title: Age-related decline in metabolic competence of small and medium-sized synaptic mitochondria.
abstract: A computer-assisted morphometric investigation of cytochrome oxidase (COX) activity, selectively evidenced by preferential diaminobenzidine cytochemistry, has been carried out on synaptic mitochondria in the cerebellar cortex of adult and old rats. The ratio (R) of the area of the cytochemical precipitate (CPA) to the overall area of each mitochondrion (MA) was calculated. R refers to the fraction of the inner mitochondrial membrane actively involved in cellular respiration, thus its quantitative estimation constitutes a reliable index of the mitochondrial metabolic competence (MMC). In adult rats a significant negative correlation between MA and R values was found, while in old animals there was just a positive trend. Paired-quartile comparisons of R values showed a significant age-related decrease in small and medium-sized mitochondria, whereas the lowest and not significant age-related reduction was found in oversized organelles. A paired decrease in number and increase in size is reported to be a general trend for mitochondria during aging, but oversized organelles, according to their low R value, constitute a scanty, though functional, compensating reaction. Thus, the present findings support the argument that the currently reported age-related cellular metabolic decay appears to rely both on the decline in MMC of the small and medium-sized mitochondria, and on their specific reduction in number. This novel result is of biological relevance since it is largely the small and medium-sized mitochondria that are required for the provision of adequate amounts of ATP for actual cellular performance, while the significantly enlarged organelles are thought to represent an intermediate ultrastructural feature in mitochondrial genesis and/or remodelling.
authors.affiliation: Neurobiology of Aging Laboratory, INRCA Research Department, Via Birarelli 8, 60121 Ancona, Italy. c.bertoni@inrca.it
authors.forename: Carlo
authors.initials: C
authors.lastname: Bertoni-Freddari
authors.forename: Patrizia
authors.initials: P
authors.lastname: Fattoretti
authors.forename: Belinda
authors.initials: B
authors.lastname: Giorgetti
authors.forename: Liana
authors.initials: L
authors.lastname: Spazzafumo
authors.forename: Moreno
authors.initials: M
authors.lastname: Solazzi
authors.forename: Marta
authors.initials: M
authors.lastname: Balietti
mesh_terms: D000818:Animals; D002531:Cerebellum / Q000502:physiology / Q000648:ultrastructure; D003576:Electron Transport Complex IV / Q000378:metabolism; D005260:Female; D008928:Mitochondria / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar; D013569:Synapses / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D003576:Electron Transport Complex IV