Fast and Slow GABAergic Transmission in Hippocampal Circuits

Cortical neuronal networks consist of excitatory glutamatergic principal cells and a heterogeneous group of GABAergic inhibitory interneurons. Interneurons are embedded in feedforward and feedback microcircuits and control key aspects of cortical network function including the timing of the activation of principal cells and the generation of network oscillations (Freund and Buzsaki, 1996; McBain and Fisahn, 2001; Klausberger and Somogyi, 2008). Although interneurons comprise only 10% of the neuronal population, they are highly diverse and can be subdivided into several types on the basis of various criteria, such as intrinsic physiological properties, neurochemical marker content, morphological features, including the laminar distribution of the axon, and finally the postsynaptic target profile of their output (Freund and Buzsaki, 1996; Avoli et al., 2006). On the basis of synaptic targets, interneurons have been classified into two major groups, perisomatic- and dendrite-targeting cells.