Model Description: 2A-Cre expression cassette was knocked into the Oprk1 gene stop codon site. Oprk1 (opioid receptor, kappa 1) encodes opioid receptor which was expressed in multiple brain regions. When crossed with a strain carrying a gene flanked by loxP sites, the flanked gene will be removed in cells expressing cre. This opioid receptor plays a role in the perception of pain and mediating the hypolocomotor, analgesic and aversive actions of synthetic opioids.