Norepinephrinergic projection from locus coeruleus to parafascicular nucleus promotes pain and anxiety-like behaviors in mice
Zhong-Yi Liu, Fei Li, Li-Ming Liu, Yao-Hua Liu, Jia Li, Zi-Ang Li, Jin Cheng, Tian-Yu Zhao, Hui-Min Tian, Dong-Ning Li, Sha-Sha Tao, Hui Li, Fen-Sheng Huang, Yun-Qing Li
Zhong-Yi Liu, Fei Li, Li-Ming Liu, Yao-Hua Liu, Jia Li, Zi-Ang Li, Jin Cheng, Tian-Yu Zhao, Hui-Min Tian, Dong-Ning Li, Sha-Sha Tao, Hui Li, Fen-Sheng Huang, Yun-Qing Li
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Research Article Cell biology Neuroscience

Norepinephrinergic projection from locus coeruleus to parafascicular nucleus promotes pain and anxiety-like behaviors in mice

Abstract

Chronic neuropathic pain is frequently comorbid with anxiety disorders, yet the neural circuits underlying this interaction remain poorly defined. The parafascicular nucleus (PF) of the thalamus integrates nociceptive and affective signals, but its specific regulatory mechanisms in pain-anxiety comorbidity are not well known. Using spared nerve injury (SNI) model mice, we combined viral neural tracing, chemogenetics, pharmacology, and electrophysiology to dissect the locus coeruleus (LC)–PF neural pathway. Viral tracing revealed monosynaptic projections from norepinephrinergic (NEergic) neurons in the dorsal LC to Ca2+/calmodulin–dependent protein kinase IIα–immunopositive (CaMKIIα+) neurons within the PF. Chemogenetic inhibition and activation of this pathway were performed in naive and SNI mice, alongside intra-PF microinjection of the α-2 adrenergic receptor (ADRA2) antagonist yohimbine. Behavioral tests assessed mechanical/thermal hypersensitivity and anxiety-like behaviors. Results showed that 92.1% of PF-projecting LC neurons were NEergic, with 70.1% localized dorsally. Chemogenetic inhibition of the LCNE-PFCaMKIIα neural pathway significantly alleviated both acute-phase mechanical hypersensitivity (<7 days after surgery) and chronic-phase anxiety-like behaviors in SNI mice, while activation of this pathway induced pain sensitization and anxiety-like behaviors in naive mice. Intra-PF yohimbine reversed SNI-induced allodynia and anxiety-like behaviors. Electrophysiology confirmed that yohimbine increased PF neuronal intrinsic excitability. These results suggest that the LCNE-PFCaMKIIα neural pathway promotes neuropathic pain and comorbid anxiety via ADRA2-mediated suppression of PF neuronal activity. Targeted inhibition of this circuit may represent a therapeutic strategy for pain-related affective disorders.

Authors

Zhong-Yi Liu, Fei Li, Li-Ming Liu, Yao-Hua Liu, Jia Li, Zi-Ang Li, Jin Cheng, Tian-Yu Zhao, Hui-Min Tian, Dong-Ning Li, Sha-Sha Tao, Hui Li, Fen-Sheng Huang, Yun-Qing Li

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Figure 3

Monosynaptic NEergic projection from the LC to the PFCaMKIIα.

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Monosynaptic NEergic projection from the LC to the PFCaMKIIα. (A) Schema...
(A) Schematic of Fluoro-Gold (FG) injection into the PF. (B) Representative image of FG injection site in the PF. (C) Representative images of FG+ neurons (red, left) colocalization with Th+ neurons (green, right) in the LC. (D) Percentage of FG+ and Th+ double-labeled (FG+Th+) neurons among FG+ neurons in the LC (n = 3). (E) Schematic of anterograde virus injection into the LC. (F) Representative image of viral injection site in the LC. (G) Representative images of EGFP-labeled fibers/terminals (green, left) in close contact with CaMKIIα+ neurons (red) in the PF (right). (H and I) Timeline and schematic for virus injection of retrograde trans-monosynaptic tracing strategy. (J) Representative image of viral injection site in the PF. (K) Representative images of DsRed+ neurons (red, left) colocalization with Th+ neurons (green) in the LC (right). (L) Percentage of DsRed+Th+ neurons among DsRed+ neurons in the LC (n = 3). (M) Representative images of Fos expression in the LC of Sham and SNI mice. (N) The number of Fos+ neurons in the LC of Sham and SNI mice (n = 6). (O) Representative images of Fos+ neurons (green) colocalization with Th+ neurons (red, left), and their high-magnification images (right). (P) Percentage of Fos+Th+ neurons among Fos+ neurons in SNI mice (n = 6). Scale bars: 120 μm (B, F, J, and M and the left panel of C, G, K, and O) and 20 μm (the right panel of C, G, K, and O). 4V, fourth ventricle. All data presented as mean ± SEM. Statistical analysis: 2-tailed unpaired t test (N). ****P < 0.0001.