Dopamine type 2 receptor expression and function in rodent sensory neurons projecting to the airways

Anti-Inflammatory Effects of Peripheral Dopamine

Dopamine is synthesized in the nervous system where it acts as a neurotransmitter. Dopamine is also synthesized in a number of peripheral organs as well as in several types of cells and has organ-specific functions and, as demonstrated more recently, is involved in the regulation of the immune response and inflammatory reaction. In particular, the renal dopaminergic system is very important in the regulation of sodium transport and blood pressure and is particularly sensitive to stimuli that cause oxidative stress and inflammation. This review is focused on how dopamine is synthesized in organs and tissues and the mechanisms by which dopamine and its receptors exert their effects on the inflammatory response.

Activation of dopamine D2 receptors attenuates neuroinflammation and ameliorates the memory impairment induced by rapid eye movement sleep deprivation in a murine model

The proinflammatory state, which may be induced by sleep deprivation, seems to be a determining factor in the development of neurodegenerative processes. Investigations of mechanisms that help to mitigate the inflammatory effects of sleep disorders are important. A new proposal involves the neurotransmitter dopamine, which may modulate the progression of the immune response by activating receptors expressed on immune cells. This study aimed to determine whether dopamine D2 receptor (D2DR) activation attenuates the proinflammatory response derived from rapid eye movement (REM) sleep deprivation in mice. REM sleep deprivation (RSD) was induced in 2-month-old male CD1 mice using the multiple platform model for three consecutive days; during this period, the D2DR receptor agonist quinpirole (QUIN) was administered (2 mg/kg/day i.p.). Proinflammatory cytokine levels were assessed in serum and homogenates of the brain cortex, hippocampus, and striatum using ELISAs. Long-term memory deficits were identified using the Morris water maze (MWM) and novel object recognition (NOR) tests. Animals were trained until learning criteria were achieved; then, they were subjected to RSD and treated with QUIN for 3 days. Memory evocation was determined afterward. Moreover, we found RSD induced anhedonia, as measured by the sucrose consumption test, which is commonly related to the dopaminergic system. Our data revealed increased levels of proinflammatory cytokines (TNFα and IL-1β) in both the hippocampus and serum from RSD mice. However, QUIN attenuated the increased levels of these cytokines. Furthermore, RSD caused a long-term memory evocation deficit in both the MWM and NOR tests. In contrast, QUIN coadministration during the RSD period significantly improved the performance of the animals. On the other hand, QUIN prevented the anhedonic condition induced by RSD. Based on our results, D2DR receptor activation protects against memory impairment induced by disturbed REM sleep by inhibiting neuroinflammation.

Dopamine relieves inflammatory responses through the D2 receptor after electroacupuncture at ST36 in a mouse model of chronic obstructive pulmonary disease

OBJECTIVE

To detect the role of dopamine in the anti-inflammatory effect of electroacupuncture (EA) at ST36 in a mouse model of chronic obstructive pulmonary disease (COPD).

METHODS

Twenty-eight male BALB/c mice were randomly divided into the control group, model group, sham EA (sham) group or ST36 EA (ST36) group in a 1:1:1:1 ratio (n = 7 each). The COPD mouse model was established through cigarette smoke (CS) exposure for 12 weeks. During the last 2 weeks, EA was applied at a sham point location or ST36 before CS exposure. Lung function, histopathological changes, inflammatory cell counts in bronchoalveolar lavage fluid (BALF), inflammatory cytokines in BALF, plasma, lung tissue homogenate (LTH), and plasma dopamine levels were detected in the different groups. Furthermore, the role of different dopamine receptors was explored through intraperitoneal injections of non-specific dopamine receptor antagonist chlorpromazine, specific dopamine D1 receptor antagonist SCH 23390 and specific dopamine D2 receptor antagonist eticlopride hydrochloride prior to ST36 EA and CS exposure.

RESULTS

EA at ST36 improved lung function, alleviated lung and systemic inflammatory responses by reducing inflammatory cells and cytokines including tumor necrosis factor (TNF)-α, interleukin (IL)-8 and IL-1β in BALF, plasma and lung tissue in this COPD mouse model. Plasma dopamine was greatly increased after EA at ST36, negatively correlated with lung histological lesions and inflammatory cytokine levels, and positively correlated with mice body weight and lung function indicators. Chlorpromazine and eticlopride hydrochloride inhibited the anti-inflammatory effect of EA at ST36, while SCH 23390 showed no neutralizing effect.

