The generation of new neurons in the human hippocampus drops sharply in children to undetectable levels in adults. It can therefore be said that adult hippocampal neurogenesis is practically non-existent, contrary to what has been thought in recent decades. The work, launched by the journal Nature last March, reconfirms the results in a review now published in Cell Stem Cell.
A work developed by the team of the neurobiologist of the Universitat de València José Manuel García Verdugo (Cavanilles Institut), in international collaboration with the laboratories of scientists Arturo Alvarez-Buylla (University of California, San Francisco) and Zhengang Yang (University of Fudan, Shanghai), so defends it and is corroborated in Cell Stem Cell through a review of the work by the team of the Cavanilles Institute of Biodiversity and Evolutionary Biology.
Over the years, numerous investigations have shown that the subgranular zone of the hippocampus' toothed gyrus of certain mammals -an area related to memory and learning processes- continues to generate new neurons in the adult brain. Although there are studies that extrapolate these data to the adult human hippocampus, the work that now corroborates Cell Stem Cell, a few months after its publication in Nature, obtains very different results.
After carrying out an extensive study of the neurogenic capacity of the human hippocampus in samples of different ages -from fetal and infant development to adult stages-, the results show that the number of proliferative parents and new neurons in the toothed gyrus decreases drastically during the first year of life.
Something similar occurs, according to the study, with the proliferative capacity of the toothed gyrus of the non-human primate Macaca mulatta. Analyses show that during the first post natal stages there is a generation of new neurons, but this is greatly diminished during juvenile development.
"The generation of new neurons in the human hippocampus and of non-human primates takes place fundamentally in embryonic stages and in a scarce way in post-natal periods, during the first months of life", assures José Manuel García Verdugo, co-principal investigator of the project and researcher of the Cavanilles Institute of Biodiversity and Evolutionary Biology, in the Scientific Park of the Universitat de València. "We have hardly observed any new neurons isolated at 7 and 13 years of age, and none in the case of studies carried out with adult patients affected by epilepsy". The analyses have been carried out in collaboration with the Functional Neurosurgery team at the Hospital Universitario y Politécnico La Fe in Valencia and its head, neurosurgeon Antonio Gutiérrez.
These data contrast with the extensive neurogenesis that takes place in the hippocampus of other more primitive mammals, rodents, a study model for thousands of research results.
"Unlike rodents, humans are born with practically all the neurons necessary for normal development, and this work points out that future modifications and treatments must be based on plasticity", assures García Verdugo´. Neuroplasticity or synaptic plasticity refers to the communication established between neurons, a property that intervenes to modulate the perception of stimuli in the environment, also related to neurogenesis until now.
It is not the first time that differences appear in the development of the human brain with respect to other species of mammals. "One of the great evolutionary leaps of the human being is the existence of currents of new neurons towards our prefrontal cortex in infants, something that does not occur in mice and that, in addition to being related to memory and learning, is linked to human social activity.
In the case of the hippocampus, the results of this work now suggest the possible implication of other mechanisms of plasticity of the adult human toothed turn in the processes of learning and memory. "More than new neurons, we will have to start talking about new neuronal circuits", concludes the scientist.
The results of this research appeared for the first time in Nature last March and the article appears in the list of 100 publications that have generated more global impact in 2018, according to Almetric. This annual ranking is based both on mentions in the media and blogs and on the dissemination of scientific papers on social networks such as Twitter, Facebook and Google+.
The project has been financed by the Ministry of Economy and Competitiveness and by the research grants PROMETEO of the Valencian Government.
Cell Stem Cell. Does Adult Neurogenesis Persist in the Human Hippocampus?
Mercedes F. Paredes, Shawn F. Sorrells, Arantxa Cebrian-Silla, Kadellyn Sandoval, Dashi Qi, Kevin W. Kelley, David James, Simone Mayer, Julia Chang, Kurtis I. Auguste, Edward F. Chang, Antonio J. Gutierrez Martin, Arnold R. Kriegstein, Gary W. Mathern, Michael C. Oldham, Eric J. Huang, Jose Manuel Garcia-Verdugo, Zhengang Yang and Arturo Alvarez-Buylla
Nature. Human hippocampal neurogenesis drops sharply in children to undetectable levels in adults
Shawn F. Sorrells, Mercedes F. Paredes, Arantxa Cebrian-Silla, Kadellyn Sandoval, Dashi Qi, Kevin W. Kelley, David James, Simone Mayer, Julia Chang, Kurtis I. Auguste, Edward F. Chang, Antonio J. Gutierrez, Arnold R. Kriegstein, Gary W. Mathern, Michael C. oldham, Eric J. huang, Jose Manuel Garcia-Verdugo, Zhengang Yang & Arturo Alvarez-Buylla