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[Published 16th November 2010 02:30 PM GMT]
Novel touch stimuli can stimulate neurogenesis in the spinal cord of mice, according to a study published online today (16 November) in Molecular Psychiatry, suggesting that neurogenesis may be an important component of touch sensation.
"This is a very interesting and unexpected result," said neuroscientist Pierre-Marie Lledo of the Institut Pasteur in France, who was not involved in the research. Neurogenesis in the spinal cord has predominately only been documented in vitro, he said. "To see indeed you have neurogenesis in vivo in the dorsal horn of the spinal cord is rather puzzling and very interesting," and suggests a new mechanism by which organisms may be able to process complex tactile environments, Lledo noted.
While researchers agree that the birth of new neurons plays an important role in the adult brain, they have long debated to which aspects of learning, memory and behavior the process contributes. A new study published today (January 30) in Nature has used a gene knockout approach to link adult neurogenesis to spatial learning.
Neurogenesis happens in humans, too
There's more evidence that neurogenesis occurs in the human olfactory bulb, but what do these new neurons actually do?
[Published 15th February 2007 05:05 PM GMT]
Neurogenesis indeed occurs in the human adult brain, according to a new paper in this week's Science. The findings provide new evidence for the long-controversial theory, and suggest that neurogenesis occurs in the olfactory bulb and follows the same pattern as in other mammalian brains.
The new paper "disproves the dogma that the human brain doesn't have similar pathways of neurogenesis to that found in other mammalian brains," author Richard L.M. Faull of the University of Auckland said in an Email.
"The data are very nice and very clear, just what we'd expect based on rodent work," agreed Heather Cameron, of the National Institute of Mental Health in Bethesda, MD, who is not connected to the study.
Many vertebrates create new central nervous system neurons at all stages of life. This talent is linked to the ability to regenerate after CNS injury, so is most common in fish and amphibians. For most of the 20th century, conventional wisdom held that neurogenesis in mammals happened exclusively during embryonic and early postnatal life. Only within the last decade have researchers come to accept that adult neurogenesis does occur in selected mammalian brain regions, notably the hippocampus and olfactory system. However, neurogenesis in the human adult olfactory bulb has remained controversial.
Faull and his colleagues found that baby neurons called neuroblasts, born in the subventricular zone (SVZ), reach the human adult olfactory bulb, and do it via the rostral migratory stream (RMS). Rodents use an RMS too, although it differs anatomically from the human RMS. Using MRI, cell-specific markers, and electron microscopy, the researchers found progenitor cells with migratory characteristics, and also cells that become mature neurons in the olfactory bulb, in the adult human RMS.
However, Arturo Alvarez-Buylla at the University of California-San Francisco said he is not convinced by the findings. "It is an interesting work, but it does not demonstrate neurogenesis and much less migration along the RMS," he said in an Email." Indeed, the findings appear to contradict a 2004 Naturepaper he co-authored, which found no migrating neuroblasts in the human SVZ or in the pathway to the olfactory bulb.
Fred Gage, of the Salk Institute for Biological Studies in La Jolla, CA, who was not connected with the study, said he expected the new paper to cite 2004 work by Andr￩anne Bedard and Andr￩ Parent, which also offered evidence of newly generated neurons in the human olfactory bulb. (Indeed, Princeton'sElizabeth Gould said in an Email she was "pleased to see these authors have corroborated and extended the work of Bedard and Parent.") The newest paper uses more technology, focuses more on the RMS, and in general provides more evidence, but "they do come to a very similar conclusion," Gage said in an Email.
Parent himself said he admired the latest findings, but was "disappointed" the authors did not mention his work. "We have the very highest respect for Dr Parent's work and we very much apologize for this oversight," Faull responded.
Questions remain, however, as to what those new neurons can actually do, given that the function of neurogenesis remains somewhat of a mystery. Seizures stimulate neuron increase in the hippocampus, "but we don't know whether [neurogenesis] is trying to compensate" for damaged neurons, Cameron told The Scientist. There's some evidence new neurons may combat depression, she noted, but increasing neuron number would not necessarily be helpful in all conditions.
According to Faull, he and his colleagues have preliminary unpublished evidence that SVZ neural precursors don't just move to the olfactory bulb, but also leave the RMS and head for adjacent regions of the basal ganglia and cerebral cortex. In experimental rat models of diseases like Parkinson's, migratory neuroblasts replace neurons lost in the basal ganglia, suggesting this neural migration could have therapeutic benefits, he said.
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