Abstract
Objective: To investigate the projections the cerebrospinal fluid-contacting (CSF-contacting) nucleus receives from the diencephalon and to speculate on the functional significance of these connections.Methods: The retrograde tracer cholera toxin B subunit (CB) was injected into the CSF-contacting nucleus in SD rats according to the experimental formula of the stereotaxic coordinates. Animals were perfused 7–10 days after the injection, and the diencephalon was sliced at 40 μm with a freezing microtome. CB-immunofluorescence was performed on all diencephalic sections. The features of CB-positive neuron distribution in the diencephalon were observed with a fluorescence microscope.Results: The retrograde labeled CB-positive neurons were found in the epithalamus, subthalamus, and hypothalamus. Three functional diencephalic areas including 43 sub-regions revealed projections to the CSF-contacting nucleus. The CB-positive neurons were distributed in different density ranges: sparse, moderate, and dense.Conclusion: Based on the connectivity patterns of the CSF-contacting nucleus that receives anatomical inputs from the diencephalon, we preliminarily assume that the CSF-contacting nucleus participates in homeostasis regulation, visceral activity, stress, emotion, pain and addiction, and sleeping and arousal. The present study firstly illustrates the broad projections of the CSF-contacting nucleus from the diencephalon, which implies the complicated functions of the nucleus especially for the unique roles of coordination in neural and body fluids regulations.
Highlights
The cerebrospinal fluid (CSF)-contacting nucleus is a unique nucleus in the brain
The tracer was confined within the boundary of the CSF-contacting nucleus, where the microsyringe needle tract can be seen to be located at the core of the CSF-contacting nucleus (Figures 1A,B)
After the retrograde tracer was injected into the CSF-contacting nucleus, it was transported retrogradely along the axons, and neuron somata projecting from the diencephalon was detected
Summary
The cerebrospinal fluid (CSF)-contacting nucleus is a unique nucleus in the brain. It is located within the ventral gray of the lower portion of the aqueduct (Aq) and upper portion of the fourth ventricle (4V) floor (Song et al, 2019). The unique characteristic of the CSF-contacting nucleus implies that this nucleus may be a key structure bridging the nerve and fluids (CSF and plasma), and play an extremely important role in physiological activities. It has been approximately 30 years since we first discovered, named and began to study this nucleus. F. et al, 2017), ion channels (Wang et al, 2014)] and its relationship with some biological activities [such as pain (Zhou et al, 2017), sodium appetite (Xing et al, 2015), stress (Wu et al, 2015), morphine dependence and withdrawal (Lu et al, 2011)] have been revealed. This nucleus is involved in pathways and mechanisms of different biological activities that are still to be clarified
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