Brain cells use neurotransmitters to communicate with themselves and the rest of the body. Neurotransmitters are synthesised in nerve cells, released into the synapse and bind to receptors on the postsynaptic cell. One group of neurotransmitters, collectively called the catecholamines, comprise of the chemicals dopamine, adrenaline and noradrenaline. They are synthesised and released by nerves of the adrenergic pathways. Adrenergic pathways occur in a number of brain areas, particularly the limbic system, and activate the sympathetic branch of the autonomic nervous system. Catecholamines are important in the arousal of emotional and motivational behaviour and in the regulation of the endocrine hypothalamus. By regulation of the hypothalamus they can have an impact on many bodily systems through the release of hormones. Because of their effects, catecholamine levels in the brain can be an important determinant of mental and physical performance. Substances such as cocaine, amphetamine and ephedrine all have a history of abuse by athletes and all act to synthetically increase certain catecholamine neurotransmitters thereby altering the physical, mental and psychological parameters of the human body.
Hard training may reduce neurotransmitter levels in the brain and thereby negatively affect both mental and physical performance levels. Animals that are acutely stressed exhibit characteristic neurochemical and behavioural changes. Depression, fatigue, mood alteration, lack of motivation and strength decrements have all been associated with neurotransmitter depletion. During stressful situations, highly active catecholaminergic neurons may require additional precursors so that catecholamine synthesis can keep pace with the increased amount of neurotransmitters being released. L-Tyrosine, an aromatic amino acid, as well as other neurotransmitter precursors may help supply additional substrate for catecholamine synthesis. Theoretically L-tyrosine can enhance neurotransmission when adrenaline and noradrenaline levels have declined. These declines might occur as a result of long periods of stress or long periods when focused attention is required. L-Tyrosine supplementation holds some promise for being an effective countermeasure to mood and performance degradation. Dietary supplementation of L-tyrosine by athletes may restore neurotransmitter levels and allow optimum physical and mental performance.
