Sex- and afferent-specific differences in histamine receptor expression in vagal afferents of rats: A potential mechanism for sexual dimorphism in prevalence and severity of asthma

Caution for Multidrug Therapy: Significant Baroreflex Afferent Neuroexcitation Coordinated by Multi-Channels/Pumps Under the Threshold Concentration of Yoda1 and Dobutamine Combination

Multi-drug therapies are common in cardiovascular disease intervention; however, io channel/pump coordination has not been tested electrophysiologically. Apparently, inward currents were not elicited by Yoda1/10 nM or Dobutamine/100 nM alone in Ah-type baroreceptor neurons, but were by their combination. To verify this, electroneurography and the whole-cell patch-clamp technique were performed. The results showed that Ah- and C-volley were dramatically increased by the combination at 0.5 V and 5 V, in contrast to A-volley, as consistent with repetitive discharge elicited by step and ramp with markedly reduced current injection/stimulus intensity. Notably, a frequency-dependent action potential (AP) duration was increased with Iberiotoxin-sensitive K+ component. Furthermore, an increased peak in AP measured in phase plots suggested enhanced Na+ influx, cytoplasmic Ca2+ accumulation through reverse mode of Na+/Ca2+ exchanger, and, consequently, functional KCa1.1 up-regulation. Strikingly, the Yoda1- or Dbtm-mediated small/transient Na+/K+-pump currents were robustly increased by their combination, implying a quick ion equilibration that may also be synchronized by hyperpolarization-induced voltage-sag, enabling faster repetitive firing. These novel findings demonstrate multi-channel/pump collaboration together to integrate neurotransmission at the cellular level for baroreflex, providing an afferent explanation in sexual dimorphic blood pressure regulation, and raising the caution regarding the individual drug concentration in multi-drug therapies to optimize efficacy and minimize toxicity.

Respiratory and allergic outcomes among farmworkers exposed to pesticides in Costa Rica

AIM

We examined the association of exposure to a pesticide mixture with respiratory and allergic outcomes among farmworkers from Costa Rica.

METHODS

We conducted a cross-sectional study of 299 farmworkers between May and August 2016. We collected information on sociodemographic factors, pesticide use, and the presence of respiratory and allergic symptoms during the last 12 months via questionnaire. We calculated specific gravity-adjusted average concentrations of 15 pesticide biomarkers measured in urine samples collected during two visits (4-5 weeks apart). We fitted "traditional" Bayesian and Bayesian Weighted Quantile Sum (BWQS) regression models to assess the association of exposure to independent and summed pesticide mixture components with the outcomes of interest. We adjusted all models for age and smoking status.

RESULTS

In "traditional" Bayesian analyses, higher urinary concentrations of 2-isopropyl-4-methyl-6-hydroxypyrimidine (IMPY, metabolite of organophosphate insecticide diazinon) were associated with increased odds of a higher asthma symptom score [adjusted OR per two-fold increase in concentrations = 1.15; 95 % credible interval (CrI): 1.04, 1.27)], asthma symptoms or medication use (aOR = 1.37; 95 % CrI: 1.13, 1.67), and rhinitis (aOR = 1.34; 95 % CrI: 1.15, 1.56). Higher urinary concentrations of boscalid-5-hydroxy (metabolite of fungicide boscalid) were associated with increased odds of asthma symptoms or medication use (aOR = 1.24; 95 % CrI: 1.00, 1.55), whereas higher concentrations of 4-hydroxypyrimethanil (metabolite of the fungicide pyrimethanil) were associated with increased odds of eczema (aOR = 1.11; 95 % CrI: 0.99, 1.24). Several inverse associations of herbicide concentrations with respiratory and allergic outcomes were observed. In BWQS analyses, a positive association was found between exposure to the pesticide mixture and increased odds of rhinitis (aOR = 1.96; 95 % CrI: 1.14, 3.20), with IMPY being the largest contributor.

CONCLUSION

Our findings indicate that exposure to pesticides may have both independent and summed mixture effects on respiratory and allergic health among farmworkers.

