Peripheral vagus nerve stimulation significantly affects lipid composition and protein secondary structure within dopamine-related brain regions in rats

The gut-brain axis and cognitive control: A role for the vagus nerve

Survival requires the integration of external information and interoceptive cues to effectively guide advantageous behaviors, particularly foraging and other behaviors that promote energy acquisition and consumption. The vagus nerve acts as a critical relay between the abdominal viscera and the brain to convey metabolic signals. This review synthesizes recent findings from rodent models and humans revealing the impact of vagus nerve signaling from the gut on the control of higher-order neurocognitive domains, including anxiety, depression, reward motivation, and learning and memory. We propose a framework where meal consumption engages gastrointestinal tract-originating vagal afferent signaling that functions to alleviate anxiety and depressive-like states, while also promoting motivational and memory functions. These concurrent processes serve to favor the encoding of meal-relevant information into memory storage, thus facilitating future foraging behaviors. Modulation of these neurocognitive domains by vagal tone is also discussed in the context of pathological conditions, including the use of transcutaneous vagus nerve stimulation for the treatment of anxiety disorders, major depressive disorder, and dementia-associated memory impairments. Collectively, these findings highlight the contributions of gastrointestinal vagus nerve signaling to the regulation of neurocognitive processes that shape various adaptive behavioral responses.

Fatty acid metabolism changes in association with neurobehavioral deficits in animal models of fetal alcohol spectrum disorders

Fetal alcohol spectrum disorders (FASD) show behavioral problems due to prenatal alcohol exposure (PAE). A previous study reports changes in gene expressions linked to fatty acid (FA) metabolism in the cerebral cortex of the PAE mouse model. We find an increase of palmitic acid and arachidonic acid in phospholipid in the cerebral cortex of PAE at postnatal day 30. The increase of palmitic acid is consistent with increase of the producing enzyme, Fasn (fatty acid synthase). Decrease of 26:6 FA is also consistent with the increase of the enzyme which uses 26:6 as a substrate for making very long chain FAs, Elovl4 (elongation of very long chain fatty acids protein 4). However, there is no increase in the elongated products. Rather, lipid droplets (LDs) accumulated in the brain. Although FA-associated metabolic measurements are not affected by PAE, the abundance of FA-related gut microbiota is altered. This suggests that the gut microbiome could serve as a tool to facilitate uncovering the brain pathophysiology of FASD and a potential target to mitigate neurobehavioral problems.

Anti-inflammatory effects of vagus nerve stimulation in pediatric patients with epilepsy

Introduction

The neural control of the immune system by the nervous system is critical to maintaining immune homeostasis, whose disruption may be an underlying cause of several diseases, including cancer, multiple sclerosis, rheumatoid arthritis, and Alzheimer's disease.

Methods

Here we studied the role of vagus nerve stimulation (VNS) on gene expression in peripheral blood mononuclear cells (PBMCs). Vagus nerve stimulation is widely used as an alternative treatment for drug-resistant epilepsy. Thus, we studied the impact that VNS treatment has on PBMCs isolated from a cohort of existing patients with medically refractory epilepsy. A comparison of genome-wide changes in gene expression was made between the epilepsy patients treated and non-treated with vagus nerve stimulation.

Results

The analysis showed downregulation of genes related to stress, inflammatory response, and immunity, suggesting an anti-inflammatory effect of VNS in epilepsy patients. VNS also resulted in the downregulation of the insulin catabolic process, which may reduce circulating blood glucose.

Discussion

These results provide a potential molecular explanation for the beneficial role of the ketogenic diet, which also controls blood glucose, in treating refractory epilepsy. The findings indicate that direct VNS might be a useful therapeutic alternative to treat chronic inflammatory conditions.

Right vagus nerve stimulation improves motor behavior by exerting neuroprotective effects in Parkinson's disease rats

Background

Parkinson's disease (PD) is a common movement disorder disease. Left vagus nerve stimulation (LVNS) is a potential treatment option for PD. Compared with the left vagus nerve, the right vagus nerve is more closely connected with the midbrain dopaminergic neurons, which are the lesion locations of PD. However, whether right vagus nerve stimulation (RVNS) has a therapeutic effect on PD has not yet been studied. Therefore, in this study, we studied the therapeutic effect and underlying mechanism of RVNS using a PD rat model.

