Physical and emotional stress have differential effects on preference for saccharine and open field behaviour in rats

Stress may influence the sensitivity of subjects to rewarding stimuli and stress modality may differentially affect this sensitivity. This relation was investigated in our animal model using chronic physical (repeated mild foot shocks) and emotional (witness) stress. Previous research has established that the two stressors have differential long-term effects on behaviour, where physical stress caused inactivity in a small open field and emotional stress hyperactivity. Rats were stressed on 5 consecutive days and tested for locomotor activity in a small open field (day 10) and saccharine preference (day 11). The preference for graded concentrations of saccharine over water was used as a measure for their sensitivity to reward. Physical stress treatment induced a long-term decrease both in preference for saccharine and open field activity compared to control treatment. Emotional stress animals showed an increase in open field behaviour activity and a slight increase in saccharine preference. Physical stress seems to cause anhedonia, while emotional stress might cause an increased sensitivity to reward. In conclusion, stress can induce differential long-term effects on sensitivity to positive stimuli and the response to novelty depending on stress modality.