Effect of intracerebroventricular injection of lipopolysaccharide on the tuberoinfundibular dopaminergic system of the rat.

Numerous studies indicate that monoaminergic systems are sensitive to both peripheral and central inflammatory stimuli, and in particular dopaminergic neurons in the nigrostriatal system degenerate after local injection of lipopolysaccharide (LPS). However, data about the response of other dopaminergic groups to local inflammation are very sparse. In this study, we have examined the effect of i.c.v. injection of LPS on the tuberoinfundibular dopaminergic (TIDA) system by using biochemical and morphological parameters. Our results show that 6 h after i.c.v. injection of LPS, in parallel to a transient and intense immunoreaction to interleukin-1beta in arcuate microglial cells, there is a decrease in tyrosine hydroxylase (TH) activity in the median eminence and in the number of TH- and TH mRNA-positive cells in the arcuate nucleus, and at 12 h, an increase of prolactin levels in serum. Posterior changes were found in the TH mRNA labeling pattern, mostly in the ventrolateral region of the arcuate nucleus, but they were not accompanied by any changes in TH activity and immunoreactivity and TH-cell count. This suggests that the TIDA system is functionally susceptible to local inflammation, but the effects are transient and do not induce neurodegeneration.