CONCLUSION

EA at ST36 could alleviate inflammation in this mouse model of COPD through the dopamine D2 receptor pathway.

Salvianolic acid A relieves cognitive disorder after chronic cerebral ischemia: Involvement of Drd2/Cryab/NF-κB pathway

Chronic cerebral ischemia (CCI) refers to long-term hypoperfusion of cerebral blood flow with the main clinical manifestations of progressive cognitive impairment. The pathological mechanism of CCI is complex, and there is a lack of effective treatments. Salvianolic acid A (SalA) is a neuroprotective extract of Salvia miltiorrhiza with the effects of anti-inflammation and anti-apoptosis. In this study, the effect of SalA on cognitive function and Drd2/Cryab/NF-κB signaling pathway in rats with CCI was investigated. Morris water maze and open field test were used to observe the effects of SalA on the cognitive function of CCI rats. The pathological changes in the brain were observed by HE, Nissl, and LFB staining. TUNEL staining, enzyme-linked immunosorbent assay, and western blot analysis were used to detect the inflammatory and apoptosis in the cortex and hippocampus. The expression of Drd2/Cryab/NF-κB pathway-related molecules and Drd2 localization were detected by western blotting and dual immunofluorescence, respectively. SH-SY5Y cells were exposed to chronic hypoglycemic and hypoxic injury in vitro, and Drd2 inhibitor haloperidol was used to verify the involved pathway. The results showed that SalA could improve the cognitive function of CCI rats, reduce pathological damage of cortex and hippocampus, inhibit neuroinflammation and apoptosis, and suppress the activation of NF-κB by regulating Drd2/Cryab pathway. And SalA inhibited NF-κB activation and nuclear translocation in SH-SY5Y cells by upregulating Drd2/Cryab pathway, which was reversed by haloperidol interference. In conclusion, SalA could relieve CCI-induced cognitive impairment in rats, at least partly through the Drd2/Cryab/NF-κB pathway.

Dopamine, a co-regulatory component, bridges the central nervous system and the immune system

Dopamine (DA) is a crucial neurotransmitter that plays an important role in maintaining physiological function in human body. In the past, most studies focused on the relationship between the dopaminergic system and neurological-related diseases. However, it has been found recently that DA is an immunomodulatory mediator and many immune cells express dopamine receptors (DRs). Some immune cells can synthesize and secrete DA and then participate in regulating immune function. DRs agonists or antagonists can improve the dysfunction of immune system through classical G protein signaling pathways or other non-receptor-dependent pathways. This article will discuss the relationship between the dopaminergic system and the immune system. It will also review the use of DRs agonists or antagonists to treat chronic and acute inflammatory diseases and corresponding immunomodulatory mechanisms.

Functional Characterization of the Prejunctional Receptors Mediating the Inhibition by Ergotamine of the Rat Perivascular Sensory Peptidergic Drive

Calcitonin gene-related peptide (α-CGRP) released from perivascular sensory nerves induces decreases in diastolic blood pressure (DBP). Experimentally, this can be shown by spinal thoracic (T₉-T₁₂) electrical stimulation of these afferent fibers. Because ergotamine inhibits these neurogenic vascular responses and displays affinity for monoaminergic receptors that inhibit neurotransmitter release, we investigated whether this ergotamine-induced inhibition results from activation of serotonin 5-HT_1B/1D, dopamine D₂-like, and α₂-adrenergic receptors. Wistar rats were pithed and, under autonomic ganglion blockade, received intravenous infusions of methoxamine followed by ergotamine (0.1-3.1 μg kg^-1 min^-1). Thoracic T₉-T₁₂ electrical stimulation or an intravenous bolus of α-CGRP resulted in decreases in DBP. Ergotamine inhibited the electrically induced, but not α-CGRP-induced, responses. The vasodilator sensory inhibition by 3.1 μg of ergotamine kg^-1 min^-1 was resistant to simultaneous blockade of 5-HT_1B/1D, D₂-like, and α₂-adrenergic receptors upon addition of antagonists GR127935, haloperidol, and rauwolscine. Moreover, the inhibition by 0.31 μg of ergotamine kg^-1 min^-1 was unaltered by GR127935 and haloperidol, partly blocked by GR127935 and rauwolscine or rauwolscine and haloperidol, and abolished by GR127935, haloperidol, and rauwolscine. These findings imply that prejunctional 5-HT_1B/1D, D₂-like, and α₂-adrenergic receptors mediate the sensory inhibition induced by 0.31 μg of ergotamine kg^-1 min^-1, whereas larger doses may involve other receptors. Thus, ergotamine's ability to inhibit the perivascular sensory peptidergic drive may result in facilitation of its systemic vasoconstrictor properties.

