Datta Atanu
National Brain Research Centre, Manesar, Gurugram, Haryana 122052, India.
IBRO Neurosci Rep. 2023 May 14;14:466-482. doi: 10.1016/j.ibneur.2023.05.005. eCollection 2023 Jun.
Spinal cord injury is a devastating condition that haunts human lives. Typically, patients experience referred phantom sensations on the hand when they are touched on the face. In adult monkeys, massive deafferentations such as chronic dorsal column lesions at higher cervical levels result in the large-scale expansion of face inputs into the deafferented hand cortex of area 3b. However, adult rats with thoracic dorsal column lesions do not demonstrate such large-scale reorganization. The large-scale face expansion in area 3b of monkeys is driven by the reorganization of the cuneate nucleus in the medulla. The sprouting of afferents from the trigeminal nucleus to the adjacent deafferented cuneate nucleus is facilitated by close proximity and compactness of the medulla in primates. Previously, in adult rats with thoracic lesions, the cuneate nucleus was not deafferented and its functional organization was not explored. The extent of the deafferentation and the duration of the recovery period are two major factors that determine the extent of reorganization. Hence, higher cervical (C3-C4) dorsal column lesions were performed, which cause massive deafferentations, and physiological maps were obtained after prolonged recovery periods (3 weeks -18 months). In spite of the above, the expansion of the intact face inputs was not observed in the deafferented zones of the primary somatosensory cortex (SI) and medulla of adult rats. The deafferented forelimb and hindlimb representations in SI were unresponsive to cutaneous stimulation of any part of the body. The cuneate and gracile nuclei in rats with complete dorsal column lesions remained mostly inactive except for a few sites which responded to stimulation of the spared upper arm. Hence, dorsal column lesions have different effects on the adult primate and rodent somatosensory systems. Appreciating this inter-species difference can aid in identifying the underlying neural substrates and restrict maladaptive reorganizations to cure phantom sensations.
脊髓损伤是一种困扰人类生活的灾难性疾病。通常，当患者面部被触摸时，手部会出现牵涉性幻肢感觉。在成年猴子中，诸如高位颈髓慢性背柱损伤之类的大规模去传入作用会导致面部输入大规模扩展到3b区去传入的手部皮层。然而，患有胸段背柱损伤的成年大鼠并未表现出这种大规模的重组。猴子3b区的大规模面部扩展是由延髓楔束核的重组驱动的。灵长类动物延髓的紧密相邻和紧凑结构促进了三叉神经核传入纤维向相邻去传入的楔束核的发芽。此前，在患有胸段损伤的成年大鼠中，楔束核并未去传入，其功能组织也未被研究。去传入的程度和恢复期的长短是决定重组程度的两个主要因素。因此，进行了高位颈髓（C3 - C4）背柱损伤，这种损伤会导致大规模去传入，并在延长的恢复期（3周 - 18个月）后获得生理图谱。尽管如此，在成年大鼠的初级体感皮层（SI）和延髓的去传入区域中并未观察到完整面部输入的扩展。SI中去传入的前肢和后肢代表区对身体任何部位的皮肤刺激均无反应。除了少数几个对保留的上臂刺激有反应的部位外，完全背柱损伤大鼠的楔束核和薄束核大多处于不活跃状态。因此，背柱损伤对成年灵长类动物和啮齿动物的体感系统有不同影响。认识到这种种间差异有助于确定潜在的神经基质，并限制适应不良的重组以治愈幻肢感觉。
