Dopaminergic regulation of orexin neurons.
Orexin/hypocretin neurons in the lateral hypothalamus and adjacent perifornical area (LH/PFA) innervate midbrain dopamine (DA) neurons that project to corticolimbic sites and subserve psychostimulant-induced locomotor activity. However, it is not known whether dopamine neurons in turn regulate the activity of orexin cells. We examined the ability of dopamine agonists to activate orexin neurons in the rat, as reflected by induction of Fos. The mixed dopamine agonist apomorphine increased Fos expression in orexin cells, with a greater effect on orexin neurons located medial to the fornix. Both the selective D1-like agonist, A-77636, and the D2-like agonist, quinpirole, also induced Fos in orexin cells, suggesting that stimulation of either receptor subtype is sufficient to activate orexin neurons. Consistent with this finding, combined SCH 23390 (D1 antagonist)-haloperidol (D2 antagonist) pretreatment blocked apomorphine-induced activation of medial as well as lateral orexin neurons; in contrast, pretreatment with either the D1-like or D2-like antagonists alone did not attenuate apomorphine-induced activation of medial orexin cells. In situ hybridization histochemistry revealed that LH/PFA cells rarely express mRNAs encoding dopamine receptors, suggesting that orexin cells are transsynaptically activated by apomorphine. We therefore lesioned the nucleus accumbens, a site known to regulate orexin cells, but this treatment did not alter apomorphine-elicited activation of medial or lateral orexin neurons. Interestingly, apomorphine failed to activate orexin cells in isoflurane-anaesthetized animals. These data suggest that apomorphine-induced arousal but not accumbens-mediated hyperactivity is required for dopamine to transsynaptically activate orexin neurons.
Bubser
Michael
M
Department of Psychiatry, Vanderbilt University Medical Center, Nashville, TN 37212, USA. michael.bubser@vanderbilt.edu
Fadel
Jim R
JR
Jackson
Lela L
LL
Meador-Woodruff
James H
JH
Jing
Deqiang
D
Deutch
Ariel Y
AY
D000344:Afferent Pathways / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001143:Arousal / Q000187:drug effects / Q000502:physiology*; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D004298:Dopamine / Q000378:metabolism*; D018491:Dopamine Agonists / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D006948:Hyperkinesis / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology; D007026:Hypothalamic Area, Lateral / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009479:Neuropeptides / Q000187:drug effects / Q000378:metabolism*; D009714:Nucleus Accumbens / Q000187:drug effects / Q000378:metabolism; D064446:Orexin Receptors; D000068797:Orexins; D016760:Proto-Oncogene Proteins c-fos / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011954:Receptors, Dopamine / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled; D018013:Receptors, Neuropeptide; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
D000697:Central Nervous System Stimulants; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D064446:Orexin Receptors; D000068797:Orexins; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D011954:Receptors, Dopamine; D043562:Receptors, G-Protein-Coupled; D018013:Receptors, Neuropeptide; D004298:Dopamine