Modulation of genioglossus muscle activity across sleep-wake states by histamine at the hypoglossal motor pool.
OBJECTIVE
Histamine neurons comprise a major component of the aminergic arousal system and significantly influence sleep-wake states, with antihistamines widely used as sedative hypnotics. Unlike the serotonergic and noradrenergic components of this arousal system, however, the role of histamine in the central control of respiratory motor activity has not been determined. The aims of this study were to characterize the effects of histamine receptor agonists and antagonists at the hypoglossal motor pool on genioglossus muscle activity across sleep and awake states, and also determine if histamine contributes an endogenous excitatory drive to modulate hypoglossal motor outflow to genioglossus muscle.


METHODS
Thirty-three rats were implanted with electroencephalogram and neck electrodes to record sleep-wake states, and genioglossus and diaphragm electrodes for respiratory muscle recordings. Microdialysis probes were inserted into the hypoglossal motor nucleus.


RESULTS
Histamine at the hypoglossal motor nucleus significantly increased tonic genioglossus muscle activity in wakefulness, non-REM sleep and REM sleep. The activating effects of histamine on genioglossus muscle activity also occurred with a histamine type-1 (H1) but not H2 receptor agonist. However, H1 receptor antagonism at the hypoglossal motor nucleus did not decrease genioglossus muscle activity in wakefulness or sleep.


CONCLUSIONS
The results suggest that histamine at the hypoglossal motor pool increases genioglossus muscle activity in freely behaving rats in wakefulness, non-REM, and REM sleep via an H1 receptor mechanism.
Department of Medicine, University of Toronto, Toronto, ON, Canada.
Timothy
T
Bastedo
Erin
E
Chan
Eileen
E
Park
Hattie
H
Liu
Richard L
RL
Horner
D000704:Analysis of Variance; D000818:Animals; D003964:Diaphragm / Q000187:drug effects; D004569:Electroencephalography / Q000379:methods / Q000706:statistics & numerical data; D006632:Histamine / Q000494:pharmacology*; D017442:Histamine Agonists / Q000494:pharmacology*; D007002:Hypoglossal Nerve / Q000187:drug effects*; D008297:Male; D017551:Microdialysis / Q000379:methods / Q000706:statistics & numerical data; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012132:Respiratory Muscles / Q000187:drug effects; D012890:Sleep / Q000187:drug effects*; D013268:Stimulation, Chemical; D014851:Wakefulness / Q000187:drug effects*
D017442:Histamine Agonists; D006632:Histamine