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Dendritic electrogenesis in rat hippocampal CA1 pyramidal neurons: functional aspects of Na + and Ca 2+ currents in apical dendrites
Author(s) -
Andreasen Mogens,
Nedergaard Steen
Publication year - 1996
Publication title -
hippocampus
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.767
H-Index - 155
eISSN - 1098-1063
pISSN - 1050-9631
DOI - 10.1002/(sici)1098-1063(1996)6:1<79::aid-hipo13>3.0.co;2-h
Subject(s) - depolarization , chemistry , neuroscience , antidromic , cnqx , tetrodotoxin , dendritic spike , electrophysiology , biophysics , local field potential , hippocampal formation , excitatory postsynaptic potential , biology , nmda receptor , inhibitory postsynaptic potential , biochemistry , receptor , ampa receptor
The regenerative properties of CA1 pyramidal neurons were studied through differential polarization with external electrical fields. Recordings were obtained from somata and apical dendrites in the presence of 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX), DL‐2‐amino‐5‐phosphonovaleric acid (APV), and bicuculline. S+ fields hyperpolarized the distal apical dendrites and depolarized the rest of the cell, whereas S÷ fields reversed the polarization. During intradendritic recordings, S+ fields evoked either fast spikes or compound spiking. The threshold response consisted of a low‐amplitude fast spike and a slow depolarizing potential. At higher field intensities the slow depolarizing potential increased in amplitude, and additional spikes of high amplitude appeared. During intrasomatic recordings, S+ field evoked repetitive firing of fast spikes, whereas S÷ fields evoked a slow depolarizing, potential on top of which high‐ and low‐amplitude spikes were evoked. Tetrodotoxin (TTX) blocked all types of responses in both dendrites and somata. Perfusion with Ca 2+ ‐free, Co 2+ ‐containing medium increased the frequency and amplitude of fast spikes evoked by S+ field and substantially reduced the slow depolarizing potential evoked by S÷ fields. Antidromic stimulation revealed that an all‐or‐none dendritic component was activated in the distal apical dendrites by back‐propagating somatic spikes. The dendritic component had an absolute refractory period of about 4 ms and a relative refractory period of 10–12 ms. Ca 2+ ‐dependent spikes in the dendrites were followed by a long‐lasting afterhyperpolarization (AHP) and a decrease in membrane input resistance, during which dendritic excitability was selectively reduced. The data suggest that generation of fast Na + currents and slow Ca 2+ currents in the distal part of apical dendrites is highly sensitive to the dynamic state of the dendritic membrane. Depending on the mode and frequency of activation these currents can exert a substantial influence on the input‐output behavior of the pyramidal neurons. © 1996 Wiley‐Liss, Inc.