Khoa hoc & Cong nghe
^ ^Neu nhu cdc noron khong phdi Id trung khu duy nhdt ciia tri tue cda con nguoi? cdc te bdo hinh sao, khong duoc hieu biet cho den luc do ngodi cdc te bdo khde cua ndo, trong thuc te co khd ndng truyen dat cdc thong tin. Hon nira, chung Id cdc to chuc xdm cua cdc noron ! Su ket thiic cua mot gido dieu."
Cd gi khac nhau giua bO nao ciia Albert Einstein va bd nao ciia mdt ga nao dd ? Van de nay da lam chay biet bao la myc... VI phia sd lugng va hinh dang giai phdu hgc Marian Diamond, Trudng Dai hpc Berkeley, California My, ldn dau tiln hanh kilm tra mdt each chat ehe cac lat cdt cua vd nao ciia ngudi dugc nhan giai thudng Nobel, ba da giam sat thay mdt dac diim ky la trong vd nao ciia nha bac hpc mpt sy tap trung cao dang kinh ngac cac t l bao phi na ron dugc biel dudi ten gpi \h "glie". (Glie la todn bd cdc t l bao phi na ron cua nao, dugc phat hidn bdi nha khoa hgc Due Rudolf Virchow vao nam
1856). Thi ma viing vo nao cd quan he din sd lugng cao hon miic cho phep dd dugc coi nhu gianh cho nhttng chirc nang nhan thirc phuc tap. Vdo thdi dd, sy quan sat nay xem nhu mdt sy ky la don gian vl gidi phau hpc: dugc phat hien tir ddu thi ky XX, cac t l bao gile trong thyc t l dugc coi nhu nhQng t l bao "choan ehd" thdng thudng, chi don gian chju trach nhiem liim gid dd va nudi dudng cac noron quy bau ma ehinh chung mdi la trung khu ciia tri tue con ngudi. Nhung bay gid, tir sau khoang ba nam, sy gidi thidu kinh diin vl nao bdt ddu da bj tan vd.
Trdn thyc tl, nhiiu nhdm ldn cac nha nghidn ciru qud'c t l nhan len nhQng phat hien vl nhQng kha
Cac te bao hinh sao lam dao Ion hieu biet ve nao
V NGUYEN PHUaC TUONGnang che giau ciia cac t l bao gile va chinh xac hon vl nhung nang lyc thdng tin ddi dao nhat, cac t l bao hinh sao. Theo cdc cdng trinh nghidn cuu dd, cdc t l bao hinh sao trdn thyc t l la cdc "td chire chat xam" dd'i vdi cac noron, cd kha nang anh hudng kin ddo din sy ddn truyen cac thdng tin va ngay ca thilt lap nhQng mang ludi thdng tin song song cua chinh chiing.
Hai mang luoi thay vi mot?
Ngay tir bay gid, ngay ca cac
"nha thdn kinh hgc" ma hg dya vao nhung kiln thirc tich luy tir tdm muoi nam nay, thira nhan rdng nhirng du kidn thu dugc ciia nhUng nha nghidn ciin gpi la "nha gile hpc" khdng thi cdn khdng dugc bilu bidt. Nha thdn kinh hpc Denis Le Bihan, mdt trong nhOng thu linh ciia nghidn cuu tham dd chirc nang eua nao da khdng djnh:
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27
Khoa hoc Si Cong nghe
"khdng cdn cd hOi thao nao cua cac nha than kinh hpc didn ra ma khdng cd mpt hay nhieu tieu ban gianh cho nhirng tiln bd sang ngdi vl cac t l bao dem than kinh". Va do la mdt nganh hpc hoan toan mdi me, da den luc cd nguy ca lam dao ldn mpi dilu tin chdc vl nao.
Cho din nay, md hinh thudng dugc sir dung nhat trong cac giao trinh ciia cac Irudng hpc dl md ta bdn trong cua hOp sp chung ta vdn cdn la md hinh cua mdt mang ludi rOng Idn luyel dd'i lao Ihanh bdi cac noron dugc nd'i liin nhirng noron nay vdi noron khac bdng nhQng doan ndi, cac xynap (khdp than kinh). Nhirng loai "sang thdng tin" cho phep mdt thdng tin tir mdt t l bao than kinh nay di qua mdt t l bao than kinh tiip theo.
