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June 19, 2026Open Access

THE SUPRACHIASMATIC NUCLEUS AND THE INTERGENICULATE LEAFLET IN THE ROCK CAVY (Kerodon rupestris): NEUROCHEMICAL ORGANIZATION

Key Points

To identify and characterize the circadian system of the rock cavy using neurochemical profiling.
Immunohistochemical techniques evaluated SCN and IGL in six anesthetized rock cavies.
Brains were perfused and sectioned for analysis of neuroactive substances and markers.
The avidin-biotin-peroxidase protocol was applied to reveal various endogenous substances.
VP-IR neurons concentrated in the dorsal SCN at rostral levels.
VIP-IR neurons found in ventromedial SCN amid dense neuropil; additional terminals for NPY, 5-HT, and ENK also present.
Intense GFAP expression observed in IGL, with similar neurochemical profiles to other species.

Abstract

*Corresponding author e-mail: expeditojunior@click21.com.br Introduction: The circadian timing system is constituted 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 study was to identify and characterize the circadian system of the rock cavy using immunohistochemical techniques, in order to establish a regional rodent model for circadian research. Methods: The SCN and the IGL were evaluated as the presence of neuroactive substances and neuronal or glial markers. Six animals were deeply anesthetized and perfused transcardially with buffered saline and 4% paraformaldehyde. Brains were coronally sectioned at 30pm on a freezing microtome. Sections through the SCN and the IGL were submitted to immunohistochemistry (avidin-biotin-peroxidase protocol) to reveal some endogenous substances, such as vasoactive intestinal polypeptide (VIP), vasopressin (VP), neuropeptide Y (NPY), serotonin (5-HT), enkephalin (ENK) and the astrocyte marker glial fibrillary acidic protein (GFAP). Results: VP-IR neurons were observed in the SCN, predominantly concentrated in the dorsal portion only at rostral levels. Some VIP-IR neurons immersed in a dense neuropil were found in a ventromedial position in the SCN. The SCN also displays NPY- 5-HT- and ENK-terminals. GFAP expression is also detected in the SCN, although without great contrast with surrounding areas. The rock cavy IGL is marked by NPY-neurons and ENK-terminals. The IGL is also marked by intense expression of GFAP. Conclusion: These results show that the SCN and IGL of Kerodon rupestris display similarities in the pattern of distribution of retinal projections and neurochemical profile in relation to other studied species. Support: CNPq, CAPES, FINEP, PROPESQ-UFRN. 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

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