: 10.3389/fncel.2024.1382010 -
Acta Pharmaceutica Sinica. B May 2024The -methyl-d-aspartate (NMDA) receptors, which belong to the ionotropic Glutamate receptors, constitute a family of ligand-gated ion channels. Within the various... (Review)
Review
The -methyl-d-aspartate (NMDA) receptors, which belong to the ionotropic Glutamate receptors, constitute a family of ligand-gated ion channels. Within the various subtypes of NMDA receptors, the GluN1/2A subtype plays a significant role in central nervous system (CNS) disorders. The present article aims to provide a comprehensive review of ligands targeting GluN2A-containing NMDA receptors, encompassing negative allosteric modulators (NAMs), positive allosteric modulators (PAMs) and competitive antagonists. Moreover, the ligands' structure-activity relationships (SARs) and the binding models of representative ligands are also discussed, providing valuable insights for the clinical rational design of effective drugs targeting CNS diseases.
PubMed: 38799621
DOI: 10.1016/j.apsb.2024.01.004 -
IScience Jun 2024Type 1 cannabinoid receptors (CB1Rs) are expressed in major retinal neurons within the rod-pathway suggesting a role in regulating night visual processing, but the...
Type 1 cannabinoid receptors (CB1Rs) are expressed in major retinal neurons within the rod-pathway suggesting a role in regulating night visual processing, but the underlying mechanisms remain poorly understood. Using acute rat retinal slices, we show that CB1R activation reduces glutamate release from rod bipolar cell (RBC) axon terminals onto AII and A17 amacrine cells through a pathway that requires exchange proteins directly activated by cAMP (EPAC1/2) signaling. Consequently, CB1R activation abrogates reciprocal GABAergic feedback inhibition from A17 amacrine cells. Moreover, the activation of CB1Rs enhances and prolongs the time course of the dim-light rod-driven visual responses, an effect that was eliminated when both GABA and GABA receptors were blocked. Altogether, our findings underscore a non-canonical mechanism by which cannabinoid signaling regulates RBC dyad synapses in the inner retina to regulate dim-light visual responses to fine-tune night vision.
PubMed: 38799553
DOI: 10.1016/j.isci.2024.109920 -
Frontiers in Immunology 2024Cerebellar ataxia is an uncommon and atypical manifestation of anti--methyl-D-aspartate receptor (NMDAR) encephalitis, often accompanied by seizures, psychiatric...
Cerebellar ataxia is an uncommon and atypical manifestation of anti--methyl-D-aspartate receptor (NMDAR) encephalitis, often accompanied by seizures, psychiatric symptoms, and cognitive deficits. Previous cases of isolated brainstem-cerebellar symptoms in patients with anti-NMDAR encephalitis have not been documented. This report presents a case of anti-NMDAR encephalitis in which the patient exhibited cerebellar ataxia, nystagmus, diplopia, positive bilateral pathological signs, and hemiparesthesia with no other accompanying symptoms or signs. The presence of positive CSF anti-NMDAR antibodies further supports the diagnosis. Other autoantibodies were excluded through the use of cell-based assays. Immunotherapy was subsequently administered, leading to a gradual recovery of the patient.
Topics: Humans; Anti-N-Methyl-D-Aspartate Receptor Encephalitis; Brain Stem; Autoantibodies; Female; Cerebellar Ataxia; Cerebellum; Receptors, N-Methyl-D-Aspartate; Adult; Immunotherapy; Male; Magnetic Resonance Imaging
PubMed: 38799430
DOI: 10.3389/fimmu.2024.1388667 -
Nature Communications May 2024Working memory (WM) is the ability to maintain and manipulate information 'in mind'. The neural codes underlying WM have been a matter of debate. We simultaneously...
Working memory (WM) is the ability to maintain and manipulate information 'in mind'. The neural codes underlying WM have been a matter of debate. We simultaneously recorded the activity of hundreds of neurons in the lateral prefrontal cortex of male macaque monkeys during a visuospatial WM task that required navigation in a virtual 3D environment. Here, we demonstrate distinct neuronal activation sequences (NASs) that encode remembered target locations in the virtual environment. This NAS code outperformed the persistent firing code for remembered locations during the virtual reality task, but not during a classical WM task using stationary stimuli and constraining eye movements. Finally, blocking NMDA receptors using low doses of ketamine deteriorated the NAS code and behavioral performance selectively during the WM task. These results reveal the versatility and adaptability of neural codes supporting working memory function in the primate lateral prefrontal cortex.
