Medium spiny neurons

Medium spiny neuron
Details
Location	Basal ganglia
Morphology	Spiny neuron
Function	Inhibitory projection neuron
Neurotransmitter	GABA
Presynaptic connections	Dopaminergic: VTA, SNc Glutamatergic: PFC, hippocampus, amygdala, thalamus, other
Postsynaptic connections	Other basal ganglia structures
Identifiers
NeuroLex ID	Medium Spiny Neuron
Anatomical terminology []

Medium spiny neurons (MSNs), also known as spiny projection neurons, are a special type of GABA-ergic inhibitory cell representing 95% of neurons within the human striatum, a structure located in the basal ganglia. Medium spiny neurons have two primary phenotypes (i.e., characteristic types): D1-type MSNs of the "direct pathway" and D2-type MSNs of the "indirect pathway". Most striatal MSNs contain only D1-type or D2-type dopamine receptors, but a subpopulation of MSNs exhibit both phenotypes.

Direct pathway MSNs excite their ultimate basal ganglia output structure (e.g., the thalamus) and promote associated behaviors; these neurons express D1-type dopamine receptors, adenosine A1 receptors, dynorphin peptides, and substance P peptides. Indirect pathway MSNs inhibit their output structure and in turn inhibit associated behaviors; these neurons express D2-type dopamine receptors, adenosine A2A receptors (A2A), DRD2–A2A heterotetramers, and enkephalin. Both types express glutamate receptors (NMDAR and AMPAR) and CB1 receptors. A subpopulation of MSNs contain both D1-type and D2-type receptors, with approximately 40% of striatal MSNs expressing both DRD1 and DRD2 mRNA. In the nucleus accumbens (NAcc), these mixed-type MSNs that contain both D1-type and D2-type receptors are mostly contained in the NAcc shell.

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