[Psychopharmacological study of enkephalins, with special reference to the relation between behavioral profiles and...

The effects of intracerebral injection of methionine-enkephalin (met-enk) and leucine-enkephalin (leu-enk) on the behavioral patterns were examined by using multi-dimensional behavioral analyser (Animex II) in relation to the mouse brain monoamine metabolism. The multi-dimensional behavioral analyser which is able to record 9 different measures of behavior exhibited by mice has been used. The results have indicated that met-enk (100 micrograms) and leu-enk (200 micrograms) caused a remarkable but transient increase in the linear locomotion recorded on the counter 1/1. In the biochemical study, it has been found that met-enk (100 micrograms) significantly increases the content of homovanillic acid (HVA) in the striatum. Leu-enk (200 micrograms) has negligible effect on the contents of dopamine (DA), 3,3-hydroxyphenylacetic acid and HVA in the cerebral cortex or the striatum. Met-enk (100 micrograms) and leu-enk (200 micrograms) did not affect the alpha-methyl-p-tyrosine-induced decrease in the content of DA and norepinephrine. Following the injection of met-enk (100 micrograms) and leu-enk (200 micrograms) and leu-enk (200 micrograms) into the cerebral ventricle, the content of 5-hydroxytryptamine in the cerebral cortex was increased but that of 5-hydroxyindoleacetic acid was not. Neither met-enk nor leu-enk influenced the activity of monoamine oxidase in the brain. These data suggest that, while monoamines in the brain are involved in the behavioral effects of enkephalins, the precise sites and/or mechanisms of enkephalins may differ.