Opioid receptor-like 1 receptor (ORL1 (also referred to as NOP or NOP receptor in some literature))

The **opioid receptor-like 1 receptor** (ORL1), also known as the **nociceptin receptor** or **NOP receptor**, is a G protein-coupled receptor that shares structural similarity with classical opioid receptors (mu, delta, kappa), but is pharmacologically distinct[3][5]. It is widely expressed in the central nervous system, including regions involved in pain processing, learning, memory, mood, and reward[1][3][5]. Its endogenous ligand is **nociceptin/orphanin FQ (N/OFQ)**, a neuropeptide with structural resemblance to dynorphin but with distinct activity[5]. Upon activation, ORL1 primarily couples to inhibitory G proteins (Gi/Go), leading to inhibition of adenylyl cyclase, reduction in cAMP, and modulation of ion channel activity, which in turn regulates neuronal excitability[1][3]. Unlike traditional opioid receptors, ORL1 does not bind classic opioid peptides or morphine-like drugs with high affinity, and its physiological effects can counteract opioid-induced analgesia and modulate pain in a context-dependent manner—sometimes causing hyperalgesia and at other times analgesia[5]. The ORL1 system has therapeutic potential in pain, addiction, mood disorders, and other neurological conditions, but clinical translation is still evolving.

Other names

Nociceptin receptorNOP receptorNOP1NON-ORORL1opioid receptor-like 1 protein

Activation of inhibitory G proteins (Gi/Go) leading to inhibition of adenylyl cyclase[1][3][5] - Modulation of potassium and calcium channel activity - Regulation of neuronal excitability and neurotransmitter release - Nociceptin-induced activation leads to decreased cAMP production and changes in ion conductance