An increase in striatal Met-enkephalin-like immunoreactivity in neonatally dopamine-depleted rats

A pronounced decrease in dopamine content in both the striatum and the mesolimbic area was observed up to 120 days of age after treatment with 6-hydroxydopamine (100 micrograms, intracisternally) following desipramine pretreatment (20 mg/kg, i.p.) at the 5th postnatal day. In the 6-hydroxydopamine-treated rats, Met-enkephalin-like immunoreactivity in the striatum was found to have increased at 35 and 70 days old, although it remained unchanged at 25 days old. The neonatal administration of 6-hydroxydopamine, however, did not affect the peptide content in the mesolimbic area at any age. These results indicate that the neonatal dopamine reduction changes the Met-enkephalinergic neuronal activity in the striatum at the adult age.