Antagonism of Synaptic Transmission in vivo: Contributions of Microiontophoresis

Abstract

Fundamental to the problems in the study of synaptic transmission in the mammalian CNS is the identification of the nature and role of transmitter substances at prescribed loci. Although recently many advances have been made in determining which compounds are endogenous to the CNS and which of these and other molecules alter neuronal activity, there can be little doubt that, at the present level of understanding of such brain constituent, merely a few of the basic materials requisite for the normal functioning of central neurones are known. Some 60 or 70 substances have been postulated as candidates for involvement in synaptic processes. Many of the receptors for these and closely related compounds have been characterized pharmacologically through the examination of the effects of agonists and antagonists. One technique which has played a principal role in these neuropharmacological investigations is the method of local drug administration termed microiontophoresis. Although this method is invaluable for helping to answer questions at the molecular and membrane level, under circumscribed conditions its advantages may be exploited for use in experiments oriented toward a more physiological level of investigation. A description of some of these conditions, and of some of the creative ways in which microiontophoresis has been utilized in vivo to reveal mechanisms by which the CNS processes information at the synaptic levels is noted.