Functional synapses require mitochondria to supply ATP and regulate local [Ca2+]i for neurotransmission. Mitochondria are thought to be transported to specific cellular regions of increased need such as synapses. However, little is known about how this occurs, including the spatiotemporal distribution of mitochondria relative to presynaptic and postsynaptic sites, whether mitochondria are dynamically recruited to synapses, and how synaptic activity affects these trafficking patterns. We used primary cortical neurons in culture that form synaptic connections and show spontaneous synaptic activity under normal conditions. Neurons were cotransfected with a mitochondrially targeted cyan fluorescent protein and an enhanced yellow fluorescent protein-tagged synaptophysin or postsynaptic density-95 plasmid to label presynaptic or postsynaptic structures, respectively. Fluorescence microscopy revealed longer dendritic mitochondria that occupied a greater fraction of neuronal process length than axonal mitochondria. Mitochondria were significantly more likely to be localized at synaptic sites. Although this localization was unchanged by inhibition of synaptic activity by tetrodotoxin, it increased in dendritic synapses and decreased in axonal synapses during overactivity by veratridine. Mitochondrial movement and recruitment to synapses also differed between axons and dendrites under basal conditions and when synaptic activity was altered. Additionally, we show that movement of dendritic mitochondria can be selectively impaired by glutamate and zinc. We conclude that mitochondrial trafficking to synapses is dynamic in neurons and is modulated by changes in synaptic activity. Furthermore, mitochondrial morphology and distribution may be optimized differentially to best serve the synaptic distributions in axons and dendrites. Last, selective cessation of mitochondrial movement in dendrites suggests early postsynaptic dysfunction in neuronal injury and degeneration.

https://www.jneurosci.org/content/jneuro/26/26/7035.full.pdf

Mitochondrial Trafficking to Synapses in Cultured Primary Cortical Neurons

Mitochondrial biogenesis and healthy aging

Background and Purpose— Studies on adult stroke patients have demonstrated functional changes in cortical excitability, metabolic rate, or blood flow after motor therapy, measures that can fluctuate rapidly over time. This study evaluated whether evidence could also be found for structural brain changes during an efficacious rehabilitation program. Methods— Chronic stroke patients were randomly assigned to receive either constraint-induced movement therapy (n=16) or a comparison therapy (n=20). Longitudinal voxel-based morphometry was performed on structural MRI scans obtained immediately before and after patients received therapy. Results— The group receiving constraint-induced movement therapy exhibited far greater improvement in use of the more affected arm in the life situation than the comparison therapy group. Structural brain changes paralleled these improvements in spontaneous use of the more impaired arm for activities of daily living. There were profuse increases in gray matter in sensory and mo...

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Remodeling the Brain Plastic Structural Brain Changes Produced by Different Motor Therapies After Stroke

Physical activity enhances hippocampal function but its effects on neuronal structure remain relatively unexplored outside of the dentate gyrus. Using Golgi impregnation and the lipophilic tracer DiI, we show that long-term voluntary running increases the density of dendritic spines in the entorhinal cortex and hippocampus of adult rats. Exercise was associated with increased dendritic spine density not only in granule neurons of the dentate gyrus, but also in CA1 pyramidal neurons, and in layer III pyramidal neurons of the entorhinal cortex. In the CA1 region, changes in dendritic spine density are accompanied by changes in dendritic arborization and alterations in the morphology of individual spines. These findings suggest that physical activity exerts pervasive effects on neuronal morphology in the hippocampus and one of its afferent populations. These structural changes may contribute to running-induced changes in cognitive function.

/pdf/running-induces-widespread-structural-alterations-in-the-31fva5z9pq.pdf

Running induces widespread structural alterations in the hippocampus and entorhinal cortex

The neurobiology of brain and cognitive reserve: mental and physical activity as modulators of brain disorders.

Neurogenesis in the mammalian brain continues throughout adulthood. Several factors have been shown to influence neurogenesis, including experience in a complex environment (EC), exercise (EX), and ischemic insult. The authors investigated the effects of behavioral rehabilitation training following transient global cerebral ischemia on the number of new cells in the dentate gyrus that incorporated bromodeoxyuridine (BrdU), a thymidine analog that labels cells undergoing DNA replication. Seventy-two animals were included in the study, and 4-vessel occlusion was used to induce cerebral ischemia while control animals were subjected to anesthesia and sham surgery alone. Within 3 days of surgery, rats were randomly assigned to either EC, EX, or control (paired housing in standard laboratory conditions) groups. All animals were sacrificed 2 weeks after behavioral training. Immunohistochemistry results showed an increased number of BrdU-labeled cells in the subgranular zone of the dentate gyrus in all ischemic groups and in the EC and EX sham groups, although no significant group differences were seen. Examination of cell phenotype showed that almost all BrdU-positive cells colabeled with TuJ1, an immature neuron marker, in all animals whereas only a few BrdU-positive cells colabeled with NeuN, a mature neuron marker. BrdU/NeuN-labeled cells were seen only in the sham and ischemia EC groups. No new cells showed glial fibrillary acidic protein, astrocyte marker, colabeling. These results suggest that the adult brain has an inherent regenerative capacity after insult and that behavioral training following injury does not have an additive effect on neurogenesis. Finally, the enhanced maturation of BrdU-positive cells seen in the EC rats is probably modulated by environmental cues.

Dentate Gyrus Neurogenesis after Cerebral Ischemia and Behavioral Training

Behaviorally induced synaptogenesis and dendritic growth in the hippocampal region following transient global cerebral ischemia are accompanied by improvement in spatial learning.

Changes in number of synapses and mitochondria in presynaptic terminals in the dentate gyrus following cerebral ischemia and rehabilitation training.

Astrocytic changes in the hippocampus and functional recovery after cerebral ischemia are facilitated by rehabilitation training.

Age is the biggest risk factor for the development of neurodegenerative diseases. Consequently, as the population ages it becomes more critical to find ways to avoid the debilitating cost of neurodegenerative diseases such as Alzheimer's. Some of the non-invasive strategies that can potentially slow down the mental decline associated with aging are exercise and use of multi-sensory environmental stimulation. The beneficial effects of both exercise and multi-sensory environmental stimulation have been well-documented, thus it is possible that these strategies can either provide neuroprotection or increase resistance to the development of age-related cognitive problems.

Teresita L. Briones

Papers

Dentate Gyrus Neurogenesis after Cerebral Ischemia and Behavioral Training

Behaviorally induced synaptogenesis and dendritic growth in the hippocampal region following transient global cerebral ischemia are accompanied by improvement in spatial learning.

Changes in number of synapses and mitochondria in presynaptic terminals in the dentate gyrus following cerebral ischemia and rehabilitation training.

Astrocytic changes in the hippocampus and functional recovery after cerebral ischemia are facilitated by rehabilitation training.

Environment, Physical Activity, and Neurogenesis: Implications for Prevention and Treatment of Alzhemiers Disease