Post-mortem analyses of neuropeptides in brains from sudden infant death victims

Sudden Infant Death Syndrome: Risk Factors and Newer Risk Reduction Strategies

Sudden infant death syndrome (SIDS) continues to be one of the top causes of infant death in the U.S. Despite significant public health initiatives focused on high-risk populations to enhance sleep environments and techniques. The SIDS rate has remained stable in recent years. Risk factors and newer risk reduction strategies for SIDS are the focus of this review article. We conducted a comprehensive literature search on Medline, Cochrane, Embase, and Google Scholar until July 2022. The following search strings and Medical Subject Heading (MeSH) terms were used: "SIDS," "Sudden Infant Death" and "SUID". We explored the literature on SIDS for its epidemiology, pathophysiology, the role of various etiologies and their influence, associated complications leading to SIDS, and preventive and treatment modalities. Despite a more than 50% drop-in rates since the start of the "Back to Sleep" campaign in 1994, sudden infant death syndrome (SIDS) continues to be the top cause of post-neonatal mortality in the United States, despite continued educational initiatives that support safe sleep and other risk reduction strategies. The new American Academy of Pediatrics guidelines for lowering the risk of SIDS include a lot of emphasis on sleeping habits, bedding, and environment but also include elements that are frequently ignored (i.e., prenatal care, smoking, alcohol and drug use, and childhood vaccinations). This study highlights these less-frequently discussed aspects and identifies treatments that have produced beneficial behavioral shifts that benefit newborns as well as their mothers' health and wellbeing.

The potential role of substance P in brainstem homeostatic control in the pathogenesis of sudden infant death syndrome (SIDS)

Victims of sudden infant death syndrome (SIDS) are believed to have an underlying dysfunction in medullary homeostatic control that impairs critical responses to life threatening challenges such as hypoxia, hypercarbia and asphyxia, often during a sleep period. This failure is thought to result from abnormalities in a network of neural pathways in the medulla oblongata that control respiration, chemosensitivity, autonomic function and arousal. Studies have mainly focused on the role of serotonin, 5-hydroxytyptamine (5HT), although the neuropeptide substance P (SP) has also been shown to play an integral role in the modulation of medullary homeostatic function, often in conjunction with 5-HT. Actions of SP include regulation of respiratory rhythm generation, integration of cardiovascular control, modulation of the baroreceptor reflex and mediation of the chemoreceptor reflex in response to hypoxia. Abnormalities in SP neurotransmission may, therefore, also play a significant role in homeostatic dysfunction of the neurotransmitter network in SIDS. This review focuses on the pathways within the medulla involving SP and its tachykinin NK1 receptor, their potential relationship with the medullary 5-HT system, and possible involvement in the pathogenesis of SIDS.

Normative distribution of substance P and its tachykinin neurokinin-1 receptor in the medullary serotonergic network of the human infant during postnatal development

Substance P (SP) and its tachykinin NK1 receptor (NK1R) function within key medullary nuclei to regulate cardiorespiratory and autonomic control. We examined the normative distribution of SP and NK1R in the serotonergic (5-Hydroxytryptamine, [5-HT]) network of the human infant medulla during postnatal development, to provide a baseline to facilitate future analysis of the SP/NK1R system and its interaction with 5-HT within pediatric brainstem disorders in early life. [¹²⁵I] labelled Bolton Hunter SP (BH-SP) tissue receptor autoradiography (n = 15), single label immunohistochemistry (IHC) and double label immunofluorescence (IF) (n = 10) were used to characterize the normative distribution profile of SP and NK1R in the 5-HT network of the human infant medulla during postnatal development. Tissue receptor autoradiography revealed extensive distribution of SP and NK1R in nuclei intimately related to cardiorespiratory function and autonomic control, with significant co-distribution and co-localization with 5-HT in the medullary network in the normal human infant during development. A trend for NK1R binding to decrease with age was observed with significantly higher binding in premature and male infants. We provide further evidence to suggest a significant role for SP/NK1R in the early postnatal period in the modulation of medullary cardiorespiratory and autonomic control in conjunction with medullary 5-HT mediated pathways and provide a baseline for future analysis of the potential consequences of abnormalities in these brainstem neurotransmitter networks during development.

Neuropeptides and breathing in health and disease

Regulatory neuropeptides control and regulate breathing in physiological and pathophysiological conditions. While they have been identified in the neurons of major respiratory areas, they can be active not only at the central level, but also at the periphery via chemoreceptors, vagal afferents, or locally within lungs and airways. Some neuropeptides, such as leptin or substance P, are respiratory stimulants; others, such as neurotensin, produce variable effects on respiration depending on the site of application. Some neuropeptides have been implicated in pathological states, such as obstructive sleep apnea or asthma. This article provides a concise review of the possible role and functions of several selected neuropeptides in the process of breathing in health and disease and in lung pathologies.

