H1R

Abstract

Histamine H1 receptor (H1R) plays a crucial role in various physiological reactions induced by histamine. Histamine H1R is thought to modulate many functions of the hypothalamus that exhibit circadian and other rhythms, such as arousal state, locomotor activity, feeding, and drinking. This chapter presents a study in which no specific binding of [3H]pyrilamine was seen in brains of homozygous mutant mice. [3H]Doxepin had two saturable binding sites with higher and lower affinities in brains of wild-type mice, but H1R-deficient mice showed only the weak labeling of [3H]doxepin that corresponded to the lower affinity binding sites. Mutant mice developed normally but the absence of H1R significantly increased the ratio of ambulation during the light period to the total ambulation for 24 hours in an accustomed environment. These results indicate that through H1R, histamine is involved in circadian rhythm of locomotor activity