Effect of intestinal inflammation on neuronal survival and function in the dorsal motor nucleus of the vagus

Inflammatory Stress Induced by Intraperitoneal Injection of LPS Increases Phoenixin Expression and Activity in Distinct Rat Brain Nuclei

Due to phoenixin’s role in restraint stress and glucocorticoid stress, as well as its recently shown effects on the inflammasome, we aimed to investigate the effects of lipopolysaccharide (LPS)-induced inflammatory stress on the activity of brain nuclei-expressing phoenixin. Male Sprague Dawley rats (n = 6/group) were intraperitoneally injected with either LPS or control (saline). Brains were processed for c-Fos and phoenixin immunohistochemistry and the resulting slides were evaluated using ImageJ software. c-Fos was counted and phoenixin was evaluated using densitometry. LPS stress significantly increased c-Fos expression in the central amygdaloid nucleus (CeM, 7.2-fold), supraoptic nucleus (SON, 34.8 ± 17.3 vs. 0.0 ± 0.0), arcuate nucleus (Arc, 4.9-fold), raphe pallidus (RPa, 5.1-fold), bed nucleus of the stria terminalis (BSt, 5.9-fold), dorsal motor nucleus of the vagus nerve (DMN, 89-fold), and medial part of the nucleus of the solitary tract (mNTS, 121-fold) compared to the control-injected group (p < 0.05). Phoenixin expression also significantly increased in the CeM (1.2-fold), SON (1.5-fold), RPa (1.3-fold), DMN (1.3-fold), and mNTS (1.9-fold, p < 0.05), leading to a positive correlation between c-Fos and phoenixin in the RPa, BSt, and mNTS (p < 0.05). In conclusion, LPS stress induces a significant increase in activity in phoenixin immunoreactive brain nuclei that is distinctively different from restraint stress.

Fluoroquinolones-Associated Disability: It Is Not All in Your Head

Fluoroquinolones (FQs) are a broad class of antibiotics typically prescribed for bacterial infections, including infections for which their use is discouraged. The FDA has proposed the existence of a permanent disability (Fluoroquinolone Associated Disability; FQAD), which is yet to be formally recognized. Previous studies suggest that FQs act as selective GABAA receptor inhibitors, preventing the binding of GABA in the central nervous system. GABA is a key regulator of the vagus nerve, involved in the control of gastrointestinal (GI) function. Indeed, GABA is released from the Nucleus of the Tractus Solitarius (NTS) to the Dorsal Motor Nucleus of the vagus (DMV) to tonically regulate vagal activity. The purpose of this review is to summarize the current knowledge on FQs in the context of the vagus nerve and examine how these drugs could lead to dysregulated signaling to the GI tract. Since there is sufficient evidence to suggest that GABA transmission is hindered by FQs, it is reasonable to postulate that the vagal circuit could be compromised at the NTS-DMV synapse after FQ use, possibly leading to the development of permanent GI disorders in FQAD.

Neuroimmune Interactions in the Gut and Their Significance for Intestinal Immunity

Inflammatory bowel diseases (IBD) have a complex, multifactorial pathophysiology with an unmet need for effective treatment. This calls for novel strategies to improve disease outcome and quality of life for patients. Increasing evidence suggests that autonomic nerves and neurotransmitters, as well as neuropeptides, modulate the intestinal immune system, and thereby regulate the intestinal inflammatory processes. Although the autonomic nervous system is classically divided in a sympathetic and parasympathetic branch, both play a pivotal role in the crosstalk with the immune system, with the enteric nervous system acting as a potential interface. Pilot clinical trials that employ vagus nerve stimulation to reduce inflammation are met with promising results. In this paper, we review current knowledge on the innervation of the gut, the potential of cholinergic and adrenergic systems to modulate intestinal immunity, and comment on ongoing developments in clinical trials.

Gastric vagal motoneuron function is maintained following experimental spinal cord injury

BACKGROUND

Clinical reports indicate that spinal cord injury (SCI) initiates profound gastric dysfunction. Gastric reflexes involve stimulation of sensory vagal fibers, which engage brainstem circuits that modulate efferent output back to the stomach, thereby completing the vago-vagal reflex. Our recent studies in a rodent model of experimental high thoracic (T3-) SCI suggest that reduced vagal afferent sensitivity to gastrointestinal (GI) stimuli may be responsible for diminished gastric function. Nevertheless, derangements in efferent signals from the dorsal motor nucleus of the vagus (DMV) to the stomach may also account for reduced motility.

