Food-elicited increases in cortical acetylcholine release require orexin transmission.

The corticopetal basal forebrain cholinergic system (BFCS) is crucial for normal attentional function and cortical acetylcholine release is increased by stimuli with high motivational salience. Projections from the lateral hypothalamus to the basal forebrain have been previously described and have been hypothesized to relay interoceptive information to this area but little is known about the phenotypic and functional nature of hypothalamic modulation of the BFCS. We have previously shown that orexin (hypocretin) fibers from the hypothalamus distribute densely among basal forebrain choline acetyltransferase-positive neurons and that intrabasalis administration of orexin A increases cortical acetylcholine release. Here, we used in vivo microdialysis to test the hypothesis that the orexin system is necessary for activation of the BFCS in response to a food-related stimulus in food-restricted rats. Elimination of the majority of orexin neurons with the toxin orexin B-saporin significantly blunted the cholinergic response to presentation of palatable food in these animals. Similar effects were seen in animals acutely pretreated with the orexin 1 receptor antagonist, SB-334867, which also increased feeding latency. Collectively, these data suggest that orexin interactions with the BFCS may be a critical component of the neurobiological substrates by which interoceptive cues bias the allocation of attentional resources toward exteroceptive stimuli related to homeostatic challenges.