Nlu nhu quan diim dd khdng sai, thi tuy vay nd lam lu md mOt niia bd nao ciia chung la: bp nao dugc cau tao bdi cac t l bao glie (tl bao than kinh dem) va dac bidt han la cac te bao hinh sao. Nha khoa hpc Christian Giaume ciia Trudng Dai hpc nudc Phap giai thich: "De bd sung cho bang md hinh dd. can phai gidi thich rdng cac noron dugc bao quanh nhiing id bao, dd la nhung t l bao hinh sao ma chiing di din bao quanh lay cac xynap.
Tren thyc tl, cac noron va cac te bao hinh sao cd thi so sanh vdi hai mang dudng sdt dugc xay dyng bdi hai dan vj. Nhu vay, mdt sd thdng tin cd the dugc van chuyin rat nhanh chdng bdi cac noron, trong khi do mdt sd thdng tin khac dugc chuyen lai 100.000 lan cham han bdi cac t l bao hinh sao. Trong md hinh nay, cac xynap se la cac nha ga tuyIn chpn ma d dd cac thdng tin giua cac naron va cdc t l bao hinh sao cd the dugc trao ddi vdi nhau".
Quan niem each mang nay ve
mdt bo nao dugc cau tao bdi hai mang ludi xep gdi ldn nhau cua cai nay trong cai kia chi mdi la mdt ly thuyet cdng trinh don gian... Nhung da cd nhidu thi nghidm di din ciing ed tinh chinh xac ciia each nhin mdi tiln bp dd bdi nhung ngudi tan ddng. Nhu vay vao giira nam 2001 va 2002, it nhat cd ba cdng trinh nghien ciiu ca ban da xac nhan sy tdn tai cua sy dieu bidn truyin dat tin hidu than kinh bdi cac t l bao hinh sao.
Chiing cung dSn truyen Tir lau ngudi ta da bidt rdng mdt kbi xung than kinh di din tai xynap, nd gay ra mdt sy phdng thich cac chat dan truyin than kinh - cac chat trung gian boa hpc (glutamat, GABA, Axdtin-cdlin, dopamin...) - ma chiing sau dd cd djnh vao cac thu thi dae hidu co mat trdn naron thu hai. Sy cd dinh do di din tai khdi phat sy lan truyin tin hidu than kinh din mdt xynap khde va cu tiip tyc nhu thi, Nhu vay, cac naron di qua rale.
Nlu ngudi ta nhin gan vao dd thi khdng the khdng nhan thay rdng nhieu xynap dugc bao quanh bdi mdt canh tay eiia t l bao than kinh.
Va dd la diim mdi: ngudi ta tudng dd la mdt loai vo bpc each ly nhung thyc t l dd la mdt viing tiip xiic uu tidn ma qua dd te bao hinh sao tae ddng anh hudng eiia nd de'n sy truyin thdng bdn trong noron nhu nghien ciVii ndi tiing cua Stephane Olliet va cac cdng tac vien (Trudng Dai hpc Bordeaux) da cho thay. Trong md hinh thyc nhiem cua hp (vung dudi ddi ciia chudt cdng), hp da nhan thay rdng sy biin mat ciia cae t l bdo hinh sao d xung quanh xynap da gay ra mdt sy bao hoa bat thudng ciia cae chat ddn tniyen than kinh, phong be hoan loan hoat ddng eua xynap. Ngugc lai, su cd mat cua cac t l bao hinh
sao dilu hoa sd lupng cac chat ddn truyin thdn kinh bdng each dat vao tai ehd mOt he tai dan truyin.
