To test this, Han's team repeatedly infused the VTA of susceptible mice, over five days, with a drug known to increase the excitatory currents.

As hypothesized, the animals showed a profound reversal in behaviors and antidepressant-like effects -- they became more sociable and regained their sweet tooth. The once-hyperactive VTA neurons were also normalized.

The researchers also achieved similar results using chronic optogenetic stimulation to drive up the neuronal activity.

The findings "reveal a highly novel mechanism that controls an individual's susceptibility or resilience to chronic social stress, " said Eric Nestler, professor of the Icahn School of Medicine, who was not involved in the study.

"The discoveries have important implications for the development of new treatments for depression and other stress- related disorders," Nestler added.