DIFFERENTIAL EFFECTS OF PHARMACOLOGICAL AND PHYSICAL STRESS ON CHECKING BEHAVIOUR IN RATS

Compulsive checking is a core feature of obsessive–compulsive disorder (OCD), yet the contribution of stress and stress-related systems to checking behaviour remains poorly understood. We investigated how distinct forms of stress influence functional and dysfunctional checking using the Observing Response Task in male rats. Two complementary studies were conducted (n = 24 each). In the first, pharmacological stressors targeting different stages of the stress response were administered: yohimbine, which enhances noradrenergic signalling via presynaptic α2 antagonism; clenbuterol, a β2-adrenergic receptor agonist; and the end-product hormone corticosterone. Preliminary analyses revealed that yohimbine robustly increased active lever pressing in a dose- and session-dependent manner, while leaving inactive responding unchanged. In contrast, observing (checking) responses, proportional checking measures, and task accuracy remained stable across doses and sessions. Clenbuterol produced broad behavioural suppression consistent with malaise, and corticosterone did not induce significant behavioural changes. In a second study, exposure to unpredictable footshocks increased active lever pressing and reduced checking responses, with effects observed following both acute and repeated stress exposure. Together, these findings show that stress robustly alters reward-directed responding, but does not act as a general driver of checking in this task. While pharmacological and physical stressors produced convergent increases in active responding, their effects on checking differed, with physical stress reducing checking responses. These differential effects suggest that checking behaviour is sensitive to features of the stressor beyond general physiological activation.