The dynamics of adult neurogenesis in human hippocampus

The phenomenon of adult neurogenesis is now an accepted occurrence in mammals and also in humans.At least two discrete places house stem cells for generation of neurons in adult brain. These are olfactory system and the hippocampus. In animals, newly generated neurons have been directly or indirectly demonstrated to generate a significant amount of new neurons to have a functional role. However, the data in humans on the extent of this process is still scanty and such as difficult to comprehend its functional role in humans. This paper explores the available data on as extent of adult hippocampal neurogenesis in humans and makes comparison to animal data.

Adult neurogenesis in the four-striped mice(Rhabdomys pumilio)

In this study, we investigated non-captive four-striped mice （Rhabdomys pumilio） for evidence that adult neurogenesis occurs in the adult brain of animal models in natural environment. Ki-67 （a marker for cell proliferation） and doublecortin （a marker for immature neurons） immunos-taining conifrmed that adult neurogenesis occurs in the active sites of subventricular zone of the lateral ventricle with the migratory stream to the olfactory bulb, and the subgranular zone of the dentate gyrus of the hippocampus. No Ki-67 proliferating cells were observed in the striatum substantia nigra, amygdala, cerebral cortex or dorsal vagal complex. Doublecortin-immunore-active cells were observed in the striatum, third ventricle, cerebral cortex, amygdala, olfactory bulb and along the rostral migratory stream but absent in the substantia nigra and dorsal vagal complex. The potential neurogenic sites in the four-striped mouse species could invariably lead to increased neural plasticity.

Putative adult neurogenesis in two domestic pigeon breeds(Columba livia domestica)：racing homer versus utility carneau pigeons

Generation of neurons in the brains of adult birds has been studied extensively in the telencephalon of song birds and few studies are reported on the distribution of PCNA and DCX in the telencephalon of adult non-song learning birds.We report here on adult neurogenesis throughout the brains of two breeds of adult domestic pigeons（Columba livia domestica）,the racing homer and utility carneau using endogenous immunohistochemical markers proliferating cell nuclear antigen（PCNA）for proliferating cells and doublecortin（DCX）for immature and migrating neurons.The distribution of PCNA and DCX immunoreactivity was very similar in both pigeon breeds with only a few minor differences.In both pigeons,PCNA and DCX immunoreactivity was observed in the olfactory bulbs,walls of the lateral ventricle,telencephalic subdivisions of the pallium and subpallium,diencephalon,mesencephalon and cerebellum.Generally,the olfactory bulbs and telencephalon had more PCNA and DCX cells than other regions.Two proliferative hotspots were evident in the dorsal and ventral poles of the lateral ventricles.PCNA-and DCX-immunoreactive cells migrated radially from the walls of the lateral ventricle into the parenchyma.In most telencephalic regions,the density of PCNA-and DCX-immunoreactive cells increased from rostral to caudal,except in the mesopallium where the density decreased from rostral to middle levels and then increased caudally.DCX immunoreactivity was more intense in fibres than in cell bodies and DCX-immunoreactive cells included small granular cells,fusiform bipolar cells,large round and or polygonal multipolar cells.The similarity in the distribution of proliferating cells and new neurons in the telencephalon of the two breeds of pigeons may suggest that adult neurogenesis is a conserved trait as an ecological adaptation irrespective of body size.