histamine

n. a compound that is synthesized from the amino acid histidine by the enzyme histidine decarboxylase. Most histamine in humans is localized in peripheral tissues, where it is involved in allergic reactions or the inflammatory response to injury, causing dilation of blood vessels. In the brain, histamine acts as a neurotransmitter to modulate such functions as arousal, appetite, and regulation of autonomic functions. Histamine receptors can be divided into three categories, designated H₁, H₂, and H₃ receptors. Many antidepressants and antipsychotics may block histamine receptors in the brain, causing sedation and other side effects.

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Psychology term of the day

May 8th 2024

valence–instrumentality–expectancy theory

a theory of work motivation holding that the level of effort exerted by employees will depend on a combination of three variables: (a) the expectancy of employees that effort will lead to success in the job, (b) the belief of employees that success will lead to particular outcomes (see instrumentality theory), and (c) the value of these outcomes (see valence). A numerical value can be obtained for variable (a) using the subjective probability estimates of employees, for variable (b) by measuring the correlation of performance to rewards, and for variable (c) by asking employees to rate the desirability of the rewards. The motivational force, or the amount of effort employees will exert, can then be calculated. See also path–goal theory of leadership; Porter–Lawler model of motivation. [proposed in 1964 by Canadian organizational psychologist Victor H. Vroom (1932– )]