Possible glial contribution of rat hippocampus lactate as assessed with microdialysis and stress

Microdialysis for the continuous monitoring of lactate ("lactography") was applied in rat brain hippocampus in an attempt to establish whether lactate is of neuronal or glial origin. Lactate was analyzed with an electrochemical assay after enzymatic oxidation in dialysates derived from a short-term (1 or 2 days after implantation of the probe) and a long-term (14 or 15 days) preparation. In the short-term experiment the lactate levels in the dialysate were higher without glucose in the perfusate, whereas in the long-term experiment a several fold increase in lactate was observed in the presence of 5 mM glucose. During stress, increases in lactate were virtually similar both in the acute (with or without glucose in the perfusate) and in the chronic preparation (response in the presence of glucose only). In the long-term preparation presence of reactive astroglia cells was visualized immunohistochemically with antibodies against glial fibrillary acidic protein. Damage of the hippocampus and the corpus callosum was seen in the chronic preparation with silver impregnation staining. These results emphasize the importance of the presence of glucose in the perfusate and they are consistent with the idea that glial cells contribute to extracellular lactate in the rat hippocampus in vivo and that stress activates the astroglial glycogen pool.