title: The spontaneous firing rates of dopamine-inhibited dorsomedial arcuate neurons exhibit a diurnal rhythm in brain slices obtained from ovariectomized plus estrogen-treated rats.
abstract: The activity of tuberoinfundibular dopaminergic (TIDA) neurons exhibits a diurnal rhythm in female rats, as determined by neurochemical investigation. Whether the spontaneous firing rates of presumed TIDA neurons in the dorsomedial arcuate nucleus (dmARN) also exhibit a diurnal pattern has yet to be ascertained. Single-unit activities of 131 dmARN neurons were recorded in brain slices prepared from 83 ovariectomized plus estrogen-primed rats, and grouped according to their responses to dopamine and the time at which they were observed. In dopamine-inhibited dmARN neurons, significantly lower firing rates were observed in the afternoon compared to those recorded in the morning (2.51 ± 0.27 Hz, n=15, from 1130 to 1330 h vs. 1.08 ± 0.07 Hz, n=47, from 1430 to 1630 h). No such change was observed in dopamine-excited or nonresponsive dmARN neurons (1.83 ± 0.32 Hz, n=9 vs. 1.46 ± 0.17 Hz, n=21). Four dmARN neurons were continuously recorded from 1130 to 1600 h or even longer until 2000 h. The averaged firing rates decreased significantly between 1300 and 1600 h, two neurons were also inhibited by dopamine and a selective D(2) receptor agonist, PHNO, in both normal and low Ca(2+), high Mg(2+) perfusion mediums. This study revealed the existence of diurnal changes in the firing rates of dopamine-inhibited dmARN neurons. These results are strongly correlated with the rhythmic changes observed in TIDA neuronal activity determined through neurochemical methods.
authors.affiliation: Department of Physiology and Pharmacology, School of Medicine, Chang Gung University, 259 Wenhwa 1st Road, Kweishan, Taoyuan 33302, Taiwan. slliang@mail.cgu.edu.tw
authors.forename: Shu-Ling
authors.initials: SL
authors.lastname: Liang
authors.forename: Jenn-Tser
authors.initials: JT
authors.lastname: Pan
mesh_terms: D000200:Action Potentials / Q000187:drug effects*; D000704:Analysis of Variance; D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects*; D004298:Dopamine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D066298:In Vitro Techniques; D020645:Mediodorsal Thalamic Nucleus / Q000166:cytology*; D009433:Neural Inhibition / Q000187:drug effects; D009474:Neurons / Q000187:drug effects*; D010052:Ovariectomy; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D004967:Estrogens; D004298:Dopamine