5'-Guanidinonaltrindole (GNTI) is an opioid

Opioid

An opioid is a psychoactive chemical that works by binding to opioid receptors, which are found principally in the central and peripheral nervous system and the gastrointestinal tract...

 antagonist used in scientific research which is highly selective for the κ opioid

Kappa Opioid receptor

The κ-opioid receptor is a protein that in humans is encoded by the OPRK1 gene. The κ-opioid receptor is one of five related receptors that bind opium-like compounds in the brain and are responsible for mediating the effects of these compounds...

 receptor

Receptor (biochemistry)

In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...

. It is 5x more potent and 500 times more selective than the commonly used κ-opioid antagonist norbinaltorphimine

Norbinaltorphimine

Norbinaltorphimine is an opioid antagonist used in scientific research. It is one of the few opioid antagonists available that is highly selective for the κ-opioid receptor, and blocks this receptor without affecting the μ- or δ-opioid receptors, although it has less selectivity in vivo than when...

. It has a slow onset and long duration of action, and produces antidepressant

Antidepressant

An antidepressant is a psychiatric medication used to alleviate mood disorders, such as major depression and dysthymia and anxiety disorders such as social anxiety disorder. According to Gelder, Mayou &*Geddes people with a depressive illness will experience a therapeutic effect to their mood;...

 effects in animal studies. It also increases allodynia

Allodynia

Allodynia is a pain due to a stimulus which does not normally provoke pain. Temperature or physical stimuli can provoke allodynia, and it often occurs after injury to a site...

 by interfering with the action of the κ-opioid peptide dynorphin

Dynorphin

Dynorphins are a class of opioid peptides that arise from the precursor protein prodynorphin. When prodynorphin is cleaved during processing by proprotein convertase 2 , multiple active peptides are released: dynorphin A, dynorphin B, and α/β-neo-endorphin...

.