Effects of Ketamine, MK-801, and Amphetamine on Regional Brain 2-Deoxyglucose Uptake in Freely Moving Mice Seiya Miyamoto, M.D., Ph.D., Jeremy N. Leipzig, B.S., Jeffrey A. Lieberman, M.D., and Gary E. Duncan, Ph.D. Although the pathophysiology of schizophrenia remains cortical regions, hippocampal formation, nucleus unclear, behavioral effects in humans induced by N-methyl- accumbens, select thalamic nuclei, and basolateral D-aspartate (NMDA) antagonists, such as ketamine, amygdala. The behavior of mice given amphetamine was provide direction for formulating new pharmacologic similar to that of mice given MK-801. However, the brain models of the illness. The purpose of the present study was activity patterns induced by amphetamine were distinctly to clarify the roles of NMDA receptor antagonism, as well different from those observed after ketamine and MK-801 as dopamine-releasing properties of ketamine, in regional treatment. These results suggest that generalized behavioral brain metabolic activity and behavioral responses in mice. activation and increased dopamine release are insufficient to The effects of acute administration of ketamine (30 mg/kg, i.p.) account for the ketamine-induced alterations in regional were compared with those of the more selective non- brain metabolism, and that the effects of ketamine on 2-DG competitive NMDA antagonist MK-801 (0.3 and 0.5 mg/ uptake are likely related to a reduction in NMDA receptor kg, i.p.), and amphetamine (4 mg/kg, i.p.) on regional brain function. The data also suggest that ketamine-induced [14C]-2-deoxyglucose (2-DG) uptake, by using a high changes in 2-DG uptake may provide a useful paradigm for resolution autoradiographic technique in the freely moving translational research to better understand the mice. Both ketamine and MK-801 induced substantial and pathophysiology of schizophrenia. similar neuroanatomically selective alterations in regional [Neuropsychopharmacology 22: 400–412, 2000] 2-DG uptake. Remarkable increases in 2-DG uptake in © 2000 American College of Neuropsychopharmacology. response to the NMDA antagonists were seen in limbic Published by Elsevier Science Inc. KEY WORDS: Ketamine; Animal model; Schizophrenia; Although the etiology and pathophysiology of schizo- NMDA antagonist; Limbic cortex; Mice phrenia have not yet been elucidated, consistent clinical observations associated with a pharmacological chal- lenge with N-methyl-D-aspartate (NMDA) antagonists provide direction for formulating new pharmacological From the Department of Psychiatry, Pharmacology and UNC models of the illness. Since the late 1950s, phenylcycli- Mental Health and Neuroscience Clinical Research Center, School of Medicine (SM, JNL, JAL, GED), The University of North Carolina dine (PCP), a potent non-competitive NMDA antago- at Chapel Hill, Chapel Hill, NC 27599. nist, has been known to induce psychotic symptoms in Address correspondence to: Seiya Miyamoto, M.D., Ph.D. healthy humans that resemble some features of schizo- Department of Psychiatry, CB#7160 The University of North Caro- lina at Chapel Hill, Chapel Hill, NC 27599-7160, USA. Tel.: 919-966- phrenia (Luby et al. 1959; Davies and Beech 1960; Bak- 8237; Fax: 919-966-8994; E-mail: [email protected] ker and Amini 1961; Allen and Young 1978; Javitt and NEUROPSYCHOPHARMACOLOGY 2000–VOL. 22, NO. 4 © 2000 American College of Neuropsychopharmacology Published by Elsevier Science Inc. 0893-133X/00/$–see front matter 655 Avenue of the Americas, New York, NY 10010 PII S0893-133X(99)00127-X NEUROPSYCHOPHARMACOLOGY 2000–VOL. 22, NO. 4 NMDA Antagonist-induced Brain Metabolic Changes 401 Zukin 1991). Recently, it has been shown that subanes- 1991), monoaminergic systems (Ylitalo et al. 1976; Smith et thetic doses of ketamine, a non-competitive NMDA re- al. 1981; Irifune et al. 1991, 1997; Lindefors et al. 1997), and ceptor antagonist, can induce positive, negative, and cholinergic systems (Cohen et al. 1974; Scheller et al. 1996). cognitive schizophrenia-like symptoms in normal hu- The potency of ketamine at opiate, sigma, monoaminergic, mans (Krystal et al. 1994; Malhotra et al. 1996, 1997; and cholinergic receptors is considerably lower in com- Breier et al. 1997, 1998; Adler et al. 1998; Krystal et al. parison to NMDA antagonistic properties of the drug 1998; Newcomer et al. 1999). In chronic stabilized (Smith et al. 1980; Øye et al. 1991). However, exactly schizophrenic patients, subanesthetic doses of ketamine which molecular mechanisms mediate the effect of ket- can exacerbate cognitive impairment and induce posi- amine on behavior and regional brain metabolic activity tive psychotic symptoms that mimic the active episodes remains unclear. Thus, one purpose of the present study of their illness (Lahti et al. 1995a, 1995b; Malhotra et al. was to clarify the role of NMDA receptor antagonism in 1997). These clinical findings have led to the hypothesis ketamine-induced alterations in brain metabolic patterns that hypofunction of NMDA receptors in the central in mice, by comparing the effects of ketamine with the nervous system (CNS) is involved