Sensitization associated with stressors and cytokine treatments.

Like stressors, interleukin-1beta and tumor necrosis factor-alpha (TNF-alpha) increase hypothalamic-pituitary-adrenal (HPA) activity and monoamine turnover at hypothalamic and extrahypothalamic sites. These effects can be re-elicited more readily upon reintroduction of these challenges (sensitization), depending on their time of re-exposure and the particular system being assessed. Following TNF-alpha administration, the co-expression of corticotropin releasing hormone (CRH) and arginine vasopressin increased within the median eminence, peaking 7-14 days after treatment, and was associated with an early corticosterone sensitization. However, the re-elicitation of sickness symptoms and corticosterone release was most pronounced at lengthy re-exposure intervals (28 days), possibly reflecting histamine release from mast cells. In addition, the cytokine engendered the sensitization of norepinephrine and serotonin utilization, and CRH immunoreactivity at mesocorticolimbic sites, but these effects were most prominent at brief re-exposure intervals (1-7 days). Cytokines may independently prime multiple regulatory systems, and by virtue of the neurochemical changes imparted, have both immediate and proactive influences on the evolution of psychopathology.