Reichling D B, Basbaum A I
Department of Neuroscience, University of California, San Francisco 94143.
J Comp Neurol. 1990 Dec 8;302(2):370-7. doi: 10.1002/cne.903020213.
The fact that GABA receptor agonists and antagonists influence nociceptive thresholds when microinjected into the rostroventral medulla or in the spinal cord may reflect the involvement of GABAergic neuronal elements in endogenous antinociceptive pathways. In the present study we used immunocytochemistry and retrograde tract tracing to investigate the contribution of GABAergic projection neurons to the antinociceptive network linking the midbrain periaqueductal gray matter (PAG), the nucleus raphe magnus (NRM), and the spinal cord dorsal horn. The tracer, WGAapoHRP-Au was injected into either the NRM or the spinal cord and the distribution of labeled neurons in sections of the PAG and medulla, respectively, was studied. The same sections were immunostained to demonstrate GABA-immunoreactive neurons. Although GABA-immunoreactive neurons were abundant in the PAG, only 1.5% were retrogradely labeled from the NRM. Similarly, very few GABA-immunoreactive neurons within the cytoarchitectural boundaries of the NRM were retrogradely labeled from the spinal cord. A much higher proportion of GABA-immunoreactive neurons in the region lateral to the NRM, however, were retrogradely labeled from the spinal cord. Eighteen percent of GABA-immunoreactive neurons were retrogradely labeled in the nucleus reticularis paragigantocellularis; conversely, 15% of the retrogradely labeled neurons in this region were GABA-immunoreactive. These results indicate that GABAergic projections constitute a very minor component of the PAG-NRM-spinal cord pathway; however, there is a significant contribution of GABAergic neurons to the spinal projections that originate lateral to the NRM. The majority of GABAergic neurons in the PAG and NRM are presumed to be inhibitory interneurons that directly or indirectly regulate activity in efferent pathways from these regions.
当向延髓腹侧吻部或脊髓微量注射γ-氨基丁酸（GABA）受体激动剂和拮抗剂时，它们会影响痛觉阈值，这一事实可能反映了GABA能神经元成分参与了内源性抗痛觉通路。在本研究中，我们使用免疫细胞化学和逆行束路追踪技术，来研究GABA能投射神经元对连接中脑导水管周围灰质（PAG）、中缝大核（NRM）和脊髓背角的抗痛觉网络的贡献。将示踪剂WGAapoHRP-Au分别注射到NRM或脊髓中，然后分别研究PAG和延髓切片中标记神经元的分布。对相同的切片进行免疫染色，以显示GABA免疫反应性神经元。虽然PAG中有大量GABA免疫反应性神经元，但只有1.5%是从NRM逆行标记的。同样，在NRM细胞构筑边界内，很少有GABA免疫反应性神经元是从脊髓逆行标记的。然而，在NRM外侧区域，有更高比例的GABA免疫反应性神经元是从脊髓逆行标记的。在巨细胞旁网状核中，18%的GABA免疫反应性神经元是逆行标记的；相反，该区域15%的逆行标记神经元是GABA免疫反应性的。这些结果表明，GABA能投射是PAG-NRM-脊髓通路中非常小的一个组成部分；然而，GABA能神经元对起源于NRM外侧的脊髓投射有显著贡献。PAG和NRM中的大多数GABA能神经元被认为是抑制性中间神经元，它们直接或间接调节来自这些区域的传出通路的活动。
