Single administration of interleukin-1 increased corticotropin releasing hormone and corticotropin releasing hormone-receptor mRNA in the hypothalamic paraventricular nucleus which paralleled long-lasting (weeks) sensitization to emotional stressors

Single exposure to the proinflammatory cytokine interleukin-1 induces sensitization of the adrenocorticotropin hormone and corticosterone responses to stressors weeks later (hypothalamus-pituitary-adrenal sensitization). Hypothalamus-pituitary-adrenal responses are controlled by corticotropin-releasing hormone and arginine-vasopressin secreted from parvocellular corticotropin-releasing hormone neurons of the hypothalamic paraventricular nucleus and may involve autoexcitatory feedback mechanisms. Therefore, we studied the temporal relationship between resting levels of corticotropin-releasing hormone, corticotropin-releasing hormone-R1 and arginine-vasopressin receptor (V1a, V1b) mRNAs in the paraventricular nucleus and the development of hypothalamus-pituitary-adrenal sensitization to an emotional stressor (novelty). The adrenocorticotropin hormone precursor molecule proopiomelanocortin hnRNA in the pituitary gland served as an index for acute activation. Single administration of interleukin-1 induced sensitization of the hypothalamus-pituitary-adrenal to novelty from 3 to 22 days later, but not after 42 days. Single administration of interleukin-1 induced biphasic increases in corticotropin-releasing hormone and corticotropin-releasing hormone-R1 mRNAs in the paraventricular nucleus: an early peak within 24 h, followed by a delayed (>7 days) increase that peaked after 22 days. Hypothalamic V1a and V1b mRNA levels were unaffected. In contrast, in the pituitary gland, there was an early decrease in corticotropin-releasing hormone-R1 mRNA (from 10.5 to 3 h after interleukin-1) and V1b receptor mRNA (3 to 6 h), which returned to control levels from 24 h onwards. Thus, interleukin-1-induced long-lasting hypothalamus-pituitary-adrenal sensitizations associated with prolonged activation of corticotropin-releasing hormone and corticotropin-releasing hormone-R1 mRNA expression in the paraventricular nucleus, but not with changes in the expression of proopiomelanocortin hnRNA or V1b receptor or corticotropin-releasing hormone R1 mRNAs in the pituitary gland. We propose that transient exposure to immune events can induce long-lasting hypothalamus-pituitary-adrenal sensitization, which at least in part involves long-term hypothalamic adaptations that enhance central corticotropin-releasing hormone signaling.