Regional distribution and migration of proliferating cell populations in the adult brain of Hyla cinerea (Anura, Amphibia)

Abstract

We examined the distribution of adult cell proliferation throughout the brain of an anuran amphibian using 5-bromo-2'-deoxyuridine (BrdU). BrdU, a thymidine analog, is a commonly used cellular marker that is incorporated into actively dividing progenitor cells. Adult green treefrogs, Hyla cinerea, received injections of BrdU and were sacrificed 2 h, 2 days, 2 weeks, or 30 days later. Immunohistochemistry revealed BrdU-immunopositive (BrdU+) cells to be distributed in ventricular zones throughout the brain. The heaviest concentrations of cells were located in the telencephalon, primarily in the ventrolateral region of the lateral ventricles, and the ventricles of olfactory bulbs. Numerous BrdU+ cells were located around the preoptic and hypothalamic recesses and few around the third ventricle in the diencephalon. Proceeding caudally towards the midbrain, there was a marked decrease in BrdU labeling and few BrdU+ cells were found in the hindbrain. Consistent with previous studies in ectothermic vertebrates, BrdU+ cells were found predominantly in the ventricular zone (VZ) and immediately adjacent to the VZ; at later time points (i.e., 30 days), the cells appeared to have migrated into parenchymal regions. The extent of cellular proliferation in anurans is similar to that of fishes and reptiles and thus is more widespread compared to mammals.

Figure 1

Schematics of brain sections showing the distribution of BrdU+ cells (black circles) at 2–48 hours. (ABBREVIATIONS: A, anterior thalamic nucleus; Ac, nucleus accumbens; AD, anterodorsal tegmentum; Al, lateral amygdala; Am, medial amygdala; BN, bed nucleus of the pallial commissure; Cb, cerebellum; Ip, interpeduncular nucleus; LP, lateral pallium; LRF, lateral reticular formation; LS, lateral septal nucleus; MP, medial pallium; MRF, medial reticular formation; MS, medial septal nucleus; NB, nucleus of Bellonci; NI, nucleus isthmi; NIs, secondary isthmal nucleu; NPv, nucleus of the periventicular organ; nIII, oculomotor nucleus, nVII, vestibular nucleus; nVIII, facial motor nucleus; OT, optic tectum; PD, posterodorsal tegmentum; PV, posteroventral tegmentum; PO, preoptic area; PtG, pretectal gray; PtrG, pretoral gray; SCN, suprachiasmatic nucleus; St, striatum; V, ventral thalamus.)

Figure 2

Photomicrographs of the anuran amphibian telencephalon: Nissl-stained sections (A, D) with squared regions containing BrdU-labeled cells (B, C, E, F). Preoptic area depicted in top row and ventral hypothalamus in bottom row (preoptic recess, POR; hypothalamic recess, HR). BrdU+ cells are in the ependymal layer at 48 hrs (B, E) and in the parenchyma at 30 days (C, F). (Scale bar in A, D = 500 μm; scale bar in B, C, E, F = 100 μm).