Amygdala circuitry mediating reversible and bidirectional control of anxiety

Abstract

The amygdala, a brain region important for learning fearful memories, is thought to have a role in generalized anxiety, but the subregions and connections involved in this response are unknown. Now, using optogenetic stimulation of basolateral amygdala terminals in the central nucleus of the amygdala of rats, a specific circuit for natural bidirectional anxiety control has been identified. Stimulating these neurons has a calming effect, whereas blocking the same projection increases anxiety-related behaviours. These findings are consistent with a role for the central nucleus of the amygdala in anxiety, although there may be other circuits working in parallel or downstream of the amygdala. The amygdala, a brain region important for learning fearful memories, is thought to have a role in generalized anxiety, but the critical subregions and connections are unknown. This paper shows that optogenetic stimulation of basolateral amygdala (BLA) terminals in the central nucleus of the amygdala of rats with channelrhodopsin has an anxiolytic effect, whereas inhibition of the same projection with eNpHR3.0 increases anxiety related behaviours. These effects were not observed with direct optogenetic control of BLA somata themselves, indicating that selective activation of certain connections can have different effects. Anxiety—a sustained state of heightened apprehension in the absence of immediate threat—becomes severely debilitating in disease states1. Anxiety disorders represent the most common of psychiatric diseases (28% lifetime prevalence)2 and contribute to the aetiology of major depression and substance abuse3,4. Although it has been proposed that the amygdala, a brain region important for emotional processing5,6,7,8, has a role in anxiety9,10,11,12,13, the neural mechanisms that control anxiety remain unclear. Here we explore the neural circuits underlying anxiety-related behaviours by using optogenetics with two-photon microscopy, anxiety assays in freely moving mice, and electrophysiology. With the capability of optogenetics14,15,16 to control not only cell types but also specific connections between cells, we observed that temporally precise optogenetic stimulation of basolateral amygdala (BLA) terminals in the central nucleus of the amygdala (CeA)—achieved by viral transduction of the BLA with a codon-optimized channelrhodopsin followed by restricted illumination in the downstream CeA—exerted an acute, reversible anxiolytic effect. Conversely, selective optogenetic inhibition of the same projection with a third-generation halorhodopsin15 (eNpHR3.0) increased anxiety-related behaviours. Importantly, these effects were not observed with direct optogenetic control of BLA somata, possibly owing to recruitment of antagonistic downstream structures. Together, these results implicate specific BLA–CeA projections as critical circuit elements for acute anxiety control in the mammalian brain, and demonstrate the importance of optogenetically targeting defined projections, beyond simply targeting cell types, in the study of circuit function relevant to neuropsychiatric disease.