Abstract
The intergeniculate leaflet (IGL) is part of the neural network involved in the regulation of the circadian timing processes. The IGL receives photic- and non-photic-inputs from retina and midbrain and projects this information to the suprachiasmatic nucleus (SCN) through the geniculohypothalamic tract (GHT) arising mostly from neuropeptide Y (NPY) containing neurons in the IGL. Based on distribution of orexin-B-ir fibers and terminal boutons in the IGL we suggest that one pathway by which orexin-B may influence circadian timing could be through interaction with NPY, the most abundant neuropeptide/neurotransmitter in the IGL of the Djungarian hamster. In order to test this idea we investigated the anatomical basis for such a interaction using dual-label immunofluorescence. Orexin B-ir fibers with terminals had close apposition on NPY-lir perikarya and fibers with terminal boutons in the rostro-caudal extension of the IGL. Furthermore, NPY-lir fibers in the peripheral structures of the SCN had apposition from orexin-B-ir fibers and terminals. These observations provide anatomical basis for orexin-B to interact with NPY and influence the circadian timing system. This study was supported by Deutsche Forschungsgemeinschaft (DFG KL973–5) and Danish Research Agancy.
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