Deschênes M, Bourassa J, Pinault D
Centre de Recherche en Neurobiologie Hôpital de l'Enfant-Jésus, Université Laval, Québec, Canada.
Brain Res. 1994 Nov 21;664(1-2):215-9. doi: 10.1016/0006-8993(94)91974-7.
The vast majority of corticothalamic (CT) axons projecting to sensory-specific thalamic nuclei arise from layer VI cells but intralaminar and associative thalamic nuclei also receive, to various degrees, a cortical input from layer V pyramidal cells. It is also well established that all long-range corticofugal projections reaching the brainstem and spinal cord arise exclusively from layer V neurons. These observations raise the possibility that the CT input from layer V cells may be collaterals of those long-range axons projecting below thalamic level. The thalamic projections of layer V cells were mapped at a single cell level following small microiontophoretic injections of biocytin performed in the motor, somatosensory and visual cortices in rats. Camera lucida reconstruction of these CT axons revealed that they are all collaterals of long-range corticofugal axons. These collaterals do not give off axonal branches within the thalamic reticular nucleus and they arborize exclusively within intralaminar and associative thalamic nuclei where they from small clusters of varicose endings. As layer V cells are involved in motor commands everywhere in the neocortex, these CT projections and their thalamic targets should be directly involved in the central organization of motor programs.
绝大多数投射到感觉特异性丘脑核的皮质丘脑（CT）轴突起源于VI层细胞，但板内核和联合丘脑核也不同程度地接受来自V层锥体细胞的皮质输入。同样公认的是，所有到达脑干和脊髓的长距离皮质传出投射都仅起源于V层神经元。这些观察结果提出了一种可能性，即来自V层细胞的CT输入可能是那些投射到丘脑水平以下的长距离轴突的侧支。在对大鼠运动、体感和视觉皮层进行微量生物胞素微电泳小注射后，在单细胞水平上绘制了V层细胞的丘脑投射图。对这些CT轴突的明视野重建显示，它们都是长距离皮质传出轴突的侧支。这些侧支在丘脑网状核内不发出轴突分支，仅在板内核和联合丘脑核内形成分支，在那里它们形成小的曲张终末簇。由于V层细胞参与新皮质各处的运动指令，这些CT投射及其丘脑靶点应直接参与运动程序的中枢组织。
