Comparative Characteristics of Hippocampus- Dependent Behavior in Hypokinesia and Aging

Hypokinesia is a widespread risk factor for the pathogenesis in a variety of organsystems, particularly for disorders of the central nervous system. For the aging population hypokinesia is frequently the main life-style; hypokinesis by the interruption of selfmotion, restriction of spatial and head direction provide a type of cognitive paralysis. We have investigated learning of spatial form radial maze in 7, 15 and 45 days repeated hypokinesia/hypodynamic conditioned rats. Five groups involved 40 young rats aged 5-6 months (body weight=160-180 g) and 10 adult rats aged 18-22 months (body weight 180-250 g). Animals were divided into 7-, 15-, and 45-day hypokinetic groups, exposed to hypokinesia 22 hours per day in narrow individual Plexiglas cages, which restricted their movements in all directions. There were also control and aged-control groups. Controls and adult rats remained undisturbed during the period of stress. Rats were tested in elevated plus maze (EPM) and Y-maze before and after hypokinesia exposure. After 7, 15 and 45 days of hypokinesia rats were trained on the spatial form of radial arm maze. Reference (RM) and working memory (WM) errors were calculated. In 15-day hypokinetic rats, the lowest level of WM errors was registered, whereas in adult rats it was the highest. The relative improvement of RM in 15-day hypokinetic group was noticed compared with control (P < 0.047). The continuous spatial alternation severely declined in 7 days of hypokinesia (P < 0.001). The EPM test revealed that short-term hypokinesia was provided by avoidance and lasting hypokinesia correlated with exploratory tendencies. Based on these findings, we consider that hippocampal-dependent allocentric spatial memory improvement is evident in 45-day hypokinetic group, while the egocentric response attitude is setting in lasting hypokinesia. We emphasize the contribution of hypokinesia to hippocampus mediated relational contextual memory among multidimensional memories.