Cutaneous pigmentation modulates skin sensitivity via tyrosinase-dependent dopaminergic signalling

We propose a new mechanism of sensory modulation through cutaneous dopaminergic signalling. We hypothesize that dopaminergic signalling contributes to differential cutaneous sensitivity in darker versus lighter pigmented humans and mouse strains. We show that thermal and mechanical cutaneous sensitivity is pigmentation dependent. Meta-analyses in humans and mice, along with our own mouse behavioural studies, reveal higher thermal sensitivity in pigmented skin relative to less-pigmented or albino skin. We show that dopamine from melanocytes activates the D₁-like dopamine receptor on primary sensory neurons. Dopaminergic activation increases expression of the heat-sensitive TRPV1 ion channel and reduces expression of the mechanically-sensitive Piezo2 channel; thermal threshold is lower and mechanical threshold is higher in pigmented skin.

Renal rescue of dopamine D2 receptor function reverses renal injury and high blood pressure

Dopamine D2 receptor (DRD2) deficiency increases renal inflammation and blood pressure in mice. We show here that long-term renal-selective silencing of Drd2 using siRNA increases renal expression of proinflammatory and profibrotic factors and blood pressure in mice. To determine the effects of renal-selective rescue of Drd2 expression in mice, the renal expression of DRD2 was first silenced using siRNA and 14 days later rescued by retrograde renal infusion of adeno-associated virus (AAV) vector with DRD2. Renal Drd2 siRNA treatment decreased the renal expression of DRD2 protein by 55%, and DRD2 AAV treatment increased the renal expression of DRD2 protein by 7.5- to 10-fold. Renal-selective DRD2 rescue reduced the expression of proinflammatory factors and kidney injury, preserved renal function, and normalized systolic and diastolic blood pressure. These results demonstrate that the deleterious effects of renal-selective Drd2 silencing on renal function and blood pressure were rescued by renal-selective overexpression of DRD2. Moreover, the deleterious effects of 45-minute bilateral ischemia/reperfusion on renal function and blood pressure in mice were ameliorated by a renal-selective increase in DRD2 expression by the retrograde ureteral infusion of DRD2 AAV immediately after the induction of ischemia/reperfusion injury. Thus, 14 days after ischemia/reperfusion injury, the renal expression of profibrotic factors, serum creatinine, and blood pressure were lower in mice infused with DRD2 AAV than in those infused with control AAV. These results indicate an important role of renal DRD2 in limiting renal injury and preserving normal renal function and blood pressure.

Dopamine D2 receptors' effects on renal inflammation are mediated by regulation of PP2A function

