Brain structural and functional alterations related to anxiety in allergic asthma

Psychiatric disorders are common in patients with allergic asthma, and they can have a significant impact on their quality of life and disease control. Recent studies have suggested that there may be potential immune-brain communication mechanisms in asthma, which can activate inflammatory responses in different brain areas, leading to structural and functional alterations and behavioral changes. However, the precise mechanisms underlying these alterations remain unclear. In this paper, we comprehensively review the relevant research on asthma-induced brain structural and functional alterations that lead to the initiation and promotion of anxiety. We summarize the possible pathways for peripheral inflammation to affect the brain's structure and function. Our review highlights the importance of addressing neuropsychiatric disorders in the clinical guidelines of asthma, to improve the quality of life of these patients. We suggest that a better understanding of the mechanisms underlying psychiatric comorbidities in asthma could lead to the development of more effective treatments for these patients.

Effects of inhaled corticosteroids on brain volumetry, depression and anxiety-like behaviors in a rat model of asthma

Brain functional deficits have been reported in asthma patients which can result in behavioral disorders like depression and anxiety. These deficits may be associated with factors like resistance to treatment, incorrect self-evaluation, and inadequate self-control. However, changes in the brain volume in allergic asthma and the effects of inhaled corticosteroids, the most common anti-inflammatory agents for asthma treatment, on these alterations remain largely unclear. Here, we evaluated depression and anxiety-like behavior as well as volume changes in different brain area, using magnetic resonance imaging in an animal model of allergic asthma with pretreatment of inhaled fluticasone propionate. Asthma-induced behavioral changes were partially, but not completely, prevented by pretreatment with inhaled fluticasone propionate. Volumetry findings showed that the allergen decreased volumes of the corpus callosum and subcortical white matter, as well as the septal region and hippocampus (especially CA1 and fimbria). However, volumes of neocortex, insular, and anterior cingulate cortex increased in asthmatic rats compared to controls. Namely, pretreatment with inhaled fluticasone propionate partially prevented asthma-induced brain volume changes, but not completely. These findings suggest that asthma is associated with structural alterations in the brain, which may contribute to the induction of psychological disorders. Thus, considering brain changes in the clinical assessments could have important implications for asthma treatment.

Allergen induces depression-like behavior in association with altered prefrontal-hippocampal circuit in male rats

Allergic asthma is a common chronic inflammatory condition associated with psychiatric comorbidities. Notably depression, correlated with adverse outcomes in asthmatic patients. Peripheral inflammation's role in depression has been shown previously. However, evidence regarding the effects of allergic asthma on the medial prefrontal cortex (mPFC)-ventral hippocampus (vHipp) interactions, an important neurocircuitry in affective regulation, is yet to be demonstrated. Herein, we investigated the effects of allergen exposure in sensitized rats on the immunoreactivity of glial cells, depression-like behavior, brain regions volume, as well as activity and connectivity of the mPFC-vHipp circuit. We found that allergen-induced depressive-like behavior was associated with more activated microglia and astrocytes in mPFC and vHipp, as well as reduced hippocampus volume. Intriguingly, depressive-like behavior was negatively correlated with mPFC and hippocampus volumes in the allergen-exposed group. Moreover, mPFC and vHipp activity were altered in asthmatic animals. Allergen disrupted the strength and direction of functional connectivity in the mPFC-vHipp circuit so that, unlike normal conditions, mPFC causes and modulates vHipp activity. Our results provide new insight into the underlying mechanism of allergic inflammation-induced psychiatric disorders, aiming to develop new interventions and therapeutic approaches for improving asthma complications.

