Somatostatin depletion by cysteamine impairs the maturation of tyrosine hydroxylase immunoreactive chick embryo pontine neuroblasts

The neuropeptide somatostatin (SRIF) is widely but selectively distributed throughout the central nervous system (CNS) of the vertebrates; it is also expressed transiently in many areas of the developing brain, suggesting its possible role on neuronal maturation. To evaluate the role exerted by SRIF on the maturation of tyrosine hydroxylase (TH) immunoreactive (ir) neuroblasts of the dorso-rostral pontine region of chick embryo brain, SRIF was depleted by treating embryos twice a day with cysteamine (CSH). Serial sections obtained from embryo brains at E (embryonic day) 13, E15, E17 and E19 were incubated with an anti-TH antibody according to ABC technique. Immunolabeled neuroblasts were photographed and the images obtained were analysed in order to measure area, perimeter, minor and major axis, diameters ratio and shape factor. The TH ir neuroblasts studied belong to the locus coeruleus (LC), the main noradrenergic nucleus of vertebrate CNS, and subcoeruleus nuclei. After CSH administration, neuroblasts area values resulted significantly reduced in chick embryo brains at E13 and E15 (treated vs controls: p<0.01). Also perimeter values were reduced in neuroblasts belonging to E13-E15 cysteamine treated embryos (p<0.01), but no significant difference at E17 was observed. Cell diameters values resulted significantly lowered by cysteamine treatment: minor axis showed lower values at all embryonic day considered, while major axis only at E13-E15 (p<0.01). Diameters ratio and shape factor resulted higher in neuroblasts from treated specimens, with higher differences at E13-E15 (p<0.01); since higher values indicates less lengthened cells, these results suggest that CSH treatment can be implicated in a reduction of the cell lengthening. SRIF depletion by CSH during the chick embryo development impairs the maturation of the pontine TH ir neuroblasts belonging to the LC, therefore it may be essential for both the correct migration and maturation of the LC TH ir neuroblasts.