Extracellular Serotonin in the Rat Hippocampus during REM Sleep Deprivation
Faustino Lopez-Rodriguez^a,e, Charles Wilson^b,e, Nigel Maidment^a,e, Rusell Poland^c,e, Michael H. Chase^d,e and Jerome Engel, Jr.^b,e
aDepartment of Psychiatry and Biobehavioral Sciences, UCLA School of Medicine, Los Angeles, CA 90024, USA
^bDepartment of Neurology, UCLA School of Medicine, Los Angeles, CA 90095, USA
^cPsychiatry, Cedars-Sinai Medical Center, Los Angeles, CA 90048, USA
^dDepartment of Physiology, and Brain Research Institute, UCLA School of Medicine, Los Angeles, CA 90095, USA
^eBrain Research Institute, UCLA School of Medicine, Los Angeles, CA 90095, USA

Rapid eye movement (REM) sleep deprivation exerts activating effects in humans and rats. The mechanisms of action of these effects are not well understood. In the present report, we used in vivo microdialysis in the rat to test the hypothesis that REM sleep deprivation increases extracellular levels of serotonin (5HT) in the hippocampus. Rats were REM deprived for 24 hours with the platform technique (rats on a small platform surrounded by water). Changes in dialysate 5HT concentration in these rats were compared with those found in stress-control rats (rats on large platform, surrounded by water), and cage-control rats. All rats were food deprived during the 24 hours of the experimental paradigm. No significant differences were found in 5HT levels in the hippocampus among the three groups of rats. There was a significant increase in 5HT levels after the rats were returned to the home cages, but again this increase was not different among the three groups, suggesting that REM sleep deprivation does not increase 5HT release. These results do not support the hypothesis that the activating effects of REM sleep deprivation are due to an increase in 5HT release.