機械感覺訊號對螯蝦尾端感光細胞感光能力的影響

The impact of the mechanosensory input on the photosensitivity of crayfish's caudal photoreceptor

吳旻芝

指導教授 ： 葉世榮

國立清華大學/生命科學院/分子醫學研究所/碩士(2010年)

https://doi.org/10.6843/NTHU.2010.00160

摘要

在螯蝦 (Procambarus clarkia)第六節神經節，成對的尾端感光細胞 (caudal photoreceptor)是個複雜、多元型態的中間神經元。尾端感光細胞對於光照刺激會產生大量的神經衝動，擁有整合尾扇上大量纖毛狀的機械感覺神經輸入的能力，而且在沒有其他刺激的情況下，本身具有自發性的神經衝動。這意味著尾端感光細胞的神經衝動輸出是感光、機械感覺和自發性反應等三種來源的整合。
去除來自尾扇機械感覺神經訊號來源後，尾端感光細胞的反應產生改變。去除掉尾端傳入神經後的尾端感光細胞相較於保有傳入神經但是沒有水流刺激的尾端感光細胞，其神經衝動頻率下降且神經衝動節奏變得規律。僅僅失去尾扇訊號的來源就改變了尾端感光細胞的反應，說明尾扇機械感覺神經訊號對尾端感光細胞有一定程度的影響力。
失去尾端訊號輸入後的尾端感光細胞仍然能感受到短暫光照的強度大小並做出反應，且提升了感光的能力。尾端訊號輸入對於感光細胞的感光能力可能帶有抑制的作用。但是尾端感光細胞對於強度大於92 lux的持續光照都會提高神經衝動頻率，與有無抑制作用無關。一個晝夜節律系統中，有三種組織層級。其中第二種為感受器和感覺途徑組成的外部刺激同步系統，該系統可以調節震盪器和外界條件。尾端感光細胞可反應出環境中的光照度，此特性類似晝夜節律系統中的一種組織層級，進而可推測尾端感光細胞參與晝夜節律系統之中。
從三種不同光照刺激方式的實驗結果中得知，尾扇機械感覺訊號會抑制尾端感光細胞的感光能力。在持續光照的實驗中，無論有無機械感覺輸入的抑制，尾端感光細胞展現出可以反應環境光照強度的特性。這樣的特性支持尾端感光細胞參與螯蝦晝夜節律系統中的調控途徑。

關鍵字

螯蝦 ； 尾端感光細胞 ； 感覺訊號整合 ； 機械感覺神經 ； 傳入神經

並列摘要

The caudal photoreceptors (CPR) in the sixth abdominal ganglion of the crayfish are complex and multi-modal interneurons. These cells respond directly to light with tonic spike discharges, and they integrate synaptic input from an array of filiform mechanoreceptors on the tailfan, moreover, they have spontaneous spikes. Thus, the photoreceptor output represents the integrated activity of photosensitive, mechanosensory and spontaneity.
After removing the afferent nerve, CPRs alter their response. In comparison with the intact CPRs not hydrodynamically stimulated, the spiking frequency of the CPRs lack of mechanosensory input decreases and exhibits a regular pulse train. Namely, CPRs have different responses merely because of losing the mechanosensory input from the tailfan. It also suggests that mechanosensory input plays an important role for CPRs.
The CPRs without mechanosensory input still can respond to light of different intensity and their photosensitivity is improved. Therefore, the mechanosensory input might inhibit CPRs’ photosensitivity. Whether there is an inhibition or not, the spiking frequency of the CPRs increases under the continuous illumination intensity greater
3
than 92 lux. Moreover, a circadian rhythm system has three main organization levels. The second level, a synchronization system of external stimuli composed of receptors and sensorial pathways, can mediate between the ensemble of oscillators and ambient conditions. The photosensitivity characteristic relates to the fact that CPR participates in the circadian rhythm system.
According to the experimental results of the three different types of illumination stimulation, the mechanosensory input from the tailfan would inhibit CPRs’ sensitivity to light. In the experiment of the continuous illumination, CPRs show the characteristic that they can react to the environmental illumination intensity. The characteristic suggests that CPRs participate in the pathway of regulation and modulation in crayfish's circadian rhythm system.

並列關鍵字

crayfish ； caudal photoreceptor ； sensory information integration ； mechanosensory neuron ； afferent nerve

參考文獻

Bahar S, Moss F. 2003. The Nonlinear Dynamics of the Crayfish Mechanoreceptor System. International Journal of Bifurcation and Chaos 13:2013-34

Crandall KA, Cronin TW. 1997. The molecular evolution of visual pigments of freshwater crayfishes (Decapoda: Cambaridae). J Mol Evol 45:524-34

Douglass JK, Wilkens LA. 1998. Directional selectivities of near-field filiform hair mechanoreceptors on the crayfish tailfan (Crustacea: Decapoda). J Comp Physiol A 183:23-34

Galeano C, Chow KL. 1971. Response of caudal photoreceptor of crayfish to continuous and intermittent photic stimulation. Can J Physiol Pharmacol 49:699-706

Hafner GS, Martin RL, Tokarski TR. 2003. Photopigment gene expression and rhabdom formation in the crayfish (Procambarus clarkii). Cell Tissue Res 311:99-105