比較周邊神經病變之疼痛模型：脊神經結紮與脊神經壓砸之異同

Abstract

周邊神經系統受到損傷後會導致神經病變引發的神經性疼痛 (peripheral neuropathic pain)，其臨床特徵有持續性的疼痛、觸摸痛以及痛覺過敏。近年來許多神經性疼痛的模型用以研究疼痛的機制以及止痛藥物的研發。我們建立脊神經壓砸模型 (spinal nerve crush, SNCr)與眾所周知的脊神經結紮 (Spinal nerve ligation, SNL)模型做比對，觀察這兩個模型在疼痛表現上的異同，進一步探討神經再生與疼痛之間的關聯性。利用機械性以及熱刺激來觀察疼痛行為，發現SNL及SNCr術後一週，動物皆發展出觸摸痛以及熱覺過敏的情形，而在兩模型中疼痛行為的表現無差異。在十二週的觀察中，觸摸痛於第十週消失，而熱覺過敏則在第六週消失，於SNL與SNCr模型上亦相同。在電生理及表皮神經支配觀察中，神經退化的情形皆發生在SNL與SNCr中。更進一步觀察活化轉錄因子-3在術後一週，ATF3於背根神經節的神經元細胞核中顯著增加且在兩模型間無差異 (350 ± 27.2 vs. 340.1 ± 32.8 neurons/mm^2, p=0.69)。而在術後十二週，ATF3表現量皆下降，然而在SNL模型中的表現量顯著多於SNCr (151.6 ± 8.9 vs. 56 ± 6.9 neurons/mm^2, p=0.001)，代表SNL造成的神經元損傷在術後十二週大於SNCr造成的損傷。最後，藉由疼痛相關分子P2X3來探討兩種模型的異同，P2X3在手術後一週顯著增加，且此增加僅在大型神經元中，與觸摸痛的產生相互呼應。而在術後十二週，P2X3的表現量回復正常值，與觸摸痛的消失相符，此變化無論在SNL與SNCr中都相同。本研究指出SNCr有潛力作為一個神經性疼痛模型，因其與SNL具有許多相似的特徵，同時亦揭示了SNL和SNCr皆具有神經再生的可能性，此一論證未來需要更進一步作探討。

Damage to the peripheral nerve system can cause peripheral neuropathic pain, which is characterized by continuous pain, tactile allodynia and thermal hyperalgesia. The model of neuropathic pain is necessary to investigate pain mechanism and discover the analgesic drugs. We established spinal nerve crush (SNCr) model compared to the well-known spinal nerve ligation (SNL) model to verify its neuropathic pain pattern and possibility of regeneration. Within one week of SNCr and SNL surgery, there were significant mechanical allodynia and thermal hyperalgesia on the ipsilateral hind paw compared to the contralateral side, according to behavior tests with a dynamic plantar aesthesiometer for mechanical thresholds and a Hargreaves-type analgesiometer for thermal withdrawal latencies. Mechanical allodynia recovered at 10 weeks and thermal hyperalgesia recovered at 6 weeks on both SNCr and SNL model. The nerve degeneration on SNCr and SNL model was validated with epidermal nerve density and electrophysiology. We than examined the expression of activating transcription factor 3 (ATF3), a neuronal injury marker, in dorsal root ganglion (DRG) neurons. ATF3 expression was increased at one week of SNCr and SNL with no difference between these two models (350 ± 27.2 vs. 340.1 ± 32.8 neurons/mm^2, p=0.69). However, ATF3 expression on SNCr group were significantly fewer than that on SNL group at week 12 (151.6 ± 8.9 vs. 56 ± 6.9 neurons/mm^2, p=0.001), indicating the degree of neuron injury on SNCr was lower than that on SNL at week 12. The neuropathic pain behaviors were further assessed with an increased expression of purinergic receptor P2X3 on ipsilateral DRG neurons at one week of SNCr and SNL with no difference between these two models (368.1 ± 38.3 vs. 309.5 ± 28.3 neurons/mm^2, p=0.41). P2X3 expression recovered at week 12 on both SNCr and SNL models without difference between these two models. (167.5 ± 28.1 vs. 139.2 ± 11.1 neurons/mm^2, p=0.91). These results provided evidence that SNCr was a potential neuropathic pain model with similar neuropathic pain pattern to the SNL model, and revealed the possibility of regeneration on both SNL and SNCr models.