Piezo1 channel activation facilitates baroreflex afferent neurotransmission with subsequent blood pressure reduction in control and hypertension rats

Mechanosensitive cation channels such as Piezo1 and Piezo2 are activated by mechanical force like a starched wall of the aorta while blood pressure (BP) rising, which helps to elucidate the underlying mechanism of mechanotransduction of baroreceptor endings. In this study we investigated how Piezo1 channel activation-mediated gender- and afferent-specific BP regulation in rats. We established high-fat diet and fructose drink-induced hypertension model rats (HFD-HTN) and deoxycorticosterone (DOCA)-sensitive hypertension model rats. We showed that the expression levels of Piezo1 and Piezo2 were significantly up-regulated in left ventricle of HFD and DOCA hypertensive rats, whereas the down-regulation of Piezo1 was likely to be compensated by Piezo2 up-regulation in the aorta. Likewise, down-regulated Piezo1 was observed in the nodose ganglion (NG), while up-regulated Piezo2 was found in the nucleus tractus solitarius (NTS), which might synergistically reduce the excitatory neurotransmitter release from the presynaptic membrane. Notably, microinjection of Yoda1 (0.025-2.5 mg/ml) into the NG concentration-dependently reduced BP in both hypertensive rat models as well as in control rats with similar EC50; the effect of Yoda1 was abolished by microinjection of a Piezo1 antagonist GsMTx4 (1.0 μM). Functional analysis in an in vitro aortic arch preparation showed that instantaneous firing frequency of single Ah-fiber of aortic depressor nerve was dramatically increased by Yoda1 (0.03-1.0 μM) and blocked by GsMTx4 (1.0 μM). Moreover, spontaneous synaptic currents recorded from identified 2nd-order Ah-type baroreceptive neurons in the NTS was also facilitated over 100% by Yoda1 (1.0 μM) and completely blocked by GsMTx4 (3.0 μM). These results demonstrate that Piezo1 expressed on Ah-type baroreceptor and baroreceptive neurons in the NG and NTS plays a key role in a sexual-dimorphic BP regulation under physiological and hypertensive condition through facilitation of baroreflex afferent neurotransmission, which is presumably collaborated by Piezo2 expression at different level of baroreflex afferent pathway via compensatory and synergistic mechanisms.

Sex-oriented perspectives in immunopharmacology

Several immunopharmacological agents are effective in the treatment of cancer and immune-mediated conditions, with a favorable impact on life expectancy and clinical outcomes for a large number of patients. Nevertheless, response variation and undesirable effects of these drugs represent major issues, and overall efficacy remains unpredictable. Males and females show a distinct difference in immune system responses, with females generally mounting stronger responses to a variety of stimuli. Therefore, exploring sex differences in the efficacy and safety of immunopharmacological agents would strengthen the practice of precision medicine. As a pharmacological target highlight, programmed cell death 1 ligand 1 (PD-L1) is the first functionally characterized ligand of the coinhibitory programmed death receptor 1 (PD-1). The PD-L1/PD-1 crosstalk plays an important role in the immune response and is relevant in cancer, infectious and autoimmune disease. Sex differences in the response to immune checkpoint inhibitors are well documented, with male patients responding better than female patients. Similarly, higher efficacy of and adherence to tumor necrosis factor inhibitors in chronic inflammatory conditions including rheumatoid arthritis and Crohn's disease have been reported in male patients. The pharmacological basis of sex-specific responses to immune system modulating drugs is actively investigated in other settings such as stroke and type 1 diabetes. Advances in therapeutics targeting the endothelium could soon be wielded against autoimmunity and metabolic disorders. Based on the established sexual dimorphism in immune-related pathophysiology and disease presentation, sex-specific immunopharmacological protocols should be integrated into clinical guidelines.

Characteristics of inpatients with atopic asthma in a tertiary center: Do age and gender have an influence?

Background: Several studies have demonstrated gender influence on asthma prevalence, being higher among males during early childhood. Little is known about the impact of gender and age on asthma exacerbation characteristics in pediatrics. This study aimed to determine the differences in acute asthma between males and females in three different age groups regarding perinatal characteristics of asthmatic patients, comorbidities, medication adherence, level of blood eosinophils, and pattern of hospitalization.Methods: The medical records of 130 pediatric patients with asthma, who presented to the emergency department at Jordan University hospital with asthma exacerbations, were retrospectively reviewed. Demographic information and clinical characteristics were collected.Results: The mean age of patients was 10.7±4.7 years. The age at diagnosis and gestational age were significantly higher in older children. Furthermore, younger children were significantly more likely to experience winter exacerbations and more emergency presentations. Male patients were considerably younger than their female counterparts and were diagnosed younger. In addition, male patients were more likely to have eosinophil levels higher than 3% than female patients.Conclusion: Gender plays a role in the development and outcome of asthma exacerbations at different ages of pediatrics. A better understanding of gender-based and age-based differences in asthma dictates a personalized approach to treatment.

