Ibogaine Administration Modifies GDNF and BDNF Expression in Brain Regions Involved in Mesocorticolimbic and Nigral Dopaminergic Circuits.

Ibogaine is an indole alkaloid traditionally used as a psychedelic and has attracted scientific interest because uncontrolled clinical observations and animal studies report reductions in craving and self-administration for several drugs of abuse after single large doses. Earlier preclinical work suggested that ibogaine’s long-lasting anti-addictive effects may be mediated in part by increased Glial Cell Derived Neurotrophic Factor (GDNF) in the midbrain, particularly the Ventral Tegmental Area (VTA). However, there had been no systematic study comparing ibogaine’s effects on the expression of multiple neurotrophic factors across distinct dopaminergic regions that form the mesocorticolimbic and nigrostriatal circuits. Lason and colleagues set out to characterise how a single intraperitoneal (i.p.) administration of ibogaine alters mRNA and protein levels of three neurotrophic factors — GDNF, Brain Derived Neurotrophic Factor (BDNF) and Nerve Growth Factor (NGF) — in four brain regions relevant to dopaminergic neurotransmission: the VTA, prefrontal cortex (PFC), nucleus accumbens (NAcc) and substantia nigra (SN). They tested two doses (20 mg/kg and 40 mg/kg) and examined outcomes at two time points (3 h and 24 h) chosen to separate acute drug/metabolite presence from longer-lasting molecular changes; locomotor behaviour in an open field was recorded at the same time points. This single‑dose, time‑course approach aimed to identify site‑ and dose‑specific patterns of neurotrophic factor regulation that could plausibly link ibogaine administration to the long‑lasting behavioural effects reported in addiction models, and to explore whether changes in mRNA were echoed by changes in mature protein or precursor forms such as proBDNF.

Thirty‑six adult male Wistar rats (270–300 g) were allocated to six groups: vehicle, 20 mg/kg ibogaine (I20) and 40 mg/kg ibogaine (I40), each assayed at 3 h and 24 h after i.p. injection (n = 6 per group). Animals were housed under a 12 h light/dark cycle with ad libitum food and water. The ibogaine hydrochloride used was chemically synthesised and prepared for injection in warm degassed saline. All procedures received institutional ethical approval. Locomotor activity was measured in an open field (45 × 45 × 40 cm) under low indirect illumination (35 lux). Video tracking (Ethovision XT 12.0) recorded total distance travelled over 30 min beginning at 3 h or 24 h post‑injection. A trained observer also monitored typical serotonergic‑syndrome‑related behaviours every 5 min during the test. Animals were used once and the open field was cleaned between tests. After behavioural testing animals were decapitated and brains rapidly removed on ice. Bilateral tissue punches/dissections were taken for whole NAcc (shell and core), PFC (including medial PFC), VTA and SN (pars compacta and reticulata), frozen and stored at −80 °C. Total RNA was extracted with Trizol, treated with DNase and reverse transcribed; qPCR was performed in triplicate using GAPDH for normalisation and the Ct method to yield relative mRNA levels. Primer sequences are reported in the Methods. Protein levels were measured by Western blot. Tissue lysates were separated on 12% SDS‑PAGE, transferred to nitrocellulose and probed with antibodies against GDNF, BDNF and proBDNF, with alpha‑tubulin as a loading control. Bands were detected on an Odyssey system and quantified with Image Studio. For qPCR and behavioural analyses six animals per group were intended, though some samples were excluded for technical reasons so that n was never below 4; Western blot analyses used samples from 4 animals per group. Statistical analyses employed one‑way ANOVA followed by Tukey’s post hoc tests for qPCR and Western blot comparisons, with P < 0.05 considered significant; two‑way repeated measures ANOVA (treatment × time) was used for locomotor data followed by Newman‑Keuls tests. Effect sizes (eta squared) and exact F and P values for significant comparisons are reported in the figures and legends (as extracted).

