5-HT neuroendocrine responses during psychotropic drug treatment: an investigation of the effects of lithium.

Increasing brain 5-hydroxytryptamine (5-HT) function in humans raises plasma concentrations of prolactin, growth hormone and ACTH. Measurement of these hormonal responses provides an index of the functional activity of brain 5-HT pathways. More recent strategies have included the use of directly-acting 5-HT receptor agonists to probe the function of specific receptor subtypes; at present these studies are limited by the questionable selectivity of the agonists employed. Using 5-HT neuroendocrine testing it can be shown that lithium specifically increases the prolactin release mediated by 5-HT pathways. Further studies are needed to determine if this effect is caused by an enhanced sensitivity of post-synaptic 5-HT1A receptors.