Estrogen-dependent depressor response of melatonin via baroreflex afferent function and intensification of PKC-mediated Nav1.9 activation

Recent studies suggest that melatonin (Mel) plays an important role in the regulation of blood pressure (BP) via the aortic baroreflex pathway. In this study, we investigated the interaction between the baroreflex afferent pathway and Mel-mediated BP regulation in rats under physiological and hypertensive conditions. Mel (0.1, 0.3, and 1.0 mg/mL) was microinjected into the nodose ganglia (NG) of rats. We showed that Mel-induced reduction of mean arterial pressure in female rats was significantly greater than that in male and in ovariectomized rats under physiological condition. Consistently, the expression of Mel receptors (MTNRs) in the NG of female rats was significantly higher than that of males. In L-NAME-induced hypertensive and spontaneously hypertensive rat models, MTNRs were upregulated in males but downregulated in female models. Interestingly, Mel-induced BP reduction was found in male hypertensive models. In whole-cell recording from identified baroreceptor neurons (BRNs) in female rats, we found that Mel (0.1 μM) significantly increased the excitability of a female-specific subpopulation of Ah-type BRNs by increasing the Nav1.9 current density via a PKC-mediated pathway. Similar results were observed in baroreceptive neurons of the nucleus tractus solitarius, showing the facilitation of spontaneous and evoked excitatory post-synaptic currents in Ah-type neurons. Collectively, this study reveals the estrogen-dependent effect of Mel/MTNRs under physiological and hypertensive conditions is mainly mediated by Ah-type BRNs, which may provide new theoretical basis and strategies for the gender-specific anti-hypertensive treatment in clinical practice.

Sex differences in carcinoid syndrome: A gap to be closed

The incidence of neuroendocrine neoplasms and related carcinoid syndrome (CS) has markedly increased over the last decades and women seem to be more at risk than men for developing CS. Nevertheless, very few studies have investigated sex differences in clinical presentation and outcomes of CS. However, as per other tumours, sex might be relevant in influencing tumour localization, delay in diagnosis, clinical outcomes, prognosis and overall survival in CS. The present review was aimed at evaluating sex differences in CS, as they emerge from an extensive search of the recent literature. It emerged that CS occurs more frequently in female than in male patients with NENs and women seem to have a better prognosis and a slight advantage in overall survival and response to therapy. Moreover, the disease likely impacts differently the quality of life of men and women, with different psychological and social consequences. Nevertheless, sex differences, even if partially known, are deeply underestimated in clinical practice and data from clinical trials are lacking. There is urgent need to increase our understanding of the sex-related differences of CS, in order to define tailored strategies of management of the disease, improving both the quality of life and the prognosis of affected patients.

Histamine and Microglia

Microglia, a category of glial cells in the central nervous system (CNS), have attracted much attention because of their important role in neuroinflammation. Many translational studies are currently ongoing to discover novel drugs targeting microglia for the treatment of various CNS disorders, such as Alzheimer's disease, Parkinson's disease (PD), and depression. Recent studies have shown that brain histamine, a neurotransmitter essential for the regulation of diverse brain functions, controls glial cells and neurons. In vitro studies using primary microglia and microglial cell lines have reported that histamine receptors are expressed in microglia and control microglial functions, including chemotaxis, migration, cytokine secretion, and autophagy. In vivo studies have demonstrated that histamine-related reagents could ameliorate abnormal symptoms in animal models of human diseases, such as amyotrophic lateral sclerosis (ALS), PD, and brain ischemia. Several human studies have revealed alterations in histamine receptor levels in ALS and PD, emphasizing the importance of the CNS histamine system, including histamine-dependent microglial modulation, as a therapeutic target for these disorders. In this review article, we summarize histamine-related research focusing on microglial functions.

Bradykinin-mediated estrogen-dependent depressor response by direct activation of female-specific distribution of myelinated Ah-type baroreceptor neurons in rats

Aim

To understand the direct impact of bradykinin in autonomic control of circulation through baroreflex afferent pathway.

Methods

The mean arterial pressure (MAP) was monitored while bradykinin and its agonists were applied via nodose (NG) microinjection, the expression of bradykinin receptors (BRs) in the NG (1^st‐order) and nucleus tractus solitarius (NTS, 2^nd‐order) were tested in adult male, age‐matched female, and ovariectomized rats under physiological and hypertensive conditions. Additionally, bradykinin‐induced depolarization was also tested in identified baroreceptor and baroreceptive neurons using whole‐cell patch‐clamp technique.

Results

Under physiological condition, bradykinin‐induced dose‐ and estrogen‐dependent reductions of MAP with lower estimated EC₅₀ in females. B₂R agonist mediated more dramatic MAP reduction with long‐lasting effect compared with B₁R activation. These functional observations were consistent with the molecular and immunostaining evidences. However, under hypertensive condition, the MAP reduction was significantly less dramatic in N^’‐Nitro‐L‐Arginine‐methyl ester (L‐NAME) induced secondary and spontaneous hypertension rats in males compared with female rats. Electrophysiological data showed that bradykinin‐elicited concentration‐dependent membrane depolarization with discharges during initial phase in identified myelinated Ah‐types baroreceptor neurons, not myelinated A‐types; while, higher concentration of bradykinin was required for depolarization of unmyelinated C‐types without initial discharges.

