Connection Input Mapping and 3D Reconstruction of the Brainstem and Spinal Cord Projections to the CSF-Contacting Nucleus

Abstract

Objective: To investigate whether the CSF-contacting nucleus receives brainstem and spinal cord projections and to understand the functional significance of these connections. Methods: The retrograde tracer cholera toxin B subunit (CB) was injected into the CSF-contacting nucleus in Sprague-Dawley rats according the previously reported stereotaxic coordinates. After 7-10 days, these rats were perfused and their brainstem and spinal cord were sliced (thickness, 40 µm) using a freezing microtome. All the sections were subjected to CB immunofluorescence staining. The distribution of CBpositive neuron in different brainstem and spinal cord areas was observed under fluorescence microscope. Results: The retrograde labeled CB-positive neurons were found in the midbrain, pons, medulla oblongata, and spinal cord. Four functional areas including one hundred and twelve sub-regions have projections to the CSF-contacting nucleus. However, the density of CB-positive neuron distribution ranged from sparse to dense. Conclusion: Based on the connectivity patterns of the CSF-contacting nucleus receives anatomical inputs from the brainstem and spinal cord, we preliminarily conclude and summarize that the CSF-contacting nucleus participates in pain, visceral activity, sleep and arousal, emotion, and drug addiction. The present study firstly illustrates the broad projections of the CSF-contacting nucleus from the brainstem and spinal cord, which implies the complicated functions of the nucleus especially for the unique roles of coordination in neural and body fluids regulation.

The CSF-Contacting Nucleus Receives Anatomical Inputs From the Cerebral Cortex: A Combination of Retrograde Tracing and 3D Reconstruction Study in Rat

“…After 7-10 days, the animals were perfused as described previously (Song et al, 2020a). The whole brain and spinal cord were isolated and placed in the same 4% paraformaldehyde solution for postfixation at 4 • C overnight.…”

“…The main aim of neuroscience research is to discuss the neural connection networks between different brain regions and thereby understand the brain functions (Watabe-Uchida et al, 2012). We have already illustrated the diencephalon (Song et al, 2020b), brainstem, and spinal cord anatomical projections to the CSF-contacting nucleus (Song et al, 2020a). The cerebral cortex is regarded as the core of the brain's cognitive system (Bota et al, 2015), and it is also important to identify the cortex→CSF-contacting nucleus.…”

Novel Projections to the Cerebrospinal Fluid-Contacting Nucleus From the Subcortex and Limbic System in Rat

“…It implies that the CSF-contacting nucleus may be considered as an important structure bridging the brain and CSF, or that it plays an extremely important role in physiological activities. Moreover, our recent studies reveal that this nucleus receives the projections from the hypothalamus (Song et al, 2020b ) and brainstem (Song et al, 2020a ), which implies that the CSF-contacting nucleus participates in complex and diverse neural circuits modulating different behaviors. The relationships with some of the life activities such as pain (Liu et al, 2017 ), stress (Wu et al, 2015 ), and drug addiction (Lu et al, 2011 ) have been already reported.…”

Hypothalamic CSF-contacting neurons project to the rostral agranular insular cortex: an immunofluorescence and ultrastructural analysis in the rat.

“…Currently, it is well known that the CSF-contacting neurons send projections to the spinal cord, brain stem structures, and many cortical areas (Song et al, 2020;Song et al, 2020;Zhou et al, 2017). Although the function of the CSF-contacting neurons has been mainly related to a form of detection of the CSF environment (e.g., pH and osmotic changes) (Jalalvand et al, 2018), we need to keep in mind that recent data tend to support the notion that this kind of neurons also can be implied in more complex responses (i.e., modulation of motor neurons and premotor excitatory neurons) (Wyart et al, 2023).…”