title: The thoracic sympathetic neurons of the chick: normal development and the effects of nerve growth factor.
abstract: The generation and degeneration of sympathetic neurons in the third thoracic ganglion (segment 19) of the chick were studied between embryonic days (E) 7-18 using 3H-Thymidine autoradiography and routine cell counts. Cumulative radiolabelling experiments indicated that few sympathetic neurons were generated on E6-7. 10% of the sympathetic neurons were generated on E8 and a further 20% on E9. The final 70% of neurons completed the mitotic cycle between E10-12. Cell counts demonstrated that the neuronal population increased from 10,166 +/- 423 (mean +/- SEM) to 22,291 +/- 767 between E8-10 and remained stable up to E14. The population subsequently declined by 37%, to 14,157 +/- 831, by E18. Pyknotic neurons were found at all stages of development, but were most apparent between E7-15. The effects of Nerve Growth Factor (NGF) on the number of both surviving and pyknotic neurons in the ganglion were also examined. E9 embryos treated with NGF from E5-8 showed a 57% increase in the number of sympathetic neurons. This increase therefore occurred prior to the decline in neuronal number and was not accompanied by a decrease in the number of visibly pyknotic neurons. It is therefore possible that early NGF treatment increases the number of sympathetic neurons through a mechanism other than the attenuation of cell death.
authors.affiliation: Department of Anatomy & Histology, School of Medicine, Flinders University of South Australia, Bedford Park.
authors.forename: P
authors.initials: P
authors.lastname: Smet
authors.forename: R A
authors.initials: RA
authors.lastname: Rush
authors.forename: C
authors.initials: C
authors.lastname: Straznicky
mesh_terms: D000818:Animals; D002452:Cell Count; D016923:Cell Death / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002642:Chick Embryo; D004247:DNA / Q000096:biosynthesis; D009414:Nerve Growth Factors / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000196:embryology*; D013909:Thorax
chemical_list: D009414:Nerve Growth Factors; D004247:DNA