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KMID : 0360419840200020023
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Korean Journal of Pharmacology
1984 Volume.20 No. 2 p.23 ~ p.34
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A Study on the Circadian Rhythm of Opiate Receptor in Rat Brain
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Abstract
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To investigate diurnal variations of opiate receptor binding and its modification by experimental condition or treatment of various centrally-acting drugs, the amount of maximum 3H-morphine binding in rat midbrain homogenates was measured at 4 hour intervals for 24 hours. Animals were conditioned under the controlled L: D, 12: 12 cycle or D: D, 12: 12 cycle for 3 weeks and treated with 0.5 ml of physiological saline or drugs for 2 weeks.
A highly significant diurnal rhythm with peak at 22 hour of early dark phase with an amplitude (0. 680.06 pmole/mg protein) of +51.1% and nadir(0.330.03 mole/mg prtein) at 18 hour of late light phase with an amplitude of -26.6% was found in control group. 24 hour mean of ´H-morphine binding was 0.450.0 3 pmole/mg protein respectively. Constant dark adaptation or treatment of reserpine, pargyline, imipramine, amphetamine and chlorpromazine modified the diurnal rhythm in the time of peak and nadir binding shape, phase, amplitude of the diurnal curve and 24 hour mean of 3H-morphine binding. However, Kd values were not changed in all experimental groups; Statistical analysis at times of least and great binding indicates that the differences in ´H-morphine binding were due to changes not in the affinity, but in the number of binding sites.
The results are interpreted with regard to the diurnal rhythm of opiate receptor binding. The modes of action of psychoactive drugs are closely related to postulated changes of receptor sensitivity in neuropharmacological aspects.
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