Circadian variations of beta endorphin in specific areas of the rat brain

C. A. Walker, D. Mash

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A circadian rhythm for beta-endorphin content in several regions of the rat brain has been established. Male Sprague-Dawley rats were maintained for three weeks under controlled light (12L:12D) and temperature (23 ± 1 °C). The animals were sacrificed by microwave for 4.25 sec. at 4 hour intervals during the 24 hour period. Three brain regions, including the hypothalamus, thalamus, and periaqueductal gray-rostral pons, were dissected and extracted with 0.1n HCL. Beta endorphin content was measured by radioimmunoassay. This method employed addition of delayed tracer to improve sensitivity. Phase separation was accomplished by the addition of goat anti-rabbit serum in the presence of carrier rabbit serum which is titered to assure mid-zone precipitation. In the hypothalamus, beta-endorphin levels increased during the dark phase with a peak concentration occurring at 0400 hour. These data show significant circadian variations in beta-endorphin content in the hypothalamus. In the thalamus, there was no significant change in the levels of beta-endorphin. The level of beta-endorphin in the periaqueductal gray-rostral pons region significantly decreased during the light phase and increased during the dark phase. These results are in agreement with previous studies which have demonstrated diurnal changes in responsivity to painful stimuli and morphine induced analgesia. In another study, the relationship between the circadian rhythm of beta-endorphin and 5-HT was established. The data obtained correlated the diurnal variations in beta-endorphins, serotonin and pain response.

Original languageEnglish (US)
Pages (from-to)85-94
Number of pages10
JournalAdvances in the Biosciences
Issue numberC
StatePublished - Dec 1 1982


  • Beta-Endorphins
  • Brain Regions
  • Circadian Rhythms
  • Serotonin


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