Neurochemical and Behavioral Effects of a New Hallucinogenic Compound 25B-NBOMe in Rats

Abstract

4-Bromo-2,5-dimethoxy-N-(2-methoxybenzyl)phenethylamine (25B-NBOMe) is a hallucinogen exhibiting high binding affinity for 5-HT_2A/C serotonin receptors. In the present work, we investigated its effect on dopamine (DA), serotonin (5-HT), acetylcholine (ACh), and glutamate release in the rat frontal cortex, striatum, and nucleus accumbens. Hallucinogenic activity, impact on cognitive and motor functions, and anxiogenic/anxiolytic properties of this compound were also tested. The release of DA, 5-HT, ACh, and glutamate was studied using microdialysis in freely moving animals. Hallucinogenic activity was investigated using head and body twitch response (WDS), cognitive functions were examined with the novel object recognition test (NOR), locomotor activity was studied in the open field (OF), while anxiogenic/anxiolytic effect was tested using the light/dark box (LDB). Neurotoxicity was evaluated with the comet assay. 25B-NBOMe increased DA, 5-HT, and glutamate release in all studied brain regions, induced hallucinogenic activity, and lowered the recognition index (Ri) vs. control in the NOR test. It also decreased locomotor activity of rats in the OF test. The effect of 25B-NBOMe in the NOR test was inhibited by scopolamine. In the LDB test, the time spent in the dark zone was longer in comparison to control and was dose-dependent. In contrast to MDMA, 25B-NBOMe showed subtle genotoxic effect observed in the comet assay.Our findings indicate that 25B-NBOMe shows hallucinogenic activity in the wide range of doses. The changes in neurotransmitter levels may be related to 25B-NBOMe affinity for 5-HT_2A receptor. Alterations in the NOR, OF, and LDB indicate that 25B-NBOMe impacts short-term memory, locomotion, and may be anxiogenic.

Keywords: 25B-NBOMe; Behavior; Genotoxicity; Hallucinogen; Neurotransmitters release.

Fig. 1

The time-course effect of 25B-NBOMe on extracellular levels of a dopamine (DA), b serotonin (5-HT), c glutamate (GLU), and d acetylcholine (ACh) in the rat frontal cortex. Values are the mean ± standard error of the mean (SEM), n = 6 per experimental group. For ACh measurements, two consecutive dialysate fractions were pooled. The time of drug injection is indicated by an arrow. The basal extracellular levels were as follows: for DA, 0.99 ± 0.06 nM, n = 30; for 5-HT, 0.19 ± 0.008 nM, n = 30; for ACh, 36.5 ± 3.93 nM, n = 30; for GLU, 1.76 ± 0.16 μM, n = 30; *p < 0.0002 vs. control group (repeated measures ANOVA and Tukey’s post hoc test)

Fig. 2

The time-course effect of 25B-NBOMe on extracellular levels of a dopamine (DA), b serotonin (5-HT), c glutamate (GLU), and d acetylcholine (ACh) in the rat striatum. Values are the mean ± standard error of the mean (SEM), n = 6 per experimental group. For ACh measurements, two consecutive dialysate fractions were pooled. The time of drug injection is indicated by an arrow. The basal extracellular levels were as follows: for DA, 5.17 ± 0.28 nM, n = 30; for 5-HT, 0.27 ± 0.014 nM, n = 30; for ACh, 48.9 ± 3.64 nM, n = 30; for GLU, 2.84 ± 0.22 μM, n = 30; *p < 0.0002 vs. control group (repeated measures ANOVA and Tukey’s post hoc test)

Fig. 3

The time-course effect of 25B-NBOMe on extracellular levels of a dopamine (DA), b serotonin (5-HT), c glutamate (GLU), and d acetylcholine (ACh) in the rat nucleus accumbens. Values are the mean ± standard error of the mean (SEM), n = 6 per experimental group. For ACh measurements, two consecutive dialysate fractions were pooled. The time of drug injection is indicated with an arrow. The basal extracellular levels were as follows: for DA, 1.05 ± 0.059 nM, n = 30; for 5-HT, 0.199 ± 0.01 nM, n = 30; for ACh, 19.5 ± 1.34 nM, n = 30; for GLU, 2.10 ± 0.13 μM, n = 30; *p < 0.0002 vs. control group (repeated measures ANOVA and Tukey’s post hoc test)

