Abstract

Projection-Targeted Photopharmacology Reveals Anxiolytic Function of Presynaptic mGluR2 in Cortical-Amygdala Circuits

Stujenske J, Munguba H, Gutzeit V, Singh A, Eghbali N, Kristt M, Shaver D, Thukral S, Lee FS, Broichhagen J, Liston C, Levitz J
61st Annual Meeting of the American College of Neuropsychopharmacology. 2022.

Abstract

Background: Anxiety disorders are the most common psychiatric disorders, affecting about 30% of US adults during their lifetime. Anxiolytic medications primarily work through serotoninergic or GABAergic signaling, while there are no approved treatments that work via a principally glutamatergic mechanism. Metabotropic glutamate receptor 2 (mGluR2) is mainly localized presynaptically and together with mGluR3 mediates feedback inhibition of glutamate release. mGluR2/3 mixed agonists have been shown to mediate anxiolytic effects in humans through an unknown mechanism. In this study, we describe distinct anxiolytic roles of mGluR2 at medial prefrontal (mPFC) and insular (IC) projections to the basolateral amygdala (BLA).

Methods: Using adeno-associated viruses in a transgenic Grm2-Cre mice, mGluR2+ projectors to the BLA were labeled. The specific roles of mPFC and IC projections in anxiety-related behavior were characterized using optogenetic techniques and fiber photometry. The specific function of presynaptic mGluR2 was probed using a novel photopharmacological tool, photoswitchable orthogonally and remotely tethered ligands, to specifically activate mGluR2 in prefrontal or insular terminals. Conventional and photopharmacological manipulations were performed during in vitro electrophysiology recordings to characterize its function in synaptic transmission and in vivo during behavioral assays that elicit various forms of anxiety-related avoidance reactions. N = 5-20 male mice per group.

Results: Systemic administration of a mGluR2/3 mixed agonist (LY37) decreased spatial avoidance, while a mixed antagonist (LY34) increased avoidance. LY37 infused into the BLA also mediated anxiolysis. mGluR2 was found to be enriched in projectors to the BLA from the mPFC and IC. Neuronal activation of both cell populations was observed during anxiety-related assays using fiber photometry. In vitro, 89% (n = 19) and 100% (n = 14) of BLA principal neurons were activated by mGluR2+ projections from the mPFC and IC, respectively. This activation was acutely dampened by mGluR2 photoactivation, while long-term depression was induced by prolonged photoactivation. Acute photoactivation of mGluR2 in mPFC, but not IC, terminals decreased spatial avoidance, and prolonged photoactivation led to anxiolysis at 4 hours but not 7 days post-light. In contrast, acute photoactivation of mGluR2 in IC, but not mPFC, led to diminished social avoidance and avoidance of predator urine. Photoactivation of mGluR2 in either projection decreased the latency during novelty-suppressed feeding.

Conclusions: We describe both distinct and overlapping anxiolytic functions of mGluR2 in mPFC and IC projections to the BLA. mGluR2 represents a promising therapeutic target for the treatment of anxiety.