Effect of arousing stimuli on circulating corticosterone and the circadian rhythms of luteinizing hormone (LH) surges and locomotor activity in estradiol-treated ovariectomized (ovx+EB) Syrian hamsters

Abstract

In most proestrous hamsters, novel wheel exposure phase advances activity rhythms and blocks the preovulatory LH surge, which occurs 2 h earlier the next day. Because wheel immobilization does not prevent these effects we hypothesized that arousal alone blocks and phase advances the LH surge. Ovariectomized (ovx) hamsters received a jugular vein cannula and estradiol benzoate (EB) or vehicle was injected sc. The next day (Day 1), at zeitgeber time (ZT) 4-5 (ZT 12=lights off), after obtaining a blood sample, each hamster was exposed to constant darkness (DD), and either remained in her home cage or was transferred to a new cage and exposed to a running wheel or a 2-h arousal paradigm. Blood samples were obtained in dim red light and activity was recorded hourly until ~ZT 10-11 on Days 1 and 2. For the next 1-2 weeks, activity was monitored in DD. Plasma LH and corticosterone were assessed by RIA. Novel wheel exposure or arousal at ZT 4 greatly attenuated the Day 1 LH surge in ovx+EB hamsters, and phase advanced the Day 2 LH surge by about 2 hours. In proestrous hamsters, novel wheel exposure led to a prolonged (>2 h) increase in corticosterone levels only when LH surges were blocked. Phase advances in activity rhythms were enhanced by estradiol and arousal. The results suggest that estradiol modulates the effectiveness of non-photic stimuli. The role of the increased activity of the hypothalamic-pituitary-adrenal axis associated with novel wheel-induced attenuation of LH surges in ovx+EB hamsters remains to be determined.

Flexible clock systems: adjusting the temporal programme

“…For example, natural increases in oestrogen concentrations during oestrous as well as experimental oestrogen administration phaseadvances behavioural activity rhythms in some rodent species [128][129][130]. Oestrogens can also increase overall behavioural locomotor activity, and oestrogens may also modulate the effectiveness of non-photic stimuli mediated through, for example, wheel-running on circadian rhythms [131]. However, the proximate mechanism underlying these oestrogenic actions in female rodents is still debated and may involve changes in activity levels, arousal, sleep and responsiveness to non-photic stimuli rather than changes in t, although species differences may also account for some divergences in mechanisms [48,130,132].…”

Screening of Differentially Expressed Genes and miRNAs in Hypothalamus and Pituitary Gland of Sheep under Different Photoperiods

“…The hypothalamus and pituitary gland are important upstream tissues that regulate HPG in sheep and control a wide range of animal behaviors [ 31 , 32 ]. To better probe the effects of the photoperiod on hypothalamic and pituitary function, we applied the OVX + E 2 sheep model, which is often used to study the response of seasonally breeding animals to photoperiodic and reproductive endocrine changes [ 33 , 34 , 35 ]. Therefore, this study used transcriptomic approaches to mine differential genes and miRNA expression patterns associated with reproduction in sheep with different photoperiods.…”

Photoperiod induced the pituitary differential regulation of lncRNAs and mRNAs related to reproduction in sheep

“…In sheep, the lncRNAs in several tissues were related to animal reproductive or estrous activities ( La et al, 2019 ; Zhang et al, 2019 ; Zheng et al, 2019 ; Feng et al, 2018 ). To better understand the effect of photoperiod on pituitary function, we established the OVX+E 2 sheep model which has been frequently used to study the response to photoperiod and reproductive endocrine changes in seasonal reproduction animals ( Legan et al, 2015 ; Scotti, Place & Demas, 2007 ; Jackson et al, 2013 ), subsequently, genome-wide analyses to identify differentially expressed mRNAs and lncRNAs in the pituitary of the above OVX+E 2 sheep which treated with different photoperiod. The DE-lncRNAs and DE-mRNAs were used to reveal their functions in ovine pituitary, therefore this research provides a valuable resource for further studies of functional lncRNAs in the sheep pituitary.…”