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.

Area Postrema

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.


A major adipokine, molecular weight 28,000 Da (monomeric form), that is secreted only from adipocytes.

It exists at high levels in the plasma and has a number of functions, including an important role in insulin sensitivity, inflammation (anti-anti-inflammatory action) and atherogenesis.

Unlike most adipokines, the plasma levels fall in obesity.


Activins are growth and differentiation factors belonging to the transforming growth factor-β superfamily. They are dimeric proteins, consisting of two inhibin-β subunits.

The structure of activins is highly conserved during vertebrate evolution. Activins signal through type I and type II receptor serine/threonine receptor kinases. Subsequently downstream signals such as Smad proteins are phosphorylated.

Activins are present in many tissues of the mammalian organism, where they function as autocrine and/or paracrine regulators of various physiological processes, including reproduction.

In the hypothalamus, activins are thought to stimulate the release of gonadotropin-releasing hormone.

In the pituitary, activins increase folliclestimulating hormone secretion and up-regulate gonadotropin- releasing hormon receptor expression. In the ovaries, activins regulate processes such as folliculogenesis, steroid hormone production and oocyte maturation.

During pregnancy, activin-A is also involved in the regulation of placental functions.