EFFECTS OF IBOGAINE, AND COCAINE AND MORPHINE AFTER IBOGAINE, ON VENTRAL TEGMENTAL DOPAMINE NEURONS

Ibogaine, an indole containing alkaloid, has been shown to reduce the rate of injection of morphine and cocaine in self-administration proto cols. Since morphine- and cocaine-induced modulation of dopamine relea se is impulse dependent and essential for their reinforcing effects, d isruption of dopamine neuronal activity by ibogaine could explain its purported 'antiaddictive' properties. Therefore, the present study was designed to determine. (1) the acute effects of ibogaine on the activ ity of VTA dopamine neurons, and (2) whether ibogaine pretreatment cau ses a persistent modification of the dopamine neuronal response to mor phine and cocaine. Extracellular recordings in anesthetized animals fo und that intravenous ibogaine markedly excited VTA dopamine neuronal f iring. However, ibogaine pretreatment (6-8 hr and 19 hr before) failed to alter either the spontaneous activity of VTA neurons, or the respo nse of these dopamine neurons to morphine or cocaine. Thus, ibogaine's excitatory effect on VTA neurons is not longlasting nor does it persi stently alter cocaine- or morphine-induced changes in dopamine neuron impulse activity. Therefore, other mechanisms must be explored to acco unt for the proposed antiaddictive properties of ibogaine.