Ultradian glucocorticoid oscillations in physiological and pathophysiological states.

<p>(A–B) In basal (unstressed) conditions, diurnal variation in hormone levels is not smooth but is reflected by a circadian modulation of ultradian pulse amplitude. Data shown is from female Sprague-Dawley rats (A) and female Lewis rats (B). (C) In male Piebald-Viral-Glaxo (PVG) rats with chronic inflammatory stress, pulse amplitude during the circadian nadir is comparable to pulse amplitude during the circadian peak. Shaded region indicates the dark phase.</p

Timing of CRH-impulse determines magnitude of CORT response.

<p>(A) Profile of CRH-impulse where the amplitude is scaled by the basal level of CRH. (B) Amplitude response curves of ACTH (solid blue) and CORT (solid red) computed for with varying phase of the CRH impulse ( corresponds to the peak of the CORT pulse). As a reference, the maximum levels of basal oscillations in ACTH (dashed blue) and CORT (dashed red) are also plotted. The shaded region indicates values of that correspond to the rising phase of the CORT oscillation. Markers on the CORT amplitude response curve correspond to the time histories plotted in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030978#pone-0030978-g004" target="_blank">Figure 4B–E</a>.</p

Parameter dependent profiles of phase response curves.

<p>(A) Phase response curves (PRCs) for different values of the stress impulse amplitude as indicated. For the model exhibits Type 1 phase-resetting (grey curves) with a sharp but continuous change in phase near . For the model exhibits Type 0 phase-resetting (black curves) with a discontinuous change in phase near . (B) Type of PRC curve plotted against .</p

Comparison of theoretical PRC with experimental data confirms a Type 0 phase resetting mechanism.

<p>The Type 0 phase response curve for as computed with the model (black curve). The experimental data, plotted at discrete points, is shown for eight female Sprague-Dawley rats (red diamonds), five female Lewis rats (black dots), and six male PVG rats (green stars). Points where two samples take the same value are circled.</p

Determining phase information from experimental stress-response data.

<p>(A–B) Illustration of how peaks are selected in order to compute the phase information from experimental stress-response data. The time histories show levels of CORT sampled at 10 min intervals in exemplar female Sprague-Dawley (A) and female Lewis (B) rats. Shaded region indicates the period of the applied noise stress. Selected peaks () are marked red.</p

Comparing the CORT response to an acute stress in the oscillatory and non-oscillatory regimes.

<p>Basal CRH is set such that basal CORT in the non-oscillatory case matches the maximum level of CORT for the oscillatory case (dashed black). In the non-oscillatory case the response to a stress is independent of the timing of the stress (grey), whilst for the oscillatory case we present the averaged response to an incoming stress applied at every point over a period of oscillation (solid black). represents the magnitude of the stress. For small stressors, the response in both cases is comparable, whilst for larger stressors the response in the oscillatory case is significantly greater. For comparison, the amplitude of the acute noise stress was estimated to be , for which case we see a much greater response within the oscillatory regime.</p

Glucocorticoid response to constant CRH infusion.

<p>(A–H) Individual (A, C, E, G) and mean (B, D, F, H) corticosterone responses to constant saline (A–B) or CRH infusion (0.5 µg/h, C–D; 1.0 µg/h, E–F; 2.5 µg/h, G–H). Grey bar indicates the period of infusion; error bars represent mean ± standard error of the mean (SEM) (<i>n</i> = 6–8 per group). (I) Dose-dependent effect of CRH on the corticosterone response. Overall effect of the CRH infusion was significant (AUC, <i>p</i><0.0001; Kruskal-Wallis ANOVA on ranks). Error bars represent mean ± SEM (<i>n</i> = 6–8 per group); *<i>p</i><0.001. (J) Synchronous corticosterone oscillations (in individual rats) in response to constant CRH infusion (0.5 µg/h; <i>n</i> = 6). Grey bar indicates the period of infusion.</p

Frequency comparison of CRH-induced and endogenous glucocorticoid oscillations.

<p>(A) Individual corticosterone oscillations in response to constant CRH infusion (0.5 µg/h). Grey bar indicates the period of infusion. (B) Normalized power spectra of the corticosterone oscillations in (A). (C) Corticosterone oscillations during the circadian peak in untreated control (UC) rats. Shaded region indicates the dark phase. (D) Normalized power spectra of the corticosterone oscillations in (C). (E) Mean peak frequency (i.e., frequency corresponding to the maximum power in the spectrum) of corticosterone oscillations in response to constant CRH infusion (0.5 µg/h; CRH; <i>n</i> = 6), and of corticosterone oscillations during the circadian peak in untreated control rats (UC; <i>n</i> = 13). Error bars represent mean ± standard error of the mean (SEM). (F) Frequency evolution of the corticosterone oscillations in (A). AU, arbitrary units.</p

ACTH and glucocorticoid response to constant CRH infusion.

<p>(A–B) Individual (A) and mean (B) ACTH and corticosterone (CORT) oscillations in response to constant CRH infusion (0.5 µg/h; <i>n</i> = 6). (C–D) Individual (C) and mean (D) time course of the ACTH and corticosterone (CORT) response to constant CRH infusion (0.5 µg/h) during the initial activation phase (0–25 min) of the oscillation (<i>n</i> = 4). There was a significant overall effect of the CRH infusion on both ACTH and corticosterone (ACTH, <i>p</i><0.0001; corticosterone, <i>p</i><0.005; one-way ANOVA). ACTH was significantly different from basal (time zero) by 10 min (<i>p</i><0.005), whereas corticosterone was not significantly different from basal (time zero) until 20 min (<i>p</i><0.05). (E) Phase-shifted ACTH and corticosterone (CORT) response to constant CRH infusion (0.5 µg/h) over the duration of the first pulse (<i>n</i> = 3–7 per time point). Grey bar indicates the period of infusion (starting at 0700 h); error bars represent mean ± standard error of the mean (SEM).</p

Effect of NK3R agonist on LH secretion following pre-treatment with GPR54 antagonist.

<p>Representative LH profiles demonstrating the effect of icv administration (long arrow) of a selective NK3R agonist, senktide (<b>C, D, E</b>), or vehicle (<b>A</b>, <b>B</b>) on pulsatile LH secretion in gonadal-intact prepubertal female rats in the presence (<b>A</b>, <b>B</b>, <b>D, E</b>; short arrows) or absence (<b>C</b>) of the selective GPR54 antagonist, Kp-234. Central administration of senktide induced a single LH pulse (<b>C</b>), while intermittent infusion of Kp-234 had no effect on basal LH levels (<b>A</b>, <b>B</b>). Kp-234 potently blocked senktide-induced LH pulses (<b>D</b>). Where spontaneous LH pulses (<b>B, E</b>) were detected during the pre-treatment period, these were excluded from analysis by comparing the previous 30-min period devoid of spontaneous LH pulses with the 30-min post-treatment period (<b>B</b>). Administration of Kp-234 immediately following a spontaneous LH pulse tended to attenuate the pulse (<b>B</b>), as compared to spontaneous LH pulses occurring considerably prior to Kp-234 administration, which were unaffected (<b>E</b>). The 30-min post-treatment period commenced at the time of the senktide/vehicle injection (long arrow). Area under the curve (AUC) values in the 30-min pre-treatment (baseline) period (AUC1) and the 30-min post-treatment period (AUC2) for the three treatment groups are compared in the experiment summary (<b>F)</b>. *<i>P</i><0.05 versus 30-min pre-treatment (baseline) period within the same treatment group, as well as versus the same 30-min period within the group treated with Kp-234 and senktide; <i>n</i> = 3−9 per group.</p