Maturation of the adrenocortical stress response: Neuroendocrine control mechanisms and the stress hyporesponsive period

background We studied the outcomes at school age in children who had participated in a doubleblind, placebo-controlled trial of early postnatal dexamethasone therapy (initiated within 12 hours after birth) for the prevention of chronic lung disease of prematurity. methods Of the 262 children included in the initial study, 159 lived to school age. Of these children, 146 (72 in the dexamethasone group and 74 in the control group) were included in our study. All the infants had had severe respiratory distress syndrome requiring mechanical ventilation shortly after birth. In the dexamethasone group, 0.25 mg of dexamethasone per kilogram of body weight was given intravenously every 12 hours for one week, and then the dose was tapered. We evaluated the children’s growth, neurologic and motor function, cognition, and school performance. results Children in the dexamethasone group were significantly shorter than the controls (P=0.03 for boys, P=0.01 for girls, and P=0.03 for all children) and had a significantly smaller head circumference (P=0.04). Children in the dexamethasone group had significantly poorer motor skills (P<0.001), motor coordination (P<0.001), and visual– motor integration (P=0.02). As compared with the controls, children in the dexamethasone group also had significantly lower full IQ scores (mean [±SD], 78.2±15.0 vs. 84.4±12.6; P=0.008), verbal IQ scores (84.1±13.2 vs. 88.4±11.8, P=0.04), and performance IQ scores (76.5±14.6 vs. 84.5±12.7, P=0.001). The frequency of clinically significant disabilities was higher among children in the dexamethasone group than among controls (28 of 72 [39 percent] vs. 16 of 74 [22 percent], P=0.04). conclusions Early postnatal dexamethasone therapy should not be recommended for the routine prevention or treatment of chronic lung disease, because it leads to substantial adverse effects on neuromotor and cognitive function at school age.

https://www.nejm.org/doi/pdf/10.1056/NEJMoa032089

Outcomes at School Age after Postnatal Dexamethasone Therapy for Lung Disease of Prematurity

Objectives.  To study the outcome at 2-year corrected age of infants who participated in a double-blind controlled trial of early ( Methods and Materials.  A total of 133 children (70 in the control group, 63 in the dexamethasone-treated group) who survived the initial study period and lived to 2 years of age were studied. All infants had birth weights of 500 to 1999 g and had severe respiratory distress syndrome requiring mechanical ventilation within 6 hours after birth. For infants in the treatment group, dexamethasone was started at a mean age of 8.1 hours and given 0.25 mg/kg every 12 hours for 1 week and then tapered off gradually over a 3-week period. The following variables were evaluated: interim medical history, socioeconomic background, physical growth, neurologic examinations, mental and psychomotor development index score (MDI and PDI), pulmonary function, electroencephalogram, and auditory and visual evoked potential. Results.  Infants in the control group tended to have a higher incidence of upper respiratory infection and rehospitalization than did the dexamethasone-treated group because of respiratory problems. Although there was no difference between the groups in somatic growth in girls, the dexamethasone-treated boys had significantly lower body weight and shorter height than the control boys (10.7 ± 3.0 vs 11.9 ± 2.0 kg; 84.9 ± 5.7 vs 87.5 ± 4.8 cm). The dexamethasone-treated group had a significantly higher incidence of neuromotor dysfunction (25/63 vs 12/70) than did the control group. The dexa-methasone-treated infants also had a lower PDI score (79 ± 26) than did the control group (87 ± 23), but the difference was not statistically significant. Both groups were comparable in MDI, incidence of vision impairment, and auditory and visual evoked potential. Significant handicap, defined as severe neurologic defect and/or intellectual defect (MDI and/or PDI ≤ 69), was seen in 22 children (31.4%) in the control group and 26 (41.2%) in the dexamethasone-treated group. Conclusions.  Although early postnatal dexamethasone therapy for 4 weeks significantly reduces the incidence of CLD, this therapeutic regimen cannot be recommended at present because of its adverse effects on neuromotor function and somatic growth in male infants, detected at 2 years of age. A longer follow-up is needed. If early dexamethasone therapy is to be used for the prevention of CLD, the therapeutic regimen should be modified. The proper route of administration, the critical time to initiate the therapy, and the dosage and duration of therapy remain to be defined further.

https://pediatrics.aappublications.org/content/pediatrics/101/5/e7.full.pdf

Early dexamethasone therapy in preterm infants: a follow-up study.

