Methamphetamine Exposure and Withdrawal Impact Gut Microbiota and Induce Depressive-Like Behavioral Effects on Rodents.

Methamphetamine (MA) is one of the most frequently used amphetamine-type stimulants in the United States. Individuals who repeatedly abuse MA can develop MA use disorder (MuD)—a chronic, relapsing condition often triggered by withdrawal symptoms that develop following cessation of use. Long term abuse MA can result in negative health consequences including extreme weight loss, severe dental problems, malnutrition, confusion, insomnia, mood disturbances, and violent behavior. Importantly, depression and anxiety are key diagnostic characteristics of MA withdrawal in humans. Despite the well-documented dangers of chronic MA use, approximately 1.2 million people reported using MA in the past year. Given the lack of effective treatments for those with MuD, novel therapeutic targets must be considered. One potential target is the gut microbiome, which has an important influence on brain, behavior, and health as a part of the gut-brain axis. The gut microbiome comprises microorganisms and their genomes that reside in the intestinal tract. Therefore, the use of psychobiotics may provide a new way for treatments for drug addiction. In this study, we evaluated the effects of MA administration (2 mg/kg, s.c.) on withdrawal- induced behaviors and in the gut microbiota in male Sprague-Dawley rats (n=8).
16 male rats (60-70 days old) were divided equally into 2 groups: METH and Vehicle (control) groups. Rats in METH group were given twice daily injection of Saline (s.c) for 14 days, during which baseline behaviors (elevated plus maze (EPM) for anxiety-like behavior; forced swim test (FST) for depressive-like behavior) were assessed. Next, rats were given twice daily injections of MA for 14 days, followed by 7 days of withdrawal, during which performance on the Elevated Plus Maze (EPM), Open Field Task (OFT), and Forced Swim Task FST were assessed. Control group were given twice daily injection of Saline (s.c.) for 28 days, followed by 7 days of withdrawal. Fecal collection for microbiome analyses occurred on day 5 of saline administration, day 1, 7, 14 of MA administration, at 24-, 48- and 96-h, and day 7 of withdrawal, during which performance on the EPM, OFT, and FST were assessed. Results indicated that MA withdrawal increased depressive-like behavior, with an increase in immobility time in the FST (p<0.05). Anxiolytic/anxiogenic effects were not observed in either group. We analyzed the gut microbiome composition of each group through 16S rRNA gene sequencing. Results revealed MA administration and withdrawal significantly changed the relative abundances of several bacterial phyla. Compared to control group, the METH group demonstrated a higher abundance of Firmicutes, Verrumcomicrobia, Actinobacteria, Tenericutes, and Proteobacteria (p <0.05, vs. saline), and lower abundance of Bacteroidetes (p <0.05, vs. saline). At the genus level, Allobaculum, Bifidobacterium, and Lactobacillus were significantly more abundant in the fecal microbiota of METH group than vehicle group during MA administration and early days of withdrawal and they were normalized completely after 7 days of withdrawal. No significant changes in Shannon diversity were observed. These findings provide direct evidence that administration of MA causes gut dysbiosis and withdrawal from chronic methamphetamine induces depressive-like but not anxiety-like behavioral effects in male rodents. Our observation will contribute to a better understanding of the function of gut microbiota in the process of drug abuse and guide the choice of target therapeutics for MuD to test in future studies.