PRESENCE OF SEROTONIN RECEPTORS IN SUPRACHIASMATIC NUCLEUS OF MARMOSET BRAIN (Callithrix jacchus)

*Corresponding author e-mail: andrelbpontes@yahoo.com.br The core nucleus of the mammalian circadian timing system (CTS) is the hypothalamic suprachiasmatic nucleus (SCN) which receives a strong serotonergic projection from the raphe. Serotonin is involved in the fine adjustments at several brain centers and in the SCN these actions are reported as been primarily mediated by the receptor type 5-HT 1 . In rodents, there is a consensus that the general 5-HT projection pattern arrives at the ventral portion of the SCN, mismatching the arriving fibers of the retinohypothalamic tract. Confronting these findings, we show here that in a New World primate species, Callithrix jacchus , the occurrence of the positive labeling for the subtypes 5-HT 1A and 5-HT 1B are mostly at the dorsal SCN. We also confirm the dualistic nature of the placement of the 5-HT-positive fibers in the SCN of Callithrix , with higher density in their dorsal and ventral contours, with a core devoid of any labeling. The presence of these two types of receptors in the dorsal SCN of marmosets appears to complement the retinal terminal plexus located in the ventral region, confirming the uniqueness of the CTS of the common marmoset as different in relation to the pattern found in other species currently studied. Since the subtypes 5-HT 1A and 5-HT 1B were preferentially found dorsally, the discussion addresses to a new interpretation of the 5-HT effects in the regulation and synchronization of the CTS itself in New World primates. Support: CAPES, CNPq, FAPESP, 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