Laterality dissociation of ventral hippocampus inhibition in learning and memory, glial activation and neural arborization in response to chronic stress in male Wistar rats

Abstract

Many studies suggest that animals exhibit lateralized behaviors during stressful situations. However, which brain structure in each hemisphere underlies such lateralized function is unclear. This study, investigated the effects of bilateral and unilateral inhibition of the ventral hippocampus (VH) on chronic restraint stress (CRS) induced memory impairment. Unilateral and bilateral VH cannulation was carried out. After a week of recovery, lidocaine hydrochloride was injected into the rat VH ten minutes before CRS induction for seven consecutive days. Behavioral (Y-maze and Morris water maze; MWM)), and histological (glial fibrillary acidic protein; GFAP, ionized calcium-binding adapter protein-1; Iba-1, as well as Golgi-Cox staining in the VH) studies were performed. The result showed no significant difference between the effect of right-only and left-only of VH inhibition induced by lidocaine on spatial learning and memory and working memory. In addition, lidocaine treated groups were significantly lower in spatial learning and memory and working memory than control groups during non-stress conditions. Furthermore, the dendritic arborization in the right-only, left-only and bilateral VH microinjected lidocaine significantly decreased after the CRS condition compared with the control group. However, lidocaine microinjection resulted in up-regulation levels of GFAP and Iba1 in the right-only, left-only and bilateral of VH and they were higher significantly than that of their control groups after CRS and during non-stress condition. Meanwhile, there is no significant difference between the effect of right-only and left-only of VH inhibition on neuronal arborization and glial cells during non-stress and after the CRS condition. In conclusion, bilateral VH inhibition can give rise to increase CRS-induced memory impairment. These findings were accompanied by elevating GFAP and Iba1 while reducing the dendritic arborization.