Hachimijiogan (HJG) is traditional herbal medicine. Recently, it has been reported that cognitive dysfunction in patients with Alzheimer‘s disease (AD) was improved by HJG treatment. However, the mechanism by which HJG improves cognitive dysfunction is still unclear. Senescence-accelerated mouse prone 8 (SAMP8) mice are used as a spontaneous animal model of AD. The present study examined the effect of HJG on cognitive dysfunction and glial cell marker expression in SAMP8 mice.
SAMP8 mice were orally administered HJG (1000 mg/kg/d) from 12 weeks of age. Three-chamber sociability and social novelty test were conducted at 38-39 weeks of age. The glial cell marker levels in the hippocampus were analyzed by western blotting.
Vehicle-treated SAMP8 mice showed the impairment of social cognition compared with SAMR1 mice, which are resistant to senescence. On the other hand, HJG-treated SAMP8 mice did not show significant impairment compared with SAMR1 mice. The levels of arginase-1, a protective microglia marker, were significantly decreased in vehicle-treated but not HJG-treated SAMP8 mice.
Our findings suggest that social cognitive dysfunction of SAMP8 mice is due, in part, to the reduced protective microglia. HJG may make the progression of cognitive dysfunction slower by attenuating reduction in protective microglia.