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The differential effects of blocking retinal orexin receptors on the expression of retinal c-fos and hypothalamic
Muhammad Haddad1, Homayoun Khazali2, Mahyar Janahmadi3
1Department of Zoology, Faculty of Sciences, Aleppo University, Aleppo, Syria; Department of Animal Sciences and Marine Biology, Faculty of Life Sciences and Biotechnology, Shahid Beheshti University, Tehran, Iran.
Abstract:
Orexin A and B (OXA and OXB) and their receptors are expressed in the majority of retinal neurons in humans, rats, and mice. Orexins modulate signal transmission between the different layers of the retina. The suprachiasmatic nucleus (SCN) and the retina are central and peripheral components of the body's biological clocks; respectively. The SCN receives photic information from the retina through the retinohypothalamic tract (RHT) to synchronize bodily functions with environmental changes. In present study, we aimed to investigate the impact of inhibiting retinal orexin receptors on the expression of retinal Bmal1 and c-fos, as well as hypothalamic c-fos, Bmal1, Vip, and PACAP at four different time-points (Zeitgeber time; ZT 3, 6, 11, and ZT-0). The intravitreal injection (IVI) of OX1R antagonist (SB-334867) and OX2R antagonist (JNJ-10397049) significantly up-regulated c-fos expression in the retina. Additionally, compared to the control group, the combined injection of SB-334867 and JNJ-10397049 showed a greater increase in retinal expression of this gene. Moreover, the expression of hypothalamic Vip and PACAP was significantly up-regulated in both the SB-334867 and JNJ-10397049 groups. In contrast, the expression of Bmal1 was down-regulated. Furthermore, the expression of hypothalamic c-fos was down-regulated in all groups treated with SB-334867 and JNJ-10397049. Additionally, the study demonstrated that blocking these receptors in the retina resulted in alterations in circadian rhythm parameters such as mesor, amplitude, and acrophase. Finally, it affected the phase of gene expression rhythms in both the retina and hypothalamus, as identified through cosinor analysis and the zero-amplitude test. This study represents the initial exploration of how retinal orexin receptors influence expression of rhythmic genes in the retina and hypothalamus. These findings could provide new insights into how the retina regulates the circadian rhythm in both regions and illuminate the role of the orexinergic system expression within the retina.
Insights
Inhibiting retinal orexin receptors significantly alters gene expression in the retina and hypothalamus, impacting circadian rhythms. This research reveals the orexinergic system
Area of Science:
- Neuroscience
- Chronobiology
- Molecular Biology
Background:
- Orexin A and B (OXA and OXB) and their receptors are present in retinal neurons.
- Orexins modulate retinal signal transmission, and the retina and suprachiasmatic nucleus (SCN) form biological clocks.
- The SCN synchronizes bodily functions with environmental cues via photic information from the retina.
Purpose of the Study:
- To investigate the impact of inhibiting retinal orexin receptors on gene expression (Bmal1, c-fos, Vip, PACAP) in the retina and hypothalamus.
- To assess changes in circadian rhythm parameters following orexin receptor blockade.
- To explore the role of the retinal orexinergic system in regulating circadian rhythms.
Main Methods:
- Intravitreal injection (IVI) of OX1R antagonist (SB-334867) and OX2R antagonist (JNJ-10397049) in rats.
- Analysis of retinal and hypothalamic gene expression (Bmal1, c-fos, Vip, PACAP) at four time-points (ZT 3, 6, 11, ZT-0).
- Cosinor analysis and zero-amplitude test to evaluate circadian rhythm parameters and gene expression phases.
Main Results:
- Retinal c-fos expression was significantly up-regulated by both antagonists, with a greater increase upon combined injection.
- Hypothalamic Vip and PACAP expression were up-regulated, while Bmal1 and c-fos expression were down-regulated.
- Blocking retinal orexin receptors altered circadian rhythm parameters (mesor, amplitude, acrophase) and gene expression phases.
Conclusions:
- Retinal orexin receptor inhibition profoundly affects rhythmic gene expression in both the retina and hypothalamus.
- These findings highlight the role of the orexinergic system in the retina for regulating circadian rhythms.
- This study provides novel insights into the retinal regulation of circadian timing and the orexinergic system's function.
