Dietary restriction modulates synaptic structural dynamics in the aging hippocampus

Abstract

A computer-assisted morphometric study has been carried out on the synaptic ultrastructural features in the hippocampus of 14-month old (DR14) and 27-month old (DR27) dietary restricted (-50% lipids and -35% carbohydrates) rats. Age-matched controls were maintained on an ad libitum (AL) feeding schedule. Synaptic numeric density (Nv), surface density (Sv) and average area (S) were the parameters measured. In old AL vs. adult AL animals, Nv decreased to a not significant extent, while S increased and Sv decreased significantly. In DR14 rats vs. AL littermates Nv increased significantly, but S and Sv were unchanged. DR27 rats vs. agematched AL controls showed a significant increase of Nv and Sv while S was significantly decreased. Comparing DR14 vs. DR27, no significant difference due to age was documented. Both in DR14 and in DR27 groups the percent distribution of S showed a marked increase of smaller contact zones. Despite reporting on discrete aspects of synaptic ultrastructure, Nv and S are supported to be in an inverse relationship which aims at maintaining Sv constant. Thus, these three ultrastructural parameters when taken together per experimental group, appear to provide information on synaptic morphological rearrangements. In this context, the percent increase of smaller synapses in DR animals is consistent with the idea of a marked remodelling process. Considering previous data from the same groups of rats reporting significant changes in neuronal membrane lipid composition and fluidity, we interpret our findings to account for a positive modulation of dietary restriction on the synaptic structural dynamics.

Communication breakdown: The impact of ageing on synapse structure

“…In rats, long-term caloric restriction results in the maintenance of numbers of synapses and size of synapses during ageing compared to control rats fed ad libitum (Bertoni-Freddari et al, 1999). In mice, dietary energy restrictions increase the density of postsynaptic spines on dendrites of hippocampal dentate granule neurons, whereas diabetes reduces dendritic spine density (Stranahan et al, 2009; and see Box 1 Figure).…”

Modulatory Effect of Aerobic Physical Activity on Synaptic Ultrastructure in the Old Mouse Hippocampus

“…Instead, in middle-aged mice physical exercise had no effect because there was no neurogenesis and the neuronal population (and consequently the synaptic contacts) remained constant during the 4 weeks of physical activity. However, in rat SMCA1 synaptic density decreases with age (Bertoni-Freddari et al, 1999 ; Balietti et al, 2008 ). The APE-associated formation of new synaptic contacts in old age is probably due to improved cardiovascular function, energy metabolism and reduction of inflammation.…”