Morphine and endorphins modulate dopamine turnover in rat median eminence

S. N. Deyo, R. M. Swift, R. J. Miller

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157 Scopus citations


There is evidence that some of the actions of both endogenous and exogenous opioids (e.g., stimulation of prolactin release) are mediated by interaction with catecholaminergic systems. Morphine (1.67, 5, and 15 mg/kg of body weight, intraperitoneally) altered dopamine turnover as measured by the α-methyl-p-tyrosine method in the median eminence, neostriatum, and frontal cortex of male Sprague-Dawley rats. The turnover rate of dopamine was reduced in the median eminence and frontal cortex but accelerated in the neostriatum. In the frontal cortex all doses were effective in decreasing dopamine turnover; however, in the median eminence the lowest dose of morphine did not significantly alter dopamine turnover. All three doses accelerated dopamine turnover in the neostriatum. Naloxone effectively reversed the effect of morphine at all doses in all brain areas, whereas it had no effect on turnover when given alone. In the median eminence, neostriatum, and and frontal cortex, intraventricular injection of [D-Ala2,D-Leu5]-enkephalin (25 μg) or β-endorphin (15 μg) produced the same effects on dopamine turnover as morphine. The actions of these peptides were blocked by naloxone. It is hypothesized that opiates and opioid peptides increase prolactin release by reducing the activity of the tuberoinfundibular dopaminergic system.

Original languageEnglish (US)
Pages (from-to)3006-3009
Number of pages4
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number6
StatePublished - 1979

ASJC Scopus subject areas

  • General


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