Neurochemical and Behavioral Profiling in Male and Female Rats of the Psychedelic Agent 25I-NBOMe

Abstract

4-Iodo-2,5-dimethoxy-N-(2-methoxybenzyl)phenethylamine (25I-NBOMe), commonly called "N-Bomb," is a synthetic phenethylamine with psychedelic and entactogenic effects; it was available on the Internet both as a legal alternative to lysergic acid diethylamide (LSD) and as a surrogate of 3,4-methylenedioxy-methamphetamine (MDMA), but now it has been scheduled among controlled substances. 25I-NBOMe acts as full agonist on serotonergic 5-HT2A receptors. Users are often unaware of ingesting fake LSD, and several cases of intoxication and fatalities have been reported. In humans, overdoses of "N-Bomb" can cause tachycardia, hypertension, seizures, and agitation. Preclinical studies have not yet widely investigated the rewarding properties and behavioral effects of this compound in both sexes. Therefore, by in vivo microdialysis, we evaluated the effects of 25I-NBOMe on dopaminergic (DA) and serotonergic (5-HT) transmissions in the nucleus accumbens (NAc) shell and core, and the medial prefrontal cortex (mPFC) of male and female rats. Moreover, we investigated the effect of 25I-NBOMe on sensorimotor modifications as well as body temperature, nociception, and startle/prepulse inhibition (PPI). We showed that administration of 25I-NBOMe affects DA transmission in the NAc shell in both sexes, although showing different patterns; moreover, this compound causes impaired visual responses in both sexes, whereas core temperature is heavily affected in females, and the highest dose tested exerts an analgesic effect prominent in male rats. Indeed, this drug is able to impair the startle amplitude with the same extent in both sexes and inhibits the PPI in male and female rats. Our study fills the gap of knowledge on the behavioral effects of 25I-NBOMe and the risks associated with its ingestion; it focuses the attention on sex differences that might be useful to understand the trend of consumption as well as to recognize and treat intoxication and overdose symptoms.

Keywords: behavior; dopamine; novel psychoactive substances; serotonin; sex differences.

Figure 1

Rat dopamine (A) and serotonin (B) basal levels in both male (blue bars) and female (magenta bars) rats. Results are expressed as the mean ± SEM of change in DA/5-HT extracellular levels expressed as fmol/20 μl sample in nucleus accumbens (NAc) shell, NAc core, and mPFC.

Figure 2

Effect of 4-iodo-2,5-dimethoxy-N-(2-methoxybenzyl)phenethylamine (25I-NBOMe) administration (0.3 and 1.0 mg/kg, i.p) on dopamine (DA) (A–F) and serotonin (5-HT) (G–L) transmissions in the nucleus accumbens (NAc) shell, NAc core, and medial prefrontal cortex (mPFC) in male (blue symbols) and female (magenta symbols) rats. Results are expressed as the mean ± SEM of change in DA/5-HT extracellular levels expressed as the percentage of basal values. The arrow indicates the start of i.p. injection at of vehicle (circles) or 25I-NBOMe 0.3 mg/kg (triangles) or 25I-NBOMe 1.0 mg/kg (squares) in NAc shell, NAc core, and mPFC. Statistical analysis was performed by three-way or two-way ANOVA followed by the Tukey’s HSD post hoc test for multiple comparisons. Solid symbol: p < 0.05 with respect to basal values (DA males: NAc shell, N = 15; NAc core, N = 10; mPFC, N = 14; DA females: NAc shell, N = 34; NAc core, N = 31; mPFC, N = 27; 5-HT males: NAc shell, N = 11; NAc core, N = 10; mPFC, N = 11; 5-HT females: NAc shell, N = 38; NAc core, N = 20; mPFC, N = 26).

Figure 3

Intraperitoneal injection (0.1–1 mg/kg) of 25I-NBOMe in male and female rats on the visual object test (A and B), on the acoustic response (C and D), and on the visual placing test (E and F). Data are expressed as arbitrary units (A, B, C, and D) or percentage of basal (E and F) and represent the mean ± SEM of six determinations for each treatment. Statistical analysis was performed by two-way ANOVA followed by Bonferroni’s test for multiple comparisons for the dose–response curve at different times. *p < 0.05, **p < 0.01, ***p < 0.001 versus vehicle.

Figure 4

Intraperitoneal injection (0.1–1 mg/kg) of 25I-NBOMe in male and female rats on the overall tactile responses (A and B) and on core temperature (C and D) and tail pinch test (E and F). Data are expressed as arbitrary units (A and B), as difference between control temperature (before injection) and temperature following drug administration (Δ°C; see Material and Methods) (B and C), or as percentage of maximum effect (E _max%; (see Material and Methods) (E and F) and represent the mean ± SEM of six animals for each treatment. Statistical analysis was performed by two-way ANOVA followed by Bonferroni’s test for multiple comparisons for the dose–response curve of each compound at different times. *p < 0.05, **p < 0.01, ***p < 0.001 versus vehicle.

Figure 5

Effect of the systemic administration of 25I-NBOMe (0.1–1 mg/kg, i.p.) on prepulse inhibition (PPI) in male (A) and female (B) rats and on startle amplitude for both sexes (C). Effects on PPI are shown for the three prepulse intensities (68, 75, and 85 dB) 30 min after treatment (A and B). Data are expressed (see Material and Methods) as percentage decrease in the amplitude of the startle reactivity caused by presentation of the prepulse (% PPI) (A and B) and absolute values (in dB) (C). Values represent the mean ± SEM of seven animals for each treatment. Statistical analysis was performed by one-way ANOVA followed by Bonferroni’s test for multiple comparisons. *p < 0.05, **p < 0.01, ***p < 0.001 versus vehicle.