Maintenance of rats on a lithium-containing diet for 3-21 days resulted in a suppression of prolactin (PRL) secretion in vivo and in vitro. Lithium treatment also resulted in an increase in the activity of tuberoinfundibular dopaminergic neurons, as evidenced by an increased accumulation of dihydroxyphenylalanine (DOPA) in the median eminence after inhibition of DOPA decarboxylase and an increased concentration of dopamine in the anterior pituitary gland. The accumulation of DOPA in the neurointer-mediate lobe of the pituitary gland, the prefrontal cortex, the striatum and the nucleus accumbens was also enhanced by lithium treatment. It is concluded that lithium treatment enhances the synthesis of dopamine in many brain regions and that an increased activity of tuberoinfundibular dopaminergic neurons results in an enhanced inhibitory control of PRL secretion.
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