Response of amygdalar norepinephrine to footshock and GABAergic drugs using in vivo microdialysis and HPLC.

These studies used in vivo microdialysis and high-performance liquid chromatography (HPLC) to examine levels of norepinephrine (NE) within the amygdala in response to both footshock and GABAergic compounds. In Experiment 1, microdialysis probes were inserted into a previously implanted guide cannula aimed at the amygdala and the level of NE was examined in response to footshock. A 0.55 mA (2 s) footshock induced a significant increase in NE levels when the microdialysis probe was located within the amygdala; levels of NE did not differ from baseline in rats with microdialysis probes located outside the amygdala. Experiment 2 examined the effects of the GABAergic antagonist, picrotoxin, the GABAergic agonist, muscimol, and saline on NE levels in the amygdala. Rats treated systemically with picrotoxin showed a dramatic increase in levels of NE within the amygdala. In contrast, systemic injection of muscimol resulted in decreased levels of NE. These findings are consistent with the hypothesis that drugs that are capable of modulating memory do so by altering levels of NE within the amygdala. Copyright 1999 Elsevier Science B.V.