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. 2024 Mar;44(1):256-261.
doi: 10.1002/npr2.12406. Epub 2023 Dec 29.

The delta opioid receptor agonist KNT-127 relieves innate anxiety-like behavior in mice by suppressing transmission from the prelimbic cortex to basolateral amygdala

Ayako Kawaminami  1 , Daisuke Yamada  1 , Toshinori Yoshioka  1 , Azumi Hatakeyama  1 , Moeno Nishida  1 , Keita Kajino  2 , Tsuyoshi Saitoh  2 , Hiroshi Nagase  3 , Akiyoshi Saitoh  1
Affiliations

The delta opioid receptor agonist KNT-127 relieves innate anxiety-like behavior in mice by suppressing transmission from the prelimbic cortex to basolateral amygdala

Ayako Kawaminami et al. Neuropsychopharmacol Rep. 2024 Mar.

Abstract

Aim: Excitatory projections from the prelimbic cortex (PL) to the basolateral nucleus of the amygdala (BLA) are implicated in the regulation of anxiety-like behaviors, and we previously demonstrated that anxiolytic-like effects of the selective delta-opioid receptor (DOP) agonist KNT-127 is involved in suppressing glutamate neurotransmission in the PL. Here, we investigated the mechanisms underlying the anxiolytic-like effect of KNT-127 in mice by combining optogenetic stimulation of the PL-BLA pathway with behavioral analyses.

Methods: Four-week-old male C57BL/6J mice received bilateral administration of adeno-associated virus (AAV)2-CaMKIIa-hChR2(H134R)-enhanced yellow fluorescent protein (EYFP) into the PL to induce expression of the light-activated excitatory ionic channel ChR2. Subsequently, an optic fiber cannula connected to a wireless photo-stimulator was implanted into the BLA for optogenetic PL-BLA pathway stimulation. We evaluated innate anxiety using the elevated plus maze (EPM) and open field (OF) tests as well as learned anxiety using the contextual fear conditioning (CFC) test.

Results: Optogenetic activation of the PL-BLA pathway enhanced anxiety-like behaviors in the EPM and OF, while prior subcutaneous administration of KNT-127 (10 mg/kg) reduced this anxiogenic effect. In contrast, optogenetic activation of the PL-BLA pathway had no significant effect on conditioned fear.

Conclusion: Our findings indicate that the PL-BLA circuit contributes to innate anxiety and that the anxiolytic-like effects of KNT-127 are mediated at least in part by suppression of PL-BLA transmission. The PL delta-opioid receptor may thus be an effective therapeutic target for anxiety disorders.

Keywords: anxiety; basic; basolateral amygdala; delta opioid receptor; excitatory synaptic transmission; prelimbic cortex.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

FIGURE 1
FIGURE 1
Experimental set‐up and behavioral analysis. (A) Schematic of the experimental procedures showing bilateral administration of adeno‐associated virus (AAV)2‐CaMKIIa‐hChR2(H134R)‐enhanced yellow fluorescent protein (EYFP) or AAV2‐CaMKIIa‐EYFP into the prelimbic cortex (PL) and implantation of a dual‐LED optic cannula into the basolateral amygdala (BLA) of 5‐week‐old mice. Parts of images were extracted from the mouse brain atlas by Paxinos and Franklin. (B, C) Effects of optogenetic PL activation on innate anxiety‐like behavior in the elevated plus maze (EPM) test. The yellow fluorescent protein (YFP) + LED group (n = 9) was injected with AAV2 vector encoding only YFP as the control treatment and stimulated by LED to activate the PL, while the ChR2 + LED group (n = 9) was injected with AAV2 vector expressing the light‐activated excitatory ionic channel ChR2 to induce PL excitation upon LED stimulation. (B) Percentage of time spent on the open arms. (C) Total arm entries. (D–F) Effects of optogenetic PL activation on innate anxiety‐like behavior in the open field (OF) test. The number of mice in each group was as follows: n = 12 for YFP + LED and n = 8 for ChR2 + LED. (D) Percentage of time mice spent in a central area. (E) Duration of central area exploration. (F) Number of crossing counts into adjacent areas. (G, H) Effects of optogenetic PL activation on conditioned anxiety‐like behavior in the contextual fear conditioning (CFC) test. The number of mice in each group was as follows: n = 12 for YFP + LED and n = 8 for ChR2 + LED. (G) Percent freezing on conditioning days (pairing of shock and context) and re‐exposure days (re‐exposure to context alone). (H) Time course of percent freezing in mice. Results are expressed as the mean ± standard error of the mean (SEM). *p < 0.05 and **p < 0.01 by unpaired Student's t��test.
FIGURE 2
FIGURE 2
Modulatory effects of KNT‐127 on anxiety‐like behavior in the elevated plus maze (EPM) test. Mice received either saline or KNT‐127 (10 mg/kg, s.c.) 30 min before the test and 10‐Hz photo‐stimulation of the prelimbic cortex (PL)–basolateral amygdala (BLA) pathway during the test. (A) Percent time spent in the open arms. (B) Time course of percent time spent in the open arms. (C) Total arm entries. Results are expressed as the mean ± standard error of the mean (SEM). The number of mice in each group was as follows: n = 5 for the yellow fluorescent protein (YFP) + saline, n = 6 for YFP + KNT‐127, n = 6 for ChR2 + saline, and n = 6 for ChR2 + KNT‐127. *p < 0.05 by one‐way or two‐way ANOVA with post‐hoc Bonferroni tests.
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