Extraordinary postmortem stability of kappa opioid receptors in guinea-pig brain

Postmortem delay can be an important variable in biochemical studies on autopsy tissue. We subjected guinea-pig brains to gradual cooling, simulating temperature conditions of human postmortem brains, in order to assess the sensitivity of kappa receptors to postmortem degradation. Kappa receptor specific binding was defined as the (-)-[3H]ethylketocyclazocine bound in the presence of 100 nM D-ala2-D-leu5-enkephalin and 30 nM morphine. Postmortem delays of up to 16 h did not alter the affinity or density of kappa binding sites. The remarkable stability of kappa receptors may greatly facilitate the study of this opioid receptor subtype in human brain.