Moffett J R, Williamson L, Palkovits M, Namboodiri M A
Department of Biology, Georgetown University, Washington, D.C. 20057.
Proc Natl Acad Sci U S A. 1990 Oct;87(20):8065-9. doi: 10.1073/pnas.87.20.8065.
The retinohypothalamic tract is the neural pathway mediating the photic entrainment of circadian rhythms in mammals. Important targets for these retinal fibers are the suprachiasmatic nuclei (SCN) of the hypothalamus, which are thought to be primary sites for the biological clock. The neurotransmitters that operate in this projection system have not yet been determined. Immunohistochemistry and radioimmunoassay performed with affinity-purified antibodies to N-acetylaspartylglutamate (NAAG) demonstrate that this neuron-specific dipeptide, which may act as an excitatory neurotransmitter, is localized extensively in the retinohypothalamic tract and its target zones, including the SCN. Optic nerve transections resulted in significant reductions in NAAG immunoreactivity in the optic chiasm and SCN. Analysis of NAAG concentrations in micropunches of SCN, by means of radioimmunoassay, showed approximately 50% reductions in NAAG levels. These results suggest that this peptide may act as one of the neurotransmitters involved in retinohypothalamic communication and circadian rhythm entrainment.
视网膜下丘脑束是介导哺乳动物昼夜节律光同步化的神经通路。这些视网膜纤维的重要靶点是下丘脑的视交叉上核（SCN），其被认为是生物钟的主要位点。在这个投射系统中起作用的神经递质尚未确定。用针对N - 乙酰天冬氨酰谷氨酸（NAAG）的亲和纯化抗体进行的免疫组织化学和放射免疫测定表明，这种可能作为兴奋性神经递质的神经元特异性二肽广泛存在于视网膜下丘脑束及其靶区，包括视交叉上核。视神经横断导致视交叉和视交叉上核中NAAG免疫反应性显著降低。通过放射免疫测定分析视交叉上核微穿孔中的NAAG浓度，结果显示NAAG水平降低了约50%。这些结果表明，这种肽可能是参与视网膜下丘脑通讯和昼夜节律同步化的神经递质之一。
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