Serotonin and stress.

Forty-five years after its discovery, brain serotonin (5-HT) is still the subject of intense research aimed at understanding its role in stress adaptation. At the presynaptic level, numerous stressors increase nerve firing and extracellular 5-HT at the level of serotonergic cell bodies or nerve terminals. Different studies have reported stressor- and region-specific changes in extracellular 5-HT, a view challenged by electrophysiological and neurochemical evidence for a nonspecific response of serotonergic neurones to stressors when activity/arousal is taken into account. In addition, early studies indicate that stress-induced elevation in 5-HT synthesis, a key counter-regulatory process allowing serotonergic homeostasis, is mediated by specific neuroendocrine mechanisms. In addition to the multiplicity of postsynaptic 5-HT receptors and their specific regulation by corticoids, specificity to stressors is also underscored when considering one receptor type such as the 5-HT1A receptor. Stress studies should consider the past experience and the genetic status of the individual as key modulators of the serotonergic responses to stress.