Differential mitochondrial morphology in ventral striatal projection neuron subtypes.

The two striatal projection neuron subtypes (medium spiny neurons- MSNs), those enriched in dopamine receptor 1 versus 2 (D1-MSNs and D2-MSNs), display dichotomous properties at the level of the transcriptome, projections, morphology, and electrophysiology. Recent work illustrates dichotomous mitochondrial length in NAc MSN subtype dendrites after cocaine self-administration, with a shift toward smaller mitochondria, due to enhanced fission, occurring in D1-MSN dendrites and a shift toward larger mitochondria in D2-MSN dendrites. However, to date there has been no comparison of mitochondrial morphological properties between MSN subtypes. In this study, we examine mitochondrial morphology in NAc D1-MSNs versus D2-MSNs. We observe an increase in the frequency of smaller length mitochondria in D2-MSN dendrites relative to D1-MSN dendrites, while D1-MSN dendrites display an increase in larger length mitochondria. The differences in mitochondrial length occur in both NAc core and shell, although to a greater extent in NAc core. Finally, we demonstrate that the mitochondrial fusion molecule, Opa1, is differentially expressed in NAc MSN subtypes, with D1-MSNs displaying higher expression of Opa1 ribosome-associated mRNA. The difference in Opa1 levels may account for the bias toward enhanced smaller mitochondria in D2-MSNs and enhanced larger mitochondria in D1-MSNs. Collectively, our study demonstrates differential mitochondrial size and a potential molecular mediator of these mitochondrial differences in NAc MSN subtypes.