Résumé
The actions of vasoactive intestinal peptide (VIP) on intracellular cyclic AMP, in primary cultures of striatal neurons, were examined. VIP stimulated cyclic AMP formation five-fold over basal levels in neurons after 6 days
in vitro (DIV); half maximal activation (EC
50) was obtained with 10 nM of the peptide. VIP stimulation was both more potent and effective than those due to adrenocorticotropin (ACTH), dopamine (DA) or serotonin (5-HT). VIP efficacy was augmented to 15–20-fold in the presence of 0.1 μM forskolin, which had virtually no effect on cyclic AMP production alone; VIP potency was unaffected. At saturating concentrations of VIP (0.1–1.0 μM), no other agonist can further activate cyclic AMP production. Under these conditions, the interaction with opiate, DA D
2 and 5-HT
1 receptors, whose activation results in the inhibition of cyclic AMP production, was shown. During the differentiation of striatal neurons, VIP stimulation of cyclic AMP over basal levels, in the presence of 0.1 μM forskolin, decreases progressively from 30-fold after 3 DIV to 11-fold after 10–13 DIV.