Involvement of the retinohypothalamic tract in the photic-like effects of the serotonin agonist quipazine in the rat.
Light is the major synchronizer of the mammalian circadian pacemaker located in the suprachiasmatic nucleus. Photic information is perceived by the retina and conveyed to the suprachiasmatic nucleus either directly by the retinohypothalamic tract or indirectly by the intergeniculate leaflet and the geniculohypothalamic tract. In addition, serotonin has been shown to affect the suprachiasmatic nucleus by both direct and indirect serotonin projections from the raphe nuclei. Indeed, systemic as well as local administrations of the serotonin agonist quipazine in the region of the suprachiasmatic nucleus mimic the effects of light on the circadian system of rats, i.e. they induce phase-advances of the locomotor activity rhythm as well as c-FOS expression in the suprachiasmatic nucleus during late subjective night. The aim of this study was to localize the site(s) of action mediating those effects. Phase shifts of the locomotor activity rhythm as well as c-FOS expression in the suprachiasmatic nucleus after s.c. injection of quipazine (10 mg/kg) were assessed in Lewis rats, which had received either radio-frequency lesions of the intergeniculate leaflet or infusions of the serotonin neurotoxin 5,7-dihydroxytryptamine into the suprachiasmatic nucleus (25 microg) or bilateral enucleation. Lesions of intergeniculate leaflet and serotonin afferents to the suprachiasmatic nucleus did not reduce the photic-like effects of quipazine, whereas bilateral enucleation and the subsequent degeneration of the retinohypothalamic tract abolished both the phase-shifting and the FOS-inducing effects of quipazine. The results indicate that photic-like effects of quipazine are mediated via the retinohypothalamic tract.
Graff
C
C
Department of Animal Physiology, Institute of Biology, University of Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart, Germany. carograff@yahoo.fr
Kohler
M
M
Pévet
P
P
Wollnik
F
F
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D002940:Circadian Rhythm / Q000502:physiology; D015353:Eye Enucleation; D007839:Functional Laterality / Q000502:physiology; D007031:Hypothalamus / Q000502:physiology*; D007150:Immunohistochemistry; D008297:Male; D009043:Motor Activity / Q000502:physiology; D009434:Neural Pathways / Q000502:physiology*; D010775:Photic Stimulation; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis; D011814:Quipazine / Q000494:pharmacology*; D051381:Rats; D011917:Rats, Inbred Lew; D012160:Retina / Q000502:physiology*; D012701:Serotonin / Q000502:physiology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*; D013493:Suprachiasmatic Nucleus / Q000502:physiology
D016760:Proto-Oncogene Proteins c-fos; D017366:Serotonin Receptor Agonists; D012701:Serotonin; D011814:Quipazine