Nociceptive responses of the posterior thalamic nucleus to peripheral noxious stimuli in anesthetized rats

目前已知丘腦對傷害覺扮演著重要的角色，並發現許多丘腦核與內側及外側痛覺路徑有關。不過，丘腦後核(Po)在傷害覺上的角色具有爭議，除位於內側及外側視丘的邊緣區域，體積並與丘腦腹後外側核(VPL)或丘腦腹後內側核(VPM)一樣大。之前有許多與痛覺有關的試驗均指出，Po屬於輔助結構，且大部分試驗均對多種感覺形式進行評估，因為僅可進行評估的傷害覺專一性(NS)反應並不多。本試驗將利用多種評估技術，探究Po在傷害覺中扮演的角色，包括微觀及巨觀的方法。針對Po神經元的特性，將與已知和外側痛覺路徑有關的丘腦神經元特性進行比較。因此，本試驗將著重於NS反應，並系統性地完整探究整個丘腦外側。為提升實驗結果品質，本試驗並研發適當的定量機械夾子刺激器。並藉由使用此次機器進行系統性胞外記錄研究，顯示9% (總共記錄245個神經元，39個為傷害性專一者)其中9個 (23%) 落在VPL，22個(56%)落在Po。此外，本研究僅著重大鼠後肢與尾巴之痛覺反應，也發現Po有體表映射的趨勢(意即尚未有明確身體映射對應)。少數傷害覺專一神經元也發現於視丘後核後側三角核(PoT)核區。傷害覺同側反應之比較，在Po有14%傷害覺專一神經元(3 of 22 units)呈現同側反應。在電流原密度分析傷害覺反應場電位初步結果也支持胞外記錄結果。本研究對於Po在傷害覺中之角色的電生理實驗結果發現，Po與傷害覺資訊的處理有關，並在外側及內側痛覺路徑上扮演著不可或缺的角色。這些發現對於痛覺處理策略的研發極為重要。The thalamus is well known to play an important role in nociception, and several thalamic nuclei are recruited to participate in the medial and lateral pain pathways. However, the role of the posterior thalamic nucleus (Po) in nociception is controversial, which is located at the border between the medial and lateral thalamus and is as large in volume as the ventral posterolateral thalamic nucleus (VPL) or the posteromedial thalamic nucleus (VPM). Previous pain-related studies often referred to the Po as an auxiliary structure, and most of these studies assessed several sensory modalities since there are only a few nociceptive-specific (NS) responses that can be assessed. In this thesis, a range of assessment techniques will be used to explore the role of the Po in nociception, using both micro- and macro-view approaches. Features of neurons of the Po were compared to characteristics of thalamic neurons known to belong to the lateral pain pathway. Therefore, NS responses were the focus of this thesis, and the entire lateral thalamus was systematically explored. To improve the quality of the experimental findings, development of an adequate quantitative mechanical pinch stimulator was also incorporated. The results of the unit recording study by use of the pinch stimulator showed that the incidence of 9% (39 of 245 units) was found in our systematic study. Nine of the 39 NS units identified (23%) were located in the VPL, and 22 of the 39 units identified (56%) were located in the Po. Otherwise, Po was found with topographical orientation (i.g., it is not clearly organized) while focus on the tail and hind paws stimulated. And few units were identified within the posterior triangular neurons of the Po (PoT). In responses of ipsi-laterality, 14% of NS units (3 of 22 units) responded ipsilaterally. The preliminary results from CSD mapping of 2.5 mm (stand for rostral portion) and 3.8 mm (caudal portion) partly supported the results above mentioned. The results of our electrophysiological investigation into the role of the Po in nociception revealed that the Po is involved in processing nociceptive information and could play an indispensable role in either the lateral or medial pain pathway. These findings may have implication for the development of pain management strategies and translational research in other species