Cerebrospinal fluid-contacting nucleus mediates nociception via release of fractalkine

Hypothalamic cerebrospinal fluid-contacting neurons project to the rostral agranular insular cortex: An immunofluorescence and ultrastructural analysis in the rat

Cerebrospinal fluid-contacting neurons (CSF-cNS) are considered mechanoreceptors and chemoreceptors involved in detecting changes in CSF circulation. However, considering that recent data suggest that this type of cell could exert an active response when an external stimulus is sensed, identification of CSF-cNS may be relevant. In this regard, some data suggest that a neuronal connection exists between the ventral region of the hypothalamic paraventricular nucleus (PVN) and rostral agranular insular cortex (RAIC); indeed, a potential CSF-cNS is hypothesized. However, a detailed analysis of this connection has not been conducted. Thus, using neuronal tracers (Fluoro-Gold® (FG) and cholera toxin (ChT)) coupled with transmission electron microscopy and immunofluorescence assays against Fluoro-Gold®, oxytocin (OXT), vasopressin (AVP) and oxytocin receptors (OTR), we describe an oxytocinergic or vasopressinergic CSF-cNS between the PVN and RAIC. Our results showed that CSF-cNS along the PVN labelled with oxytocin and/or AVP were present in dendritic projections near the third ventricle. This CSF-cNS in the PVN seems to project to the RAIC. Inside the RAIC, ultrastructural analysis showed that axons immunopositive for oxytocin from the PVN sustained synaptic connections with neurons that expressed OTR. These findings show that the CSF-cNS from the PVN sends projections to the RAIC. To the best of our knowledge, the relevance of CSF-cNS has not been elucidated; however, we hypothesized that the activation of cells could concomitantly release neuropeptides (i.e., oxytocin and AVP) in the CSF and RAIC. Thus, further analysis of the impact of neuropeptides released into the third ventricle and RAIC is warranted.

Activation of P2X4 receptors in midbrain cerebrospinal fluid-contacting nucleus leads to mechanical hyperalgesia in chronic constriction injury rats

Neuropathic pain is a refractory pain state, and its mechanism is still not clear. Previous studies have shown that the purine receptor P2X4R expressed on hyperactive microglia in the spinal cord is essential for the occurrence and development of neuropathic pain. The cerebrospinal fluid-contacting nucleus (CSF-contacting nucleus) in the midbrain has been found to play an important role in the descending inhibition system of modulation. However, there have been no studies on P2X4R in the CSF-contacting nucleus involved in neuropathic pain. To investigate whether P2X4R is expressed in the CSF-contacting nucleus and whether its expression in the CSF-contacting nucleus is involved in the regulation of neuropathic pain, we used a model of chronic sciatic nerve ligation injury (CCI) to simulate neuropathic pain conditions. Immunohistochemistry experiments were conducted to identify the expression of P2X4R in the CSF-contacting nuclei in CCI rats, and western blot analysis showed a significant increase in P2X4R levels 7 days after modeling. Then, we packaged a P2rx4 gene-targeting shRNA in scAAV9 to knock down the P2X4R level in the CSF-contacting nucleus, and we found that CCI-induced mechanical hyperalgesia was reversed. In conclusion, P2X4R expressed in the CSF-contacting nucleus is involved in the process of neuropathic pain, and downregulating P2X4R protein in the CSF-contacting nucleus can reverse the occurrence and development of hyperalgesia, which could represent a potent therapeutic strategy for neuropathic pain.

Release of Endocannabinoids into the Cerebrospinal Fluid during the Induction of the Trigemino-Hypoglossal Reflex in Rats

The endocannabinoid system (ECS) plays an important role in pain processing and modulation. Since the specific effects of endocannabinoids within the orofacial area are largely unknown, we aimed to determine whether an increase in the endocannabinoid concentration in the cerebrospinal fluid (CSF) caused by the peripheral administration of the FAAH inhibitor URB597 and tooth pulp stimulation would affect the transmission of impulses between the sensory and motor centers localized in the vicinity of the third and fourth cerebral ventricles. The study objectives were evaluated on rats using a method that allowed the recording of the amplitude of evoked tongue jerks (ETJ) in response to noxious tooth pulp stimulation and URB597 treatment. The amplitude of ETJ was a measure of the effect of endocannabinoids on the neural structures. The concentrations of the endocannabinoids tested (AEA and 2-AG) were determined in the CSF, along with the expression of the cannabinoid receptors (CB1 and CB2) in the tissues of the mesencephalon, thalamus, and hypothalamus. We demonstrated that anandamide (AEA), but not 2-arachidonoylglycerol (2-AG), was significantly increased in the CSF after treatment with a FAAH inhibitor, while tooth pulp stimulation had no effect on the AEA and 2-AG concentrations in the CSF. We also found positive correlations between the CSF AEA concentration and cannabinoid receptor type 1 (CB1R) expression in the brain, and between 2-AG and cannabinoid receptor type 2 (CB2R), and negative correlations between the CSF concentration of AEA and brain CB2R expression, and between 2-AG and CB1R. Our study shows that endogenous AEA, which diffuses through the cerebroventricular ependyma into CSF and exerts a modulatory effect mediated by CB1Rs, alters the properties of neurons in the trigeminal sensory nuclei, interneurons, and motoneurons of the hypoglossal nerve. In addition, our findings may be consistent with the emerging concept that AEA and 2-AG have different regulatory mechanisms because they are involved differently in orofacial pain. We also suggest that FAAH inhibition may offer a therapeutic approach to the treatment of orofacial pain.

