Brain chemical with key role in substance abuse identified
NIH release
August 26, 2005
New research performed in rats suggests that orexin, a brain chemical
involved in feeding behavior, arousal, and sleep, also plays a
role in reward function and drug-seeking behavior.
Dr. Glenda Harris and her colleagues at the University of Pennsylvania
showed that the activation of orexin-secreting brain cells in the
hypothalamus, a brain region that controls many vital functions
such as eating, body temperature, fat metabolism, etc. is strongly
correlated with food- and drug-seeking behaviors. Past anatomical
studies have shown that these cells in the lateral hypothalamus
also project to adjacent reward-associated areas of the brain.
This study suggests that orexin may be a factor in modulating
reward-seeking characteristic of substance abuse. The findings
help to better identify neural pathways involved in drug abuse,
craving and relapse, which may ultimately help scientists find
more effective therapies.
This study is published online August 14, 2005 in the journal
Nature.
The brain cells that secrete this substance, orexin, are in an
area of the brain called the lateral hypothalamus, says Dr. Nora
D. Volkow, director of the National Institute on Drug Abuse (NIDA),
National Institutes of Health, which supported the study. This
brain region has been implicated in reward function for many years,
but no one was sure which brain chemicals, or neurotransmitters,
were involved. For the first time, we now know exactly which substances
are involved, which is a significant step forward in developing
treatments.
The hypothalamus is a small area of the brain above and behind
the roof of the mouth. It is involved with the involuntary nervous
system and control of processes such as fluid maintenance, sugar
balance, fat metabolism, regulation of body temperature, and control
of hormonal secretion. The lateral hypothalamus is referred to
as the brains hunger center.
We found that the more animals seek out cues associated with
food or drug reward, the more activated these neurons become, says
Dr. Harris. In rats that had their drug-seeking behavior extinguished,
the preference for drug-associated cues was reinstated by chemically
activating these cells and orexin production. These data suggest
that this brain system may be involved in the development of drug
craving that can perpetuate both addiction and relapse.
This neural system may be activated by environmental cues that
cause addicts to relapse back to drug-taking behavior even after
successfully going through rehabilitation and achieving abstinence, says
Dr. Volkow.
The National Institute on Drug Abuse is a component of the National
Institutes of Health, U.S. Department of Health and Human Services.
NIDA supports most of the worlds research on the health aspects
of drug abuse and addiction. The Institute carries out a large
variety of programs to ensure the rapid dissemination of research
information and its implementation in policy and practice. Fact
sheets on the health effects of drugs of abuse and information
on NIDA research and other activities can be found on the NIDA
home page at http://www.drugabuse.gov/.
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This is a NIH news release. The original version appears here