New evidence from experimental mice further supports the idea that the early postnatal period is a critical time for establishing lifelong anxiety behaviour. The findings implicate serotonin, known to be important in mood regulation, with its agonists used therapeutically in humans as anxiolytics. American scientists had previously shown that mice bred with no serotonin-1A receptors (5-HT1AR knockouts) were more “anxious” than wild mice on three standard tests (eg, in a novel environment they took longer to start eating). In a new transgenic mouse, it is possible to turn off the expression of these serotonin receptors at will by feeding the mouse doxycycline. Researchers found that mice fed doxycycline to switch off the receptors during the embryonic and early postnatal period developed pronounced anxiety as adults (similar to 5-HT1AR knockouts). Mice fed doxycycline as adults were not affected.
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