RELATIONSHIPS BETWEEN STRESS-INDUCED INCREASES IN MEDIAL PREFRONTAL CORTICAL DOPAMINE AND PLASMA-CORTICOSTERONE LEVELS IN RATS - ROLE OF CEREBRAL LATERALITY

In the present study, in vivo voltammetry was used to monitor changes in dopamine levels in the left and right medial prefrontal cortex of r ats exposed to mild physical and psychological stress. These were 2 mi n of tail-pinch and 15 min exposure to cat odour, respectively. Fourte en male Long-Evans rats with bilateral carbon fibre recording electrod es were tested on four consecutive days, and records obtained in each medial prefrontal cortex for each stressor. A week later, animals unde rwent a 20 min restraint stress, with plasma samples taken at 0, 20 an d 80 min to determine stress-induced corticosterone responses. It was found that dopamine responses to tail-pinch were significantly longer- lasting in the left hemisphere than in the right, while this asymmetry was not present for the dopamine response to cat odour. Stress-induce d dopamine increases elicited by the two stressors were significantly correlated only in the right medial prefrontal cortex. Restraint stres s-induced increases in plasma corticosterone were positively correlate d with dopaminergic responses to tail-pinch, but were only related to dopamine cat odour responses when individual asymmetries favoured the right medial prefrontal cortex. The data suggest that asymmetric mesoc ortical dopamine activation depends on the type of stress, and that re gulation of dopamine responses to both types of stress is most tightly coupled in the right hemisphere. While neuroendocrine and dopaminergi c stress responses are positively linked, this relationship is only as ymmetrical for the psychological stressor, suggesting a specialized ro le for right cortical mechanisms in the integration of emotional and p hysiological responses to stressful situations. A preliminary report o f this work was presented at the Society for Neuroscience meeting in W ashington DC, November, 1996.(76) (C) 1997 IBRO. Published by Elsevier Science Ltd.