METHODS

We assessed the anatomical, neurophysiological, and functional integrity of gastric-projecting DMV neurons in T3-SCI rats using: (i) retrograde labeling of gastric-projecting DMV neurons; (ii) whole cell recordings from gastric-projecting neurons of the DMV; and, (iii) in vivo measurements of gastric contractions following unilateral microinjection of thyrotropin-releasing hormone (TRH) into the DMV.

KEY RESULTS

Immunohistochemical analysis of gastric-projecting DMV neurons demonstrated no difference between control and T3-SCI rats. Whole cell in vitro recordings showed no alteration in DMV membrane properties and the neuronal morphology of these same, neurobiotin-labeled, DMV neurons were unchanged after T3-SCI with regard to cell size and dendritic arborization. Central microinjection of TRH induced a significant facilitation of gastric contractions in both control and T3-SCI rats and there were no significant dose-dependent differences between groups.

CONCLUSIONS & INFERENCES

Our data suggest that the acute, 3 day to 1 week post-SCI, dysfunction of vagally mediated gastric reflexes do not include derangements in the efferent DMV motoneurons.

Air pollution is associated with brainstem auditory nuclei pathology and delayed brainstem auditory evoked potentials

We assessed brainstem inflammation in children exposed to air pollutants by comparing brainstem auditory evoked potentials (BAEPs) and blood inflammatory markers in children age 96.3±8.5 months from highly polluted (n=34) versus a low polluted city (n=17). The brainstems of nine children with accidental deaths were also examined. Children from the highly polluted environment had significant delays in wave III (t(50)=17.038; p<0.0001) and wave V (t(50)=19.730; p<0.0001) but no delay in wave I (p=0.548). They also had significantly longer latencies than controls for interwave intervals I-III, III-V, and I-V (all t(50)>7.501; p<0.0001), consisting with delayed central conduction time of brainstem neural transmission. Highly exposed children showed significant evidence of inflammatory markers and their auditory and vestibular nuclei accumulated α synuclein and/or β amyloid(1-42). Medial superior olive neurons, critically involved in BAEPs, displayed significant pathology. Children's exposure to urban air pollution increases their risk for auditory and vestibular impairment.

Urban air pollution targets the dorsal vagal complex and dark chocolate offers neuroprotection

Mexico City (MC) residents exposed to fine particulate matter and endotoxin exhibit inflammation of the olfactory bulb, substantia nigra, and vagus nerve. The goal of this study was to model these endpoints in mice and examine the neuroprotective effects of chocolate. Mice exposed to MC air received no treatment or oral dark chocolate and were compared to clean-air mice either untreated or treated intraperitoneally with endotoxin. Cyclooxygenase-2 (COX-2), interleukin 1 beta (IL-1β), and CD14 messenger RNA (mRNA) were quantified after 4, 8, and 16 months of exposure in target brain regions. After 16 months of exposure, the dorsal vagal complex (DVC) exhibited significant inflammation in endotoxin-treated and MC mice (COX-2 and IL-1β P<.001). Mexico City mice had olfactory bulb upregulation of CD14 (P=.002) and significant DVC imbalance in genes for antioxidant defenses, apoptosis, and neurodegeneration. These findings demonstrate sustained DVC inflammation in mice exposed to MC air, which is mitigated by chocolate administration.

Combined administration of secretin and oxytocin inhibits chronic colitis and associated activation of forebrain neurons

BACKGROUND

The pathogenesis of inflammatory bowel disease is unknown; however, the disorder is aggravated by psychological stress and is itself psychologically stressful. Chronic intestinal inflammation, moreover, has been reported to activate forebrain neurons. We tested the hypotheses that the chronically inflamed bowel signals to the brain through the vagi and that administration of a combination of secretin (S) and oxytocin (OT) inhibits this signaling.

METHODS

Three daily enemas containing 2,4,6-trinitrobenzene sulfonic acid (TNBS), which were given to rats produced chronic colitis and ongoing activation of Fos in brain neurons.

