Dopamine inhibition of histamine-mediated cutaneous responses

How "Neuronal" Are Human Skin Mast Cells?

Mast cells are evolutionarily old cells and the principal effectors in allergic responses and inflammation. They are seeded from the yolk sac during embryogenesis or are derived from hematopoietic progenitors and are therefore related to other leukocyte subsets, even though they form a separate clade in the hematopoietic system. Herein, we systematically bundle information from several recent high-throughput endeavors, especially those comparing MCs with other cell types, and combine such information with knowledge on the genes’ functions to reveal groups of neuronal markers specifically expressed by MCs. We focus on recent advances made regarding human tissue MCs, but also refer to studies in mice. In broad terms, genes hyper-expressed in MCs, but largely inactive in other myelocytes, can be classified into subcategories such as traffic/lysosomes (MLPH and RAB27B), the dopamine system (MAOB, DRD2, SLC6A3, and SLC18A2), Ca²⁺-related entities (CALB2), adhesion molecules (L1CAM and NTM) and, as an overall principle, the transcription factors and modulators of transcriptional activity (LMO4, PBX1, MEIS2, and EHMT2). Their function in MCs is generally unknown but may tentatively be deduced by comparison with other systems. MCs share functions with the nervous system, as they express typical neurotransmitters (histamine and serotonin) and a degranulation machinery that shares features with the neuronal apparatus at the synapse. Therefore, selective overlaps are plausible, and they further highlight the uniqueness of MCs within the myeloid system, as well as when compared with basophils. Apart from investigating their functional implications in MCs, a key question is whether their expression in the lineage is due to the specific reactivation of genes normally silenced in leukocytes or whether the genes are not switched off during mastocytic development from early progenitors.

Neurotransmitter and neuropeptide regulation of mast cell function: a systematic review

The existence of the neural control of mast cell functions has long been proposed. Mast cells (MCs) are localized in association with the peripheral nervous system (PNS) and the brain, where they are closely aligned, anatomically and functionally, with neurons and neuronal processes throughout the body. They express receptors for and are regulated by various neurotransmitters, neuropeptides, and other neuromodulators. Consequently, modulation provided by these neurotransmitters and neuromodulators allows neural control of MC functions and involvement in the pathogenesis of mast cell–related disease states. Recently, the roles of individual neurotransmitters and neuropeptides in regulating mast cell actions have been investigated extensively. This review offers a systematic review of recent advances in our understanding of the contributions of neurotransmitters and neuropeptides to mast cell activation and the pathological implications of this regulation on mast cell–related disease states, though the full extent to which such control influences health and disease is still unclear, and a complete understanding of the mechanisms underlying the control is lacking. Future validation of animal and in vitro models also is needed, which incorporates the integration of microenvironment-specific influences and the complex, multifaceted cross-talk between mast cells and various neural signals. Moreover, new biological agents directed against neurotransmitter receptors on mast cells that can be used for therapeutic intervention need to be more specific, which will reduce their ability to support inflammatory responses and enhance their potential roles in protecting against mast cell–related pathogenesis.

Cutaneous responses to anticholinergics: evidence for muscarinic receptor subtype participation

We conducted a series of experiments to determine if anticholinergics induce immediate cutaneous wheal-and-flare responses in normal volunteers. We performed intradermal skin testing in seven healthy volunteers (three atopic and four nonatopic) with 20 nmol of atropine. All subjects had an immediate wheal-and-flare response to atropine. To determine if this cutaneous response was due to anticholinergics in general, skin testing was also performed to scopolamine and ipratropium. These agents also produced immediate wheal-and-flare responses in all subjects, but they less potent than atropine. Pretreatment with antihistamines equivalently inhibited wheal-and-flare responses to both histamine and atropine, indicating a possible mast cell role. The potential role of M1, M2, and M3 muscarinic receptor subtypes was evaluated by use of the selective antagonists, pirenzepine (M1), 11[[2-1[(diethylamino)methyl]-1-piperidinyl]-acetyl]-5, 11-dihydro-6H-pyrido[2,3-b][1,4]benzodiazepine-6-one (AFDX-116) (M2), and 4-diphenylacetoxy-N-methylpiperidine (4-DAMP) (M3). Cutaneous wheal responses induced by pirenzepine and 4-DAMP were relatively equivalent and larger than responses induced by AFDX-116 at doses less than 200 nmol. At 200 nmol, all three muscarinic receptor subtype antagonists induced equivalent wheal formation. We then compared the cutaneous wheal responses to these specific muscarinic receptor antagonists based on their relative affinity for their respective muscarinic receptor subtype. This comparison suggested that M1 or M2, but not M3, muscarinic receptor subtypes may be important in anticholinergic-induced cutaneous wheal-and-flare responses. We propose that there may be an M1 or M2 muscarinic autoreceptor that inhibits the release of acetylcholine and other neurotransmitters.(ABSTRACT TRUNCATED AT 250 WORDS)