The melanocortin-4 receptor (MC4R) is a G protein-coupled receptor (GPCR) that is expressed in several brain locations encompassing the hypothalamus and the brainstem, where the receptor controls several body functions, including metabolism. In a well-defined pathway to decrease appetite, hypothalamic proopiomelanocortin (POMC) neurons localized in the arcuate nucleus (Arc) project to MC4R neurons in the paraventricular nuclei (PVN) to release the natural MC4R agonist α-melanocyte-stimulating hormone (α-MSH). Arc neurons also project excitatory glutamatergic fibers to the MC4R neurons in the PVN for a fast synaptic transmission to regulate a satiety pathway potentiated by α-MSH. By using super-resolution microscopy, we found that in hypothalamic neurons in a primary culture, postsynaptic density protein 95 (PSD95) colocalizes with GluN1, a subunit of the ionotropic N-methyl-D-aspartate receptor (NMDAR). Thus, hypothalamic neurons form excitatory postsynaptic specializations. To study the MC4R distribution at these sites, tagged HA-MC4R under the synapsin promoter was expressed in neurons by adeno-associated virus (AAV) gene transduction. HA-MC4R immunofluorescence peaked at the center and in proximity to the PSD95- and NMDAR-expressing sites. These data provide morphological evidence that MC4R localizes together with glutamate receptors at postsynaptic and peri-postsynaptic sites.

