The ameliorating effect of exercise on long-term memory impairment and dendritic retraction via the mild activation of AMP-activated protein kinase in chronically stressed hippocampal CA1 neurons

AMP-Activated Protein Kinase Treatment Ameliorates Chronic Restraint Stress Induced Memory Impairment in Early Adolescent Rat by Restoring Metabolite Profile and Synaptic Proteins

Recent studies highlight the role of brain metabolites in regulation of neuronal signals and behaviour. To understand the underlying mechanism, brain metabolites and associated signaling molecules were examined in early adolescent rat experienced CRS. Rats were tested for their learning and memory ability, and their metabolite profile was evaluated using Gas chromatography-mass spectrometry (GC-MS). Differences in metabolites were examined by variable importance in projection (VIP) and multivariate analysis. Ingenuity Pathway Analysis (IPA) and KEGG ID were performed for the identified metabolites. We found that CRS altered the metabolites that were involved in biosynthesis of steroid hormone, aminoacyl t-RNA, L-Dopa biosynthesis, and metabolism of tyrosine, fatty acid, and purine. Further analysis showed reduction of 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR, a metabolite involved in purine metabolism) an AMP kinase activator, influenced the hypoxanthine-guanine phosphoribosyltransferase (HPRT), serotonin transporter (SERT), postsynaptic density protein (PSD) -95, its phosphorylation and brain-derived neurotrophic factor (BDNF) in CRS animals, which displayed deficit in memory. The AICAR treated CRS rats showed improved memory and altered metabolites and other molecules (HPRT, SERT, PSD-95 and BDNF) levels were restored. Our analysis revealed that CRS induced changes in metabolites possibly altered synaptic plasticity and memory in which HPRT, SERT-PSD95-BDNF associated pathway involved. Taken together, our observation provides initial insight into how stress differently influences the metabolic pathway, and associated behaviour. Further study will help to develop pharmacological intervention strategies.

Central Adiponectin Signaling – A Metabolic Regulator in Support of Brain Plasticity

Brain plasticity and metabolism are tightly connected by a constant influx of peripheral glucose to the central nervous system in order to meet the high metabolic demands imposed by neuronal activity. Metabolic disturbances highly affect neuronal plasticity, which underlies the prevalent comorbidity between metabolic disorders, cognitive impairment, and mood dysfunction. Effective pro-cognitive and neuropsychiatric interventions, therefore, should consider the metabolic aspect of brain plasticity to achieve high effectiveness. The adipocyte-secreted hormone, adiponectin, is a metabolic regulator that crosses the blood-brain barrier and modulates neuronal activity in several brain regions, where it exerts neurotrophic and neuroprotective properties. Moreover, adiponectin has been shown to improve neuronal metabolism in different animal models, including obesity, diabetes, and Alzheimer’s disease. Here, we aim at linking the adiponectin’s neurotrophic and neuroprotective properties with its main role as a metabolic regulator and to summarize the possible mechanisms of action on improving brain plasticity via its role in regulating the intracellular energetic activity. Such properties suggest adiponectin signaling as a potential target to counteract the central metabolic disturbances and impaired neuronal plasticity underlying many neuropsychiatric disorders.

Brain-derived neurotrophic factor upregulates synaptic GluA1 in the amygdala to promote depression in response to psychological stress

Psychological stress impairs neuronal structure and function and leads to emotional disorders, but the underlying mechanisms have not yet been fully elucidated. The amygdala is closely correlated with emotional regulation. In the present study, we analyzed whether the amygdala plasticity is regulated by psychological stress and explored their regulatory mechanism. We established a mouse psychological stress model using an improved communication box, wherein mice were exposed to chronic fear and avoided physical stress interference. After the 14-day psychological stress paradigm, mice exhibited significantly increased depressive behaviors (decreased sucrose consumption in the sucrose preference test and longer immobility time in the forced swimming test). HPLC, ELISA, and molecular and morphological evidences showed that psychological stress increased the content of glutamate and the expression of glutamatergic neurons, upregulated the content of the stress hormone corticosterone, and activated the CREB/BDNF pathway in the amygdala. Furthermore, psychological stress induced an increased density of dendritic spines and LTD impairment in the amygdala. Importantly, virus-mediated silencing of BDNF in the basolateral amygdala (BLA) nuclei reversed the depression-like behaviors and the increase of synaptic GluA1 and its phosphorylation at Ser831 and Ser845 sites in psychologically stressed mice. This process was likely achieved through mTOR signaling activation. Finally, we treated primary amygdala neurons with corticosterone to mimic psychological stress; corticosterone-induced upregulation of GluA1 was prevented by BDNF and mTOR antagonists. Thus, activation of the CREB/BDNF pathway in the amygdala following psychological stress upregulates synaptic GluA1 via mTOR signaling, which dysregulates synaptic plasticity of the amygdala, eventually promoting depression.