Behavioural Brain Research 217 (2011) 240–243 Contents lists available at ScienceDirect Behavioural Brain Research journal homepage: www.elsevier.com/locate/bbr Short communication Glutamate microinjection at the medial preoptic area enhances slow wave sleep in rats Mahesh K. Kaushik a , Velayudhan Mohan Kumar b , Hruda Nanda Mallick a,∗ a Department of Physiology, All India Institute of Medical Sciences, Ansari Nagar, New Delhi 110029, India b Department of Neurology, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum 695011, India article info Article history: Received 25 September 2010 Received in revised form 21 October 2010 Accepted 1 November 2010 Available online 9 November 2010 Key words: Sleep–wakefulness Medial preoptic area Glutamate Microinjection abstract A large body of evidence has established the role of the medial preoptic area (mPOA) in regulation of slow wave sleep (SWS). Although the mPOA neurons contain excitatory neurotransmitter glutamate, its role in sleep–wakefulness is not known. In the present study microinjection of monosodium glutamate (40, 80 and 120 ng) into the mPOA augmented SWS. Earlier reports have shown enhancement of paradoxical sleep by glutamate in other brain areas. © 2010 Elsevier B.V. All rights reserved. Glutamate is the major excitatory neurotransmitter in the cen- tral nervous system. Intracerebral injection of glutamate agonists at various brain areas has been shown to alter sleep and wakefulness. Application of glutamate agonist kainate in the peri-locus coeruleus alpha in cats produced marked increase in rapid eye movement (REM) sleep [20]. The microinjection of glutamate into the pedun- culopontine tegmentum in the brain stem induces REM sleep and wakefulness in the rats depending on the amount injected [5,8,9]. Perfusion of glutamate at the basal forebrain increased subsequent sleep, which was attributed to resultant increase in adenosine level [22]. Glutamatergic stimulation of perifornical hypothalamus results in increased arousal [1]. The glutamate level in nucleus accumbens decreases during both slow wave sleep (SWS) and REM sleep [16]. Increase in glutamate level has been found in the nucleus magnocellularis during REM sleep [15]. The medial preoptic area (mPOA) is the key neural structure involved in the regulation of sleep, besides the regulation of many other physiological functions [6,7,11,12,14,18,19]. Presynaptic but- tons of the preoptic area contain large concentrations of glutamate [4]. The glutamate terminals at the mPOA have been suggested to have a role in endocrine functions [4,17]. The glutamate level in the mPOA has been shown to increase during wakefulness and decrease during SWS [2]. Although the role of mPOA in initiation and main- tenance of SWS is well documented, information about the role of glutamate at this area in sleep is lacking and needs investigation. ∗ Corresponding author. Tel.: +91 11 26594881; fax: +91 11 26588663/641. E-mail address: drhmallick@yahoo.com (H.N. Mallick). The study was conducted on 18 adult male Wistar rats, weigh- ing between 180 and 220 g, divided equally into three groups. These animals were obtained from the experimental animal facility of All India Institute of Medical Sciences, New Delhi, India. The rats were kept in individual cages at ambient temperature of 24 ± 1 ◦ C with 14 h light and 10 h dark, and lights on from 6:00 AM. Food and water were provided ad libitum. All procedures were conducted in accordance with the rules of the Committee for the Purpose of Control and Supervision of Experiments on Animals (CPCSEA), India and approved by the Institutional Animal Ethics Commit- tee, AIIMS, New Delhi, India. The rats were chronically implanted with electroencephalogram (EEG), electromyogram (EMG) and electrooculogram (EOG) electrodes, under sodium pentobarbitone anaesthesia (40 mg/kg BW, i.p.), for the assessment of sleep- wakefulness (S-W). A bilateral stainless steel guide cannulae, with indwelling styli, was stereotaxically implanted, 2 mm above the mPOA (A – 7.8, L – 0.6 and – 1.0 mm as per DeGroots atlas) [10]. The assembly was then fixed to the skull using dental acrylic. After seven days post-operative recovery, the rats were allowed to get habituated to the recording chamber with connected cables for at least 24 h. S-W parameters were recorded four times (on alternate days) on each animal for 6 h (10:00–16:00 h), using 6- channel Grass polygraph (Grass Instrument Co., Quincy, USA). During the fourth recording, the l-glutamate (Sigma, St. Louis, USA), in doses of 40, 80 or 120 ng, dissolved in 200 nl of 0.9% saline, was bilaterally injected slowly into the mPOA in rats belong- ing to three groups, as per the technique described earlier [21]. Drugs were injected at 12:00 h, and recordings were discontinued from 12:00 to 12:15 h (during which time the injection proce- 0166-4328/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.bbr.2010.11.007