Chronic [D-Ala2, D-Leu5]enkephalin treatment increases the nerve growth factor in adult mouse brain.

The delta opioid peptide [D-Ala(2), D-Leu(5)]enkephalin (DADLE) has been shown to enhance the survival of dopaminergic neurons. Here, we found that chronic treatment with DADLE caused a significant increase in nerve growth factor (NGF) in the hippocampus and the midbrain of adult albino Swiss (CD-1) mice, but not in the striatum or frontal cortex. Glia-derived neurotrophic factor (GDNF) was not significantly affected. Thus, the neuroprotective action of DADLE may be mediated in part by NGF.