Although the relationships between brain structure and emotions may alter across the life span, this relationship is of particular importance during aging when significant alterations in emotions may be manifested. Understanding the structural–behavioral relationship could not only provide a neurobiological basis of these changes, but could also suggest potential intervention. Since anxiety is commonly observed in aging population, we undertook this study to determine the extent of this behavioral manifestations as well as the associated ultrastructural changes in the amygdala. Rats of various age groups, adolescent, adult, and aged were tested for anxiety‐like behavior and the ultrastructure/presynaptic architecture of the central nucleus of amygdala (CNA) were evaluated using transmission electron microscopy (EM). Aged rats were consistently more anxious than the other groups as evidenced by their scores in the elevated plus maze. Morphometric EM analysis of axodendritic synapses revealed that the aged rats had a lower presynaptic area as well as number of synapses, but unexpectedly a higher number of presynaptic mitochondria in CNA. Since presynaptic mitochondria are known to provide the energy for neurotransmission, it may be concluded that compensatory mechanisms are still operational during aging, and hence, may be a target for therapeutic intervention at this stage of life span.

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It is now well established that aging is associated with emotional and cognitive changes. Although the basis of such changes is not fully understood, ultrastructural alterations in key brain areas are likely contributing factors. Recently, we reported that aging‐related anxiety in male Wistar rats is associated with ultrastructural changes in the central nucleus of amygdala, an area that plays important role in emotional regulation. In this study, we evaluated the cognitive performance of adolescent, adult, and aged male Wistar rats in multi‐branch maze (MBM) as well as in Morris water maze (MWM). We also performed ultrastructural analysis of the CA1 region of the hippocampus, an area intimately involved in cognitive function. The behavioral data indicate significant impairments in few indices of cognitive functions in both tests in aged rats compared to the other two age groups. Concomitantly, a total number of presynaptic vesicles as well as vesicles in the resting pool were significantly lower, whereas postsynaptic mitochondrial area was significantly higher in aged rats compared to the other age groups. No significant differences in presynaptic terminal area or postsynaptic mitochondrial number were detected between the three age groups. These results indicate that selective ultrastructural changes in specific hippocampal region may accompany cognitive decline in aging rats.

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