Neonatal Nervous System Research Articles

Neuropathology of trimethyltin: A proposed pathogenetic mechanism

The pathological changes in the limbic system induced by trimethyltin (TMT) in mouse, rat, and neonatal rats were reviewed and compared. It becomes apparent that there was an inverse pathological pattern between the fascia dentata granule cells and the Ammon's horn CA 3 pyramidal neurons. This inverse pathological relationship could be demonstrated along the septotemporal axis of the adult brain as well as in neonatal nervous system. Thus it becomes apparent that the induction of pathological lesion in the Ammon's horn requires the functional integrity of the granule cells. The hypothesis of “hyperexcitory” and “hyperstimulatory” damage of neurons was proposed. In view that this inverse relationship also exists between the entorhinal cortical cells and the fascia dentate granule cells as well as between the CA 3 and CA 1,2 neurons in the Ammon's horn, a theory on the hyperexcitory cascade between the entorhinal cortex → fascia dentate → CA 3 → CA 1,2 neurons was constructed. The present proposal represents a working hypothesis which helps to explain the various patterns of pathological lesions induced in the nervous system by TMT.

Psychiatric sequelae of manganese exposure in the adult, foetal and neonatal nervous systems.

It is important for psychiatrists to recognise that vulnerability to the trace element manganese is different in the adult, foetal and neonatal nervous systems, and that different syndromes may result from exposure.

Neurology of the Newborn

For those who have awaited arrival of book on neonatal neurology: this is it! Amazingly, one person assembled this comprehensive treatise. The task was monumental, but worth effort, because this book has a cohesiveness of approach and style not possible in multiauthored texts. This signal publication provides most thorough review of field available. Volpe correctly asserts, the neurology of newborn has come of age. I have no doubt that this book will be landmark publication that establishes this fact. It is exciting to see conventional neurological wisdom applied to this age group in a productive fashion. The virtues of a careful neurological approach are demonstrated. Simple and useful observations performed routine in older children are often overlooked in nursery. Quite appropriately, three chapters deal with examination, monitoring, and laboratory assessment of neonatal nervous system. More specific tests are discussed where

Serotonin metabolism in neonatal rat brain during asphyxia and recovery.

Neonatal rats were exposed to 20 or 30 min of total or partial oxygen deprivation. During asphyxia and subsequent recovery the endogenous levels of tryptophan and 5-hydroxytryptamine (5-HT, serotonin) were measured. The activity of tryptophan hydroxylase, the first and rate limiting enzyme in the 5-HT synthesis pathway, was studied in vivo by measuring the accumulation of 5-hydroxytryptophan (5-HTP) after inhibition of aromatic L-amino acid decarboxylase with NSD 1015. During asphyxia there was a decrease in tryptophan hydroxylase activity in the whole brain and various regions studied. The levels of tryptophan, 5-HTP and 5-HT all increased after 30 min of recovery from asphyxia. In the whole brain, 5-HTP and 5-HT levels were normal 2 h after anoxia while tryptophan levels normalized more slowly to reach control values after 6 h. In the regional brain study, the 5-HTP levels returned quickly to control levels after asphyxia in the striatum and midbrain but not in the brainstem and hemispheres regions. The whole brain 5-HTP and 5-HT levels did not differ from controls 24 to 48 h after the asphyxia. Although the neonatal nervous system exhibits a great resistance to asphyxia, the metabolism of the neurotransmitter 5-HT is affected already during a short period of asphyxia and subsequent recovery. As 5-HT is ascribed important neurotransmitter functions, this might be relevant to the neurological sequelae of human asphyxia neonatorum.

Brain stem–evoked response in neonates

Twenty-one premature infants of less than 36 weeks’ gestational age at the time of initial study were tested sequentially with auditory BSER and the results obtained were compared to those in 30 normal term infants and 30 normal adults. The latency of the wave I response decreases progressively from a mean of 2.75 ± 0.68 msec at 31 weeks to 1.53 ± 0.14 msec in adults; wave V latency decreases from a mean of 8.77 ± 0.38 msec at 31 weeks to 5.56 ± 0.20 msec in adults. There is a differential maturation between peripheral conduction represented by wave I latency as compared to central conduction represented by the wave I to wave V latency period. The presence of waves II, IV, and combined IV and V varies as a function of age when testing parameters are constant. The BSER to auditory stimuli is a feasible testing method for objectively evaluating neonatal nervous system function.

Influence of glucocorticoid administration and inhibition on fetal baboon pulmonary maturity and the amniotic fluid L/S ratio.

The pregnant baboon feto-placental unit responded to intra-amniotic dexamethasone by a rise in the lecithin-sphingomyelin ratio (L/S ratio) and accelerated pulmonary maturity with evidence of increased amounts of pulmonary surfactant. Metyrapone 11 beta-hydroxylase inhibition of corticoid synthesis prevented the expected rise in the L/S ratio without influencing the normal development of pulmonary maturity. The L/S ratio did not accurately reflect pulmonary maturity when metyrapone was administered to the pregnant baboon. Prudently, model systems such as the baboon should be used for more detailed studies of endocrine effects on pulmonary development because of the reported untoward effects of exogenous steroid administration on the human neonatal nervous system.

Influence of ionizing radiations on the development of the nervous system

SUMMARYThe first cellular differentiation in the process of segmentation leads to the embryonic period, the major organogenetic period for the nervous system. In man, it appears between the second and the eighth week after conception.During the foetal and perinatal periods, the nervous organization mainly develops at the cerebellum and cerebral cortex levels. The cerebrum functional maturation continues well beyond birth.Neuroblasts are the most widespread mother-cells in the developing nervous system during the embryonic period, but some are still to be found after birth.Animal experiment has demonstrated that ionizing radiations were able to disorganize neurogenesis in any of its maturation stages, even at very low doses. It is possible to establish a chronological table showing the anatomical or functional deformities in relation with the embryonic age at which rays have been given.It appears that in man the most dangerous period is between the beginning of the second and the end of the eighth week after conception. At that moment, pregnancy is often ignored and a dose of 20 to 40 r is sufficient to entail serious damages, such as microcephaly, protrusions of the brain or mental retardation. On drawing near to birth the foetal or neonatal nervous system of rodents or primates is still radiosensitive, especially at the cerebral cortex level and the consequences will be of a neurophysiologic or psychosensorial nature. Certain embryopathies or neurologic alterations would only be apparent in subsequent generations, following mutations induced into the mother-cells of the nervous system. Genetic deformities of the nervous system can also result from moderate irradiations of the gonads.Further to the precise experimental research work on the radiovulnerability of the embryonic or foetal nervous system of the animal, certain clinical observations are presented, which lead to similar conclusions.The atomic bombardments have caused numerous neurological trouble among the children who had been irradiated in utero. And the genetic effects are not yet perfectly known to-date.This set of experimental and clinical data must prompt us to be very careful when using ionizing radiations, even at low doses, in pregnant women and newborn.