Increased expression of vasoactive intestinal polypeptide in cultured myenteric neurons from adult rat small intestine

Adult neurons possess the ability to adapt to a changing environment. Loss of target-derived neurotrophic factors due to axotomy or isolation by culturing is known to induce changes in neuropeptide expression in several types of peripheral neurons. The aim of the present study was to investigate changes in the expression of vasoactive intestinal polypeptide (VIP) and nitric oxide synthase (NOS) in cultured myenteric ganglia and dissociated neurons. Myenteric ganglia and neurons from rat small intestine were dissociated and cultured for up to 21 days. Immunocytochemistry was used to determine the total number of neurons and the proportions of subpopulations containing VIP or NOS or both in preparations of whole mounts (controls used to determine the conditions in vivo), myenteric ganglion culture and dissociated myenteric neuronal culture. In situ hybridization was used to determine changes in the expressions of NOS and VIP mRNA. The relative number of VIP-expressing neurons increased significantly during culturing. The percentage of all neurons expressing VIP was 3.6±0.3% in whole mounts, 22–24% in cultured myenteric ganglia, and up to 35% in cultured dissociated neurons. NOS-expressing neurons constituted approximately 30–40% of all neurons in whole mounts as well as in cultured ganglia or dissociated neurons. A dramatic increase in NOS/VIP-containing neurons were detected in cultured neurons irrespective of whether they were arranged in ganglia or dissociated, as compared to whole mount preparations. This suggests that the NOS-containing neurons are the ones that increase their VIP expression. The induced expression of VIP in cultured adult myenteric neurons indicates that VIP is important for neuronal adaptation, maintenance and survival.