SCIENTISTS SEPARATE PAIN, PLEASURE EFFECTS OF OPIATES

LONDON - Drugs that block the effects of a gene could
prevent opiates from becoming addictive while still retaining their
painkilling properties, British and Spanish scientists said Wednesday.

They discovered that the gene essential for the euphoria that keeps
addicts hooked on heroin or morphine can be shut off in mice without
changing the drug's analgesic effects -- possibly opening a new avenue
for treating addiction.

``Opiates are both the best analgesics we have, as well as drugs
producing euphoria leading to addiction,'' Stephen Hunt, of University
College in London, told Reuters.

``What we've shown is that you can knock out one particular gene, the
substance P receptor gene, and you can disassociate these effects. So
analgesia is retained intact whereas the pleasurable effects of
opiates are apparently abolished.''

The research, published in the science journal Nature, could have
important implications in understanding drug addiction and provide a
new tool for researchers.

``This could give us a way of blocking the addictive effects of
opiates while leaving the pain-controlling aspects intact,'' Hunt said
in a telephone interview.

``It gives us, for the first time, a really good opportunity -- a
signpost -- to the molecular events underlying opiate
addiction.''

But he added that the findings do not apply to cocaine, suggesting
that opiates act on the brain to produce an addictive effect in a
different way.

Drug Target For New Antidepressants

Scientists are already using substance P as a target for new compounds
to treat depression which could challenge the dominance of Prozac.

Hunt and researchers at the Miguel Hernandez University in Alicante,
who contributed to the research, believe the findings could lead to
the development of novel drugs that antagonize the actions of
substance P. That could potentially reduce the severity of drug
withdrawal and prevent relapse.

``It is the first novel target for addiction, for anxiety and
depression, that has been around for many years. I think that is what
makes it very exciting,'' Hunt said.

``It could lead to reorientation and to some unexpected findings in
how we deal with things like addiction.''

The researchers used transgenic mice in which the gene for substance P
was knocked out, or silenced. They measured the pleasurable impact on
the mice by giving them a choice between boxes containing morphine or
cocaine.

The so-called knockout mice invariably preferred the cocaine box and
showed no interest in the morphine.