Differential effects of alpha-, beta- and gamma-endorphins on dopamine metabolism in the mouse brain

The effects of intracerebral injection of alpha-, beta- and gamma-endorphins on the mouse brain dopamine (DA) metabolism were contrasted in relation to the previously identified patterns of behavior. alpha-Endorphin (20 micrograms) decreased the content of homovanillic acid (HVA) in the striatum, while gamma-endorphin (10 micrograms) the contents of DA, 3,4-dihydroxyphenylacetic acid and HVA. beta-Endorphin (1 and 2 micrograms) had no effects on the mouse DA metabolism in the brain. The changes in the DA metabolism induced by alpha- and gamma-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 alpha- and gamma-endorphins occur via opiate receptors in the mouse brain.