# Adenosine A2A receptors regulate D2-type medium spiny neurons in the nucleus accumbens to mediate pain and depression comorbidity

## TL;DR

This study shows how specific brain cells in the nucleus accumbens regulate both pain and depression-like symptoms through adenosine A2A receptors.

## Contribution

The study identifies a novel role for adenosine A2A receptors in regulating pain and depression comorbidity via D2-type medium spiny neurons in the nucleus accumbens.

## Key findings

- Chemogenetic activation of NAcS D2-MSNs induces pain and behavioral despair in mice.
- A2ARs modulate the excitability of D2-MSNs and influence pain and depression-like behaviors.
- Local A2AR agonists and antagonists bidirectionally affect pain and despair in both healthy and injured mice.

## Abstract

Persistent pathological pain often induces comorbid depressive-like symptoms, yet the underlying neuronal and molecular mechanisms remain unclear. The nucleus accumbens shell (NAcS) has been implicated in mediating pain sensation and emotional disorders, including depression. However, how it regulates pain-depression comorbidity (PDC) is not well-known. In the present study, we demonstrated that D2-type medium spiny neurons (D2-MSNs) in the NAcS bidirectionally modulated pain and its comorbid behavioral despair measured in the forced swimming test (FST), an effect possibly involving adenosine A2A receptors (A2ARs). Specifically, acute chemogenetic activation of NAcS D2-MSNs induced thermal/mechanical pain in naïve mice but did not affect despair-like behavior in the FST, a phenomenon that occurred after repeated activation of these neurons. Conversely, chemogenetic inhibition of NAcS D2-MSNs alleviated spared nerve injury (SNI) induced neuropathic pain and its comorbid behavioral despair. Our immunofluorescent staining revealed a relatively enriched expression of A2ARs in NAcS D2-MSNs. Ex vivo electrophysiological recordings revealed that activating and inhibiting A2ARs increased and decreased the neuronal excitability of NAcS D2-MSNs. Consistently, local infusion of the agonist and antagonist of A2ARs into the NAcS bidirectionally modulated pain and despair-like behaviors in both naïve and SNI mice. Together, these findings demonstrate the functional role of NAcS D2-MSNs in mediating PDC, which was possibly modulated by local A2ARs, thus providing a potential therapeutic target for PDC.