Localization of histamine H 4 receptors in the central nervous system of human and rat

Abstract

Existing data on the expression of H 4 histamine receptor in the CNS are conflicting and inconclusive. In this report, we present the results of experiments that were conducted in order to elucidate H 4 receptor expression and localization in the brain, spinal cord, and dorsal root ganglia (DRG). Here we show that transcripts of H 4 receptor are present in all analyzed regions of the human CNS, including spinal cord, hippocampus, cortex, thalamus and amygdala, with the highest levels of H 4 mRNA detected in the spinal cord. In rat, H 4 mRNA was detected in cortex, cerebellum, brainstem, amygdala, thalamus and striatum. Very low levels of H 4 mRNA were detected in hypothalamus, and no H 4 signal was detected in the rat hippocampus. Fairly low levels of H 4 mRNA were detected in examined peripheral tissues including spleen and liver. Interestingly, strong expression of H 4 mRNA was detected in the rat DRG and spinal cord. Immunohistochemical analysis revealed expression of H 4 receptors on neurons in the rat lumbar DRG and in the lumbar spinal cord. Our observations provide evidence of the H 4 presence in both human and rodent CNS and offer some insight into possible role of H 4 in itch and pain.