Ray J P, Price J L
Department of Anatomy & Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110.
J Comp Neurol. 1992 Sep 8;323(2):167-97. doi: 10.1002/cne.903230204.
The medial and central segments of the mediodorsal nucleus of the thalamus (MD) receive afferents from the ventral forebrain, including the piriform cortex, the ventral pallidum, and the amygdaloid complex. Because MD is reciprocally interconnected with prefrontal and agranular insular cortical areas, it provides a relay of ventral forebrain activity to these cortical areas. However, there are also direct projections from the piriform cortex and the amygdala to the prefrontal and agranular insular cortices. This study addresses whether this system has a "triangular" organization, such that structures in the ventral forebrain project to interconnected areas in MD and the prefrontal/insular cortex. The thalamocortical projections of MD have been studied in experiments with injections of retrograde tracers into prefrontal or agranular insular cortical areas. In many of the same experiments, projections from the ventral forebrain to MD and to the prefrontal/insular cortex have been demonstrated with anterograde axonal tracers. The connections of the piriform cortex (PC) with MD and the prefrontal/insular cortex form an organized triangular system. The PC projections to the central and medial segments of MD and to the lateral orbital cortex (LO) and the ventral and posterior agranular insular cortices (AIv and AIp) are topographically organized, such that more caudal parts of PC tend to project more medially in MD and more caudally within the orbital/insular cortex. The central and medial portions of MD also send matching, topographically organized projections to LO, AIv and AIp, with more medial parts of MD projecting further caudally. The anterior cortical nucleus of the amygdala (COa) also projects to the dorsal part of the medial segment of MD and to its cortical targets, the medial orbital area (MO) and AIp. The projections of the basal/accessory basal amygdaloid nuclei to MD and to prefrontal cortex, and from MD to amygdaloceptive parts of prefrontal cortex, are not as tightly organized. Amygdalothalamic afferents in MD are concentrated in the dorsal half of the medial segment. Cells in this part of the nucleus project to the amygdaloceptive prelimbic area (PL) and AIp. However, other amygdaloceptive prefrontal areas are connected to parts of MD that do not receive fibers from the amygdala. Ventral pallidal afferents are distributed to all parts of the central and medial segments of MD, overlapping with the fibers from the amygdala and piriform cortex. Fibers from other parts of the pallidum, or related areas such as the substantia nigra, pars reticulata, terminate in the lateral and ventral parts of MD, where they overlap with inputs from the superior colliculus and other brainstem structures.(ABSTRACT TRUNCATED AT 400 WORDS)
丘脑背内侧核（MD）的内侧段和中央段接收来自腹侧前脑的传入纤维，包括梨状皮质、腹侧苍白球和杏仁复合体。由于MD与前额叶和无颗粒岛叶皮质区域相互连接，它为这些皮质区域传递腹侧前脑的活动。然而，从梨状皮质和杏仁核到前额叶和无颗粒岛叶皮质也存在直接投射。本研究探讨该系统是否具有“三角形”组织结构，即腹侧前脑的结构投射到MD以及前额叶/岛叶皮质中相互连接的区域。在将逆行示踪剂注射到前额叶或无颗粒岛叶皮质区域的实验中，对MD的丘脑皮质投射进行了研究。在许多相同的实验中，利用顺行轴突示踪剂证明了从腹侧前脑到MD以及到前额叶/岛叶皮质的投射。梨状皮质（PC）与MD以及前额叶/岛叶皮质的连接形成了一个有组织的三角形系统。PC向MD的中央段和内侧段、外侧眶额皮质（LO）、腹侧和后无颗粒岛叶皮质（AIv和AIp）的投射具有拓扑组织，使得PC更靠尾侧的部分倾向于在MD中更向内侧投射，并且在眶额/岛叶皮质内更靠尾侧投射。MD的中央和内侧部分也向LO、AIv和AIp发送匹配的、具有拓扑组织的投射，MD更靠内侧的部分向更靠尾侧投射。杏仁核的前皮质核（COa）也投射到MD内侧段的背侧部分及其皮质靶点，即内侧眶额区（MO）和AIp。基底/副基底杏仁核向MD和前额叶皮质的投射，以及从MD到前额叶皮质杏仁核感受区的投射，组织不如前者紧密。MD中的杏仁核丘脑传入纤维集中在内侧段的背侧半部分。该核这一部分的细胞投射到杏仁核感受性的前边缘区（PL）和AIp。然而，其他杏仁核感受性前额叶区域与MD中未接受杏仁核纤维的部分相连。腹侧苍白球的传入纤维分布到MD中央段和内侧段的所有部分，与来自杏仁核和梨状皮质的纤维重叠。苍白球其他部分或相关区域（如黑质网状部）的纤维终止于MD的外侧和腹侧部分，在那里它们与来自上丘和其他脑干结构的输入重叠。（摘要截断于400字）
