Local Circuit Neurons in the Frontal Cortico-striatal System

The neostriatum is the principal recipient of afferents to basal ganglia from the cerebral cortex, especially, from the frontal cortex. These two large forebrain structures, the neostriatum (caudate-putamen) and cortex, are both composed of morphologically diverse types of neurons. Recently striatal and frontal cortical interneurons have been characterized from various points of view and they are now known to be not only morphologically but also physiologically and chemically very diverse. Since the functional roles of each neuron type remain to be investigated, we do not understand the meaning of the neuronal diversity. In recent times it has been shown that striatal and cortical interneurons developmentally originate from the same distant sites then migrating to their location. This suggests that the cortex and striatum may have a similar interneuronal organization. In fact, chemically similar interneurons exist in both structures. One chemical type shared in common contains the calcium-binding protein, parvalbumin (PV), and another the peptide, somatostatin (SOM) (somatotrophin-release inhibiting factor), these being expressed in separate interneuron populations. To facilitate understanding of the meaning of neuronal diversity and local circuit organization, we compare various characteristics of PV and SOM cells in the functionally intimately related frontal cortex and striatum here.