Postmortem μ-opioid receptor binding in suicide victims and controls

Summary.

Background: Endogenous opiates may reinforce self-injurious behavior in animal and human subjects. Higher postmortem μ-opioid receptor binding is reported in some brain regions in young compared with older suicide victims. The present study compared opioid receptor binding kinetics in postmortem brains of young suicide victims and matched controls in two brain areas. Methods: The density (Bmax) and affinity (K_D) of the μ-opioid receptors were assayed postmortem using [³H] DAGO in prefrontal cortex (PFC) and pre-post central gyri (PPCG) in 9 suicide victims and 10 controls, matched for age and gender ratio. Results: Binding indices did not differ between suicide victims and controls in either brain area and did not correlate with age. PFC Bmax was higher than PPCG Bmax (F=8.030; df=1,16; p=.012) for the combined sample. There was no brain region difference in K_D between PFC and PPCG, but the interaction between K_D and group was significant (F = 5.890; df = 1,16; p = .027). The K_D in the suicide victims was lower than controls in the PFC and higher than controls in the PPCG. Conclusion: Our study demonstrated more μ-opioid receptors in PFC compared with PPCG binding regardless of suicide status. The region-dependent differences in binding affinity in suicide victims may reflect regionally different opiate transmission.