Effects of a Bacterial Multi‐Strain Formulation on Locomotor Sensitization and the Gut Microbiota Structure Induced by Repeated Volatilized Cocaine Exposure in Rats

The gut microbiota (GM), the community of microorganisms inhabiting the gastrointestinal tract, has emerged as a relevant factor in the pathogenesis of substance use disorders (SUD). However, more evidence is required to advance in this field of research. In previous research we showed that exposure to volatilized cocaine altered GM composition in rats, suggesting that its modulation could attenuate cocaine effects. In this study, we investigated whether GM modulation through a lactobacilli-based multi-strain formulation influenced behavioral and microbiological outcomes in rats repeatedly exposed to volatilized cocaine. Adult male Wistar rats were given the bacterial formulation or vehicle (milk) orally for 28 days. During the last 7 days, animals were exposed to volatilized cocaine, and locomotor sensitization and anxiety-related behaviors were assessed. Fecal microbiota composition, short-chain fatty acids, and plasma cytokine levels were also evaluated. Results showed that cocaine induced locomotor sensitization, which was not significantly attenuated by the bacterial treatment. Interestingly, cocaine-sensitized animals showed a decrease in locomotor activity on days 6 and 7, suggesting a tolerance-like effect, while bacterial treatment tended to prevent it, maintaining an elevated activity. No significant differences were observed in anxiety-related behaviors. Marked GM structural changes, particularly in β-diversity, were detected in animals receiving bacteria and cocaine treatments. Amplicon sequence variants (ASVs) belonging to the genera Limosilactobacillus and Negativibacillus were reduced, whereas ASVs related to the genus Helicobacter and Parasutterella excrementihominis increased in the bacteria/cocaine group compared to control and the other treated groups. Propionic acid levels were reduced only in cocaine-treated rats, while interleukin (IL)-6 and IL-10 plasma concentrations remained unchanged. Although the multi-strain formulation induced behavioral changes alongside modifications in GM structure, accurate strain selection is required to mitigate cocaine-related effects. Furthermore, new studies are needed to elucidate the mechanisms underlying GM-brain interactions in SUD.