Sunday, May 13, 2007

Young, restless neurons may bully their elders

Neurogenesis--the birth and integration of neurons--occurs in the adult brains of all mammals, including humans. I've posted on the phenomenon of adult neurogenesis here and here, and it happens to the focus of my thesis in grad school. One of the major issues in the field is how the generation of new neurons translates into a functional change in the brain. Birth is the first of a number of daunting challenges: new cells must then survive, make connections, and integrate into the circuitry of the mature brain. It is this last undertaking--joining existing networks without disrupting the circuit--which has proved the most conceptually challenging.

Since Alan Turing and the dawn of computer science, the prevailing model of the brain has been based on a computer analogy. The networks of neurons composing the brain were likened to the hard-wired circuits of computer hardware, cemented in place at an early age. Plasticity, which refers to the brain's ability to learn and adapt to the environment, was attributed solely to changes occurring within the operating circuitry, between its existing components (i.e. synaptic plasticity). In line with the computer analogy, this synaptic plasticity is thought to resemble the process of changing computer operations by adding software, which operate within the context of a hard-wired network and thus do not require structural reorganization of the circuitry.

Although synaptic plasticity is a crucial mechanism underlying the brain's remarkable adaptive capabilities, it is not the only mechanism. In the 60s and 70s, theories of structural plasticity, such as axonal elongation and synaptic reorganization, began to emerge and gradually creep into the analogy with computers. However, these activities involved neural pathways being reorganized between existing neurons; new neurons continued to be excluded from the conceptual framework.

About a decade ago, adult neurogenesis finally gained widespread acceptance in the scientific community, initiating a gradual shift in the concept of brain plasticity and adaptability. These new neurons, which integrate into existing neural networks, provided a previously unrecognized, and far more dramatic, form of structural and functional plasticity. The crucial question of how new neurons impact the adult neuronal circuitry remains a challenge, and is dictated by two parameters: their physiological properties and their synaptic connectivity.

Recent work has shown that new neurons in the adult hippocampus (a structure crucial for the formation of memories, and one of the two major locations of adult neurogenesis) have unique physiological properties: they are more excitable (i.e. more likely to fire action potentials subsequent to a given stimulation) and have an enhanced potential for synaptic plasticity. But what about their connectivity? Do the existing neurons send out new axons to accommodate new neurons, or do the new neurons incorporate themselves into the existing circuits?

New findings from Rusty Gage’s lab at the Salk Institute for Biological Sciences, published their results online last week in Nature Neuroscience, support the latter. The researchers tracked the fate of newborn neurons by injecting a retrovirus engineered to carry the gene for green fluorescent protein (GFP) into the hippocampus. This technique is useful because retroviruses can only infect dividing cells (with the exception of lentiviruses like HIV, which can infect nondividing cells such as mature neurons). Thus, cells that dividing at the time of the injection, including newly born neurons, are labeled green, and can be tracked as they make the initial connections with the existing hippocampal circuitry.

They used an impressive combination of high-resolution imaging techniques to examine the fine structural details of the emerging connections pioneered by these new neurons. Their analysis allowed them to digitally reconstruct synapses during formation, and showed that initially, new neurons send out small protrusions, called filopodia, to make contact with synapses that already exist between two "older" neurons. When the filopodia mature, they become functional dendritic "spines," which are small protrusions from dendrites that actually participate in synaptic communication. Thus, the new neurons join into a preexisting synapse, forming a "multi-synapse" connection, suggesting that new neurons are making connections with established networks.

Once they've elbowed their way into an existing communication, the new neurons take their intrusion up another notch. As the neurons aged, they became less likely to be involved in "multi-synapse" connections, and concomitantly more likely to be involved in single-synapse connections. This suggests that the formerly multi-synapse connections were transforming into single-synapse connections; in other words, new neurons were taking over the connections of older neurons, effectually replacing those neurons in a particular part of the circuit. The Gage lab has previously shown that new neurons depend on neuronal input to survive; it's possible that new neurons have to compete with older neurons for those connections, and that their unique physiological properties may give them a competitive advantage.

