(+)-Amphetamine Binding to Rat Hypothalamus: Relation to Anorexic Potency for Phenylethylamines

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Abstract
Saturable and stereospecific binding sites for (+)-[ 3 H]amphetamine were demonstrated in membrane preparations from rat brain. The density of these binding sites varies among brain regions and is highest in the hypothalamus and brainstem. Specific (+)-[ 3 H]amphetamine binding in hypothalamus is largely confined to synaptosomal membranes, rapidly reversible, and sensitive to both heat and proteolytic enzymes. Scatchard analysis of the equilibrium binding data revealed two distinct sites with apparent affinity constants of 93 and 300 nanomoles per liter, respectively. The effects of various psychotropic drugs as well as a number of putative neurotransmitters and related agonists and antagonists in displacing specific (+)-[ 3 H]amphetamine binding demonstrate that these binding sites are not associated with any previously described neurotransmitter or drug receptors, but are specific for amphetamine and related phenylethylamine derivatives. Furthermore, the relative affinities of a series of phenylethylamine derivates for (+)-[ 3 H]amphetamine binding sites in hypothalamic membranes is highly correlated to their potencies as anorexic agents. These results suggest the presence of specific receptor sites in hypothalamus that mediate the anorexic activity of amphetamine and related drugs.