Modulation of neuronal [Ca2+]i by caffeine is altered with aging

Insights into CNS ageing from animal models of senescence

In recent years, novel model systems have made significant contributions to our understanding of the processes that control the ageing of whole organisms. However, there are limited data to show that the mechanisms that gerontologists have identified as having a role in organismal ageing contribute significantly to the ageing of the central nervous system. Two recent discoveries illustrate this particularly well. The first is the consistent failure of researchers to demonstrate a simple relationship between organismal ageing and oxidative stress--a mechanism often assumed to have a primary role in brain ageing. The second is the demonstration that senescent cells play a causal part in organismal ageing but remain essentially unstudied in a CNS context. We argue that the animal models now available (including rodents, flies, molluscs and worms), if properly applied, will allow a paradigm shift in our current understanding of the normal processes of brain ageing.

Expansion of the calcium hypothesis of brain aging and Alzheimer's disease: minding the store

Evidence accumulated over more than two decades has implicated Ca²⁺ dysregulation in brain aging and Alzheimer's disease (AD), giving rise to the Ca²⁺ hypothesis of brain aging and dementia. Electrophysiological, imaging, and behavioral studies in hippocampal or cortical neurons of rodents and rabbits have revealed aging-related increases in the slow afterhyperpolarization, Ca²⁺ spikes and currents, Ca²⁺ transients, and L-type voltage-gated Ca²⁺ channel (L-VGCC) activity. Several of these changes have been associated with age-related deficits in learning or memory. Consequently, one version of the Ca²⁺ hypothesis has been that increased L-VGCC activity drives many of the other Ca²⁺-related biomarkers of hippocampal aging. In addition, other studies have reported aging- or AD model-related alterations in Ca²⁺ release from ryanodine receptors (RyR) on intracellular stores. The Ca²⁺-sensitive RyR channels amplify plasmalemmal Ca²⁺ influx by the mechanism of Ca²⁺-induced Ca²⁺ release (CICR). Considerable evidence indicates that a preferred functional link is present between L-VGCCs and RyRs which operate in series in heart and some brain cells. Here, we review studies implicating RyRs in altered Ca²⁺ regulation in cell toxicity, aging, and AD. A recent study from our laboratory showed that increased CICR plays a necessary role in the emergence of Ca²⁺-related biomarkers of aging. Consequently, we propose an expanded L-VGCC/Ca²⁺ hypothesis, in which aging/pathological changes occur in both L-type Ca²⁺ channels and RyRs, and interact to abnormally amplify Ca²⁺ transients. In turn, the increased transients result in dysregulation of multiple Ca²⁺-dependent processes and, through somewhat different pathways, in accelerated functional decline during aging and AD.