Intrinsic synaptic connectivity of the nucleus accumbens: Lateral inhibition, functions of fast-spiking interneurons and neuromodulation

In the striatum, local projections from axon collaterals originating from medium-sized spiny neurons and fast-spiking interneurons axons are likely important for regulating the activity of basal ganglia output areas; therefore, we need to understand how striatal microcircuits are built and how they function. The shared GABAergic nature of multiple cell types within the striatum, including its principal cells, has long precluded the ability to identify the source of inhibitory inputs when local extracellular stimulation was used. However, simultaneous dual whole-cell recordings have been recently used to study the synapses that connect pairs of identified individual cells in the nucleus accumbens and dorsal striatum. These studies have provided quantitative and qualitative data that have greatly contributed to our knowledge of the connectional architecture and physiology of the striatum. Here we review the characteristics and functions of GABAergic contacts between medium-sized spiny neurons, of intrastriatal projections from fast-spiking interneurons onto medium-sized spiny neurons, and the neuromodulation of these fast-acting types of synaptic transmission, most notably by dopamine.