Activity of Tachykinin1-Expressing Pet1 Raphe Neurons Modulates the Respiratory Chemoreflex

Homeostatic control of breathing, heart rate, and body temperature relies on circuits within the brainstem modulated by the neurotransmitter serotonin (5-HT). Mounting evidence points to specialized neuronal subtypes within the serotonergic neuronal system, borne out in functional studies, for the modulation of distinct facets of homeostasis. Such functional differences, read out at the organismal level, are likely subserved by differences among 5-HT neuron subtypes at the cellular and molecular levels, including differences in the capacity to coexpress other neurotransmitters such as glutamate, GABA, thyrotropin releasing hormone, and substance P encoded by the Tachykinin-1 (Tac1) gene. Here, we characterize in mice a 5-HT neuron subtype identified by expression of Tac1 and the serotonergic transcription factor gene Pet1, referred to as the Tac1-Pet1 neuron subtype. Transgenic cell labeling showed Tac1-Pet1 soma resident largely in the caudal medulla. Chemogenetic [clozapine-N-oxide (CNO)-hM4Di] perturbation of Tac1-Pet1 neuron activity blunted the ventilatory response of the respiratory CO₂ chemoreflex, which normally augments ventilation in response to hypercapnic acidosis to restore normal pH and PCO₂Tac1-Pet1 axonal boutons were found localized to brainstem areas implicated in respiratory modulation, with highest density in motor regions. These findings demonstrate that the activity of a Pet1 neuron subtype with the potential to release both 5-HT and substance P is necessary for normal respiratory dynamics, perhaps via motor outputs that engage muscles of respiration and maintain airway patency. These Tac1-Pet1 neurons may act downstream of Egr2-Pet1 serotonergic neurons, which were previously established in respiratory chemoreception, but do not innervate respiratory motor nuclei.SIGNIFICANCE STATEMENT Serotonin (5-HT) neurons modulate physiological processes and behaviors as diverse as body temperature, respiration, aggression, and mood. Using genetic tools, we characterize a 5-HT neuron subtype defined by expression of Tachykinin1 and Pet1 (Tac1-Pet1 neurons), mapping soma localization to the caudal medulla primarily and axonal projections to brainstem motor nuclei most prominently, and, when silenced, observed blunting of the ventilatory response to inhaled CO₂Tac1-Pet1 neurons thus appear distinct from and contrast previously described Egr2-Pet1 neurons, which project primarily to chemosensory integration centers and are themselves chemosensitive.

Neurochemical abnormalities in the brainstem of the Sudden Infant Death Syndrome (SIDS)

The brainstem has been a focus in Sudden Infant Death Syndrome (SIDS) research for 30 years. Physiological and animal model data show that cardiorespiratory, sleep, and arousal mechanisms are abnormal after exposure to SIDS risk factors or in infants who subsequently die from SIDS. As the brainstem houses the regulatory centres for these functions, it is the most likely site to find abnormalities. True to this hypothesis, data derived over the last 30 years shows that the brainstem of infants who died from SIDS exhibits abnormalities in a number of major neurotransmitter and receptor systems including: catecholamines, neuropeptides, acetylcholinergic, indole amines (predominantly serotonin and its receptors), amino acids (predominantly glutamate), brain derived neurotrophic growth factor (BDNF), and some cytokines. A pattern is emerging of particular brainstem nuclei being consistently affected including the dorsal motor nucleus of the vagus (DMNV), nucleus of the solitary tract (NTS), arcuate nucleus (AN) and raphe. We discuss the implications of these findings and directions that this may lead in future research.

Cardiac muscarinic receptor overexpression in sudden infant death syndrome

BACKGROUND

Sudden infant death syndrome (SIDS) remains the leading cause of death among infants less than 1 year of age. Disturbed expression of some neurotransmitters and their receptors has been shown in the central nervous system of SIDS victims but no biological abnormality of the peripheral vago-cardiac system has been demonstrated to date. The present study aimed to seek vago-cardiac abnormalities in SIDS victims. The cardiac level of expression of muscarinic receptors, as well as acetylcholinesterase enzyme activity were investigated.

