Prolactin regulation of dopaminergic neurons in the infundibulum pituitary stalk of bull calves |
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Authors: | S A Zinn K J Lookingland L T Chapin K E Moore H A Tucker |
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Institution: | Department of Animal Science, Michigan State University, East Lansing 48824. |
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Abstract: | The effects of elevated circulating concentrations of prolactin were examined on neurochemical estimates of activity of dopaminergic neurons in the infundibulum/pituitary stalk of Holstein bull calves (8-10 weeks of age). Activity of these neurons was estimated by measuring the accumulation of dihydroxyphenylalanine, the immediate precursor of dopamine, 15 min after an intravenous injection of the aromatic L-amino acid decarboxylase inhibitor, 3-hydroxybenzylhydrazine. Subcutaneous injections of the dopamine antagonist haloperidol every 6 hr for 1 day increased serum concentrations of prolactin and accumulation of dihydroxyphenylalanine in the infundibulum/stalk. Intravenous infusions of prolactin for 1 or 9 days increased accumulation of dihydroxyphenylalanine in the infundibulum/stalk, indicating that these neurons remain responsive to elevated prolactin for at least 9 days. It is concluded that elevated concentrations of prolactin in blood stimulate dopaminergic neurons in the infundibulum/pituitary stalk of bull calves. We speculate that these neurons may be analogous to the tuberoinfundibular dopaminergic neurons that regulate prolactin in rats. |
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