Conclusion

These datasets have demonstrated for the first time that bradykinin mediates direct activation of baroreflex afferent function to trigger estrogen‐dependent depressor response, which is due mainly to the direct activation/neuroexcitation of female‐specific myelinated Ah‐type baroreceptor neurons leading to a sexual dimorphism in parasympathetic domination of blood pressure regulation via activation of B₂R/B₁R expression in baroreflex afferent pathway.

Estrogen-dependent KCa1.1 modulation is essential for retaining neuroexcitation of female-specific subpopulation of myelinated Ah-type baroreceptor neurons in rats

Female-specific subpopulation of myelinated Ah-type baroreceptor neurons (BRNs) in nodose ganglia is the neuroanatomical base of sexual-dimorphic autonomic control of blood pressure regulation, and KCa1.1 is a key player in modulating the neuroexcitation in nodose ganglia. In this study we investigated the exact mechanisms underlying KCa1.1-mediated neuroexcitation of myelinated Ah-type BRNs in the presence or absence of estrogen. BRNs were isolated from adult ovary intact (OVI) or ovariectomized (OVX) female rats, and identified electrophysiologically and fluorescently. Action potential (AP) and potassium currents were recorded using whole-cell recording. Consistently, myelinated Ah-type BRNs displayed a characteristic discharge pattern and significantly reduced excitability after OVX with narrowed AP duration and faster repolarization largely due to an upregulated iberiotoxin (IbTX)-sensitive component; the changes in AP waveform and repetitive discharge of Ah-types from OVX female rats were reversed by G1 (a selective agonist for estrogen membrane receptor GPR30, 100 nM) and/or IbTX (100 nM). In addition, the effect of G1 on repetitive discharge could be completely blocked by G15 (a selective antagonist for estrogen membrane receptor GPR30, 3 μM). These data suggest that estrogen deficiency by removing ovaries upregulates KCa1.1 channel protein in Ah-type BRNs, and subsequently increases AP repolarization and blunts neuroexcitation through estrogen membrane receptor signaling. Intriguingly, this upregulated KCa1.1 predicted electrophysiologically was confirmed by increased mean fluorescent intensity that was abolished by estrogen treatment. These electrophysiological findings combined with immunostaining and pharmacological manipulations reveal the crucial role of KCa1.1 in modulation of neuroexcitation especially in female-specific subpopulation of myelinated Ah-type BRNs and extend our current understanding of sexual dimorphism of neurocontrol of BP regulation.

Acute vagus nerve stimulation enhances reversal learning in rats

Cognitive flexibility is a prefrontal cortex-dependent neurocognitive process that enables behavioral adaptation in response to changes in environmental contingencies. Electrical vagus nerve stimulation (VNS) enhances several forms of learning and neuroplasticity, but its effects on cognitive flexibility have not been evaluated. In the current study, a within-subjects design was used to assess the effects of VNS on performance in a novel visual discrimination reversal learning task conducted in touchscreen operant chambers. The task design enabled simultaneous assessment of acute VNS both on reversal learning and on recall of a well-learned discrimination problem. Acute VNS delivered in conjunction with stimuli presentation during reversal learning reliably enhanced learning of new reward contingencies. Enhancement was not observed, however, if VNS was delivered during the session but was not coincident with presentation of to-be-learned stimuli. In addition, whereas VNS delivered at 30 HZ enhanced performance, the same enhancement was not observed using 10 or 50 Hz. Together, these data show that acute VNS facilitates reversal learning and indicate that the timing and frequency of the VNS are critical for these enhancing effects. In separate rats, administration of the norepinephrine reuptake inhibitor atomoxetine also enhanced reversal learning in the same task, consistent with a noradrenergic mechanism through which VNS enhances cognitive flexibility.

