Fig. 3

Dendritic spines of CA1 neurons are not decreased nor ultrastructurally altered by demyelination. We used 3D EM to characterize the dendritic spines of CA1 neurons. a Low magnification of a CA1 neuron and its primary dendrite. Box shows an area of spine analyses that corresponds to regions where electrophysiology studies were performed in acute slices. b Three-dimensional reconstructions of dendritic spines from myelinated (Ctr), demyelinated (Dem), and remyelinated (Rem) hippocampi. Four reconstructed dendrites from 3 mice were created for each condition. Each reconstruction included 300–500 serial, 75 nm-thick sections captured at 5–7 nm per pixel resolution. c Higher magnification of 3D reconstructions showing spine shape (green) and post-synaptic densities (red). d Spine density was similar in myelinated and demyelinated hippocampi and significantly increased in remyelinated hippocampi. e–g Based upon shape, spines were divided into three categories (thin, mushroom and stubby). h The percentage of the structurally more mature mushroom-shaped spines was significantly increased in demyelinated and remyelinated hippocampi, while less mature thin spines were decreased. i-j Compared to myelinated hippocampi, total spine volume and spine length were increased in demyelinated hippocampi. Compared to demyelinated hippocampi, remyelinated hippocampi had smaller spine volumes and lengths. k RNA-seq analysis identified alterations in 19 Gene Ontology synaptic signaling transcripts. See the Results section for possible roles of protein encoded by these transcripts in reduced synaptic function