Multiple chemical sensitivity: towards the end of controversy

Townsend Letter for Doctors and Patients, August-Sept, 2005 by Martin L. Pall

(a) The NMDA receptors are receptors for glutamate found primarily in the central and peripheral nervous system. They are called NMDA receptors because they are specifically stimulated by the compound N-methyl-D-aspartate whereas other glutamate receptors are not. While the NMDA receptors appear to have the most important role of the glutamate receptors in these illnesses, in some cases other glutamate receptors may also have a role.

(b) Nitric oxide is a compound found in the body that has important functions, particularly in controlling the circulatory system (it dilates the blood vessels), in the brain and in the immune system. However when its levels are too high, it can produce substantial pathophysiological effects, impacting the body in many negative ways. These elevated levels are proposed to be important in these illnesses and also occur in a wide variety of chronic inflammatory diseases and in acute inflammatory responses such as sepsis. Much of the damage produced by excessive nitric oxide is actually a consequence of its oxidant product, peroxynitrite.

** Peroxynitrite is a potent oxidant formed by the reaction of nitric oxide with another compound superoxide. It is a potent oxidant that is thought to break down to produce a number of reactive free radicals and cause various types of oxidative damage.

#& The vanilloid receptor is the receptor for the "hot" compound in hot peppers, known as capsaicin. We have argued in reference 7 that this receptor has a complex role in MCS and specifically that it is the likely target for volatile organic solvents that produce sensitive responses in that illness. It also is reported to have a role in fibromyalgia and in irritable bowel syndrome but has not been studied in these other illnesses.

%% A retrograde messenger is a compound which does just this--it diffuses from the post-synaptic neuron to the presynaptic neuron, causing the latter to release more neurotransmitter. In this way it can increase the activity of a synapse, thus producing LTP. Nitric oxide is not the only known retrograde messenger but it may be the most important one.

%$# Neurogenic inflammation has been reported by Meggs and coworkers in peripheral sensitivity regions involved in MCS. It is an overt inflammatory response at the nerve endings involving several inflammatory messengers. It should be noted that the peripheral sensitivity responses seen in MCS are overt inflammatory responses.