Lack or downregulation of the dopamine D2 receptor (D2R) results in increased renal expression of injury markers and proinflammatory factors that is independent of a blood pressure increase. This study aimed to determine the mechanisms involved in the regulation of renal inflammation by D2Rs. Silencing D2Rs in mouse renal proximal tubule cells increased the expression of the proinflammatory TNF-α, monocyte chemoattractant protein-1 (MCP-1), and IL-6. D2R downregulation also increased Akt phosphorylation and activity, and glycogen synthase kinase-3β (GSK3β) phosphorylation and cyclin D1 expression, downstream targets of Akt; however. phosphatidylinositol 3-kinase (PI3K) activity was not affected. Conversely, D2R stimulation decreased Akt and GSK3β phosphorylation and cyclin D1 expression. Increased phospho-Akt, in the absence of increased PI3K activity, may result from decreased Akt dephosphorylation. Inhibition of protein phosphatase 2A (PP2A) with okadaic acid reproduced the effects of D2R downregulation on Akt, GSK3β, and cyclin D1. The PP2A catalytic subunit and regulatory subunit PPP2R2C coimmunoprecipitated with the D2R. Basal phosphatase activity and the expression of PPP2R2C were decreased by D2R silencing that also blunted the increase in phosphatase activity induced by D2R stimulation. Similarly, silencing PPP2R2C also increased the phosphorylation of Akt and GSK3β. Moreover, downregulation of PPP2R2C resulted in increased expression of TNF-α, MCP-1, and IL-6, indicating that decreased phosphatase activity may be responsible for the D2R effect on inflammatory factors. Indeed, the increase in NF-κB reporter activity induced by D2R silencing was blunted by increasing PP2A activity with protamine. Our results show that D2R controls renal inflammation, at least in part, by modulation of the Akt pathway through effects on PP2A activity/expression.

Dopamine modulation of transient receptor potential vanilloid type 1 (TRPV1) receptor in dorsal root ganglia neurons

The transient receptor potential vanilloid type 1 (TRPV1) receptor plays a key role in the modulation of nociceptor excitability. To address whether dopamine can modulate the activity of TRPV1 channels in nociceptive neurons, the effects of dopamine and dopamine receptor agonists were tested on the capsaicin-activated current recorded from acutely dissociated small diameter (<27 μm) dorsal root ganglia (DRG) neurons. Dopamine or SKF 81297 (an agonist at D1/D5 receptors), caused inhibition of both inward and outward currents by ∼60% and ∼48%, respectively. The effect of SKF 81297 was reversed by SCH 23390 (an antagonist at D1/D5 receptors), confirming that it was mediated by activation of D1/D5 dopamine receptors. In contrast, quinpirole (an agonist at D2 receptors) had no significant effect on the capsaicin-activated current. Inhibition of the capsaicin-activated current by SKF 81297 was mediated by G protein coupled receptors (GPCRs), and highly dependent on external calcium. The inhibitory effect of SKF 81297 on the capsaicin-activated current was not affected when the protein kinase A (PKA) activity was blocked with H89, or when the protein kinase C (PKC) activity was blocked with bisindolylmaleimide II (BIM). In contrast, when the calcium-calmodulin-dependent protein kinase II (CaMKII) was blocked with KN-93, the inhibitory effect of SKF 81297 on the capsaicin-activated current was greatly reduced, suggesting that activation of D1/D5 dopamine receptors may be preferentially linked to CaMKII activity. We suggest that modulation of TRPV1 channels by dopamine in nociceptive neurons may represent a way for dopamine to modulate incoming noxious stimuli.

Activation of Dopamine D2 Receptor Suppresses Neuroinflammation Through αB-Crystalline by Inhibition of NF-κB Nuclear Translocation in Experimental ICH Mice Model

BACKGROUND AND PURPOSE

Inflammatory injury plays a critical role in intracerebral hemorrhage (ICH)-induced secondary brain injury. Recently, dopamine D2 receptor (DRD2) is identified as an important component controlling innate immunity and inflammatory response in central nervous system, and αB-crystallin (CRYAB) is a potent negative regulator on inflammatory pathways. Here, we sought to investigate the role of DRD2 on neuroinflammation after experimental ICH and the potential mechanism mediated by CRYAB.

METHODS

Two hundred and twenty-four (224) male CD-1 mice were subjected to intrastriatal infusion of bacterial collagenase or autologous blood. Two DRD2 agonists quinpirole and ropinirole were administrated by daily intraperitoneal injection starting at 1 hour after ICH. DRD2 and CRYAB in vivo knockdown was performed 48 hours before ICH insult. Behavioral deficits and brain water content, Western blots, immunofluorescence staining, coimmunoprecipitation (Co-IP) assay, and proteome cytokine array were evaluated.

