Thyroid and Thyroxine Effects on Adrenoreceptors in Relation to Circadian Activity
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Pharmacology Biochemistry and Behavior
Original Item ID
Experiments were conducted to ascertain if changes in central adrenergic receptors could be associated with altered circadian activity patterns induced by thyroparathyroidecomy (TPX) and thyroxine. An initial experiment used TPX and sham-operated rats that had been exposed to dim red light for 7 months. The α and β receptor densities were compared in the suprachiasmatic nuclei (SCN), preoptic (PO), septum, and caudate-putamen. TPX animals showed significant reductions in β1 and β2 receptor densities in SCN and PO, and α1 densities in SCN, but no other changes A second experiment, lasting 4 months, examined the effects of thyroxine, which has been shown to reverse the period-shortening effects of TPX surgery. Thyroxine signicantly increased β1 receptors in both the SCN and ventromedial hypothalamus (VMH), the only regions that displayed significant reductions in TPXs during the second experiment. Increases of sevenfold and threefold were observed in the SCNs of TPXs and sham, respectively, but thyroxine's action in the VMH was limited to TPX animals, an affect that mimics thyroxine's antion on circadian activity rhythms.