Clark A S, Schwartz M L, Goldman-Rakic P S
Section of Neuroanatomy, Yale University School of Medicine, New Haven, CT 06510.
J Chem Neuroanat. 1989 Sep-Oct;2(5):259-67.
The mediodorsal nucleus of the thalamus is an important component of the brain's circuitry for memory 9,20 and yet surprisingly little is known of its intrinsic organization. In the present study we have examined the distribution, spatial relationships and morphology of gamma-aminobutyric acid (GABA)-containing cells within the magnocellular and parvocellular subdivisions of the mediodorsal nucleus. These subdivisions have anatomically and functionally distinct connections with the orbital (limbic) and dorsolateral (association) areas of the prefrontal cortex, and accordingly, we investigated whether there were corresponding differences in their local circuit organization. Our findings show that round or ovoid GABA-immunoreactive neurons were abundant in both subdivisions. However, these neurons were larger in diameter in the magnocellular aspect (mean diameter = 10.4 +/- 0.1 micron) than in the parvocellular moiety (mean diameter = 9.9 +/- 0.1 micron) and the intensity of reactivity was also greater for the magnocellular neurons. Comparison of the densities of GABA-immunoreactive neurons revealed not only a greater density of neurons in the parvocellular division but also that the proportion of all neurons which were GABA-containing was greater in this region. These differences in the morphology and density of inhibitory local circuit neurons may contribute to the functional duality of prefrontal cortex innervated by these thalamo-cortical pathways. Certain qualitative features were common to both subdivisions; thus GABA-immunoreactive neurons were found in small clusters throughout the magnocellular and parvocellular divisions of the mediodorsal nucleus and, in addition, regions with few or no GABA-immunoreactive cells were often surrounded by strings of GABA-containing neurons.(ABSTRACT TRUNCATED AT 250 WORDS)
丘脑腹内侧核是大脑记忆回路的重要组成部分9,20，但令人惊讶的是，人们对其内在结构知之甚少。在本研究中，我们检查了腹内侧核大细胞和小细胞亚区内含γ-氨基丁酸（GABA）细胞的分布、空间关系和形态。这些亚区在前额叶皮质的眶部（边缘）和背外侧（联合）区域具有解剖学和功能上不同的连接，因此，我们研究了它们的局部回路组织是否存在相应差异。我们的研究结果表明，在两个亚区内圆形或椭圆形的GABA免疫反应性神经元都很丰富。然而，这些神经元在大细胞部分的直径较大（平均直径 = 10.4 +/- 0.1微米），而在小细胞部分则较小（平均直径 = 9.9 +/- 0.1微米），并且大细胞神经元的反应强度也更大。对GABA免疫反应性神经元密度的比较不仅显示小细胞部分的神经元密度更大，而且该区域中所有含GABA神经元的比例也更大。抑制性局部回路神经元在形态和密度上的这些差异可能有助于这些丘脑-皮质通路支配的前额叶皮质的功能二元性。两个亚区都有某些共同的定性特征；因此，在腹内侧核的大细胞和小细胞部分都发现了小簇的GABA免疫反应性神经元，此外，几乎没有或没有GABA免疫反应性细胞的区域常常被一串含GABA的神经元包围。（摘要截断于250字）
