Association between Na⁺,K⁺-ATPase activity and the vulnerability/resilience to mood disorders induced by early life experience.

Early experience changes the brain’s response to later stress

Why does the same prolonged stress affect individuals differently? This rat experiment tested whether a brief early-life intervention altered later behavioral responses and the activity of a cellular pump essential to nerve-cell function.

Combining early experience with adult stress. Newborn rats were either handled for ten minutes a day during their first ten days or left undisturbed. In adulthood, some animals from each group experienced forty days of varied stressors. Researchers then measured behavior, baseline corticosterone, insulin sensitivity and the activity of sodium–potassium ATPase in several brain regions. This enzyme uses energy to maintain the balance of sodium and potassium across cell membranes, which helps nerve cells function and communicate.

The effect depended on developmental history and brain region. Handled rats spent less time immobile in the forced-swim test, regardless of the adult stress condition. Early handling was also associated with lower enzyme activity in the hippocampus and higher activity in the amygdala. Adult chronic stress reduced activity in all three regions examined, particularly in animals that had not been handled early in life.

Baseline corticosterone and insulin sensitivity did not differ between the groups. The observed behavioral and brain-enzyme changes therefore occurred without corresponding differences in those two metabolic or hormonal measures.

The findings suggest that early experience can alter the later biological response to chronic stress. They also caution against describing resilience as uniformly higher or lower activity of one molecule: the pattern varied by brain region and exposure.

The experiment used laboratory measures related to stress coping, not a diagnosis of human depression. It identifies a cellular process associated with differing responses to adult stress, while leaving open whether changes in the enzyme actively produce those behavioral differences.