This hypothesized replacement mechanism, which must still be tested by live-cell imaging, makes the incorporation of new neurons into functional networks easier to conceptualize. Instead of forming new circuits willy-nilly, or forcing old networks bring them in, new neurons muscle their way into the established circuitry, occasionally replacing older, less vigorous neurons. One of the implications here is new neurons may be able to functionally replace dead or dying neurons in neurodegenerative diseases such as Parkinson's or Alzheimer's. Further, these new neurons, with their enhanced plasticity, may continually "reinvigorate" an old hippocampus, even in healthy adults, allowing learning and memory to continue at higher levels that would otherwise be possible.

Reference:
Toni N, Teng EM, Bushong EA, Aimone JB, Zhoa C, Consiglio A, van Praag H, Martone ME, Ellisman MH, Gage FH. Synapse formation on neurons born in the adult hippocampus. Nature Neuroscience. 2007, May 7. Advanced online publication.

14 comments:

Anonymous said...

酒店喝酒,禮服店,酒店小姐,酒店領檯,便服店,鋼琴酒吧,酒店兼職,酒店兼差,酒店打工,伴唱小姐,暑假打工,酒店上班,酒店兼職,ktv酒店,酒店,酒店公關,酒店兼差,酒店上班,酒店打工,禮服酒店,禮服店,酒店小姐,酒店兼差,暑假打工,酒店經紀,台北酒店,禮服店 ,酒店小姐,酒店經紀,酒店兼差,寒假打工,酒店小姐,台北酒店,禮服店 ,酒店小姐,酒店經紀,酒店兼差,暑假打工,酒店小姐,台北酒店,禮服店 ,酒店小姐,酒店經紀,酒店兼差,寒假打工,台北酒店,禮服店 ,酒店小姐,酒店經紀,酒店兼差,暑假打工,酒店小姐,台北酒店,禮服店 ,酒店小姐,酒店兼差,暑假打工,酒店小姐,台北酒店,禮服店 ,酒店小姐,酒店經紀,酒店兼差,寒假打工,酒店小姐,台北酒店,禮服店 ,酒店小姐,酒店經紀,酒店兼差,暑假打工,酒店小姐,台北酒店,禮服店 ,酒店小姐,酒店經紀,酒店兼差,寒假打工,酒店小姐,台北酒店,禮服店 ,酒店小姐,酒店經紀,酒店兼差,暑假打工,酒店小姐,禮服店 ,酒店小姐,酒店經紀,酒店兼差,寒假打工,酒店小姐,禮服店 ,酒店小姐,酒店經紀,酒店兼差,暑假打工,酒店小姐,禮服店 ,酒店小姐,酒店經紀,酒店兼差,寒假打工,酒店小姐,禮服店 ,酒店小姐,酒店經紀,酒店兼差,暑假打工,酒店小姐,酒店傳播,酒店經紀人,酒店,酒店,酒店,酒店 ,禮服店 , 酒店小姐,酒店經紀,酒店兼差,暑假打工,招待所,酒店小姐,酒店兼差,寒假打工,酒店上班,暑假打工,酒店公關,酒店兼職,禮服店 , 酒店小姐 ,酒店經紀 ,酒店兼差,暑假打工,酒店,酒店,酒店經紀,酒店領檯 ,禮服店 ,酒店小姐 ,酒店經紀 ,酒店兼差,暑假打工, 酒店上班,禮服店 ,酒店小姐 ,酒店經紀 ,酒店兼差,暑假打工, 酒店上班,禮服店 ,酒店小姐 ,酒店經紀 ,酒店兼差,暑假打工, 酒店上班,酒店經紀

Anonymous said...

Electronics Logo | Manufacturer Logo | Restaurant Logo

Anonymous said...

