Semicircadian Rhythm of Tuberoinfundibular Dopamine Neuronal Activity during Early Pregnancy and Pseudopregnancy in the Rat

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Abstract
Changes in serum prolactin and luteinizing hormone concentrations and dopamine (DA) neuronal activity in selected brain regions were determined over a 24-hour period in pregnant, pseudopregnant, and diestrus rats. On day 6 of pregnancy or pseudopregnancy, blood samples were collected for analysis of prolactin and luteinizing hormone. On day 7 the DA neuronal activity was estimated by measuring the rate of accumulation of dihydroxyphenylalanine (DOPA) in median eminence, corpus striatum, nucleus accumbens, olfactory tubercle, and posterior pituitary after the administration of a decarboxylase inhibitor. For animals in diestrus, DOPA accumulation was determined on the corresponding day of the cycle which followed the collection of blood samples. Two daily surges of prolactin were observed in pregnant and pseudopregnant but not in diestrus rats. Similarly, biphasic changes in the rate of DOPA accumulation were observed in the median eminence, but not in other brain regions, of pregnant and pseudopregnant rats, while there were no changes in diestrus rats.