Autoradiographic distribution of mu opioid receptors in the brains of Cu/Zn-superoxide dismutase mice.

Superoxide dismutase (SOD) is an important free radical scavenging enzyme which dismutates the superoxide anion radical. We have evaluated the role of SOD in the regulation of opioid receptors by comparing the concentration of mu opioid receptors labeled with [3H]DAGO (Tyr-D-Ala-Gly-NMe-Phe-Gly-ol) in SOD-transgenic (SOD-Tg) mice and their non-transgenic (Non-Tg) littermates. SOD-Tg mice had higher maximal binding capacity (Bmax) in the shell division of the nucleus accumbens (NAc-shell) in comparison to Non-Tg littermates. There were no differences in Bmax in mu receptors in the core subdivision of the nucleus accumbens (NAc-core). There were no significant differences in receptor affinity (Kd) in either the NAc-shell or in the NAc-core. Moreover, there were no significant differences in either Bmax or Kd in the matrices nor in the patches of any of the striatal subdivisions. However, in a fashion similar to the situation in the NAc-shell, [3H]DAGO binding in the substantia nigra pars compacta (SNpc), the ventral tegmental area (VTA), and the ventral part of the central grey was significantly higher in the SOD-Tg mice in comparison to Non-Tg mice. The present results are discussed in terms of their support for a possible involvement of free radicals in the differences observed in various regions of the SOD-Tg and control mice, which differ in their ability to scavenge the superoxide anion.(ABSTRACT TRUNCATED AT 250 WORDS)