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.

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