Kramer Phillip R, Hornung Rebecca S, Umorin Mikhail, Benson M Douglas, Kinchington Paul R
Department of Biomedical Sciences, Texas A&M University School of Dentistry, Dallas, TX, USA.
Department of Ophthalmology and of Molecular Microbiology and Genetics, University of Pittsburgh, Pittsburgh, PA, USA.
J Pain Res. 2024 Jul 2;17:2311-2324. doi: 10.2147/JPR.S441706. eCollection 2024.
Herpes Zoster in humans is the result of varicella zoster virus (VZV) infection. Injecting rats with varicella zoster virus produces pain similar to herpes zoster "shingles" pain in humans. . In a previous study, orofacial pain was induced by injecting the whisker pad of male rats with VZV and the pain response increased after attenuating neurexin 3 (Nrxn3) expression in the central amygdala. Neurons descend from the central amygdala to the lateral parabrachial nucleus and orofacial pain signals ascend to the lateral parabrachial nucleus. GABAergic neurons within the central amygdala regulate pain by inhibiting activity within the lateral parabrachial nucleus. Attenuating Nrxn3 expression in the central amygdala increased GABA release in the lateral parabrachial nucleus suggesting Nrxn3 controls pain by regulating GABA release. Nrxn3 can also control synaptic connections between neurons, and we hypothesized that Nrxn3 knockdown in the central amygdala would reduce the number of GABAergic synaptic connections in the lateral parabrachial nucleus and increase VZV associated pain.
To test this idea, the number of synaptic connections between GABAergic cells of the central amygdala and excitatory or dynorphin positive neurons within the lateral parabrachial nucleus were quantitated after infusion of a virus expressing synaptophysin. Synaptophysin is a synaptic vesicle protein that labels neuronal synaptic connections. These connections were measured in rats with and without whisker pad injection of VZV and knockdown of Nrxn3 within the central amygdala. Orofacial pain was measured using a place escape avoidance paradigm.
GABAergic synaptic connections were reduced in the lateral parabrachial nucleus after Nrxn3 knockdown. Rats with a reduction in the number of connections had an increase in VZV associated orofacial pain. Immunostaining with the pain marker prodynorphin indicated that the reduction in GABAergic connections was primarily associated with prodynorphin positive neurons.
The results suggest Nrxn3 reduces VZV associated orofacial pain, in part, by enhancing synaptic connections between GABA cells of the central amygdala and pain neurons within the lateral parabrachial nucleus.
人类的带状疱疹是水痘-带状疱疹病毒（VZV）感染的结果。给大鼠注射水痘-带状疱疹病毒会产生类似于人类带状疱疹“带状疱疹”疼痛的疼痛。在先前的一项研究中，通过给雄性大鼠的触须垫注射VZV诱导口面部疼痛，并且在减弱中央杏仁核中的神经连接蛋白3（Nrxn3）表达后疼痛反应增强。神经元从中枢杏仁核下行至臂旁外侧核，口面部疼痛信号上行至臂旁外侧核。中央杏仁核内的GABA能神经元通过抑制臂旁外侧核内的活动来调节疼痛。减弱中央杏仁核中的Nrxn3表达会增加臂旁外侧核中的GABA释放，这表明Nrxn3通过调节GABA释放来控制疼痛。Nrxn3还可以控制神经元之间的突触连接，并且我们假设在中央杏仁核中敲低Nrxn3会减少臂旁外侧核中GABA能突触连接的数量并增加与VZV相关的疼痛。
为了验证这一想法，在注入表达突触素的病毒后，对中央杏仁核的GABA能细胞与臂旁外侧核内的兴奋性或强啡肽阳性神经元之间的突触连接数量进行定量。突触素是一种标记神经元突触连接的突触小泡蛋白。在有或没有触须垫注射VZV以及中央杏仁核内敲低Nrxn3的大鼠中测量这些连接。使用位置逃避回避范式测量口面部疼痛。
敲低Nrxn3后，臂旁外侧核中的GABA能突触连接减少。连接数量减少的大鼠与VZV相关的口面部疼痛增加。用疼痛标志物前强啡肽进行免疫染色表明，GABA能连接的减少主要与前强啡肽阳性神经元有关。
结果表明，Nrxn3部分地通过增强中央杏仁核的GABA细胞与臂旁外侧核内的疼痛神经元之间的突触连接来减轻与VZV相关的口面部疼痛。
