Article: mitochondria, viral spread, estrogen, and ketones.

[Ema]

Every time it fires, a neuron is invaded by sodium ions. If enough of them have gotten inside, channels are unblocked that let calcium ions in as well.

Both types of ions must be removed before the neuron can fire again; mitochondria give a hand by temporarily locking calcium away and dispensing energy for other structures in the neuron to do so.

When somewhere in the neuron ATP runs low or calcium gets in, approaching mitochondria are disengaged from the transport system so that they can do their job at that particular site (Sheng & Cai, 2012).

However, an inordinate accumulation of calcium in mitochondria causes them to kill both their host neuron and themselves—which can happen when firing is excessive, as in epileptic seizures (Delorenzo, Sun, & Deshpande, 2005).

As shown in vitro, the cold sore virus (herpes-simplex virus type 1) can boost neuronal calcium levels while at the same time impeding mitochondria from killing their host. The raised calcium levels prevent the transport system from taking mitochondria as passengers and possibly allow the virus to take a ride instead, speeding up its spread through the brain (T. Kramer & Enquist, 2012).

As an interesting aside, the formation of donuts can be prevented by antioxidants, and estrogen is a formidable one. If female monkeys’ ovaries are removed, a maneuver that cuts off estrogen and induces menopause, the number of misshaped mitochondria increases nearly by half and monkeys become much worse on the test. Both changes are reversed by cyclic injections of estrogen—suggesting that it is, at least partly, by restoring mitochondrial health that hormone replacement therapy may improve cognitive functioning (Hara et al., 2014; Sherwin, 1988)

During sleep, the body and brain continue to spend energy, but the usual source of that energy, glucose, is gradually depleted and not replenished. The same happens during prolonged exercise. Mitochondria must switch to burning something else, and on that account the liver breaks down stored fat into molecules called ketone bodies. This switch means that metabolic circumstances have changed; besides acting as a circulating source of energy, ketone bodies appear to serve as carriers of this useful piece of information too (Newman & Verdin, 2014; Sleiman et al., 2016). Through the bloodstream, they reach the brain where they proceed to signal the news by regulating gene expression— targeting specifically the gene responsible for the production of BDNF.

Full text here: http://journals.sagepub.com/doi/pdf/10.1177/1745691617718356