Melchitzky D S, Lewis D A
Department of Psychiatry, University of Pittsburgh, Pittsburgh, PA 15213, USA.
Neuroscience. 2001;103(4):1033-42. doi: 10.1016/s0306-4522(01)00021-5.
The reciprocal connections between the mediodorsal thalamic nucleus and the prefrontal cortex participate in a circuit that is essential to a number of higher cognitive processes. Projections from the dopamine-containing cells of the ventral mesencephalon to the prefrontal cortex are also critical for these cognitive abilities. It is unclear, however, whether dopamine axons innervate the mediodorsal thalamic nucleus in primates. In order to address this question, we examined the distribution of dopamine transporter-immunoreactive axons in the mediodorsal thalamic nucleus of macaque monkeys. Labeled axons were distributed quite heterogeneously in this nucleus, and did not strictly follow cytoarchitectonic subdivision boundaries. The ventral and lateral portions of the mediodorsal thalamic nucleus, which include parts of the parvicellular and multiform subdivisions, had the highest density of dopamine transporter-immunoreactive axons. In contrast, the dorsomedial portion, which included primarily the magnocellular subdivision, had the lowest density of labeled axons. In both lightly and densely innervated portions of the nucleus, small, dense clusters of dopamine transporter-immunoreactive axons were present. Axons immunoreactive for tyrosine hydroxylase were distributed in a pattern very similar to that of dopamine transporter-labeled axons. In contrast, noradrenergic axons, as revealed by dopamine beta-hydroxylase immunoreactivity, were present in higher density and were more evenly distributed throughout the mediodorsal thalamic nucleus. This dopamine innervation of the mediodorsal thalamic nucleus reveals another possible anatomical substrate through which dopamine may influence the cognitive functions mediated by thalamo-prefrontal circuitry.
丘脑背内侧核与前额叶皮质之间的相互连接参与了对许多高级认知过程至关重要的神经回路。从中脑腹侧含多巴胺的细胞向前额叶皮质的投射对这些认知能力也至关重要。然而，在灵长类动物中，多巴胺轴突是否支配丘脑背内侧核尚不清楚。为了解决这个问题，我们研究了猕猴丘脑背内侧核中多巴胺转运体免疫反应性轴突的分布。标记的轴突在该核中的分布非常不均匀，并不严格遵循细胞构筑分区边界。丘脑背内侧核的腹侧和外侧部分，包括小细胞和多形细胞亚区的部分，多巴胺转运体免疫反应性轴突的密度最高。相比之下，主要包括大细胞亚区的背内侧部分，标记轴突的密度最低。在该核轻度和密集支配的部分，都存在小而密集的多巴胺转运体免疫反应性轴突簇。酪氨酸羟化酶免疫反应性的轴突分布模式与多巴胺转运体标记的轴突非常相似。相比之下，多巴胺β-羟化酶免疫反应性显示的去甲肾上腺素能轴突密度更高，且更均匀地分布在整个丘脑背内侧核中。丘脑背内侧核的这种多巴胺神经支配揭示了多巴胺可能影响丘脑-前额叶回路介导的认知功能的另一种可能的解剖学基础。
