Effects of bacterial superantigens on behavior of mice in the elevated plus maze and light–dark box Alba Rossi-George, Fred LeBlanc, Takehiro Kaneta, Daniella Urbach, and Alexander W. Kusnecov * Department of Psychology, Biopsychology and Behavioral Neuroscience Program, Rutgers, The State University of New Jersey, Piscatway, NJ, USA Received 9 March 2003; received in revised form 19 April 2003; accepted 29 April 2003 Abstract Bacterial superantigens, such as staphylococcal enteroxins A and B (SEA/SEB) stimulate T cells to produce high levels of cy- tokines in blood. Previously it had been shown that these toxins were capable of stimulating increased neuroendocrine activity and enhanced behavioral reactivity to novel gustatory and non-gustatory stimuli. Therefore, it was suggested that these superantigens may promote anxiety-like behavior. In the current set of experiments, BALB/cByJ and C57BL/6J male mice were challenged with either SEB (50 lg) or SEA (5 or 10 lg) and tested for behavior in the elevated plus maze (EPM). Results suggested an absence of increased anxiety-like behavior, with exploration of the open arms being enhanced by SEA or SEB treatment. In another test of anxiety, the light–dark box, SEB challenge of BALB/cByJ mice 90 min prior to testing, did not alter exit latency, activity nor time spent in the dark. However, in a second experiment, it was found that if animals were first tested for consumption, followed by testing in the light–dark box, SEB challenged animals displayed increased exit latency and reduced exploration. These studies suggest that in standard tests of rodent anxiety-like behavior, evidence for the induction of anxiety-like processes subsequent to challenge with SEA or SEB is not patently discernable. However, neurobiological events induced by immunological challenge might synergize with reactivity to psychogenic and/or gustatory stimuli, thereby resulting in increased anxiety-like behavior that could be unmasked by standard behavioral tests such as the light–dark box or EPM. Ó 2003 Elsevier Science (USA). All rights reserved. 1. Introduction Superantigens (SAg) are viral and bacterial proteins that have received considerable attention in terms of their strong T cell stimulating effects and the promotion of pathophysiological conditions, including septic shock and autoimmune disease (Herman et al., 1991; Llewelyn and Cohen, 2002; Macphail, 1999). The best studied of these SAg are the enterotoxins produced by the gram positive bacteria Staphylococcus aureus, and in particu- lar, the staphylococcal enterotoxins A and B (SEA/SEB) (Llewelyn and Cohen, 2002). As T cell stimuli, SEA and SEB are unique in that T cell activation proceeds inde- pendently of intracellular digestion by antigen process- ing cells (APC), albeit still involving MHC Class II molecules (Dellabona et al., 1990; Yagi et al., 1991). Ultimately, however, T cell activation occurs via the T cell receptor (TCR) (Hong et al., 1996). In animal studies involving challenge with SEA or SEB, this in- teraction has been shown to result in rapid cytokine gene induction, and appearance of measureable levels of plasma TNF and IL-2 within 1–2 h of administration (Bette et al., 1993; Sundstedt et al., 1994). Expanding on the initial observations by Gonzalo et al. (1993) of increased corticosterone production following SEA or SEB treatment, it has been firmly established that consequent to administration of these bacterial superantigens to mice and rats, there are sig- nificant alterations in endocrine, neurobiological, and behavioral functions (Goehler et al., 2001; Gonzalo et al., 1993; Kawashima and Kusnecov, 2002; Kawashima et al., 2002; Kusnecov et al., 1999). For instance, chal- lenge of BALB/cByJ mice with SEB stimulates the HPA axis, resulting in increased plasma levels of ACTH and BRAIN, BEHAVIOR, and IMMUNITY www.elsevier.com/locate/ybrbi Brain, Behavior, and Immunity 18 (2004) 46–54 * Corresponding author. Fax: 1-732-445-2263. E-mail address: kusnecov@rci.rutgers.edu (A.W. Kusnecov). 0889-1591/$ - see front matter Ó 2003 Elsevier Science (USA). All rights reserved. doi:10.1016/S0889-1591(03)00087-4