Methods

To establish the PD rat model, 8-week-old male Sprague-Dawley rats were intraperitoneally injected with rotenone for 21 days. The cuff electrodes were implanted into the right cervical vagal carotid sheaths of the rats. The right vagus nerve was continuously stimulated for 14 days using a radio stimulation system. Behavioral tests were performed before and after stimulation. Finally, tyrosine hydroxylase (TH), vesicular monoamine transporter 2 (VMAT2), and α-synuclein in the midbrain, including the substantia nigra (SN) and ventral tegmental area (VTA), were detected by immunofluorescence.

Results

A markedly lower distance traveled and rearing number was observed in the rotenone, rotenone + sham, and rotenone + RVNS groups compared to the vehicle group. After the stimulation days, the distance traveled and rearing number were both higher in the rotenone + RVNS group compared to the rotenone and rotenone + sham groups (P<0.01, P<0.0001). A remarkable increase in distance traveled and rearing number was observed in the rotenone + RVNS group after stimulation. TH expression in the vehicle group was significantly up-regulated than the other groups. RVNS markedly up-regulated TH expression level. A significantly higher expression of α-synuclein was observed in the rotenone, rotenone + sham, and rotenone + RVNS groups compared to the vehicle group. The expression of α-synuclein was lower in the rotenone + RVNS group compared to the rotenone and rotenone + sham groups. A markedly higher VMAT2 expression was observed in the vehicle group compared to other groups. RVNS significantly up-regulated VMAT2 expression.

Conclusions

The improved motor behavior and neuroprotective effects on the midbrain dopaminergic neurons in the PD rat model suggest that RVNS could be used as a potential treatment for PD.

Rapid Effects of Vagus Nerve Stimulation on Sensory Processing Through Activation of Neuromodulatory Systems

After sensory information is encoded into neural signals at the periphery, it is processed through multiple brain regions before perception occurs (i.e., sensory processing). Recent work has begun to tease apart how neuromodulatory systems influence sensory processing. Vagus nerve stimulation (VNS) is well-known as an effective and safe method of activating neuromodulatory systems. There is a growing body of studies confirming VNS has immediate effects on sensory processing across multiple sensory modalities. These immediate effects of VNS on sensory processing are distinct from the more well-documented method of inducing lasting neuroplastic changes to the sensory pathways through repeatedly delivering a brief VNS burst paired with a sensory stimulus. Immediate effects occur upon VNS onset, often disappear upon VNS offset, and the modulation is present for all sensory stimuli. Conversely, the neuroplastic effect of pairing sub-second bursts of VNS with a sensory stimulus alters sensory processing only after multiple pairing sessions, this alteration remains after cessation of pairing sessions, and the alteration selectively affects the response properties of neurons encoding the specific paired sensory stimulus. Here, we call attention to the immediate effects VNS has on sensory processing. This review discusses existing studies on this topic, provides an overview of the underlying neuromodulatory systems that likely play a role, and briefly explores the potential translational applications of using VNS to rapidly regulate sensory processing.

Model-based correction algorithm for Fourier Transform infrared microscopy measurements of complex tissue-substrate systems

Model-based algorithms have recently attracted much attention for data pre-processing in tissue mapping and imaging by Fourier transform infrared micro-spectroscopy (FTIR). Their versatility, robustness and computational performance enabled the improvement of spectral quality by mitigating the impact of scattering and fringing in FTIR spectra of chemically homogeneous biological systems. However, to date, no comprehensive algorithm has been optimized and automated for large-area FTIR imaging of histologically complex tissue samples. Herein, for the first time, we propose a unique, integrated and fully-automated Multiple Linear Regression Multi-Reference (MLR-MR) method for correcting linear baseline effects due to diffuse scattering, for compensating substrate thickness inhomogeneity and accounting for sample chemical heterogeneity in FTIR images. In particular, the algorithm uses multiple-reference spectra for histologically heterogeneous biological samples. The performance of the procedure was demonstrated for FTIR imaging of chemically complex rat brain frontal cortex tissue samples, mounted onto Ultralene® films. The proposed MLR-MR correction algorithm allows the efficient retrieval of "pure" absorbance spectra and greatly improves the histological fidelity of FTIR imaging data, as compared with the one-reference approach. In addition, the MLR-MR algorithm here presented opens up the possibility for extracting information on substrate thickness variability, thus enabling the indirect evaluation of its topography. As a whole, the MLR-MR procedure can be easily extended to more complex systems for which Mie scattering effects must also be eliminated.