RESULTS

Endogenous DRD2 and CRYAB expressions were increased after ICH. DRD2 knockdown aggravated the neurobehavioral deficits and the pronounced cytokine expressions. DRD2 activation by quinpirole and ropinirole ameliorated neurological outcome, brain edema, interleukin-1β, and monocyte chemoattractant protein-1 expression, as well as microglia/macrophages activation, in the perihematomal region. These effects were abolished by pretreatment with CRYAB siRNAs. Quinpirole enhanced cytoplasmic binding activity between CRYAB and NF-κB and decreased nuclear NF-κB expression. Similar therapeutic benefits were observed using autologous blood injection model and intranasal delivery of quinpirole.

CONCLUSIONS

DRD2 may have anti-inflammatory effects after ICH. DRD2 agonists inhibited neuroinflammation and attenuated brain injury after ICH, which is probably mediated by CRYAB and enhanced cytoplasmic binding activity with NF-κB.

Airway smooth muscle in airway reactivity and remodeling: what have we learned?

It is now established that airway smooth muscle (ASM) has roles in determining airway structure and function, well beyond that as the major contractile element. Indeed, changes in ASM function are central to the manifestation of allergic, inflammatory, and fibrotic airway diseases in both children and adults, as well as to airway responses to local and environmental exposures. Emerging evidence points to novel signaling mechanisms within ASM cells of different species that serve to control diverse features, including 1) [Ca(2+)]i contractility and relaxation, 2) cell proliferation and apoptosis, 3) production and modulation of extracellular components, and 4) release of pro- vs. anti-inflammatory mediators and factors that regulate immunity as well as the function of other airway cell types, such as epithelium, fibroblasts, and nerves. These diverse effects of ASM "activity" result in modulation of bronchoconstriction vs. bronchodilation relevant to airway hyperresponsiveness, airway thickening, and fibrosis that influence compliance. This perspective highlights recent discoveries that reveal the central role of ASM in this regard and helps set the stage for future research toward understanding the pathways regulating ASM and, in turn, the influence of ASM on airway structure and function. Such exploration is key to development of novel therapeutic strategies that influence the pathophysiology of diseases such as asthma, chronic obstructive pulmonary disease, and pulmonary fibrosis.

Inhibition of tetrodotoxin-resistant sodium current in dorsal root ganglia neurons mediated by D1/D5 dopamine receptors

Background

Dopaminergic fibers originating from area A11 of the hypothalamus project to different levels of the spinal cord and represent the major source of dopamine. In addition, tyrosine hydroxylase, the rate-limiting enzyme for the synthesis of catecholamines, is expressed in 8-10% of dorsal root ganglia (DRG) neurons, suggesting that dopamine may be released in the dorsal root ganglia. Dopamine has been shown to modulate calcium current in DRG neurons, but the effects of dopamine on sodium current and on the firing properties of small DRG neurons are poorly understood.

Results

The effects of dopamine and dopamine receptor agonists were tested on the tetrodotoxin-resistant (TTX-R) sodium current recorded from acutely dissociated small (diameter ≤ 25 μm) DRG neurons. Dopamine (20 μM) and SKF 81297 (10 μM) caused inhibition of TTX-R sodium current in small DRG neurons by 23% and 37%, respectively. In contrast, quinpirole (20 μM) had no effects on the TTX-R sodium current. Inhibition by SKF 81297 of the TTX-R sodium current was not affected when the protein kinase A (PKA) activity was blocked with the PKA inhibitory peptide (6–22), but was greatly reduced when the protein kinase C (PKC) activity was blocked with the PKC inhibitory peptide (19–36), suggesting that activation of D1/D5 dopamine receptors is linked to PKC activity. Expression of D1and D5 dopamine receptors in small DRG neurons, but not D2 dopamine receptors, was confirmed by Western blotting and immunofluorescence analysis. In current clamp experiments, the number of action potentials elicited in small DRG neurons by current injection was reduced by ~ 30% by SKF 81297.

Conclusions

We conclude that activation of D1/D5 dopamine receptors inhibits TTX-R sodium current in unmyelinated nociceptive neurons and dampens their intrinsic excitability by reducing the number of action potentials in response to stimulus. Increasing or decreasing levels of dopamine in the dorsal root ganglia may serve to adjust the sensitivity of nociceptors to noxious stimuli.

