Trends in Neurosciences
Volume 38, Issue 9, September 2015, Pages 517-523
Journal home page for Trends in Neurosciences

Opinion
New neurons in the adult striatum: from rodents to humans

https://doi.org/10.1016/j.tins.2015.07.005Get rights and content

Highlights

  • Recently, adult neurogenesis was shown to occur in the normal human striatum.

  • Similar newborn-specific striatal interneurons were described in different species.

  • Adult-generated striatal neurons may derive from the pallium/subventricular zone.

  • Adult striatal neurogenesis could be of relevance for neuropsychiatric disorders.

Most neurons are generated during development and are not replaced during adulthood, even if they are lost to injury or disease. However, it is firmly established that new neurons are generated in the dentate gyrus of the hippocampus of almost all adult mammals, including humans. Nevertheless, many questions remain regarding adult neurogenesis in other brain regions and particularly in humans, where standard birth-dating methods are not generally feasible. Exciting recent evidence indicates that calretinin-expressing interneurons are added to the adult human striatum at a substantial rate. The role of new neurons is unknown, but studies in rodents will be able to further elucidate their identity and origin and then we may begin to understand their regulation and function.

Section snippets

Sites of adult neurogenesis in humans

For nearly 15 years, the dentate gyrus was the only brain region in which adult neurogenesis had been demonstrated in humans [1]. This situation recently changed due to the development of a novel technique for retrospective cellular birth-dating in humans that takes advantage of changes in levels of the isotope carbon-14 (14C) following Cold War atomic weapons testing. The level of 14C in genomic DNA closely parallels atmospheric levels and, therefore, can be used to reliably determine the time

Local striatal or SVZ progenitors?

The morphologies of new neurons in the adult rat striatum and changes in location with time both suggest a possible origin in the SVZ [9]. However, the widespread localization and relative paucity of these new neurons under normal conditions in the adult brain, particularly in mice 12, 13, have hampered direct investigation of their origin via fate-mapping studies. During early postnatal development, a period of increased SVZ neurogenesis, several fate-mapping and/or time-lapse imaging studies

Technical considerations

Many features of adult neurogenesis are remarkably similar across species, but dramatic differences in the rates of neurogenesis have been described 5, 46. However, it is difficult to determine with any certainty how rates compare across species. Radiocarbon-14 dating cannot be used in rodents due to their relatively short lifespan, while bromodeoxyuridine (BrdU), the gold standard for cell birth-dating, is rarely be used in humans. Endogenous markers of immature neurons, such as DCX, have been

Functional features as olfactory bulb granule cells?

The function of newborn striatal neurons is unknown. Knowledge of striatal CR+ interneurons as a whole is limited to morphological and neurochemical descriptions, since they have never been recorded, much less silenced or eliminated 4, 17. There is also only limited knowledge of the functional properties of ICj granule cells [63]. The tightly apposed granule cells forming the ICj are connected via gap junctions [64]; there are no data about the existence of similar electrical connections

Concluding remarks

The human striatum generates CR+ GABAergic interneurons into adulthood, similar to what occurs in rats and rabbits. There are still conflicting data regarding the origin of these neurons in the adjacent SVZ and their turnover rate. Studies in rodents have shown that the generation of these interneurons occurs at high levels during early postnatal stages in the SVZ and decreases but is maintained at a lower level in the adult. Therefore, rodents, especially rats, are a good model for postnatal

Acknowledgments

This work was supported by the Deutsche Forschungsgemeinschaft – Collaborative Research Center (Sonderforschungsbereich) 636, grant GA427/11-1 and the German Ministry of Education and Research (BMBF, 01GQ1003B) to P.G and D.I., and the Intramural Program of the National Institute of Mental Health, National Institutes of Health (1ZIAMH002784) to H.A.C.

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