Parkinson’s disease (PD) is a progressive, irreversible neurodegenerative disorder characterized by motor impairments and a wide spectrum of non-motor symptoms, including gastrointestinal dysfunction, sleep disturbances, depression, and cognitive decline. These manifestations arise from disturbances across multiple systems—gastrointestinal, neuroendocrine, immune, enteric, and central nervous systems. Alterations in the gut microbiota may play a causal role in PD onset and frequently accompany disease progression. The gut–brain axis, particularly the vagus nerve, is increasingly recognized as a key communication pathway whose dysregulation contributes to systemic dysfunction and the breakdown of homeostasis, ultimately driving PD pathology. Currently, there is no cure for PD, and existing treatments primarily target symptom relief. Effective management of PD requires a comprehensive approach that integrates multiple pharmacologically active agents aimed at restoring impaired organ functions and, when possible, neutralizing toxic factors that accelerate disease progression. One promising therapeutic avenue lies in functional gut bacteria, which form the basis for developing live biotherapeutic products, postbiotics, and bacterial vesicles. In this review, we summarize current data on the effects of probiotics in PD, drawing on both animal models and clinical studies. We highlight the role of probiotics in modulating PD pathophysiology and discuss their potential as adjunctive therapeutic agents. To provide a broader perspective, we also include sections describing the clinical manifestations of PD, gut microbiota alterations associated with the disease, and the role of artificial intelligence, particularly machine learning, in constructing functional models of PD.

Parkinson’s disease (PD) is characterized by slow progression with a long prodromal stage and the gradual evolution of both neuropsychological symptoms and subtle motor changes, preceding motor dysfunction. Thus, in order for animal models of PD to be valid, they should reproduce these characteristics of the disease. One of such models, in which neuropathology is induced by chronic injections of low doses of mitochondrial toxin rotenone, is well established in rats. However, data on this model adapted to mice remain controversial. We have designed the study to describe the timecourse of motor and non-motor symptoms during chronic subcutaneous administration of rotenone (4 mg/kg daily for 35 days) in C57BL/6 mice. We characterize the underlying neuropathological processes (dopaminergic neuron degeneration, regional brain metabolism, monoamine neurotransmitter and lipid peroxidation changes) at different timepoints: 1 day, 2 weeks and 5 weeks of daily rotenone exposure. Based on the behavioral data, we can describe three stages of pathology: cognitive changes from week 2 of rotenone exposure, subtle motor changes in week 3–4 and motor dysfunction starting roughly from week 4. Neuropathological changes in this model include a general decrease in COX activity in different areas of the brain (acute effect of rotenone) and a more specific decrease in midbrain (chronic effect), followed by significant neurodegeneration in SNpc but not VTA by the 5th week of rotenone exposure. However, we were unable to find changes in the level of monoamine neurotransmitters neither in the striatum nor in the cortex, nor in the level of lipid peroxidation in the brainstem. Thus, the gradual progression of pathology in this model is linked with metabolic changes, rather than with oxidative stress or tonic neurotransmitter release levels. Overall, this study supports the idea that a low-dose rotenone mouse model can also reproduce different stages of PD as well as rats.

Since there is currently no cure for Parkinson’s disease, pharmacobiotic approaches based on gut microbiota—capable of producing pharmacologically active compounds—are under development. In this study, we propose LfU21, derived from the strain Limosilactobacillus fermentum U-21, as a candidate pharmacobiotic. To evaluate its efficacy, a combined LPS- and lactacystin (LAC)-induced Parkinson’s disease model was established in Wistar rats. Effects were assessed using behavioral, biochemical, immunomodulatory, and transcriptomic biomarkers. LfU21 administration reduced α-synuclein levels, altered motor performance in the “Rung ladder” test, and modulated bdnf gene expression in the right and left striata. Under LPS exposure, LfU21 prevented alterations in immune response markers, GSH levels, drd2 and bdnf gene expression, and intestinal goblet cell counts. In LAC and LAC + LPS groups, LfU21 mitigated the rise in α-synuclein, the decline in bdnf expression, and behavioral deficits in the “Open Field” and “Rung ladder” tests, respectively. The multifunctional activity of LfU21 in a combined Parkinson’s disease model underscores its therapeutic potential and helps identify a target patient cohort for future clinical trials.

