Diurnal Variation in the Responsiveness of the Hypothalamic‐Pituitary‐Adrenal Axis of the Male Rat to Noise Stress

Abstract

Basal activity of the rat hypothalamic-pituitary-adrenal (HPA) axis is highly dynamic and displays both circadian and ultradian rhythmicity in corticosterone secretion. This study investigated the relationship between basal corticosterone pulsatility and the corticosterone response to noise during the early light phase when there are no endogenous corticosterone pulses and during the early dark phase when there are hourly pulses of corticosterone. An automated blood sampling system was used to collect blood in conscious male rats at 5-min intervals before, during and after exposure to 10-min periods of white noise (104 dB). Behavioural responses to noise were also monitored during these periods. During the early light phase (morning), there was a consistent corticosteroid response to noise with corticosterone concentrations rising rapidly and reaching peak values 10-15 min after the noise had ceased, following which circulating concentrations declined at a rate comparable to the hormones half-life. A second noise stress, 80 min later, resulted in adaptation of the corticosterone response. During the early dark phase (evening), the corticosterone response to the noise was similar to that seen in the morning, although there was no adaptation to a second stimulus. During the evening, the inhibition of endogenous HPA activity after the sound was limited to 40 min following stress.

Dynamics of chromatin accessibility and long-range interactions in response to glucocorticoid pulsing

“…Release of glucocorticoids from the adrenal glands follows two superimposed temporal patterns: a daily (circadian) pattern and an hourly ultradian pattern (Lightman et al 2002Young et al 2004;Atkinson et al 2006;Lightman 2006;Droste et al 2008;Lightman and Conway-Campbell 2010;Walker et al 2012). The effects of GR activation are further influenced by the cell-specific chromatin landscape (Stalder et al 1980;John et al 2008John et al , 2011Biddie et al 2011;Siersbaek et al 2011;Mandrup and Hager 2012) and by the action of other transcription factors and chromatin modifiers Voss et al 2011;Miranda et al 2013b;Morris et al 2014) genome-wide.…”

“…Glucocorticoids, the GR-activating hormones are released from the adrenal glands in a circadian, as well as highly pulsatile (ultradian) fashion-e.g., short (20 min) hourly pulses (Lightman et al 2002Young et al 2004;Atkinson et al 2006;Lightman 2006;Droste et al 2008;Lightman and Conway-Campbell 2010;Conway-Campbell et al 2011;Walker et al 2012). This pulsatile hormone release pattern is further influenced by the physiological and the psychological status of the animal.…”

Sex, social status and physiological stress in primates: the importance of social and glucocorticoid dynamics

“…Rodent and primate genetic background further influences the duration and intensity of GC production, which are not necessarily linked to behavioural differences [23,103]. Time of day can further influence peak amplitude and duration of GC responses [104], and the sex and age of an organism affect response dynamics in humans and rodents [21,22,26,27,105,106].…”

Adrenal peripheral clock controls the autonomous circadian rhythm of glucocorticoid by causing rhythmic steroid production

“…For instance, it has been argued that the diurnal changes in GC require splanchnic nerve integrity but are not mediated by differential responsiveness to ACTH (12). It has also been shown that the response to a mild stress failed to support increased HPA axis reactivity during the active period (13).…”