Cytokine effects on cortical neuron MAP-2 immunoreactivity: implications for schizophrenia

Cytokines demonstrate diverse actions in the brain and modulate systemic and central nervous system (CNS) responses to injury, infection, and inflammation. 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.

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-1beta (IL-1beta), interleukin-6 (IL-6), or tumor necrosis factor-alpha (TNF-alpha; 0, 10, 100, or 1000 units/mL).

IL-1beta (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-alpha also tended to decrease MAP-2 immunostaining at the highest dose tested.

Our data suggest a role for cytokines in the modulation of neuronal survival during neurodevelopment, 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 pharmacologic modulation of these molecules may have clinical utility.