The arginine vasopressin and corticotrophin‐releasing hormone gene transcription responses to varied frequencies of repeated stress in rats

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Abstract
1 Rats habituate to repeated exposure to homotypic stressors. The present studies were designed to define how altered frequency of exposure to a stressor affects the development of habituation and how this habituation is reflected in alterations in basal expression and responsiveness of hypothalamic corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) messenger and heteronuclear RNA (hnRNA). 2 Rats were exposed to a 60 min period of restraint stress every 7th day, every 3rd day, alternate days or daily for 2 weeks and their response to a final episode of stress on day 15 was compared with that of a control group of unstressed rats. 3 The response of plasma corticosterone to the final stressor on day 15 was diminished in animals which had been stressed on only two previous occasions, 7 days apart, and diminished further with increasing frequency of previous stressors until it failed to respond at all in animals stressed daily. 4 The pattern of CRH hnRNA and mRNA responses were similar, decreasing with increasing frequency of exposure to the stressor, while AVP mRNA responses increased in response to repeated stress. 5 The gradual emergence of increased AVP transcription at a time of diminishing CRH response suggests that repeated stress results in a specific facilitation of AVP gene expression, perhaps by impairment of corticosterone feedback.

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