Brain Chemical Shows Way To New Drug Treatments

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NEW YORK (Reuters Health) - Alterations of a brain chemical called
``substance P'' promise a new approach for managing depression, anxiety and
stress, and possibly controlling opiate addiction, researchers report.

Substance P receptor is found not only in areas of the brain that are
associated with depression, anxiety and stress, but also those parts that
interfere with the effects of rewards such as food and drugs.

Stephen P. Hunt of University College, London, and colleagues examined the
effects of the substance P receptor gene in mice to determine its role in
morphine and cocaine addiction.

According to the report published in the May 11th issue of Nature, mice bred
to lack the receptor for substance P do not experience the pleasurable
experiences of morphine and therefore do not become addicted to the opiates.
The mice also were unable to detect withdrawal symptoms from the morphine.

However, the researchers found that mice without the substance P receptor
still experienced enjoyment from cocaine, which suggests that this drug may
function differently than opiates.

Drugs that block the substance P receptor not only have the potential to
treat drug addiction, but also to prevent relapses into drug abuse resulting
from stress. The investigators found that substance P receptor antagonists,
or the genetic disruption of the substance P receptor, can weaken the stress
response.

``Substance P antagonists may be useful in the prevention of relapse, which
is the most important aspect of addiction,'' Hunt noted.

The authors conclude that substance P has an important and specific role in
interfering with the motivational aspects of opiates and may present a new
pharmacological route for the control of drug abuse. Substance P antagonist
drugs are in the final phases of clinical trials for depression and anxiety,
and appear to be as effective as Prozac, Hunt added.