DENDRITIC PROPERTIES OF HIPPOCAMPAL CA1 PYRAMIDAL NEURONS IN THE RAT - INTRACELLULAR STAINING IN-VIVO AND IN-VITRO

Dendritic morphology and passive cable properties determine many aspec ts of synaptic integration in complex neurons, together with voltage-d ependent membrane conductances. We investigated dendritic properties o f CA1 pyramidal neurons intracellularly labeled during in vivo and in vitro physiologic recordings, by using similar intracellular staining and three-dimensional reconstruction techniques. Total dendritic lengt h of the in vive neurons was similar to that of the in vitro cells. Af ter correction for shrinkage, cell extent in three-dimensional represe ntation was not different between the two groups. Both in vive and in vitro neurons demonstrated a variable degree of symmetry, with some ne urons showing more cylindrical symmetry around the main apical axis, w hereas other neurons were more elliptical, with the variation likely d ue to preparation and preservation conditions. Branch order analysis r evealed no difference in the number of branch orders or dendritic comp lexity. Passive conduction of dendritic signals to the soma in these n eurons shows considerable attenuation, particularly with higher freque ncy signals (such as synaptic potentials compared with steady-state si gnals), despite a relatively short electrotonic length. Essential aspe cts of morphometric appearance and complex dendritic integration criti cal to CA1 pyramidal cell functioning are preserved across neurons def ined from the two different hippocampal preparations used in this stud y. (C) 1998 Wiley-Liss, Inc.