Ontogeny of peptides in human hypothalamus in relation to sudden infant death syndrome (SIDS)

Loss of the centrosomal protein Cenpj leads to dysfunction of the hypothalamus and obesity in mice

Cenpj is a centrosomal protein located at the centrosomes and the base of cilia, it plays essential roles in regulating neurogenesis and cerebral cortex development. Although centrosomal and cilium dysfunction are one of the causes of obesity, insulin resistance, and type 2 diabetes, the role that Cenpj plays in the regulation of body weight remains unclear. Here, we deleted Cenpj by crossing Cenpj^flox/flox mice with Nkx2.1-Cre mice. Loss of the centrosomal protein Cenpj in Nkx2.1-expressing cells causes morbid obesity in mice at approximately 4 months of age with expended brain ventricles but no change of brain size. We found that hypothalamic cells exhibited reduced proliferation and increased apoptosis upon Cenpj depletion at the embryonic stages, resulting in a dramatic decrease in the number of Proopiomelanocortin (POMC) neurons and electrophysiological dysfunction of NPY neurons in the arcuate nucleus (ARC) in adults. Furthermore, depletion of Cenpj also reduced the neuronal projection from the ARC to the paraventricular nucleus (PVN), with decreased melanocortin-4 receptors (MC4R) expression in PVN neurons. The study defines the roles that Cenpj plays in regulating hypothalamus development and body weight, providing a foundation for further understanding of the pathological mechanisms of related diseases.

Neuropathological Developments in Sudden Infant Death Syndrome

A wide variety of neuropathological abnormalities have been investigated in infants who have died of sudden infant death syndrome (SIDS). Issues which detracted from early studies included failure to use uniform definitions of SIDS and lack of appropriately matched control populations. Development of the triple risk model focused attention on the concept of an inherent susceptibility to unexpected death in certain infants, with research demonstrating a role for the neurotransmitter serotonin within the brainstem. However, it now appears that neuropathological abnormalities in SIDS infants are more complex than a simple serotonergic deficiency in certain medullary nuclei but instead could involve failure of an integrated network of neurochemical transmitters in a variety of subcortical locations. The following overview examines recent research developments looking particularly at the potential role of the peptide neurotransmitter substance P and its neurokinin-1 receptor in multiple nuclei within the brainstem, asymmetry and microdysgenesis of the hippocampus, and decreased orexin levels within dorsomedial, perifornical, and lateral levels in the hypothalamus. Whether such research will lead to identifiable biomarker for infants at risk of SIDS is yet to be established. Use of standardized and consistent methods of classifying and categorizing infant deaths will be pivotal in generating reproducible research results.

Developmental dynamics of neurotensin binding sites in the human hypothalamus during the first postnatal year

The aim of the present study was to determine a detailed mapping of neurotensin (NT) in the human hypothalamus, during the first postnatal year using an in vitro quantitative autoradiography technique and the selective radioligand monoiodo-Tyr3-NT. Ten human postmortem hypothalami obtained from control neonates and infants (aged from 2 h to 1 year of postnatal age) were used. The biochemical kinetics of the binding in all obtained in this study revealed that the binding affinity constants were of high affinity (in the nanomolar range) and did not differ significantly between all cases investigated. Furthermore, competition experiments show insensitivity to levocabastine and were in favor of the presence of the high affinity site of NT receptor. Autoradiographic distribution showed that NT binding sites were widely distributed throughout the rostrocaudal extent of the hypothalamus. However, the distribution of NT binding sites was not homogenous and regional variations exist. In general, the highest densities were mainly present in the anterior hypothalamic level, particularly in the preoptic area. High NT binding site densities are also present at the mediobasal hypothalamic level, particularly in the paraventricular, parafornical, and dorsomedial nuclei. At the posterior level, low to very low densities could be observed in all the mammillary complex subdivisions, as well as the posterior hypothalamic area. Although this topographical distribution is almost identical during the postnatal period analyzed, age-related variations exist in discrete structures of the hypothalamus. The densities were higher in neonates/less aged infants than older infants in preoptic area (medial and lateral parts). The developmental profile is characterized by a progressive decrease from the neonate period to 1 year of postnatal age with a tendency to reach adult levels. On the other hand, the low levels of NT binding sites observed in posterior hypothalamus did not vary during the first postnatal year. They contrast in that with the very high levels we reported previously in adult. In conclusion, the present study demonstrates the occurrence of high NT binding sites density in various structures in many regions in the human neonate/infant hypothalamus, involved in the control of neuroendocrine and/or neurovegetative functions.

