Norepinephrine release in the amygdala after systemic injection of epinephrine or escapable footshock: contribution of the nucleus of the solitary tract

Several findings based largely on lesions and drug manipulations within the amygdala suggest that norepinephrine (NE) systems in the amygdala contribute to enhancement of memory processes by epinephrine (EPI). However, no studies to date have directly measured changes in the release of NE in the amygdala after EPI injection. In Experiment 1, in vivo microdialysis was used to assess amygdala NE release after systemic injection of saline, EPI (0.1 or 0.3 mg/kg), and administration of an escapable footshock (0.8 mA, 1 s). Both doses of EPI produced a significant elevation in NE release that persisted for up to 60 min. In Experiment 2, the local anesthetic lidocaine (2%) was infused (0.5 microl) into the nucleus of the solitary tract (NTS) immediately before injection of 0.3 mg/kg EPI. The EPI-induced elevation in amygdala NE release observed in Experiment I was attenuated by inactivation of the NTS. These findings indicate that systemic injection of EPI increases release of NE in the amygdala and suggest that the effects are mediated in part by activation of brainstem neurons in the NTS that project to the amygdala.