Differential effects of stable elevated levels of corticotropin-releasing hormone and systemic corticosterone on various types of rat learning.

OBJECTIVES

Stress activates the hypothalamic-pituitary-adrenal (HPA) axis. This activation is executed mainly through the release of corticosteroids from adrenal that subsequently exert negative feedback on corticosterone-releasing hormone (CRH) production. The effects of corticosterone on learning and memory has been studied intensively. Less is known about the effect of CRH on cognitive phenomena.

DESIGN AND SETTING

The present study aimed at studying the separate effects of stress cascade hormones, namely CRH and corticosterone, on learning and memory in a battery of learning tasks.

RESULTS

Long-term administration of CRH led to a transient impairment of spatial performance in the active allothetic place avoidance (AAPA) task requiring cognitive coordination, whilst co-application of CRH and corticosterone resulted in permanent impairment in this task. Corticosterone alone impaired the long-term retention of passive avoidance. CRH alone exerted no effect on the working memory version of the Morris water maze (MWM) and inhibitory avoidance.

CONCLUSIONS

Our results suggest differential effects of stress cascade hormones on various types of behavior.