Antagonism of synaptic transmission in vivo: contributions of microiontophoresis.

Fundamental to the problems in the study of synaptic transmission in the mammalian central nervous system 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 central nervous system and which of these and other molecules alter neuronal activity, there can be little doubt that at the present level of our understanding of such brain constituent we are encountering merely a few of the basic materials requisite for the normal functioning of central neurones. Some 60 or 70 substances have now 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. This short account is an attempt to provide a description of some of these conditions and further will describe some of the creative ways in which microiontophoresis has been utilized in vivo to reveal mechanisms by which the central nervous system processes information at the synaptic level.