INTRODUCTION It has already been established that the functional state of the central nervous system changes under the influence of magnetic fields. This effect has been demonstrated on both systemic and cellular levels of the information processing in the central nervous system (Young, 1969; Õîëoäîâ, 1975; Õîëoäîâ è Øèøëî, 1979; Liburdy and Tenforde, 1986; Gustson et al., 1982; Gustsons, 1992; Ueno and Iwasaka, 1996). Most important, the selective effect of the two oppo- site directions of static magnetic field has been previously reported by Gustsons and his collaborators. Their data show that the magnetic field applications have prolonging or in- hibitory effects on brain functions, depending on the vector direction (Gustsons et al., 1982; Gustsons, 1992; Veliks et al., 2000) and possible effects of magnetic field on the com- ponents of biochemical reaction pathways. This includes the enzyme and substrate conformation change in response to the electrical charges on the aminoacids, and the changes of environmental conditions due to magnetic field applica- tion alter biochemical reactions in the brain on both solvent phase level as well as protein-membrane complex level (Schwartz, 1979; Easterly, 1982). Taking the above into account, the aim of this study was to evaluate the influence of static magnetic field on rat brain monoamine metabolism using bitemporally placed magnets with field intensity 250 mT. MATERIALS AND METHODS Animals. The acute experiments were carried out on 30 male Wistar population rats with weight 300–400 g (Breeding House of the Latvian State Pharmaceutical Com- pany “Grindex,” Latvia). Rats were taken directly from vi- varia to the place of experiment; they were kept under stan- dard conditions, and food (“Grindex,” Latvia) and water was given ad libitum. Rats were anaesthetised by intra- peritoneal (i.p.) injection of urethane (770 mg/kg (Shering- Kahlbaum A. G.), and i.p. injection of ketamine (30 mg/kg) mixed with xylasine (3.5 mg/kg) (both DOPHARMA). Thirty rats were divided into six parts by five animals per group: 1, without anaesthesia and static magnetic field (SMF) in- fluence (C2); 2, with anaesthesia, without SMF influence (C1); 3, with anaesthesia, SMF vector: right side of the head— south pole, left side of the head—North pole (rS-lN); 4, with anesthesia, SMF vector: right side of the head— north pole, left side of the head—South pole (rN-lS); 5, with anesthesia, SMF vector: right side of the head— south pole, left side of the head—South pole (rS-lS); PROCEEDINGS OF THE LATVIAN ACADEMY OF SCIENCES. Section B, Vol. 60 (2006), No. 1 (642), pp. 28–33. CHANGES OF MONOAMINE CONCENTRATION IN RAT BRAIN UNDER THE INFLUENCE OF A STATIC MAGNETIC FIELD Viktors Veliks* + , Pçteris Gustsons*, Gunita Praulîte*, Juris Aivars*, Ingvars Birznieks*, and Ðimons Svirskis** *Faculty of Biology, University of Latvia, Kronvalda bulv. 4, Rîga, LV-1586, LATVIA **Faculty of Medicine, University of Latvia, J. Asara ielâ 5, Rîga, LV-1009, LATVIA + E-mail: vicwell@hotmail.com Communicated by Henriks Zenkeviès The influence of a static magnetic field (SMF) on rat brain was performed by two bitemporally placed samarium–cobalt fused magnets 20×20×10 mm in size. The SMF was strictly symmetrical with magnetic induction intensity 250 mT on the surface of the magnets. Varying of magnetic poles on both sides of the head changed the direction of the magnetic induction vector. Tissue samples of different brain areas—frontal cortex, corpus striatum, hypothalamus, hippocam- pus—were examined to determine the concentrations of the following neurotransmitters: dopa- mine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), 3-metoxy-4-hydroxyphenylacetic acid (HVA), noradrenalin (NA), serotonin (5-HT), and 5-hydroxyindolaceatic acid (5-HIAA). The results suggested that the static magnetic field had an influence on brain monoamine metabolism; the ef- fectiveness of SMF application differed to various areas of brain and depended upon the direction of the magnetic field vector relative to the anatomic projection of brain structures. Key words: rat brain, static magnetic field, monoamine concentration. 28 Proc. Latvian Acad. Sci., Section B, Vol. 60 (2006), No. 1.