Papp Ildikó, Szucs Péter, Holló Krisztina, Erdélyi Ferenc, Szabó Gábor, Antal Miklós
Department of Anatomy, Histology and Embryology, Faculty of Medicine, Medical and Health Science Center, University of Debrecen, H-4012 Debrecen, Hungary.
Eur J Neurosci. 2006 Sep;24(5):1341-52. doi: 10.1111/j.1460-9568.2006.05013.x.
We have previously demonstrated that hyperpolarization-activated and cyclic nucleotide-gated cation channel subunit 2 (HCN2) is expressed by terminals of peptidergic nociceptive primary afferents in laminae I-IIo of the rat spinal dorsal horn. In this study, we investigated the possible neurotransmitters and postsynaptic targets of these HCN2-expressing primary afferent terminals in the superficial spinal dorsal horn by using immunocytochemical methods. We demonstrated that HCN2 widely colocalizes with substance P (SP), and that HCN2-positive terminals that are also immunoreactive for SP form serial close appositions with dendrites and perikarya of neurokinin 1 receptor-immunoreactive neurons. It was also found that HCN2-immunoreactive terminals are frequently apposed to neurons that are immunoreactive for calbindin, micro-opioid receptor and the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor subunit GluR2, markers for excitatory interneurons. Investigating HCN2 immunoreactivity in glutamic acid decarboxylase 65-green fluorescent protein transgenic mice, we found that HCN2-positive terminals occasionally also contact cells that contain an isoform of glutamic acid decarboxylase (glutamic acid decarboxylase 65), a marker for GABAergic inhibitory neurons. Application of ZD7288, an antagonist of HCN channels, onto neurons that were recorded in spinal cord slices with whole-cell patch-clamp electrodes reduced the number of monosynaptic excitatory postsynaptic potentials evoked by electrical stimulation of primary afferents at nociceptive intensities. The results suggest that HCN2 may contribute to the modulation of membrane excitability of SP-containing nociceptive primary afferent terminals, may increase the reliability of synaptic transmission from primary afferents to secondary sensory neurons and thus may play a role in the fine-tuning of pain transmission from nociceptive primary afferents to neurons in the spinal dorsal horn.
我们之前已经证明，超极化激活的环核苷酸门控阳离子通道亚基2（HCN2）在大鼠脊髓背角I-IIo层的肽能伤害性初级传入神经末梢中表达。在本研究中，我们通过免疫细胞化学方法研究了这些表达HCN2的初级传入神经末梢在脊髓背角浅层可能的神经递质和突触后靶点。我们证明HCN2与P物质（SP）广泛共定位，并且对SP也有免疫反应性的HCN2阳性末梢与神经激肽1受体免疫反应性神经元的树突和胞体形成连续紧密的并列。还发现HCN2免疫反应性末梢经常与对钙结合蛋白、微阿片受体和α-氨基-3-羟基-5-甲基异恶唑-4-丙酸受体亚基GluR2有免疫反应性的神经元并列，这些是兴奋性中间神经元的标志物。在谷氨酸脱羧酶65-绿色荧光蛋白转基因小鼠中研究HCN2免疫反应性时，我们发现HCN2阳性末梢偶尔也会接触含有谷氨酸脱羧酶（谷氨酸脱羧酶65）异构体的细胞，这是GABA能抑制性神经元的标志物。将HCN通道拮抗剂ZD7288应用于用全细胞膜片钳电极记录的脊髓切片中的神经元，可减少伤害性强度下电刺激初级传入神经诱发的单突触兴奋性突触后电位的数量。结果表明，HCN2可能有助于调节含SP的伤害性初级传入神经末梢的膜兴奋性，可能增加从初级传入神经到二级感觉神经元的突触传递的可靠性，因此可能在从伤害性初级传入神经到脊髓背角神经元的疼痛传递的微调中发挥作用。
