*Corresponding author e-mail: rayanebartira@yahoo.com.br Introduction: The circadian timing system (CTS) it is composed by a group of neural structures specialized that establish a temporal organization of the physiologic processes and behaviors. Their central components are the suprachiasmatic nucleus (SCN) of hypothalamus and the intergeniculate leaflet (IGL) of thalamus. The objective of this work was to verify, through the immunohistochemical technique, the presence of the protein nuclear specific neuronal (NeuN) in CTS of the capuchin monkey ( Cebus apella ), a primate of the New World. Methods: The animals were previously anesthetized and perfused transcardially with saline containing heparine, followed by 4% paraformaldehyde solution in phosphate buffer 0,1M, pH 7,4. The brains were removed, frozen and sectioned on a sliding microtome in coronal plane (30 µm). The sections were collected in six series. Then, sections of a series were submmited to Nissl method of staining (Thionin) for cytoarchitectonic delimitation. Another series were processed immunohistochemically (ABC protocol) to reveal the presence of NeuN. Results: NeuN positives neurons were observed in the central structures of CTS of the Capuchin Monkey, SCN and Pre- Geniculate nuclei (PGN). The PGN is the equivalent structure to IGL of the rodents. Conclusion: The neurons that compose the central structures of CTS in this primate species, express the protein NeuN. Support: CNPq, CAPES, 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
Nascimento et al. (Thu,) studied this question.