We have previously reported that in slices from adult monkey dorsolateral prefrontal cortex (DLPFC, areas 9 and 46), layers 2/3 Fast Spiking (FS) interneurons have homogeneous membrane properties but can be grouped in at least 4 morphological classes: Local, Medium or Wide Arbor neurons and Chandelier cells (SFN 2001 Abstr 729.14). Despite this diverse morphology, unitary IPSPs (uIPSPs) elicited by FS neurons in pyramidal cells (PCs) have very similar latency, rise time, exponential decay and are GABAA-receptor-mediated, suggesting a similar inhibitory synaptic output (SFN 2001 Abstr 467.4). Here, we report the effects of repetitive firing of different subclasses of FS neurons on the efficacy of uIPSPs elicited in postsynaptic PCs. In every synaptic connection examined to date (n=9), the uIPSPs depressed during 10 spike-20 Hz trains elicited in the FS neuron, as revealed by the IPSP(10)/IPSP(1) ratio. uIPSP depression was strong in some connections and relatively weaker in others. Interestingly, if the pre...