Williams F G, Beitz A J
Department of Veterinary Biology, University of Minnesota, St. Paul 55108.
J Neurocytol. 1990 Oct;19(5):686-96. doi: 10.1007/BF01188037.
The periaqueductal grey (PAG) plays an important role in the descending modulation of nociception. Inhibitory influences of GABAergic terminals, located within the periaqueductal grey, are thought to play a role in antinociception by influencing the activity of neurons that project to the nucleus raphe magnus and adjacent reticular nuclei. The present study utilized electron microscopic immunocytochemistry to quantitate the normal neuronal associations of GABA-immunoreactive terminals, and to visualize the neuronal distribution of the GABAA receptor in the ventrolateral periaqueductal grey of the rat. Of particular interest was a quantitative description of the interaction between GABA-immunoreactive axon terminals and periaqueductal grey neurons that were retrogradely-labelled from the nucleus raphe magnus and adjacent medullary reticular nuclei. Most terminals were observed to be immediately apposed only to two or three dendrites, although axonal and perikaryal associations were also observed. In the ventrolateral periaqueductal grey, 37.5% of all GABA-immunoreactive terminals were adjacent to periaqueductal grey-nucleus raphe magnus and periaqueductal grey-reticular nucleus projection neurons. Symmetrical synapses with these retrogradely-labelled neurons were formed by 17% of GABA-immunoreactive terminals in the ventrolateral periaqueductal grey. We also noted that 13.2% of the GABA-immunoreactive terminals formed symmetrical synapses with GABA-immunoreactive dendrites in the periaqueductal grey, and occasionally those dendrites were retrogradely labelled. Only 0.8% of the GABA-immunoreactive terminals formed putative symmetrical synapses with other GABA-immunoreactive terminals. Consistent with these findings, GABAA receptor immunoreactivity was only associated with dendrites and perikarya in neurons of the ventrolateral PAG. These results are consistent with an inhibitory role for GABA on PAG neurons, a configuration required by hypothetical models for opoid disinhibitory circuitry within the PAG. In addition, the data further suggest that other kinds of GABAergic connections may be important in descending antinociception, and that a population of GABAergic PAG projection neurons exists that may be inhibitory within nucleus raphe magnus and the adjacent reticular nuclei.
导水管周围灰质（PAG）在伤害性感受的下行调制中起重要作用。位于导水管周围灰质内的GABA能终末的抑制性影响，被认为通过影响投射到中缝大核和相邻网状核的神经元活动，在抗伤害感受中发挥作用。本研究利用电子显微镜免疫细胞化学技术，对GABA免疫反应性终末的正常神经元联系进行定量，并观察大鼠腹外侧导水管周围灰质中GABAA受体的神经元分布。特别感兴趣的是对GABA免疫反应性轴突终末与从中缝大核和相邻延髓网状核逆行标记的导水管周围灰质神经元之间相互作用的定量描述。尽管也观察到轴突与胞体的联系，但大多数终末仅紧邻两三个树突。在腹外侧导水管周围灰质中，所有GABA免疫反应性终末的37.5%与导水管周围灰质 - 中缝大核和导水管周围灰质 - 网状核投射神经元相邻。腹外侧导水管周围灰质中17%的GABA免疫反应性终末与这些逆行标记的神经元形成对称突触。我们还注意到，13.2%的GABA免疫反应性终末在导水管周围灰质中与GABA免疫反应性树突形成对称突触，偶尔这些树突是逆行标记的。仅0.8%的GABA免疫反应性终末与其他GABA免疫反应性终末形成假定的对称突触。与这些发现一致，GABAA受体免疫反应性仅与腹外侧导水管周围灰质神经元的树突和胞体相关。这些结果与GABA对导水管周围灰质神经元的抑制作用一致，这是导水管周围灰质内阿片类去抑制回路假设模型所要求的一种结构。此外，数据进一步表明，其他类型的GABA能连接在下行抗伤害感受中可能很重要，并且存在一群GABA能导水管周围灰质投射神经元，它们在中缝大核和相邻网状核内可能具有抑制作用。
