Development of binding sites for vasoactive intestinal polypeptide in mouse cerebral cortex and cultured cortical neurons

Binding sites for vasoactive intestinal polypeptide (VIP) and the content of immunoreactive VIP were measured in the foetal and neonatal mouse brain cortex and primary cultures of foetal murine brain-cortical neurons and astrocytes. The amount of cortical VIP binding sites and the concentration of immunoreactive VIP were low before birth, but increased postnatally reaching adult level at about 3 weeks of age. In cultures, a similar rise in neuronal binding sites occurred after 10 days, whereas the VIP concentration remained lower than in adult brain cortex. No binding sites or immunoreactive VIP could be detected in cultured astrocytes. The VIP binding sites were heterogeneous both in developing brain cortex and cultured neurons, and consisted of two classes of binding sites. The high affinity constants (2.5–2.9 nM) as well as low affinity constants (50–76 nM) were unchanged during the development, whereas the number of binding sites increased. In cultured neurons the binding constants were similar to those found in the adult mouse brain cortex. The peptide specificity for the VIP binding was similar in brain cortex and neuronal culture. In conclusion, the maturation of murine brain cortical neurons is accompanied by the development of synaptosomal VIP receptors in support of the neurotransmitter function of VIP.