Interleukin‐1β stimulates tyrosine hydroxylase activity in the median eminence

The effects of intracerebroventricularly (i.c.v.) injected interleukin-1 beta (IL-1 beta) on tyrosine hydroxylase (TH) activity in the median eminence and on serum adrenocorticotropin hormone (ACTH) and prolactin (PRL) levels were studied in freely moving male rats chronically implanted with i.c.v. cannulas. IL-1 beta stimulated TH activity of the median eminence in a dose-dependent manner. Intracerebroventricular injections of 100 ng and 200 ng IL-1 beta significantly increased TH activity in the median eminence by 40.6% and 74.7% respectively over the saline-injected control group. The stimulation of ACTH secretion was statistically significant for all doses used, however i.c.v. injections of IL-1 beta failed to elicit significant changes in the serum PRL concentrations. These results suggest that IL-1 beta increases dopaminergic activity of the medial basal hypothalamus to produce its neuroendocrine effects.