THE SUPRACHIASMATIC NUCLEUS AND THE INTERGENICULATE LEAFLET IN THE ROCK CAVY (Kerodon rupestris): RETINAL PROJECTIONS

*Corresponding author e-mail: expeditojunior@click21.com.br Introduction: A wide variety of behavioural and physiological processes show circadian rhythms which are generated by a timekeeping system, also called circadian timing system. This system in mammals is built by two principal brain centers: a known central pacemaker, the hypothalamic suprachiasmatic nucleus (SCN), and a secondary component, the thalamic intergeniculate leaflet (IGL). The aim of this work was to characterize the retinal projections in the SCN and the IGL in a Brazilian rodent species, the rock cavy ( Kerodon rupestris ). Methods: Six animals were deeply anesthetized and subjected to unilateral intraocular injections of cholera toxin subunit B (CTb). Following a 5 to 7 days survival time, the animals were again anesthetized and perfused transcardially with buffered saline and 4% paraformaldehyde. Brains were coronally and sagittally sectioned at 30pm on a freezing microtome. Sections through the SCN and the IGL were submitted to immunohistochemistry (avidin-biotinperoxidase protocol) to reveal the anterogradely transported CTb. Results: In coronal sections from animals intraocularly injected with CTb, both SCNs, with a contralateral predominance, were filled with CTb-immunoreactive (IR) terminals, forming a dense plexus in the ventral region, denser in the ventrolateral portion and spreading sparsely to the dorsal portion. Retinal afferents to the IGL were shown by anterograde transport of intraocularly injected CTb. CTb-IR terminals were observed in the IGL and the entire lateral geniculate complex of the rock cavy with a strong predominance on the side contralateral to the injected eye. The sections in the sagittal plane allowed seen whole extension of the retinal projections inside the studied nuclei. Conclusion: These results show that the SCN and IGL of Kerodon rupestris display similarities in the pattern of distribution of retinal projections profile in relation to other studied species. Support: CNPq, CAPES, PROPESQ-UFRN-Brazil. Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil