Hypothalamic and zona incerta neurons expressing hypocretin, but not melanin concentrating hormone, project to the hamster intergeniculate leaflet.
The hypocretins (Hcrt; also known as orexins) and melanin-concentrating hormone comprise distinct families of neuropeptides synthesized in cells located in the lateral hypothalamus and adjacent areas. The Hcrts are thought to modulate food intake and sleep/wake patterns in mammals. Melanin-concentrating hormone has a well-documented role in energy metabolism. A moderate plexus of Hcrt immunoreactive terminals has been described in the hamster intergeniculate leaflet, part of the circadian rhythm system. This study investigated the origin of Hcrt-immunoreactive terminals in the intergeniculate leaflet and determined whether melanin-concentrating hormone neurons also project to the intergeniculate leaflet. The tracer, cholera toxin beta-subunit, was injected into the intergeniculate leaflet of the golden hamster. Double-label fluorescent immunohistochemistry for cholera toxin beta-subunit and Hcrt or melanin-concentrating hormone was then performed to identify retrogradely labeled cells also containing immunoreactive peptide. Most cholera toxin beta-subunit-labeled cells were detected in the medial zona incerta and sub-incertal zone, with few observed in the lateral hypothalamus. Hcrt-immunoreactive cells were abundant and found largely in the lateral hypothalamus and adjacent nuclei. Melanin-concentrating hormone cells were also abundant in the medial zona incerta, in close proximity to cholera toxin beta-subunit-labeled cells, but ventral to them. Cells containing both cholera toxin beta-subunit and Hcrt-immunoreactive, were present in the dorsal aspect of the lateral hypothalamus. The number observed was small, < or = 1% of the total number of Hcrt cells counted in the hamster. No cholera toxin beta-subunit-immunoreactive cells also contained melanin-concentrating hormone and no melanin-concentrating hormone-immunoreactive processes were evident in the intergeniculate leaflet. The results show that a small number of lateral hypothalamus cells containing Hcrt-immunoreactivity project to the intergeniculate leaflet, but they are scattered rather than collected into a discrete group. At the present time there is no information regarding the function of these cells, although they may contribute to the regulation of sleep/arousal, circadian rhythmicity, or vestibulo-oculomotor function.
Department of Psychiatry and Behavioral Sciences, Health Sciences Center, Stony Brook University, Stony Brook, NY 11794-8101, USA.
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Vidal
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Blanchard
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Morin
D000818:Animals; D001931:Brain Mapping; D002772:Cholera Toxin / Q000378:metabolism; D006224:Cricetinae; D005829:Geniculate Bodies / Q000378:metabolism*; D007028:Hypothalamic Hormones / Q000378:metabolism; D007031:Hypothalamus / Q000166:cytology*; D007150:Immunohistochemistry / Q000379:methods; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008297:Male; D008543:Melanins / Q000378:metabolism; D009434:Neural Pathways / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D009479:Neuropeptides / Q000378:metabolism*; D000068797:Orexins; D010907:Pituitary Hormones / Q000378:metabolism; D020530:Subthalamus / Q000166:cytology*
D007028:Hypothalamic Hormones; D047908:Intracellular Signaling Peptides and Proteins; D008543:Melanins; D009479:Neuropeptides; D000068797:Orexins; D010907:Pituitary Hormones; C019463:melanin-concentrating hormone; D002772:Cholera Toxin