This article reviews studies of the formation of synaptic junctions in the vertebrate central nervous system. It is focused on electron microscopic investigations of synaptogenesis, although insights from other disciplines are interwoven where appropriate, as are findings from developing peripheral and invertebrate nervous systems. The first part of the review is concerned with the morphological maturation of synapses as described from both qualitative and quantitative perspectives. Next, epigenetic influences on synaptogenesis are examined, and later in the article the concept of epigenesis is integrated with that of hierarchy. It is suggested that the formation of synaptic junctions may take place as an ordered progression of epigenetically modulated events wherein each level of cellular affinity becomes subordinate to the one that follows. The ultimate determination of whether a synapse is maintained, modified or dissolved would be made by the changing molecular fabric of its junctional membranes. In closing, a hypothetical model of synaptogenesis is proposed, and an hierarchial order of events is associated with a speculative synaptogenic sequence. Key elements of this hypothesis are 1) epigenetic factors that facilitate generally appropriate interactions between neurites; 2) independent expression of surface specializations that contain sufficient information for establishing threshold recognition between interacting neurites; 3) exchange of molecular information that biases the course of subsequent junctional differentiation and ultimately results in 4) the stabilization of synaptic junctions into functional connectivity patterns.

Review: Fine structure of synaptogenesis in the vertebrate central nervous system

Effect of corticosteroids on brain growth in fetal sheep.

(1) Treatment with cortisol acetate (0.2 mg daily during the first 4 days after birth) reduced the rate of growth in the rat: at 35 days of age the body weight was reduced by 50 per cent and the brain weight, depending on the region, by up to 30 per cent.

(2) In the brain the normal increase in cell number was severely inhibited during the period of cortisol treatment; this resulted in a final deficit in cell number of about 20 per cent in the cerebrum and 30 per cent in the cerebellum.

(3) To determine whether cortisol affected primarily cell formation or cell destruction the labelling of brain DNA was studied 1 h after a subcutaneous injection of 20 Ci/100 g [2-14C]thymidine. In the controls the amount of labelled DNA increased by a factor of two in the cerebrum and seven in the cerebellum during the period 2-13 days, and it decreased to 40 and 27 per cent of the peak values in the cerebrum and cerebellum respectively in the following 7 days. The results indicated that mitotic activity is higher in the cerebellum than in the cerebrum in the 2nd week of life. It would appear that in the cerebrum appreciable cell death accompanies new cell formation, especially during the period 13-35 days of age.

(4) Cortisol treatment affected cell division rather than cell destruction in the brain since it strongly inhibited the incorporation of [2-14C]thymidine into DNA. The inhibition was severe during the period of treatment but it did not result in a lasting fall in mitotic activity. At the age of 13 days the amount of labelled DNA formed approached the normal level and it was twice that in controls at 20 days, indicating a tendency for compensating cell deficit by an accelerated mitotic activity. Nevertheless, massive cell proliferation ceased at about the same age as in normals; the labelling of DNA decreased markedly between 13 and 20 days after birth, and the DNA content did not increase after the age of 20 days.

(5) In contrast to the marked effect on cell number, cortisol treatment did not influence significantly the maturational changes related to average cell size (DNA concentration) or the chemical composition of cells (RNA/DNA and protein/DNA).

A. L. Johnson

Papers

Effects of corticosteroids on the biochemical maturation of rat brain: postnatal cell formation.