Object and spatial recognition in the ischemic gerbil

Abstract

The Mongolian gerbil is extensively used to model transient cerebral ischemia, a type of stroke that can occur with anoxia and cardiac arrest. A global ischemic insult in the gerbil produces damage to hippocampal CA1 pyramidal cells comparable to that observed in humans. A limited number of models are available to evaluate the behavioral consequences of cerebral ischemia in the gerbil. The goal of the present experiments was to evaluate the impact of transient cerebral ischemia on object and spatial recognition memory as these tasks have not been previously utilized with the gerbil model. Following ischemic insult (5-min bilateral carotid occlusion) or sham procedure, gerbils were tested in a familiar environment with novel objects. A familiarization phase followed by separate test phases for presentations of a novel object or object location were conducted. Exploratory behavior for the novel object or object location was evaluated using an automated tracking system. Results indicated that both ischemic and sham subjects were able to recognize the novel object when placed in the environment. However, when confronted with a familiar object, placed in a novel location, neither group exhibited a significant increase in exploratory behavior. A second experiment was conducted to further investigate the spatial recognition task. Subjects were habituated to the apparatus in addition to the experimental objects. Under this experimental condition, both groups exhibited significant exploratory behavior for the object placed in the novel location. The ischemic and control groups differed from each other during habituation with ischemic subject showing significantly higher activity levels. It is possible that differences between the groups remain but that these recognition findings are a result of extended habituation to the experimental objects. Further investigation of this matter is needed to determine the effect of prior object exposure on exploratory behavior in the spatial recognition task.