The parabrachial nucleus (PBN) is one of the major targets of spinal projection neurons and plays important roles in pain. However, the architecture of the spinoparabrachial pathway underlying its functional role in nociceptive information processing remains elusive. Here, we report that the PBN directly relays nociceptive signals from the spinal cord to the intralaminar thalamic nuclei (ILN). We demonstrate that the spinal cord connects with the PBN in a bilateral manner and that the ipsilateral spinoparabrachial pathway is critical for nocifensive behavior. We identify Tacr1-expressing neurons as the major neuronal subtype in the PBN that receives direct spinal input and show that these neurons are critical for processing nociceptive information. Furthermore, PBN neurons receiving spinal input form functional monosynaptic excitatory connections with neurons in the ILN, but not the amygdala. Together, our results delineate the neural circuit underlying nocifensive behavior, providing crucial insight into the circuit mechanism underlying nociceptive information processing.

臂旁核（PBN）是脊柱投射神经元的主要靶标之一，在疼痛中起重要作用。然而，其在伤害性信息处理中的功能作用背后的脊椎旁臂途径的结构仍然难以捉摸。在这里，我们报道PBN直接将伤害性信号从脊髓传递到丘脑内丘脑核（ILN）。我们证明，脊髓以双侧方式与PBN连接，并且同侧脊髓旁臂旁通路对于伤害行为至关重要。我们确定Tacr1-表达神经元是PBN中主要的神经元亚型，接受直接的脊柱输入，表明这些神经元对于处理伤害性信息至关重要。此外，接受脊柱输入的PBN神经元与ILN中的神经元形成功能性单突触兴奋性连接，但与杏仁核无关。总之，我们的结果描述了伤害性行为背后的神经回路，从而为伤害性信息处理背后的回路机制提供了重要的见识。