Institute of Neuroscience, Sant Joan d’Alacant, Spain
A developmental neurobiologist looks at how damage induces cell birth in the adult brain.
The Spanish neuroscientist and 1906 Nobel Laureate Santiago Ramón y Cajal made hundreds of predictions about the organization and function of the nervous system. He was mostly correct, although not where the generation of new neurons in adults was concerned: this he persistently denied. The process is now widely accepted, but I find it fascinating that we have not yet reached consensus on where and when this phenomenon occurs.
Adult neurogenesis has been identified in two brain regions: the olfactory bulb and the hippocampus. Whether it also occurs in the adult neocortex, the region responsible for functions including language and thought, remains highly controversial. So I was intrigued by work by Koji Ohira of Fujita Health University in Toyoake and Takeshi Kaneko of Kyoto University, both in Japan, and their colleagues.
They found a small population of neuronal progenitor or precursor cells in the marginal zone of the adult neocortex (K. Ohira et al. Nature Neurosci. 13, 173–180; 2010). These generate interneurons — cells that modulate and synchronize the activity of principal neurons — that then disperse throughout the neocortex. Although this process is rare in normal circumstances, it is greatly enhanced by ischaemia (restricted blood supply due to damage), the authors show.
The message from Ohira et al. is intriguing and has profound implications. For example, the fact that many of the newborn interneurons express neuropeptide Y, a well-known anti-convulsant and anti-epileptogenic agent, suggests that newly generated neurons might protect the brain from damage. More sophisticated electrophysiological experiments are needed to explain how these interneurons are wired into specific neocortical circuitries and how they modulate neuronal activity.