Differential effects of α-, β- and γ-endorphins on dopamine metabolism in the mouse brain

The effects of intracerebral injection of α-, β- and γ-endorphins on the mouse brain dopamine (DA) metabolism were contrasted in relation to the previously identified patterns of behavior. α-Endorphin (20 μg) decreased the content of homovanillic acid (HVA) in the striatum, while γ-endorphin (10 μg) the contents of DA, 3,4-dihydroxyphenylacetic acid and HVA. β-Endorphin (1 and 2 μg) had no effects on the mouse DA metabolism in the brain. The changes in the DA metabolism induced by α- and γ-endorphins were readily reversed by the pretreatment with naloxone (1 mg/kg). Results suggested: (1) the patterns of behavior in mice treated with endorphins are mediated by these differences in DA metabolism; (2) changes in DA metabolism induced by α- and γ-endorphins occur via opiate receptors in the mouse brain.