Modulatory actions of steroid hormones and neuropeptides on electrical activity in brain

Electrophysiological studies over the past decades have shown that many com pounds in addition to 'classical' neurotransmitters affect electrical activ ity in the brain. These compounds include neuropeptides synthesized in brai n as well as compounds which are released from peripheral sources and subse quently enter the brain compartment, such as corticosteroid hormones from t he adrenal gland. In the present review, this principle is illustrated by d escribing the effects of two substances, i.e, vasopressin and corticosteron e. Neuropeptides and corticosteroid hormones add at least two essential asp ects to information processing in the brain. First, they both act condition al, i.e. they modulate the actions of 'classical' neurotransmitters, rather than changing basal neuronal activity by themselves. Second, the time-fram e in which modulation of electrical properties takes place differs from tha t generally seen with 'classical' neurotransmitters. Neuropeptides modulate electrical activity over a period of minutes, while effects of corticoster oid hormones usually become apparent after at least an hour but then last f or hours. In this way, neuropeptides and steroid hormones expand the repert oire of responses through which the brain reacts to environmental challenge s. (C) 2000 Elsevier Science B.V. All rights reserved.