Adaptive anxious states and down-regulation of dopamine activity under amygdala activation in rats

All individuals face different challenges every day. Under threats, the basolateral nucleus of the amygdala (BLA) is engaged to initiate proper physiological and behavioral responses. In this study, we pharmacologically activated the BLA in rats with no stress history to examine how animals regulated their anxiety- and despair-like behaviors in face of different task demands, as well as their dopamine (DA) activity in ventral tegmental area (VTA). The number of spontaneously firing VTA DA neurons, defined as "population activity", decides the amplitude of DA response to external stimuli, which can be assessed by the behavioral responses of the animals to amphetamine (AMPH) administration; several studies have shown that the level is positively correlated with the AMPH-induced increase in locomotor activity. Our results showed that for anxiety-like behaviors, rats displayed lower anxiety levels in elevated plus maze (EPM) and marble burying test, but increased anxiety level in social interaction test. For despair-like behaviors, there was no difference in performance in the forced swim test (FST) we conducted. Finally, systemic injection of AMPH increased locomotor activity, which was dampened with BLA activation. The inconsistency in anxiety levels in different tasks demonstrated that rats adapted their behavioral strategies to different experimental settings. Together, our results suggested that BLA activation prepared the animals towards different modality of challenges and down-regulated their DA reward system.