Stimulating olfactory epithelium mitigates mechanical ventilation-induced hippocampal inflammation and apoptosis

Mechanical ventilation (MV), as a life-saving procedure in critical patients, is a risk factor to develop of neurocognitive dysfunction and triggers of inflammation and apoptosis in the brain. Since diversion of breathing route to the tracheal tube diminishes brain activity entrained by physiological nasal breathing, we hypothesized that simulating nasal breathing using rhythmic air-puff (AP) into the nasal cavity of mechanically ventilated rats can reduce hippocampal inflammation and apoptosis in association with restoring respiration-coupled oscillations. We found that stimulating olfactory epithelium through applying rhythmic nasal AP, in association with reviving respiration-coupled brain rhythm, mitigates MV-induced hippocampal apoptosis and inflammation involving microglia and astrocytes. The current translational study opens a window for a novel therapeutic approach to reduce neurological complications induced by MV.

Corticosteroid treatment attenuates anxiety and mPFC-amygdala circuit dysfunction in allergic asthma

AIMS

Allergic asthma is associated with anxiety-related behaviors, leading to poor quality of life. Previous studies mainly described the neuropathophysiology of asthma-induced anxiety. However, the effects of corticosteroids, the most common anti-inflammatory agents for asthma treatment, on the neurophysiological foundations of allergic asthma-induced anxiety are unexplored.

MAIN METHODS

Here, we evaluated lung and brain inflammation as well as anxiety in an animal model of allergic asthma pretreated with inhaled fluticasone propionate. Furthermore, to define the neurophysiological bases of these conditions, we studied the medial prefrontal cortex (mPFC)-amygdala circuit, which is previously shown to accompany asthma-induced anxiety.

KEY FINDINGS

Our data showed that allergen induces anxiety, mPFC and amygdala inflammation, as well as disruptions in the local and long-range oscillatory activities within the mPFC-amygdala circuit. Interestingly, we observed a roughly consistent trend of changes with inhaled fluticasone pretreatment. Namely, the asthma-induced behavioral, inflammatory, and neurophysiological changes were partly, but not totally, prevented by inhaled fluticasone pretreatment.

SIGNIFICANCE

We suggest that early treatment of asthmatic patients with inhaled corticosteroids improves mPFC-amygdala circuit function by attenuating neuroinflammation leading to reduced anxiety. These findings could lead clinical guidelines of asthma to consider the neuropsychiatric disorders of patients in treatment recommendations.

Disrupted connectivity in the olfactory bulb-entorhinal cortex-dorsal hippocampus circuit is associated with recognition memory deficit in Alzheimer's disease model

Neural synchrony in brain circuits is the mainstay of cognition, including memory processes. Alzheimer's disease (AD) is a progressive neurodegenerative disorder that disrupts neural synchrony in specific circuits, associated with memory dysfunction before a substantial neural loss. Recognition memory impairment is a prominent cognitive symptom in the early stages of AD. The entorhinal–hippocampal circuit is critically engaged in recognition memory and is known as one of the earliest circuits involved due to AD pathology. Notably, the olfactory bulb is closely connected with the entorhinal–hippocampal circuit and is suggested as one of the earliest regions affected by AD. Therefore, we recorded simultaneous local field potential from the olfactory bulb (OB), entorhinal cortex (EC), and dorsal hippocampus (dHPC) to explore the functional connectivity in the OB-EC-dHPC circuit during novel object recognition (NOR) task performance in a rat model of AD. Animals that received amyloid-beta (Aβ) showed a significant impairment in task performance and a marked reduction in OB survived cells. We revealed that Aβ reduced coherence and synchrony in the OB-EC-dHPC circuit at theta and gamma bands during NOR performance. Importantly, our results exhibit that disrupted functional connectivity in the OB-EC-dHPC circuit was correlated with impaired recognition memory induced by Aβ. These findings can elucidate dynamic changes in neural activities underlying AD, helping to find novel diagnostic and therapeutic targets.

Allergen disrupts amygdala-respiration coupling

Allergic asthma affects both the respiratory function and central nervous system. Communication between the amygdala and respiratory control system is critical for regulating breathing function. To date, no study provides the effect of allergic inflammation on amygdala-respiration coupling. Here, we simultaneously recorded respiration and local field potentials of the amygdala during awake immobility in a rat model of allergic asthma. A decreased synchrony was found between amygdala and respiration in asthmatic rats. Allergen also reduced the modulatory effect of the respiration phase on amygdala power at delta, theta and gamma2 (80-120 Hz) frequencies. Moreover, in the animal model of allergic asthma, delta and theta oscillations strongly coordinate local gamma2 activity in the amygdala. These findings suggest that allergen can induce brain alterations and therefore shed light on future works to address how disruption of amygdala-respiration coupling contributes to respiratory dysfunction in allergic asthma.

