DOPAMINERGIC-NEURONS OF PERIVENTRICULAR AND ARCUATE NUCLEI OF PSEUDOPREGNANT RATS - SEMICIRCADIAN RHYTHM IN FOS-RELATED ANTIGENS IMMUNOREACTIVITIES AND IN DOPAMINE CONCENTRATION

The activity of the A(14) and A(12) hypothalamic dopaminergic (DAergic ) neurons were characterized throughout a day of pseudo-pregnancy to e stablish their relationship to the generation of PRL surges during tha t time. Double-label immunocytochemistry was performed using fos-relat ed antigens as markers of neuronal activity, and tyrosine hydroxylase antibody to identify DAergic neurons of the periventricular nucleus an d the arcuate nucleus (ARN). Dopamine concentrations were measured wit h HPLC with electrochemical detection from micropunched samples to app roximate synthetic activities of A(14) and A(12) neurons. Serum PRL le vels were determined by RIA. On the fifth and sixth day of pseudopregn ancy, five rats/time point were killed at 1100 h, 1300 h, 1500 h, 1800 h, 2100 h, 2400 h, 0300 h, and 0600 h. When the serum PRL was low, th e incidence of fos-related antigens/tyrosine hydroxylase double-labele d neurons was high, and it decreased twice a day by 1500 and 0300 h in the periventricular nucleus, rostral ARN, dorsomedial subpopulation o f the middle ARN, and in the caudalARN, corresponding to the initiatio n of PRL surges. Concentrations of DA were high in these areas, and de creased before PRL surges in agreement with the immunocytochemical dat a. These findings suggest a semicircadian rhythm in the activities of A(14) and A(12) neurons which, in concert with PRL releasing factors, contribute to the generation of PRL surges in pseudopregnant animals.