(+)-AJ 76 hydrochloride is an antagonist of dopamine autoreceptor with pKi values of 6.95, 6.67, 6.37, 6.21 and 6.07 for hD3, hD4, hD2S, hD2L and rD2 receptors, respectively. Dopamine receptor is a G protein-coupled receptor and mainly exists in the vertebrate central nervous system (CNS). Dopamine receptor is a receptor for dopamine and plays a critical role in memory, learning, pleasure, cognition, motivation and fine motor control. (+)-AJ 76 hydrochloride is a dopamine receptor antagonist. In rats, AJ76 stimulated locomotor activity and increased the levels of 3,4-dihydroxyphenylacetic acid (DOPAC) and HVA in brain, which were dopamine metabolites . In rats injected with cocaine, (+)-A J76 increased the locomotor stimulation during the first 30 min. However, (+)-AJ76 inhibited the later more intense locomotor stimulation and cocaine-induced stereotypies . In vivo, (+)-AJ76 induced dopamine release mainly through interaction with dopamine receptors in the terminal regions of the A9 and A10 dopaminergic fibers. However, (+)-AJ76 increased the level of DOPAC via the somatodendritic autoreceptors .References:. Kullingsj H, Carlsson A, Svensson K. Effects of repeated administration of the preferential dopamine autoreceptor antagonist, (+)-AJ76, on locomotor activity and brain DA metabolism in the rat. Eur J Pharmacol, 1991, 205(3): 241-246.. Piercey MF, Lum JT, Hoffmann WE, et al. Antagonism of cocaine's pharmacological effects by the stimulant dopaminergic antagonists, (+)-AJ76 and (+)-UH232. Brain Res, 1992; 588(2): 217-222.. Waters N, Hansson L, L fberg L, et al. Intracerebral infusion of (+)-AJ76 and (+)-UH232: effects on dopamine release and metabolism in vivo. Eur J Pharmacol, 1994, 251(2-3): 181-190.