Senok S S, Baumann K I, Halata Z
Department of Physiology, Faculty of Medicine, Chinese University of Hong Kong, Shatin, N.T., Hong Kong.
Exp Brain Res. 1996 Aug;110(3):325-34. doi: 10.1007/BF00229133.
Experiments were performed on slowly adapting type I mechanoreceptors in an isolated rat skin-nerve preparation (SA I receptors) and in an isolated rat sinus hair preparation (St I receptors). Merkel cells were stained in vitro with the fluorescent dye quinacrine and irradiated with ultraviolet (UV) light (2 mW for up to 1 h) while recording receptor responses to standard mechanical stimuli every 30 s. In addition, thresholds for electrically evoked action potentials were tested by applying electrical stimuli to the skin through the same stylus used for mechanical stimulation. UV irradiation resulted in abrupt failure to respond to mechanical stimuli in 73% of the SA I receptors examined (n = 37) within less than 1 h. This confirms previous reports of phototoxic destruction of Merkel cells. However, several minutes after the receptors failed to respond to mechanical stimulation, thresholds for electrical stimuli applied to the receptive field increased sharply. About 40% of the St I receptors (n = 13) irradiated with UV light following quinacrine staining stopped responding to bending of the hair within 1 h. In contrast, none of the seven St II receptors treated in the same way showed significant changes in the responses. Electron microscopic examination of sinus hairs after quinacrine staining alone showed slight changes in the appearance of Merkel cells, and in particular enlargement of the perinuclear space. These changes did not affect receptor responses. Electron microscopic studies of sinus hairs with receptors that had maintained normal responses to mechanical stimuli after quinacrine staining and 1 h of UV irradiation revealed that a substantial number of Merkel cells still had a normal ultrastructure while adjacent nerve terminals were severely swollen and partially compressing the Merkel cells. No changes were observed in lanceolate nerve terminals forming the morphological substrate of St II receptors. These results demonstrate that sensitivity to phototoxic destruction following quinacrine staining varies greatly among Merkel cells, with some maintaining normal function and ultrastructural appearance even after 1 h of UV irradiation. On the other hand there is clear evidence that the phototoxic damage affects the nerve terminals as well. Such experiments can therefore not provide conclusive proof about the role of Merkel cells in these mechanoreceptors.
实验在分离的大鼠皮肤 - 神经标本（SA I 受体）中的慢适应 I 型机械感受器以及分离的大鼠鼻窦毛标本（St I 受体）上进行。体外使用荧光染料喹吖因对默克尔细胞进行染色，并用紫外线（UV）照射（2 毫瓦，照射时间长达 1 小时），同时每隔 30 秒记录受体对标准机械刺激的反应。此外，通过用于机械刺激的同一探针向皮肤施加电刺激，测试诱发动作电位的阈值。紫外线照射导致在不到 1 小时内，所检测的 73%的 SA I 受体（n = 37）突然对机械刺激无反应。这证实了先前关于默克尔细胞光毒性破坏的报道。然而，在这些受体对机械刺激无反应几分钟后，施加到感受野的电刺激阈值急剧增加。喹吖因染色后用紫外线照射的约 40%的 St I 受体（n = 13）在 1 小时内停止对毛发弯曲产生反应。相比之下，以相同方式处理的七个 St II 受体的反应均未显示出显著变化。仅用喹吖因染色后对鼻窦毛进行电子显微镜检查显示默克尔细胞外观有轻微变化，特别是核周间隙增大。这些变化并未影响受体反应。对喹吖因染色和 1 小时紫外线照射后对机械刺激仍保持正常反应的受体的鼻窦毛进行电子显微镜研究发现，大量默克尔细胞仍具有正常的超微结构，而相邻的神经末梢严重肿胀并部分压迫默克尔细胞。形成 St II 受体形态学基础的柳叶状神经末梢未观察到变化。这些结果表明，喹吖因染色后对光毒性破坏的敏感性在默克尔细胞之间差异很大，一些默克尔细胞即使在紫外线照射 1 小时后仍保持正常功能和超微结构外观。另一方面，有明确证据表明光毒性损伤也影响神经末梢。因此，此类实验无法提供关于默克尔细胞在这些机械感受器中作用的确凿证据。
