Barriers and fluids that connect and divide blood, brain, and neurons

Methodology — Tags: , , , — 11:07 am

BRAIN EXTRACELLULAR FLUID

Read also: The History of Artificial Cerebrospinal Fluid (ACSF)

The brain is protected by a rigid bony case so it cannot expand in the case of fluid imbalance. Because of that, the brain needs to tightly control the flux across the cerebral capillaries and this line of defence or restriction of chemical communications between blood and brain, called blood-brain barrier, was introduced by the work of Erhlich et al., in nineteenth century and the classic experiment of Goldman confirmed the concept of the blood-brain barrier (reviewed in 1). (more…)

The astrocyte–neuron ketone body shuttle

Astrocyte–neuron ketone shuttle,Ketone bodies — Tags: , , , , — 6:20 am

In the brain, to each one neurone, there are 9 astrocytes (1). They are surrounded by capillaries and are close to the both blood-brain and blood-cerebrospinal “the first cellular barrier encountered by glucose entering the brain tissue, which makes them a prevalent site of glucose uptake”(2)

Astrocytes interacts with neurons and synapses; they express neurotransmitter receptors and transporters. The delivery of lactate from astrocytes to neurons is enhanced during increased synaptic activity. But astrocytes (according to 2) are also able to process fatty acids for the ketogenesis depending on neuronal energy demands. The ketone bodies and acetoacetate can replace glucose as the major source of brain energy during starvation and in the immature brain. Ketone bodies produced by astrocytes seem to be used together with lactate as substrates for neuronal oxidative metabolism in situations such as enhanced synaptic activity and hypoxia . (more…)

The Selfish Brain Theory

Energy Homeostasis,The selfish brain,Theories — Tags: , , , , , — 7:55 am

The unique position of the brain as a body organ is characterized by:

1. its chemical isolation from the rest of the body by the blood-bran barrier
2. its high energy consumption: though weighing as little as 2% of the body mass the brain consumes above 20% of all available energy
3. its low energy depot capacity,
4. its energy substrate selectivity,
5. its plasticity – ability to adjust reactions to circumstances and learn how to anticipate the consequences,
6. its ability to record information from both peripheral organs and its own environment.
So how these peculiarities of the brain’s energy demands are being satisfied by the entire organism and how do they influence the way organism works?

Researchers from University of Luebeck and Universite de Lausanne proposed a new framework for describing the regulation of energy flow in the organism. In the article “The selfish brain: competition for energy resources” they wrote:

“The brain prioritizes adjustment of its own ATP concentration. For this reason it activates its stress system and in so doing competes for energy resources with the rest of the organism (allocation). The brain then alters the appetite (food intake) so that it can alleviate the stress system and return it to a state of rest.”

Important points of the process of restoration of homeostatic balancing of energy supply are the following:

  1. When there’s a shortage of of glucose-based energy supply in the body, glucose allocation to the brain is provided anyway, even if the rest of the body is energy-starving.
  2. Alternative substrates than can provide a portion of the brains energy supply, such as ketones, lead to a “disburdening” of the regulatory system.
  3. This “disburdening” of the regulatory system works through ketogenesis, to ensure which the lipolysis starts leading to body mass reduction.
  4. Replenishment of the stores can be later possible due to glucose allocation to the muscle and adipose tissue leading to normalization of body mass.
  5. Return of the system of glucose sensors (in hypothalamus) in the brain to a state of balance (setpoint).


 

 

 

 

Source: Neuroscience and Biobehavioral Reviews 28 (2004) 143-180

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