Bai-Ren Wang

Strong Expression of Interleukin-1 Receptor Type I in the Rat Carotid Body

One of the unsolved key questions in neuroimmunomodulation is how peripheral immune signals are transmitted to the brain. It has been reported that the vagus might play a role in this regard. The underlying mechanism for this immune system-to-brain communication route is related to the binding of cytokines, such as interleukin (IL)-1β originating from activated immune cells, to their receptors in glomus cells of the vagal paraganglia. The existence of IL-1 receptor type I (IL-1RI) in vagal paraganglia has been proved. On the basis of these studies, a hypothesis is raised that the carotid body, as the largest paraganglion, might play a similar role to that of its abdominal partner. In this study we examined the distribution of IL-1RI in the carotid body by immunohistochemistry (IHC) and Western blotting techniques. The IHC results showed that almost all glomus cells in the carotid body displayed strong IL-1RI immunoreactivity. The IL-1RI-immunoreactive products were localized in the cytoplasm, nucleus, and cell membrane of the glomus cells. The Western blotting results also confirmed the existence of IL-1RI in both membranous and cytoplasmic elements of the carotid body. These results imply that the carotid body not only serves as a chemoreceptor for modulation of cardiorespiratory performance, as traditionally recognized, but also acts as a cytokine chemorereceptor for sensing immune signals.

IL‐1β inhibits IK and increases [Ca2+]i in the carotid body glomus cells and increases carotid sinus nerve firings in the rat

Increasing evidence indicates that there exists a reciprocal communication between the immune system and the brain. Interleukin 1β (IL‐1β), a proinflammatory cytokine produced during immune challenge, is believed to be one of the mediators of immune‐to‐brain communication, but how it gets into the brain is unknown because of its large molecular weight and difficulty in crossing the blood–brain barrier. Our previous work has demonstrated that IL‐1 receptor type I is strongly expressed in the glomus cells of rat carotid body (CB), a well characterized polymodal chemoreceptive organ which serves not only for the detection of hypoxia, hypercapnia and acidity, but also for low temperature and blood glucose. The present study was designed to test whether IL‐1β could stimulate the CB glomus cells and alter the discharge properties in the carotid sinus nerve, the afferent nerve innervating the organ. The results from whole‐cell patch‐clamp recordings and calcium imaging showed that extracellular application of IL‐1β significantly decreased the outward potassium current and triggered a transient rise in [Ca2+]i in the cultured glomus cells of rat CB. Furthermore, by using extracellular recordings and pharmacological intervention, it was found that IL‐1β stimulation of the CB in the anaesthetized rat in vivo significantly increased the discharge rate in the carotid sinus nerve, most probably mediated by ATP release. This experiment provides evidence that the CB responds to cytokine stimulation and proposes the possibility that the CB might play a role in immune‐to‐brain communication.

EXTRAVASATION OF BLOOD-BORNE IMMUNOGLOBULIN G THROUGH BLOOD-BRAIN BARRIER DURING ADRENALINE-INDUCED TRANSIENT HYPERTENSION IN THE RAT

The effect of transient hypertension on blood-brain barrier (BBB) permeability, particularly on extravasation of immunoglobulin G (IgG), has not been fully understood. In the present experiment, we investigated- the time course of endogenous albumin and IgG extravasation through BBB and the localization of extravasated IgG in brain parenchyma during- adrenaline (AD)-induced transient hypertension in the rat by using Evans blue fluorescence, immunohistochemistry, and Western blot. The results showed that a bolus injection of AD (10 μg/kg) induced a transient elevation of arterial pressure lasting about 1 min. The endogenous albumin and IgG entered the brain parenchyma via BBB only when hyper--tension occurred. Electron microscopically, the IgG-like immunoreactivities were predominantly seen in the cytoplasm of endothelia of capillaries, pericytes, extracellular space of parenchyma, and the cytoplasm of glial cells. The results suggest that circulating IgG or antibodies might contact the structures of brain parenchyma through passage of BBB when its permeability is temporally changed by transient hypertension. This phenomenon implies a possible mechanism of pathogenesis for immune-mediated diseases in the brain.