in the pathophysiol- more selective NMDA antagonist MK-801. ogy of schizophrenia (Deutsch et al. 1989; Olney 1989; NMDA antagonists, including ketamine and MK-801, Javitt and Zukin 1991; Ulas and Cotman 1993; Olney increase dopamine metabolism and release in several and Farber 1995; Coyle 1996; Jentsch and Roth 1999). brain regions in rodents (Doherty et al. 1980; Rao et al. The well-documented psychotomimetic effects of 1989; Wędzony et al. 1993; Hondo et al. 1994; Verma and NMDA antagonists in humans suggest that effects of the Moghaddam 1996; Irifune et al. 1997; Lindefors et al. drugs in experimental animals could represent useful 1997; Adams and Moghaddam 1998; Irifune et al. 1998). pharmacological models of schizophrenia. In our recent Activation of dopaminergic systems may participate in studies, striking effects of subanesthetic doses of ketamine certain behavioral effects induced by NMDA antago- were observed on regional patterns of 14C-2-deoxyglucose nists, since behavioral responses to NMDA receptor an- (2-DG) uptake in the rat brain (Duncan et al. 1998a, 1998b, tagonists are, at least in part, suppressed by dopamine 1999). Administration of subanesthetic doses of ketamine receptor antagonists in rats and mice (Corbett et al. to rats increased 2-DG uptake in neuroanatomically spe- 1995; Irifune et al. 1995; Lapin and Rogawski 1995; cific brain regions (Duncan et al. 1998a, 1999). Ketamine- Verma and Moghaddam 1996). To determine the in- induced metabolic activation was blocked by the atypical volvement of dopamine-releasing properties of keta- antipsychotic drug clozapine, but not by the typical anti- mine and MK-801 on regional 2-DG uptake, effects of psychotic haloperidol (Duncan et al. 1998b). Therefore, de- these drugs were compared to those of amphetamine, fining neurochemical mechanisms responsible for the which is well known to robustly induce dopamine re- brain metabolic effects induced by ketamine in laboratory lease (Snyder et al. 1972; Zetterstrom et al. 1983; Car- animals could suggest potential pathophysiological mech- boni et al. 1989; Kuczenski and Segal 1989). Comparison anisms in schizophrenia and pharmacotherapeutic actions of the effects of amphetamine with those of ketamine of atypical antipsychotic drugs. and MK-801 also allows assessment of the role of general- Studies of the effects of NMDA antagonists such as ized behavioral arousal and increased locomotor activity ketamine on brain 2-DG uptake have been limited to rats after 2-DG uptake induced by the NMDA antagonists. (Hawkins et al. 1979; Nelson et al. 1980; Crosby et al. 1982; Oguchi et al. 1982; Hammer and Herkenham 1983; Davis et al. 1988; Kurumaji et al. 1989; Duncan et al. 1998a, MATERIALS AND METHODS 1998b, 1999). The availability of transgenic mice deficient Animals in specific dopamine, serotonin, or NMDA receptor sub- units may present an opportunity to define neurochemical Twenty-six male ICR mice (Harlan Laboratories) weigh- mechanisms of ketamine-induced metabolic responses ing 37–49 g were used. The mice were housed under a 12 and effects of antipsychotic drugs in the 2-DG-ketamine h light-dark cycle with lights on at 0700 h and had contin- challenge model. For example, the paradigm of NMDA uous access to food and water. All animal use procedures antagonist-induced alterations in brain 2-DG uptake in were in strict accordance with the National Institute of transgenic mice could be a useful tool to explore the po- Health (NIH) Guide for the Care and Use of Laboratory tential involvement of individual neurotransmitter recep- Animals and were approved by the University of North tor subtypes in the mechanisms of action of antipsychotic Carolina Institutional Animal Care Committee. drugs, as well as ketamine itself. The goal of the present study was to characterize the neurobiological responses High Resolution Autoradiographic Analysis of to NMDA antagonist administration in mice. 14C-2-DG Uptake While ketamine has well-documented NMDA receptor antagonistic properties, the drug has a number of other The high-resolution autoradiographic procedures for pharmacological actions in the CNS. Ketamine acts on opi- analysis of [14C]-2-deoxyglucose (2-DG) uptake were ate receptors (Smith et al. 1980), sigma receptors (Øye et al. performed according to the method described previ- 402 S. Miyamoto et al. NEUROPSYCHOPHARMACOLOGY 2000–VOL. 22, NO. 4 ously (Duncan and Stumpf 1990, 1991; Duncan 1992) Happauge NY) and quantified using NIH Image Soft- with the following slight modifications. Mice were ware. The optical densities in autoradiograms were in transported from the animal quarters to the laboratory the linear range of the film as assessed in relation to 14C- and singly housed for 3 h before initiation of the 2-DG standards (Amersham Microscale). Data are expressed experiment. Mice exhibited minimal locomotor activity as ratios of optical density in gray matter regions rela- after this habituation period. Ketamine (30 mg/kg), tiveto that in the corpus callosum as previously de- MK-801 (0.3 or 0.5 mg/kg), amphetamine (4 mg/kg), or scribed (Duncan et al.