The effects of aging on diurnal water intake and melatonin binding in the suprachiasmatic nucleus.

In vitro autoradiography was used to quantify [125I]melatonin binding in young rats and in aged rats that were screened for diurnal drinking prior to neurobiological study. Among the aged subjects studied, some rats exhibited a blunted diurnal rhythm in that a decreased percentage of water was consumed during the dark phase. Other aged animals maintained a strong nocturnal pattern of water intake similar to young rats. The density of [125I]melatonin binding in the suprachiasmatic nucleus (SCN) of the hypothalamus was significantly correlated with diurnal drinking, i.e. lower binding was associated with a more blunted rhythm. Thus, [125I]melatonin binding in the SCN may provide a marker for age-related decline in some aspects of biological functions.