Intercalated (ITC) cell masses are putative GABAergic neurons located at both borders of the lateral and basolateral amygdala (1). By virtue of its location the intercalated system is ideally situated to gate incoming and outcoming information of the amygdala. ITC neurons are also innervated by cortical fibers and can thus mediate cortical control in a feedforward manner over the basolateral complex and the central nucleus. It has been suggested that ITC cells disinhibit brain stem neurons during fear conditioning by means of their projections to the central nucleus (2). However, information on synaptic connections between ITC neurons is lacking (see also: 3). Therefore, we are studying properties of unitary GABAergic synaptic responses of ITC cells by using GAD65-GFP transgenic mice. In these mice ITC cells can be identified as clusters of densely packed fluorescent units. Whole cell patch-clamp recordings were performed with K-gluconate and biocytin containing pipettes in acute coronal slices (330 μm thick, age range: 15-24 days old, recording temperature range: 34-35°C) from ITC neurons mainly located in the intermediate capsula, where fibre bundles between the basolateral complex and the central nucleus are located. Neurons had heterogeneous passive and active electrophysiological properties (n=83) and were confirmed as ITC after histological processing. Several ITC cells have been reconstructed with the help of a drawing tube and we are currently attempting to correlate their anatomical features with functional properties. Double patch recordings revealed GABA_A receptor-mediated unitary inhibitory postsynaptic currents (uIPSCs) with peak amplitude (mean±SEM) 20.8±3.9pA, rise time 1.4±0.1ms, decay time 12.7±1ms and jitter 0.46±0.05ms (n=28). We found that ITC cells interconnected by at least three modalities, which were identified by fitting with a regression curve (ANOVA, p<0.05) the number of uIPSC events plotted against the frequency of stimulation. The three groups were characterised by: 1) synapses that mostly failed at low frequency (0.1Hz) but became responsive at higher frequency of stimulation (10Hz) (n=7); 2) synapses that were activated at 0.1Hz and became unreliable at 10Hz stimulation (n=8) and 3) synapses in which the occurrence of uIPSCs was frequency-independent (n=13). These phenotypes appeared to be linked to differences in release probabilities according to experiments where paired-pulse uIPSCs and manipulation of extracellular calcium concentrations were performed (n=7 and 3, respectively). Thus, we demonstrate that ITC cell masses are tuned to respond to a wide dynamic range of frequencies and these properties are likely to affect the computational operations of amygdala.