Estimating the synaptic concentration of norepinephrine in dentate gyrus which produces β-receptor mediated long-lasting potentiation in vivo using microdialysis and intracerebroventricular norepinephrine

Abstract

Norepinephrine in the hippocampus of urethane anesthetized rats was monitored by microdialysis prior to, and following, an intracerebroventricular injection of 5 μg [−]NE in 2 μl of ACSF. The perforant path evoked potential in dentate gyrus was concurrently monitored by a microelectrode adjacent to the dialysis probe. NE levels 30 X basal values or greater at the recording site were related to long-lasting potentiation of the perforant path-evoked population spike. Increases of 3 X to 6 X basal NE values were not accompanied by any potentiation. NE in the midline ventricles alone did not produce potentiation. These results suggest effective NE concentrations for β-receptor activation of long-term potentiation would only occur near the NE release site.