Dopaminergic modulation of ganglion-cell photoreceptors in rat

A novel class of photoreceptors, the intrinsically photosensitive retinal ganglion cells (ipRGCs), express the photopigment melanopsin and drive non-image-forming responses to light such as circadian photoentrainment, the pupillary light reflex and suppression of nocturnal melatonin production in the pineal. Because dendrites from one subclass of these cells - the M1-type ipRGCs - make presumptive synaptic contacts at sites of dopamine release from dopaminergic amacrine cells, they are prime targets for modulation by dopamine, a neuromodulator implicated in retinal circadian rhythms and light adaptation. In patch-clamp recordings from ipRGCs in intact rat retinas, dopamine attenuated the melanopsin-based photocurrent. We confirmed that this was the result of direct action on ipRGCs by replicating the effect in dissociated ipRGCs that were isolated from influences of other retinal neurons. In these recordings, the D1-family dopamine receptor agonist SKF38393 attenuated the photocurrent, caused a modest depolarization, and reduced the input resistance of ipRGCs. The D2-family agonist quinpirole had no effect on the photocurrent. Single-cell reverse-transcriptase polymerase chain reaction revealed that the majority of ipRGCs tested expressed drd1a, the gene coding for the D1a dopamine receptor. This finding was supported by immunohistochemical localization of D1a receptor protein in melanopsin-expressing ganglion cells. Finally, the adenylate cyclase activator forskolin, applied in combination with the phosphodiesterase inhibitor IBMX (isobutylmethylxanthine), mimicked the effects of SKF38393 on the ipRGC photocurrent, membrane potential and input resistance, consistent with a D1-receptor signaling pathway. These data suggest that dopamine, acting via D1-family receptors, alters the responses of ipRGCs and thus of non-image-forming vision.

The dopamine D(2) receptor is expressed and sensitizes adenylyl cyclase activity in airway smooth muscle

Dopamine receptors are G protein-coupled receptors that are divided into two subgroups, "D(1)-like" receptors (D(1) and D(5)) that couple to the G(s) protein and "D(2)-like" receptors (D(2), D(3), and D(4)) that couple to G(i). Although inhaled dopamine has been reported to induce bronchodilation in patients with asthma, functional expression of dopamine receptor subtypes has never been described on airway smooth muscle (ASM) cells. Acute activation of G(i)-coupled receptors inhibits adenylyl cyclase activity and cAMP synthesis, which classically impairs ASM relaxation. In contrast, chronic activation of G(i)-coupled receptors produces a paradoxical enhancement of adenylyl cyclase activity referred to as heterologous sensitization. We questioned whether the dopamine D(2)-like receptor is expressed on ASM, whether it exhibits classical G(i)-coupling, and whether it modulates ASM function. We detected the mRNA encoding the dopamine D(2) receptor in total RNA isolated from native human ASM and from cultured human airway smooth muscle (HASM) cells. Immunoblots identified the dopamine D(2) receptor protein in both native human and guinea pig ASM and cultured HASM cells. The dopamine D(2) receptor protein was immunohistochemically localized to both human and guinea pig ASM. Acute activation of the dopamine D(2) receptor by quinpirole inhibited forskolin-stimulated adenylyl cyclase activity in HASM cells, which was blocked by the dopamine D(2) receptor antagonist L-741626. In contrast, the chronic pretreatment (1 h) with quinpirole potentiated forskolin-stimulated adenylyl cyclase activity, which was inhibited by L-741626, the phospholipase C inhibitor U73122, or the protein kinase C inhibitor GF109203X. Quinpirole also stimulated inositol phosphate synthesis, which was inhibited by L-741626 or U73122. Chronic pretreatment (1 h) of the guinea pig tracheal rings with quinpirole significantly potentiated forskolin-induced airway relaxation, which was inhibited by L-741626. These results demonstrate that functional dopamine D(2) receptors are expressed on ASM and could be a novel therapeutic target for the relaxation of ASM.

