Tatyana N. Sergeyeva

BACKGROUND: Olfactory dysfunction is a prodromal symptom of many neurodegenerative diseases. Neuroinflammatory and neurodegenerative processes in the olfactory bulbs may be initiated by infectious agents in the nasal cavity, particularly bacterial lipopolysaccharide (LPS). The molecular mechanisms mediating the effects of this endotoxin on the olfactory epithelium and the development of pathological processes in the olfactory bulbs remain insufficiently studied. AIM: This study aimed to investigate the effects of different doses of intranasally administered lipopolysaccharide on the intensity of immunopositive staining of the olfactory epithelium with antibodies against alpha-synuclein (α-syn) and the adaptor protein MyD88, as well as of olfactory bulbs with antibodies against α-syn and glial fibrillary acidic protein (GFAP). METHODS: The study included 18 male BALB/c mice weighing 20–33 g. Animals received unilateral intranasal injections of sterile saline 10 μL daily (control) or lipopolysaccharide at a high (0.1 μg/mL) or low (0.01 μg/mL) concentration. After 28 days, the brains and nasal structure complexes were excised and frozen using dry ice. Serial cryostat sections (14 μm) were prepared and stained with methylene blue and antibodies against α-syn, MyD88, and GFAP. The intensity of immunolabeling was quantitatively assessed using Image-Pro Insight 8.0 software. RESULTS: Unilateral intranasal administration of lipopolysaccharide solution to mice resulted in a dose-dependent increase in α-syn levels in receptor cells, olfactory nerve bundles, and olfactory bulb glomeruli, along with a dose-dependent increase in MyD88 in the receptor epithelium and GFAP in the glomerular layer of the olfactory bulb ipsilateral to endotoxin administration. CONCLUSION: The observed morphological and immunohistochemical changes in the olfactory bulbs following intranasal lipopolysaccharide administration indicate the development of dose-dependent neuroinflammation in the glomerular layer. Neuroinflammation in the olfactory bulb appears to be initiated by LPS-induced upregulation of α-syn expression in receptor neurons projecting to the bulbs, mediated by activation of MyD88, which participates in intracellular signaling downstream of Toll-like receptors and interleukin-1 receptor family members.

BACKGROUND: Neuroinflammation is a key pathophysiological mechanism in age-related neurodegenerative diseases such as Parkinson's disease. Dihydroquercetin's water-soluble form (DHQ-WF) is considered a promising agent capable of inhibiting the neuroinflammatory process. Nevertheless, uncertainties persist regarding the cellular and molecular mechanisms governing its effects, taking into account nervous tissue's gliovascular organization. AIM: To study structural changes of microcirculatory vessels and functional responses of micro- and astroglial cells in the substantia nigra of young and old rats in response to intranigral injection of lipopolysaccharide (LPS) and subsequent oral administration of DHQ-WF. MATERIALS AND METHODS: Young (250–320 g) and old (390–450 g) Wistar rats were injected into the substantia nigra using a stereotaxic device with 2 μL of LPS solution at a concentration of 0.01 μL/mL (experimental groups; n=24) or 2 μL of sterile saline (control groups; n=12). Half of the animals in the experimental groups (6 animals of each age group) received 2 ml of a solution containing DHQ-WF ("Taxifolin aqua"; Advanced Technologies Ltd., Russia) at a concentration of 3 mg/mL by gavage daily for 8 weeks. At the end of the experiment, the animals were transcardially perfused with 4% paraformaldehyde, the brain was extracted and frozen on dry ice. Cryostat sections obtained on the cryotome were stained with FITC-labelled tomato lectin for the detection of vascular endothelium and antibodies against GFAP and CD-11β for the immunohistochemical detection of astrocytes and microglia, respectively. The length and number of vessels and their branches were counted using AngioTool software. The areas of glial cell bodies and their processes were measured using the morphometric software ImagePro Inside 8.0. RESULTS: 8 weeks after LPS administration into the substantia nigra (SN) of old rats, a significant excess of areas occupied by cell bodies and processes of microglial and astroglial cells, as well as the number of vessels on the standard plot, was found both in young animals that had experienced similar effects and in old control animals. Oral administration of DHQ-WF to rats significantly reduced LPS-induced glial activation in young and old animals. In addition, administration of DHQ-WF to old animals reduced the intensity of microvascular SN remodeling induced by LPS administration. CONCLUSIONS: Administration of LPS to the SN of rats of different ages causes neuroinflammation, which is maximally expressed in aged animals. In addition, LPS-induced microvessel angiogenesis is observed in aged animals. Administration of DHQ-WF for 8 weeks significantly reduces these LPS-induced changes, which allows us to consider it as a promising anti-neuroinflammatory agent.