title: Direct and indirect retinohypothalamic projections to the supraoptic nucleus in the female albino rat.
abstract: Earlier studies have shown that retinohypothalamic projections terminate extensively within the hypothalamus of the rat. Recently, we identified a light retinal projection to the supraoptic nucleus as well as a larger, well-focused projection resulting in a peri-supraoptic nucleus terminal field. In this study, we employed a double labeling method with cholera toxin conjugated to horseradish peroxidase (CT-HRP) and pseudorabies virus, a transsynaptic neural tracer, to evaluate retinorecipient neurons in both the supraoptic nucleus and peri-supraoptic nucleus terminal field. In addition, we looked for evidence that cells in the peri-supraoptic nucleus terminal field project into the supraoptic nucleus. Three strains of pseudorabies virus were compared. A direct retinosupraoptic nucleus circuit was confirmed with all three strains. Retinorecipient neurons in the peri-supraoptic nucleus terminal field were also confirmed. However, there was a strain-based difference in the identification of these neurons. The wild-type Becker strain labeled cells in the peri-supraoptic nucleus terminal field in a manner paralleling the early, intermediate and late stages of infection of the suprachiasmatic nucleus. This parallel time course suggests that retinal ganglion cells terminate directly on cells in the peri-supraoptic nucleus terminal field. Conversely, the Bartha and PRV-91 strains showed appreciable labeling of peri-supraoptic neurons only at long survival times. This longer time course suggests that these mutant strains label neurons in the peri-supraoptic nucleus terminal field indirectly, after passing through additional neurons. In addition, experiments with monocular injection of CT-HRP and posterior pituitary injection of pseudorabies virus showed retrogradely labeled second-order cells in the peri-supraoptic nucleus amidst the CT-HRP labeled terminal field of the retinohypothalamic tract. These results demonstrate a direct projection from the retina to the supraoptic nucleus and provide evidence for an indirect circuit from the retina to the supraoptic nucleus via neurons located in the peri-supraoptic nucleus terminal field. The strain-based differences imply that those retinal ganglion cells that project to the peri-supraoptic nucleus terminal field differ from those that project to the suprachiasmatic nucleus. In addition, these results suggest a neuroanatomic basis for photic effects on physiological mechanisms that are not mediated by the circadian timing system.
authors.affiliation: Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia 19104-6045.
authors.forename: J D
authors.initials: JD
authors.lastname: Levine
authors.forename: X S
authors.initials: XS
authors.lastname: Zhao
authors.forename: R R
authors.initials: RR
authors.lastname: Miselis
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology / Q000648:ultrastructure; D002772:Cholera Toxin; D005260:Female; D011558:Herpesvirus 1, Suid; D006651:Histocytochemistry; D006735:Horseradish Peroxidase; D007031:Hypothalamus / Q000502:physiology* / Q000648:ultrastructure; D009411:Nerve Endings / Q000502:physiology / Q000648:ultrastructure; D010904:Pituitary Gland, Posterior / Q000502:physiology / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D012160:Retina / Q000502:physiology* / Q000648:ultrastructure; D013495:Supraoptic Nucleus / Q000502:physiology* / Q000648:ultrastructure; D013569:Synapses / Q000502:physiology / Q000648:ultrastructure; D014795:Visual Pathways / Q000502:physiology* / Q000648:ultrastructure
chemical_list: C052635:cholera toxin, B subunit-horseradish peroxidase; D002772:Cholera Toxin; D006735:Horseradish Peroxidase