Coclaurine is a nicotinic acetylcholine receptor antagonist isolated from Nelumbo nucifera and belongs to the class of Tetrahydroisoquinolines. An intracerebroventricular injection of d-coclaurine, a benzyltetrahydroisoquinoline alkaloid extracted from Magnolia salicifolia, produced a slight increase in 3,4-dihydroxyphenylacetic acid level and a significant increase in homovanillic acid level in the mouse striatum. Another alkaloid d-reticuline (200 micrograms) increased only homovanillic acid level. An intracerebroventricular pretreatment with d-coclaurine (50 micrograms) did not antagonize suppressive effect of apomorphine on l-dopa formation produced by gamma-butyrolactone (750 mg/kg i.p.) plus aromatic amino acid decarboxylase inhibitor, NSD-1015 (100 mg/kg i.p.). These results suggest that d-coclaurine blocks postsynaptic but not presynaptic dopamine receptors in the mouse striatum.
-V936.gif)