Effects of stress and exercise on rat hippocampus and striatum extracellular lactate

Extracellular lactate was continuously monitored (lactography) to determine the effect of various stressors to assess glucose metabolism in the rat hippocampus and striatum. It appeared that immobilization, emotional stress, and exercise (physiological stress) all resulted in an increase in hippocampal extracellular lactate. Exercise had the most pronounced effect. These increases were different for rats raised in different laboratories. Only during exercise a transient increase in lactate was seen in striatum. Peripheral infusions of epinephrine and/or corticosterone did not affect the basal levels of hippocampal lactate. Adrenodemedullated rats showed an attenuated lactate increase compared with control rats during and shortly after exercise. Administration of ipsapirone, an anxiolytic drug, attenuated the stress-induced formation of the hippocampal lactate. The present study demonstrates the usefulness of lactography to monitor regional brain metabolism in freely moving animals, exposed to various stressors, breeding conditions, or drugs. The observed different responsiveness of the two brain-region studies emphasizes the different involvement of the striatum and hippocampus in motor and emotional behavior, respectively. Lactate formation is stimulated by excitatory neuronal activity, presumably originating in the cerebral cortex, although adrenal hormones appear to contribute.