Because of the vital role that<unk> s play in the inactivation of neurotransmitters,<unk>  dysfunction (too much or too little<unk>  activity) is thought to be responsible for a number of psychiatric and neurological disorders. For example, unusually high or low levels of<unk> s in the body have been associated with schizophrenia, depression, attention deficit disorder, substance abuse, migraines, and irregular sexual maturation.<unk>  inhibitors are one of the major classes of drug prescribed for the treatment of depression, although they are often last-line treatment due to risk of the drug's interaction with diet or other drugs. Excessive levels of catecholamines (epinephrine, norepinephrine, and dopamine) may lead to a hypertensive crisis, and excessive levels of serotonin may lead to serotonin syndrome. In fact,<unk> -A inhibitors act as antidepressant and anti-anxiety agents, whereas<unk> -B inhibitors are used alone or in combination to treat Alzheimer's disease and Parkinson's disease. Some research suggests that certain phenotypes of depression, such as those with anxiety, and "atypical" symptoms involving psychomotor retardation, weight gain and interpersonal sensitivity. However the findings related to this have not been consistent.<unk> Is may be effective in treatment resistant depression, especially those that do not respond to tricyclic antidepressants. PET research shows that use of tobacco cigarettes heavily depletes<unk> -B, mimicking the action of an<unk> -B inhibitor. Smokers who smoke for emotional relief may therefore be unintentionally treating depression and/or anxiety that is better addressed by an<unk> -B inhibitor. Parasite interactions Sleeping sickness - caused by trypanosomes - gets its name from the sleep disruption it causes in mammals. That sleep disruption is caused, at least in part, by trypanosomes' tendency to disrupt<unk>  activity in the orexin system. Animal models There are significant differences in<unk>  activity in different species. Dopamine is primarily deaminated by<unk> -A in rats, but by<unk> -B in vervet monkeys and humans. Mice unable to produce either<unk> -A or<unk> -B display autistic-like traits. These knockout mice display an increased response to stress. Arthropods Insects Insect brains express<unk> s, and some insecticides work by inhibiting them. An<unk> I effect is especially important for chlordimeform (although one result shows little or no effect in Periplaneta americana); and dieldrin may or may not be an<unk> I in Locusta migratoria. Acari<unk>  activity has been detected in Rhipicephalus microplus and chlordimeform is an<unk> I in R. m..
Monoamine oxidase
Tyrosine hydroxylase
Catechol-O-methyltransferase
Phenylalanine hydroxylase
Glutamate dehydrogenase
Dopamine beta-hydroxylase
Aromatic L-amino acid decarboxylase
Flavin containing monooxygenase 1