Age-related changes in brain catecholamine responses to a single footshock.
The responses of forebrain and brainstem catecholamine levels to a single footshock were studied in 70-day, one-year, and two-year-old Fischer-344 rats. Brain catecholamine concentrations were assessed 10 minutes after a single 2 second footshock (0, 0.3, or 2.0 mA). In samples taken from non-footshocked rats, only forebrain dopamine concentrations showed a significant age-related decline. However, because the net weights of both the forebrain and the brainstem samples increased significantly with age, the content of forebrain dopamine did not exhibit a significant decline. Both norepinephrine and dopamine levels showed age-related changes in responsiveness to footshock. Norepinephrine concentrations were reduced in both the forebrain and brainstem samples obtained 10 minutes after the high footshock in both the 70-day and one-year-old animals. In two-year-old rats, however, neither forebrain nor brainstem norepinephrine concentrations were altered in response to footshock. Seventy-day-old rats demonstrated significant footshock-induced increases in brainstem dopamine levels, one-year olds showed no appreciable change, and two-year olds demonstrated a non-significant footshock-induced decrease. Thus, both noradrenergic and dopaminergic systems demonstrated age-related changes in their responsiveness to a single brief footshock. These alterations may contribute to the declining ability of the senescent animals to adapt to stressful situations.
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