en Neurophysiology/Pharmacology Neurophysiology/Pharmacology Experimental research article Experimental research article Introduction: Noradrenergic cells in LC participate in the process of cortical activation and behavioral arousal. The evidence suggests that locus ceoruleus (LC) plays an important role in the sleep-wake cycle. The aim of this study was stereological estimation of cavity caused by lesion and assessment of sleep stages after bilateral lesion of the LC. Materials and Methods: Male Wistar rats weighting 250-275 gr were divided into four groups (control: n=6, sham: n=6, lesion1: n=6 and lesion2: n=6). 6 hydroxydopamine (6 OHDA) (2μg/0.5μl and 4μg/1μl) was sterotaxically injected bilaterally into LC to produced lesion. For sleep recording 3 EEG and 2 EMG electrodes were implanted respectively in the skull and dorsal neck muscle. Recordings were taken before and 7, 21 and 42 days after lesion. After 7 weeks, Rats first were anesthetized and then their brains were removed and cut in 7 μm serial sections and stained with cresyl violet. The volume of LC and the lesion induced cavity were evaluated through the stereological technique. Results: Lesion - induced cavity volume (0.5 μl) was restricted to LC, whereas Another group (1 μl), total LC and structures adjacent to the LC were also damaged. A significant decrease was seen in non-rapid eye movement (NREM) and paradoxical sleep (PS) stages and a significant increase was seen in duration of wake and paradoxical sleep without atonia (PS-A) in lesion group in comparison with control and sham groups. Conclusion: The results of this study demonstrate 2μg/0.5μl 6-OHDA is suitable dose for LC lesion and bilateral lesion of LC causing disrupt wake, NREM ,PS and also produce the PS-A. Locus Coeruleus, Bilateral Lesion Model, Sleep-Wake Cycle, 6_ hydroxydopamine. 22 30 http://ppj.phypha.ir/browse.php?a_code=A-10-820-1&slc_lang=en&sid=1 Vahid Pirhajati Mahabadi vpirhajati.1@gmail.com 3200319475328460015019 3200319475328460015019 No Anatomical Sciences Department, Faculty of Medicine, Tarbiat Modares University, Tehran, Iran mansoureh movahedin movahed.m@modares.ac.ir 3200319475328460015020 3200319475328460015020 Yes Anatomical Sciences Department, Faculty of Medicine, Tarbiat Modares University, Tehran, Iran Zohreh Mazaheri 0@mazaheri202yahoo.com 3200319475328460015021 3200319475328460015021 No Anatomical Sciences Department, Faculty of Medicine, Tarbiat Modares University, Tehran, Iran Saeed Semnanian ssemnan@modares.ac.ir 3200319475328460015022 3200319475328460015022 No Physiology Department, Faculty of Medicine, Tarbiat Modares University, Tehran, Iran Javad Mirnajafi_zadeh mirnajaf@modares.ac.ir 3200319475328460015023 3200319475328460015023 No Physiology Department, Faculty of Medicine, Tarbiat Modares University, Tehran, Iran Mehrdad Faizi faizi64@yahoo.com 3200319475328460015024 3200319475328460015024 No Pharmacology and Toxicology Department, Faculty of Pharmacy, Shahid Beheshti University of medical sciences, Tehran, Iran