Fos expression in the rat brain after intraperitoneal injection of Staphylococcus enterotoxin B and the effect of vagotomy

The current study was designed to locate the neuronal activation in rat brain following intraperitoneal injection of Staphylococcus enterotoxin B (SEB) and observe the consequence of preliminary subdiaphragmatic vagotomy on SEB-induced brain Fos expression to clarify the role of the vagus nerve in sensation and transmission of abdominal SEB stimulation. The results showed that intraperitoneal SEB (1 mg/kg) induced a robust Fos expression in widespread brain areas. A significant increase of Fos immunoreactive cells were observed in the solitary tract nucleus, locus ceruleus, lateral parabrachial nucleus, ventrolateral part of central gray, medial amygdaloid nucleus, central amygdaloid nucleus, ventromedial part of thalamus, dorsomedial part of thalamus, hypothalamic paraventricular nucleus, lateral habenula, and lateral septum nucleus following SEB challenge. In hypothalamic paraventricular nucleus, in addition to the dense Fos expression in the parvocellular portion, some Fos-positive cells were also observed in the anterior magnocellular nucleus of the complex. Double immunofluorescence studies showed that these Fos-immunoreactive cells were mostly oxytocinergic. The results also showed that subdiaphragmatic vagotomy largely attenuated, but not totally abrogated, the brain Fos expression induced by abdominal administration of SEB. Our data suggest that peripheral SEB stimulation can induce activation of neurons in widespread brain areas and that the vagus plays a crucial role in transmitting the signal of abdominal immune stimulation to the brain.

Alterations of Fc gamma receptor I and Toll-like receptor 4 mediate the antiinflammatory actions of microglia and astrocytes after adrenaline-induced blood–brain barrier opening in rats

Blood–brain barrier (BBB) opening occurs under many physiological and pathological conditions. BBB opening will lead to the leakage of large circulating molecules into the brain parenchyma. These invasive molecules will induce immune responses. Microglia and astrocytes are the two major cell types responsible for immune responses in the brain, and Fc gamma receptor I (FcγRI) and Toll‐like receptor 4 (TLR4) are the two important receptors mediating these processes. Data suggest that activation of the FcγRI pathway mediates antiinflammatory processes, whereas activation of TLR4 pathway leads to proinflammatory activities. In the present study, we tested the hypothesis that BBB opening could lead to alterations in FcγRI and TLR4 pathways in microglia and astrocytes, thus limiting excessive inflammation in the brain. The transient BBB opening was induced by adrenaline injection through a caudal vein in Sprague‐Dawley rats. We found that the FcγRI pathway was significantly activated in both microglia and astrocytes, as exhibited by the up‐regulation of FcγRI and its key downstream molecule Syk, as well as the increased production of the effector cytokines, interleukin (IL)‐10 and IL‐4. Interestingly, after transient BBB opening, TLR4 expression was also increased. However, the expression of MyD88, the central adapter of the TLR4 pathway, was significantly inhibited, with decreased production of the effector cytokines IL‐12a and IL‐1β. These results indicate that, after transient BBB opening, FcγRI‐mediated antiinflammatory processes were activated, whereas TLR4‐mediated proinflammatory activities were inhibited in microglia and astrocytes. This may represent an important neuroprotective mechanism of microglia and astrocytes that limits excessive inflammation after BBB opening.

Enhancement of antibody production and expression of c-Fos in the insular cortex in response to a conditioned stimulus after a single-trial learning paradigm.

Immune responses can be modulated by Pavlovian conditioning techniques. In this study, to evaluate the conditionability of antibody response via a single-trial conditioning paradigm, we used a protein antigen ovalbumin as an unconditioned stimulus (UCS) that was paired with a novel taste of saccharin in a single-trial learning protocol. A significant enhancement of anti-ovalbumin antibody production was observed in the conditioned rats at Days 15, 20 and 25 after re-exposure to the conditioned stimulus. The pattern of conditioned antibody response is similar to that of antigen-induced antibody response. Furthermore, to identify the involvement of a limbic brain structure in the expression of conditioned antibody response, immediate-early gene c-fos expression was used as a marker of neuronal activation to detect the functional activation in the insular cortex (IC) in response to the conditioned stimulus. The re-exposure of conditioned rats to the conditioned stimulus resulted in a significant increase of c-Fos immunoreactivity in all three areas of the IC including the agranular, dysgranular, and granular areas, suggesting that IC is involved in the neural mechanism of expression of conditioned immune response.

Interleukin-6 increases intracellular Ca2+ concentration and induces catecholamine secretion in rat carotid body glomus cells.