In vivo evaluation of effects of histamine H3 receptor antagonists on methamphetamine-induced hyperlocomotion in mice

A single administration with METH (3 mg/kg) induced a hyperlocomotion in male ICR mice. Pretreatment of mice with pitolisant, a histamine H₃ receptor antagonist (5 and 10 mg/kg), for 30 min showed a significant reduction of the hyperlocomotion induced by METH, as compared with vehicle (saline)-pretreated subjects. Pretreatment of mice with the histamine H₃ receptor antagonists JNJ-10181457 (5 and 10 mg/kg) or conessine (20 mg/kg), also showed similar inhibitory effects on METH-induced hyperlocomotion, similar to pitolisant. No significant change in locomotion was observed in mice pretreated with pitolisant, JNJ-10181457, or conessine alone. The pitolisant (10 mg/kg) action on METH-induced hyperlocomotion was completely abolished by the histamine H₁ receptor antagonist pyrilamine (10 mg/kg), but not by the peripherally acting histamine H₁ receptor antagonist fexofenadine (20 mg/kg), the brain-penetrating histamine H₂ receptor antagonist zolantidine (10 mg/kg), or the brain-penetrating histamine H₄ receptor antagonist JNJ-7777120 (40 mg/kg). Pretreatment with a histamine H₃ receptor agonist immepip (10 mg/kg) augmented METH--induced behavior, including hyperlocomotion and stereotyped biting, and combined pretreatment with pitolisant (10 mg/kg) significantly attenuated stereotyped biting. These observations suggest that pretreatment with histamine H₃ receptor antagonists attenuate METH-induced hyperlocomotion via releasing histamine after blocking H₃ receptors, which then bind to the post-synaptic histamine receptor H₁ (but not H₂ or H₄). It is likely that activation of brain histamine systems may be a good strategy for the development of agents, which treat METH abuse and dependence.

Sex in Respiratory and Skin Allergies

A bulk of literature demonstrated that respiratory allergy, and especially asthma, is prevalent in males during childhood, while it becomes more frequent in females from adolescence, i.e., after menarche, to adulthood. The mechanisms underlying the difference between females and males are the effects on the immune response of female hormones and in particular the modulation of inflammatory response by estrogens, as well as the result of the activity of various cells, such as dendritic cells, innate lymphoid cells, Th1, Th2, T regulatory (Treg) and B regulatory (Bregs) cells, and a number of proteins and cytokines, which include interleukin (IL)-4, IL-5, IL-10, and IL-13. As far as sexual dimorphism is concerned, a gender difference in the expression profiles of histamine receptors and of mast cells was demonstrated in experimental studies. A critical phase of hormone production is the menstrual cycle, which often is associated with asthma deterioration, as assessed by worsening of clinical symptoms and increase of bronchial hyperresponsiveness. In asthmatic woman, there is a high risk to develop more severe asthma during menstruation. The higher prevalence of asthma in females is confirmed also in the post-menopause age, but the underlying mechanisms are not yet understood. In pregnancy, asthma may worsen but may also improve or remain unchanged, with no significant difference in frequency of these three outcomes. For allergic rhinitis, the available studies indicate, likewise asthma, a male predominance in prevalence in childhood that shifts to a female predominance in adolescence and adulthood, but further investigation is needed.

FGF-21 ameliorates essential hypertension of SHR via baroreflex afferent function

Hypertension is a common complication of metabolic abnormalities associated with cardiovascular system and characterized by sexual dimorphism in mammals. Fibroblast growth factor-21 (FGF-21) plays a critical role in metabolic-disorder related hypertension through the afferent loop of baroreflex. However, the gender difference in FGF-21-mediated blood pressure (BP) regulation via sexual dimorphic expression of FGFRs in the nodose (NG) and nucleus tractus solitarius (NTS) were not elucidated in physiological and genomic form of hypertension. The gene and protein expression of FGFRs were tested by qRT-PCR, immunoblotting and immunostaining; the serum level of FGF21 was tested using ELISA; The BP was monitored while FGF21 was nodose microinjected. The results showed that more potent BP reduction was confirmed in female vs. male rats by nodose microinjection of rhFGF-21 along with higher expression of FGFR2 and FGFR4 in the nodose compared with age-match male and ovariectomized (OVX) rats, rather than other receptor subtypes, which is consistent well with immunohistochemical analysis. Additionally, serum FGF-21 was significantly higher in female-WKY, and this level of FGF-21 was dramatically declined in spontaneous hypertensive rats (SHR) with significant down-regulation of FGFR1/R4 for male-SHR and FGFR2/FGFR4 for female-SHR, respectively. Apparently, high BP of SHR of either sex could be reduced by rhFGF-21 nodose microinjection. These data extends our current understanding that sexual-specific distribution/expression of FGF-21/FGFRs is likely to contribute at least partially to sexual dimorphism of baroreflex afferent function on BP regulation in rats. FGF-21-mdiated BP reduction sheds new light on clinical management of primary/genomic form of hypertension.

