Table 4.

Summary of findings on alcohol and substance use disorders

Sample studied	Main finding	Sample size	Reference
Alcohol Dependent (AD) patients undergoing 3-week abstinence	Intestinal permeability, LPS, and cytokine levels elevated at T1 (admission); full recovery of intestinal permeability and LPS and slight recovery of cytokines at T2 (after 3 weeks of abstinence) AD subjects showed elevated depression, anxiety, and craving, with slight decrease over short-term abstinence Conclusion: Inflammation and intestinal permeability associated with AD diagnosis and AD-related behavioral measures, suggesting role of gut-brain axis in AD pathogenesis	T1 n = 52 T2 n = 40 Control n = 16	Leclercq et al. (2012)
Actively drinking AD patients undergoing alcohol detoxification	LPS and PGN, and associated TLR4 and TLR2 Complexes elevated in AD patients Plasma levels of pro-inflammatory cytokines elevated and positively correlated with consumption of, and craving for, alcohol at T1 Short-term withdrawal associated with recovery of LPS-dependent receptors Conclusion: LPS and PGN from gut microbiota stimulate inflammatory pathways that are correlated with behavioral measures of AD	T1 n = 63 T2 n = 41 Control n = 14	Leclercq et al. (2014a)
AD patients undergoing 3-week abstinence	Preliminary Study: A subset of AD patients demonstrated IP; this group had higher scores on depression, anxiety, and craving after 3 weeks of abstinence Main Study: High intestinal permeability associated with altered gut microbiota composition and activity Conclusion: Evidence for involvement of gut-brain axis in AD with a role of IP and inflammation in behavioral correlates of AD	Preliminary: T1 n = 60 T2 n = 44 Control n = 15 Main: AD n = 13 Control n = 15	Leclercq et al. (2014b)
Male C57Bl/6 Mice	Diminished gut bacteria associated with enhanced cocaine-induced conditioned place preference Reduced gut bacteria associated with increased sensitivity to locomotor-sensitizing effects of repeated cocaine dosing Altered behavioral outcomes correlated to altered transcription encoding for reward circuitry proteins Conclusion: Alterations to the gut microbiota impact behavioral responses to cocaine in mice	n = 5–22/group	Kiraly et al. (2016)