Open field test. (A) The open field with a floor divided into 16 squares to measure motor activity and exploration. (B) Number of fields entered during a test session. (C) Activity score in control, stress and corticosterone-treated animals prior to treatment (baseline), after 16 days of treatment (pre-lesion) and 28 days after unilateral 6-OHDA lesion (post-lesion). Note that the 6-OHDA lesion reduced locomotor activity in all animals; however, chronic stress and CORT treatment significantly increased exploratory activity as compared with untreated control animals. Asterisks indicate significant differences: *P = 0.05, ***P = 0.001, t-test compared with control animals.