hide
Free keywords:
-
Abstract:
Prolonged exposure to morphine down-regulates mu opioid receptors (MOR) on both undifferentiated and differentiated (retinoic acid or phorbol ester treated) SHSY-5Y cells. However, morphine pretreatment does not alter MOR receptor affinity for morphine. To investigate the molecular basis for morphine’s regulatory effects, we have developed a quantitative competitive reverse transcriptase-polymerase chain reaction (QC-RT-PCR) to quantify the amount of MOR present in SHSY-5Y cells. SHSY-5Y cells were differentiated and then incubated for 24 h with vehicle, morphine, naloxone, or both morphine and naloxone. Expression of MOR mRNA in undifferentiated SHSY-5Y cells was determined to be 369 fmol MOR mRNA/mg total RNA. Differentiation of SHSY-5Y cells with retinoic acid or phorbol ester up-regulated MOR mRNA expression by 40 \% and 78\%, respectively. A 24 hour treatment with morphine (10 mM) down-regulated MOR mRNA, an effect that was partially reversed by naloxone. Naloxone treatment alone upregulated MOR mRNA in undifferentiated, but not in RA-differentiated SHSY-5Y cells. Taken together, a significant component of SHSY-5Y cellular adaptation during chronic morphine treatment may occur at the mRNA level.
