Altering D1 receptor activity in the basolateral amygdala impairs fear suppression during a safety cue

Abstract

Accurate discrimination among cues signifying reward, danger or safety initiates the proper emotional response in order to guide behavior. Appropriate conditioned inhibition of fear in the presence of a safety cue would allow an organism to engage in reward seeking behaviors. There is currently little known about the mechanisms of reward, fear and safety cue discrimination and how a safety cue can inhibit fear and release reward seeking from inhibition. Here we assess reward, fear and safety cue learning together using a behavioral paradigm that has identified neurons that discriminate among these cues in the basolateral amygdala (BLA) (Sangha, Chadick, & Janak, 2013). Dopamine signaling in the BLA has been implicated in discriminatory reward learning, learned fear responses and fear extinction. We tested the hypothesis that D1 receptor activity will influence reward-fear-safety cue discrimination by using the D1 receptor agonist, SKF-3839, and antagonist, SCH-23390, either systemically or within the BLA during discrimination learning in male Long Evans rats. We show that both the agonist and antagonist interfered with fear suppression in the presence of the safety cue, when administered systemically or when infused directly into the BLA. This indicates that altering D1 receptor activity in the basolateral amygdala impairs fear suppression during a safety cue. Neither the agonist or antagonist had a consistent negative impact on discriminatory reward seeking when infused into the BLA. However, systemic administration of the D1 receptor agonist did reduce reward seeking behavior during a task that included fear and safety cues. We did not observe a negative impact on reward seeking during systemic administration of a D1 receptor agonist in a task that only included reward cue + sucrose and nonreward cue + no sucrose pairings. This indicates the impairments we saw with the systemically applied agonist in the safety-fear-reward cue discrimination task were more likely due to effects on fear and/or motivation rather than on cue discrimination. Together, our data indicate that altered dopamine D1 receptor activity in the BLA may be a potential mechanism that leads to the impairment in fear suppression to the safety signal seen with PTSD patients.

Keywords: Amygdala; Dopamine; Fear; Safety.