From inhibition to excitation: functional effects of interaction between opioid receptors.
Opioids have excitatory effects in multiple regions of the nervous system. Excitation by opioids is generally attributed to inhibition of inhibitory pathways (disinhibition). However, recent studies indicate that opioids can directly excite individual cells. These effects may occur when opioid receptors interact with other G protein coupled receptors, when different subtypes of opioid receptors interact, or when opioids transactivate other receptors such as receptor tyrosine kinases. Changes in the relative level of expression of different receptors in an individual cell may therefore determine its functional response to a given ligand. This phenomenon could represent an adaptive mechanism involved in tolerance, dependence and subsequent withdrawal.
Charles
Andrew C
AC
Department of Neurology, David Geffen School of Medicine at UCLA, 710 Westwood Plaza, Los Angeles, CA 90095, USA. acharles@ucla.edu
Hales
Tim G
TG
D000818:Animals; D004361:Drug Tolerance / Q000502:physiology; D006801:Humans; D009292:Narcotic Antagonists; D009294:Narcotics / Q000494:pharmacology*; D009293:Opioid-Related Disorders / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D011957:Receptors, Opioid / Q000819:agonists / Q000502:physiology; D013375:Substance Withdrawal Syndrome / Q000378:metabolism
D009292:Narcotic Antagonists; D009294:Narcotics; D043562:Receptors, G-Protein-Coupled; D011957:Receptors, Opioid