ORIGINAL ARTICLES Cytokine Effects on Cortical Neuron MAP-2 Immunoreactivity: Implications for Schizophrenia Christine E. Marx, L. Fredrik Jarskog, Jean M. Lauder, Jeffrey A. Lieberman, and John H. Gilmore Background: Cytokines demonstrate diverse actions in the brain and modulate systemic and central nervous system (CNS) responses to injury, infection, and inflam- mation. Cytokines in the CNS are elevated during infection and ischemia, two neurodevelopmental insults associated with increased schizophrenia risk. We hypothesize that cytokine-mediated neuronal injury during development may contribute to schizophrenia pathophysiology, causing subtle alterations in neuronal number and density. Methods: We examined cytokine regulation of neuronal number in embryonic day 18 rat cortical cultures using MAP-2 immunohistochemistry. Mixed cultures derived from frontal cortex were fixed and stained after 48-hour exposure to the proinflammatory interleukin-1 (IL-1), interleukin-6 (IL-6), or tumor necrosis factor- (TNF-; 0, 10, 100, or 1000 units/mL). Results: IL-1 (maximum effect 35%) and IL-6 (maximum effect 29%) produced dose-dependent decreases in the number of cells (neurons) immunoreactive for MAP-2 antibody, suggesting decreased neuronal survival. TNF- also tended to decrease MAP-2 immunostaining at the highest dose tested. Conclusions: Our data suggest a role for cytokines in the modulation of neuronal survival during neurodevelop- ment, a finding potentially relevant to schizophrenia pathophysiology. If cytokine-mediated neuronal injury proves to be a common response to gestational insults associated with increased schizophrenia risk, the pharma- cologic modulation of these molecules may have clinical utility. Biol Psychiatry 2001;50:743–749 © 2001 Soci- ety of Biological Psychiatry Key Words: Cytokine, neuron, infection, hypoxia, neuro- development, schizophrenia Introduction C ytokines are low-molecular-weight proteins that me- diate immune system and inflammatory responses (Hopkins and Rothwell 1995). They are expressed by neuronal and glial elements in the central nervous system (CNS) and regulate normal and abnormal brain develop- ment (Mehler and Kessler 1997; Merrill 1992; Vitkovic et al 2000). Cytokines demonstrate diverse actions in the brain and modulate both systemic and CNS responses to injury, infection, and inflammation (Rothwell 1999). Cy- tokine expression in brain is generally low in the absence of a physiologic stressor, but levels increase markedly in the setting of infection, ischemia, trauma, or other CNS insults (Rothwell and Hopkins 1995; Van Wagoner and Benveniste 1999). Several lines of evidence indicate that cytokines may be important in schizophrenia. Specifically, proinflammatory cytokines such as interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor- (TNF-) may play a mechanistic role in the association between prenatal exposure to infection and schizophrenia (Gilmore and Jarskog 1997). Since the association between in utero exposure to infection and the development of schizophre- nia in adulthood does not appear to be limited to a single infectious agent, factors common to all infections such as cytokine activation may be relevant. Prior work supports this hypothesis and demonstrates that cytokines are altered in human pregnancies complicated by infection (Dam- mann and Leviton 1997; Romero et al 1989a, 1989b) and contribute to perinatal brain injury (Silverstein et al 1997). In addition, systemically generated maternal cytokines cross the placenta (Medlock et al 1993), and maternal infection alters placental and fetal brain cytokine expres- sion in rodents (Urakubo et al 2001). Since infection during early neurodevelopment increases schizophrenia risk, cytokine responses to this stressor may be relevant to the disorder. In addition to infection, IL-1, IL-6, and TNF- are also increased during CNS ischemia (Orzylowska et al 1999; Saito et al 1996) and appear to modulate ischemic injury (for review see, Gadient and Otten 1997; see also Barone et al 1997; Bruce et al 1996; Hara et al 1997; From the Departments of Psychiatry (CEM, LFJ, JAL, JHG) and Cell Biology and Anatomy (JML) and the Mental Health and Neuroscience Clinical Research Center (CEM, LFJ, JAL, JHG), University of North Carolina, Chapel Hill, North Carolina. Address reprint requests to Christine E. Marx, M.D., Assistant Professor, Depart- ment of Psychiatry and Behavioral Sciences, Duke University Medical Center, Durham VA Medical Center, Mental Health Service Line (116A), 508 Fulton Street, Durham, NC 27705. Received November 10, 2000; revised April 27, 2001; accepted May 24, 2001. © 2001 Society of Biological Psychiatry 0006-3223/01/$20.00 PII S0006-3223(01)01209-4