Neuropeptide FF receptor 2 inhibits capsaicin-induced CGRP Upregulation in mouse trigeminal ganglion

Abstract

Background Stimulation of trigeminovascular pathway is widely used to establish the headache animal model. Headache is a common neurological disorder, in which symptomatic attacks are mediated by calcitonin-gene-related peptide (CGRP). CGRP is synthesized and released from the trigeminal ganglion to transmit pain signals under stimulation. On the other hand, Neuropeptide FF (NPFF) is a candidate transmitter/modulator for migraine, and stimulation of its receptor, NPFFR2, increases the expression and release of CGRP in mice sensory neurons. Here, we investigate the impact of NPFFR2 on trigeminal CGRP level in a capsaicin-induced headache mouse model. Methods Mice were intracisternally injected with capsaicin into the cisterna magna to activate the trigeminovascular pathway and induce headache symptoms. Mice pretreated with Npffr2 -shRNA or NPFFR2 knockouts were adopted to test the impact of NPFFR2 on capsaicin-induced CGRP upregulation in trigeminal ganglion. The gene silencing effect of Npffr2 -shRNA in trigeminal ganglion was confirmed by real-time PCR. Trigeminal CGRP level was determined by immunofluorescence staining, and the percentage of CGRP-positive cell was calculated after setting the signal intensity threshold by Image J software. Amount of trigeminal CGRP in NPFFR2 overexpressed mice was also measured by CGRP ELISA. Findings Infusion of capsaicin into the cisterna magna upregulated the CGRP in trigeminal ganglion and induced spontaneous pain behaviors including the reduction of locomotor activity and the increase of freezing behavior. Intracisternal injection of Npffr2 -shRNA reduced the mRNA of Npffr2 in trigeminal ganglion. Mice pretreatment with Npffr2 -shRNA prevented capsaicin-induced CGRP upregulation in trigeminal ganglion. Similarly, CGRP upregulation was also reduced in NPFFR2 knockout mice. On the contrary, trigeminal CGRP was increased in NPFFR2 overexpressed mice. Conclusions Reducing the level of NPFFR2 leads to the downregulation of capsaicin-induced CGRP in trigeminal ganglion, which would consequently attenuate the activation of trigeminovascular pathway. Thus, NPFFR2 could serve as a potential target for neuromodulation of cephalic pain.

Ablation of NPFFR2 in Mice Reduces Response to Single Prolonged Stress Model

“…Neuropeptide FF (NPFF, FLFQPQRF-NH2) was first isolated from bovine brain and is known to regulate the pharmacological response to morphine, pain sensation, food intake, and mood disorders [ 6 , 7 , 8 , 9 ]. In the past decade, the function of NPFF in hypothalamus has been studied, with most of the focus on its regulation of the neuroendocrine system [ 10 , 11 ].…”

Preclinical orofacial pain assays and measures and chronic primary orofacial pain research: where we are and where we need to go

“…Going forward, it is important that pre-clinical studies of TN assess behaviors that could demonstrate the paroxysmal nature of pain, which could include, for instance, freezing behaviors in addition to face-grooming. Freezing is an instinctive behavior in animals to avoid physical pain ( 289 ) and is commonly assessed in pre-clinical migraine/headache research to infer pain ( 290 ) that would likely be informative for TN research.…”

Effect of chronic intermittent hypoxia on ocular and intraoral mechanical allodynia mediated via the calcitonin gene-related peptide in a rat

“…CIH may exert more substantial effects on the characteristics of daytime sleepiness in patients with OSA compared to sleep fragmentation or sleep loss [ 2 ]. However, in a migraine model, mice also showed reduced locomotor activity accompanied by increased CGRP expression in the TG [ 46 ]. Thus, the possibility that nociceptive states can reduce locomotor activity in CIH-exposed rats cannot be excluded.…”