The June 23 issue of the Proceedings of the National Academy of Sciences (PNAS) carries the paradoxical findings of a report on the effects of certain general anesthesia drugs, including how they decrease feelings of pain during surgery but cause pain afterward. A research team from Georgetown University Medical Center conducted the study, funded by the National Multiple Sclerosis Society and the National Institutes of Health.

According to the researchers, led by Gerard Ahern, PhD, assistant professor at Georgetown’s Department of Pharmacology, it’s the noxious type of anesthesia that causes inflammation and discomfort during the post-surgical recovery period. This type of drug, which includes most general anesthetics, acts on the peripheral nervous system whereas others act on the central nervous system (the brain and spinal cord) instead.

The research team focused on two receptors specific to nerve cells in the peripheral nervous system – TRPV1 and TRPA1. These two receptors are frequently triggered in tandem and can be stimulated by eating foods such as garlic, wasabi, and mustard. In fact, the TRPA1 is sometimes called the mustard-oil receptor and the inflammation-causing reaction to ingesting these foods is thought to be a part of the plant’s natural defense mechanism evolved to deter animals from eating them. Most forms of general anesthetic drugs activate this mustard-oil receptor.

Laboratory mice bred to have no TRPA1 genes experience no pain or inflammation when under the influence of these drugs, leading the research team to suggest direct involvement between general anesthetic drugs and TRPA1. Inflammation in the nerves was found to be greater when the general anesthetic used is a pungent chemical irritant instead of a non-pungent inhaled drug.

Ahern describes a release of many chemicals throughout the body when these drugs are administered, a process that is said to recruit immune cells to the affected tissue, which, in turn, generates inflammation and pain even after a patient wakes from surgery. He suggests the findings of this study will become valuable in the clinical setting and feels that the findings of this study identify room for improvement when administering general anesthetic drugs. Not all such drugs activate TRPA1 but those that don’t may prove to be less effective.

Source: Georgetown University Medical Center