Medium Spiny Neuron

2022-04-16: reference:

Inhibitory GABAergic; key characteristic of the Striatum. They do not function as interneurons though they are connected to them.
Projections are diveded into direct or indirect pathway:
- Direct: Disinhibitory, as it inhibits inhibitory regions.
  - These express D1-type, Adenosine A1 (Gi), Dynorphin, and Substance P.
- Indirect: Dis-dis-inhibitory, as it inhibits regions that are themselves disinhibitory.
  - As depicted below, D2 seems to inhibit the firing dis-disinhibition. Therefore the lack of dopaminergic input blocks both direct and indirect. Overkill? I’m sure there’s reasons.
- ~40% of striatal MSNs express both D1 and D2 mRNA. In the NAc, 17%, and 5-6% in the dorsal striatum.
- I guess they never just inhibit excitatory synapses directly?
They also express AMPAR, GABA receptors, mGluR, etc. On that note, this is kind of a mess. I’m pretty sure indirect also expresses substance P, for instance.
Has glutamateric input from the Prefrontal Cortex, Hippocampus, Amygdala, the Thalamus, etc. somatodendritically.
Their supposed main phenotype is whether they express D1 or D2 postsynaptically (for input from the Ventral Tegmental Area/Substantia Nigra.)
Have a looksie:

yana-notes