The fastspiking parvalbumin expressing basketcells (FS BC) and the neurogliaform interneurons (NGF IN) innervate somatic and dendritic compartments of postsynaptic pyramidal neurons, respectively. Here we have used paired recordings of each type of interneuron with a postsynaptic pyramidal neuron in layer II-IV of the adult rat prefrontal cortex (PFC) to characterize the interneuron action potentials (AP), evoked IPSC characteristics and response to the GAT-1 inhibitor NNC 711 and the N-type Ca-channel inhibitor ω-conotoxin GVIA. GABA released from FS BCs were insensitive to ω-conotoxin GVIA (0.5 μM), the postsynaptic response did not desensitize and the IPSC was unchanged in NNC 711 (2 μM). Conversely, IPSCs generated by APs from NGF INs were 80 % inhibited by ω-conotoxin GVIA, displayed a strong degree of desensitization and the decay-time of the IPSCs doubled in NNC 711. We used these pharmacological differences to identify the source of GABA in paradigms of synaptic overspill induced by extracellular stimulation. The decaytime of the electrically evoked event doubled in NNC 711 and this increase was reversed by subsequent application of ω-conotoxin GVIA, suggesting that the source of GABA responding to NNC 711 originate from axons that terminate on pyramidal neuron dendrites and employ N-type Ca-channels for release.
