REM-enhancing effects of the adrenergic antagonist idazoxan infused into the medial pontine reticular formation of the freely moving cat.

Adrenergic input to the medial pontine reticular formation (mPRF) has been postulated to play an important role in behavioral state control. Previous work has shown that direct microinjections of the alpha 2 agonist clonidine and of norepinephrine into the mPRF suppress the REM phase of sleep. Here, we report that the alpha 2 antagonist idazoxan (IZ) enhances REM-like sleep states in the cat when microinfused into the rostral part of the mPRF at sites where carbachol produced a marked increase in REM. Significant increases in the absolute number of min in REM (70%) were observed over the entire 5 h of recordings and an especially robust increase occurred in the first hour (1000%). Other effects of IZ included increased REM duration and decreased latency to REM onset. These results represent the most marked REM-enhancing effects thus far reported for any antagonist at any brain site.