[3H]dihydroergocryptine binding in rat brain

[3H]dihydroergocryptine (DHE) appears to bind to alpha-adrenergic receptor sites in rabbit uterine membranes. We have characterized the binding of [3H]DHE to membranes prepared from rat cerebral cortex. alpha-Adrenergic agents were less potent and dopamine and serotonin, more potent, in displacing brain DHE binding than in uterus. Furthermore brain DHE binding sites demonstrated less stereospecificity for catecholamines than sites in uterus. Dopamine displaced DHE binding with about the same potency in cerebellar and cerebral cortical membranes, but was 10 times as potent in displacing DHE binding in the striatum. The binding of [3H]DHE in brain is complex and differs significantly from the rabbit uterus. There are two possible explanations for this discrepancy. [3H]DHE may bind a single site in brain with properties differing from known peripheral adrenergic receptors or DHE may bind to multiple sites in brain, sites which may or may not represent other neurotransmitter receptors.