Involvement of dopamine D2 receptor in the diurnal changes of tuberoinfundibular dopaminergic neuron activity and prolactin secretion in female rats

J Biomed Sci. 2014 May 3;21(1):37. doi: 10.1186/1423-0127-21-37.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Circadian Rhythm / genetics*
  • Dopamine / metabolism
  • Dopaminergic Neurons / metabolism*
  • Estrogens / metabolism
  • Female
  • Hypothalamus / metabolism
  • Infusions, Intraventricular
  • Oligodeoxyribonucleotides, Antisense / administration & dosage
  • Oligodeoxyribonucleotides, Antisense / genetics
  • Prolactin / blood
  • Prolactin / metabolism*
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Dopamine D2 / agonists
  • Receptors, Dopamine D2 / metabolism*

Substances

  • Estrogens
  • Oligodeoxyribonucleotides, Antisense
  • Receptors, Dopamine D2
  • Prolactin
  • Dopamine