Melanocortin and MCH precursor-derived NEI effects on striatum-midbrain co-cultures

The possibility of developmental effects of POMC-derived melanocortins and analogs on neurons of fetal rat brain regions exhibiting marked developmental melanocortin receptor expression, was studied in serum-free co-cultures of gestational day 18 striatal and mesencephalic cells, and compared with NEI and NGE. These two peptide fragments of the melanin concentrating hormone precursor, occurring in brain areas devoid of POMC terminals, cross-react with alpha-MSH antibodies; NEI elicits grooming similar to alpha-MSH. Neurofilament protein (NF), growth-associated protein (GAP-43) and synaptophysin of the synaptosomal fraction were determined by ELISA as markers for neuritogenesis, growth cones, and nerve terminal differentiation. Cell survival was analyzed by MTT assay, proportions of major cell types by immunocytochemistry. alpha-Melanocyte-stimulating hormone (alpha-MSH, effective concentration 250-2500 nM), the analog Nle4-, D-Phe7-alpha-MSH (NDP, 3.1-750 nM), and NEI (250 nM) increased NF in 3 day cultures by 11%, 17%, and 22%, respectively, whereas ACTH(1-24) and ACTH(1-39) (25 2500 nM) were ineffective. In 11 day cultures, alpha-MSH (250-750 nM), but not NDP, ACTH(1-24) or ACTH(1-39), increased synaptosomal synaptophysin by 11%. GAP-43 and cell survival remained unaffected. These data indicate that selected melanocortins as well as NEI can influence differentiation of neural processes in brain neurons.