Anti-Hypertensive Action of Fenofibrate via UCP2 Upregulation Mediated by PPAR Activation in Baroreflex Afferent Pathway

Fenofibrate, an agonist for peroxisome proliferator-activated receptor alpha (PPAR-α), lowers blood pressure, but whether this action is mediated via baroreflex afferents has not been elucidated. In this study, the distribution of PPAR-α and PPAR-γ was assessed in the nodose ganglion (NG) and the nucleus of the solitary tract (NTS). Hypertension induced by drinking high fructose (HFD) was reduced, along with complete restoration of impaired baroreceptor sensitivity, by chronic treatment with fenofibrate. The molecular data also showed that both PPAR-α and PPAR-γ were dramatically up-regulated in the NG and NTS of the HFD group. Expression of the downstream signaling molecule of PPAR-α, the mitochondrial uncoupling protein 2 (UCP2), was up-regulated in the baroreflex afferent pathway under similar experimental conditions, along with amelioration of reduced superoxide dismutase activity and increased superoxide in HFD rats. These results suggest that chronic treatment with fenofibrate plays a crucial role in the neural control of blood pressure by improving baroreflex afferent function due at least partially to PPAR-mediated up-regulation of UCP2 expression and reduction of oxidative stress.

Role of Histamine in Modulating the Immune Response and Inflammation

Inflammatory mediators, including cytokines, histamine, bradykinin, prostaglandins, and leukotrienes, impact the immune system, usually as proinflammatory factors. Other mediators act as regulatory components to establish homeostasis after injury or prevent the inflammatory process. Histamine, a biogenic vasoactive amine, causes symptoms such as allergies and has a pleiotropic effect that is dependent on its interaction with its four histamine receptors. In this review, we discuss the dualistic effects of histamine: how histamine affects inflammation of the immune system through the activation of intracellular pathways that induce the production of inflammatory mediators and cytokines in different immune cells and how histamine exerts regulatory functions in innate and adaptive immune responses. We also evaluate the interactions between these effects.

Direct activation of tachykinin receptors within baroreflex afferent pathway and neurocontrol of blood pressure regulation

AIM

Substance P (SP) causes vasodilation and blood pressure (BP) reduction. However, the involvement of tachykinin receptors (NKRs) within baroreflex afferent pathway in SP-mediated BP regulation is largely unknown.

METHODS

Under control and hypertensive condition, NKRs' expressions were evaluated in nodose (NG) and nucleus of tractus solitary (NTS) of male, female, and ovariectomized (OVX) rats; BP was recorded after microinjection of SP and NKRs agonists into NG; Baroreceptor sensitivity (BRS) was tested as well.

RESULTS

Immunostaining and immunoblotting data showed that NK1R and NK2R were estrogen-dependently expressed on myelinated and unmyelinated afferents in NG. A functional study showed that BP was reduced dose-dependently by SP microinjection, which was more dramatic in males and can be mimicked by NK1R and NK2R agonists. Notably, further BP elevation and BRS dysfunction were confirmed in desoxycorticosterone acetate (DOCA)-salt model in OVX compared with DOCA-salt model in intact female rats. Additionally, similar changes in NKRs' expression in NG were also detected using DOCA-salt and SHR. Compared with NG, inversed expression profiles of NKRs were also found in NTS with either gender.

CONCLUSION

The estrogen-dependent NKRs' expression in baroreflex afferent pathway participates at least partially in sexual-dimorphic and SP-mediated BP regulation under physiological and hypertensive conditions.

Neuro-immune interactions in allergic diseases: novel targets for therapeutics

Recent studies have highlighted an emerging role for neuro-immune interactions in mediating allergic diseases. Allergies are caused by an overactive immune response to a foreign antigen. The peripheral sensory and autonomic nervous system densely innervates mucosal barrier tissues including the skin, respiratory tract and gastrointestinal (GI) tract that are exposed to allergens. It is increasingly clear that neurons actively communicate with and regulate the function of mast cells, dendritic cells, eosinophils, Th2 cells and type 2 innate lymphoid cells in allergic inflammation. Several mechanisms of cross-talk between the two systems have been uncovered, with potential anatomical specificity. Immune cells release inflammatory mediators including histamine, cytokines or neurotrophins that directly activate sensory neurons to mediate itch in the skin, cough/sneezing and bronchoconstriction in the respiratory tract and motility in the GI tract. Upon activation, these peripheral neurons release neurotransmitters and neuropeptides that directly act on immune cells to modulate their function. Somatosensory and visceral afferent neurons release neuropeptides including calcitonin gene-related peptide, substance P and vasoactive intestinal peptide, which can act on type 2 immune cells to drive allergic inflammation. Autonomic neurons release neurotransmitters including acetylcholine and noradrenaline that signal to both innate and adaptive immune cells. Neuro-immune signaling may play a central role in the physiopathology of allergic diseases including atopic dermatitis, asthma and food allergies. Therefore, getting a better understanding of these cellular and molecular neuro-immune interactions could lead to novel therapeutic approaches to treat allergic diseases.

