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  • Title: A neuroactive steroid, dehydroepiandrosterone sulfate, prevents the development of morphine dependence and tolerance via c-fos expression linked to the extracellular signal-regulated protein kinase.
    Author: Ren X, Noda Y, Mamiya T, Nagai T, Nabeshima T.
    Journal: Behav Brain Res; 2004 Jul 09; 152(2):243-50. PubMed ID: 15196791.
    Abstract:
    In the present study, we investigated how the neurosteroid, dehydroepiandrosterone sulfate (DHEAS) affects the development of morphine dependence and tolerance in mice. Mice administered morphine (10 mg/kg) twice a day for 5 days developed tolerance to the analgesic effect and dependence as shown by a severe withdrawal syndrome induced by naloxone. Co-administration of DHEAS (10 mg/kg) with morphine significantly inhibited the development, but not the expression, of tolerance to morphine-induced analgesia and the naloxone-precipitated withdrawal. The expression of c-fos mRNA was observed in the frontal cortex and thalamus of mice showing signs of naloxone-precipitated withdrawal, while the expression of c-fos mRNA was significantly diminished by co-administration of DHEAS with morphine. On the naloxone-precipitated withdrawal, mice showed a significant elevation of cyclic AMP (cAMP) levels in the thalamus, whereas chronic administration of DHEAS with morphine did not affect the increase in cAMP. Interestingly, repeated co-administration of DHEAS with morphine prevented the withdrawal-induced phosphorylation of extracellular signal-regulated protein kinase (ERK) 2 in the frontal cortex. These results showed that DHEAS prevented the development of morphine tolerance and dependence and suggested that the attenuating effects of DHEAS might result from the regulation of c-fos mRNA expression, which is possibly involved the signaling activation of ERK, but not of cAMP pathway.
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