Saturable (3H)cocaine binding in central nervous system of mouse

(³H)Cocaine was bound saturably to mouse brain membrane preparations, with a dissociation constant (K_d) of 0.6 μM and a maximal binding capacity of 3 pmol/mg of membrane protein. Binding was virtually maximal at 2°C, was sodium-insensitive, and was distributed rather uniformly throughout the brain. No, or only slight, displacing activities were observed for the neuro-transmitters norepinephrine, dopamine, acetylcholine, serotonin, and GABA, and for nicotine (nicotinic cholinergic receptor agonist), tubocurarine (nicotinic cholinergic receptor antagonist), morphine (opiate receptor agonist), and naloxone (opiate receptor antagonist). The cocaine analogs WIN 35,065-2 and WIN 35,428, which have enhanced stimulatory potency as compared with cocaine and only 15% of its local anesthetic activity, had affinities for the binding site similar to the affinity of cocaine itself. Displacing activities between 1 and 2 orders of magnitude weaker than those of cocaine itself were displayed by the local anesthetics, d-amphetamine, decamethonium, and atropine.