Inappropriate mediastinal baroreceptor reflex as a possible cause of sudden infant death syndrome – Is thorough burping before sleep protective?

Despite extensive research, a link between the assumed mechanisms of death and known risk factors for sudden infant death syndrome (SIDS) has not yet been established. Modifiable risk factors such as prone sleeping position, nicotine exposure and thermal stress and non-avoidable risk factors like male gender and some risky socio-economic conditions could be detected, but the etiology of SIDS remains unknown. In many SIDS cases histopathological findings suggest an involvement of vital autonomic control functions and unidentified trigger factors seem to play a role. From a hypothetical point of view, a developmental sympatheticovagal imbalance of the cardiovascular reflex control could cause a predisposition for SIDS. An assumed gastroesophageal trigger impulse is possibly developed during the first weeks of life and could lead to the infant's vagal reflex death. Air swallowed during feeding escapes through the esophagus while the infant is sleeping. The temporarily bloated esophagus exerts pressure on neighboring mediastinal baroreceptors, which is potentially misinterpreted as a rise in arterial pressure. The following cardiodepressoric baroreceptor reflex could lead to arterial hypotension, bradycardia and cardiac arrest. Sleeping in prone position may create an increased thoracic pressure on mediastinal baroreceptors, causing a more pronounced vagal reflex and an increased likelihood of SIDS. Prone position in connection with soft objects in the infant's sleeping environment potentially generates an increased oculobulbar pressure, resulting in an additional cardiodepressoric condition (Aschner-Dagnini phenomenon). From the sixth month of life onwards the sympatheticovagal balance seems to have matured sufficiently to compensate the life-threatening challenges in most infants. Insufficient postprandial burping could either create another independent modifiable risk factor or present the missing link to a common trigger mechanism for SIDS. Further investigations may possibly lead to the explicit recommendation to burp all infants sufficiently and repeatedly before sleep.

Morphological and immunohistochemical studies of the pituitary in sudden infant death syndrome (SIDS)

The morphological structure and immunohistochemical reactions of 100 pituitaries from cases of SIDS children (58 males and 42 females, average age 5.34 +/- 3.12 months) were studied. Controls consisted of 19 pituitaries from children (14 males and 5 females, average age 5.63 +/- 2.52 months) with a clearly identifiable cause of death e.g. drowing or strangulation. The microscopical and immunohistochemical studies for identifying pituitary cell types revealed normally developed organs. Unspecific necroses and haemorrhages were observed in 2 cases of SIDS but in none of the controls. Hyperaemia was detected in 51 (30 male/21 female) cases of SIDS. No significant differences were found in the distribution of microfollicles (54%), cysts of the intermediate zone (14%), persistency of the Rathke's pouch (44%), Erdheim's squamous epithelium (8%) or heterotopic salivary glands (3%). The semiquantitative immunohistochemical evaluations of the different cell types showed no significant variations from the control group. The pattern of distribution of the intracytoplasmic vacuolisations of the ACTH and gonadotropic cells showed no significant differences. Folliculo-stellate cells were either not demonstrable--commensurate with age--or showed a normal distribution. The results for both study groups may be defined as consequences of terminal agony, but failed to reveal the cause of the sudden infant death.