Social isolation delays the positive effects of running on adult neurogenesis – Nature Neuroscience
From the Apr 9, Nature Neurosci:
Social isolation delays the positive effects of running on adult neurogenesis
Alexis M Stranahan, David Khalil & Elizabeth Gould
Social isolation can exacerbate the negative consequences of stress and increase the risk of developing psychopathology. However, the influence of living alone on experiences generally considered to be beneficial to the brain, such as physical exercise, remains unknown. We report here that individual housing precludes the positive influence of short-term running on adult neurogenesis in the hippocampus of rats and, in the presence of additional stress, suppresses the generation of new neurons. Individual housing also influenced corticosterone levels—runners in both housing conditions had elevated corticosterone during the active phase, but individually housed runners had higher levels of this hormone in response to stress. Moreover, lowering corticosterone levels converted the influence of short-term running on neurogenesis in individually housed rats from negative to positive. These results suggest that, in the absence of social interaction, a normally beneficial experience can exert a potentially deleterious influence on the brain.
We’ve heard in the past about neurogenesis in adults, but as far as we understand, this only happens in limited locations throughout the brain. However, what if those new neurons migrate to different places?
New evidence in mice suggests that after being born, new neurons can travel along the flow of spinal fluid to end up in the olfactory bulb.
If there is migration to other locations in the brain, the ramifications for computational models of brain systems are significant.
In the August PLoS Biology, there is an article showing the production of pure neural stem cells from human embryonic stem cells.
The procedure is quite simple: Add growth factors FGF-2 and EGF to the ES cells and you get pure NS cells, which overcomes several of the limitations of previous neurosphere-based assays [Nature Methods].
Some recent work in Neuron (full article; easy to read summary) shows how hippocampal neurons can cause neural progenitor cells to produce new neurons in the hippocampus. I find this fascinating since the network literally is replacing itself through its own dynamics.
The mechanism seems to be that GABAergic cells synapse onto progenitor cells and cause calcium entry due to the depolarization. (GABAergic synapses are often excitatory in young cells which have elevated intracellular chloride levels.) The increased calcium entry leads then to activation of genes coding for neuronal differentiation-related proteins.
Also, here’s some earlier work from Malenka’s lab along the same lines.
This research suggests that neuronal variety within a single person may be partly due to “jumping genes” which change their position from cell to cell.
Alysson R. Muotri, Vi T. Chu, Maria C. N. Marchetto, Wei Deng, John V. Moran and Fred H. Gage. Somatic mosaicism in neuronal precursor cells mediated by L1 retrotransposition p903. Nature 435, 903-910 (16 June 2005). doi: 10.1038/nature03663
News and Views
“…a difference in concentration of a single molecule across the tip of an axon can measurably impact the direction in which the axons grow”
Press release: http://gumc.georgetown.edu/communications/releases/release.cfm?ObjectID=2670