候鳥長途遷徙中如何準(zhǔn)確辨認(rèn)出方向,？德國科學(xué)家近日研究證實(shí),，候鳥眼中的分子與大腦引導(dǎo)飛行方向的區(qū)域有關(guān),。由此可以說,，候鳥是用眼睛“看”地球磁場,，辨認(rèn)出正確的方向。相關(guān)研究論文9月26日發(fā)表在《公共科學(xué)圖書館·綜合》（PLoS ONE）上,。
在最新研究中,，德國奧爾登堡大學(xué)的Dominik Heyers和同事分別向園鶯（Sylvia borin）的前腦區(qū)和視網(wǎng)膜中注射了兩種不同的“追蹤器”（tracer）。該前腦區(qū)稱為Cluster N,，被認(rèn)為是在鳥類確定方向時唯一有活性的區(qū)域,。注射的追蹤器能夠與神經(jīng)信號一道，沿著神經(jīng)纖維移動,。
結(jié)果發(fā)現(xiàn),，在園鶯經(jīng)歷過遷徙的渴望后，這兩種不同的追蹤器都停在了丘腦負(fù)責(zé)視覺的區(qū)域。研究人員表示,，這種解剖學(xué)上的聯(lián)系強(qiáng)有力地表明,，候鳥很可能是用視覺感受到磁場的。
此前的德國馬克斯普朗克鳥類研究中心的Claudia Mettke-Hofmann和Eberhard Gwinner追蹤了超過一百只的花園鶯（Sylvia borin）和薩丁尼亞鶯（Sylvia melanocephala momus）,，并且利用解剖學(xué)方法研究發(fā)現(xiàn)鳥兒們在路途中增長不少見識,。花園鶯從非洲返回中歐時就帶著個較大的海馬回－－腦中處理空間學(xué)習(xí)的區(qū)域,。而非遷徒性的薩丁尼亞鶯則無該變化,。然而遷徒能增長鳥兒記憶力的證據(jù)還是缺乏的。之前的研究表明,，候鳥眼中的某種蛋白分子——藍(lán)光受體（cryptochromes）可能在確定飛行方向中發(fā)揮了重要作用,。此次研究為此提供了支持。Heyers表示,，當(dāng)候鳥專注于某一個方向時,，磁北（magnetic north）看起來就像一個黑點(diǎn)。
英國牛津大學(xué)研究鳥類遷徙的Miriam Liedvogel認(rèn)為,，此次研究很好地顯示了視網(wǎng)膜與Cluster N之間的聯(lián)系,。不過她并不認(rèn)為據(jù)此就能證明鳥類能夠“看見”磁場。她表示,，希望將來有實(shí)驗(yàn)?zāi)軌蜃C明,，改變磁場會使鳥類丘腦的神經(jīng)活動發(fā)生變化。
此次研究也并不意味著鳥類飛行方向研究的終結(jié),，其他一些工作已經(jīng)表明,，候鳥的喙也與它們的飛行方向有關(guān)。Heyers認(rèn)為,，喙和視覺可能是互為補(bǔ)充的,，喙用來測量磁場的強(qiáng)度，而藍(lán)光受體則發(fā)揮著指南針的作用,。
原始出處:
A Visual Pathway Links Brain Structures Active during Magnetic Compass Orientation in Migratory Birds
Dominik Heyers1*, Martina Manns2, Harald Luksch3, Onur Güntürkün2, Henrik Mouritsen1
1 AG Neurosensorik, Institute of Biology, University of Oldenburg, Oldenburg, Germany, 2 Department of Biopsychology, Institute for Cognitive Neuroscience, Ruhr-University Bochum, Bochum, Germany, 3 Chair of Zoology, Department of Zoology, Technical University Munich, Freising-Weihenstephan, Germany
Abstract
The magnetic compass of migratory birds has been suggested to be light-dependent. Retinal cryptochrome-expressing neurons and a forebrain region, “Cluster N”, show high neuronal activity when night-migratory songbirds perform magnetic compass orientation. By combining neuronal tracing with behavioral experiments leading to sensory-driven gene expression of the neuronal activity marker ZENK during magnetic compass orientation, we demonstrate a functional neuronal connection between the retinal neurons and Cluster N via the visual thalamus. Thus, the two areas of the central nervous system being most active during magnetic compass orientation are part of an ascending visual processing stream, the thalamofugal pathway. Furthermore, Cluster N seems to be a specialized part of the visual wulst. These findings strongly support the hypothesis that migratory birds use their visual system to perceive the reference compass direction of the geomagnetic field and that migratory birds “see” the reference compass direction provided by the geomagnetic field.
Received: April 10, 2007; Accepted: September 5, 2007; Published: September 26, 2007
Figure 1. Neuronal tracing reveals that Cluster N receives input through the thalamofugal visual pathway.
A: Schematic side view of the bird's brain indicating the locations of tracer application. Retrograde tracer (BDA, shown in green) was iontophoretically applied into Cluster N (shown in magenta). Anterograde tracer (CtB, shown in red) was injected into the vitreous of the contralateral eye. B: Double-labeling of ZENK and the retrograde tracer BDA in sagittal brain sections at the level of Cluster N proves the correct placement of tracer into Cluster N: arrows point to examples of neurons displaying ZENK-immunoreactivity (shown in magenta) in the nucleus together with BDA (shown in green) in the somata. Scale bar: 25 µm. C: Tracer distribution in frontal brain sections at the level of the thalamic Gld. Anterogradely labeled fibers from the retina (shown in red) project upon all substructures of the Gld, i.e. LdOPT, SpRt and lateral/ventral parts of the DLL. Retrogradely labeled neurons projecting upon Cluster N (visualised green) mainly originate within the DLL, with few additional connections from the LdOPT and SpRt. Scale bar: 50 µm. D: Confocal 3D-stacks in the thalamic Gld at high magnification indicate direct contact (arrows) between retinofugal fibers (shown in red) and somata/proximal dendrites retrogradely labeled from Cluster N (shown in green). Scale bar: 4 µm. Abbreviations: DLL, Nucleus dorsolateralis anterior thalami, pars lateralis; Gld, dorsolateral geniculate complex; LdOPT, Nucleus lateralis dorsalis nuclei optici principalis thalami; Rt, Nucleus rotundus; SPC, Nervus superficialis parvocellularis; SpRt, Nucleus suprarotundus; TSM, Tractus septomesencephalicus.
全文鏈接：http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0000937