DA1 receptors modulation in rat isolated trachea

We have previously demonstrated that low dose of inhaled dopamine (0.5-2 microg kg(-1) min(-1)) induces broncodilatacion in patients with acute asthma attack, suggesting that this dopamine effect is mediated by dopaminergic rather than by adrenergic receptors. To understand better these dopamine effect, rat tracheal smooth muscle was used as a model to evaluate the responses of beta2-, alpha1-, alpha2-adrenergic and DA1 and DA2 dopaminergic antagonists. Tracheal rings from male Sprague-Dawley rats (n = 90) were excised and placed in an organ bath containing modified Krebs-Ringer bicarbonate buffer at 37 degrees C, and gassed with O2 (95%) and CO2 (5%). Contractile responses were recorded with an isometric transducer in a polygraph (Letica, Spain). Contraction was induced by accumulative doses of acetylcholine (0.1, 0.3, 1, 3, 10 mM) or by electric field stimulation (10 Hz at 2 milliseconds), and accumulative doses of dopamine were added to the bath. Low concentration (0.1-0.3 mM) elicited a small initial contraction, followed by a marked relaxation. Cholinergic contraction was completely reversed at 6 mM of dopamine. This biphasic dopaminergic response was not blocked by incubation with beta2-adrenergic antagonist propranolol (0.1 microM), alpha1-antagonist, terazosin (0.1 mM), alpha2-antagonist, yohimbine (0.1 mM), or by DA2 antagonist metoclopramide (1-8 mM); DA1 antagonist SCH23390 (0.1 microM) produced a sustained increase of basal tone but did not block initial dopaminergic contraction and partially inhibited bronchodilator effect of dopamine. Dopaminergic relaxation in rat trachea is mediated by DA1 rather than by DA2 receptors; and adrenergic receptors are not involved in such dopamine-induced response. Finally, DA1 antagonist SCH23390 exerts intrinsic contractile activity on airway smooth muscle that deserves further research.

Dopamine D2 receptor mRNA expression is increased in the jugular-nodose ganglia of rats with nitrogen dioxide-induced chronic bronchitis

The bronchodilatatory effect of inhaled dopamine or dopamine D(2) receptor agonists in cases of bronchial constriction may involve the suppression of pathologically increased airway sensory nerve activity. The aim of this study is to investigate the regulation of the dopamine D(2) receptor mRNA expression in the ganglia of rats with nitrogen dioxide-induced chronic bronchitis compared with that in ganglia of healthy control animals. Rats were exposed to nitrogen dioxide (10 ppm, 20 d) and dopamine D(2) receptor mRNA levels in sensory ganglia (jugular-nodose, trigeminal, cervical dorsal root and thoracic dorsal root ganglia) were examined by quantitative real-time polymerase chain reaction and compared to control tissues. Whereas for trigeminal and dorsal root ganglia the dopamine D(2) receptor expression levels showed no difference between both animal groups, there was a significant (p<0.05) increase in the jugular-nodose ganglia with a 2.1-fold factor. The increase of dopamine D(2) receptor mRNA in jugular-nodose sensory neurons which innervate the airways may represent a neurochemical basis for the effects seen in man and animal models following topical administration of dopamine or dopamine agonists onto the respiratory epithelium.

The effects of dopamine on the respiratory system: Friend or foe?

Dopamine (DA) is an immediate precursor of noradrenaline that has stimulatory or inhibitory effects on a variety of adrenergic receptors. DA is primarily used in the management of circulatory shock for its combined vasopressor and inotropic effects, but it may also exert significant effects on the respiratory system Although the respiratory effects of intravenous DA attract less attention than its hemodynamic effects, there is evidence that DA affects ventilation, pulmonary circulation, bronchial diameter, neuromodulation of sensory pulmonary nerves and lung water clearance. Through these complex mechanisms, DA may exert beneficial as well as detrimental effects on respiration. DA may have beneficial effects on the respiratory system by decreasing oedema formation and improving respiratory muscle function, but can also have deleterious effects, by inhibiting ventilation. Hence, DA may be beneficial in lung oedema, but harmful in cases of difficult weaning from mechanical ventilation. DA should be used with caution in patients with heart failure during weaning from mechanical respiration; however, critically ill patients with chronic obstructive pulmonary disease (COPD) do not show this negative effect of DA on ventilatory drive.

