Abstract
Prolonged maternal deprivation during early infancy increases basal- and stress-induced corticosterone (CORT) levels, but the underlying mechanism is not clear. In general, stressors activate the hypothalamic-pituitary-adrenal (HPA) axis, with secretion and compensatory synthesis of hypothalamic corticotropin-releasing hormone (CRH). In the infant rat, we have demonstrated that maximally tolerated acute cold stress induced a robust elevation of plasma CORT throughout the first 2 postnatal weeks. However CRH messenger RNA (CRH-mRNA) abundance 4 h subsequent to cold stress was enhanced only in rats aged 9 days or older. This suggests a developmental regulation of the CRH component of the HPA-response to this stressor. The present study examined whether increased basal and cold stress-induced CORT levels after 24 h of maternal deprivation were due to enhanced CRH-mRNA abundance in the hypothalamic paraventricular nucleus (PVN). CRH-mRNA abundance, and basal- and cold-induced plasma CORT levels were measured in maternally deprived 6 and 9-day-old pups compared to non-deprived controls. Maternal deprivation increased basal and cold-induced CORT levels on both 6 and 9-day-old rats. CRH-mRNA abundance in the PVN of deprived rats did not differ from that in non-deprived rats. Our results indicate that the enhanced basal and stress-induced plasma CORT observed after 24 h maternal deprivation is not due to increased CRH-mRNA abundance in the PVN.
Highlights
Mechanisms of the activation of the hormonal stress response in the immature rat are not fully understood [7,10,14,18]
The purpose of this study was to examine whether the enhanced basal HPA tone and the altered response of plasma CORT to acute stress observed after 24 h maternal deprivation were due to increased hypothalamic CRHmRNA abundance
Pups on postnatal day (PND) 5 or 8 were divided to 3 groups: (1) individual maternal deprivation (I-DEP) pups were placed individually in divided plastic cages; (2) maternal deprivation as a group (G-DEP) pups were kept with their littermates; (3) non-deprived (N-DEP) rats were left in home cages
Summary
Mechanisms of the activation of the hormonal stress response in the immature rat are not fully understood [7,10,14,18]. 24 h maternal deprivation has been found to increase basal plasma corticosterone (CORT) levels and to enhance HPA axis responsiveness to further stressors [6,9,16]. Shorter periods of maternal deprivation (1, 2, 4, and 8 h) have been shown to have only a minimal effect on basal CORT levels and the response to acute stress [9,16]. The mechanisms underlying increased basal and cold-induced plasma CORT subsequent to maternal deprivation have not been elucidated.
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