Role of quercetin and caloric restriction on the biomolecular composition of aged rat cerebral cortex: An FTIR study

Aging brain is characterized by a change in biomolecular composition leading to a diverse range of neurological diseases. Anti-aging research is of current interest, to lessen the burden of age-related macromolecular damage through antioxidant supplementation and caloric restriction. However, data concerning the effect of these anti-aging regimens on age-related biomolecular changes in rat brain is still lacking. In the present study, for the first time, we employed Fourier transform infrared (FTIR) spectroscopy, to investigate the effect of quercetin, caloric restriction (CR) and combination of both on alterations in the composition of lipids and proteins of aged rat brain cerebral cortex. Aged male Wistar rats (21 months old) were divided into four groups: Control (CONT), fed pellet diet; Quercetin (QUER), fed quercetin (50 mg/kg/day); CR (caloric restriction) (fed 40% reduced CONT), and CRQ (40% CR and 50 mg/kg/day QUER). Three-month-old rats served as young control (YOUNG). Our short-term study (45 days) shows decreased band area of unsaturated lipids, decreased area ratios of olefinic/lipid and CH₂ antisymmetric stretching (2925 cm^-1)/lipids in CONT group compared to young rats, suggesting age-associated lipid peroxidation in aged rats. A slight decrease in the frequency of CH₂ antisymmetric mode of lipids (whereas no change in CH₂ symmetric mode), but a decrease in bandwidths of both CH₂ antisymmetric and symmetric modes of lipids was observed for CONT group compared to YOUNG. Further, a significant decrease in the peak area of infrared bands of proteins and an increase in the peak area of the CO band of lipids was observed in the CONT group. Our data also show that lower levels of α-helical structures and higher levels of random coils, representing altered protein secondary structure composition in the CONT group compared to YOUNG group. Reduction in neuronal cell density and shrinked nucleus was also observed in aged rats. Increase in the accumulation of oxidative mediated damage to macromolecules and diminished antioxidant levels, could be the possible reason for the age-related alterations in the composition of lipids and proteins. However, the combination of quercetin and CR, but not either treatment alone, significantly prevented the age associated alterations in the lipid and protein profiles in the rat cerebral cortex. Further, our results help to understand the mechanism of action of antioxidants under non-restriction and CR conditions, this might help in the development of novel anti-aging treatments to ameliorate oxidative stress in age-related disorders.

Lactobacillus plantarum PS128 ameliorates 2,5-Dimethoxy-4-iodoamphetamine-induced tic-like behaviors via its influences on the microbiota-gut-brain-axis

We previously reported a novel psychobiotic strain of Lactobacillus plantarum PS128 (PS128) which could ameliorate anxiety-like& depression-like behaviors and modulate cerebral dopamine (DA) and serotonin (5-HT) in mice. Here, we examine the possibility of using PS128 administration to improve tic-like behaviors by using a 5-HT_2A and 5-HT_2C receptor agonist 2,5-Dimethoxy-4-iodoamphetamine (DOI). PS128 was orally administered to male Wistar rat for 2 weeks before two daily DOI injections. We recorded the behaviors immediately after the second DOI injection and compared the results with control and haloperidol treatment groups. PS128 significantly reduced tic-like behaviors and pre-pulse inhibition deficit in a threshold-dose of 10⁹ CFU per day. Brain tissue analysis showed that DOI induced abnormal DA efflux in the striatum and prefrontal cortex, while PS128 ingestion improved DA metabolism and increased norepinephrine (NE) levels in these two regions. In addition, PS128 ingestion increased DA transporter and β-arrestin expressions and decreased DOI-induced phosphorylation of DA and cAMP regulated phosphoprotein of molecular weight 32 kDa (DARPP-32) at Thr34 and extracellular regulated protein kinases (ERK). PS128 ingestion also modulated peripheral 5-HT levels and shaped the cecal microbiota composition, which helps to alleviate DOI-induced dysbiosis. These results suggested that PS128 ameliorated DOI-induced tic-like hyper-active behaviors via stabilizing cerebral dopaminergic pathways through its modulation of host's microbiota-gut-brain axis. Thus, we believe there are potentials for utilizing psychobiotics to improve syndromes caused by DA dysregulation in DA-related neurological disorders and movement disorders such as Tourette syndrome.

