title: Orexinergic input to dopaminergic neurons of the human ventral tegmental area.
abstract: The mesolimbic reward pathway arising from dopaminergic (DA) neurons of the ventral tegmental area (VTA) has been strongly implicated in reward processing and drug abuse. In rodents, behaviors associated with this projection are profoundly influenced by an orexinergic input from the lateral hypothalamus to the VTA. Because the existence and significance of an analogous orexigenic regulatory mechanism acting in the human VTA have been elusive, here we addressed the possibility that orexinergic neurons provide direct input to DA neurons of the human VTA. Dual-label immunohistochemistry was used and orexinergic projections to the VTA and to DA neurons of the neighboring substantia nigra (SN) were analyzed comparatively in adult male humans and rats. Orexin B-immunoreactive (IR) axons apposed to tyrosine hydroxylase (TH)-IR DA and to non-DA neurons were scarce in the VTA and SN of both species. In the VTA, 15.0±2.8% of TH-IR perikarya in humans and 3.2±0.3% in rats received orexin B-IR afferent contacts. On average, 0.24±0.05 and 0.05±0.005 orexinergic appositions per TH-IR perikaryon were detected in humans and rats, respectively. The majority (86-88%) of randomly encountered orexinergic contacts targeted the dendritic compartment of DA neurons. Finally, DA neurons of the SN also received orexinergic innervation in both species. Based on the observation of five times heavier orexinergic input to TH-IR neurons of the human, compared with the rat, VTA, we propose that orexinergic mechanism acting in the VTA may play just as important roles in reward processing and drug abuse in humans, as already established well in rodents.
authors.affiliation: Laboratory of Endocrine Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary.
authors.forename: Erik
authors.initials: E
authors.lastname: Hrabovszky
authors.affiliation: Laboratory of Endocrine Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary.
authors.forename: Csilla S
authors.initials: CS
authors.lastname: Molnár
authors.affiliation: Department of Forensic Medicine, Faculty of Medicine of the University of Debrecen, Debrecen, Hungary.
authors.forename: Beáta Á
authors.initials: BÁ
authors.lastname: Borsay
authors.affiliation: Department of Forensic Medicine, Faculty of Medicine of the University of Debrecen, Debrecen, Hungary.
authors.forename: Péter
authors.initials: P
authors.lastname: Gergely
authors.affiliation: Department of Forensic Medicine, Faculty of Medicine of the University of Debrecen, Debrecen, Hungary.
authors.forename: László
authors.initials: L
authors.lastname: Herczeg
authors.affiliation: Laboratory of Endocrine Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary ; Department of Neuroscience, Faculty of Information Technology, Pázmány Péter Catholic University, Budapest, Hungary.
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Liposits
mesh_terms: D000328:Adult; D000818:Animals; D001369:Axons / Q000378:metabolism / Q000648:ultrastructure*; D059290:Dopaminergic Neurons / Q000378:metabolism / Q000648:ultrastructure*; D015870:Gene Expression; D006801:Humans; D007031:Hypothalamus / Q000378:metabolism / Q000648:ultrastructure*; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009479:Neuropeptides / Q000235:genetics* / Q000378:metabolism; D000068797:Orexins; D051381:Rats; D017208:Rats, Wistar; D012201:Reward; D019966:Substance-Related Disorders / Q000378:metabolism / Q000503:physiopathology / Q000523:psychology; D013378:Substantia Nigra / Q000378:metabolism / Q000648:ultrastructure*; D014446:Tyrosine 3-Monooxygenase / Q000235:genetics / Q000378:metabolism; D017557:Ventral Tegmental Area / Q000378:metabolism / Q000648:ultrastructure*
chemical_list: C000596229:HCRT protein, human; D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D000068797:Orexins; D014446:Tyrosine 3-Monooxygenase