Vanderhorst V G, Terasawa E, Ralston H J, Holstege G
Department of Anatomy, University California San Francisco, San Francisco, California 94143, USA.
J Comp Neurol. 2000 Aug 21;424(2):251-68. doi: 10.1002/1096-9861(20000821)424:2<251::aid-cne5>3.0.co;2-d.
The periaqueductal gray (PAG) is known to be essential for vocalization and reproductive behavior. The PAG controls components of these behaviors by means of projections to the nucleus retroambiguus (NRA), a group of premotor neurons in the caudal medulla oblongata. In the accompanying study (VanderHorst et al., 2000 [accompanying study]), the NRA and its lumbosacral projections have been identified in the rhesus monkey. The present light and electron microscopical tracing study describes the PAG-NRA pathway in primates. To locate midbrain neurons projecting to the NRA, wheat germ agglutinin horseradish peroxidase (WGA-HRP) was injected into the NRA in six monkeys. To determine the distribution pattern of PAG axons in the medulla oblongata, WGA-HRP was injected into the PAG and adjacent tegmentum in three additional monkeys. In one of these three monkeys, biotinylated dextran amine and cholera toxin subunit b were injected into the lumbosacral cord to retrogradely identify NRA neurons. The results show that a compact group of neurons in the medial part of the lateral PAG at the intercollicular level sends a dense projection to the NRA. The projection is bilateral with a clear ipsilateral predominance. At the ultrastructural level, there are monosynaptic contacts between PAG fibers and NRA neurons, including NRA neurons that project to the lumbosacral cord. The synaptic contacts were primarily asymmetrical and the labeled terminal profiles contained spherical and dense core vesicles. It is concluded that there exists a strong and direct PAG-NRA pathway in the rhesus monkey. Because NRA neurons projecting to the lower lumbar cord are included, the PAG-NRA projection is likely to be involved not only in vocalization but also in other behaviors, such as receptive posture.
中脑导水管周围灰质（PAG）已知对发声和生殖行为至关重要。PAG通过投射到延髓尾端的一群运动前神经元——疑核（NRA）来控制这些行为的组成部分。在随附的研究（VanderHorst等人，2000年[随附研究]）中，已在恒河猴中鉴定出NRA及其腰骶部投射。本光镜和电镜追踪研究描述了灵长类动物的PAG - NRA通路。为了定位投射到NRA的中脑神经元，将小麦胚凝集素辣根过氧化物酶（WGA - HRP）注入六只猴子的NRA中。为了确定PAG轴突在延髓中的分布模式，将WGA - HRP注入另外三只猴子的PAG和相邻被盖区。在这三只猴子中的一只中，将生物素化葡聚糖胺和霍乱毒素亚基b注入腰骶脊髓以逆行鉴定NRA神经元。结果表明，在中脑间丘水平外侧PAG内侧部分的一群紧密神经元向NRA发出密集投射。该投射是双侧的，同侧明显占优势。在超微结构水平上，PAG纤维与NRA神经元之间存在单突触联系，包括投射到腰骶脊髓的NRA神经元。突触联系主要是不对称的，标记的终末轮廓包含球形和致密核心小泡。得出的结论是，恒河猴中存在强大而直接的PAG - NRA通路。由于包括投射到下腰脊髓的NRA神经元，PAG - NRA投射可能不仅参与发声，还参与其他行为，如接受姿势。
