Differential responses by neurotensin systems in extrapyramidal and limbic structures to ibogaine and cocaine.

Ibogaine, a psychoactive compound from the West African shrub Tabernanthe iboga, increases neurotensin-like immunoreactivity (NTLI) in the striatum, nucleus accumbens, and substantia nigra of rats 12 hours after administration, but not in the frontal cortex. These increases are blocked by a D1 dopamine receptor antagonist in all three regions and by a D2 antagonist only in the substantia nigra. Ibogaine pretreatment also blocks cocaine-induced NTLI increases in the striatum and substantia nigra. The findings suggest neurotensin may mediate ibogaine's interactions with the dopamine system and contribute to its pharmacological effects against stimulant addiction.

Study at a glance

Abstract

Ibogaine (Endabuse) is a psychoactive indole alkaloid found in the West African shrub, Tabernanthe iboga. This drug interrupts cocaine and amphetamine abuse and has been proposed for treatment of addiction to these stimulants. However, the mechanism of action that explains its pharmacological properties is unclear. Since previous studies demonstrated differential effects of psychotomimetic drugs (cocaine and methamphetamine) on neuropeptides such as neurotensin (NT), the present study was designed to determine: (1) the effects of ibogaine on striatal, nigral, cortical, and accumbens neurotensin-like immunoreactivity (NTLI); (2) the effects of selective dopamine antagonists on ibogaine-induced changes in NT concentrations in these brain areas; and (3) the effects of ibogaine pretreatment on cocaine-induced changes in striatal, nigral, cortical and accumbens NTLI content. Ibogaine treatments profoundly affected NT systems by increasing striatal, nigral, and accumbens NTLI content 12 h after the last drug administration. In contrast, NTLI concentrations were not significantly increased in the frontal cortex after ibogaine treatment. The ibogaine-induced increases in NTLI in striatum, nucleus accumbens and substantia nigra were blocked by coadministration of the selective D1 receptor antagonist, SCH 23390. The D2 receptor antagonist, eticlopride, blocked the ibogaine-induced increase in nigral NTLI, but not in striatum and nucleus accumbens. Ibogaine pretreatment significantly blocked the striatal and nigral increases of NTLI resulting from a single cocaine administration. Whereas many of the responses by NT systems to ibogaine resembled those which occur after cocaine, there were also some important differences. These data suggest that NT may contribute to an interaction between ibogaine and the DA system and may participate in the pharmacological actions of this drug.