OBJECTIVE: To observe the effects of electroacupuncture (EA) on fear extinction and sleep phase in single prolonged stress (SPS) mice, and explore its mechanism in view of the expression of relevant synaptic proteins.
METHODS: Thirty-two C57BL/6J male mice were randomly divided into a control group, a model group, an EA group and a paroxetine (PRX) group, with 8 mice in each one. Modified SPS method was used to establish PTSD model in the model group, the EA group and the PRX group. Seven days after modeling completion, in the EA group, the intervention was delivered at \"Baihui\" (GV 20) and bilateral \"Zusanli\" (ST 36), with disperse-dense wave, 3 Hz/15 Hz in frequency and 1 mA in current intensity, for 30 min. In the PRX group, paroxetine solution (2.5 g/L) was administered intragastrically (10 mg/kg). The intervention was given once daily and for consecutive 10 days in the above two groups. The fear conditioning task and the elevated plus-maze test were adopted to evaluate the fear extinction and anxiety of the mice in each group. Using Medusa electroencephalogram (EEG) and electromyography (EMG) recording system from rats and mice, the sleep phase was determined in the mice. With Western blot method adopted, the protein expression of the postsynaptic density protein 95 (PSD95), activity-regulated cytoskeleton-associated protein (ARC), brain-derived neurotrophic factor (BDNF), N-methyl-D-aspartic acid receptor 2A (GluN2A), N-methyl-D-aspartic acid receptor 2B (GluN2B) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor 1 (GluA1) in the hippocampus was detected in the mice.
RESULTS: Compared with the control group, the freezing time for the fear re-exposure in 3 min to 15 min and the fear extinction in 0 min to 3 min were prolonged (P<0.05), the fear extinction index decreased (P<0.05), and the open arm time (OT) of the elevated plus-maze was shortened (P<0.05) in the model group. When compared with the model group, in the EA group and the PRX group, the freezing time for the fear re-exposure in 3 min to 6 min and 12 min to 15 min, as well as the fear extinction in 0 min to 3 min was shortened (P<0.05), the fear extinction index increased (P<0.05); the OT in elevated plus-maze was longer in the mice of the EA group (P<0.05). The period of wake (Wake) was prolonged (P<0.05), the non-rapid eye movement period (NREM) and the total sleep time (Sleep) were reduced in the model group (P<0.05) in comparison with the control group. Compared with the model group, the Wake was declined (P<0.05), and the NREM and Sleep increased in the EA group and the PRX group (P<0.05). When compared with the control group, the protein expression of PSD95, ARC, BDNF, GluN2A and GluA1 in the hippocampus decreased (P<0.05), and that of GluN2B increased (P<0.05) in the model group. In the EA group and the PRX group, the protein expression of PSD95, ARC, BDNF, GluN2A and GluA1 in the hippocampus was elevated (P<0.05), and that of GluN2B reduced (P<0.05) when compared with the model group.
CONCLUSIONS: Electroacupuncture at \"Baihui\" (GV 29) and \"Zusanli\" (ST 36) can ameliorate anxiety-like behavior, fear extinction disorder and abnormal sleep phase in SPS mice, which may be related to the regulation of synaptic transmission and synaptic plasticity expression in the hippocampus.
目的：观察电针对单次长时间应激（SPS）小鼠恐惧记忆消退及睡眠时相的影响，从突触相关蛋白表达探究作用机制。方法：将32只雄性C57BL/6J小鼠随机分成对照组、模型组、电针组和帕罗西汀组，每组8只。采用改良SPS法对模型组、电针组和帕罗西汀组小鼠进行模型制备。造模结束后7 d，电针组小鼠于“百会”和双侧“足三里”行电针干预，选用疏密波，频率3 Hz/15 Hz，电流强度1 mA，干预30 min；帕罗西汀组小鼠予帕罗西汀溶液（2.5 g/L）灌胃（10 mg/kg）。两组均每日干预1次，连续10 d。采用条件性恐惧实验和高架十字迷宫实验观察各组小鼠恐惧记忆消退和焦虑样行为；Medusa大小鼠脑电肌电记录系统检测小鼠睡眠时相；Western blot法检测小鼠海马组织突触后密度蛋白95（PSD95）、活性调节细胞骨架（ARC）、脑源性神经营养因子（BDNF）、谷氨酸受体2A（GluN2A）、谷氨酸受体2B（GluN2B）和谷氨酸受体1（GluA1）的蛋白表达。结果：与对照组比较，模型组小鼠恐惧再暴露3~;15 min及恐惧消退0~;3 min的凝滞时间延长（P<0.05），恐惧消退指数降低（P<0.05），在高架十字迷宫开放臂的停留时间缩短（P<0.05）。与模型组比较，电针组和帕罗西汀组小鼠恐惧再暴露3~;6 min、12~;15 min及恐惧消退0~;3 min的凝滞时间缩短（P<0.05），恐惧消退指数升高（P<0.05）；电针组小鼠在高架十字迷宫开放臂的停留时间延长（P<0.05）。与对照组比较，模型组小鼠觉醒期（Wake）延长（P<0.05），非快速眼动睡眠期（NREM）和总睡眠时间（Sleep）缩短（P<0.05）；与模型组比较，电针组和帕罗西汀组小鼠Wake缩短（P<0.05），NREM和Sleep延长（P<0.05）。与对照组比较，模型组小鼠海马组织PSD95、ARC、BDNF、GluN2A和GluA1蛋白表达降低（P<0.05），GluN2B蛋白表达升高（P<0.05）；与模型组比较，电针组和帕罗西汀组小鼠海马组织PSD95、ARC、BDNF、GluN2A和GluA1蛋白表达升高（P<0.05），GluN2B蛋白表达降低（P<0.05）。结论：电针“百会”“足三里”可改善SPS小鼠的焦虑样行为、恐惧记忆消退障碍和睡眠时相异常，其机制可能与调控海马突触传递和可塑性蛋白表达有关。.

Aging is characterized by a functional decline in several physiological systems. α-Klotho-hypomorphic mice (Kl-/-) exhibit accelerated aging and cognitive decline. We evaluated whether male and female α-Klotho-hypomorphic mice show changes in the expression of synaptic proteins, N-methyl-d-aspartate receptor (NMDAR) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) subunits, postsynaptic density protein 95 (PSD-95), synaptophysin and synapsin, and the activity of Na+, K+-ATPase (NaK) isoforms in the cerebellum and hippocampus. In this study, we demonstrated that in the cerebellum, Kl-/- male mice have reduced expression of GluA1 (AMPA) compared to wild-type (Kl+/+) males and Kl-/- females. Also, Kl-/- male and female mice show reduced ɑ2/ɑ3-NaK and Mg2+-ATPase activities in the cerebellum, respectively, and sex-based differences in NaK and Mg2+-ATPase activities in both the regions. Our findings suggest that α-Klotho could influence the expression of AMPAR and the activity of NaK isoforms in the cerebellum in a sex-dependent manner, and these changes may contribute, in part, to cognitive decline.