Va chua phai la tat ca. Bdi vi cung liic dd, nhdm August Smit ciia Trudng Dai hpc Amsterdam da phat hien cac t l bao than kinh dem cd thi tao ra nhQng cai bay bdng cac chat ddn truyin than kinh, dilu nay lam giam sy dan truyen qua xynap nhung tin hieu than kinh. Cae te bao hinh sao cung cd thi dilu hoa dugc so lupng eac thy thi ed mat trdn be mat cac naron bang each gui cho chung mdt thdng didp dudi dang mpt phan tu hoa hpc (mdt cytokin), do la dilu it hon nhOng gi ma cdc cdng trinh eiia Robert Malenka, nhd nghien ciiu d Trudng Dai hoc Stanford (California, My) da cho thay.
Nhung cdn hay hon: khdng chi nhung trao ddi thdng tin xay ra dudi anh hudng ciia nhung t l bao hinh sao, nhung nhQng t l bdo ndy cung cd kha nang truyin dat cac thdng tin tir mdt xynap nay din mpt xynap khac bdng chinh mang ludi ciia minh. Andrea Volterra, Trudng 9ai hpc Lausanne, mdt trong nhung nha tidn phong vl
"khoa hpc te bao dem than kinh"
dl xuat: "Neu cdc nha nghien cuu da tir lau danh gia rang cae t l bdo hinh sao la khdng cd kha nang trao ddi thong tin, chinh vi hp khdng bilt cdch idng nghe nhiing thdng diep ciia chung".
Vi do nguydn nhan: Tu khi nha than kinh-tam than hpc Due Hans Berger hoan thien dien nao dd, trong nhirng nam 20 (ciia thi ky trudc), cac nha khoa hpc da quan lam den nhat la hoat ddng dien eiia nao. Do mgi sy truyin di ciia mdt "ddng dien" (hieu thi tdc ddng), sy truyin dien khulch tdn dpc theo cae sgi thdn kinh. Nhu vay ma eac nhd than kinh hpc da
90 Khoa hoc
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Khoa hoc & Cong nghe
gia thilt rdng nlu cac t l bdo hinh sao thdng tin thi dd la mOt kilu tirong ty vdi cac naron. Thi ma hp lai nhan thay chi cd cac xung than kinh quat sat dugc toa ra lir cac noron... ma khdng phai la tir cac te bao khac. Dieu dd md ra ky nguydn "lat ca la do naron". Cdn vl cac t l bao hinh sao ma hoat dpng cua chung khdng phai la dien m* la hoa hpc, chung dugc don gian xem nhu nhung vat cam!
Bj xdp ra ria tam thdi, cac te bdo hinh sao, nhd mdt quan diim chiln thdng mdi, di din vugt qua
"mdt doan dai sa mac" khoa hgc.
Quan diem noron bj phan chia
Trdn thyc tl, phai chd dgi cho den cud'i nhung nam 90 (ciia the ky trudc) dl cac "thdng diep" ddu tien vl ddn truyin giua cac t l bao hinh sao va ca giua cac t l bao hinh sao va cdc noron mdi dugc giai thich tren thdi gian thyc, nhat la bdi Eric Newman, Tnrdng Dai hpc Minnesota): "Nhu thudng thay trudng hgp trong khoa hpc, Ijch su khdi ddu mdt tiln bd ky thuat. O day ngudi ta sir dung cac tham dd bdng cac chat huynh quang, nhd chiing ma ngudi ta cd thi theo doi nhung di chuyin cua cdc phan tii trong cac t l bao. Sy danh ddu bdng cac ion calci da cho phep xdc djnh dirge vj tri ciia sy tang ldn ve so lugng tu cac t l bao hlnh sao va cho phep thyc hien cd thi la mOt trong nhirng chd dya cua sy ddn truyin than kinh trong nao". Andrea Volterra phan tich. Dilu gi da lam quan diim bj phan chia.
Nhtrng nhd nghidn cun vl t l bao dem thdn kinh noi vl "con sdng canxi" dl xac djnh sy tang khulch tan cac ion calci. Christian Giaume xac djnh "Trong mgi nghien cuu, idc dd lan truyin cdc con sdng la vao khoang tir 15 din
30 micro met trong mdt giay, trong thyc t l dilu nay la mdt phuang thirc truyen tin hieu rat cham so vdi sy lan truyin ciia mOt xung than kinh ma nd cd the dat tdi 1 met trong mOt giay". Ve phia minh, Philipp Haydon, Trudng Dai hpc Pensylvania, da tim tha'y mdt mdi lien quan giua cac dgt sdng canxi va nhung biin ddi hoat ddng cua noron. Mdt dgt sdng canxi gay ra sy phdng thich gluta- mat bdi cac te bao hinh sao tai Xynap. Va phan tir dd, dugc xem nhu chat ddn truyin than kinh, dugc bilt dl lam khdi ddng mdt phan irng kich thich cac naron.
