Age-related behavioral and ultrastructural changes in the rat amygdala.

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.