Biomedical subjects

Y M Kershaw

Publications and source records attributed to Y M Kershaw.

6 recordsLinked to original sources

PubMed2006

Diurnal variation in the responsiveness of the hypothalamic-pituitary-adrenal axis of the male rat to noise stress.

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.

Acoustic Stimulation↗

PubMed2002

Hypothalamic-pituitary-adrenal function.

Basal hypothalamic-pituitary-adrenal (HPA) function is characterised by pulses of corticosterone secretion followed by a transient refractory period when the axis appears to be inhibited. In females pulses of corticosterone secretion occur approximately once per hour with variation in pulse amplitude underlying a diurnal rhythm. Males show smaller pulses of secretion which become widely spaced during the early light phase nadir. Pulsatility is altered by genetic programming, early life experiences and reproductive status. Activation of the HPA axis during adjuvant induced arthritis results in an increase in the pulse frequency. This is associated with a marked change in hypothalamic gene expression with a diminution of CRH mRNA and a marked increase of AVP mRNA which becomes the predominant HPA secretagogue.

Adrenal Glands↗

PubMed2001

Peripartum plasticity within the hypothalamo-pituitary-adrenal axis.

The hypothalamo-pituitary-adrenal (HPA) axis plays important roles in the adaptive changes in physiology that occur during pregnancy and lactation. Although the axis still exhibits a pulsatile pattern of secretion, the normal diurnal rhythm of pulse amplitude is lost during lactation, such that mean basal levels remain constant throughout the day. In addition, the peripartum period is associated with a remarkable plasticity in stress-induced HPA activity, in that the increase of HPA activity normally seen in response to either physical or psychological stresses in the non-reproductive state become severely attenuated or absent in the lactating animal. This stabilization of both basal and stress-induced HPA activity may be important for maintaining a constant endocrine environment, thereby preventing any programming effects on the developing offspring. Attenuation of the stress response is initiated in late pregnancy and is temporally associated with luteolysis, indicating possible steroid hormone involvement. Indeed, mimicking the luteolytic changes in oestrogen and progesterone levels in non-pregnant animals induces a similar attenuation of the stress response. Furthermore down-regulation of the stress response is, at least in part, centrally mediated since in the period following luteolysis rats will show a decreased level of stress-induced neuronal activation of the PVN, as measured by the expression of either c-fos or CRH mRNAs. Persistence of this adapted state is dependent upon the continued suckling stimulus, as removal of the offspring litter rapidly leads to resumption of HPA responses to and the appearance of an exaggerated diurnal rhythm. The underlying mechanisms responsible for this stress hyporesponsiveness may include plasticity of noradrenergic and oxytocin pathways. In view of its role in other reproductive behaviors, a stress-inhibiting effect of oxytocin may reflect a more widespread co-ordinating role in the peripartum animal.

Animals↗

PubMed2001

Increased corticosterone pulse frequency during adjuvant-induced arthritis and its relationship to alterations in stress responsiveness.

Frequent blood sampling from males rats was used to study hypothalamic-pituitary-adrenal (HPA) axis activation during arthritis and its association with diminished responses to acute psychological stress. In control rats, corticosterone release occurred in a series of 13 +/- 1 pulses per 24 h. Induction of arthritis by Mycobacterium-adjuvant injection initially increased the rate of hormone release within each pulse and, by day 14 postinjection, when hind-paw inflammation was established, caused a marked increase in pulse frequency to 22 +/- 1 per 24 h leading directly to elevated circulating corticosterone levels. In both control and adjuvant-treated rats, there was a marked response to a 10-min noise stress when the stimulus coincided with a rising or interpulse phase of the endogenous corticosterone rhythm. However, when the noise stress coincided with a falling phase of this rhythm, the response was greatly diminished. Since corticosterone pulse frequency was markedly increased and hence interpulse interval decreased by day 14, there was an increased probability of the noise stress occurring during the nonstress responsive falling phase of the corticosterone secretory cycle. As a result, the group mean response to noise stress was significantly smaller in the arthritic than the controls (70.2 +/- 9.2 versus 107.8 +/- 13.0 ng/ml, respectively). In contrast to the differential response to noise stress, all rats showed similar responses to the acute immunological challenge with i.v. lipopolysaccharide. Thus, altered basal pulse frequency is a major factor influencing HPA activation during acute psychological stress.

Animals↗

PubMed2000

Significance of pulsatility in the HPA axis.

A stress-free automated blood sampling system has been employed to demonstrate pulsatile hypothalamo-pituitary-adrenal (HPA) activity in the rat. In females, pulses of corticosterone secretion occur approximately once/hour throughout the 24 h cycle, with variation in pulse amplitude underlying a diurnal rhythm. Males show smaller pulses of secretion which become widely spaced during the early light phase nadir. Ageing does not affect the occurrence of pulses but the diurnal variation is lost. Analysis of the relationship between the HPA response to an acute noise stress and its coincidence with the various phases of the pulse, suggests that pulsatile activity arises from alternating periods of activation and suppression. Responses to i.v. corticotropin-releasing factor are not affected by pulse phase, indicating that this relationship is not generated at the pituitary-adrenal level. This phase relationship holds for all strains of rat except the hyperresponsive Fischer-344 in which an exaggerated stress response arises from a lack of phase-dependent suppression. Patterns of pulsatile activity are also modulated by neonatal programming or chronic HPA activation arising from adjuvant-induced arthritis, with consequent impact upon the response to acute stimuli. Thus, variations in the patterns of pulsatile activity are important determinants of both basal secretion and acute responses of the HPA axis.

Animals↗

PubMed2000

Chronic iodine deprivation attenuates stress-induced and diurnal variation in corticosterone secretion in female Wistar rats.

Many millions of people throughout the world are at risk of developing iodine deficiency-associated disorders. The underlying effects of iodine deficiency on neuroendocrine function are poorly defined. We have studied stress-induced and diurnal variation in corticosterone secretion in female rats rendered chronically hypothyroid by feeding them an iodine-free diet for 6 months. Corticosterone secretory responses in iodine deficient animals were compared to those seen in animals rendered hypothyroid with propylthiouracil and untreated controls. By using a well-validated, automated blood sampling system to collect small samples of blood over the complete daily cycle in unrestrained animals, we have demonstrated for the first time that the normal diurnal rhythm of corticosterone secretion is lost in chronic iodine deficiency and that the corticosterone secretory response to the psychological stress of 10 min exposure to white noise is attenuated. Despite restoration of circulating triiodothyronine and thyrotropin releasing hormone- and thyroid stimulating hormone beta-transcript prevalence in the hypothalamus and pituitary, respectively, 1 month after restoration of normal iodine-containing diet both the diurnal variation in corticosterone levels and the corticosterone secretory response to the noise stress remained reduced in amplitude compared to control animals. Thus, chronic hypothyroidism induced by iodine deficiency significantly attenuates hypothalamo-pituitary-adrenal axis activity, an effect that persists after functional recovery of the thyroid axis.

Acoustic Stimulation↗