Andrea Volterra danh gia:
"Nhung chat ddn truyin than kinh hay ca nhung chat ddn truyen cua cac t l bao dem than kinh khac cd the nhap cudc. Chung tdi gia thiet sy tdn tai cua cac tuyp phu ciia cac t l bao hinh sao, ma cac tinh chat cd kha nang thay ddi tuy theo viing nao dugc xem xet, cQng nhu tdn tai cac naron gpi la "phdng thich dopamin", dac hidu trong dilu trj cua dopamin". Nhung nhung ca chi naron chinh xac nao ma chiing da khdi ddng sau sy phdng thich mdt thdng diep hoa hpc bdi mdt le bao hinh sao? Bi mat vdn cdn dd.
Canh cira van md cho nhiJTig bien luan mdi la
Tren thyc tl, tdt ca nhirng quan sat diu dugc thyc hien invitro tren cac canh trudng t l bao hay trdn cac lat cdt nao. Gilles Bonvento, Trung tam chup hinh nao Joliot- Curie xac nhan: "Sy tdn tai nhung hien tugng nhu vay cdn phai dugc chiing minh. Va dl bilt rd rang, trudc hit cdn phai hoan thien nhQng cdng cu nghidn cuu va chup hinh nao thich hgp (nhu chup X - quang Idp nhd phat xa poziton)". Ndi chung, nhQng kit qua dd ggi y rdng mdt con dudng
Imi thdng song song cd thi giir mdt vai trd trong mdt so qua trinh nao nhu la tri nhd hay sy ren luyen.
Jean Lorenceau, phdng thi nghiem khoa hpc than kinh va khoa hpc vl kha nang nhan thirc cua Trung tam nghien cim khoa hpc Qud'c gia Phap giai thich:
"Chung ta biet rdng cdn cd nhung dang ghi nhd it nhieu nhanh chdng. Tai sao khdng tudng tugng rdng cd sy tdn tai cua mot gia dd kliac ciia cac noron hoac it ra la bd sung, de xir ly mdi sd thdng tin.
Cung phai quan tam de'n vai trd cua cac t l bao hinh sao trong sy lam ddng bd cac mang lirdi noron d each xa nhau. Chdng han, ngudi ta cd the tudng tugng rdng cac viing nao khac nhau dugc huy ddng dl phan tich mdt tin hidu thi giac phirc lap deu dugc Ihdng tin tren tinh trang ridng le bdi cac t l bao hlnh sao... Nhung ngay bay gid dd la mOt sy bidn luan don gian ma ngudi ta can phai xac nhan hay bac bd".
Vide cdn lai la sy so sanh giua cac loai lam ngudi ta bd'i rdi: bd nao d con vat cang phat triln thi ty le cac te bao hlnh sao tren mdt noron cang tang len (1,6 d ngudi;
1,2 d meo; 0,8 d chudt...). Vi vay, loai dia cd t l bao hinh sao 3 lan it hon loai ech ma nd lai cd t l bao hinh sao 2 ldn it ban loai chudt ddng. Cdn vl con ngudi, nd han hdn vdi binh quan 1,4 t l bao hinh sao trdn 1 naron. Va nlu nhu mat dd cao vl cdc t l bao ddm than kinh cho phep dung len tren cac loai khac? Khdng thi ihl dugc...
Nhu Einstein da ndi dua khi nhdc lai vl ly thuylt lugng tir "Thugng d l khdng chai cd": nlu nhu bd nao cua Abert vl dai la cd sire manh, dilu dd cd Ihl la do cac t l bao hinh sao ciia dng. Mdt sy kit thiic vl mpi dieu bi mat ldn? •
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