Enhanced release of norepinephrine in rat hippocampus during spontaneous alternation tests

Recent evidence suggests that release of acetylcholine (ACh) in the hippoca mpus is associated with performance on a spontaneous alternation task and w ith enhancement of that performance by systemic and central injections of g lucose. The present study extended these findings by examining norepinephri ne (NE) release in the hippocampus using in vivo microdialysis while rats w ere tested for spontaneous alternation performance with and without prior i njections (ip) of glucose. Microdialysis samples were collected every 12 mi n and assayed for NE content by HPLC-ECD. Like ACh, NE release in hippocamp us increased during spontaneous alternation testing. As in past experiments , administration of glucose (250 mg/kg) significantly enhanced alternation scores. However, glucose did not influence NE release either during behavio ral testing or at rest. These findings contrast with prior evidence showing that glucose augments testing-related increases in ACh release. The findin gs suggest that norepinephrine is released within the hippocampus while rat s are engaged in alternation performance. However, increased release of nor epinephrine apparently does not contribute to the enhancement of alternatio n scores produced by glucose. (C) 1999 Academic Press.