The key DNA repair enzyme DNA-PKcs has several and important cellular functions. Loss of DNA-PKcs activity in mice has revealed essential roles in immune and nervous systems. In humans, DNA-PKcs is a critical factor for brain development and function since mutation of the prkdc gene causes severe neurological deficits such as microcephaly and seizures, predicting yet unknown roles of DNA-PKcs in neurons. Here we show that DNA-PKcs modulates synaptic plasticity. We demonstrate that DNA-PKcs localizes at synapses and phosphorylates PSD-95 at newly identified residues controlling PSD-95 protein stability. DNA-PKcs -/- mice are characterized by impaired Long-Term Potentiation (LTP), changes in neuronal morphology, and reduced levels of postsynaptic proteins. A PSD-95 mutant that is constitutively phosphorylated rescues LTP impairment when over-expressed in DNA-PKcs -/- mice. Our study identifies an emergent physiological function of DNA-PKcs in regulating neuronal plasticity, beyond genome stability.

The aim of this study was to evaluate the effects of swimming in the brain and behavior of young and aged mice. Forty-eight male C57BL/6 J mice were randomly distributed into 4 groups (n = 12 per group, 3 and 18 months old). The subdivision of the groups was: 3 months-SED, 18 months-SED, 3 months-EXE, and 18 months-EXE. SED mice did not swim, while EXE mice performed the physical exercise protocol. Training was initiated 48 h after the adaptation week. Swimming sessions consisted of 30 min, with no overload, 5 days per week, for 4 weeks. After the exercise protocol, it was revealed working and spatial memory were impaired in the 18 months-SED group. Pre- and post-synaptic proteins were enhanced in the groups that swam when compared to the 3- and 8 months-SED groups. Lipid peroxidation was greater in the aged mice that did not perform the physical exercise protocol and might have contributed to the cognitive impairment in this group. In conclusion, an aerobic physical exercise protocol, performed through regular swimming sessions, inhibited cognitive impairment, memory loss and lipid peroxidation in the aged mice, while pre- and post-synaptic proteins were enhanced in the hippocampus of young and aged mice.

OBJECTIVE: To study the role of the P2X4 receptor (P2X4R) in regulating hippocampal synaptic impairment in lipopolysaccharide (LPS)-induced depression.
METHODS: A rat model of depression was established by LPS injection. P2X4R expression was inhibited by 5-(3-bromophenyl)-1, 3-dihydro-2H-benzofuro[3,2-e]-1,4-diazepin-2-one (5-BDBD). Depressive symptoms were identified through behavioral tests. P2X4R and cytokine mRNA levels were measured by qRT-PCR, while synaptic protein levels were measured by Western blotting. Synaptic ultrastructure was assessed by transmission electron microscopy, and the colocalization of brain-derived neurotrophic factor (BDNF) with microglia, astrocytes, and neurons was determined by double immunofluorescence staining.
RESULTS: Injection of 5-BDBD alleviated LPS-induced depressive symptoms. LPS injection significantly increased the mRNA levels of P2X4R and proinflammatory cytokines in the hippocampus, especially in the CA1 region. The levels of synaptic proteins (BDNF, PSD95, and synapsin I) in the CA1 region were significantly lower than those in the other two regions of the hippocampus, and the synaptic ultrastructure in the hippocampal CA1 region was significantly altered. As expected, the Pearson\'s correlation R and the overlap coefficient R for the hippocampal colocalization of IBA-1 with BDNF were decreased, and 5-BDBD injection reversed these trends. Injection of 5-BDBD increased hippocampal BDNF mRNA expression.
CONCLUSIONS: P2X4R may induce synaptic impairment in the hippocampal CA1 region by influencing microglial BDNF expression in the context of LPS-induced depression in rats.

