Chronic lithium administration significantly changes characteristics of the circadian rhythms in rat brain alpha- and beta-adrenergic, muscarinic acetylcholine, dopamine, opiate, and benzodiazepine receptors. There are changes in the timing of the peak number of receptors (phase-position), in the amplitude of the rhythms, and in the 24-hour mean number of receptors. The circadian rhythm in the number of forebrain alpha- and beta-adrenergic and benzodiazepine receptors is abolished. The phase-position of forebrain acetylcholine and opiate receptors and striatal benzodiazepine receptors is delayed. As the rhythms of the dopamine receptor number and alpha-melanocyte-stimulating hormone secretion become bimodal, their phase positions are difficult to evaluate. The mean number of forebrain alpha- and beta-adrenergic, acetylcholine, opiate, and striatal benzodiazepine receptors increases. The mean number of forebrain benzodiazepine and striatal dopamine receptors and the mean concentration of alpha-melanocyte-stimulating hormone decreases. Lithium has profound effects on each of the receptor rhythms measured. Slowing and altering circadian rhythms may contribute to the therapeutic effects of chronic lithium treatment in affective disorders.
