Valence dependent asymmetric release of norepinephrine in the basolateral amygdala.
Emerging evidence from literature on humans suggests the valence of emotionally laden environmental stimuli may dictate whether amygdala activation is greater in one hemisphere relative to the contralateral side. However, only a paucity of animal studies attempt to unravel the mechanisms underlying the selective, valence-dependent initiation of activity in the amygdala of opposing hemispheres. The present studies assessed whether exposure to positive or negative appetitive conditions in an operant learning task differentially impacts norepinephrine activation of the left versus right amygdala, respectively. Dialysate samples of norepinephrine were collected from the basolateral nucleus of male Sprague-Dawley rats. Fluctuations in norepinephrine activity were sampled during training conditions involving an abrupt shift (i.e., increase or decrease) in the magnitude of food rewards normally provided for bar press responses. In a subsequent study, dialysate samples of norepinephrine were collected before, during, and after presentation of a negatively valenced stimulus involving footshock delivery during Pavlovian fear conditioning. Norepinephrine concentrations in the left but not right basolateral amygdala were elevated in groups presented with a positive experience of an unexpected increase in food reward after bar pressing (p < .01), relative to respective controls. In contrast, exposure to negatively valenced events involving a reduction in expected food rewards after bar pressing or presentation of a footshock during fear conditioning produced significant increases in norepinephrine output sampled from only the right but not left basolateral amygdala. These findings demonstrate that the valence of a learning event is selective in initiating asymmetric activation of the basolateral amygdala.