The combined effects of corticosterone and brain-derived neurotrophic factor on plasticity-related receptor phosphorylation and expression at the synaptic surface in male Sprague-Dawley rats

Following acute exercise, a temporal window exists wherein neuroplasticity is thought to be heightened. Although a number of studies have established that pairing this post-exercise period with motor training enhances learning, the mechanisms through which exercise-induced priming occurs are not well understood. Previously, we characterized a rodent model of acute exercise that generates significant enhancement in glutamatergic receptor phosphorylation as a possible mechanism to explain how exercise-induced priming might occur. However, whether these changes are stimulated by peripheral factors (e.g., glucocorticoids), central effects (e.g., brain-derived neurotrophic factor (BDNF), or a combination of the two remains unclear. Herein, we explored the possible individual and/or cumulative contribution corticosterone (CORT) and BDNF may have on glutamate receptor phosphorylation and synaptic surface expression. Tissue slices from the sensorimotor cortex were prepared and acutely (30 min) incubated with either CORT (200 nM), BDNF (20 ng/mL), or the simultaneous application of CORT and BDNF (CORT+BDNF). Immunoblotting with biotinylated synaptoneurosomes (which provide an enrichment of proteins from the synaptic surface) suggested divergent effects between CORT and BDNF. Acute CORT application enhanced NMDA- (GluN2A, B) and AMPA- (GluA1) receptor phosphorylation, whereas BDNF preferentially increased synaptic surface expression of both NMDA- and AMPA-receptor subunits. The combined effects of CORT+BDNF resulted in a unique subset of signaling patterns that favored phosphorylation in the absence of surface expression. Taken together, these data provide a mechanistic framework for how CORT and BDNF may alter glutamatergic synapses during exercise-induced priming.

Ketamine Rescues Hippocampal Reelin Expression and Synaptic Markers in the Repeated-Corticosterone Chronic Stress Paradigm

Depression is the leading cause of disability worldwide, which necessitates novel therapeutics and biomarkers to approach treatment of this neuropsychiatric disorder. To assess potential mechanisms underlying the fast-acting antidepressant actions of ketamine we used a repeated corticosterone paradigm in adult male rats to assess the effects of ketamine on reelin-positive cells, a protein largely implicated in the pathophysiology of depression. We also assessed the effects of reelin and ketamine on hippocampal and cerebellar synpatosomes, and on serotonin transporter clustering in peripheral lymphocytes to determine reelin and ketamine's impact at the synaptic and peripheral levels. Reelin and ketamine similarly rescue synaptic expression of mTOR and p-mTOR that were decreased by corticosterone. Reelin, but not ketamine, was able to rescue patterns of serotonin transporter clustering in the periphery. These findings display ketamine as a powerful modulator of reelin expression and lend strength to further evaluation of the putative fast antidepressant-like actions of reelin.

Interplay between hormones and exercise on hippocampal plasticity across the lifespan

The hippocampus is a brain structure known to play a central role in cognitive function (namely learning and memory) as well as mood regulation and affective behaviors due in part to its ability to undergo structural and functional changes in response to intrinsic and extrinsic stimuli. While structural changes are achieved through modulation of hippocampal neurogenesis as well as alterations in dendritic morphology and spine remodeling, functional (i.e., synaptic) changes can be noted through the strengthening (i.e., long-term potentiation) or weakening (i.e., long-term depression) of the synapses. While age, hormone homeostasis, and levels of physical activity are some of the factors known to module these forms of hippocampal plasticity, the exact mechanisms through which these factors interact with each other at a given moment in time are not completely understood. It is well known that hormonal levels vary throughout the lifespan of an individual and it is also known that physical exercise can impact hormonal homeostasis. Thus, it is reasonable to speculate that hormone modulation might be one of the various mechanisms through which physical exercise differently impacts hippocampal plasticity throughout distinct periods of an individual's life. The present review summarizes the potential relationship between physical exercise and different types of hormones (namely sex, metabolic, and stress hormones) and how this relationship may mediate the effects of physical activity during three distinct life periods, adolescence, adulthood, and senescence. Overall, the vast majority of studies support a beneficial role of exercise in maintaining hippocampal hormonal levels and consequently, hippocampal plasticity, cognition, and mood regulation.

Building your best day for healthy brain aging-The neuroprotective effects of optimal time use

As the number of older people increases, so too does the prevalence of neurodegenerative disease. Worldwide, health organisations have identified the need for practical, affordable interventions to slow or delay the onset of neurodegenerative diseases such as dementia, for which there are multiple modifiable risk factors. The effects of various interventions on brain health has been investigated, including achieving sufficient physical activity, getting appropriate amounts and quality of sleep, and limiting sedentary behaviours. Few of these studies, though, have taken into account more than one lifestyle behaviour within a single study. Epidemiologists have recently initiated a paradigm shift to move away from studying the independent effects of each physical activity, sleep and sedentary behaviour, and towards an integrated 24-h time-use paradigm. Time is finite, and thus to increase time in one activity (for example physical activity), equal time must be taken away from other activities (sleep and sedentary behaviour). This 24-h time-use paradigm has begun to be used when studying obesity, adiposity and quality of life; however, to the authors' knowledge, it has not yet been adopted by cognitive neuroscientists for the study of cognition or brain function. This narrative review synthesises the evidence for the neurophysiological effects of physical activity, sleep and sedentary behaviour independently, with a particular focus on brain structure, function and neurodegenerative disease risk. Then, we conclude with a call to action, addressing the need for studies to move towards an integrated 24-h time-use paradigm.

The influence of an acute bout of aerobic exercise on cortical contributions to motor preparation and execution

Increasing evidence supports the use of physical activity for modifying brain activity and overall neurological health. Specifically, aerobic exercise appears to have a positive effect on cognitive function, which some have suggested to be a result of increasing levels of arousal. However, the role of aerobic exercise on movement-related cortical activity is less clear. We tested the hypothesis that (1) an acute bout of exercise modulates excitability within motor areas and (2) transient effects would be sustained as long as sympathetic drive remained elevated (indicated by heart rate). In experiment 1, participants performed unimanual self-paced wrist extension movements before and after a 20-min, moderate intensity aerobic exercise intervention on a recumbent cycle ergometer. After the cessation of exercise, Bereitschaftspotentials (BP), representative cortical markers for motor preparation, were recorded immediately postexercise (Post) and following a return to baseline heart rate (Post[Rest]). Electroencephalography (EEG) was used to measure the BP time-locked to onset of muscle activity and separated into three main components: early, late and reafferent potentials. In experiment 2, two additional time points postexercise were added to the original protocol following the Post[Rest] condition. Early BP but not late BP was influenced by aerobic exercise, evidenced by an earlier onset, indicative of a regionally selective effect across BP generators. Moreover, this effect was sustained for up to an hour following exercise cessation and this effect was following a return to baseline heart rate. These data demonstrate that acute aerobic exercise may alter and possibly enhance the cortical substrates required for the preparation of movement.