J Neurophysiol (February 1, 2003). 10.1152/jn.00750.2002
Submitted on Submitted 3 September 2002; accepted in final form 20 October 2002

Distinct Local Circuits Between Neocortical Pyramidal Cells and Fast-Spiking Interneurons in Young Adult Rats

 ¹Neurobiologie et Diversité Cellulaire, Centre National de la Recherche Scientifique Unité Mixte de Recherche 7637, Ecole Supérieure de Physique et de Chimie Industrielles de la ville de Paris, 10 rue Vauquelin, 75005 Paris, France; and  ²Heinrich-Heine University, C. & O. Vogt-Institute for Brain Research, D-40001 Düsseldorf, Germany

Angulo, María Cecilia, Jochen F. Staiger, Jean Rossier, and Etienne Audinat. Distinct Local Circuits Between Neocortical Pyramidal Cells and Fast-Spiking Interneurons in Young Adult Rats. J. Neurophysiol. 89: 943-953, 2003. Connections between layer V pyramidal cells and GABAergic fast-spiking interneurons (pyramidal-FS) were studied by paired recordings combined with morphological analyses in acute neocortical slices from 28- to 52-day-old rats. Pairs of spikes elicited in pyramidal cells at a stimulation rate of 0.2 Hz induced unitary excitatory postsynaptic currents (EPSCs) in FS interneurons that displayed facilitation (48%), depression (38.5%), or neither depression nor facilitation (13.5%). Analyses of the EPSC amplitude distributions indicate that depressing connections always showed multiple functional release sites. On the contrary, facilitating connections consisted either of one or several release sites. At a holding potential of 72 mV, the quantal size (q) and the release probability (p) of facilitating connections with a single release site were -21.9 ± 7.5 pA and 0.49 ± 0.19 (SD), respectively. The mean q and the estimated number of release sites (n) at connections showing multiple sites were obtained by decreasing the release probability and did not differ between depressing and facilitating synapses (depressing connections: q = -15.3 ± 2.5 pA, n = 5.1 ± 3, facilitating connections: q = -23.9 ± 9.8 pA, n = 7.8 ± 5.4). However, the quantal content at facilitating synapses with multiple sites (1.9 ± 1.5) was significantly different from that at depressing connections (4.1 ± 3.9). Finally, quantitative morphological analyses revealed that most of the pyramidal cells displaying facilitation can be differentiated from those displaying depression by a more densely branched apical dendritic tree. Therefore two types of morphologically distinct pyramidal cells form excitatory connections with FS interneurons that differ in their short-term plasticity characteristics. Facilitating and depressing connections may provide a differential control of the temporal information processing of FS cells and thus finely regulate the inhibitory effect of these interneurons in neocortical networks of young adult rats.