Dorsal raphe nucleus administration of 5-HT1A receptor agonist and antagonists: effect on rapid eye movement sleep in the rat.

The effect of flesinoxan, a selective 5-HT1A receptor agonist, WAY 100635, a selective 5-HT1A receptor antagonist, and (+/-)pindolol, a mixed beta-adrenoceptor and 5-HT1A/B receptor antagonist, on spontaneous sleep was studied in adult rats implanted for chronic sleep recordings. Drugs were infused directly into the dorsal raphe nucleus (DRN). Direct application of flesinoxan (25.0 and/or 50.0 ng) into the DRN induced a significant increment of REM sleep (REMS) during the second and third 2 h period of recording. On the other hand, microinjection into the DRN of (+/-)pindolol (100.0 and/or 200.0 ng), and WAY 100635 (12.5, 25.0 and 50.0 ng) significantly reduced REMS during the first and/or second 2 h recording period. Our findings support previous studies indicating that microdialysis perfusion of the 5-HT1A receptor agonist 8-OHDPAT into the DRN increases REMS. In addition, they favor the proposal that microinjection of 5-HT1A receptor antagonists into the DRN would suppress 5-HT inhibition and reduce REMS.