Autacoids are literally ‘self-medicating agents’ that are liberated from or produced by cells in response to a stimulus. They differ from hormones in that they usually act locally after release, rather than reaching their target organ via the bloodstream.

Arrestins act as adaptor proteins that bind to phosphorylated G protein-coupled receptors (GPCR) and link the receptors to clathrin-coated pits. β-Arrestins are essential in the internalization of many GPCRs.

alpha-2  antiplasmin, a naturally occurring inhibitor of fibrinolysis, is a single chain glycoprotein that forms a stable, inactive complex within plasmin and thereby prevents plasmin’s activity.

Annexins form an evolutionary conserved family of Ca2+ and phospholipid binding proteins implicated in membrane trafficking and the regulation of Ca2+ currents across membranes.

An allergen is usually an inert substance (e.g. pollen, house dust mite faeces) that in some individuals can trigger the generation of an (inappropriate) antigenic response. Mediated by TH2 lymphocytes, it causes B-Lymphocytes to produce lgE.

Subsequent exposure of a sensitized individual to the allergen is therefore able to cross-link IgE antibodies on the surface of mast cells and trigger an immune response and histamine release.

The sensation of pain, following injury or disease, in response to a previously non-noxious stimulus is termed ‘allodynia’.

Tactile allodynia is caused by recruitment of low-threshold (non-nociceptive) sensory fibres (Aβ) in nociceptive pathways.

Arousal is a state of vigilance regulated by subcortical parts of the nervous system, especially connections between the nuclei of the amygdala, the hypothalamus and the brain stem.

These unconscious responses prepare the body for action. In terms of sleep/wake regulation, the arousal systems are those that have highest activity during wake, for example the aminergic (noradrenaline, 5-HT, histamine) systems.

The arousal systems inhibit, and are themselves inhibited by the GABAergic system emanating from the ventrolateral preoptic nucleus (VLPO), in a so-called “flip flop” arrangement that is stabilised via orexinergic activity.

The area postrema is a circumventricular brain region positioned on the dorsal surface of the medulla on the floor of the fourth ventricle.

The  blood–brain barrier and the cerebrospinal fluid–brain barrier are absent in this region and consequently many substances that do not pass across capillaries in other regions of the brain can do so in the area postrema.

The chemoreceptor trigger zone (CTZ), located in the lateral area postrema is sensitive to blood-borne emetogens. Nerves from the CTZ connect with the vomiting centre.