ABSTRACT
Pronounced environmental changes between the day and night forced living organisms to evolve specialised mechanisms organising their daily physiology, named circadian clocks. Currently, it has become clear that the master clock in the suprachiasmatic nuclei of the hypothalamus is not an exclusive brain site to generate daily rhythms. Indeed, several brain areas, including the subcortical visual system have been recently shown to change their neuronal activity across the daily cycle. Here we focus our investigation on the olivary pretectal nucleus (OPN) – a retinorecipient structure primarily involved in the pupillary light reflex. Using the multi-electrode array technology ex vivo we provide evidence for OPN neurons to elevate their firing during the behaviourally quiescent light phase. Additionally, we report the robust sensitivity to orexin A via the identified OX2 receptor in this pretectal centre, with higher responsiveness noted during the night. Interestingly, we likewise report a daily variation in the response to PAC1 receptor activation, with implications for the convergence of orexinergic and visual input on the same OPN neurons. Altogether, our report is first to suggest a daily modulation of the OPN activity via intrinsic and extrinsic mechanisms, organising its temporal physiology.
HIGHLIGHTS
Neurons in the olivary pretectal nucleus (OPN) increase their firing during the day
Orexin A robustly excites the OPN via the OX2 receptor
Orexin A and the activation of PAC1 receptor are more effective during the night
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Funding: This work was financially supported by a project ‘Sonatina 2’ 2018/28/C/NZ4/00099 given to LC from the Polish National Science Centre. KP was additionally supported by ‘Etiuda 8’ doctoral scholarship 2020/36/T/NZ4/00341.
Conflict of interest: The authors declare no competing financial interests.
Ethics approval: Experiments were approved by the Local (Krakow) Ethical Commission and performed in accordance with the European Community Council Directive of 24 November 1986 (86/0609/EEC) and the Polish Animal Welfare Act of 23 May 2012 (82/2012).
Data availability: The data that support the findings of this study are available from the corresponding authors upon reasonable request.