The effect of presynaptic alpha blocker yohimbine on rat paradoxical sleep.

In rats, the presynaptic alpha-receptor blocking drug yohimbine given at low doses increases paradoxical sleep (PS) while much higher doses are necessary to depress it. These results are in line with the postulated preferential affinity of this drug for presynaptic noradrenergic (NA) receptors, resulting in an increased activity in NA synapses. The depression of PS under high doses of yohimbine may be related to a post-synaptic blockade of NA receptors, thus cancelling the presynaptic effect. This type of study illustrates the necessity of investigating the temporal evolution of PS instead of simply counting its total amount in a given period of time.