Targeting RGSz1 actions in the periaqueductal gray promotes opioid analgesia and decreases reward sensitivity
Authors: sakloth Farhana , Gaspari Sevasti , Singh Mandakini , Pryce Kerri , Zachariou Venetia 
Published: June 2021

Synthetic opioids such as morphine and oxycodone are prescribed for the alleviation of chronic pain symptoms, but their prolonged use leads to analgesic tolerance, hyperalgesia, dependence and transition to addiction. The current opioid epidemic urges for novel and safer pain treatments. A better understanding of the cellular pathways mediating the analgesic effects of opioids may provide information for novel therapeutic avenues.

Regulator of G protein signaling z1 (RGSz1), a member of the RGS family of proteins, is present in several networks expressing mu opioid receptors. Using genetic mouse models for constitutive knockout of the RGSz1 gene, we found that prevention of RGSz1 action increases the analgesic efficacy of synthetic opioids, and delays the development of tolerance. On the other hand, knockout of RGSz1 decreased the rewarding efficacy of morphine in the place conditioning paradigm and prevented the locomotor sensitizing actions of the drug (Gaspari et al, 2018).

When we conditionally downregulated RGSz1 in different brain areas we identified that RGSz1 actions in the ventrolateral periaqueductal gray (vlPAG) negatively modulate morphine analgesia and promote the development of analgesic tolerance (Gaspari et al, 2018). Importantly, knockdown of RGSz1 in the vlPAG by stereotaxic infections of RGSz1fl\fl mice with adenoassociated vectors expressing Cre recombinase, decreased sensitivity to the rewarding effects of morphine. Using the spared nerve injury model of peripheral neuropathy we demonstrated that RGSz1 plays a similar modulatory role in opioid reward under chronic pain states. We hypothesized that RGSz1 actions in vlPAG projections to the ventral tegmental area (part of the brain reward center) modulate the rewarding actions of opioids, and we applied a chemogenetic approach to test if activating of vlPAG‐VTA circuits promote morphine place preference. For these studies, the VTA of adult male C57/BL6 was infected with pAAV‐pkg‐Cre vectors and the vlPAG with pAAV‐hSyn‐DIO‐hM3D(Gq)‐mCherry (AAV8), and pAAV‐hSyn‐DIO‐mCherry (AAV8) and mice were tested in the place conditioning assay five weeks later. Clozapine 1 mg/kg,(ip) was administered 30–40 minutes before morphine or saline, during conditioning sessions. Activation of vlPAG‐VTA circuits increases reward sensitivity as pAAV‐hSyn‐DIO‐hM3D(Gq)‐mCherry expressing mice condition place preference to 3 mg/kg (sc), whereas control animals condition place preference to 5 mg/kg,(sc) of morphine. Notably, this intervention does not affect the analgesic actions of opioids.

Current studies involve identifying the chemical signature of the neurons involved in this pathway and also overexpression of RGSz1 in the chemogenetic model established above.

Future studies will investigate the role of RGSz1 in the PAG‐Rostro ventral medulla pathway, a pathway well‐established to play a role in analgesia.

Overall, our studies provide insight on the mechanism of RGSz1 action in vlPAG circuits and point to RGSz1 and downstream pathways as potential avenues for interventions that optimize the actions of prescription opioids.

Support or Funding Information

P01 DA008227 NIDA

This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.