Parkinson’s disease is the second most common neurodegenerative movement disorder caused by the death of dopaminergic neurons in the Substantia nigra. The motor symptoms of Parkinson’s disease only become apparent in the late stages, whereas non-motor impairments often manifest earlier. Therefore, devising adequate experimental models to study the pathogenesis of Parkinson’s disease is of fundamental scientific importance. In this study, we aimed to evaluate the behavioral and neurochemical characteristics in a model of the premotor stage of parkinsonism in mice induced by chronic administration of a low dose of methyl-4-phenyl-1,2,3,6-tetrahydropyridine MPTP. Administering 3 mg/kg of the toxin for 35 days does not cause motor deficits, except in fine motor skills, and results in impaired spatial learning. In addition, this stage is characterized by the depletion of striatum and prefrontal cortex dopamine, decreased tyrosine hydroxylase in striatum and Substantia nigra, increased cytochrome oxidase and superoxide dismutase expression, and microglia activation. Concluding, the presented model made it possible to identify a complex of physiological and neurochemical disorders characteristic of the early stage of Parkinsonism.

Background: Glucagon-like peptide-1 receptor (GLP1R) agonists, particularly semaglutide, show neuroprotective effects in genetic models of Alzheimer’s disease (AD). However, their delayed and long-term effects in sporadic AD, such as the intracerebroventricular streptozotocin (STZ) injection, remain insufficient. It is unclear how long the effects of GLP1R agonists persist after discontinuation and whether a single course can suppress progressive neurodegeneration. This study aimed to evaluate the delayed effects of semaglutide administration on morphological changes in neurons and glial cells in the hippocampus associated with cognitive impairment in an STZ-induced rat model of AD. Methods: Rats received bilateral intracerebroventricular STZ injections (3 mg/kg) followed by a 5-week course of intraperitoneal administration of semaglutide (0.1 mg/kg, every other day), and were euthanized 60 days after discontinuation of semaglutide administration. Immunomorphological methods were used to detect neuronal, astrocytic and microglial alterations. A novel object recognition test was performed to assess behavioral effects. Results: STZ-treated animals demonstrated cognitive impairments, ventriculomegaly, a significant increase in p-tau protein fluorescence intensity (p = 0.02), a decrease in CA1–CA3 field area (by 23%, p = 0.008), and reduced hippocampal neuronal density. Decreases in TOMM20 (mitochondrial marker) and synaptophysin levels were accompanied by significant glial activation in the hippocampal CA3 field. Semaglutide administration significantly reduced the enlarged ventricular lumen (by 43.5%), decreased p-tau fluorescence intensity, reduced vimentin-positive reactive astrocytes (by 68.4%), and increased synaptophysin fluorescence intensity. Furthermore, it reduced microglial activation (decreasing IBA1 cell density and elongation) and alleviated the disrupted AQP4 distribution. However, semaglutide did not completely halt the neurodegenerative process and showed no effect on the number of doublecortin-positive cells in the dentate gyrus. Conclusions: Hippocampal changes assessment revealed that course administration of semaglutide exerts prolonged effects, attenuating the severity of pathomorphological alterations and behavioral changes in a sporadic AD model after drug discontinuation.

The use of substances that modulate mitochondrial dynamics in cells of nervous tissue represents a new direction in targeted therapy for neurodegeneration. The aim of this study was to evaluate the effect of mitochondrial division inhibitor-1 (Mdivi-1) on neurons and microgliocytes of the substantia nigra under conditions of partial damage to the dopaminergic system. This study was conducted using the 6-hydroxydopamine model of parkinsonism in rats; a separate experimental group of animals received Mdivi-1 intraperitoneally at a dose of 20 mg/kg for 5 days. The intensity of immunofluorescence staining for Tomm20, MTCO1, pDrp1, and Mfn2 was evaluated in neurons of the substantia nigra, and microglial activation was morphologically assessed. It was found that unilateral administration of 6-OHDA led to pro-inflammatory changes in microglia and changes in mitochondrial markers of neurons on the side of the substantia nigra contralateral to the toxin injection. Mdivi-1 did not affect the damage and mitochondrial proteins of neurons in pars compacta of the substantia nigra; however, it changed mitochondrial markers in nervous cells of the pars reticulata. The use of Mdivi-1 to address abnormal processes in neurodegeneration requires additional studies that include a differential assessment of its effects on various cell types.