Evaluation of Methylmercury-Induced Motor Dysfunction and Proteomic Analysis of Cerebrospinal Fluid in Common Marmosets (Callithrix jacchus).

Methylmercury (MeHg) poisoning can lead to Minamata disease, often manifesting as motor dysfunction. We aimed to establish a quantitative evaluation method for MeHg exposure-associated motor dysfunction in the common marmoset (Callithrix jacchus). Three male marmosets were orally administered MeHg (1.5 mg Hg/kg/day) for 2 weeks, followed by a 2-week non-treatment period; three control marmosets received vehicle. Walking and spontaneous behavior were recorded weekly. After marking body segments, bounding gait videos were analyzed to assess locomotion speed, hip joint position, knee angle, dorsal neck-to-torso angle, and spontaneous behavior. In Hg-1 (MeHg-exposed marmoset with earliest symptom onset), locomotion speed and stride length decreased, while stride time increased. In Hg-2 (second marmoset to exhibit symptom onset), hip joint position and knee angle initially showed relatively normal fluctuations during bounding gait. However, their lower limits decreased following MeHg administration, and the dorsal neck-to-torso angle shifted from negative to positive. Spontaneous activity of Hg-1 and Hg-2 significantly decreased after MeHg administration. These results indicate that MeHg exposure-associated motor dysfunction in marmosets can be detected using our method, with particularly prominent lower-limb abnormalities. Furthermore, cerebrospinal fluid proteomic profiling revealed coordinated disruptions converging on three pathological axes-neuronal injury and neuroprotective responses, neuronal metabolic failure and cytosolic enzyme leakage, and impaired transport and homeostatic regulation-identifying nine proteins as candidate biomarkers. Proteomic alterations were consistent with the observed neuronal injury, neuroinflammation, metabolic dysfunction, and impaired homeostatic regulation in affected motor pathways. These findings establish the marmoset as a translational primate model for neurotoxicological assessments and biomarker discovery.