家鸽头部的磁性物质

Magnetite in the head of the homing pigeon

磁铁矿可以在很多生物组织中被发现,国外研究者同样在家鸽上喙皮肤组织中发现了规则分布的超顺磁磁铁矿颗粒。他们应用透射电子显微镜确认了这些小磁铁矿晶体为尺寸在1—5 nm的聚集体,集中存在于皮下组织中。这些超顺磁粒子聚集体又形成直径为1—3μm的粒子束,分布在大细胞之间的长形结构中,并且与神经组织紧密相连。应用光学显微镜和电子显微镜,国外研究者也对家鸽上喙传入三叉神经末梢的次细胞组织进行了研究。这些神经末梢组织直径大约5μm,内部包含着聚集成束的超顺磁磁铁矿颗粒。大约10到15个粒子束存在于一个神经末梢中,沿着细胞膜排列。每一个超顺磁粒子束包埋在一个纤维杯中,口朝向细胞表面,通过纤维组织,这些粒子束粘附在细胞表面上。除了超顺磁颗粒,非晶态铁磷酸盐也被发现,它们沿着神经末梢的纤维中心分布。解剖特征表明,这些神经末端可以探测很小的地磁场强度的变化,考虑到以超顺磁磁铁矿颗粒为基础的"磁接收器"理论,他们还给出了几个"磁接收器"的模型。

Magnetite can be found in many life forms, including superparamagnetic （SPM） particles in the upper-beak skin of homing pigeons. Using transmission electron microsco- py it has been found that these superparamagnetic particles are concentrated in the subcutis and are identified as aggregates of magnetite nanocrystals with grain sizes between 1 and 5 nm. These particles form clusters of 1--3 μm diameter, which are distributed in distinct coherent elongated structures, associated with nervous tissue and located between fat cells. Studies on the subcellular organization of afferent trigeminal terminals in the upper beak of the homing pigeon based on optical and electron microscopy have been reported. They are about 5μm in diameter and contain SPM crystals. The SPM nanocrystals are assembled in clusters, and about I0 to 15 of these clusters occur inside one nerve terminal, arranged along the cell membrane. Each SPM cluster is em- bedded in a solid fibrous cup open towards the cell surface, to which the cluster adheres by fiber strands. In addition to the SPM, iron phosphate is also found along a fibrous core of the terminal. The anatomic features suggest that these nerve endings can detect small intensity changes of the geomagnetic field. Several models about SPM based magnetoreceptor have been suggested. In this paper, a brief overview is presented of the above issues.