Abstract
We have previously reported that the administration of cyclo(Leu-Gly) to mice prior to morphinization blocked the development of tolerance to the analgesic effects of morphine as well as the development of some signs of physical dependence. In the present series of experiments, the effect of the same peptide treatment on changes in dopamine receptor sensitivity induced by chronic morphine treatment were determined. Changes in dopamine receptor sensitivity were determined by measuring (i) the effect of the dopamine agonist apomorphine on locomotor activity and (ii) the hypothermic response to another dopamine agonist, piribedil. Mice that had received the chronic morphine treatment were found to require significantly less apomorphine to produce an increase in locomotor activity, and they exhibited a significantly greater hypothermic response to piribedil than did morphine-naive mice. The injection of 0.2 mumol of cyclo(Leu-Gly) per mouse 2 hr prio to morphine treatment prevented this increased response to both dopamine agonists. Administration of the peptide after the tolerance and dependence had developed did not alter morphine tolerant and dependent states states or the enhanced response to apomorphine or piribedil. It is concluded that dopamine receptor supersensitivity may be involved in the development of narcotic tolerance and physical dependence.
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Selected References
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- Ary M., Cox B., Lomax P. Dopaminergic mechanisms in precipitated withdrawal in morphine-dependent rats. J Pharmacol Exp Ther. 1977 Feb;200(2):271–276. [PubMed] [Google Scholar]
- Bhargava H. N. The effects of naltrexone on the development of physical dependence on morphine. Eur J Pharmacol. 1978 Aug 1;50(3):193–202. doi: 10.1016/0014-2999(78)90351-5. [DOI] [PubMed] [Google Scholar]
- Cox B., Ary M., Lomax P. Dopaminergic mechanisms in withdrawal hypothermia in morphine dependent rats. Life Sci. 1975 Jul 1;17(1):41–42. doi: 10.1016/0024-3205(75)90231-3. [DOI] [PubMed] [Google Scholar]
- Hoffman P. L., Walter R., Bulat M. An enzymatically stable peptide with activity in the central nervous system: its penetration through the blood-CSF barrier. Brain Res. 1977 Feb 11;122(1):87–94. doi: 10.1016/0006-8993(77)90664-3. [DOI] [PubMed] [Google Scholar]
- Walter R., Ritzmann R. F., Bhargava H. N., Flexner L. B. Prolyl-leucyl-glycinamide, cyclo(leucylglycine), and derivatives block development of physical dependence on morphine in mice. Proc Natl Acad Sci U S A. 1979 Jan;76(1):518–520. doi: 10.1073/pnas.76.1.518. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Walter R., Ritzmann R. F., Bhargava H. N., Rainbow T. C., Flexner L. B., Krivoy W. A. Inhibition by Z-Pro-D-Leu of development of tolerance to and physical dependence on morphine in mice. Proc Natl Acad Sci U S A. 1978 Sep;75(9):4573–4576. doi: 10.1073/pnas.75.9.4573. [DOI] [PMC free article] [PubMed] [Google Scholar]