Protective role of melatonin in pinealectomized rat brains: in vivo magnetic resonance spectroscopic analysis Introduction Melatonin, the pineal secretory product, is known to possess free radical scavenging properties [1, 2]. It also activates several antioxidative enzymes, modulates the expression of several protective enzymes, and reduces peroxidation of lipids [3]. Melatonin is a lipophilic agent, and it easily permeates through biologic membranes within minutes after peripheral administration. This gives an advantage to mela- tonin over other antioxidants which has a slower penetration [4]. Melatonin exhibits a diurnal variation and its level declines with the advance of age [5, 6]. The reduction in circulating melatonin levels during aging is consequential with the accelerated accumulation of oxidatively mutilated products late in life [7]. However the exact levels required for the prevention of oxidative damage, which also accumulates with the advance of age, remains unknown. Proton magnetic resonance spectroscopy (MRS) allows in vivo measurements of various neurochemicals and it provides information on metabolic processes and the cellular composition of the brain [8]. N-acetyl aspartate (NAA), choline (Cho) and creatine (Cr) are the major metabolites in the MRS spectra. NAA is generally recognized as a marker of functional neurons. It is reduced in many neurologic diseases, suggesting neuronal injury and death [9]. Cr is considered an indicator of brain energy metabolism [10]. As its level is quite constant under various metabolic conditions, it is used as an internal standard to which resonance intensities of other com- pounds are normalized. Cho plays an important role in the structure and biochemical activity of the cell membranes and it is a marker for the cell membrane and the myelin sheath [11]. It is elevated following demyelinization pro- cesses or gliosis. It is known that estrogen could not protect women from the normal decline in cognitive functions [12]. Combined estrogen–progestin therapy also fails to prevent mild cognitive impairment in postmenopausal women aged 65 yr or older [13]. There are several reports on the possible modulating effects of melatonin. Yun et al. [14] have reported a contribution of pineal involution to plasticity decay. Therefore, melatonin may modulate cognitive plas- ticity, independent of the effects of sex steroids, and low sex steroids and high melatonin may simultaneously be required to maintain cognitive plasticity. However, to date no one has investigated the effects of pinealectomy on basic cerebral metabolites. We therefore investigated the effect of pinealectomy and subsequent melatonin supplementation on rat brain using MRS. Materials and methods Experimental conditions Twenty-one female Wistar rats, aged 6–8 wk, weighing 150–200 g were kept in a temperature (21 ± 2°C) and humidity (60 ± 5%) controlled room. A 12:12-hr light and dark cycle was maintained. Food and water were available ad libitum. During the surgical procedure, aseptic condi- tions were maintained by providing a local sterile environ- ment. The rats were divided into three groups of seven rats per group as follows: (i) pinealectomized rats (Px); (ii) Px + melatonin-treated rats; (iii) sham-operated rats (non-Px). Abstract: The goal of this study was to investigate the effect of melatonin on basic cerebral metabolites in pinealectomized (Px) rat brains. Twenty-one rats were randomly divided into three groups with seven rats per group. The study groups included sham-operated rats, Px rats and Px rats treated with melatonin. Melatonin administration began at 60 days following pinealectomy and continued for 21 days. At the end of the study, in vivo single voxel magnetic resonance spectroscopy was performed on whole brains to determine choline (Cho), creatine and N-acetyl aspartate (NAA) concentrations. Px rats had significantly lower NAA levels (P < 0.05), and significantly higher Cho levels (P < 0.05) when compared with sham- operated rats. Administration of melatonin had normalized NAA and Cho levels in Px rats. We propose that pinealectomy causes significant changes in cerebral metabolites which are compatible with neural loss. Melatonin administration prevents the disruptive effects of pinealectomy on brain tissue. Seyma Hascalik 1 , Onder Celik 1 , Hakki Muammer Karakas 2 , Hakan Parlakpinar 3 , Ahmet K. Firat 2 and Murat Ozsahin 1 Departments of 1 Obstetrics and Gynecology, 2 Radiology, and 3 Pharmacology, Inonu University Medical Faculty, Malatya, Turkey Key words: antioxidants, magnetic resonance spectroscopy, melatonin, pinealectomy, rat brain Address reprint requests to Seyma Hascalik, Inonu University, Turgut Ozal Medical Center, Department of Obstetrics and Gynecology, 44069, Malatya, Turkey. E-mail: shascalik@inonu.edu.tr Received February 28, 2005; accepted May 10, 2005. J. Pineal Res. 2005; 39:342–345 Doi:10.1111/j.1600-079X.2005.00255.x Copyright Ó Blackwell Munksgaard, 2005 Journal of Pineal Research 342