Receptor amplifying effect of serotonin and serotonin analogues in a protozoan (Tetrahymena) model system

A 72-hour treatment of Tetrahymena with serotonin analogues at a concentration of 10(-9) mmole/l resulted in a decrease of the reproduction rate, whereas serotonin itself was ineffective. On the second exposure to antagonists, cellular division was enhanced but its rate remained around or below the control value, while the second exposure to serotonin produced a more marked effect than the first one did, which finding implies a receptor amplification. The most pronounced receptor amplification was caused by the first exposure to serotonin. This observation indicates that the receptor is rather selective as regards the amplification effect.