DIFFERENTIAL AUTORECEPTOR CONTROL OF SOMATODENDRITIC AND AXON TERMINAL DOPAMINE RELEASE IN SUBSTANTIA-NIGRA, VENTRAL TEGMENTAL AREA, AND STRIATUM

Dopamine (DA) is released from somatodendritic sites of neurons in the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA] , where it has neuromodulatory effects. The aim of this study was to e valuate the role of D-2 autoreceptor inhibition in the regulation of t his somatodendritic release in each region. Fast cyclic voltammetry at carbon fiber microelectrodes was used to measure electrically evoked DA release in vitro. Furthermore, we compared D-2 regulation of somato dendritic release with the more familiar axon terminal release in caud ate putamen (CPu) and nucleus accumbens (NAc). Evoked DA release was T TX-sensitive at all sites. There was significant D-2 autoinhibition of DA release in SNc; however, this mechanism was two-to threefold less powerful, as compared with axon terminal release in CPu. In contrast t o SNc, somatodendritic release in VTA was not under significant D, rec eptor control, whereas release in the respective axon terminal region (NAc) was controlled strongly by autoinhibition. Thus, these data indi cate that, first, autoinhibition via D-2 receptors consistently plays a less significant role in the control of somatodendritic than axon te rminal DA release, and, second, even at the level of somatodendrites t hemselves, D-2 autoinhibition displays marked regional variation. In t he light of previous data indicating that DA uptake processes are also less active in somatodendritic than in terminal regions, these result s are interpreted as indicating that DA transmission is regulated diff erently in somatodendritic zones, as compared with axon terminals, and thus may have different functional consequences.