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How do aspiny striatal neurons differ from spiny striatal neurons?

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Within the striatum, neurons are categorized into two primary types based on their structure and connectivity: spiny and aspiny striatal neurons.1

Spiny Striatal Neurons

These are medium-sized cells characterized by radiating dendrites covered in dendritic spines. They serve as the primary functional units for both input and output: all incoming signals to the striatum terminate on their spines, and all striatal output is transmitted via their axons, which project beyond the boundaries of the caudate nucleus and putamen. Chemically, they are heterogeneous, primarily utilizing gamma-aminobutyric acid (GABA), substance P, and enkephalin.1

Aspiny Striatal Neurons

In contrast, these neurons possess smooth dendrites and have short axons that remain confined within the caudate nucleus or putamen, functioning as interneurons. Their chemical profile differs as well:
* Small aspiny neurons secrete GABA, neuropeptide Y, or somatostatin.
* Large aspiny neurons are evenly distributed and play a critical role in maintaining the balance of dopamine and GABA.1