Peripheral and central compensatory mechanisms for impaired vagus nerve function during peripheral immune activation

BACKGROUND

Determining the etiology and possible treatment strategies for numerous diseases requires a comprehensive understanding of compensatory mechanisms in physiological systems. The vagus nerve acts as a key interface between the brain and the peripheral internal organs. We set out to identify mechanisms compensating for a lack of neuronal communication between the immune and the central nervous system (CNS) during infection.

METHODS

We assessed biochemical and central neurotransmitter changes resulting from subdiaphragmatic vagotomy and whether they are modulated by intraperitoneal infection. We performed a series of subdiaphragmatic vagotomy or sham operations on male Wistar rats. Next, after full, 30-day recovery period, they were randomly assigned to receive an injection of Escherichia coli lipopolysaccharide or saline. Two hours later, animal were euthanized and we measured the plasma concentration of prostaglandin E2 (with HPLC-MS), interleukin-6 (ELISA), and corticosterone (RIA). We also had measured the concentration of monoaminergic neurotransmitters and their metabolites in the amygdala, brainstem, hippocampus, hypothalamus, motor cortex, periaqueductal gray, and prefrontal medial cortex using RP-HPLC-ED. A subset of the animals was evaluated in the elevated plus maze test immediately before euthanization.

RESULTS

The lack of immunosensory signaling of the vagus nerve stimulated increased activity of discrete inflammatory marker signals, which we confirmed by quantifying biochemical changes in blood plasma. Behavioral results, although preliminary, support the observed biochemical alterations. Many of the neurotransmitter changes observed after vagotomy indicated that the vagus nerve influences the activity of many brain areas involved in control of immune response and sickness behavior. Our studies show that these changes are largely eliminated during experimental infection.

CONCLUSIONS

Our results suggest that in vagotomized animals with blocked CNS, communication may transmit via a pathway independent of the vagus nerve to permit restoration of CNS activity for peripheral inflammation control.

Defining Dysbiosis in Disorders of Movement and Motivation

The gut microbiota has emerged as a critical player in shaping and modulating brain function and has been shown to influence numerous behaviors, including anxiety and depression-like behaviors, sociability, and cognition. However, the effects of the gut microbiota on specific disorders associated with thalamo-cortico-basal ganglia circuits, ranging from compulsive behavior and addiction to altered sensation and motor output, are only recently being explored. Wholesale depletion and alteration of gut microbial communities in rodent models of disorders, such as Parkinson's disease, autism, and addiction, robustly affect movement and motivated behavior. A new frontier therefore lies in identifying specific microbial alterations that affect these behaviors and understanding the underlying mechanisms of action. Comparing alterations in gut microbiota across multiple basal-ganglia associated disease states allows for identification of common mechanistic pathways that may interact with distinct environmental and genetic risk factors to produce disease-specific outcomes.

