L-theanine (LT), which is a major amino acid found in green tea, was shown to alleviate Vincristine (VCR)-induced peripheral neuropathy and associated neuronal functional changes in rats. To induce peripheral neuropathy, rats were administered VCR at a dose of 100 mg/kg/day intraperitoneally on days 1–5 and 8–12, while control rats received LT at doses of 30, 100, and 300 mg/kg/day intraperitoneally for 21 days or saline solution. Electrophysiological measurements were taken to evaluate the nerve functional loss and recovery through motor and sensory nerve conduction velocities. The sciatic nerve was examined for several biomarkers, including nitric oxide (NO), malondialdehyde (MDA), glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), total calcium, IL-6, IL-10, MPO, and caspase-3. The results showed that VCR caused significant hyperalgesia and allodynia in rats; decreased nerve conduction velocity; increased NO and MDA levels; and decreased GSH, SOD, CAT, and IL-10 levels. LT was found to significantly reduce VCR-induced nociceptive pain thresholds, decrease oxidative stress levels (NO, MDA), increase antioxidative strength (GSH, SOD, CAT), and reduce neuroinflammatory activity and apoptosis markers (caspase-3). LT’s antioxidant, calcium homeostasis, anti-inflammatory, anti-apoptotic, and neuroprotective properties make it a potential adjuvant to conventional treatment in VCR-induced neuropathy in rats.

Vitexin (VTX), a C-glycosylated flavone found in various medicinal herbs, is known for its antioxidant, anti-inflammatory, and neuroprotective properties. This study investigated the protective effects of VTX against orofacial dyskinesia (OD) in rats, induced by haloperidol (HPD), along with the neuroprotective mechanisms underlying these effects. OD was induced by administering HPD (1 mg/kg i.p.) to rats for 21 days, which led to an increase in the frequency of vacuous chewing movements (VCMs) and tongue protrusion (TP). VTX (10 and 30 mg/kg) was given intraperitoneally 60 min after each HPD injection during the same period. On the 21st day, following assessments of OD, the rats were sacrificed, and nitrosative and oxidative stress, antioxidant capacity, mitochondrial function, neuroinflammation, and apoptosis markers in the striatum were measured. HPD effectively induced OD, while VTX significantly reduced HPD-induced OD, decreased oxidative stress, enhanced antioxidant capacity, prevented mitochondrial dysfunction, and reduced neuroinflammatory and apoptotic markers in the striatum, and the protective effects of VTX on both behavioral and biochemical aspects of HPD-induced OD were significantly reduced when trigonelline (TGN), an inhibitor of the nuclear factor erythroid-2-related factor 2 (Nrf2)-mediated pathway, was administered. These findings suggest that VTX provides neuroprotection against HPD-induced OD, potentially through the Nrf2 pathway, indicating its potential as a therapeutic candidate for the prevention or treatment of tardive dyskinesia (TD) in clinical settings. However, further detailed research is required to confirm these preclinical findings and fully elucidate VTX’s therapeutic potential in human studies.

Background/Objectives: Rotenone (RT)-induced neurotoxicity is widely used to model Parkinsonism-like nigrostriatal injury and recapitulates several PD-relevant pathological features, including oxidative stress, mitochondrial dysfunction, neuroinflammation, and dopaminergic neurochemical disturbance. Loganin (LG), an iridoid glycoside isolated from Cornus officinalis, has been reported to possess antioxidant, anti-inflammatory, anti-apoptotic, and neuroprotective properties. However, its protective effects in a unilateral stereotaxic RT lesion model have not been fully elucidated. This study aimed to investigate the neuroprotective potential of LG against RT-induced Parkinsonism-like pathology in rats and to explore the possible involvement of antioxidant-related signaling mechanisms. Methods: Adult male Wistar rats were randomly assigned to twelve experimental groups (n = 8/group), including control, sham, RT, sham + LG, RT + LG, RT + trigonelline (TG) + LG, and RT + selegiline (SL). RT was stereotaxically injected once into the right substantia nigra pars compacta (SNpc) on Day 0 to induce unilateral nigrostriatal injury. LG was administered orally once daily from Day 1 to Day 21 at doses of 3, 10, and 30 mg/kg. TG was given intraperitoneally 30 min before LG treatment, while SL served as a reference antiparkinsonian drug. Behavioral assessments and biochemical analyses were conducted to evaluate motor dysfunction, oxidative and nitrosative stress, endogenous antioxidant status, mitochondrial dysfunction, inflammatory and apoptotic responses in the SNpc, and striatal catecholamine disturbances. Results: RT lesioning produced significant motor deficits, oxidative and nitrosative stress, depletion of endogenous antioxidant defenses, mitochondrial dysfunction, inflammatory and apoptotic activation in the SNpc, and abnormalities in striatal catecholamine levels. LG treatment significantly attenuated these pathological changes, with more pronounced protective effects observed at 10 and 30 mg/kg. Co-administration of TG partially weakened the beneficial effects of LG, suggesting the possible involvement of antioxidant defense-related signaling while not providing direct proof of a single pathway. SL also ameliorated RT-induced behavioral and biochemical abnormalities. Conclusions: These findings suggest that LG confers multi-target neuroprotective effects against RT-induced Parkinsonism-like features in rats. The protective actions of LG were associated with attenuation of oxidative stress, mitochondrial dysfunction, neuroinflammation, apoptosis, and catecholaminergic disturbances. Because the pathway analysis remains pharmacological and indirect, additional studies using direct molecular validation are warranted before LG can be considered a disease-modifying candidate for PD-related neurodegeneration.