Anxiety and depression significantly contribute to heroin relapse, and addressing these issues could lower relapse rates. The basolateral amygdala (BLA) and nucleus tractus solitarius (NTS) are involved in regulating these emotions, but the molecular mechanisms during heroin withdrawal are not yet understood. Subcutaneous injection of heroin into C57BL/6J mice to simulate chronic dependence, withdrawal, and Exendin-4 treatment. Assess anxiety and depression-like behaviors using open field test (OFT), elevated plus maze (EPM), forced swimming test (FST), and tail suspension test (TST). Analyze neuronal and protein expression changes in the BLA brain area with Western blotting (WB) and immunofluorescence staining. Heroin dependence reduces glutamatergic neurons in BLA without affecting anxiety and depression-like behaviors, due to the inhibitory effect of heroin reward. During withdrawal, GLP-1 secretion by the NTS rises, increasing c-Fos and GLP-1 receptor expression in glutamatergic neurons of BLA, linked to heightened anxiety but not depression. A 7-day treatment with Exendin-4 (2 µg/kg) alleviates anxiety in withdrawal mice by downregulating GLP-1 signaling in the NTS-BLA circuit, indicating GLP-1’s role in regulating anxiety during heroin withdrawal. GLP-1 receptors within BLA may serve as molecular targets for modulating emotional states, thereby offering empirical support for strategies aimed at preventing heroin relapse.

Background/Objectives: Major depressive disorder (MDD) is a highly prevalent and disabling psychiatric condition for which current therapies remain inadequate. Probiotics acting on the microbiota–gut–brain axis are a promising preventive strategy, but their benefits are strain-specific. Here we examined whether Lacticaseibacillus paracasei LP36 alleviates lipopolysaccharide (LPS)-induced depression-like behavior in mice, and we characterized its metabolic actions using serum untargeted metabolomics. Methods: Sixty male C57BL/6J mice were randomized into eight groups (58 completed the study and were analyzed) and received saline or LP36 (1 × 10⁸, 1 × 10⁹, or 1 × 10¹⁰ colony-forming units (CFU)/mL) by gavage for 28 days, with LPS (0.5 mg/kg, i.p.) or saline given during the last 10 days. Results: LP36 pretreatment alleviated LPS-induced depression-like behavior in the sucrose preference, forced swimming, and tail suspension tests. Of 2867 annotated serum metabolites, 404 differed between the LPS and control groups, and 601 between the LP36 (10¹⁰)-treated and LPS groups. Among 180 shared differential metabolites, 172 (95.6%) changed in opposite directions, indicating that LP36 mainly reverses LPS-induced metabolic perturbations. KEGG enrichment localized these effects to lipid-related pathways, with lower relative signal intensities of polyunsaturated fatty acids and sphingolipids under LPS and higher relative signal intensities after LP36. In addition, the relative signal intensities of several microbiota-derived metabolites, including indoles, kynurenines, and secondary bile acids, shifted toward control-group values after LP36 intervention, which might reflect a contribution of the gut microbiota. Conclusions: LP36 is thus a candidate psychobiotic that may alleviate depression by reshaping gut microbiota-related metabolism and the associated lipid remodeling.