Blocking microglial pannexin-1 channels alleviates morphine withdrawal in rodents.

Nicole E Burma,Jaideep S Bains,Michael C Antle,Heather Leduc-Pessah,Stephanie L Borgland,Gerald W Zamponi,Corey Baimel,Yves De Koninck,Patrick L Stemkowski,Dinara Baimoukhametova,Robert P Bonin,Tuan Trang,Zoe F Cairncross,Jhenkruthi Vijaya Shankara,Catherine M Cahill,Michael Mousseau

doi:10.1038/nm.4281

Abstract

Opiates are essential for treating pain, but termination of opiate therapy can cause a debilitating withdrawal syndrome in chronic users. To alleviate or avoid the aversive symptoms of withdrawal, many of these individuals continue to use opiates. Withdrawal is therefore a key determinant of opiate use in dependent individuals, yet its underlying mechanisms are poorly understood and effective therapies are lacking. Here, we identify the pannexin-1 (Panx1) channel as a therapeutic target in opiate withdrawal. We show that withdrawal from morphine induces long-term synaptic facilitation in lamina I and II neurons within the rodent spinal dorsal horn, a principal site of action for opiate analgesia. Genetic ablation of Panx1 in microglia abolished the spinal synaptic facilitation and ameliorated the sequelae of morphine withdrawal. Panx1 is unique in its permeability to molecules up to 1 kDa in size and its release of ATP. We show that Panx1 activation drives ATP release from microglia during morphine withdrawal and that degrading endogenous spinal ATP by administering apyrase produces a reduction in withdrawal behaviors. Conversely, we found that pharmacological inhibition of ATP breakdown exacerbates withdrawal. Treatment with a Panx1-blocking peptide (10panx) or the clinically used broad-spectrum Panx1 blockers, mefloquine or probenecid, suppressed ATP release and reduced withdrawal severity. Our results demonstrate that Panx1-mediated ATP release from microglia is required for morphine withdrawal in rodents and that blocking Panx1 alleviates the severity of withdrawal without affecting opiate analgesia.

Highlights

Opiates are essential for treating pain, but termination of opiate therapy can cause a debilitating withdrawal syndrome in chronic users
We show that Panx[1] activation drives ATP release from microglia during morphine withdrawal and that degrading endogenous spinal ATP by administering apyrase produces a reduction in withdrawal behaviors
Our results demonstrate that Panx1-mediated ATP release from microglia is required for morphine withdrawal in rodents and that blocking Panx[1] alleviates the severity of withdrawal without affecting opiate analgesia

Summary

Blocking microglial pannexin-1 channels alleviates morphine withdrawal in rodents. Nicole E Burma[1,2], Robert P Bonin[3], Heather Leduc-Pessah[1,2], Corey Baimel[2], Zoe F Cairncross[1,2], Michael Mousseau[1,2], Jhenkruthi Vijaya Shankara[4], Patrick L Stemkowski[2], Dinara Baimoukhametova[2], Jaideep S Bains[2], Michael C Antle[2,4], Gerald W Zamponi[2], Catherine M Cahill[5], Stephanie L Borgland[2], Yves De Koninck6 & Tuan Trang[1,2]. Our results demonstrate that Panx1-mediated ATP release from microglia is required for morphine withdrawal in rodents and that blocking Panx[1] alleviates the severity of withdrawal without affecting opiate analgesia. We acutely isolated CD11b-positive cells from the spinal cord of morphine- or saline-treated rats and assessed Panx[1] channel function by measuring BzATP-evoked uptake of YOPRO-1 dye, an indicator of Panx[1] channel activation[9,10]. YO-PRO-1 uptake was significantly greater in CD11b-positive cells isolated from morphine-treated rats (Fig. 1e) This response was blocked by 10panx (10 μM)[5,11] but was not affected by a scrambled peptide (scrpanx) (Fig. 1e). Received 7 July 2016; accepted 8 January 2017; published online 30 January 2017; corrected online 15 February 2017; doi:10.1038/nm.4281

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