title: Circadian-dependent and circadian-independent behavioral actions of hypocretin/orexin.
abstract: The hypocretins/orexins modulate behavioral state as well as a variety of state-dependent behaviors. Levels of hypocretin-1 and prepro-hypocretin mRNA vary in a circadian fashion, suggesting that hypocretin neurotransmission may vary across the circadian cycle. To better assess the circadian dependency of the behavioral actions of hypocretin-1, the behavioral effects of intracerebroventricular hypocretin-1 administration (3.0 nmol/2 microl) were examined at differing portions of the circadian cycle, when animals display either low levels of waking (light-period) or high levels of waking (dark-period). In addition, mediation analyses were conducted to better assess the contribution of the wake-promoting actions to other behavioral actions of hypocretin-1. During the light-period, hypocretin-1 administration increased time spent awake, grooming, feeding, locomotor activity and chewing of inedible material, a stress-related behavior. Comparable effects of hypocretin-1 on time spent awake, locomotor activity and the chewing of inedible material were observed during the dark-period. In contrast, hypocretin-1-induced feeding and drinking appeared largely circadian-dependent: hypocretin-1 had minimal effects on these behaviors during the dark-period. Hypocretin-1-induced increases in grooming appeared moderately circadian-dependent. These observations suggest that the previously described ability of hypocretin to increase feeding and drinking during the light-period may reflect, at least in part, a general behavioral activation associated with waking. Results from the mediation analyses support these conclusions, indicating that hypocretin-1-induced increases in waking largely account for hypocretin-1-induced increases in feeding and drinking. Additionally, given that chewing and grooming are stress-related behaviors, these observations provide further support for a possible function of HCRT in stress.
authors.affiliation: Department of Psychology, University of Wisconsin, 1202 W. Johnson St., Madison, WI 53706-1611, USA.
authors.forename: Rodrigo A
authors.initials: RA
authors.lastname: España
authors.forename: Stacey
authors.initials: S
authors.lastname: Plahn
authors.forename: Craig W
authors.initials: CW
authors.lastname: Berridge
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism* / Q000494:pharmacology; D002940:Circadian Rhythm / Q000187:drug effects / Q000502:physiology*; D003623:Dark Adaptation / Q000187:drug effects / Q000502:physiology; D004327:Drinking Behavior / Q000187:drug effects / Q000502:physiology; D005247:Feeding Behavior / Q000187:drug effects / Q000502:physiology; D006120:Grooming / Q000187:drug effects / Q000502:physiology; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D008409:Mastication / Q000187:drug effects / Q000502:physiology; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009479:Neuropeptides / Q000378:metabolism* / Q000494:pharmacology; D000068797:Orexins; D010775:Photic Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012890:Sleep / Q000187:drug effects / Q000502:physiology; D013312:Stress, Physiological / Q000503:physiopathology; D014851:Wakefulness / Q000187:drug effects / Q000502:physiology*
chemical_list: D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D000068797:Orexins