Cysteamine impairs the migration of tyrosine hydroxylase -like immunoreactive chick embryo pontine neuroblasts: possible role of somatostatin

Cysteamine (2-mercaptoethylamine, CSH) is a thiol reagent which has been found to produce a rapid and relatively selective depletion of somatostatin (SRIF) in the rat central nervous system (CNS) [1]. SRIF is widely distributed throughout the adult vertebrate CNS; moreover, is transiently expressed in specific areas of the developing brain, suggesting a role in the control of CNS differentiation. In this work, we evaluated the SRIF depletion effects on tyrosine hydroxylase (TH) like immunoreactive (ir) CNS neuroblasts of the dorso-rostral pontine region of chick embryos treated twice a day with 150 mg/kg CSH dropped on chorioallantoic membrane. 10 μm thick paraffin serial sagittal sections obtained from embryo brains at E (embryonic day) 13, E 15, E 17 and E 19 were incubated with an anti-TH antibody according to ABC technique. In the area studied, the distribution of TH ir neuroblasts corresponded with that of neurons belonging to the nucleus of the locus coeruleus and subcoeruleus. Neuroblasts were counted in both CSH-treated and control specimens obtained from embryos at different days of development: there was a slight significant difference only in the first day considered (E 13), suggesting that this cell group had already completed its proliferative phase. Following image analysis of the sections, the areas including dorso-rostral pontine TH ir neuroblasts were measured: we observed a significant values decrease in CSH treated embryos at all the embryonic days considered. In treated specimens we also observed a significant reduction of the estimated volumes containing those neuroblasts. Finally, CSH administration determined a dramatic increase of cell density, especially at E13. These results indicate that somatostatin depletion during the chick embryo development has profound effects on the migration of the pontine TH-ir neuroblasts belonging to the locus coeruleus and subcoeruleus nuclei. Therefore somatostatin may be essential for the correct migration of immature neurons of this brain area, as already shown in cerebellar cortex [2].