SUMMARYTo determine whether opioid receptors in sensory neurons are regulated by chronic exposure to opioids, we assessed the binding of various opioid ligands to membranes derived from isolated rat dorsal root ganglia neurons grown in culture. ]diprenorphine binding sites, respectively. Preexposure of neurons to 10 M naloxone for 48 hr up-regulated the receptors by 40%, whereas incubation with 100 nM to 10 M DAMGO for 48 hr resulted in a significant decrease in the B max value of opioid receptors, with a maximum reduction of 70%. The identification of a high level of opioid receptors expressed in isolated sensory neurons and their modulation by opioids demonstrates that cultured sensory neurons are an excellent model with which to study opioid receptor regulation.

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