The present study utilized the spared nerve injury (SNI) to create a mouse model of depression to investigate the impact of esketamine on depressive-like behaviors, on the expression of PSD-95 and CRMP2 proteins, and on changes in neuronal dendritic spine plasticity in the prefrontal cortex (PFC). Depressive-like behavioral tests were performed 1 h after esketamine treatment, and the PFC tissues were obtained on the fourth day after completing the behavioral tests. Then, dendritic spine density and morphology in the PFC were measured using Golgi staining, and CRMP2 and PSD-95 proteins were obtained from PFC tissue by western blotting. The results of this study showed that esketamine significantly increased the immobility time in the forced swimming test and tail suspension test. In the open field test, esketamine increased the time spent in the open arms, the time spent in the central area, and the total distance covered. It also increased the protein expression levels of CRMP2 and PSD-95 in addition to the total and mature dendritic spine density of the PFC in SNI-depressed mice. Esketamine can significantly improve depression-like behaviors in SNI-depressed mice and promote an increase in dendritic spine density and maturation in the PFC. These effects may be associated with changes in CRMP2 and PSD-95 expression.

The postsynaptic density (PSD) comprises numerous scaffolding proteins, receptors, and signaling molecules that coordinate synaptic transmission in the brain. Postsynaptic density protein 95 (PSD-95) is a master scaffold protein within the PSD and one of its most abundant proteins and therefore constitutes a very attractive biomarker of PSD function and its pathological changes. Here, we exploit a high-affinity inhibitor of PSD-95, AVLX-144, as a template for developing probes for molecular imaging of the PSD. AVLX-144-based probes were labeled with the radioisotopes fluorine-18 and tritium, as well as a fluorescent tag. Tracer binding showed saturable, displaceable, and uneven distribution in rat brain slices, proving effective in quantitative autoradiography and cell imaging studies. Notably, we observed diminished tracer binding in human post-mortem Parkinson\'s disease (PD) brain slices, suggesting postsynaptic impairment in PD. We thus offer a suite of translational probes for visualizing and understanding PSD-related pathologies.

BACKGROUND: Growing evidence highlights the role of the spleen-brain axis in inflammation-associated depression. The α7-subtype of nicotinic acetylcholine receptor (α7 nAChR, encoded by the Chrna7 gene) is implicated in systemic inflammation, with Chrna7 knock-out (KO) mice displaying depression-like behaviors. Yet, the influence of spleen nerve on depression-like behaviors in these KO mice remains to be elucidated.
METHODS: We investigated the effects of the splenic nerve denervation (SND) on depression-like behaviors, the protein expression in the prefrontal cortex (PFC), and the gut microbiota composition in Chrna7 KO mice.
RESULTS: SND markedly alleviated depression-like behaviors and the reduced expression of GluA1 and postsynaptic density protein-95 (PSD-95) in the PFC of Chrna7 KO mice. No changes in α-diversity of gut microbiota were noted among the control, KO + sham, and KO + SND groups. However, significant differences in β-diversity of gut microbiota were noted among the groups. Notable alterations in various microbiota (e.g., Fluviimonas_pallidilutea, Maribacter_arcticus, Parvibacter_caecicola) and plasma metabolites (e.g., helicide, N-acetyl-L-aspartic acid, α-D-galactose 1-phosphate, choline, creatine) were observed between KO + sham and KO + SND groups. Interestingly, correlations were found between the relative abundance of specific microbiota and other outcomes, including synaptic proteins, metabolites and behavioral data.
CONCLUSIONS: The underlying mechanisms remain to be fully understood.
CONCLUSIONS: Our findings indicate that the splenic nerve contributes to depression-like phenotypes in Chrna7 KO mice via the spleen-gut-brain axis.

TPN672MA, an innovative antipsychotic drug candidate currently in clinical trials, acts as a dopamine D2/D3 receptor partial agonist, serotonin 5-HT1A receptor agonist, and serotonin 5-HT2A receptor antagonist. Preclinical investigations have demonstrated its potential in treating the core symptoms of schizophrenia. The present study highlights TPN672MA\'s significant antidepressant-like effects in classical behavioral models, such as the chronic social defeat stress paradigm. The pronounced 5-HT1A receptor agonism and D2/D3 receptor partial agonism of TPN672MA likely contribute to its therapeutic effects in depression. Additionally, TPN672MA\'s antidepressant-like efficacy may be linked to its ability to enhance the expression levels of brain-derived neurotrophic factor (BDNF) and postsynaptic density protein-95 (PSD95) in the hippocampus. Furthermore, TPN672MA displayed a more rapid onset of antidepressant-like action. In conclusion, TPN672MA represents a promising new drug candidate for the treatment of symptoms of schizophrenia and depression.