title: 3H-thymidine long survival autoradiography as a method for dating the time of neuronal origin in the chick embryo: the locus coeruleus and cerebellar Purkinje cells.
abstract: Contrary to previous assumptions, we have found that a single dose of 3H-thymidine (25 muCi), injected into the yolk sac of White Leghorn chick eggs on 2 days of incubation (d.i.) only remains available for DNA-synthesizing (proliferating) cells for 48 hours following the time of injection. This finding now makes it possible to date the time of neuronal origin in the avian embryo using a single injection of isotope and a long survival time (30 days posthatch) as in mammalian studies where 3H-thymidine is only available as a short "pulse." Using this method, we have determined that neurons in the chick locus coeruleus (LC) cease proliferation on 2-6 d.i. with a peak of neuronal genesis on 3-5 d.i. In addition, neuronal genesis is not homogeneous throughout the LC cell population, but occurs in a predominantly caudorostral gradient. Conversely, the cerebellar Purkinje cells cease division on 3-8 d.i. with a peak of heavy labeling on 4-6 d.i., 1 day later than that observed in the LC.
mesh_terms: D000818:Animals; D001345:Autoradiography; D002452:Cell Count; D002454:Cell Differentiation; D002525:Cerebellar Cortex / Q000166:cytology*; D002642:Chick Embryo; D008125:Locus Coeruleus / Q000166:cytology*; D009434:Neural Pathways / Q000166:cytology; D009474:Neurons / Q000166:cytology; D011689:Purkinje Cells / Q000166:cytology*