Histamine receptor H1 in the nucleus tractus solitarii regulates arterial pressure and heart rate in rats

Abstract

Axons of histamine (HA)-containing neurons are known to project from the posterior hypothalamus to many areas of the brain, including the nucleus tractus solitarii (NTS), a central brain structure that plays an important role in regulating arterial pressure. However, the functional significance of NTS HA is still not fully established. In this study, we microinjected HA or 2-pyridylethylamine, a HA-receptor H1-specific agonist, into the NTS of urethane-anesthetized Wister rats to identify the potential functions of NTS HA on cardiovascular regulation. When HA or H1-receptor-specific agonist was bilaterally microinjected into the NTS, mean arterial pressure (MAP) and heart rate (HR) were significantly increased, whereas pretreatment with the H1-receptor-specific antagonist cetirizine into the NTS significantly inhibited the cardiovascular responses. The maximal responses of MAP and HR changes induced by HA or H1-receptor-specific agonist were dose dependent. We also confirmed gene expression of HA receptors in the NTS and that the expression level of H1 mRNA was higher than that of the other subtypes. In addition, we found that H1 receptors are mainly expressed in neurons of the NTS. These findings suggested that HA within the NTS may play a role in regulating cardiovascular homeostasis via activation of H1 receptors expressed in the NTS neurons.