The relationship between the functional activity of the brain, energy supply, pH and blood flow

A significant proportion of all the energy expended by the brain goes to the creation and maintenance of membrane potentials of nerve and glial cells, as well as to the transport of substances through the BBB. The generation of all types of membrane potentials is associated with the energy consumption necessary to create and maintain ionic gradients and the functioning of onion pumps .

With an increase in the functional activity of the brain, cerebral energy exchange increases: energy consumption of glucose increases, as a result of its aerobic and anaerobic oxidation, the production of HCO 3 – and lactate is increased, which requires an increase in local cerebral blood flow.

The main factor causing an increase in local cerebral blood flow is the accumulation of potassium ions in the intercellular space, under the influence of which the small cerebral vessels expand. The content of potassium ions in the intercellular fluid increases with the depolarization of nerve cells and glia, resulting from an increase in neural activity.

Hydrogen ions, the concentration of which increases with increasing functional activity of the brain due to the formation of HCO 3 – and lactate during aerobic and anaerobic oxidation of glucose, also contribute to an increase in local cerebral blood flow . In both systems ontogenesis (glucose consumption and local blood flow) are developed independently of each other uga .

In experimental animals, after 1-2 second photostimulation, the pH of the intercellular fluid of the brain shifts to the alkaline side (apparently, due to the compensatory increase in blood flow and leaching of H + ions ), and after 10-15 seconds – into acidic. Acidosis reaches a maximum after the termination of stimulation and is maintained up to 4-5 minutes. The cause of acidosis is the accumulation of lactate and other acidic metabolic products. In epileptic seizures, at the initial stage, alkalosis occurs due to leaching of hydrogen ions by enhanced cerebral blood flow, and then persistent acidosis develops, and the pH shift reaches 0.2 units .

Using NMR spectroscopy, it was shown that prolonged activation of the human brain is accompanied by its acidification. Changes in glucose consumption, lactate production and blood oxygenation were measured with prolonged neuronal stimulation (4-6 min) in the primary visual cortex. A decrease in glucose level due to an increase in its consumption was accompanied by a transient increase in lactate 2.5 minutes after the start of stimulation. Rapidly occurring blood oversignition indicated a separation of blood flow and oxidative metabolism, which returned to normal compliance after 3 minutes. Thus, the initial anoxic conversion of glucose during functional activation gradually turns into aerobic oxidation, while the intensity of blood flow and oxygen consumption is set at a new, higher level .

Many authors indicate an increase in the role of glycolysis with an increase in the functional activity of the brain. The concentration of lactate in the brain is assumed to be stable with the exception of the mismatch between glycolysis and respiration, which is observed with significant stress. Using NMR spectroscopy, which allows you to measure lactate in vivo, recorded an increase in lactate by 0.3-0.9 mm in the visual cortex in humans with photostimulation. The maximum growth was observed during the first minutes of stimulation, after which, despite its continuation, the concentration of lactate decreased. These results are consistent with transient predominance of glycolysis aerobic oxidation in the visual cortex, which is observed in the normal physiological range at fotostimu lyatsii .

local_offerevent_note September 25, 2019

account_box admin

Leave a Reply

Your email address will not be published. Required fields are marked *