Mice homozygous for this kappa-opioid receptor mutant allele (KOR-) are viable and fertile. KOR-selective ligand binding is absent on brain membranes from homozygous mice. In contrast to mutant mice deficient of delta- or mu-opioid receptors (Stock No. 007557 or 007559), KOR- homozygotes have normal mechanical pain thresholds, but greatly increased sensitivity to chemical visceral pain. KOR- homozygotes also exhibit normal spontaneous stress responses (unlike delta-opioid receptor null mice). Homozygous KOR- mice also show decreased ethanol self-administration and decreased THC-conditioned place aversion. These KOR mutant mice may be useful in studying biological activity of opioids, analgesics, spinally mediated thermal nociception and chemical visceral pain thresholds. In an attempt to offer alleles on well-characterized or multiple genetic backgrounds, alleles are frequently moved to a genetic background different from that on which an allele was first characterized. These mutant mice were originally published on a mixed genetic background. It should be noted that the phenotype could vary from that originally described. We will modify the strain description if necessary as published results become available.

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These Oprk1 knock-out mice may be useful in studying biological activity of opioids, analgesics, spinally mediated thermal nociception and chemical visceral pain thresholds.

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