发育中大鼠视觉与听觉皮质胼胝体联系的轴突形态学研究

用顺行示踪剂 BDA标记研究了发育中大鼠视觉与听觉皮质胼胝体轴突的形态学。 BDA应用于出生后第 4d的视觉皮质后 ,整个视觉皮质包括 17区内侧部 、 层已可见一些标记的胼胝体轴突。第 5～ 8d时 ,许多标记的胼胝体轴突已到达皮质浅层 ( ～ 层 )。第 13 d时 ,17区内侧部又不见胼胝体轴突 ,表明早期此区的胼胝体轴突为暂时性的 ;17/ 18界区则含大量胼胝体轴突 ,并在 层和 / 、 、 层分别形成致密的和稀疏的终末丛。第 17d时 ,致密的终末丛可见于上述各层 ,与成年的分布模式类似。 BDA应用于听觉皮质后 ,标记的胼胝体轴突见于对侧听觉和视觉皮质 (即同源性和异源性胼胝体轴突 )。第 13～ 2 8d期间 ,虽然同源性胼胝体轴突的形态逐渐变化 ,但它们显示类似的明显的柱状构筑。第 13～ 2 4d,一定数量的异源性胼胝体轴突可见于整个视觉皮质包括 17区内侧部。但至第 2 8d,这些轴突大多被排除 ,并且此时的轴突标记模式已类似成年。提示 ,视觉皮质大多数异源性胼胝体轴突是暂时性的

A MORPHOLOGICAL STUDY OF CALLOSAL AXONS IN DEVELOPING RAT VISUAL AND AUDITORY CORTICES

Detailed morphology of developing callosal axons in rat visual and auditory cortices was studied with sensitive anterograde tracer, biotinylated dextran amine (BDA). Following BDA placement in visual cortex, labeled callosal axons were seen in contralateral visual cortex and retrosplenial cortex (area 29). At postnatal day (PD) 4, some labeled callosal axons were observed in layers Ⅴ and Ⅵ throughout the visual cortex including area 17. At PD 5～8, many of the callosal axons reached superficial layers Ⅰ～Ⅲ. By PD 13, few callosal axons were found in medial area 17, indicating the existence of transitory callosal axons in area 17 at younger ages. Many callosal axons were seen at areas 17/18a border forming terminal arbors in layers I (dense), Ⅱ/Ⅲ, Ⅴ and Ⅵ (sparse). By PD 17, callosal terminal arbors were clustered densely in layers Ⅰ, Ⅱ/Ⅲ, Ⅴ and Ⅵ, similar to the pattern in the adult. Following BDA placement in auditory cortex, callosal axons to both auditory (homotopic callosal axons) and visual (heterotopic callosal axons) cortex were observed. During PD 13～28, the homotopic callosal axons showed similar labeling patterns, i.e., distinct columnar organization although their morphology changed gradually. At PD 13～24, the heterotopic callosal axons were present in all visual cortical areas including medial area 17 in significant numbers but were mostly eliminated by PD 28, when a labeling pattern similar to the adult was found. This indicates that most of the heterotopic callosal axons are transitory. Therefore, the present study has revealed several aspects of morphological changes of calosal axons in the rat visual and auditory cortices during postnatal development.