CHARACTERIZATION OF OPIOID RECEPTORS IN THE MONGOLIAN GERBIL CEREBELLUM

Characteristics of opioid receptors binding in the Mongolian gerbil ce rebellum were determined by in vitro radioligand binding technique. Ho mogenate of cerebellar membranes possessed a binding capacity for H-3- DAMGO, a mu-agonist, and for H-3-diprenorphine, an antagonist of mu, d elta and kappa-receptors. These bindings were saturable, and character ized by high affinity (Kd value: 1.55 +/- 0.43 nM for H-3-DAMGO and 0. 56 +/- 0.20 nM for H-3-diprenorphine) and high density (Bmax: 127.8 +/ - 23.8 fmoles/mg protein for H-3-DAMGO and 135.8 +/- 9.03 fmoles/mg pr otein for H-3-diprenorphine). Autoradiographically, the binding sites were predominantly located in the molecular layer of the cerebellum. H -3-DPDPE, a delta-agonist, showed only very small binding capacity to the cerebellar membranes. The kappa- agonist, H-3-U-69593, also showed very small binding capacity to the cerebellar membranes except in the early postnatal period. Thus, the gerbil cerebellum can be considered as a tissue containing a homogeneous population of p-opioid receptors .