METHODOLOGY/PRINCIPAL FINDINGS

Left ventricular samples and blood samples were obtained from autopsies of SIDS and children deceased from non cardiac causes. Binding experiments performed with [(3)H]NMS, a selective muscarinic ligand, in cardiac membrane preparations showed that the density of cardiac muscarinic receptors was increased as shown by a more than doubled B(max) value in SIDS (n = 9 SIDS versus 8 controls). On average, the erythrocyte acetylcholinesterase enzyme activity was also significantly increased (n = 9 SIDS versus 11 controls).

CONCLUSIONS

In the present study, it has been shown for the first time that cardiac muscarinic receptor overexpression is associated with SIDS. The increase of acetylcholinesterase enzyme activity appears as a possible regulatory mechanism.

The brainstem and serotonin in the sudden infant death syndrome

The sudden infant death syndrome (SIDS) is the sudden death of an infant under one year of age that is typically associated with sleep and that remains unexplained after a complete autopsy and death scene investigation. A leading hypothesis about its pathogenesis is that many cases result from defects in brainstem-mediated protective responses to homeostatic stressors occurring during sleep in a critical developmental period. Here we review the evidence for the brainstem hypothesis in SIDS with a focus upon abnormalities related to the neurotransmitter serotonin in the medulla oblongata, as these are the most robust pathologic findings to date. In this context, we synthesize the human autopsy data with genetic, whole-animal, and cellular data concerning the function and development of the medullary serotonergic system. These emerging data suggest an important underlying mechanism in SIDS that may help lead to identification of infants at risk and specific interventions to prevent death.

Prenatal exposure to nicotine affects substance p and preprotachykinin-A mRNA levels in newborn rat

Prenatal nicotine exposure influences neuronal development including effects on several neurotransmitter systems. It also attenuates the ventilatory response to hypoxia, known to require a functional substance P-ergic system. Previous studies have shown that nicotine increases the risk for sudden infant death syndrome (SIDS) by 4-fold, and that SIDS-victims have elevated brainstem levels of substance P. We, therefore, studied the effect of prenatal nicotine exposure on the levels of substance P-like immunoreactivity by RIA in the brain in newborn rat pups. The expression of the substance P precursor preprotachykinin A mRNA was also determined by real-time reverse transcriptase-polymerase chain reaction in carotid body, in petrosal/jugular and trigeminal ganglia, in cervical and lumbar dorsal root ganglia, and in the brainstem. We found that prenatal nicotine exposure increased levels of substance P-like immunoreactivity in the brainstem without changing levels in other parts of the brain or in the adrenals. Furthermore, mRNA levels were increased in the carotid bodies and in the petrosal ganglia, in contrast to the decreased levels in the cervical dorsal root ganglia. We conclude that nicotine causes alterations in the substance P-ergic system in the brainstem, possibly linked to the increased risk for SIDS after prenatal nicotine exposure.

Altered respiratory pattern and hypoxic response in transgenic newborn mice lacking the tachykinin-1 gene

Substance P is known to be involved in respiratory rhythm and central pattern-generating mechanisms, especially during early development. We therefore studied respiratory responses in transgenic newborn mice (Tac1(-/-)) lacking substance P and neurokinin A (NKA). In vivo, the effects of intermittent isocapnic hypoxia (IH) and hypercapnia were studied using whole body flow plethysmography at P2-3 and P8-10. In vitro, anoxic responses and the effects of hypocapnic and hypercapnic conditions were studied in brain stem-spinal cord preparations (C4 activity) at P2. Hypoxic challenge considerably modified the respiratory activity in transgenic mice displayed in vivo as an attenuated increase in tidal volume during IH. Transgenic mice also showed a more prominent posthypoxic frequency decline in vivo, and posthypoxic neuronal arrests appeared more often in vitro. We recognized two types of sigh activity: with or without a following pause. During IH, the amount of sighs with a pause decreased and those without increased, a redistribution that became stronger with age only in controls. Intermittent anoxia induced long-term facilitation effects in controls, but not in Tac1(-/-) animals, manifested as an increase in burst frequency in vitro and by an augmentation of ventilation during posthypoxic periods in vivo. Thus our data demonstrate that a functional substance P/NKA system is of great importance for the generation of an adequate respiratory response to hypoxic provocation in newborn mice and during early maturation. It also indicates that substance P (and/or NKA) is involved in the development of the plasticity of the respiratory system.

