title: Photic induction of c-Fos in enkephalin neurons of the rat intergeniculate leaflet innervated by retinal PACAP fibres.
abstract: The brain's biological clock, located in the suprachiasmatic nucleus (SCN), is synchronised with the cyclic environment by photic and non-photic cues. Photic information to the SCN is mediated by pituitary adenylate-cyclase-activating polypeptide (PACAP)-containing retinal ganglion cells (RGCs), whereas non-photic input originates primarily from neuropeptide Y (NPY) cells in the ipsilateral thalamic intergeniculate leaflet (IGL). RGCs also seem to project to the IGL, indicating a role for this structure in the integration of photic and non-photic inputs related to the resetting of the biological clock. In the present study, we have used anterograde tracing from both eyes, bilateral eye enucleation, double-immunofluorescence histochemistry, high-resolution confocal laser scanning microscopy and three-dimensional computer analysis to show that (1) PACAP-containing RGCs project to the IGL and are the only source for the PACAP-immunoreactive fibres in the IGL; (2) a few NPY-containing neurons in the IGL are innervated by PACAP-containing retinal nerve fibres and the contacts are both axodendritic and axosomatic; (3) most enkephalin-immunoreactive neurons in the IGL are innervated by PACAP-containing retinal afferents and the contacts are mainly axodendritic; (4) light stimulation at various time points activates (as evidenced by c-Fos induction) enkephalin-positive neurons but not NPY-immunoreactive neurons. The findings suggest that PACAP-immunoreactive retinal afferents in the IGL primarily innervate enkephalin-immunoactive neurons and that the enkephalin-containing neurons, which project locally and to the contralateral IGL, are activated by light independent of diurnal time.
authors.affiliation: Department of Clinical Biochemistry, Bispebjerg University Hospital, DK-2400 Copenhagen NV, Denmark.
authors.forename: Fie
authors.initials: F
authors.lastname: Juhl
authors.forename: Jens
authors.initials: J
authors.lastname: Hannibal
authors.forename: Jan
authors.initials: J
authors.lastname: Fahrenkrug
mesh_terms: D000818:Animals; D001683:Biological Clocks; D004745:Enkephalins / Q000378:metabolism*; D007091:Image Processing, Computer-Assisted; D008297:Male; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D009478:Neuropeptide Y / Q000378:metabolism; D010775:Photic Stimulation; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide / Q000302:isolation & purification / Q000378:metabolism*; D016760:Proto-Oncogene Proteins c-fos / Q000302:isolation & purification / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012165:Retinal Ganglion Cells / Q000166:cytology / Q000378:metabolism*; D013493:Suprachiasmatic Nucleus / Q000378:metabolism; D013788:Thalamus / Q000166:cytology / Q000378:metabolism*
chemical_list: D004745:Enkephalins; D009478:Neuropeptide Y; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D016760:Proto-Oncogene Proteins c-fos