M. Andreasen et S. Nedergaard, DENDRITIC ELECTROGENESIS IN RAT HIPPOCAMPAL CA1 PYRAMIDAL NEURONS - FUNCTIONAL-ASPECTS OF NA+ AND CA2+ CURRENTS IN APICAL DENDRITES, Hippocampus, 6(1), 1996, pp. 79-95
The regenerative properties of CA1 pyramidal neurons were studied thro
ugh differential polarization with external electrical fields. Recordi
ngs were obtained from somata and apical dendrites in the presence of
6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), DL-2-amino-5-phosphonoval
eric acid (APV), and bicuculline. S+ fields hyperpolarized the distal
apical dendrites and depolarized the rest of the cell, whereas S divid
ed by fields reversed the polarization. During intradendritic recordin
gs, S+ fields evoked either fast spikes or compound spiking. The thres
hold response consisted of a low-amplitude fast spike and a slow depol
arizing potential. At higher field intensities the slow depolarizing p
otential increased in amplitude, and additional spikes of high amplitu
de appeared. During intrasomatic recordings, S+ field evoked repetitiv
e firing of fast spikes, whereas S divided by fields evoked a slow dep
olarizing potential on top of which high- and low-amplitude spikes wer
e evoked. Tetrodotoxin (TTX) blocked all types of responses in both de
ndrites and somata. Perfusion with Ca2+-free, Co2+-containing medium i
ncreased the frequency and amplitude of fast spikes evoked by S+ field
and substantially reduced the slow depolarizing potential evoked by S
divided by fields. Antidromic stimulation revealed that an all-or-non
e dendritic component was activated in the distal apical dendrites by
back-propagating somatic spikes. The dendritic component had an absolu
te refractory period of about 4 ms and a relative refractory period of
10-12 ms. Ca2+-dependent spikes in the dendrites were followed by a l
ong-lasting afterhyperpolarization (AHP) and a decrease in membrane in
put resistance, during which dendritic excitability was selectively re
duced. The data suggest that generation of fast Na+ currents and slow
Ca2+ currents in the distal part of apical dendrites is highly sensiti
ve to the dynamic state of the dendritic membrane. Depending on the mo
de and frequency of activation these currents can exert a substantial
influence on the input-output behavior of the pyramidal neurons. (C) 1
996 Wiley-Liss, Inc.