Behaviour: I20 did not alter novelty‑induced locomotion at either time point. I40 produced no behavioural changes at 3 h but caused a significant reduction in total locomotor activity at 24 h compared with vehicle; no abnormal stereotypies or overt serotonergic syndrome signs were observed at the tested time points. GDNF mRNA and protein: At 3 h there were no significant changes in GDNF transcript levels in any region for either dose. At 24 h I40, but not I20, selectively increased GDNF mRNA in midbrain regions: a reported ~12‑fold rise in the VTA and ~6‑fold increase in the SN versus control, with no appreciable effect in PFC or NAcc. Western blot analysis showed a corresponding 2‑fold increase in mature GDNF protein in the VTA for I40; no significant GDNF protein changes were detected in NAcc, SN or PFC. BDNF mRNA and protein: A transient downregulation of BDNF mRNA occurred in the PFC at 3 h for both doses (approximately 1.7–2.0‑fold decrease). By 24 h there was a striking, dose‑dependent upregulation of BDNF transcripts across regions. The NAcc showed the largest increases (I20 ~220‑fold; I40 ~340‑fold over control). In the PFC BDNF mRNA rose ~55‑fold (I20) and ~107‑fold (I40). I40 but not I20 increased BDNF transcript levels in the VTA (~43‑fold) and SN (~21‑fold). Despite these large mRNA increases, mature BDNF protein levels measured by Western blot did not show significant increases in any region for either dose at 24 h. However, the precursor proBDNF was selectively elevated in the NAcc (2.7‑fold for I20 and 2.8‑fold for I40); proBDNF was not significantly changed in other regions. NGF mRNA: No changes were detected at 3 h. At 24 h I40 increased NGF transcripts in all studied regions: PFC (~14‑fold), NAcc (~15‑fold), VTA (~11‑fold) and SN (~4‑fold). I20 induced more modest increases limited to PFC (~7‑fold) and VTA (~5‑fold). The magnitude of NGF induction was smaller than that observed for BDNF. Additional notes: Sample sizes and exclusions are reported; qPCR and behavioural groups began with n = 6 but some samples were excluded for technical reasons so n was never less than 4. Western blot analyses were performed on samples from 4 animals per group.

Lason and colleagues interpret their findings as evidence that a single ibogaine administration produces dose‑ and time‑dependent changes in neurotrophic factor expression across multiple dopaminergic regions, with the VTA emerging as a key site for GDNF upregulation after the 40 mg/kg dose. The selective increase in mature GDNF protein in the VTA at 24 h aligns with prior reports linking VTA GDNF to reductions in ethanol self‑administration, and the investigators propose this as a plausible mechanism contributing to ibogaine’s anti‑addictive effects. The authors note a complex picture for BDNF: despite very large increases in BDNF mRNA at 24 h, mature BDNF protein did not significantly rise, whereas the precursor proBDNF was selectively increased in the NAcc. Because mature BDNF and proBDNF have opposing actions mediated via TrkB and p75 receptors respectively, the shift toward proBDNF in the NAcc could have functional consequences distinct from those predicted by mRNA increases alone. The discrepancy between mRNA and protein is discussed in terms of post‑transcriptional regulation, translational control, protein trafficking (for example sortilin‑dependent routing) or differences in temporal kinetics of protein synthesis. Mechanistically, the investigators suggest that enhanced serotonergic transmission produced by ibogaine and its metabolite noribogaine — both known to inhibit serotonin reuptake, with noribogaine being the more potent SERT inhibitor — may drive increases in BDNF and GDNF expression, citing parallels with SSRI effects on neurotrophic factors. They acknowledge uncertainty about the relative contributions of parent drug versus metabolite because noribogaine persists longer in vivo in some species but is reportedly low or absent in rodent brain at later time points; further work is required to disentangle their roles. The discussion also considers the behavioural findings: I40 reduced novelty‑induced locomotion at 24 h but not at 3 h, and the authors state there is currently no direct evidence linking this motor change to the observed neurotrophic factor alterations. They propose that changes in SN expression could plausibly affect basal ganglia output and motor behaviour, but stress that dedicated behavioural paradigms for reward and motivation are needed to test causality. Key limitations acknowledged by the authors include the narrow temporal sampling (only 3 h and 24 h), incomplete alignment between transcript and mature protein measures, and the inability of the present data to establish causal links between molecular changes and anti‑addictive behavioural outcomes. They also note clinical safety concerns about ibogaine (for example QT interval prolongation) and suggest that understanding the molecular mechanisms could support the development of safer analogues.

The study demonstrates that a single i.p. dose of ibogaine produces dose‑ and time‑dependent alterations in GDNF, BDNF and NGF transcripts in rat brain regions implicated in dopaminergic neurotransmission. Importantly, only the 40 mg/kg dose increased mature GDNF protein in the VTA at 24 h, a finding consistent with prior reports linking VTA GDNF to reduced ethanol self‑administration. Both doses elevated proBDNF in the NAcc at 24 h, which may influence reward‑related plasticity differently from mature BDNF. The authors conclude that these region‑specific neurotrophic changes could contribute to ibogaine’s long‑lasting effects on drug‑seeking behaviour, but emphasise that further experiments are required to clarify mechanisms and to inform the design of safer, more effective ibogaine‑based therapeutics.