PFKFB3 Inhibition Sensitizes DNA Crosslinking Chemotherapies by Suppressing Fanconi Anemia Repair

Simple Summary

DNA-damaging chemotherapeutics, such as platinum drugs, are cornerstones in cancer treatment. The efficacy of such treatment is intimately linked to the DNA repair capacity of the cancer cells, as DNA damage above a tolerable threshold culminates in cell death. Cancer cells often have deregulated DNA repair mechanisms, making them initially more sensitive to DNA-damaging chemotherapies. Unfortunately, over time, cancer cells often develop resistance to such treatments by rewiring their DNA damage response pathways. Here, we identify that targeting the recognized anti-cancer target 6-phosphofructo-2-kinase/fructose-2,6,-bisphophatase 3 (PFKFB3), commonly overexpressed in cancer, with the small molecule inhibitor KAN0438757, selectively sensitizes cancer cells to platinum drugs, including treatment-resistant cancer cells, while sparing normal cells. Mechanistically, PFKFB3 promotes tolerance to and the repair of platinum-induced DNA interstrand crosslinks (ICLs) through modulation of the Fanconi anemia (FA) DNA repair pathway. Thus targeting PFKFB3 opens up therapeutic possibilities to improve the efficacy of ICL-inducing cancer treatments.

Abstract

Replicative repair of interstrand crosslinks (ICL) generated by platinum chemotherapeutics is orchestrated by the Fanconi anemia (FA) repair pathway to ensure resolution of stalled replication forks and the maintenance of genomic integrity. Here, we identify novel regulation of FA repair by the cancer-associated glycolytic enzyme PFKFB3 that has functional consequences for replication-associated ICL repair and cancer cell survival. Inhibition of PFKFB3 displays a cancer-specific synergy with platinum compounds in blocking cell viability and restores sensitivity in treatment-resistant models. Notably, the synergies are associated with DNA-damage-induced chromatin association of PFKFB3 upon cancer transformation, which further increases upon platinum resistance. FA pathway activation triggers the PFKFB3 assembly into nuclear foci in an ATR- and FANCM-dependent manner. Blocking PFKFB3 activity disrupts the assembly of key FA repair factors and consequently prevents fork restart. This results in an incapacity to replicate cells to progress through S-phase, an accumulation of DNA damage in replicating cells, and fork collapse. We further validate PFKFB3-dependent regulation of FA repair in ex vivo cultures from cancer patients. Collectively, targeting PFKFB3 opens up therapeutic possibilities to improve the efficacy of ICL-inducing cancer treatments.

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

Objective

This study aimed to investigate the direct monosynaptic projections from cortical functional regions to the cerebrospinal fluid (CSF)-contacting nucleus for understanding the functions of the CSF-contacting nucleus.

Methods

The Sprague-Dawley rats received cholera toxin B subunit (CB) injections into the CSF-contacting nucleus. After 7-10 days of survival time, the rats were perfused, and the whole brain and spinal cord were sliced under a freezing microtome at 40 μm. All sections were treated with the CB immunofluorescence reaction. The retrogradely labeled neurons in different cortical areas were revealed under a confocal microscope. The distribution features were further illustrated under 3D reconstruction.

Results

The retrogradely labeled neurons were identified in the olfactory, orbital, cingulate, insula, retrosplenial, somatosensory, motor, visual, auditory, association, rhinal, and parietal cortical areas. A total of 12 functional areas and 34 functional subregions showed projections to the CSF-contacting nucleus in different cell intensities.

Conclusion

According to the connectivity patterns, we conclude that the CSF-contacting nucleus participates in cognition, emotion, pain, visceral activity, etc. The present study firstly reveals the cerebral cortex→CSF-contacting nucleus connections, which implies the multiple functions of this special nucleus in neural and body fluid regulations.

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

Objective: To identify the novel projections received by the cerebrospinal fluid (CSF)-contacting nucleus from the subcortex and limbic system to understand the biological functions of the nucleus.

Methods: The cholera toxin subunit B (CB), a retrograde tracer, was injected into the CSF-contacting nucleus in Sprague–Dawley rats. After 7–10 days, the surviving rats were perfused, and the whole brain and spinal cord were sliced for CB immunofluorescence detection. The CB-positive neurons in the subcortex and limbic system were observed under a fluorescence microscope, followed by 3D reconstructed with the imaris software.

Results: CB-positive neurons were found in the basal forebrain, septum, periventricular organs, preoptic area, and amygdaloid structures. Five functional areas including 46 sub-regions sent projections to the CSF-contacting nucleus. However, the projections had different densities, ranging from sparse to moderate, to dense.

Conclusions: According to the projections from the subcortex and limbic system, we hypothesize that the CSF-contacting nucleus participates in emotion, cognition, homeostasis regulation, visceral activity, pain, and addiction. In this study, we illustrate the novel projections from the subcortex and limbic system to the CSF-contacting nucleus, which underlies the diverse and complicated circuits of the nucleus in body regulations.

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

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 CB-positive 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.

Monosynaptic Input Mapping of Diencephalic Projections to the Cerebrospinal Fluid-Contacting Nucleus in the Rat

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.