Cornel iridoid glycoside improves memory ability and promotes neuronal survival in fimbria–fornix transected rats

Cornel iridoid glycoside (CIG) is a main component extracted from a traditional Chinese herb Cornus officinalis. Our previous study found that CIG improved neurological function in cerebral ischemic rats. The aim of this study was to investigate the therapeutic benefit of CIG in rats with fimbria–fornix transection (FFT) and explore the underlying molecular mechanisms. CIG (20, 60 and 180 mg/kg) or vehicle was intragastrically administered once daily to rats, starting immediately after the surgery and lasting for 4 weeks. Morris water maze and step-through tests showed that the memory deficits seen in FFT rats were significantly improved by CIG treatment. Immunohistochemical analysis showed that CIG treatment attenuated the loss of neurons in hippocampus. To elucidate the memory-improving mechanism of CIG, the neurotrophic factors, synaptic proteins and Bcl-2 family proteins in hippocampus were measured by Western blot analysis. FFT reduced hippocampal protein levels of nerve growth factor (NGF), tyrosine receptor kinase A (Trk A), brain-derived neurotrophic factor (BDNF), synaptophysin (SYP) and B-cell lymphoma-2 (Bcl-2), but not levels of tyrosine receptor kinase B (Trk B) and growth-associated protein 43 (GAP-43). FFT also elevated cytochorome C (Cyt c) and bcl-2-associated X protein (Bax). Administration of CIG to FFT rats significantly elevated the expression of NGF, TrkA, BDNF, SYP, GAP-43 and Bcl-2, and decreased the expression of Cyt c and Bax. These results indicated that CIG effectively counteracted cognitive impairments caused by fimbria–fornix lesions, and the mechanisms might be related to promoting neuronal survival and providing a beneficial environment for brain repair.