Contextual generalization of social stress learning is modulated by orexin receptors in basolateral amygdala

Fear-associated memories and behavior are often expressed in contexts/environments distinctively different from those in which they are created. This generalization process contributes to psychological disorders, particularly PTSD. Stress-related neurocircuits in the basolateral amygdala (BLA) receive inputs from hypothalamic orexin (Orx) neurons, which mediate neuronal activity by targeting orexin 1 (Orx(1)R) and orexin 2 (Orx(2)R) receptors via opposing functions. In BLA, inhibition of Orx(1)R or activation of Orx(2)R ameliorate stress responsiveness and behavior. We discovered that most Orx(1)R(+) cells also express CamKIIα, while a majority of Orx(2)R(+) cells are colocalized with GAD67. Further, Orx(1)R gene Hcrtr1 expression was positively correlated, and Orx(2)R gene Hcrtr2 expression was negatively correlated, with freezing in a phenotype-dependent fashion (Escape vs Stay) in the Stress Alternatives Model (SAM). The SAM consists of 4-days of social interaction between test mice and novel larger aggressors. Exits positioned at opposite ends of the SAM oval arena provide opportunities to actively avoid aggression. By Day 2, mice commit to behavioral phenotypes: Escape or Stay. Pharmacologically manipulating Orx receptor activity in the BLA, before Day 3 of the SAM, was followed with standard tests of anxiety: Open Field (OF) and Elevated Plus Maze (EPM). In Stay mice, freezing in response to social conflict and locomotion during SAM interaction (not home cage locomotion) were generalized to OF, and blocked by intra-BLA Orx(1)R antagonism, but not Orx(2)R antagonism. Moreover, patterns of social avoidance for Escape and Stay mice were recapitulated in OF, with generalization mediated by Orx(1)R and Orx(2)R antagonism, plus Orx(2)R stimulation.