Turner R W, Maler L, Deerinck T, Levinson S R, Ellisman M H
Department of Anatomy and Neurobiology, University of Ottawa, Ontario, Canada.
J Neurosci. 1994 Nov;14(11 Pt 1):6453-71. doi: 10.1523/JNEUROSCI.14-11-06453.1994.
Immunocytochemical and electrophysiological techniques were used to localize TTX-sensitive sodium channels (NaChs) over the soma-dendritic axis of basilar and nonbasilar pyramidal cells of the electrosensory lateral line lobe (ELL) of weakly electric fish (Apteronotus leptorhynchus). Dense NaCh-like immunolabel was detected on the membranes of basilar and nonbasilar pyramidal cell somata. Punctate regions of immunolabel (approximately 15 microns) were separated by nonlabeled expanses of membrane over the entire extent of basal dendrites. Similar punctate immunolabel was observed over the apical dendrites, and frequently on membranes of afferent parallel fiber boutons in the distal apical dendritic region. Intracellular recordings from pyramidal cell somata or proximal apical dendrites (75-200 microns) were obtained using an in vitro ELL slice preparation. TTX-sensitive potentials were identified by focal pressure ejection of TTX. Somatic recordings demonstrated both TTX-sensitive fast spike discharge and a slow prepotential; similar but lower amplitude potentials were recorded in apical dendrites. Dendritic spikes were composed of at least two active components triggered by a fast prepotential (FPP) generated by the somatic spike. TTX-sensitive spikes propagated in a retrograde fashion over at least the proximal 200 microns of the apical dendrites, as determined by the conduction of an antidromic population spike and focal TTX ejections. Somatic spikes were followed by a depolarizing afterpotential (DAP) that was similar in duration and refractory period to that of proximal dendritic spikes. During repetitive spike discharge, the DAP could increase in amplitude and attain somatic spike threshold, generating a high-frequency spike doublet and a subsequent hyperpolarization that terminated spike discharge. Repetition of this process gave rise to an oscillatory burst discharge (2-6 spikes/burst) with a frequency of 40-80 Hz. Both the DAP and oscillatory discharge were selectively blocked by TTX ejections restricted to the proximal apical dendritic region. The present study demonstrates an immunolocalization of NaChs over somatic and dendritic membranes of a vertebrate sensory neuron that correlates with the distribution of TTX-sensitive potentials. The interaction of somatic and dendritic action potentials is further shown to underlie an oscillatory discharge believed to be important in electrosensory processing.
免疫细胞化学和电生理技术被用于在弱电鱼（细吻线翎电鳗）电感觉侧线叶（ELL）的基底和非基底锥体细胞的胞体 - 树突轴上定位对河豚毒素（TTX）敏感的钠通道（NaChs）。在基底和非基底锥体细胞胞体的膜上检测到密集的类NaCh免疫标记。在基底树突的整个范围内，免疫标记的点状区域（约15微米）被无标记的膜区域隔开。在顶端树突上观察到类似的点状免疫标记，并且在远端顶端树突区域的传入平行纤维终扣的膜上也经常观察到。使用体外ELL脑片制备从锥体细胞胞体或近端顶端树突（75 - 200微米）进行细胞内记录。通过TTX的局部压力喷射来识别对TTX敏感的电位。胞体记录显示出对TTX敏感的快速动作电位发放和一个缓慢的预电位；在顶端树突中记录到类似但幅度较低的电位。树突动作电位由至少两个由胞体动作电位产生的快速预电位（FPP）触发的活性成分组成。如通过逆向群体动作电位的传导和局部TTX喷射所确定的，对TTX敏感的动作电位以逆行方式在顶端树突的至少近端200微米上传播。胞体动作电位之后是一个去极化后电位（DAP），其持续时间和不应期与近端树突动作电位相似。在重复动作电位发放期间，DAP的幅度可能增加并达到胞体动作电位阈值，产生高频动作电位双峰以及随后终止动作电位发放的超极化。这个过程的重复产生了频率为40 - 80Hz的振荡爆发式放电（2 - 6个动作电位/爆发）。DAP和振荡放电都被局限于近端顶端树突区域的TTX喷射选择性阻断。本研究证明了NaChs在脊椎动物感觉神经元的胞体和树突膜上的免疫定位，这与对TTX敏感电位的分布相关。进一步表明，胞体和树突动作电位的相互作用是一种振荡放电的基础，这种振荡放电被认为在电感觉处理中很重要。
