Role of Histamine H1 and H3 Receptors in Emotion Regulation in Intermittent Sleep-Deprived Mice.

The central histamine system is involved in several physiological behaviors and neurological disorders, including the sleep-wake cycle, anxiety-related behaviors (both high and low anxiety), and attention deficit hyperactivity disorder (ADHD). Histamine is synthesized from l-histidine by histidine decarboxylase (HDC) and primarily metabolized by histamine-N-methyltransferase (HNMT) in the central nervous system. We previously reported that mice with intermittent sleep deprivation may exhibit impulsive-like symptoms resembling ADHD and low-anxiety behavior. However, the specific role of histaminergic systems in these behaviors remains unclear. In this study, we evaluated HDC expression levels in the hypothalamus as well as the expression of histamine H1 to H4 receptors and HNMT in the hypothalamus and frontal cortex of sleep-deprived mice. Moreover, the effects of administering histidine, a histamine precursor, and inhibitors of each histamine receptor on sleep deprivation-induced low-anxiety and impulsive-like behaviors were examined using an elevated plus maze test. The expressions of HDC and histamine H1 and H3 receptors in the hypothalamus increased, while that of histamine H1 receptors in the frontal cortex of sleep-deprived mice decreased. The low-anxiety and impulsive-like behaviors in intermittent sleep-deprived mice significantly decreased and increased, respectively, following the administration of histamine H1 and H3 receptor blockers and histidine. Collectively, these findings suggest that the low-anxiety behavior and impulsive-like ADHD symptoms induced by intermittent sleep deprivation may result from the overstimulation of histamine H1 and H3 receptors by elevated histamine, together with increased hypothalamic HDC expression. Furthermore, they suggest that sufficient sleep may contribute to ameliorating ADHD symptoms.