Age-Related Memory Decline Is Accelerated by Pinealectomy in Young Adult and Middle-Aged Rats via BDNF / ERK / CREB Signalling in the Hippocampus

Memory decline is considered a normal part of aging, while the relationship between melatonin deficiency and cognitive function is complex and not fully understood. The present study investigated the role of melatonin deficiency functioning as a hormone at different ages on working and short-term recognition and spatial memory in rats. An age-related decline in memory function was tested in the Y-maze, the object recognition test, and the radial arm maze. Aging was associated with reduced expression of brain-derived neurotrophic factor (BDNF) throughout the hippocampus, whereas pinealectomy exacerbated this process specifically in the CA3 region of 3- and 14-month-old rats. The region-specific reduced expression of the extracellular signal-regulated kinase (ERK)1/2 and pERK1/2 was observed in young adult rats with pinealectomy. However, in middle-aged rats, the expression of these signaling molecules was either downregulated or upregulated in different hippocampal regions. The reduced ratio of pCREB/CREB in the frontal cortex and hippocampus was associated with memory impairment in young adult and middle-aged melatonin-deficient rats, whereas old rats were unaffected. Our study provides insights into the molecular pathways involved in age-related memory changes associated with melatonin deficiency, highlighting the importance of the BDNF / ERK1/2 / CREB pathway in the hippocampus and suggesting a critical period for intervention.