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

Abstract

Ibogaine is an atypical psychedelic alkaloid, which has been subject of research due to its reported ability to attenuate drug-seeking behavior. Recent work has suggested that ibogaine effects on alcohol self-administration in rats are related to the release of Glial cell Derived Neurotrophic Factor (GDNF) in the Ventral Tegmental Area (VTA), a mesencephalic region which hosts the soma of dopaminergic neurons. Although previous reports have shown ibogaine's ability to induce GDNF expression in rat midbrain, there are no studies addressing its effect on the expression of GDNF and other neurotrophic factors (NFs) such as Brain Derived Neurotrophic Factor (BDNF) or Nerve Growth Factor (NGF) in distinct brain regions containing dopaminergic neurons. In this work, we examined the effect of ibogaine acute administration on the expression of these NFs in the VTA, Prefrontal Cortex (PFC), Nucleus Accumbens (NAcc) and the Substantia Nigra (SN). Rats were i.p. treated with ibogaine 20 mg/kg (I₂₀), 40 mg/kg (I₄₀) or vehicle, and NFs expression was analyzed after 3 and 24 h. At 24 h an increase of the expression of the NFs transcripts was observed in a site and dose dependent manner. Only for I₄₀, GDNF was selectively upregulated in the VTA and SN. Both doses elicited a large increase in the expression of BDNF transcripts in the NAcc, SN and PFC, while in the VTA a significant effect was found only for I₄₀. Finally, NGF mRNA was upregulated in all regions after I₄₀, while I₂₀ showed a selective upregulation in PFC and VTA. Regarding protein levels, an increase of GDNF was observed in the VTA only for I₄₀ but no significant increase for BDNF was found in all the studied areas. Interestingly, an increase of proBDNF was detected in the NAcc for both doses. These results show for the first time a selective increase of GDNF specifically in the VTA for I₄₀ but not for I₂₀ after 24 h of administration, which agrees with the effective dose found in previous self-administration studies in rodents. Further research is needed to understand the contribution of these changes to ibogaine's ability to attenuate drug-seeking behavior.

Keywords: BDNF; GDNF; NGF; ibogaine; neurotrophic factors.

FIGURE 1

Schematic showing the experimental design of this work. Experimental groups of animals were i.p. treated with ibogaine 20 mg/kg (I₂₀), 40 mg/kg (I₄₀) or vehicle. After 3 and 24 h, locomotion of control and treated animals was recorded using an open field test. Afterward, animals were sacrificed, and selected brain regions were dissected. mRNA levels for BDNF, GDNF, and NGF were determined by qPCR. Western Blot was used to determine BDNF, proBDNF, and GDNF protein content. PFC = Prefrontal Cortex, NAcc = Nucleus Accumbens, VTA = Ventral Tegmental Area, and SN = Substantia Nigra, GDNF = Glial Cell Derived Neurotrophic Factor, BDNF = Brain Derived Neurotrophic Factor, NGF = Nerve Growth Factor.

FIGURE 2

Effects of ibogaine administration on locomotor activity. Locomotor activity of rats was recorded in the OF test during 30 min, at 3 h (A) and 24 h (B) after ibogaine (40 mg/kg) i.p. administration. The inset graphs represent the total locomotor activity (30 min). Data are expressed as mean + SEM. Data were analyzed by the two-way ANOVA of repeated measured followed by Newman–Keuls test and Unpaired t-test (insets). For 24 h after treatment, two-way ANOVA revealed a significant effect of the treatment F_(1,8) = 11.14, P < 0.01, η²= 0.059; time F_(5,40) = 66.56, P < 0.001, η²= 0.75; and treatment × time interaction F_(5,40) = 4.85, P < 0.01, η²= 0.055. ^∗, respective to saline group. ^∗∗∗P < 0.001; ^∗∗P < 0.01; ^∗P < 0.05. N = 18, n = 6 per group.

FIGURE 3

Effects of ibogaine administration on GDNF expression in specific brain areas. Quantitative analysis of GDNF transcript levels in the indicated brain areas after 3 h (upper panels) or 24 h (lower panels) of vehicle (0), 20 or 40 mg/kg ibogaine administration. For 24 h after treatment VTA, N = 16, P < 0.0001, F_2,13 = 96.11, η² = 0.94; For 24 h after treatment SN, N = 14, P < 0.0001, F_2,11 = 60.75, η² = 0.92; ^∗∗∗P < 0.001 between indicated groups.

FIGURE 4

Effects of ibogaine administration on BDNF expression in specific brain areas. Quantitative analysis of BDNF transcript levels in the indicated brain areas after 3 h (upper panels) or 24 h (lower panels) of vehicle (0), 20 or 40 mg/kg ibogaine administration. For 3 h after treatment PFC, N = 16, P < 0.0001, F_2,13 = 9.80, η² = 0.61; For 24 h after treatment PFC, N = 16, P < 0.0001, F_2,13 = 25.26, η² = 0.80; For 24 h after treatment NAcc, N = 15, P < 0.0001, F_2,12 = 46.62, η² = 0.89; For 24 h after treatment VTA, N = 14, P < 0.0001, F_2,11 = 46.46, η² = 0.88; For 24 h after treatment SN, N = 16, P < 0.0001, F_2,13 = 45.50, η² = 0.88; ^∗ P < 0.05, ^∗∗ P < 0.01 and ^∗∗∗P < 0.001 between indicated groups.

FIGURE 5

Effects of ibogaine administration on NGF expression in specific brain areas. Quantitative analysis of NGF transcript levels in the indicated brain areas after 3 h (upper panels) or 24 h (lower panels) of vehicle (0), 20 or 40 mg/kg ibogaine administration. For 24 h after treatment PFC, N = 17, P < 0.0001, F_2,14 = 76.40, η² = 0.92; For 24 h after treatment NAcc, N = 17, P < 0.0001, F_2,14 = 107.1, η² = 0.94; For 24 h after treatment VTA, N = 17, P < 0.0001, F_2,14 = 44.88, η² = 0.87; For 24 h after treatment SN, N = 16, P = 0.0050, F_2,13 = 8.16, η² = 0.61; ^∗∗P < 0.01 and ^∗∗∗P < 0.001 between indicated groups.

FIGURE 6

Effects of ibogaine administration on GDNF, BDNF, and proBDNF protein levels in specific brain areas. Western blot analysis of GDNF (A,B), BDNF (C,D) and proBDNF (E,F) protein levels in the indicated brain areas after 24 h of vehicle (0), 20, or 40 mg/kg ibogaine administration. A representative image from immunostained membrane of each condition is shown (A,C,E) with the corresponding quantification below (B,D,F). Data represent mean ± SEM of n = 4 biological replicates assayed in triplicate. For GDNF/VTA, N = 12, P < 0.05, F_2,9 = 6.86, η² = 0.60; For proBDNF/NAcc, N = 12, P < 0.05, F_2,9 = 5.87, η² = 0.57; ^∗P < 0.05 between indicated groups.