Kappa opiate binding sites in the substantia nigra and bulbus olfactorius of the guinea pig as shown by in vitro autoradiography.

The purpose of the present study was to further map the distribution of the kappa subtype of opiate binding sites in the guinea pig brain. Cryostat sections of brain were incubated in 2 nM [3H] (-)-bremazocine with or without the addition of D-Ala2,MePhe4,Gly-ol5-enkephalin and/or D-Ala2,D-Leu5-enkephalin at 1 - 3000 nM. A sheet of [3H] Ultrofilm R (LKB) was exposed to the dry sections for up to 207 days. A computer coupled to a microdensitometer and a television camera was used to convert grey areas of the film to femtomoles of binding sites per mg protein. The substantia nigra and lamina plexiformis externa of the bulbus olfactorius remained densely labeled even in the presence of 3000 nM of both enkephalins. The guinea pig is the only species studied thus far which exhibits this distribution, but the physiological significance is not yet understood.