van Bockstaele E J, Colago E E, Pickel V M
Department of Neurology and Neuroscience, Cornell University Medical College, New York, NY 10021, USA.
Neuroscience. 1996 Mar;71(2):429-42. doi: 10.1016/0306-4522(95)00432-7.
Norepinephrine-containing fibres in the medial prefrontal cortex derive from the locus coeruleus, a brainstem nucleus which also receives a dense innervation of enkephalin-immunoreactive axon terminals. We combined immunogold-silver labelling of retrogradely transported FluoroGold from the medial prefrontal cortex with immunoperoxidase detection of leucine5-enkephalin in the same section of tissue through the locus coeruleus of adult rats. This dual-labelling experiment was conducted to determine whether axon terminals containing lecuine5-enkephalin target neurons in the locus coeruleus that project to the frontal cortex and, if so, what are their morphological characteristics. By light microscopy, enkephalin-labelled processes overlapped FluoroGold retrogradely labelled neurons in the locus coeruleus. By electron microscopy, retrogradely labelled perikarya and dendrites were commonly enveloped by astrocytic processes and received few afferents in the plane of section examined. However, at sites unoccupied by glial processes, abundant afferent input could be identified. In addition, some FluoroGold-labelled perikarya and dendrites lacked this glial ensheathment but were more frequently apposed by axon terminals. Of 163 FluoroGold-labelled perikarya and dendrites examined where enkephalin immunoreactivity was present in the neuropil, 42% were contacted by enkephalin-immunoreactive axon terminals. The peroxidase-labelled enkephalin terminals as well as the unlabelled terminals often contained both small, clear and large dense core vesicles. Both labelled and unlabelled terminals also formed primary symmetric synapses characteristic of inhibitory transmitters with retrogradely labelled perikarya and proximal dendrites. At times, more than one enkephalin-labelled terminal was found to converge on a common retrogradely labelled perikarya or dendrite. These results demonstrate cellular sites where enkephalin-containing afferents may directly modulate and most likely inhibit the activity of cortically projecting neurons in the locus coeruleus.
内侧前额叶皮质中含去甲肾上腺素的纤维源自蓝斑，蓝斑是一个脑干核团，它也接受脑啡肽免疫反应性轴突终末的密集神经支配。我们将从内侧前额叶皮质逆行转运的荧光金的免疫金银标记与通过成年大鼠蓝斑在同一组织切片中对亮氨酸脑啡肽的免疫过氧化物酶检测相结合。进行这个双重标记实验是为了确定含有亮氨酸脑啡肽的轴突终末是否靶向投射到额叶皮质的蓝斑中的神经元，如果是，它们的形态特征是什么。通过光学显微镜观察，脑啡肽标记的突起与蓝斑中逆行标记的荧光金神经元重叠。通过电子显微镜观察，逆行标记的胞体和树突通常被星形胶质细胞突起包裹，并且在所检查的切片平面中接受的传入纤维很少。然而，在未被胶质细胞突起占据的部位，可以识别出丰富的传入输入。此外，一些荧光金标记的胞体和树突缺乏这种胶质细胞的包被，但更频繁地与轴突终末相邻。在163个荧光金标记的胞体和树突中，在神经毡中存在脑啡肽免疫反应性，其中42%与脑啡肽免疫反应性轴突终末接触。过氧化物酶标记的脑啡肽终末以及未标记的终末通常都含有小而清亮的囊泡和大的致密核心囊泡。标记和未标记的终末也都与逆行标记的胞体和近端树突形成了抑制性递质特有的初级对称突触。有时，发现不止一个脑啡肽标记的终末汇聚在一个共同的逆行标记的胞体或树突上。这些结果表明了含脑啡肽的传入纤维可能直接调节并最有可能抑制蓝斑中投射到皮质的神经元活动的细胞位点。
