European Neuropsychopharmacology 13 (2003) 369–380 www.elsevier.com / locate / euroneuro Behavioural changes after different stress paradigms: prepulse inhibition increased after physical, but not emotional stress a b b b Femke T.A. Pijlman , Arnoud H.J. Herremans , Jan van de Kieft , Chris G. Kruse , a, * Jan M. van Ree a Rudolf Magnus Institute for Neurosciences, Department of Pharmacology and Anatomy, UMC Utrecht, The Netherlands b Solvay Pharmaceuticals, Weesp, The Netherlands Received 2 April 2002; received in revised form 18 December 2002; accepted 24 January 2003 Abstract Physical (PS) and emotional (ES) stress have opposite long-term effects on open field behaviour, i.e., response to novelty. PS induced a long-term reduction in locomotor activity, while ES increased it. Additionally, sensitivity to rewarding stimuli was differentially affected by PS and ES. Whether the stress effects were specific for locomotor activity and reward or if these two stress treatments also have differential effects on other behaviours and brain functions is not known. In the present study, temperature regulation, sensory gating, learning capacity, locomotor activity and coping style were examined. PS consisted of a repeated mild foot shock treatment, which the ES animals witnessed. The tests pose additional challenges, to which all groups can respond differently depending on their previous experience. All tests were performed several days after the last stress treatment. Stress effects were specifically observed on locomotor activity, startle response and prepulse inhibition (PPI). The PS animals showed a potentiated inhibition of the startle when a prepulse (PPI) was used, although the initial startle response was already significantly lower than that of controls. ES animals did not differ from controls on PPI and startle. Additionally PS animals showed an initial decrease in activity, which turned into an increase when the tests continued. ES showed a constant increase in activity compared to controls. Stress effects on the tests for other brain processes and behaviour were not found. In addition, PS animals appeared to be less sensitive to the dopamine agonist apomorphine than control animal. In summary, physical and emotional stress induce differential changes on locomotor activity, startle response and PPI. Underlying mechanisms explaining the differences in stress effects are discussed, i.e., the role of the mesolimbic dopamine system and opioid systems.  2003 Elsevier B.V./ECNP. All rights reserved. Keywords: Stress; Prepulse inhibition; Dopamine; Locomotor activity; Animal 1. Introduction able to see, hear and smell the foot shock rat. Control animals (CON) were placed in the same boxes in pairs, Physical and emotional stress have opposite long-term without receiving any treatment. After the animals were effects on open field behaviour, i.e., response to novelty chronically stressed, a long-term change in open field ( Van den Berg et al., 1998; Pijlman et al., 2002). Physical behaviour was observed. Physical stress decreased stress (PS) consisted of a repeated mild foot shock locomotor activity and active exploration behaviours and treatment, which the emotional stress (ES) animals witnes- increased immobility. Emotional stress induced an increase sed. ES animals received no further treatment, but were in locomotor activity and exploration ( Van den Berg et al., 1998; Pijlman et al., 2002). Additionally, sensitivity to rewarding stimuli was differentially affected by PS and *Corresponding author. Rudolf Magnus Institute for Neurosciences, ES. PS reduced preference for saccharine, while ES Department of Pharmacology and Anatomy, P.O. Box 85060, 3508 AB increased saccharine preference and initiation of cocaine Utrecht, The Netherlands. Tel.: 131-30-253-8847; fax: 131-30-253- and morphine self-administration ( Ramsey and Van Ree, 8155. E-mail address: j.m.vanree@med.uu.nl (J.M. van Ree). 1993; Kuzmin et al., 1996; Pijlman et al., 2003). Whether 0924-977X / 03 / $ – see front matter  2003 Elsevier B.V./ECNP. All rights reserved. doi:10.1016 / S0924-977X(03)00040-3