These movements abate during sleep and exacerbate during times of stress. 1 TD may result from long-term dopamine blockade of striatal dopaminergic receptors with resultant hypersensitivity of those receptors. It remains as long as hypersensitivity exists alone, but it becomes irreversible when dopamine receptors have structural changes-with or without an increase in the number of dopamine receptors. Up-regulation of dopamine D 2 receptors in parts of striatum controlling mouth, lip, and tongue motion is more reversible in younger patients. Role of Free Radicals in TD Causation Another causation theory concerns free radical production from metabolism of dopamine, norepinephrine, and antipsychotic drugs.
Antipsychotic agents cause an increase in the metabolic turnover of catecholamines.
Free radicals produced during monoamine oxidation of catecholamines cause cellular damage, producing lipid peroxides that in turn change the membrane characteristics and thereby affect neurotransmission. These processes deplete the natural supply of free radical scavengers. Response to therapy has been limited, and no consensus has emerged supporting use of any of these therapies. 1-4 Naturally occurring vitamin E contains a mixture of eight tocopherols. It occurs naturally in grains, nuts, vegetables, fish, and meats.