The tachykinin peptide substance P (SP) is expressed by many interneurons and some projection neurons in the superficial dorsal horn of the spinal cord. We have recently shown that SP-expressing excitatory interneurons in lamina II correspond largely to a morphological class known as radial cells. However, little is known about their function, or their synaptic connectivity. Here we use a modification of the Brainbow technique to define the excitatory synaptic input to SP radial cells. We show that around half of their excitatory synapses (identified by expression of Homer) are from boutons with VGLUT2, which are likely to originate mainly from local interneurons. The remaining synapses presumably include primary afferents, which generally have very low levels of VGLUT2. Our results also suggest that the SP cells are preferentially innervated by a population of excitatory interneurons defined by expression of green fluorescent protein under control of the gene for gastrin-releasing peptide, and that they receive sparser input from other types of excitatory interneuron. We show that around 40% of lamina I projection neurons express Tac1, the gene encoding substance P. Finally, we show that silencing Tac1-expressing cells in the dorsal horn results in a significant reduction in reflex responses to cold and radiant heat, but does not affect withdrawal to von Frey hairs, or chloroquine-evoked itch.

速激肽物质 P (SP) 由脊髓背角浅表的许多中间神经元和一些投射神经元表达。我们最近表明，叶片 II 中表达 SP 的兴奋性中间神经元在很大程度上对应于称为放射状细胞的形态学类别。然而，人们对它们的功能或突触连接知之甚少。在这里，我们使用 Brainbow 技术的修改来定义对 SP 径向细胞的兴奋性突触输入。我们表明，大约一半的兴奋性突触（通过荷马的表达识别）来自带有 VGLUT2 的 boutons，这可能主要来自局部中间神经元。其余的突触可能包括初级传入神经，它们通常具有非常低水平的 VGLUT2。我们的研究结果还表明，SP 细胞优先受一群兴奋性中间神经元的支配，这些兴奋性中间神经元由在胃泌素释放肽基因控制下的绿色荧光蛋白表达定义，并且它们从其他类型的兴奋性中间神经元接收较少的输入。我们表明，大约 40% 的椎板 I 投射神经元表达Tac1，编码物质 P 的基因。最后，我们表明沉默背角中表达 Tac1 的细胞会导致对冷和辐射热的反射反应显着降低，但不影响对 von Frey 毛发或氯喹诱发的退缩痒。