Age-related ultrastructural changes in the lateral cortex of the inferior colliculus

Age-related upregulation of dense core vesicles in the central inferior colliculus

“…Initial borders of the ICc were delineated according to the rat anatomical atlas of the brain ( Paxinos and Watson, 1998 ). Osmium fixation revealing the conspicuous lateral lemniscal fibers, libraries of decarboxylase (GAD) immunoreactivity in EM prepared tissue, adjacent sections reacted for Nissl, and our experience with EM in the IC further guided our block trimming to best ensure tissue was from ICc ( Nakamoto et al, 2013 ; Mellott et al, 2014 ; Mafi et al, 2022 ). More specific details on the trimming process can be found in Mafi et al (2022) .…”

“…Osmium fixation revealing the conspicuous lateral lemniscal fibers, libraries of decarboxylase (GAD) immunoreactivity in EM prepared tissue, adjacent sections reacted for Nissl, and our experience with EM in the IC further guided our block trimming to best ensure tissue was from ICc ( Nakamoto et al, 2013 ; Mellott et al, 2014 ; Mafi et al, 2022 ). More specific details on the trimming process can be found in Mafi et al (2022) . Tissue blocks were glued to a cylindric resin base with cyanoacrylate (Krazy Glue, Columbus, OH, USA).…”

“…We recorded each DCV that was present in a bouton, axon, and dendrite. Our classification of ultrastructure is largely based on the criteria defined by Peters et al (1991) and our previous work ( Mellott et al, 2014 ; Nakamoto et al, 2014 ; Mafi et al, 2022 ). Briefly, boutons have a “pool” of vesicles with clear centers and generally an absence of a cytoskeleton.…”

“…When identifying a presynaptic terminal with a DCV we first note if the postsynaptic density is symmetric or asymmetric. We then classified each profile (bouton, axon, and dendrite) as non-GABAergic or GABAergic based on the accumulation of gold particles as compared to background ( Nakamoto et al, 2013 ; Mellott et al, 2014 ; Mafi et al, 2022 ). In our previous report on the aging ultrastructure of the IC, we found that immunogold labeling was reduced in the aged tissue ( Mafi et al, 2022 ).…”

“…We then classified each profile (bouton, axon, and dendrite) as non-GABAergic or GABAergic based on the accumulation of gold particles as compared to background ( Nakamoto et al, 2013 ; Mellott et al, 2014 ; Mafi et al, 2022 ). In our previous report on the aging ultrastructure of the IC, we found that immunogold labeling was reduced in the aged tissue ( Mafi et al, 2022 ). To maintain consistency between studies, older structures that were characterized as GABAergic had to have a density of gold particles that was at least three times greater than background.…”