Seasonal changes in vertebrate dentate gyrus, but was as effective as long-term photobrain function are pervasive, but annual cycles in the periodic exposure in the subependymal zone. Photorates of neuronal incorporation are established only period also had similar effects in the hypothalamus in songbirds. Although cell division continues in the and cingulate/retrosplenial cortex, but not in the censubependymal and hippocampal subgranular zones of tral gray or preoptic area. Double-label immunocytoadult rodents, there exists no parallel evidence that chemistry indicated that very few of the BrdU-ir cells seasonal plasticity in mammals extends to changes in were glia, but that a majority had neuronal phenoneuronal or glial number. We examined the effect of type. In the subependymal zone, short days signifiphotoperiod on incorporation of new neurons in the cantly increased the number of BrdU-labeled neurons. brain of the adult golden hamster, a long-day breeder.
We did not detect significant effects of photoperiod We administered the cell birth marker 5-bromodeon the volume of either the granule cell layer of the oxyuridine (BrdU) to males which had either been hippocampus or the dentate gyrus as a whole. We maintained in long days, transferred to short days for conclude that short day lengths increase neuronal 10 weeks, or moved acutely from long to short or short birth and/or survival in several brain regions of adult to long days. The number of cells in specific brain hamsters. แญง 1998 John Wiley & Sons, Inc. J Neurobiol 36: 410- regions immunoreactive (ir) for this thymidine analog 420, 1998 was determined 7 weeks later. The number of BrdU-ir Keywords: photoperiod; bromodeoxyuridine; season; cells in the dentate gyrus and subependymal zone inneurogenesis; hamster; dentate gyrus; subependymal creased twofold in short days. Transfer between phozone toperiods 10 days before the BrdU injections produced Striking seasonal changes in brain structure occur Seasonal changes in the environment trigger marked in songbirds. These include cycles of incorporation alterations in brain function among animals of the of new cells in the ventricular zone which migrate temperate zone. Day length (photoperiod) is the along radial glia to reach the caudal nucleus of the most potent environmental signal regulating fluctuhigh vocal center (HVC), a structure critical for ations in behavior and neuroendocrine activity.