Human brain methionine- and leucine-enkephalins and their receptors during ageing.

Brain Met- and Leu-enk levels were investigated with radioimmunoassay and their binding to enkephalin receptors was studied with [3H]Met- and [3H]Leu-enkephalin in 56 human subjects (4-93 yr). Of the brain areas investigated, the head of the caudate nucleus and pallidum showed an age-associated decline for both Met- and Leu-enk content. In the substantia nigra and in putamen, no significant age-effect was seen. Binding of the enkephalins, which was studied in the head of the caudate nucleus and hippocampus, did not show significant age dependency. In conclusion, ageing affects human brain enkephalin levels but not their receptor binding, at least in brain areas investigated in the present study.