Figure 2. Ultrastructural evidence for corticosterone-mediated reductions in thin spines as a structural correlate of functional impairment in db/db mice.

(A), Electron micrographs (with dendrites highlighted in yellow) from the middle of the dentate molecular layer in a vehicle-treated wildtype mouse (Wt/Veh); a vehicle-treated db/db mouse (db/Veh); a metyrapone-treated wildtype mouse (Wt/Met), and a metyrapone-treated db/db mouse (db/Met). Scale bar=0.5µm, arrows indicate dendritic spines. (B), Pharmacological inhibition of adrenal steroidogenesis attenuates spine density deficits in db/db mice, particularly among thin spines. (C), Reconstruction of dendritic segments from serial sections revealed that db/Veh mice have deficits in thin spine density that are attenuated with metyrapone treatment. Scale cube, XYZ=1µm. (D), Metyrapone treatment normalizes spine synapse density, without influencing shaft synapses in db/db mice. (E), Thin spines exhibit corticosterone-mediated synaptic atrophy in db/db mice. (F), There were no differences in the density of filopodia, defined as thin spines lacking a synapse, across genotypes and treatment conditions. (G), No effect of drug or genotype on the density of spines bearing perforated synapses. (H), Dendrite caliber, defined as the 2-dimensional area of the dendritic shaft at the start, middle, and end of the segment divided by the number of microtubules within the shaft at that position on the Z-axis, was also similar between db/db and wildtype mice. (I), There was no change in the density of mitochondria in the dendritic shaft. For all graphs, asterisks (*) indicate statistical significance at p<0.05 relative to vehicle-treated wildtype mice following 2×2 ANOVA with Bonferroni’s post hoc. Error bars represent the s.e.m. For color interpretation, the reader is referred to the web version of this article.