Dietary restriction suppresses age-related changes in dendritic spines

Abstract

The effects of dietary restriction by every-other-day (EOD) feeding on dendritic spines in the aging rat neocortex were evaluated in Golgi preparations. After weaning, male Wistar rats were offered a 24% protein diet either ad lib (AL) or EOD. AL-fed groups were sacrificed at 6 and 24–25 months of age. EOD-fed groups were sacrificed at 6, 24, and 30 months. To assess the effects of EOD feeding late in life, another group was fed AL for 19 months, then EOD for 5 months and sacrificed when 24 months old. Spine density and configuration were quantified along 20 μm terminal tip segments from the basilar tree of layer V pyramidal cells of the parietal cortex. Evaluation of spine densities from the 6 and 24 months AL-fed groups showed that there was a significant loss of spines with normal aging (−38%). In EOD-fed rats, spine density did not differ significantly from AL age-matched controls at either 6 or 24 months of age. However, spine densities in 24-month-old rats diet restricted late in life and EOD-fed 30-month-old rats were the same as 6-month-old AL-fed controls and EOD 6-month-old rats, an observation suggesting protection of dendritic spines from age-related loss. Spines were categorized as either L-type (lollipop-shaped), which are more prevalent in young adults, or N-type (nubbin). With normal aging (comparing 6- and 24-month-old AL-fed groups) there was a significant decrease in L-type spines. However, all dietarily restricted groups showed retention of L-type spines. The results indicate that age differences in neuronal morphology may be attenuated by chronic dietary restriction initiated after weaning or late in life.