Abstract

Il a ete demontre que les terminaisons axonales peuvent liberer des neurotransmetteurs sans etre envahies par un potentiel d'action. Meme si chaque terminaison presentait un faible taux de liberation, la densite synaptique des cellules pyramidales est si grande que ce phenomene pourrait alterer leurs proprietes integratives. Ici, nous demontrons que la liberation spontanee de transmetteur est presente in vivo, que son impact est fonction du compartiment cellulaire (somatique ou dendritique); et, que sa frequence est beaucoup plus elevee que celles rapportees dans des etudes in vitro. De plus, ces evenements synaptiques spontanes produisent une diminution de la resistance d'entree qui est plus importante au niveau des dendrites que du soma. Nos resultats suggerent que, dans un cerveau intact, les neurones pyramidaux subissent un intense bombardement synaptique qui les divise en compartiments electrotoniquement distants les un des autres.

Alternate abstract:

It has been demonstrated that axonal terminals can release neurotransmitters without being invaded by an action potential. Even if each terminal presented a low rate of release, the synaptic density of pyramidal cells is so great that this phenomenon could alter their integrative properties. Here, we demonstrate that spontaneous transmitter release is present in vivo, that its impact depends on the cellular compartment (somatic or dendritic); and, that its frequency is much higher than those reported in in vitro studies. Furthermore, these spontaneous synaptic events produce a decrease in input resistance which is greater at the level of the dendrites than at the soma. Our results suggest that, in an intact brain, pyramidal neurons undergo intense synaptic bombardment that divides them into compartments electrotonically distant from each other.