Neuropeptide Y-mediated sex- and afferent-specific neurotransmissions contribute to sexual dimorphism of baroreflex afferent function

Background

Molecular and cellular mechanisms of neuropeptide-Y (NPY)-mediated gender-difference in blood pressure (BP) regulation are largely unknown.

Methods

Baroreceptor sensitivity (BRS) was evaluated by measuring the response of BP to phenylephrine/nitroprusside. Serum NPY concentration was determined using ELISA. The mRNA and protein expression of NPY receptors were assessed in tissue and single-cell by RT-PCR, immunoblot, and immunohistochemistry. NPY was injected into the nodose while arterial pressure was monitored. Electrophysiological recordings were performed on nodose neurons from rats by patch-clamp technique.

Results

The BRS was higher in female than male and ovariectomized rats, while serum NPY concentration was similar among groups. The sex-difference was detected in Y₁R, not Y₂R protein expression, however, both were upregulated upon ovariectomy and canceled by estrogen replacement. Immunostaining confirmed Y₁R and Y₂R expression in myelinated and unmyelinated afferents. Single-cell PCR demonstrated that Y₁R expression/distribution was identical between A- and C-types, whereas, expressed level of Y₂R was ∼15 and ∼7 folds higher in Ah- and C-types than A-types despite similar distribution. Activation of Y₁R in nodose elevated BP, while activation of Y₂R did the opposite. Activation of Y₁R did not alter action potential duration (APD) of A-types, but activation of Y₂R- and Y₁R/Y₂R in Ah- and C-types frequency-dependently prolonged APD. N-type I_Ca was reduced in A-, Ah- and C-types when either Y₁R, Y₂R, or both were activated. The sex-difference in Y₁R expression was also observed in NTS.

Conclusions

Sex- and afferent-specific expression of Neuropeptide-Y receptors in baroreflex afferent pathway may contribute to sexual-dimorphic neurocontrol of BP regulation.

Ketamine-mediated afferent-specific presynaptic transmission blocks in low-threshold and sex-specific subpopulation of myelinated Ah-type baroreceptor neurons of rats

Background

Ketamine enhances autonomic activity, and unmyelinated C-type baroreceptor afferents are more susceptible to be blocked by ketamine than myelinated A-types. However, the presynaptic transmission block in low-threshold and sex-specific myelinated Ah-type baroreceptor neurons (BRNs) is not elucidated.

Methods

Action potentials (APs) and excitatory post-synaptic currents (EPSCs) were investigated in BRNs/barosensitive neurons identified by conduction velocity (CV), capsaicin-conjugated with Iberiotoxin-sensitivity and fluorescent dye using intact nodose slice and brainstem slice in adult female rats. The expression of mRNA and targeted protein for NMDAR1 was also evaluated.

Results

Ketamine time-dependently blocked afferent CV in Ah-types in nodose slice with significant changes in AP discharge. The concentration-dependent inhibition of ketamine on AP discharge profiles were also assessed and observed using isolated Ah-type BRNs with dramatic reduction in neuroexcitability. In brainstem slice, the 2^nd-order capsaicin-resistant EPSCs were identified and ∼50% of them were blocked by ketamine concentration-dependently with IC₅₀ estimated at 84.4 μM compared with the rest (708.2 μM). Interestingly, the peak, decay time constant, and area under curve of EPSCs were significantly enhanced by 100 nM iberiotoxin in ketamine-more sensitive myelinated NTS neurons (most likely Ah-types), rather than ketamine-less sensitive ones (A-types).

Conclusions

These data have demonstrated, for the first time, that low-threshold and sex-specific myelinated Ah-type BRNs in nodose and Ah-type barosensitive neurons in NTS are more susceptible to ketamine and may play crucial roles in not only mean blood pressure regulation but also buffering dynamic changes in pressure, as well as the ketamine-mediated cardiovascular dysfunction through sexual-dimorphic baroreflex afferent pathway.