Topics: Animals; Prefrontal Cortex; Memory, Short-Term; Male; Neurons; Macaca mulatta; Virtual Reality; Ketamine; Spatial Navigation; Receptors, N-Methyl-D-Aspartate
PubMed: 38796480
DOI: 10.1038/s41467-024-48664-9 -
Cell Reports May 2024Astrocytic receptors influence cognitive function and can promote behavioral deficits in disease. These effects may vary based on variables such as biological sex, but...
Astrocytic receptors influence cognitive function and can promote behavioral deficits in disease. These effects may vary based on variables such as biological sex, but it is not known if the effects of astrocytic receptors are dependent on sex. We leveraged in vivo gene editing and chemogenetics to examine the roles of astrocytic receptors in spatial memory and other processes. We show that reductions in metabotropic glutamate receptor 3 (mGluR3), the main astrocytic glutamate receptor in adults, impair memory in females but enhance memory in males. Similarly, increases in astrocytic mGluR3 levels have sex-dependent effects and enhance memory in females. mGluR3 manipulations also alter spatial search strategies during recall in a sex-specific manner. In addition, acute chemogenetic stimulation of G-coupled or G-coupled receptors in hippocampal astrocytes induces bidirectional and sex-dimorphic effects on memory. Thus, astrocytes are sex-dependent modulators of cognitive function and may promote sex differences in aging and disease.
PubMed: 38795347
DOI: 10.1016/j.celrep.2024.114278 -
Cellular and Molecular Life Sciences :... May 2024N-methyl-D-aspartate receptors (NMDARs emerging from GRIN genes) are tetrameric receptors that form diverse channel compositions in neurons, typically consisting of two...
N-methyl-D-aspartate receptors (NMDARs emerging from GRIN genes) are tetrameric receptors that form diverse channel compositions in neurons, typically consisting of two GluN1 subunits combined with two GluN2(A-D) subunits. During prenatal stages, the predominant channels are di-heteromers with two GluN1 and two GluN2B subunits due to the high abundance of GluN2B subunits. Postnatally, the expression of GluN2A subunits increases, giving rise to additional subtypes, including GluN2A-containing di-heteromers and tri-heteromers with GluN1, GluN2A, and GluN2B subunits. The latter emerge as the major receptor subtype at mature synapses in the hippocampus. Despite extensive research on purely di-heteromeric receptors containing two identical GRIN variants, the impact of a single variant on the function of other channel forms, notably tri-heteromers, is lagging. In this study, we systematically investigated the effects of two de novo GRIN2B variants (G689C and G689S) in pure, mixed di- and tri-heteromers. Our findings reveal that incorporating a single variant in mixed di-heteromers or tri-heteromers exerts a dominant negative effect on glutamate potency, although 'mixed' channels show improved potency compared to pure variant-containing di-heteromers. We show that a single variant within a receptor complex does not impair the response of all receptor subtypes to the positive allosteric modulator pregnenolone-sulfate (PS), whereas spermine completely fails to potentiate tri-heteromers containing GluN2A and -2B-subunits. We examined PS on primary cultured hippocampal neurons transfected with the variants, and observed a positive impact over current amplitudes and synaptic activity. Together, our study supports previous observations showing that mixed di-heteromers exhibit improved glutamate potency and extend these findings towards the exploration of the effect of Loss-of-Function variants over tri-heteromers. Notably, we provide an initial and crucial demonstration of the beneficial effects of GRIN2B-relevant potentiators on tri-heteromers. Our results underscore the significance of studying how different variants affect distinct receptor subtypes, as these effects cannot be inferred solely from observations made on pure di-heteromers. Overall, this study contributes to ongoing efforts to understand the pathophysiology of GRINopathies and provides insights into potential treatment strategies.
Topics: Receptors, N-Methyl-D-Aspartate; Pregnenolone; Humans; Animals; HEK293 Cells; Hippocampus; Loss of Function Mutation; Protein Multimerization; Neurons; Protein Subunits
PubMed: 38795169
DOI: 10.1007/s00018-024-05243-x