Characterization of opioid receptors in the Mongolian gerbil cerebellum

Characteristics of opioid receptors binding in the Mongolian gerbil cerebellum were determined by in vitro radioligand binding technique. Homogenate of cerebellar membranes possessed a binding capacity for 3H-DAMGO, a mu-agonist, and for 3H-diprenorphine, an antagonist of mu, delta and kappa-receptors. These bindings were saturable, and characterized by high affinity (Kd values: 1.55 +/- 0.43 nM for 3H-DAMGO and 0.56 +/- 0.20 nM for 3H-diprenorphine) and high density (Bmax: 127.8 +/- 23.8 fmoles/mg protein for 3H-DAMGO and 135.8 +/- 9.03 fmoles/mg protein for 3H-diprenorphine). Autoradiographically, the binding sites were predominantly located in the molecular layer of the cerebellum. 3H-DPDPE, a delta-agonist, showed only very small binding capacity to the cerebellar membranes. The kappa-agonist, 3H-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 mu-opioid receptors.