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Light → SCN : -direct via the retinohypothalamic (RHT) pathway -indirect via geniculohypothalamic (GHT) pathway. SCN: some morphological features. Parvocellular, paired structure, ~16-20,000 neurons in rodent, miniscule in man Phenotypes: multiple potential transmitters
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Light →SCN: -direct via the retinohypothalamic (RHT) pathway -indirect via geniculohypothalamic (GHT) pathway
SCN: some morphological features • Parvocellular, paired structure, ~16-20,000 neurons in rodent, miniscule in man • Phenotypes: multiple potential transmitters • most express GABA(1993 proposal: SCN output is inhibitory) • Peptides: • vasoactive intestinal peptide (VIP) in cells in ventrolateral part; receives retinal input; forms part of the output projection • vasopressin (VP) in cells in dorsomedial part; forms part of the output projection • somatostatin (SS) in cells whose axons remain intrinsic to SCN
Lets consider the neural connections of SCN A schematic outline from Ibata et al Frontiers in Neuroendocrinology 20: 241-268, 1999
Notes:1 -Based on immunocytochemical grounds, SCN can be subdivided into dorsomedial (shell) and ventrolateral (core) segments2 -Retinal input is to the VIPergic neurons in the ventrolateral SCN3 -output pathways arise from both VIPergic and vasopressinergic neurons in SCN4 -most projections are local, to hypothalamic sites (exceptions: LGB, TPV)
SCN: techniques to define input-output pathways • Using retrograde and/or anterograde transport of suitable markers e.g. wheat germ agglutin (WGA)
SCN: techniques to define input-output pathways • Using retrograde and anterograde transport of suitable markers e.g. WGA • Using viral retrograde transneuronal traceing (pseudorabies)
Retrograde transneuronal labeling with pseudorabies virus (PRV) injected in the adrenal gland
SCN: techniques to define input-output pathways • Using retrograde and/or anterograde transport of suitable markers e.g. WGA • Using viral retrograde transneuronal tracing (PRV) • Using double label immunocytochemistry to define phenotype (peptides)
PRV (green)A-C: in PVN oxytocin (red)D-E: in SCNvasopressin (red)F: in SCNVIP (red)
Anatomical and functional demonstration of a multisynaptic suprachiasmatic nucleus adrenal (cortex) pathwayEuropean Journal of Neuroscience 11: 15351544, 1999RM Buijs, J Wortel, JJ van Heerikhuize, MGP Feenstra, GJ Ter Horst,HJ Romijn, A Kalsbeek
Suprachiasmatic nucleus (SCN) • Brain Res. 1972 Jul 13;42(1):201-6. • Loss of a circadian adrenal corticosterone rhythm following suprachiasmatic lesions in the rat.Moore RY, Eichler VB.