Fig. 4

The total effect of 25B-NBOMe on extracellular levels of dopamine (DA), serotonin (5-HT), glutamate (GLU) and acetylcholine (ACh) in the rat frontal cortex (a), striatum (b), and nucleus accumbens (c) calculated as an area under the curve (AUC) and expressed as the percent of each basal level. Values are the mean ± standard error of the mean (SEM), n = 6 per experimental group. *p < 0.0002 vs. control group, ^p < 0.05 vs. 0.3 mg/kg (one-way ANOVA and Tukey’s post hoc test)

Fig. 5

The effect of 25B-NBOMe and LSD on head and body twitches (WDS) in rats. The number of episodes counted for 240 min starting immediately after the injection is shown. Values are the mean ± standard error of the mean (SEM), n = 8 per experimental group. *p < 0.0001 vs. control group (one-way ANOVA and Tukey’s post hoc test)

Fig. 6

The effect of 25B-NBOMe (0.3 and 3 mg/kg) on performance of rats in the novel object recognition (a, b) test and on locomotor behavior of rats in the open field (c) test. a Exploration time in the recognition session for the familiar (A) and novel object (B). b Ri expressed as the time spent on novel object exploration in relation to the total exploration time of both novel and familiar objects. c The time spent on walking, the number of episodes of crossing and the number of episodes of peeping. Values are the mean ± standard error of the mean (SEM), n = 6–10 per experimental group. a *p < 0.05, **p < 0.01 novel vs. familiar object (t test); ^#p < 0.01 vs. control (one-way ANOVA and Tukey’s post hoc test); b ^#p < 0.01 vs. control; ^p < 0.01 vs. 25B-NBOMe 0.3 mg/kg (one-way ANOVA and Tukey’s post hoc test); c *p < 0.05, **p < 0.01 vs. control; ^p < 0.05; ^^p < 0.01 vs. 25B-NBOMe 0.3 mg/kg (one-way ANOVA and Tukey’s post hoc test)

Fig. 7

The effect of scopolamine (1 mg/kg) on 25B-NBOMe (3 mg/kg)-induced changes in rats’ performance in the novel object recognition (a, b) test and locomotor activity in the open field (c) test. a Exploration time in the recognition session for the familiar (A) and novel object (B). b Ri expressed as the time spent on novel object exploration in relation to the total exploration time of both the novel and familiar objects. c The time spent on walking, the number of episodes of crossing, and the number of episodes of peeping. Values are the mean ± standard error of the mean (SEM), n = 6–12 per experimental group. a *p < 0.05, **p < 0.01 novel vs. familiar object (t test); ^#p < 0.01 vs. control; ^$p < 0.01 vs. scopolamine (one-way ANOVA and Tukey’s post hoc test); b ^#p < 0.01 vs. control; ^p < 0.01 vs. 25B-NBOMe 0.3 mg/kg (one-way ANOVA and Tukey’s post hoc test); c *p < 0.05, **p < 0.01 vs. control; ^$p < 0.01 vs. scopolamine (one-way ANOVA and Tukey’s post hoc test)

Fig. 8

The effect of 25B-NBOMe (0.3 and 3 mg/kg) on activity of rats in the light/dark box test. a The time spent in the dark and light zone; b–d ambulatory distance, vertical, and stereotypical activity, respectively in the dark and light zone. Values are the mean ± standard error of the mean (SEM), n = 8 per experimental group. *p < 0.05, **p < 0.01 vs. control, ^p < 0.001 light vs. dark zone (Mann–Whitney’s test)

Fig. 9

The effect of 25B-NBOMe (0.3, 3 mg/kg) and MDMA (10 mg/kg) on the oxidative damage of DNA in the nuclei from the rat frontal cortex. Data are the mean ± SEM (n = 6 animals per group) and represent tail moment shown as the product of the tail length and the fraction of total DNA in the tail. Typical microscopic images of nuclei from control, 25B-NBOMe- and MDMA-treated rats; *p < 0.01 in comparison to control group (t test). DNA damage is presented in arbitrary units