insides of the boxes were wiped with a damp sponge and the litter paper beneath the floors was changed between animals. The main principles of CPP have been described earlier (Cunningham, 1993). Briefly, the place-conditioning study involved one habituation session, eight conditioning sessions, and one test session. No pretest sessions were used. A 2-d weekend break occurred between the first four and last four conditioning sessions. For the habituation session, mice received an injection of saline immediately before being placed in the conditioning box for 30 min on a smooth metal plate covering the floor. During the habituation session, both compartments were available for the mice. The purpose of the habituation session was to reduce the stress associated with the novelty of experimental procedures and exposure to the apparatus. Mice were not exposed to the distinctive floor textures to avoid latent inhibition. For conditioning, mice of each of two pretreated (saline or LPS) groups were randomly assigned to one of two conditioning subgroups, GRID + or GRID−, and exposed to a Pavlovian differential conditioning procedure. On alternating days, mice in the GRID + group received an injection of ethanol (2 g/kg, i.p.) immediately before a 5-min session on the grid
