Most people who've stayed up all night know the "tired and nervous" feeling the next day. The body might be exhausted, but the brain feels active or even crazy. Even after these changes fade away, sleep loss can have a strong anti-depression effect on people for several days.
To figure it out, a team of biologists from Northwestern University looked at the effects of sleep loss in mice. In the beginning, they created a depressed state in all the mice by repeatedly giving them small shocks. In response to these shocks, the mice entered a depressive-like state and eventually stopped trying to escape their cages. Subsequently, some were allowed to sleep while others were forced to stay up. Later, they tested the mice's response to shocks again. They found that after this sleepless night, the mice that had stayed up were less depressed and showed more attempts to escape the shocks.
What causes these changes in mice? To see how the mice's brains responded to their sleepless night, the researchers measured dopamine neuron (神经元) activity. They saw that mice lacking in sleep showed higher dopamine activity in three regions: the prefrontal cortex (前额叶皮质), nucleus accumbens (伏隔核) and hypothalamus (下丘脑).
To figure out which areas were related to the mice's anti-depression effect, they silenced dopamine reactions in each of these areas of the brain. The anti-depression effect disappeared in mice when the team silenced the dopamine input in the prefrontal cortex, while it continued to exist when they do the same to the other two regions. That's why Yevgenia Kozorovitskiy, the leading researcher, says that this region may be important in relieving depression.
Based on the belief that transitions between a depressed state and a non-depressed state are influenced by the brain's ability to reorganize connections, Kozorovitskiy and her team looked at individual neurons in the prefrontal cortex for signs of growth. They saw evidence of the new connections, suggesting that dopamine had reconnected neurons in the mice brains to maintain their mood for several days. Kozorovitskiy says this work may help future studies on depression treatment, but whether it'll cure depression remains to be seen.