KEY RESULTS

Fos was induced in neurons in the paraventricular nucleus of the hypothalamus, basolateral amygdala, central amygdala, and piriform cortex. Subdiaphragmatic vagotomy failed to inhibit this activation of Fos, suggesting that colitis activates forebrain neurons independently of the vagi. When administered intravenously, but not when given intracerebroventricularly, in doses that were individually ineffective, combined S/OT prevented colitis-associated activation of central neurons. Strikingly, S/OT decreased inflammatory infiltrates into the colon and colonic expression of tumor necrosis factor-alpha and interferon-gamma.

CONCLUSIONS & INFERENCES

These observations suggest that chronic colonic inflammation is ameliorated by the systemic administration of S/OT, which probably explains the parallel ability of systemic S/OT to inhibit the colitis-associated activation of forebrain neurons. It is possible that S and OT, which are endogenous to the colon, might normally combine to restrict the severity of colonic inflammatory responses and that advantage might be taken of this system to develop novel means of treating inflammation-associated intestinal disorders.

Functional protease-activated receptors in the dorsal motor nucleus of the vagus

BACKGROUND

Protease-activated receptors (PARs), a family member of G-protein coupled receptors, are present and functionally active in a wide variety of cells. The object of this study was to demonstrate the presence and function of PAR-1 and PAR-2 in the dorsal motor nucleus of the vagus (DMV).

METHODS

DMNV neurons were isolated from neonatal rat brainstems using micro-dissection and enzymatic digestion. Neurons were cultured in Neurobasal medium A containing 2% B27 supplement. Intracellular calcium concentration ([Ca(2+)](i)) was measured using fura-2 based microspectrometry. Expression of PARs was detected by RT-PCR and immunofluorescent staining. KEY RESULT: Thrombin and PAR-1 agonist peptide activate PAR-1 with a maximum change in [Ca(2+)](i) expressed as DeltaF/F0 of 229 +/- 14% and 137 +/- 7%, respectively. Trypsin and PAR-2 agonist peptide activate PAR-2 with a maximum DeltaF/F0 change of 258 +/- 12% and 242 +/- 10%, respectively. Inhibition of phospholipase C (PLC) by U73312 (1 microm) decreased the maximal change in DeltaF/F0 induced by PAR-1 activation from 140 +/- 17% to 21 +/- 3%, while the PAR-2-mediated maximal change in DeltaF/F0 decreased from 185 +/- 21% to 19 +/- 6%. Blockade of IP3 receptor with 2APB inhibited the maximal change in DeltaF/F0 due to PAR-1 and PAR-2 activation by 72 +/- 13% and 71 +/- 20% respectively. PAR-1 immnuoreactivity was present in DMV neurons. Increase in transcripts for PAR-1 and PAR-2 were detected in DMV tissues derived from IBD rats relative to control animals.

CONCLUSIONS & INFERENCES

Our results indicate that PAR-1 and PAR-2 are present in the DMV neurons, and their activation leads to increases in intracellular calcium via signal transduction mechanism that involves activation of PLC and the production of IP3.

Protease-activated receptors: novel central role in modulation of gastric functions

Protease-activated receptors (PARs) are members of a subfamily of G-protein-coupled receptors that regulate diverse cell functions in response to proteolytic cleavage of an anchored peptide domain that acts as a 'tethered' receptor-activating ligand. PAR-1 and PAR-2 in particular are present throughout the gastrointestinal (GI) tract and play prominent roles in the regulation of GI epithelial function, motility, inflammation and nociception. In a recent article in Neurogastroenterology and Motility, Wang et al. demonstrate, for the first time, that PAR-1 and PAR-2 are present on preganglionic parasympathetic neurons within the rat brainstem. As in other cellular systems, proteases such as thrombin and trypsin activate PAR-1 and PAR-2 on neurons of the dorsal motor nucleus of the vagus (DMV), leading to an increase in intracellular calcium levels via signal transduction mechanisms involving activation of phospholipase C and inositol triphosphate (IP3). The authors also report that the level of PAR-1 and PAR-2 transcripts in DMV tissue is increased following experimental colitis, suggesting that inflammatory conditions may modulate neuronal behavior or induce plasticity within central vagal neurocircuits. It seems reasonable to hypothesize, therefore, that the activity and behavior of vagal efferent motoneurons may be modulated directly by local and/or systemic proteases released during inflammation. This, in turn, may contribute to the increased incidence of functional GI disorders, including gastric dysmotility, delayed emptying and gastritis observed in patients with inflammatory bowel diseases.