Researchers hypothesize that neurogenesis, or neuron growth, is an antidepressant action. This hypothesis is linked to the understanding that nearly all antidepressants increase birth of granule neurons in rodents. Ketamine, however, has such rapid antidepressant effects, suggesting that the mechanisms involved with ketamine are not involved with neuron birth. Instead, researchers hypothesized that ketamine’s rapid effects are due to it enhancing the maturation of neurons born previously.
To test this hypothesis, researchers injected rats with ketamine, assessing the effects of the ketamine on granule neurons. Researchers found that the ketamine rapidly affected the neurons, increasing mature neurons within two hours. A single injection of ketamine increased cell proliferation and functional maturation. For at least four weeks following the injection, depressive symptoms in rats were decreased.
In conclusion, ketamine has rapid, lasting effects on the recruitment of neurons into the hippocampal region of the brain. The hippocampus is believed to play a role in memory, spacial recognition, and avoidance-approach conflict processing. However, new neuron growth was independent of the antidepressant effects of the ketamine. The antidepressant effect may be due to ketamine’s work on neuron growth, but not on new neuron growth.