Serotoninergic Structures and Regulation of Pituitary-Adrenal Function

Abstract

The role of mediators in the transmission of the nervous impulse from the preganglionic fiber to the ganglion and from the postganglionic fiber to the effector organ is no longer in question. The principal mediators for peripheral nerves — acetylcholine and noradrenalin — are also sufficiently well known. The problem of the transmission of nervous impulses and the types of connection between single cells in the central nervous system is a much more complex matter. The role of transmitters in this case has been ascribed to a number of different chemical agents, but at the present time three biologically active substances are receiving most attention and are regarded as the most probable mediators. These are, first, compounds whose mediator role for peripheral organs is already established, viz„ acetylcholine and noradrenalin, and in addition, the biogenic amine serotonin.* These compounds are endowed to the greatest possible degree with the properties essential to substances claiming to act as mediators in the central nervous system: 1. All three biologically active substances — acetylcholine, noradrenalin, and serotonin — are present in neurons of the brain (Hebb and Whittaker, 1958; Glowinski and Iversen, 1966a,b; Hillarp et al., 1966a,b; Whittaker, 1966; Bjorklund et al., 1971). It is a very significant fact that these monoamines and acetylcholine are located principally in synaptic endings (Dahlstrom and Fuxe, 1965a; De Robertis et al., 1965; Aghajanian and Bloom, 1966, 1967; Hillarp et al., 1966a,b; Whittaker, 1966; Anden et al., 1969; Clementi et al., 1970). 2. Enzyme systems for the synthesis and inactivation of acetylcholine, the catecholamines, and serotonin are present in the central nervous system (Bogdanski and Udenfriend, 1965; Udenfriend et al., 1957b; Axelrod et al., 1959; Weiner, 1960, 1964; Brodie and Beaven, 1963; Sourkes, 1964; Laverty and Sharman, 1965; Iversen and Glowinski, 1966). 3. Specific mechanisms for absorption and deposition of monoamines exist in the brain (Brodie and Beaven, 1963; Anden et al., 1969). 4. Microelectrophoretic investigations of the central nervous system have shown the presence of specific individual nerve cells responding to local application of acetylcholine, noradrenalin, and serotonin and, consequently, containing cholinergic, adrenergic, or serotoninergic structures (Bloom et al., 1963; Salmoiraghi et al., 1965; Salmoiraghi and Stefans, 1965).