Dysphoria is mediated by which opioid receptor:
**Core Concept**
Dysphoria is a state of unease or discomfort, often associated with opioid use. It is a complex phenomenon involving the activation of specific opioid receptors in the brain.
**Why the Correct Answer is Right**
Dysphoria is primarily mediated by the kappa opioid receptor (KOR). Activation of KOR is associated with anxiogenic and aversive effects, such as anxiety, fear, and discomfort. KOR is distinct from the mu (μ) and delta (Δ) opioid receptors, which are primarily involved in analgesia and euphoria.
**Why Each Wrong Option is Incorrect**
**Option A:** Mu opioid receptors are primarily involved in analgesia and euphoria, not dysphoria. Activation of mu receptors leads to feelings of relaxation and well-being.
**Option B:** Delta opioid receptors are involved in analgesia and mood modulation, but not specifically in the mediation of dysphoria.
**Option C:** This option is missing, but we'll proceed with the correct answer.
**Clinical Pearl / High-Yield Fact**
Kappa opioid receptors are also involved in the regulation of stress and anxiety responses, and have been implicated in the development of opioid use disorder.
**Correct Answer: D. Kappa opioid receptor.**