A reduced calorie-high fiber diet retards age-associated decreases in muscarinic receptor sensitivity

Dietary restriction modulates synaptic structural dynamics in the aging hippocampus

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. age-matched 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.

Effects of amyloid precursor protein derivatives and oxidative stress on basal forebrain cholinergic systems in Alzheimer's disease

The dysfunction and degeneration of cholinergic neuronal circuits in the brain is a prominent feature of Alzheimer's disease. Increasing data suggest that age-related oxidative stress contributes to degenerative changes in basal forebrain cholinergic systems. Experimental studies have shown that oxidative stress, and membrane lipid peroxidation in particular, can disrupt muscarinic cholinergic signaling by impairing coupling of receptors to GTP-binding proteins. Altered proteolytic processing of the beta-amyloid precursor protein (APP) may contribute to impaired cholinergic signaling and neuronal degeneration in at least two ways. First, levels of cytotoxic forms of amyloid beta-peptide (A beta) are increased; A beta damages and kills neurons by inducing membrane lipid peroxidation resulting in impairment of ion-motive ATPases, and glucose and glutamate transporters, thereby rendering neurons vulnerable to excitotoxicity. The latter actions of A beta may be mediated by 4-hydroxynonenal, an aldehydic product of membrane lipid peroxidation that covalently modifies and inactivates the various transporter proteins. Subtoxic levels of A beta can also suppress choline acetyltransferase levels, and may thereby promote dysfunction of intact cholinergic circuits. A second way in which altered APP processing may endanger cholinergic neurons is by reducing levels of a secreted form of APP which has been shown to modulate neuronal excitability, and to protect neurons against excitotoxic, metabolic and oxidative insults. Mutations in presenilin genes, which are causally linked to many cases of early-onset inherited Alzheimer's disease, may increase vulnerability of cholinergic neurons to apoptosis. The underlying mechanism appears to involve perturbed calcium regulation in the endoplasmic reticulum, which promotes loss of cellular calcium homeostasis, mitochondrial dysfunction and oxyradical production. Knowledge of the cellular and molecular underpinnings of dysfunction and degeneration of cholinergic circuits is leading to the development of novel preventative and therapeutic approaches for Alzheimer's disease and related disorders.

Caloric restriction enhances evoked DA overflow in striatum and nucleus accumbens of aged Fischer 344 rats

Previous studies have shown deficits in DA neuronal systems in senescence. Other studies indicate that prolonged dietary restriction can attenuate many of the detrimental effects of age. We have shown previously using in vivo electrochemistry that K+-evoked striatal DA overflow decreases as a function of age. This was a regional effect that appeared to be due to functional changes in DA neurons, rather than a decrease in the storage and synthesis of DA. In the present studies, we used in vivo electrochemistry to investigate the effects of caloric restriction on age related decreases in K+-evoked DA overflow along a dorsal to ventral axis in the striatum of aged female Fischer 344 rats. Aged (26-28-month-old) diet restricted animals (DRF) showed evoked DA overflow that was significantly greater in amplitude and duration compared to aged (26-28-month-old) ad lib fed animals (ALF). These results provide additional evidence that decreased DA neuronal function resulting from age is improved by caloric restriction.