title: Involvement of dopamine D2 receptor in the diurnal changes of tuberoinfundibular dopaminergic neuron activity and prolactin secretion in female rats.
abstract: BACKGROUND
  An endogenous dopaminergic (DA) tone acting on D3 receptors has been shown to inhibit tuberoinfundibular (TI) DA neuron activity and stimulate prolactin (PRL) surge in the afternoon of estrogen-primed ovariectomized (OVX+E2) rats. Whether D2 receptor (D2R) is also involved in the regulation of TIDA and PRL rhythms was determined in this study.
  
  
  RESULTS
  Intracerebroventricular (icv) injection of PHNO, a D2R agonist, in the morning inhibited TIDA and midbrain DA neurons' activities, and stimulated PRL secretion. The effects of PHNO were significantly reversed by co-administration of raclopride, a D2R antagonist. A single injection of raclopride at 1200 h significantly reversed the lowered TIDA neuron activity and the increased serum PRL level at 1500 h. Dopamine D2R mRNA expression in medial basal hypothalamus (MBH) exhibited a diurnal rhythm, i.e., low in the morning and high in the afternoon, which was opposite to that of TIDA neuron activity. The D2R rhythm was abolished in OVX+E2 rats kept under constant lighting but not in OVX rats with regular lighting exposures. Pretreatment with an antisense oligodeoxynucleotides (AODN, 10 μg/3 μl/day, icv) against D2R mRNA for 2 days significantly reduced D2R mRNAs in central DA neurons, and reversed both lowered TIDA neuron activity and increased serum PRL level in the afternoon on day 3. A diurnal rhythm of D2R mRNA expression was also observed in midbrain DA neurons and the rhythm was significantly knocked down by the AODN pretreatment.
  
  
  CONCLUSIONS
  We conclude that a diurnal change of D2R mRNA expression in MBH may underlie the diurnal rhythms of TIDA neuron activity and PRL secretion in OVX+E2 rats.
authors.affiliation: Department of Physiology and Pharmacology, College of Medicine, Chang Gung University, Tao-Yuan 33302, Taiwan. slliang@mail.cgu.edu.tw.
authors.forename: Shu-Ling
authors.initials: SL
authors.lastname: Liang
authors.forename: Sheng-Chieh
authors.initials: SC
authors.lastname: Hsu
authors.forename: Jenn-Tser
authors.initials: JT
authors.lastname: Pan
mesh_terms: D000818:Animals; D002940:Circadian Rhythm / Q000235:genetics*; D004298:Dopamine / Q000378:metabolism; D059290:Dopaminergic Neurons / Q000378:metabolism*; D004967:Estrogens / Q000378:metabolism; D005260:Female; D007031:Hypothalamus / Q000378:metabolism; D057967:Infusions, Intraventricular; D020319:Oligodeoxyribonucleotides, Antisense / Q000008:administration & dosage / Q000235:genetics; D011388:Prolactin / Q000097:blood / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017448:Receptors, Dopamine D2 / Q000819:agonists / Q000378:metabolism*
chemical_list: D004967:Estrogens; D020319:Oligodeoxyribonucleotides, Antisense; D017448:Receptors, Dopamine D2; D011388:Prolactin; D004298:Dopamine