Nicolelis M A, Chapin J K, Lin R C
Department of Physiology and Biophysics, Hahnemann University, Philadelphia, PA 19102, USA.
Neuroscience. 1995 Mar;65(2):609-31. doi: 10.1016/0306-4522(94)00493-o.
The postnatal development of direct thalamocortical projections from the zona incerta of the ventral thalamus to the whisker representation area of the rat primary somatosensory cortex was investigated. Cytoarchitectonic analysis based on Nissl staining, cytochrome oxidase histochemistry and immunohistochemistry for glutamic acid decarboxylase, GABA, parvalbumin and calbindin D28K revealed that the zona incerta can be clearly distinguished from surrounding diencephalic structures from the day of birth. Moreover, four distinct anatomical subdivisions of this nucleus were identified: the rostral, dorsal, ventral and caudal. Of these, the ventral subdivision is by far the most conspicuous, containing the highest density of neurons, and the highest levels of cytochrome oxidase, glutamate decarboxylase, GABA, parvalbumin and calbindin D28K. In contrast, the dorsal, rostral and caudal subdivisions contain fewer cells, lower levels of glutamic acid decarboxylase and GABA and very few parvalbumin-positive and calbindin-positive neurons. Small injections of rhodamine coated microspheres or Fluoro-gold in the primary somatosensory cortex of animals at different stages of development revealed the existence of retrogradely labeled neurons in the rostral and dorsal subdivisions of the zona incerta from postnatal day 1. At this age, retrogradely labeled cells were also found in the ventral lateral, ventral posterior medial, posterior medial, centrolateral, ventral medial and magnocellular subdivision of the medial geniculate nuclei of the dorsal thalamus. The density of the incertocortical projection reaches its maximum between the first and second postnatal weeks, decreasing subsequently, until an adult pattern of labeling is achieved. Tracer injections combined with immunohistochemistry revealed that the majority of the incertocortical projection derives from GABAergic neurons, implying a potentially inhibitory role for the incertocortical projection. These results demonstrate that the rat trigeminal system contains parallel thalamocortical pathways of opposite polarity, emerging from both the dorsal (glutamatergic, excitatory) and ventral (GABAergic, inhibitory) thalamus since the day of birth. As such, these findings suggest that, contrary to the classical notion, not only the dorsal but also the ventral thalamus may play a special role in both cortical maturation and function.
研究了大鼠腹侧丘脑未定带到初级体感皮层触须代表区的丘脑皮质直接投射的产后发育。基于尼氏染色、细胞色素氧化酶组织化学以及谷氨酸脱羧酶、γ-氨基丁酸（GABA）、小白蛋白和钙结合蛋白D28K的免疫组织化学的细胞构筑分析表明，从出生日起，未定带就能与周围的间脑结构清楚地区分开来。此外，还确定了该核的四个不同的解剖亚区：嘴侧、背侧、腹侧和尾侧。其中，腹侧亚区最为明显，神经元密度最高，细胞色素氧化酶、谷氨酸脱羧酶、GABA、小白蛋白和钙结合蛋白D28K的水平也最高。相比之下，背侧、嘴侧和尾侧亚区的细胞较少，谷氨酸脱羧酶和GABA水平较低，小白蛋白阳性和钙结合蛋白阳性神经元极少。在动物发育的不同阶段，向初级体感皮层小剂量注射罗丹明包被的微球或荧光金，结果显示，从出生后第1天起，在未定带的嘴侧和背侧亚区就存在逆行标记的神经元。在这个年龄段，在背侧丘脑内侧膝状体核的腹外侧、腹后内侧、后内侧、中央外侧、腹内侧和大细胞亚区也发现了逆行标记的细胞。未定带到皮层的投射密度在出生后的第一周和第二周之间达到最大值，随后逐渐下降，直至形成成年期的标记模式。示踪剂注射与免疫组织化学相结合表明，大多数未定带到皮层的投射来自GABA能神经元，这意味着未定带到皮层的投射可能具有潜在的抑制作用。这些结果表明，大鼠三叉神经系统包含极性相反的平行丘脑皮质通路，自出生日起就起源于背侧（谷氨酸能，兴奋性）和腹侧（GABA能，抑制性）丘脑。因此，这些发现表明，与传统观念相反，不仅背侧丘脑，腹侧丘脑在皮层成熟和功能方面可能也发挥着特殊作用。
