Functional independence of endogenous μ- and δ-opioid receptors co-expressed in cholinergic interneurons

Abstract

Learning to be safe is central for adaptive behaviour when threats are no longer present. Detecting the absence of an expected threat is key for threat extinction learning and an essential process for the behavioural treatment of anxiety related disorders. One possible mechanism underlying extinction learning is a dopaminergic mismatch signal that encodes the absence of an expected threat. Here we show that such a dopamine-related pathway underlies extinction learning in humans. Dopaminergic enhancement via administration of L-DOPA (vs. Placebo) was associated with reduced retention of differential psychophysiological threat responses at later test, which was mediated by activity in the ventromedial prefrontal cortex that was specific to extinction learning. L-DOPA administration enhanced signals at the time-point of an expected, but omitted threat in extinction learning within the nucleus accumbens, which were functionally coupled with the ventral tegmental area and the amygdala. Computational modelling of threat expectancies further revealed prediction error encoding in nucleus accumbens that was reduced when L-DOPA was administered. Our results thereby provide evidence that extinction learning is influenced by L-DOPA and provide a mechanistic perspective to augment extinction learning by dopaminergic enhancement in humans.

Ligand-directed labeling of opioid receptors for covalent attachment of fluorophores or small-molecule probes

“… (C) Agonist-dependent endocytosis of endogenous MOR and DOR in striatal cholinergic interneurons. 2 Arrow heads indicate fluorescence staining along plasma membrane, which appears as a line. Arrows show some pools of endosomes as fluorescence puncta throughout the cytoplasm after agonist activation.…”

“… 3 The development of a chemical labeling approach that resulted in naltrexamine-acylimidazole compounds (NAIs) offers alternative ways to study endogenous ORs from any cells or animals. 1 , 2 The labeling of ORs with NAI compounds relies on a high affinity antagonist naltrexamine to initiate binding at the orthosteric pocket of receptor, which then guide a chemical bond to take place between the reactive acylimidazole moiety of NAI and a nucleophile of amino acid side chains including Lys, Ser, Thr, Tyr or His on the receptor ( Figure 1 A). The reaction yields a permanent attachment of a reporter or fluorescent dye to the receptor.…”

“…This protocol details the synthesis and specific labeling of NAI compounds for visualization and functional studies of ORs. 1 , 2 …”

“…For complete details on the use and execution of this protocol, please refer to Arttamangkul et al. 1 , 2 …”

Knock-In Mouse Models to Investigate the Functions of Opioid Receptors in vivo

“…Given that this first-of-kind approach could presumably be transposed to other GPCRs, the use of such probes might eventually be applied for the study of OPr. Similarly, although it was not carried out in living animals, advances have also been recently denoted for the visualization of endogenous MOPr and DOPr in striatal cholinergic interneurons (Arttamangkul et al, 2021). Using NAI-A594, a ligand-directed labeling agent, the authors fluorescently labeled both OPr from live brain slices and concluded that MOPr and DOPr function independently, despite being localized in the same neurons (Arttamangkul et al, 2021).…”