Sci­en­tists find signs of new brain cells in adults as old as 79

The Star Malaysia - Star2 - - Science - By DEB­O­RAH NET­BURN

DO we con­tinue to add new neu­rons to our brain cir­cuitry through­out our lives? Or does our neu­ron count re­main fixed once we reach adult­hood?

The sci­en­tific de­bate rages on.

In a re­cent re­port in Cell Stem Cell, sci­en­tists from Columbia Univer­sity present new ev­i­dence that our brains con­tinue to make hun­dreds of new neu­rons a day, even af­ter we reach our 70s, in a process known as neu­ro­ge­n­e­sis.

To come to this con­clu­sion, lead au­thor Dr Maura Boldrini, a re­search sci­en­tist at Columbia Univer­sity’s de­part­ment of psy­chi­a­try, and her col­leagues looked at the brains of 28 de­ceased peo­ple aged 14 to 79. Their goal was to see whether age­ing af­fects neu­ron pro­duc­tion.

Pre­vi­ous re­search had shown that neu­ro­ge­n­e­sis slows down in age­ing mice and non­hu­man pri­mates. Boldrini’s group wanted to see whether a sim­i­lar pat­tern oc­curred in hu­mans.

In each brain sam­ple the re­searchers looked for ev­i­dence of neu­rons in var­i­ous stages of de­vel­op­ment, in­clud­ing stem cells, in­ter­me­di­ate pro­gen­i­tor cells that would even­tu­ally be­come neu­rons, im­ma­ture neu­rons that had not fully de­vel­oped, and new neu­rons.

The team looked only at the hip­pocam­pus, in part be­cause it is one of the few ar­eas of the brain that pre­vi­ous re­search has shown can pro­duce new neu­rons into adult­hood. This re­gion is in­volved in emo­tional con­trol and re­siliency, as well as mem­ory, Boldrini said.

In all their sam­ples the re­searchers found sim­i­lar num­bers of neu­ral pro­gen­i­tor cells and im­ma­ture neu­rons, re­gard­less of age. This led them to con­clude that the hu­man brain con­tin­ues to make neu­rons even into old age.

How­ever, the re­searchers did un­cover some dif­fer­ences in the brains of young peo­ple and older peo­ple.

Specif­i­cally, they found that de­vel­op­ment of new blood ves­sels in the brain de­creases pro­gres­sively as peo­ple get older. They also dis­cov­ered that a pro­tein as­so­ci­ated with help­ing new neu­rons to make con­nec­tions in the brain de­creased with age.

“We don’t find fewer of the new neu­rons or fewer of the pro­gen­i­tors of new neu­rons, but we find that new neu­rons might make fewer con­nec­tions,” Boldrini said.

This might ex­plain why some older peo­ple suf­fer from mem­ory loss or ex­hibit less emo­tional re­siliency, she said.

These new find­ings were pub­lished one month af­ter a team of re­searchers from the Univer­sity of Cal­i­for­nia, San Fran­cisco re­ported in Na­ture that it was un­able to find any ev­i­dence of neu­ro­ge­n­e­sis af­ter ado­les­cence in hu­mans at all.

In an email state­ment, that group, which works out of de­vel­op­men­tal neu­ro­sci­en­tist Ar­turo Al­varez-Buylla’s lab, said that while they found the new study’s ev­i­dence of de­clin­ing blood ves­sel growth in the adult hip­pocam­pus in­ter­est­ing, they are not con­vinced that Boldrini and her col­leagues found con­clu­sive ev­i­dence of adult neu­ro­ge­n­e­sis.

“Based on the rep­re­sen­ta­tive im­ages they present, the cells they call new neu­rons in the adult hip­pocam­pus are very dif­fer­ent in shape and ap­pear­ance from what would be con­sid­ered a young neu­ron in other species, or what we have ob­served in hu­mans in young chil­dren,” they wrote.

They added that in their study, they looked not just at pro­tein mark­ers as­so­ci­ated with dif­fer­ent types of cells, as Boldrini and her team did, but also per­formed care­ful anal­y­sis of cell shape and struc­ture us­ing light and elec­tron mi­cro­scopes.

“That re­vealed that sim­i­larly la­beled cells in our own adult brain sam­ples proved to be nei­ther young neu­rons nor neu­ral pro­gen­i­tors, but rather non-neu­ronal glial cells ex­press­ing sim­i­lar molec­u­lar mark­ers,” they wrote.

Boldrini points out that the two groups were work­ing with very dif­fer­ent sam­ples.

She and her team ex­am­ined more than two dozen flash-frozen hu­man brains, which were do­nated by fam­i­lies of the de­ceased at the time of death.

The brains were im­me­di­ately frozen and stored at -112ºFahren­heit, which keeps the tis­sue from de­grad­ing.

The other re­search team re­ceived brain sam­ples from hos­pi­tals in China, Spain and the US, and the brain tis­sue they ex­am­ined had not been pre­served in the same way. Boldrini said the chem­i­cals that were used to fix the brains could have in­ter­fered with their abil­ity to de­tect new neu­rons.

She also noted that while both groups were look­ing for signs of neu­ro­ge­n­e­sis in the hip­pocam­pus re­gion of the brain, her group had ac­cess to the en­tire hip­pocam­pus while the UCSF team was look­ing at thin slices of the tis­sue rep­re­sent­ing a small frac­tion of the brain.

“In sci­ence, the ab­sence of ev­i­dence is not ev­i­dence of ab­sence,” she said. “If you can’t find some­thing it doesn’t mean that it is not there 100 per­cent.”

The de­bate con­tin­ues. – Los An­ge­les Times/ Tri­bune News Ser­vice

A new­born neu­ron (up­per left) in the brain of an older adult. — Maura Boldrini/Columbia Univer­sity Vage­los Col­lege of Physi­cians and Sur­geons/TNS

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