Abstract
BackgroundThere is a unique nucleus (CSF-contacting nucleus) in the brain of rat. It has been demonstrated in our previous research. The extraordinary feature of this nucleus is that it is not connected to any parenchymal organ but to the CSF. In primates, however, the presence or absence of this nucleus has not been proven. Confirmation of the presence of this nucleus in primates will provide the structural basis for brain-CSF communication and help to understand the neurohumoral regulatory mechanisms in humans.MethodsThe tracer cholera toxin B subunit conjugated to horseradish peroxidase (CB-HRP) was injected into the CSF in the lateral ventricle (LV) of primate rhesus monkeys. After 48 h, the monkeys were perfused and the brain was dissected out, and sectioned for CB-HRP staining. The CB-HRP positive structures were observed under confocal and electron microscopy. The three-dimensional (3D) structure of the CB-HRP positive neurons cluster was reconstructed by computer software.Results(1) CB-HRP labeling is confined within the ventricle, but not leakage into the brain parenchyma. (2) From the midbrain inferior colliculus superior border plane ventral to the aqueduct to the upper part of the fourth ventricle (4V) floor, a large number of CB-HRP positive neurons are consistently located, form a cluster, and are symmetrically located on both sides of the midline. (3) 3D reconstruction shows that the CB-HRP positive neurons cluster in the monkey brain occupies certain space. The rostral part is large and caudal part is thin appearing a “rivet”-like shape. (4) Under electron microscopy, the CB-HRP positive neurons show different types of synaptic connections with the non-CSF-contacting structures in the brain. Some of the processes stretch directly into the ventricle cavity.ConclusionSame as we did in rats, the CSF-contacting nucleus is also existed in the primate brain parenchyma. We also recommend listing it as the XIII pair of cranial nucleus, which is specialized in the communications between the brain and the CSF. It is significant to the completing of innervation in the organism.
Highlights
The animal body consists of parenchymal organs, and of fluids
In the past 30 years, our studies revealed that after injecting peripheral nerve tracer CB-HRP into the rat ventricular system, the tracer is confined to the ventricular wall because of the existence of the brain barriers
Monkeys were anesthetized with ketamine (10 mg/kg, i.m.), and the head was fixed on a stereotaxic instrument. 50 μl 30% CB-HRP (Sigma, United States), a specific tracer of the CSFcontacting nucleus through the ventricular system, was injected into the lateral ventricle (LV) according to the stereotaxic coordinates provided by Paxinos et al (2000)
Summary
The animal body consists of parenchymal organs, and of fluids (such as brain interstitial fluid, plasma, and CSF). The neural processes that stretch into the CSF can be labeled These neurons have a consistent location, form an independent cluster, occupy a certain space, and have a clear boundary with the nearby structures. The CSF-contacting neurons cluster is in accordance with the definition of the nucleus. We name it as the “cerebrospinal fluid-contacting nucleus” or “CSF-contacting nucleus” (Song and Zhang, 2018; Song et al, 2019). Studies have confirmed that the CSF-contacting nucleus has broad synaptic and non-synaptic connections with the other neurons and the blood vessels, and has the morphology for sensing and modulating the body fluids (Zhang et al, 2003; Liang et al, 2007; Song et al, 2020a,b). Confirmation of the presence of this nucleus in primates will provide the structural basis for brainCSF communication and help to understand the neurohumoral regulatory mechanisms in humans
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