Effects of selective activation or blockade of the histamine H3 receptor on sleep and wakefulness.

The effects of the histamine H3 receptor agonist, (R)-alpha-methylhistamine were compared with those of the histamine H3 antagonist, thioperamide, in rats implanted with electrodes for chronic sleep recordings. (R)-alpha-Methylhistamine (1.0-4.0 micrograms) injected bilaterally into the premammillary area where histamine immunoreactive neurons have been detected increased slow wave sleep, whereas wakefulness and REM sleep were decreased. No significant effects were observed when (R)-alpha-methylhistamine (1.0-8.0 mg/kg) was administered i.p. Thioperamide (1.0-4.0 mg/kg i.p.) increased wakefulness and decreased slow wave sleep and REM sleep. Pretreatment with thioperamide (4.0 mg/kg) prevented the effects of (R)-alpha-methylhistamine (2.0 micrograms) on slow wave sleep and wakefulness. Our results further support an active role for histamine in the control of the waking state.