Abstract
have neural structures that allow them to anticipate environmental changes and then regulate physiological and behavioral functions in response to these alterations. The suprachiasmatic nucleus of the hypothalamus (SCN) is the main circadian pacemaker in many mammalian species. This structure synchronizes the biological rhythm based on photic information that is transmitted to the SCN through the retinohypothalamic tract. The aging process changes the structural complexity of the nervous system, from individual nerve cells to global changes, including the atrophy of total gray matter. Aged animals show internal time disruptions caused by morphological and neurochemical changes in SCN components. The effects of aging on circadian rhythm range from effects on simple physiological functions to effects on complex cognitive performance, including many psychiatric disorders that influence the well-being of the elderly. In this review, we summarize the effects of aging on morphological, neurochemical, and circadian rhythmic functions coordinated by the main circadian pacemaker, the SCN.
Highlights
Animals have neural structures that allow them to anticipate environmental changes and regulate physiological and behavioral functions in response to these alterations
Photic information is transmitted to the suprachiasmatic nucleus of the hypothalamus (SCN) through the retinohypothalamic tract (RHT), which originates from melanopsincontaining retinal ganglion cells
These cells project bilaterally to the SCN (Hendrickson et al, 1972; Moore & Lenn, 1972) and geniculohypothalamic tract (GHT), which originates in the intergeniculate leaflet and, similar to RHT, terminate at the ventrolateral portion of the SCN
Summary
Environmental cues strongly influence living organisms, and the light/dark cycle is considered the most influential aspect of the regulation of rhythmic behavior (Dibner, Schibler & Albrecht, 2010). Periodic changes in the environment are recognized by an endogenous circadian clock. Organisms have developed numerous strategies to maintain an appropriate internal temporal order in response to alterations in the ecological niche (Hut & Beersma, 2011).
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