Although abundant evidence indicates mutual regulation between the immune and the central nervous systems, how the immune signals are transmitted to the brain is still an unresolved question. In a previous study we found strong expression of proinflammatory cytokine receptors, including interleukin (IL)‐1 receptor I and IL‐6 receptor α in the rat carotid body (CB), a well‐known arterial chemoreceptor that senses a variety of chemostimuli in the arterial blood. We demonstrated that IL‐1 stimulation increases intracellular calcium ([Ca2+]i) in CB glomus cells, releases ATP, and increases the discharge rate in carotid sinus nerve. To explore the effect of IL‐6 on CB, here we examine the effect of IL‐6 on [Ca2+]i and catecholamine (CA) secretion in rat CB glomus cells. Calcium imaging showed that extracellular application of IL‐6 induced a rise in [Ca2+]i in cultured glomus cells. Amperometry showed that local application of IL‐6 evoked CA release from glomus cells. Furthermore, the CA secretory response to IL‐6 was blocked by 200 μM Cd2+, a well‐known Ca2+ channel blocker. Our experiments provide further evidence for the responsiveness of the CB to proinflammatory cytokines and indicate that the CB might play a role in inflammation sensing and transmission of such information to the brain.

Role of Extracellular Signal-Regulated Kinase in Glutamate-Stimulated Apoptosis of Rat Retinal Ganglion Cells

Purpose: To investigate the involvement of the extracellular signal-regulated kinase (ERK) signaling pathway after intravitrevous injection of glutamate in rat retina. Methods: Three groups of five Sprague-Dawley rats each were studied. Group I was a normal control group, intravitreal saline injections. In Group II, one eye received an intravitreal glutamate injection (375 nmol, dissolved in saline) while the contralateral eye served as control. In Group III, intravitreal PD98059 (100 μ mol, an inhibitor of ERK) injections were administered 1 hr before glutamate injections. Seven days after injections, phosphorylated (activated) ERK in retina was localized by immunohistochemistry and fluorescent double labeling of retinal cryosections. Specific ERK blockade was documented to assess the functional significance of activated ERK. TUNEL staining was performed to assess apoptotic cell death. Results: Expression of phosphorylated ERK in rat retina was observed in the inner nuclear layer, the outer nuclear layer, and the nerve fiber layer after 3 days intravitreous injection of glutamate, increasing significantly after 7 days. Double immunofluorescence labling demonstrated that the increased retinal immunostaining for phospho-ERK was predominantly localized to the retinal Müller cells after 7 days intravitreous injection of glutamate. Moreover, blocking activation of ERK significantly improved the number of TUNEL-positive cells in the eyes receiving intravitreal PD98059 injections compared with the eyes receiving glutamate injections. Conclusions: The ERK pathway is involved in signal transduction in the retina after excessive stimulation by glutamate, which may contribute to the antiapoptotic role in retinal ganglion cell death induced by glutamate.

Sertraline promotes hippocampus-derived neural stem cells differentiating into neurons but not glia and attenuates LPS-induced cellular damage.

Sertraline is one of the most commonly used antidepressants in clinic. Although it is well accepted that sertraline exerts its action through inhibition of the reuptake of serotonin at presynaptic site in the brain, its effect on the neural stem cells (NSCs) has not been well elucidated. In this study, we utilized NSCs separated from the hippocampus of fetal rat to investigate the effect of sertraline on the proliferation and differentiation of NSCs. The study demonstrated that sertraline had no effect on NSCs proliferation but it significantly promoted NSCs to differentiate into serotoninergic neurons other than glia cells. Furthermore, we found that sertraline protected NSCs against the lipopolysaccharide-induced cellular damage. These data indicate that sertraline can promote neurogenesis and protect the viability of neural stem cells.

GABAergic synapses upon neurons expressing substance P receptors in the nucleus of the solitary tract: an immunocytochemical electron microscope study in the rat ☆

Morphological substrates for interactions between gamma-aminobutyric acid (GABA) and substance P upon neurons expressing substance P receptor (SPR) in the nucleus of the solitary tract (NST) were investigated by immunocytochemical electron microscopy. In the NST of the rat, many GABA-like immunoreactive axon terminals were in symmetric synaptic contacts with dendritic profiles; they were observed on nearly a half of the SPR-like immunoreactive dendritic profiles in the medial part of the caudal half of the NST.