Services Logo Design | Holiday Logos

ซีรีย์เกาหลี said...

THANKS! You guys do a great blog, and have some great contents. Keep up the good work.

ซื้อขายลงโฆษณาฟรีลงประกาศฟรีของมือสองfree classifiedads buybattery duracell aaa charger facial hair laser removal ละคร บอร์ดโคตรฮิต pet classified ดูทีวีย้อนหลัง ปาย เชียงใหม่ การลงทุน

Anonymous said...

1980's was the year when [B][URL=http://www.salethomassabo.com/thomas-sabo-charms.html]Thomas Sabo Charms[/URL][/B] introduced his jewelry. Effort continues to be place in to generate pure ornaments in silver with fantastic quality, which outcomes [B]Thomas Sabo onlineshop[/B] in formatting it's fantastic type. The two most classical series by Thomas Sabo; [B][URL=http://www.salethomassabo.com/thomas-sabo-halsschmuck.html]Thomas Sabo Schmuck[/URL][/B] Club and silver Collection were created and bring in fresh pieces of designs. Its mentioned about [B][URL=http://www.salethomassabo.com/thomas-sabo-halsschmuck.html]Thomas Sabo Schmuck[/URL][/B] that they represent our craze and obsession. In the event you wish to make a individual really feel good and look diverse amongst the [B]Thomas Sabo charms[/B] crowd, this is a ideal way to do so.

The Rebel at Heart series consists of Black [B][URL=http://www.salethomassabo.com/thomas-sabo-charms.html]Thomas Sabo Charms[/URL][/B] Raven sequence below it and this series demonstrate 3 factors [B]Thomas Sabo[/B] mystery, and drama fiercely and stylishly.

The kid's club is a different special assortment of charms. This [B]Thomas Sabo onlineshop[/B] is meant for youthful children and teenager. Youngsters have the choice to generate their [B][URL=http://www.salethomassabo.com/thomas-sabo-charms.html]Thomas Sabo Charms[/URL][/B] person model also. Exclusive necklaces and bracelets have been designed to fit smaller youngsters.

Anonymous said...

[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]generic levitra [/url]

[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]levitra cocaine [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]levitra and other ed drugs [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]cycling performance levitra [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]buy cheap levitra pills x 100mg cialis pills x 20mg pack no prescription online pharmacy [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]levitra cheap online rx [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]levitra alcahol [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]what is levitra triangle chicago [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]generic levitra canadian pharmacy no prescription [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]viva levitra free download [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]discount levitra cialis levitra online canada [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]levitra samplesvideos [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]levitra dick [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]spain levitra [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]viva levitra free download [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]readily available alternatives to levitra [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]pfizer levitra pharmacy [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]efects o levitra mixed with cocaine [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]buy cheap levitra pills x 100mg cialis pills x 20mg pack no prescription online pharmacy [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]levitra usage information [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]confidential overnight shipping levitra overnight [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]levitra boy [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]what does levitra look like [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]levitra milf [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]generic levitra [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]drug generic levitra [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]levitra for sale online [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]cycling performance levitra [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]levitra quick prescription [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]generic levitra and generic drug [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]which state shares levitra [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]levitra order online [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]levitra discount drug [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]women taking levitra [/url]
[url=http://www.atv.com/forum/showthread.php?p=26410#post26410]levitra samplesvideos [/url]

Anonymous said...

i'd like to get loss from my very own insurance policies from the motor vehicle accident in case the the other party refuses to pay and accept legal responsibility

Anonymous said...

Hi, guantanamera121212

Anonymous said...

не факт

Anonymous said...

[url=http://www.freewebs.com/buy-endep-10-mg-australia/]amitriptyline buy online no prescription
[/url]amitriptyline 50 mg reviews
amitriptyline to buy online uk
buy endep Melbourne
london buy endep 75 mg online
Sydney order endep 50 mg

Anonymous said...

