Melatonin and mental capacities in newborn infants

Postnatal Development of the Circadian Rhythmicity of Human Pineal Melatonin Synthesis and Secretion (Systematic Review)

Introduction: According to current knowledge, at birth, the pineal gland and melatonin receptors are already present and the suprachiasmatic nucleus is largely functional, and noradrenaline, the key pineal transmitter, can be detected in the early foetal period. It is still unclear why the pineal gland is not able to start its own pulsatile synthesis and secretion of melatonin in the first months of life, and as a result, infants during this time are dependent on an external supply of melatonin. Method: The causes and consequences of this physiological melatonin deficiency in human infancy are examined in a systematic review of the literature, in which 40 of 115 initially selected publications were evaluated in detail. The references of these studies were checked for relevant studies on this topic. References from previous reviews by the author were taken into account. Results: The development and differentiation of the pineal gland, the pinealocytes, as the site of melatonin synthesis, and the development and synaptic coupling of the associated predominantly noradrenergic neural pathways and vessels and the associated Lhx4 homebox only occurs during the first year of life. Discussion: The resulting physiological melatonin deficiency is associated with sleep disorders, infant colic, and increased crying in babies. Intervention studies indicate that this deficiency should be compensated for through breastfeeding, the administration of nonpooled donor milk, or through industrially produced chrononutrition made from nonpooled cow's milk with melatonin-poor day milk and melatonin-rich night milk.

Peculiarities of melatonin levels in preterm infants

BACKGROUND

Melatonin plays an important role in organism functioning, child growth, and development. Of particular importance is melatonin for preterm infants. The aim of our research was to study the peculiarities of melatonin levels depending on various factors in preterm infants with gestational age (GA) of less than 34 weeks.

METHODS

The study involved 104 preterm infants with GA less than 34 weeks who were treated in the neonatal intensive care unit (NICU). The level of melatonin in urine samples was determined by an enzyme-linked immunosorbent assay.

RESULTS

Melatonin concentration was significantly lower in extremely and very preterm infants compared to moderate preterm (3.57 [2.10; 5.06] ng/ml vs. 4.96 [3.20; 8.42] ng/ml, p = 0.007) and was positively correlated with GA (Spearman r = 0.32; p < 0.001). Positive correlations were revealed between melatonin levels and Apgar scores at the 1st (Spearman r = 0.31; p = 0.001) and 5th minutes after birth (Spearman r = 0.35; p < 0.001). Melatonin levels were lower in newborns with respiratory distress syndrome (p = 0.011). No significant correlations were found between melatonin concentration and birth weight (Spearman r = 0.15; p = 0.130). There were no associations of melatonin concentrations and mode of delivery (p = 0.914), the incidence of early-onset sepsis (p = 0.370) and intraventricular hemorrhages (p = 0.501), and mechanical ventilation (p = 0.090). The results of multiple regression showed that gestational age at birth was the most significant predictor of melatonin level in preterm infants (B = 0.507; p = 0.001).

CONCLUSION

Gestational age and the Apgar score were associated with decreased melatonin levels in preterm infants. The level of melatonin in extremely and very preterm infants was lower compared to moderate preterm infants.

Multi-level hypothalamic neuromodulation of self-regulation and cognition in preterm infants: Towards a control systems model

Preterm infants, age-corrected for prematurity, score on average, 10 points lower on IQ tests than full-term infants tested at comparable ages. This review focuses on the potential contribution of the hypothalamus to cognitive neuro-regulatory development in preterm infants through its bidirectional neural connections with the prefrontal cortex and its neuroendocrine activity. It aims to clarify the central role of the hypothalamus in preterm high stress situations and in influencing cognitive development via its connectivity to the cerebral cortex. The review further evaluates epigenomic sensitivity to environmental inputs. Recent results suggest that an optimal range of DNA methylations (via a continuous process of decreasing levels of receptor methylations that are too high, and increasing levels that are too low) appears necessary in order to reach an adaptive level of receptor availability. Several studies have demonstrated amelioration of preterm infants' stress while in the Newborn Intensive Care Unit (NICUs) and following discharge. The authors postulate that feedback mechanisms and correction signals are the basis for a hypothalamic homeostatic modulating function, a "hypothalamic resistance response", which may account for the stress reduction brought about by in- and post-NICU early interventions and their results of promoting self-regulation and cognition.

Development of the Ontogenetic Self-Regulation Clock

To date, there is no overarching proposition for the ontogenetic-neurobiological basis of self-regulation. This paper suggests that the balanced self-regulatory reaction of the fetus, newborn and infant is based on a complex mechanism starting from early brainstem development and continuing to progressive control of the cortex over the brainstem. It is suggested that this balance occurs through the synchronous reactivity between the sympathetic and parasympathetic systems, both which originate from the brainstem. The paper presents an evidence-based approach in which molecular excitation-inhibition balance, interchanges between excitatory and inhibitory roles of neurotransmitters as well as cardiovascular and white matter development across gestational ages, are shown to create sympathetic-parasympathetic synchrony, including the postnatal development of electroencephalogram waves and vagal tone. These occur in developmental milestones detectable in the same time windows (sensitive periods of development) within a convergent systematic progress. This ontogenetic stepwise process is termed "the self-regulation clock" and suggest that this clock is located in the largest connection between the brainstem and the cortex, the corticospinal tract. This novel evidence-based new theory paves the way towards more accurate hypotheses and complex studies of self-regulation and its biological basis, as well as pointing to time windows for interventions in preterm infants. The paper also describes the developing indirect signaling between the suprachiasmatic nucleus and the corticospinal tract. Finally, the paper proposes novel hypotheses for molecular, structural and functional investigation of the "clock" circuitry, including its associations with other biological clocks. This complex circuitry is suggested to be responsible for the developing self-regulatory functions and their neurobehavioral correlates.