SUBCELLULAR ANALYSIS OF TYR-AMINOPEPTIDASE ACTIVITIES IN THE DEVELOPING RAT CEREBELLUM

The endogenous opioid system seems to play important roles in the deve loping cerebellum. The first opioid peptide isolated, Met-enkephalin, is expressed transiently in this brain area. In the present study, sev eral enzyme activities capable of hydrolyzing enkephalins are measured during the first month of cerebellar development, using Tyr-beta-naph thylamyde as substrate and puromycin as inhibitor of one of the membra ne-bound aminopeptidases. Puromycin-sensitive soluble and membrane-bou nd aminopeptidase activities decrease in the synaptosomal and mitochon drial fractions at the end of the first month of life, just when enkep halin-like immunoreactivity decreases in the cerebellum. Membrane-boun d enzyme also decreases in the myelinic fraction. Synaptosomal activit y increases after birth, coinciding with decreases in the activity in the microsomal fraction. Puromycin-insensitive and membrane-bound amin opeptidase shows less significant developmental changes and they occur mainly in the first week of life, coinciding with the axonal and dend rite growth. These results could suggest a possible role of these enzy mes, together with the rest of the opioid system, in cerebellar develo pment.