Adult neurogenesis in mammals: an identity crisis - PubMed (original) (raw)

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Adult neurogenesis in mammals: an identity crisis

Pasko Rakic. J Neurosci. 2002.

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Fig. 1.

Fig. 1.

a, Graphic representation of the level of DNA during different phases of cell cycle (G 1 and_G2_, gap phases; D, mitotic division; S, synthesis phase). The synthesis of DNA can be detected by the incorporation of 3H-dT or its analog BrdU. The method of 3H-dT incorporation after a single injection of the isotope is stoichiometric, and thus allows distinction between doubling of DNA content during the S phase, signifying mitotic division, and the light label of <50% of the maximum grain counts. b, The Purkinje cells in the_middle_ and on the left can be considered as heavily labeled, whereas the five grains over the cell nucleus on the right may be caused by the variety of biological and technological factors, some of which are discussed in the text. Importantly, if the animal were injected with 10, instead of a single3H-dT dose, this cell may be as heavily labeled as the one in the middle and could be falsely interpreted as divided.c, Interference (Nomarski) contrast microphotograph of a heavily labeled satellite glial cell in the frontal lobe of a monkey found 35 d after a single injection of 3H-dT (10 mCi/kg). d, Image of a cell in the adult macaque monkey prefrontal cortex that appears to be double-labeled for BrdU and NeuN, but was proven to belong to two closely apposed single-labeled cells by the use of z-series analyses on a confocal microscope. An NeuN-positive neuron (red) appeared to be colabeled with BrdU (green) at +0 level (arrow in_d_), but examination of a different focal plane (+2.8 μm level) reveals that the NeuN-positive nucleus and nucleolus actually belong to a neuron that is not BrdU-labeled (arrowhead in e). The BrdU-labeled nucleus apparently belongs to adult-generated satellite glia, which in the cerebral cortex typically associate with neuronal perikarya as seen also in c. Astrocytes in d and_e_ are indicated by GFAP immunoreactivity (blue). For further information, see Kornack and Rakic (2001b) and Rakic (2002).

Fig. 2.

Fig. 2.

Exogenous 3H-dT (red dots) or BrdU (blue squares) compete with the natural endogenous H-dT for incorporation into nuclear DNA.a, During S phase of cell cycle, incorporation occurs predominately into new stands of DNA, and provided that the cell stops dividing, significant presence of these marks indicates the time of final cell division. b, Incorporation of nucleotides occurs at a slower rate as part of DNA turnover or repair (of both strands) or at the higher rate during an abortive cell cycle (predominately in a single strand) leading to recovery or death (for further explanation, see text and Fig. 1).

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