Effects of 3-methylmethcathinone on conditioned place preference and anxiety-like behavior: Comparison with methamphetamine

Abstract

3-Methylmethcathinone (3-MMC), a drug belonging to synthetic cathinones family, raised public attention due to its harmful health effects and abuse potential. Although it has similar properties to other cathinone derivatives, the behavioral effects of 3-MMC remain largely unknown. In the present research, we evaluated the rewarding effect of 3-MMC using conditioned place preference (CPP) paradigm and its effect on anxiety-like behavior using elevated plus maze (EPM) and compared with methamphetamine (METH). Then, we performed a whole-brain c-Fos mapping to identify the specific brain regions in response to 3-MMC exposure and explored the changes of synaptic transmission in nucleus accumbens (NAc) using patch-clamp recording after chronic 3-MMC and METH exposure. 3-MMC induced CPP at higher doses of 3 or 10 mg/kg in rats and acute exposure of 3 mg/kg 3-MMC to rats produced anxiolytic-like effect, while anxiety-like behavior was increased after 7 days of injection with 3-MMC. Whole-brain immunostaining revealed increased c-Fos expression in anterior cingulate cortex (ACC), NAc and ventral tegmental area (VTA) after chronic 3-MMC injection compared with saline, which was similar to METH. Especially, 3-MMC induced more neural activation of VTA compared with METH. Finally, we found that amplitude of spontaneous inhibitory postsynaptic currents (sIPSCs) in NAc was decreased after chronic 3-MMC injection, while frequency of sIPSCs and spontaneous excitatory postsynaptic currents (sEPSCs) were not affected. Taken together, our results revealed the addictive potential of 3-MMC and its effect on anxiety-like behavior, which warn the risks of 3-MMC abuse and justify the control of synthetic cathinones. And 3-MMC selectively inhibit inhibitory but not excitatory transmission onto neurons in NAc, which may contribute to its effects.

Keywords: 3-methylmethcathinone; conditioned place preference; elevated plus maze; nucleus accumbens; synaptic transmission.

FIGURE 1

The effects of 3-MMC on CPP and locomotor activity. (A) Experimental timeline showing the CPP training. The rats trained with saline, METH (1 mg/kg) or 3-MMC (1, 3, or 10 mg/kg) for 8 days and tested in day 9, paired t-test, *P < 0.05, **P < 0.01 significant differences for each drug in CPP test, n = 10 for each group. (B) A single injection of 3-MMC (3 mg/kg) or METH (1 mg/kg) increased locomotor activity. Each point represents the average distance traveled in 5-min bins. Saline, Meth and 3-MMC group, post hoc test, *P < 0.05 significant differences in distance for 3-MMC vs saline, ^#P < 0.05 significant differences for METH vs saline, n = 8, 9, and 8, respectively. Data are presented as mean values ± SEM.

FIGURE 2

The effects of acute and chronic injection of 3-MMC on EPM. (A) A single injection of 3-MMC (3 mg/kg) increased the time in open arms, paired t-test, *P < 0.05 significant differences for each drug in EPM test, n = 7 for each group. (B) Representative diagrams of travel trace in EPM after acute 3-MMC exposure. (C) 7 consecutive days of 3-MMC (3 mg/kg) injection decreased the time in open arms, paired t-test, *P < 0.05 significant differences for each drug in EPM test, n = 9 for each group. (D) Representative diagrams of travel trace in EPM after chronic 3-MMC exposure. Data are presented as mean values ± SEM.

FIGURE 3

Specific brain regions response to chronic 3-MMC exposure. (A) The c-Fos expression of rats 90 min after last injection of drugs, post hoc test, *P < 0.05, **P < 0.01 significant differences for 3-MMC vs saline or METH vs saline, ^#P < 0.05 significant differences for 3-MMC vs METH, n = 4 for each group. (B) Representative immunofluorescent images of c-Fos expression in ACC, NAc, and VTA. Scale bar, 100 μm. ACC, anterior cingulate cortex; PrL, prelimbic cortex; IL, infralimbic cortex; OFC, orbitofrontal cortex; aIC, anterior insular cortex; NAc, nucleus accumbens; DS, dorsal striatum; BLA, basolateral amygdala; CeA, central amygdala; VTA, ventral tegmental area. Data are presented as mean values ± SEM.

FIGURE 4

Changes of synaptic transmission in nucleus accumbens (NAc) after chronic 3-MMC injection. (A) Representative sEPSCs traces recorded in NAC 24 h after the last injection of drugs. (B,C) No difference in the frequency and the amplitude of sEPSCs in NAc after chronic 3-MMC injection. (D) Representative sIPSCs traces recorded in NAC 24 h after the last injection of drugs. (E,F) The amplitude of sIPSCs was decreased after chronic 3-MMC injection without change of frequency of sIPSCs, post hoc test, *P < 0.05, ***P < 0.001 significant differences for 3-MMC vs saline and METH vs saline respectively. For slice electrophysiology: 25 neurons from three rats with saline injection, 32 neurons from three rats with METH injection and 27 neurons from three rats with 3-MMC injection. Data are presented as mean values ± SEM.