Postmortem μ-opioid receptor binding in suicide victims and controls

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 post-mortem 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.