Molecular and elemental effects underlying the biochemical action of transcranial direct current stimulation (tDCS) in appetite control

Recent studies highlight that obesity may alter the electric activity in brain areas triggering appetite and craving. Transcranial direct current brain stimulation (tDCS) has recently emerged as a safe alternative for treating food addiction via modulating cortical excitability without any high-risk surgical procedure to be utilized. As for anodal-type tDCS (atDCS), we observe increased excitability and spontaneous firing of the cortical neurons, whilst for the cathodal-type tDCS (ctDCS) a significant decrease is induced. Unfortunately, for the method to be fully used in a clinical setting, its biochemical action mechanism must be precisely defined, although it is proposed that molecular remodelling processes play in concert with brain activity changes involving the ions of: Na, Cl, K and Ca. Herein, we proposed for the first time Fourier transform infrared (FTIR) and synchrotron X-ray fluorescence (SRXRF) microprobes for a combined molecular and elemental analysis in the brain areas implicated appetite control, upon experimental treatment by either atDCS or ctDCS. The study, although preliminary, shows that by stimulating the prefrontal cortex in the rats fed high-caloric nutrients, the feeding behavior can be significantly changed, resulting in significantly inhibited appetite. Both, atDCS and ctDCS produced significant molecular changes involving qualitative and structural properties of lipids, whereas atDCS was found with a somewhat more significant effect on protein secondary structure in all the brain areas investigated. Also, tDCS was reported to reduce surface masses of Na, Cl, K, and Ca in almost all brain areas investigated, although the atDCS deemed to have a stronger neuro-modulating effect. Taken together, one can report that tDCS is an effective treatment technique, and its action mechanism in the appetite control seems to involve a variety of lipid-, protein- and metal/non-metal-ion-driven biochemical changes, regardless the current polarization.

A Role of the Parasympathetic Nervous System in Cognitive Training

BACKGROUND

Vision-based speed of processing (VSOP) training can result in broad cognitive improvements in older adults with amnestic mild cognitive impairment (aMCI). What remains unknown, however, is what neurophysiological mechanisms account for the observed training effect. Much of the work in this area has focused on the central nervous system, neglecting the fact that the peripheral system can contributes to changes of the central nervous system and vice versa.

OBJECTIVE

We examined the prospective relationship between an adaptive parasympathetic nervous system response to cognitive stimuli and VSOP training-induced plasticity.

METHOD

Twenty-one participants with aMCI (10 for VSOP training, and 11 for mental leisure activities (MLA) control) were enrolled. We assessed high-frequency heart rate variability (HF-HRV) during training sessions, and striatum-related neural networks and cognition at baseline and post-training.

RESULTS

Compared to MLA, the VSOP group showed a significant U-shaped pattern of HF-HRV response during training, as well as decreases in connectivity strength between bilateral striatal and prefrontal regions. These two effects were associated with training-induced improvements in both the trained (attention and processing speed) and transferred (working memory) cognitive domains.

CONCLUSION

This work provides novel support for interactions between the central and the peripheral nervous systems in relation to cognitive training, and motivates further studies to elucidate the causality of the observed link.

Bidirectional Neural Interaction Between Central Dopaminergic and Gut Lesions in Parkinson's Disease Models

The exact mechanism of gut dysfunction in Parkinson's disease and, conversely, the role of gut pathology in brain dopaminergic degeneration are controversial. We investigated the effects of nigral lesions on the colonic neurotransmission, the effect of gut inflammation on the nigrostriatal dopaminergic function, and the possible involvement of the vagus nerve and the local renin-angiotensin system (RAS). Nigrostriatal dopamine depletion was performed by bilateral injection 6-hydroxydopamine, and gut inflammation was induced by dextran sulfate sodium salt treatment in rats and mice, respectively, with or without vagal disruption. A decrease in central dopamine levels induced a decrease in colonic dopamine types 1 and 2 receptor expression together with an increase in the colonic levels of dopamine and a decrease in the levels of acetylcholine, which may explain a decrease in gut motility. Central dopaminergic depletion also induced an increase in the colonic levels of inflammatory and oxidative stress markers together with activation of the pro-inflammatory arm of the local RAS. Mice with acute (1 week) or subchronic (3 weeks) gut inflammation did not show a significant increase in colonic α-synuclein and phosphorylated α-synuclein expression during this relatively short survival period. Interestingly, we observed early changes in the nigrostriatal dopaminergic homeostasis, dopaminergic neuron death, and increased levels of nigral pro-inflammatory markers and RAS pro-inflammatory activity. The present results show that a dysregulation of the neural bidirectional gut-brain interaction may explain the early gut disturbances observed in parkinsonian patients, and also the increase in vulnerability of nigral dopaminergic neurons after gut inflammation.