Hippocampal Extracellular Measurements of Ascorbic Acid, Glucose and Lactate During Memory Formation

Astrocytes in the central nervous system (CNS) produce lactate, which will be preferably used as an energy source by neurons during memory formation. It is hypothesized that ascorbic acid functions as a mediator between lactate and glucose during neuronal activity, since it is able to inhibit glucose consumption and stimulate lactate uptake in neuronal cells. In this experiment, a biosensor probe able to detect lactate, ascorbic acid or glucose, was inserted in the hippocampus of young Sprague Dawley male rats to determine the concentration of these molecules during training on hippocampus-dependent place and striatum-dependent response learning tasks. The hippocampus-dependent place learning task was performed by placing a rat in a maze in which a reward will always be in the same location of a cue-rich room.  On the other hand, the striatum-dependent response learning task was performed in a maze in which the rat would learn to obtain a reward every time it turns to the same direction in a cue-poor room. It is hypothesized that the levels of extracellular ascorbic acid and lactate will be higher during place learning.  Future work will consist of inserting a biosensor with the same probes into the striatum to determine the levels of glucose, lactate and ascorbic acid during both place and response tasks. It is expected that the levels of lactate and ascorbic acid in the striatum will be higher during the response task.  These findings suggest a specific role for astrocytes during memory formation in controlling ascorbic acid and lactate release.