Contributions of impaired hippocampal plasticity and neurodegeneration to age-related deficits in hormonal pulsatility

Abstract

Connectivity between the hippocampus and hypothalamus plays an essential role in circadian rhythmicity and stress responsiveness. Both hippocampal dysfunction and loss of hormonal pulsatility have been demonstrated in aged animals, but the possibility of a functional interaction between these two processes remains unexplored. Correlated hippocampal neuropathology and flattening of the circadian rhythms occur in the elderly, and we propose that these processes are causally linked. In this review, we discuss the anatomical and functional nature of hippocampal interconnections with the hypothalamus. We also discuss the results of studies exploring the relationship between circadian phase and hippocampal plasticity in young animals, with the goal of understanding how these mechanisms might be restored in the aging brain.

The impact of different fructose loads on insulin sensitivity, inflammation, and PSA-NCAM-mediated plasticity in the hippocampus of fructose-fed male rats

“…31 Importantly, Stranahan et al 2,32 have demonstrated that glucocorticoids are responsible for an impaired hippocampal function in diabetes. In the present study, consumption of 10% fructose solution did not affect microsomal 11β-HSD1 level in the hippocampus (Fig.…”

Time–place learning over a lifetime: absence of memory loss in trained old mice

“…One of the sites that undergo the earliest changes with aging is the hippocampus, which has a well-known role in remembering events (Squire et al 2004;Stranahan et al 2008;Berke et al 2009). Wilson et al (2006) proposed that small concurrent changes during aging may strengthen the auto-associative network of the CA3 subregion at the cost of processing new information arising from the entorhinal cortex.…”

“…Recent studies have indicated that the circadian system supports temporally regulated events underlying memory processes, such as acquisition, consolidation, and retrieval (Eckel-Mahan and Storm 2009;Gerstner et al 2009;Gerstner and Yin 2010;Jilg et al 2010;Kondratova et al 2010;Rawashdeh and Stehle 2010). It has been proposed that the aging-related flattening of circadian rhythms is causally linked to hippocampal neuropathology (Stranahan et al 2008;Kondratova and Kondratov 2012).…”

“…On the occurrence of biological significant events, TOD derived from this clock is stored into memory as a contextual cue (referred to as a time stamp) and associated with place-and event-specific information to guide future behavior. In addition to circadian system involvement, TPL is likely hippocampus-dependent as it involves memories for spatial representations and "what-where -when" associations over time (Stranahan et al 2008). Hippocampus-dependent associative (episodic-like) memory is particularly age-sensitive, as opposed to for instance procedural (implicit) memory (Newman and Kaszniak 2000;Fleischman et al 2004).…”

“…Evidence suggests that these processes may be interrelated (Antoniadis et al 2000;Biemans et al 2003;Cain et al 2004;Eckel-Mahan et al 2008;Stranahan et al 2008; Van der Zee et al 2009;Kondratova et al 2010). With time-place learning (TPL), animals link biological significant events (e.g., localizing a food source, encountering a mate or predator) with the location and time of day (TOD).…”