Structural and functional connections between the median and the ventrolateral preoptic nucleus
The median preoptic nucleus (MnPO) and the ventrolateral preoptic nucleus (VLPO) are two brain structures that contain neurons essential for promoting non-rapid eye movement (NREM) sleep. However, their connections are still largely unknown. Here, we describe for the first time a slice preparation with an oblique coronal slicing angle at 70° from the horizontal in which their connectivity is preserved. Using the in vivo iDISCO method following viral infection of the MnPO or ex vivo biocytin crystal deposition in the MnPO of mouse brain slices, we revealed a strong axonal pathway from the MnPO to the VLPO. Then, to further explore the functionality of these projections, acute 70° slices were placed on multielectrode arrays (MEAs) and electrical stimulations were performed near the MnPO. Recordings of the signals propagation throughout the slices revealed a preferential pathway from the MnPO to the VLPO. Finally, we performed an input–output curve of field responses evoked by stimulation of the MnPO and recorded in the VLPO. We found that field responses were inhibited by GABAA receptor antagonist, suggesting that afferent inputs from the MnPO activate VLPO neuronal networks by disinhibition.
KeywordsSleep-promoting neuron Field recordings VLPO MnPO NREM sleep MEA
This work was supported by grants from the Centre National de la Recherche Scientifique (CNRS), the Institut National de la Santé et de la Recherche Médicale (Inserm), Collège de France and the Marie Sklodowska-Curie Research and Innovation Programme EU-GliaPhD (722053) (N.R.). We thank all the members of the animal house facility and imaging platform from Collège de France, including Philippe Mailly in particular. We gratefully acknowledge Yves Dupraz for the design of the brain cutting angles and IT people including Aurélien Agneray, in particular, for excellent and prompt technical assistance.
Compliance with ethical standards
Conflict of interest
The authors have no conflicts of interest to declare.
All animal procedures were carried out according to the guidelines of European Community Council Directives of January first 2013 (2010/63/EU) and followed our local guidelines for the ethical treatment of animal care [Center for Interdisciplinary Research in Biology in College de France (France)]. The number of animals in our study was kept to the necessary minimum.
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