FGF21 ameliorates the neurocontrol of blood pressure in the high fructose-drinking rats

Fibroblast growth factor-21 (FGF21) is closely related to various metabolic and cardiovascular disorders. However, the direct targets and mechanisms linking FGF21 to blood pressure control and hypertension are still elusive. Here we demonstrated a novel regulatory function of FGF21 in the baroreflex afferent pathway (the nucleus tractus solitarii, NTS; nodose ganglion, NG). As the critical co-receptor of FGF21, β-klotho (klb) significantly expressed on the NTS and NG. Furthermore, we evaluated the beneficial effects of chronic intraperitoneal infusion of recombinant human FGF21 (rhFGF21) on the dysregulated systolic blood pressure, cardiac parameters, baroreflex sensitivity (BRS) and hyperinsulinemia in the high fructose-drinking (HFD) rats. The BRS up-regulation is associated with Akt-eNOS-NO signaling activation in the NTS and NG induced by acute intravenous rhFGF21 administration in HFD and control rats. Moreover, the expressions of FGF21 receptors were aberrantly down-regulated in HFD rats. In addition, the up-regulated peroxisome proliferator-activated receptor-γ and -α (PPAR-γ/-α) in the NTS and NG in HFD rats were markedly reversed by chronic rhFGF21 infusion. Our study extends the work of the FGF21 actions on the neurocontrol of blood pressure regulations through baroreflex afferent pathway in HFD rats.

Prostaglandin E2-mediated upregulation of neuroexcitation and persistent tetrodotoxin-resistant Na(+) currents in Ah-type trigeminal ganglion neurons isolated from adult female rats

Prostaglandin-E2 (PGE2) is a very important inflammatory mediator and PGE2-mediated neuroexcitation in sex-specific distribution of Ah-type trigeminal ganglion neurons (TGNs) isolated from adult female rats is not fully addressed. The whole-cell patch-clamp experiment was performed to verify the effects of PGE2, forskolin, and GPR30-selective agonist (G-1) on action potential (AP) and tetrodotoxin-resistant (TTX-R) Na(+) currents in identified Ah-type TGNs. The results showed that the firing frequency was increased in Ah- and C-types by PGE2, which was simulated by forskolin and inhibited by Rp-cyclic adenosine monophosphate (cAMP), while G-1 mimicked this effect only in Ah-types, which was abolished by GPR30-selective antagonist (G-15). Although the amplitude of AP was increased in Ah- and C-types, increased maximal upstroke velocity was confirmed only in Ah-types, suggesting distinct alternations in current density and/or voltage-dependent property of Na(+) channels. With 1.0 μM PGE2, TTX-R Na(+) currents were upregulated without changing the current-voltage relationship and voltage-dependent activation in C-types, however, the TTX-R Na(+) current was augmented in Ah-types, peaked voltage and the voltage-dependent activation were both shifted toward hyperpolarized direction with faster slope. Intriguingly, the low-threshold persistent TTX-R component was activated from -60 mV and increased almost double at -30 mV compared with ∼30-40% increment of TTX-R component being activated at ∼-10 mV. Additionally, the change in TTX-R component of Ah-types was equivalent well with that in C-type TGNs. Taken these data together, we conclude that PGE2 modulates the neuroexcitation via cAMP-mediated upregulation of TTX-R Na(+) currents in both cell-types with hormone-dependent feature, especially persistent TTX-R Na(+) currents in sex-specific distribution of myelinated Ah-type TGNs.

Effect of estrogen on vagal afferent projections to the brainstem in the female

The effects of 17β-estradiol (E) on the distribution and density of brainstem projections of small or large diameter primary vagal afferents were investigated in Wistar rats using transganglionic transport of wheat germ agglutinin- (WGA; preferentially transported by non-myelinated afferent C-fibers; 2%), or cholera toxin B-subunit- (CTB, 5%; preferentially transported by large myelinated afferent A-fibers) conjugated horseradish peroxidase (HRP) in combination with the tetramethylbenzidine method in age matched ovariectomized (OVX) only or OVX and treated with E (OVX+E; 30 pg/ml plasma) females for 12 weeks. Additionally, these projections were compared to aged matched males. Unilateral microinjection of WGA-HRP into the nodose ganglion resulted in dense anterograde labeling bilaterally, with an ipsilateral predominance in several subnuclei of the nucleus of the solitary tract (NTS) and in area postrema that was greatest in OVX+E animals compared to OVX only and males. Moderately dense anterograde labeling was also observed in paratrigeminal nucleus (PAT) of the OVX+E animals. CTB-HRP produced less dense anterograde labeling in the NTS complex, but had a wider distribution within the brainstem including the area postrema, dorsal motor nucleus of the vagus, PAT, the nucleus ambiguus complex and ventrolateral medulla in all groups. The distribution of CTB-HRP anterograde labeling was densest in OVX+E, less dense in OVX only females and least dense in male rats. Little, if any, labeling was found within PAT in males using either WGA-or CTB-HRP. Taken together, these data suggest that small, non-myelinated (WGA-labeled) and large myelinated (CTB-labeled) diameter vagal afferents projecting to brainstem autonomic areas are differentially affected by circulating levels of estrogen. These effects of estrogen on connectivity may contribute to the sex differences observed in central autonomic mechanisms between gender, and in females with and without estrogen.