Premitotic DNA synthesis in the brain of the adult frog (Rana esculenta L.): An autoradiographic 3H‐thymidine study

Abstract

Replicative synthesis of DNA in the brain of the adult frog was studied by light microscope autoradiography. Animals collected during the active period (May-June) and in hibernation (January) were used. In active frogs, 3H-thymidine labelling occurred mainly in the ependymal cells which line the ventricles. The mean labelling index (LI%) was higher in the ependyma of the lateral and fourth ventricles than in the ependyma of the lateral diencephalon and tectal parts of the mesencephalon. In the recessus infundibularis and preopticus the number of labelled cells (LCs) was several times greater than in the lateral parts of the third ventricle. LCs were seen subependymally only occasionally. The incidence of LCs in the parenchyma of the brain was much lower in most regions than in the ventricular ependyma; LCs were mainly small and, from their nuclear morphology, they were glial cells. The LI% reached the highest value in the septum hippocampi and in the nucleus entopeduncularis. In these locations, LCs were larger and closer in size to the nerve cells of these regions. From comparison with data obtained earlier in the brain of mammals, it is evident that the distribution of proliferating cells in the olfactory and limbic system is phylogenetically conservative. The occurrence of pyknotic cells in the same areas which contain LCs, suggests that cell division reflects in part the process of cell renewal observed in mammals. However, proliferating cells could also be linked to the continuous growth observed in non-mammalian vertebrates. In hibernating frogs, LCs and pyknoses were not seen or were found occasionally, which further indicates the functional significance of both processes.

Cell Proliferation in the Forebrain and Midbrain of the Adult Bullfrog, <i>Rana catesbeiana</i>

“…These studies all agree that considerable numbers of proliferating cells are found in ventricular zones at all levels of the neuraxis. The present data and those of Bernocchi et al [1990] and Raucci et al [2006] all show that considerably fewer proliferating cells are found around the fourth ventricle than around the lateral, third and tectal ventricles. Both Bernocchi et al [1990] and Chetverukhin and Polenov [1993] observed few 3 H-thymidine-labeled cells in brain parenchyma 2 h after treatment; we observed no BrdU-labeled cells outside of the ventricular zones at 2 days survival time, suggesting that migration does not occur at these short time periods.…”

“…There is only limited information on the extent of cell proliferation in the brains of any amphibian species during adulthood, even though adult amphibians show functional recovery after injury [Dieringer, 1995]. Previous analyses of proliferative activity in the adult Rana brain were based on the techniques of 3 Hthymidine autoradiography [Bernocchi et al, 1990;Chetverukhin and Polenov, 1993;Polenov and Chetverukhin, 1993] and immunohistochemistry using proliferating cell nuclear antigen (PCNA) [Margotta et al, 2000[Margotta et al, , 2005Raucci et al, 2006]. The former technique was employed only at two time periods after administration of the marker, thus limiting the data on long-term survival of newly-born cells, whereas the latter technique is not amenable to pulse-chase analysis to assess cell migration and survival.…”

Seasonal Cell Proliferation in the Chemosensory Epithelium and Brain of Red-Backed Salamanders, <i>Plethodon cinereus</i>

“…Continued proliferation of periventricular cells was reported in the telencephalon of postembryonic and adult axolotls [Ambystoma mexicanum, Richter and Kranz, 1981;Kirsche, 1983] and the optic tectum of adult newts [Triturus cristatus, Minelli and Quaglia, 1968]. In frogs in the genus Rana, proliferating periventricular cells are found in the forebrain [septum hippocampi and preoptic area in R. esculenta, Bernocchi et al, 1990 andpreoptic area in R. temporaria, Polenov and. Chetverukhin and Polenov [1993] suggested that neurosecretory cells in the preoptic area are replaced seasonally after the summer breeding season and before hibernation.…”

Effects of water pollution on the proliferative activity in the developing frog brain

“…With regard to amphibians, the ependyma of brain ventricles, and the preoptic and infundibular recesses showed proliferating cells in adult frogs (Bernocchi et al, 1990;Chetverukhin & Polenov, 1993); proliferation was also found in some brain parenchymal areas (Bernocchi et al, 1990).…”