Gene and protein expression of protease-activated receptor 2 in structural and inflammatory cells in the nasal mucosa in seasonal allergic rhinitis

BACKGROUND

Protease-activated receptor 2 (PAR 2) has been shown to be responsible for trypsin and mast cell tryptase-induced airway inflammation. Here, the present study aimed to explore the expression of PAR 2 in the nasal mucosa of seasonal allergic rhinitis (SAR).

METHODS

Study subjects were recruited for the study by medical history, physical examination and laboratory screening tests. Using immunohistochemistry, laser-assisted cell picking and subsequently real-time PCR, nasal mucosa biopsies of SAR patients were investigated for PAR 2 gene and protein expression in complex tissues of the nasal mucosa.

RESULTS

Gene and protein expression of PAR 2 was firstly detected in nasal mucosa of SAR patients. The relative gene expression level of PAR 2 was significantly increased in complex tissues of the nasal mucosa of SAR (6.21+/-4.02 vs. controls: 1.38+/-0.86, P=0.004). Moreover, PAR 2 mRNA expression in epithelial cells (SAR: 4.78+/-4.64 vs. controls: 0.84+/-0.61, P=0.003) but not in mucus (SAR: 1.51+/-1.15 vs. controls: 1.35+/-1.02, P=0.78) and endothelial cells (SAR: 1.20+/-0.57 vs. controls: 1.73+/-1.30, P=0.5) was found to be significantly changed in the nasal mucosa in SAR. Using double immunohistochemistry the present study demonstrated that the total numbers of mast cells (P=0.0003) and eosinophils (P=0.03) and the numbers of eosinophils expressing PAR 2 (P=0.006) were significantly elevated in the nasal mucosa of SAR compared with the controls.

CONCLUSION

The abundant presence and distribution of gene and protein expression of PAR 2 in different cell types in the nasal mucosa under normal situation, the increased expression of PAR 2 in epithelial cells and the increased number of eosinophils with PAR 2 suggest that PAR 2 may contribute to the pathogenesis of allergic diseases such as SAR.

Shift work and pathological conditions

Shift work exerts major influences on the physiological functions of the human body. These are primarily mediated by the disruption of circadian rhythms since most body functions are circadian rhythmic. Next to the disturbances caused by changes in the circadian system, shift work has also been suggested to be related to a number of other health disorders. The present study summarizes recently published data on the potential relationship between disorders and shift working.

Tyrosine hydroxylase is expressed in a subpopulation of small dorsal root ganglion neurons in the adult mouse

The expression of tyrosine hydroxylase (TH) was studied in adult mouse dorsal root ganglia (DRGs) and spinal cord by means of immunohistochemistry and in situ hybridization. TH immunoreactivity and TH mRNA were present in 10-15% of lumbar DRG neurons, in most cases being small/medium-sized. Only very few of these neurons coexpressed calcitonin gene-related peptide (CGRP), and only around 6% bound isolectin B4 (IB4). Dopamine beta-hydroxylase-positive(+) or aromatic amino acid decarboxylase (AADC)+ DRG neurons were rare and did not colocalize TH. No evidence for dopamine transporter expression was obtained. Axotomy of the sciatic nerve only showed a tendency towards reduction in the number of TH+ neurons. In the dorsal horn of the spinal cord, moderately dense and widespread TH+ nerve terminals were observed, mainly in the gray matter and they did not show a typical primary afferent pattern. Also, dorsal rhizotomy or peripheral axotomy had no apparent effect on TH-LI in the dorsal horn. In the skin, along with an abundant TH+ innervation of blood vessels and sweat gland acini, a number of fibers was observed in close relation to the skin surface, some even penetrating into the epithelium. These results demonstrate presence, in normal adult mouse DRGs, of a subpopulation of TH+, essentially CGRP- and IB4-negative small/medium-sized neurons. No evidence for transport of TH into central afferents was obtained, but the enzyme may be present in some sensory fibers in the skin. The fact that neither AADC nor the dopamine transporter could be visualized suggests of non-dopaminergic transmitter phenotype, but the levels of these two dopaminergic markers may be too low to be detected with the present methodology. A further alternative is that L-DOPA after release is extracellularly converted to dopamine.