Role of the 5-HT receptor in neurogenic inflammation in Fisher 344 rat airways

Extending the understanding of sensory neuropeptides

The tachykinins substance P and neurokinin A are present in human airways, in sensory nerves and immune cells. Tachykinins can be recovered from the airways after inhalation of ozone, cigarette smoke or allergen. They interact in the airways with tachykinin NK1, NK2 and NK3 receptors to cause bronchoconstriction, plasma protein extravasation, and mucus secretion and to attract and activate immune cells. In preclinical studies they have been implicated in the pathophysiology of asthma and chronic obstructive pulmonary disease, including allergen- and cigarette smoke induced airway inflammation and bronchial hyperresponsiveness and mucus secretion. Dual NK1/NK2 or triple NK1/NK2/NK3 tachykinin receptor antagonists offer therapeutic potential in airway diseases such as asthma and chronic obstructive pulmonary disease.

Sensory nerves, neurogenic inflammation and pain: missing components of alternative irritation strategies? A review and a potential strategy

The eyes and skin are highly innervated by sensory nerves; stimulation of these nerves by irritants may give rise to neurogenic inflammation, leading to sensory irritation and pain. Few in vitro models of neurogenic inflammation have been described in conjunction with alternative skin and eye irritation methods, despite the fact that the sensory innervation of these organs is well-documented. To date, alternative approaches to the Draize skin and eye irritation tests have proved largely successful at classifying severe irritants, but are generally poor at discriminating between agents with mild to moderate irritant potential. We propose that the development of in vitro models for the prediction of sensory stimulation will assist in the re-classification of the irritant potential of agents that are under-predicted by current in vitro strategies. This review describes the range of xenobiotics known to cause inflammation and pain through the stimulation of sensory nerves, as well as the endogenous mediators and receptor types that are involved. In particular, it focuses on the vanilloid receptor, its activators and its regulation, as these receptors function as integrators of responses to numerous noxious stimuli. Cell culture models and ex vivo preparations that have the potential to serve as predictors of sensory irritation are also described. In addition, as readily available sensory neuron cell line models are few in number, stem cell lines (with the capacity to differentiate into sensory neurons) are explored. Finally, a preliminary strategy to enable assessment of whether incorporation of a sensory component will enhance the predictive power of current in vitro eye and skin testing strategies is proposed.

The role of neural inflammation in asthma and chronic obstructive pulmonary disease

The tachykinins substance P and neurokinin A are found within airway nerves and immune cells. They have various effects on the airways that can contribute to the changes observed in asthma and chronic obstructive pulmonary disease. Both tachykinin NK(1) and NK(2) receptors have been involved in the bronchoconstriction and the proinflammatory changes induced by substance P and neurokinin A. Tachykinin NK(1) and NK(2) receptor antagonists have activity in various animal models of allergic asthma and chronic bronchitis. It is suggested that dual NK(1)/NK(2) and triple NK(1)/NK(2)/NK(3) tachykinin receptor antagonists have potential in the treatment of obstructive airway diseases.

The 5-HT3 subtype of serotonin receptor contributes to nociceptive processing via a novel subset of myelinated and unmyelinated nociceptors

Serotonin is a major component of the inflammatory chemical milieu and contributes to the pain of tissue injury via an action on multiple receptor subtypes. Here we studied mice after genetic or pharmacological disruption of the 5-HT(3) receptor, an excitatory serotonin-gated ion channel. We demonstrate that tissue injury-induced persistent, but not acute, nociception is significantly reduced after functional elimination of this receptor subtype. Specifically, in the setting of tissue injury, the 5-HT(3) receptor mediates activation of nociceptors but does not contribute to injury-associated edema. This result is explained by the localization of 5-HT(3) receptor transcripts to a previously uncharacterized subset of myelinated and unmyelinated afferents, few of which express the proinflammatory neuropeptide substance P. Finally, we provide evidence that central serotonergic circuits modulate nociceptive transmission via a facilitatory action at spinal 5-HT(3) receptors. We conclude that activation of both peripheral and central 5-HT(3) receptors is pronociceptive and that the contribution of peripheral 5-HT(3) receptors involves a novel complement of primary afferent nociceptors.

Airway inflammation and tachykinins: prospects for the development of tachykinin receptor antagonists

The tachykinins substance P and neurokinin A are contained within sensory airway nerves. Immune cells form an additional source of tachykinins in inflamed airways. Elevated levels of tachykinins have been recovered from the airways of patients with asthma and chronic obstructive pulmonary disease. Airway inflammation leads to an upregulation of tachykinin NK(1) and NK(2) receptors. Preclinical studies have indicated a role for the tachykinin NK(1), NK(2) and NK(3) receptors in bronchoconstriction, airway hyperresponsiveness and airway inflammation caused by allergic and nonallergic stimuli. Compounds that are able to block two or three tachykinin receptors hold promise for the treatment of airways diseases such as asthma and/or chronic obstructive pulmonary disease.

Airway vasculature after mycoplasma infection: chronic leakiness and selective hypersensitivity to substance P

Angiogenesis and microvascular remodeling are features of chronic airway inflammation caused by Mycoplasma pulmonis infection in rats. As airway blood vessels undergo remodeling, they become unusually sensitive to substance P-induced plasma leakage. Here we determined whether the remodeled vessels are leaky under baseline conditions, whether their heightened sensitivity is specific to substance P, and whether the leakage is reversible. Four weeks after infection, the amount of baseline leakage of Evans blue in the tracheal mucosa was two to five times the normal level. Gaps < 1 microm in diameter were located between endothelial cells in some remodeled vessels. Substance P, but not platelet-activating factor or 5-hydroxytryptamine, produced an exaggerated leakage response. Inhalation of the beta2-adrenergic receptor agonist salmeterol reduced the leakage by <60%. We conclude that the blood vessel remodeling after M. pulmonis infection is associated with microvascular leakiness due, in part, to the formation of endothelial gaps. This leakage is accompanied by an abnormal sensitivity to substance P but not to platelet-activating factor or 5-hydroxytryptamine and can be reduced by beta2-agonists.