3.5: Section Summary

3.1 General Neurochemistry Principles

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The brain obtains lipids, amino acids, and sugars from the metabolism of fats, proteins, and carbohydrates from the diet. Neurons modify these precursor molecules enzymatically into neurotransmitters, store them inside small lipid-walled vesicles and maintain them until the neuron determines that they should be released. The arrival of an action potential induces the neuron to release its neurotransmitter(s) into the synaptic cleft so that it can interact with specialized receptor proteins floating on the surface of a nearby neuron. The production, storage, release and inactivation of neurotransmitter molecules require the contribution of many genes and proteins, and lots of energy. However, these neurotransmitters are the only way that the majority of neurons in the brain can communicate with each other.

3.2 Neurotransmitters Made from Amino Acids

Neurons in the brain absorb metabolites of the food we consume and enzymatically convert them into neurotransmitters. Sometimes the conversion process involves multiple enzymes working together; in contrast, sometimes amino acids become neurotransmitters with little or no modification. The function of these neurotransmitters is determined by the region of the brain they innervate, the type and location of the receptor, and the nature of the mechanisms induced by the receptor. Numerous cognitive disorders and neurological diseases involve dysfunction or degeneration of one or more of these neural systems. An understanding of the chemistry of these neurotransmitters has led to many effective and safe drugs to treat these disorders and diseases.

3.3 Neurotransmitters Made from Fats

Fatty acids obtained from either the diet or pieces of neural membrane are modified into neurotransmitters. In contrast to the amino acid-derived neurotransmitters, two of the fatty acid-derived neurotransmitters discussed are not stored in vesicles; they are produced and immediately released only when needed. Their diffuse distribution underlies the large variety of functions that are assigned to them, including the control of mood, learning and memory and pain. Dysfunction of acetylcholine is well known and studied. In contrast, much less is known about the functions of the endocannabinoid system.