Touch stimulates neurogenesis

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Touch stimulates neurogenesis

Mice exposed to novel tactile stimuli produced new immature neurons in the

spinal cord, suggesting that neurogenesis may play a role in touch and vice

versa

[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.

Image: Wikimedia commons, Logan

" 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.

Recently, however, neuroimmunologist Michal Schwartz of The Weizmann Institute

of Science and her colleagues discovered proliferating neural progenitor cells

in the dorsal horn of the mouse spinal cord. Because this part of the spinal

cord is known to be composed of predominately sensory neurons, " it gave us an

idea that [these new neurons] are participating in pain and/or touch sensation, "

Schwartz said.

To test this idea, the team placed mice in enriched cages containing sandpaper,

gravel, or sponge substrates, or a combination, for 2 hours and measured new

cell production in the spinal cord. Just 2 hours after exposure to the enriched

environments, the mice showed a dramatic increase in the number of new cells in

the dorsal horn. The amount of neurogenesis was greater in mice exposed to

environments with a combination of substrate types, suggesting that cell

proliferation may be a response not only to the novelty of an environment, but

to its diversity as well.

" We had not expected to have such an amazing effect, " said Ravid Shechter, a

graduate student in Schwartz's lab who helped execute the experiments. " It was a

very fast response to the environment. "

" It was a huge surprise, " agreed neuroimmunologist and coauthor Asya Rolls, a

prior member of the Schwartz lab and a current postdoc at Stanford University.

" [Neurogenesis is] an additional component that was never even suggested in this

field [of touch sensation]. "

To test the role of neurogenesis in habituation to stimuli, the team exposed the

mice to the environments repeatedly over a 7-day period, or permanently housed

them in the enriched cages. In contrast to the single exposure experiments,

repeated exposures did not result in increased neurogenesis, and continuous

exposure even seemed to inhibit the process. Further analysis of the cells

revealed that instead of proliferating, the newly formed cells had begun to

differentiate, mostly into GABAergic immature neurons. As inhibitory neurons,

these GABAergic cells may play a role in habituation.

The immature neurons tended to die within just four weeks, however, Lledo noted.

What drives neuronal death is unclear, but even at a young age, these neurons

can be active. " The same category of neurons the same age in the olfactory bulb,

we have been able to demonstrate about one week after birth these newborn

neurons indeed release GABA. " Thus, even though the neurons fail to mature, they

may still have functional consequences, he said.

Indeed, the findings show a striking similarity to the process of adult

neurogenesis in the olfactory bulb, said Lledo, where exposure to different

odors has been found to stimulate cell proliferation. " If you look at the brain

of a mouse living in a very clean and boring cage, the number of neurons is

quite reduced, " he said. " But as soon as you change the odorants every day, you

stimulate the neurons two or three [fold]. " Thus, the process of neurogenesis

and differentiation may be " a more general phenomenon of plasticity in the

sensory organs, " he said.

The finding that neurogenesis may be an integral component of touch sensation

may have implications for pain management and the treatment of pain diseases,

Lledo added. Because these new GABAergic neurons, which are known to be

inhibitory, are generated where pain fibers terminate in the spinal cord, " more

newborn neurons located here will provide more inhibition to these nocioceptive

fibers, and therefore will change the threshold of pain. "

Furthermore, the results may provide some answers with regard to touch

treatments used in alternative medicine, Schwartz said, for which the mechanisms

are currently a bit of a mystery. " In this regard, [our results] may give a

scientific basis to unexplained effects of touch treatment. "

R. Shechter, et al., " Touch gives new life: mechanosensation modulates spinal

cord adult neurogenesis, " Molecular Psychiatry, 1-11, 2010.

Read more: Touch stimulates neurogenesis - The Scientist - Magazine of the Life

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