Protein extracts from the gut wall influence the postnatal development of rat myenteric neurons in vitro

Neurons migrating from the neural crest into the presumptive gut wall need an appropriate microenvironment to survive and differentiate during ontogenesis. The rat enteric nervous system (ENS) keeps developing beyond birth. The aim of this study was to investigate the neurotrophic effects of the postnatal microenvironment. Myenteric plexus was isolated from the smooth muscle layer of newborn rats at different ages (postnatal day (p)1, p7, p14) and grown as dissociated cell cultures. The culture medium (hormone-supplemented, serum-free) was supplemented either with glial-cell-line-derived-neurotrophic factor (GDNF) or with protein extracts from homogenized smooth muscle layer of p7 rats. Cultures kept in defined medium alone were used as controls. After 18 h in vitro both GDNF and protein extract had a neuritogenic effect upon p1 and p7 neurons, while p14 neurons were only stimulated by the protein extracts. The GDNF effect upon these neurons did not differ significantly from the effects in defined medium alone. The average neurite outgrowth in extract-supplemented cultures was always longer than that seen in those treated with GDNF. Although GDNF influences the postnatal development of myentric neurons in vitro it could not be detected immunohistochemically either in Western blots of the protein extracts or in cryostat sections of the gut.