Abstract
Abstract
The effects of ambient temperature on serum concentrations of prolactin and neurochemical estimates of activity of dopaminergic neurons projecting to the infundib-ulum/pituitary stalk were investigated in Holstein bull calves. Accumulation of 3,4-dihydroxyphenylalanine (DOPA) in the infundibulum/pituitary stalk after intravenous injection of a decarboxylase inhibitor was used to estimate activity of these dopaminergic neurons. Increasing ambient temperature from 21 to 33°C for 22 hr increased serum concentrations of prolactin and decreased activity of the dopaminergic neurons. Conversely, reducing ambient temperature from 22°C to 11°C decreased serum concentrations of prolactin and increased activity of these dopaminergic neruons. It is suggested that alterations in activity of dopaminergic neurons terminating in the infundibulum/pituitary stalk of bull calves may mediate acute temperature-induced changes in secretion of prolactin.
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