SYNAPTIC OUTPUT OF PHYSIOLOGICALLY IDENTIFIED SPINY STELLATE NEURONS IN CAT VISUAL-CORTEX

Spiny stellate neurons of area 17 of the cat's visual cortex were phys iologically characterised and injected intracellularly with horseradis h peroxidase. Six neurons from sublamina 4A were selected. Five had th e S-type of simple receptive fields; one had a complex receptive field . Their axons formed boutons mainly in layers 3 and 4. An electron mic roscopic examination of 45 boutons showed that each bouton formed one asymmetric synapse on average. Spines were the most frequent synaptic target (74%); dendritic shafts formed the remainder (26%). On the basi s of ultrastructural characteristics, 8% of the target dendrites were characterised as originating from smooth gamma-aminobutyrate-ergic (GA BAergic) neurons. Thus the major output of spiny stellate neurons is t o other spiny neurons, probably pyramidal neurons in layer 3 and spiny stellates in layer 4. (C) 1994 Wiley-Liss, Inc.