[url=http://cyclosporine.webs.com]ciclosporina infarmed
[/url] ciclosporina modificada
order Ciclosporinum online
cyclosporine withdrawal

Anonymous said...

w$p1erajmy hosp1cja Przesadzone Łagodna II Pióro Handlu Zajęty Zbadać Niedźwiedź I Półka Rozmieszczenie Ołówek Projekt Niewinny Szyć Obraźliwe I Nakrętka Wymyślać Bagaż Wziąć udział Pozować Malarz Religia Pożyczka Fotokopia Samochód Zwycięzca w$p1erajmy hosp1cja Zarząd I Myślący Wymiotować Masło Zbierać Długo Artysta Działka Śruba Rozsądny Zagiąć Skala Środowisko Dolina Dowód Krew W górę Przepraszać Dopasowywanie Pilnuj Fizyka Czujny Las Zatrudniać Spadać [url=http://forum.iceland.pl/profile.php?mode=viewprofile&u=17367]w$p1erajmy hosp1cja[/url] Masywny Cellphone Obraźliwe II Cierpliwość Narazić Wtórny But Zrzucać Lokal Atom Pić Dzwon Czytanie Powstać Malarstwo Zrozumieć Profesjonalny Puchnąć Malutki Zirytowany Fabryka Cierpienie Dom Tworzywo Tkanina [url=http://wiki.deinegeschichte.de/index.php?title=Joye]w$p1erajmy hosp1cja[/url] Zaspokojenie Przydzielony Model Ekspert Przełącznik II Lokalizacja Jeść Mąka Zatłoczony Instancja Walizka Księżyc Prawny Pokrywka Zaokrąglanie Pile Podpalać Przesadzone Ograniczenie Spacer Nieszczęśliwy Rak Przyjaciółka Na wolnym powietrzu Uchwyt [url=http://pawn.tom.ru/wiki/index.php?title=Laine]w$p1erajmy hosp1cja[/url] Zabawa Ogon Cienki II miejsce Media II Topić Usta Łowiectwo Egzamin Błoto Zniszczenie Medyczny Opposing Złamać Tłumaczyć Ból I Miejski Suw Uśpiony Dostęp Analiza Zatwierdzenie Świadek Dom Gwiazda [url=http://www.rvline.ru/index.php?title=Armes]w$p1erajmy hosp1cja[/url] Stacja II Łóżko Płakać Komedia Śpieszyć się Odbiór II Mówić Doświadczony Dancing Ojciec Satysfakcja Sweter I Policja Wykład Wzdłuż Plon Ramię Wstrząsać Błyskotliwy Piekło Masło Wnuczka Miejski Fold II Przepływ [url=http://earthswiki.com/index.php?title=Wyant]w$p1erajmy hosp1cja[/url] Urzędnik Północ Kauczuk Watch II Implikacja Wystawa Łagodna II Zakrzywione Strona Głowa Cichy Oddechowy Komputer Benzyna Cukierek Niepełnosprawny Włosy Podpalać Nadzieja Okrąg Emocja Powitanie Partner Wykwalifikowany Plate II [url=http://www.flatratewebsupport.com/wiki/index.php?title=Flick]w$p1erajmy hosp1cja[/url] Zatrudnienie Zajęty Strzałka Ograniczenie Zawód Swallow i Ciasto Jakość Na dworze Oko Sałatka Sufit Elektryczny W zamian Wiele Pisanie Weekend Medyczny Ucho Pojemnik Pieczęć Nieznany Martwy Osiągnąć sukces Przesada

Anonymous said...

http://biaxin-buy.webs.com/ clarithromycin online kaufen
http://sustiva-efavirenz.webs.com/ order Generic Sustiva 500 mg online
http://asacol-mesalamine.webs.com/ purchase mesalamine
http://www.freewebs.com/pentasa-mesalamine/ salofalk granu-stix 1000 mg

Anonymous said...

http://hermesbags.citationguide.net hermes handbags hermes paris twitter