Allergic rhinitis impairs working memory in association with drop of hippocampal - Prefrontal coupling

Allergic rhinitis (AR) is a chronic inflammatory disease frequently associated with a deficit in learning and memory. Working memory is an important system for decision making and guidance, which depends on interactions between the ventral hippocampus (vHipp) and the prelimbic prefrontal cortex (plPFC). It is still unclear whether AR influences the activity and coupling of these brain areas, which consequently may impair working memory. The current study aimed to examine alterations of the vHipp-plPFC circuit in a rat model of AR. Our results show decreased working memory performance in AR animals, accompanied by a reduction of theta and gamma oscillations in plPFC. Also, AR reduces coherence between vHipp and plPFC in both theta and gamma frequency bands. Cross-frequency coupling analyses confirmed a reduced interaction between hippocampal theta and plPFC gamma oscillations. Granger causality analysis revealed a reduction in the causal effects of vHipp activity on plPFC oscillations and vice versa. A significant correlation was found between working memory performance with disruption of functional connectivity in AR animals. In summary, our data show that in AR, there is a deficit of functional coupling between hippocampal and prefrontal network, and suggest that this mechanism might contribute to working memory impairment in individuals with AR.

Rhythmic air-puff into nasal cavity modulates activity across multiple brain areas: A non-invasive brain stimulation method to reduce ventilator-induced memory impairment

Mechanical ventilation (MV) can result in long-term brain impairments that are resistant to treatment. The mechanisms underlying MV-induced brain function impairment remain unclear. Since nasal airflow modulates brain activity, here we evaluated whether reinstating airflow during MV could influence the memory performance of rats after recovery. Rats were allocated into two study groups: one group received rhythmic air-puff into the nasal cavity during MV and a control group that underwent ventilation without air-puff. During MV, air-puffs induced time-locked event potentials in OB, mPFC and vHPC and significantly increased the oscillatory activity at the air-puff frequency. Furthermore, in mPFC and vHPC, (but not in OB), delta and theta oscillations were more prominent during air-puff application. After recovery, working memory performance was significantly higher in the air-puff group compared to control. Our study thus suggests a promising non-invasive brain stimulation approach to alleviate the neurological complications of prolonged mechanical ventilation.

Allergen-induced anxiety-like behavior is associated with disruption of medial prefrontal cortex - amygdala circuit

Anxiety is prevalent in asthma, and is associated with disease severity and poor quality of life. However, no study to date provides direct experimental evidence for the effect of allergic inflammation on the structure and function of medial prefrontal cortex (mPFC) and amygdala, which are essential regions for modulating anxiety and its behavioral expression. We assessed the impact of ovalbumin (OVA)-induced allergic inflammation on the appearance of anxiety-like behavior, mPFC and amygdala volumes using MRI, and the mPFC-amygdala circuit activity in sensitized rats. Our findings exhibited that the OVA challenge in sensitized rats induced anxiety-like behavior, and led to more activated microglia and astrocytes in the mPFC and amygdala. We also found a negative correlation between anxiety-like behavior and amygdala volume. Moreover, OVA challenge in sensitized rats was associated with increases in mPFC and amygdala activity, elevation of amygdala delta-gamma coupling, and the enhancement of functional connectivity within mPFC-amygdala circuit – accompanied by an inverted direction of information transferred from the amygdala to the mPFC. We indicated that disrupting the dynamic interactions of the mPFC-amygdala circuit may contribute to the induction of anxiety-related behaviors with asthma. These findings could provide new insight to clarify the underlying mechanisms of allergic inflammation-induced psychiatric disorders related to asthma.