Early postnatal changes in respiratory activity in ratin vitroand modulatory effects of substance P

Developmental changes in the respiratory activity and its modulation by substance P (SP) were studied in the neonatal rat brainstem-spinal cord preparation from the day of birth to day 3 (P0-P3). The respiratory network activity in the ventrolateral medulla was represented by two types of bursts: basic regular bursts with typical decrementing shape and biphasic bursts appearing after augmented biphasic discharges in inspiratory neurons. With advancing postnatal age the respiratory output was considerably modified; the basic rhythm became faster by 20%, whereas the biphasic burst rate, which was originally 15 times slower, declined further by 180% and the C4 burst duration significantly decreased by 20% due to reduced decay time without preceding changes in the central inspiratory drive. SP had an age-dependent excitatory effect on respiratory activity. In the basic rhythm, SP could induce transient rhythm cessations on P0-P2 but not on P3. For the biphasic burst frequency, the sensitivity to SP significantly decreased from P0 to P3, whereas the range of SP-induced changes increased. In both types of bursts, SP prolonged C4 burst duration due to increasing decay time. This effect was three times greater on P3 and did not depend on the central inspiratory drive. Our results suggest that the potency of SP to regulate the respiratory activity elevates during the early postnatal period. The developmental changes in the respiratory activity appear to represent the transient stage in the maturation of rhythm and pattern generation mechanisms facilitating adaptive behavior of a quickly growing organism.

The importance of ‘awareness’ for understanding fetal pain

Our understanding of when the fetus can experience pain has been largely shaped by neuroanatomy. However, completion of the cortical nociceptive connections just after mid-gestation is only one part of the story. In addition to critically reviewing evidence for whether the fetus is ever awake or aware, and thus able to truly experience pain, we examine the role of endogenous neuro-inhibitors, such as adenosine and pregnanolone, produced within the feto-placental unit that contribute to fetal sleep states, and thus mediate suppression of fetal awareness. The uncritical view that the nature of presumed fetal pain perception can be assessed by reference to the prematurely born infant is challenged. Rigorously controlled studies of invasive procedures and analgesia in the fetus are required to clarify the impact of fetal nociception on postnatal pain sensitivity and neural development, and the potential benefits or harm of using analgesia in this unique setting.

Development of neurotransmitter systems during critical periods

Neurotransmitters are released from neurons and mediate neuronal communication. Neuromodulators can also be released from other cells and influence the neuronal signaling. Both neurotransmitters and neuromodulators play an important role in the shaping and the wiring of the nervous system possibly during critical windows of the development. Monoamines are expressed in the very early embryo, at which stage the notochord already contains high noradrenaline levels. Purines and neuropeptides are probably also expressed at an early stage, in a similar way as they occur during early phylogenesis. The levels of most neurotransmitters and neuromodulators increase concomitantly with synapse formation. Some of them surge during the perinatal period (such as glutamate, catecholamines, and some neuropeptides) and then level off. The interesting question is to what extent the expression of neuroactive agents is related to the functional state of the fetus and the newborn. Monoamines are expressed in the very early embryo, at which stage the notochord already contains high noradrenaline levels. They may have an important role for neurotransmission in the fetus. In the adult mammal, the fast switching excitatory amino acids dominate. However, they also seem to be important for the wiring of the brain and the plasticity before birth. NMDA receptors that are supposed to mediate these effects dominate and are then substituted by AMPA receptors. The main inhibitory amino acids gamma-aminobutyric acid (GABA) and glycine are excitatory in the developing brain by depolarizing developing neurons that have high Cl- concentrations. This seems to be of major importance for the wiring of neuronal circuits. Prenatal or neonatal stress, for example, hypoxia, can affect the programming of neurotransmitter and receptor expression, which can lead to long-term behavioral effects.

Glial and neuronal alterations in the nucleus tractus solitarii of sudden infant death syndrome victims

The factors underlying the sudden infant death syndrome (SIDS) are still unknown, but in recent years much attention has been focused on the central cardiorespiratory control system. In the present work we analyzed the nucleus tractus solitarii (nTS) of 23 SIDS victims and 17 age-matched control cases. We studied the functional and morphological alterations of neurons and glial cells to evaluate the results of possible hypoxic-ischemic injury that could have led to sudden death. Morphometric and immunohistochemical analyses were performed on medullary sections. In the nTS of SIDS victims we observed modifications of both neuronal and glial cells. Brain injury triggers the activation of both astrocytes and microglia, which respond to neuronal damage by characteristic changes that could explain our observations in the nTS of SIDS victims. In our investigation of the nTS of SIDS victims we found a significant increase of reactive astrocytes density, a significantly higher percentage of necrotic cells, an increase of reactive microglial cells density, a significantly higher expression of substance P and the presence of NMDA receptors immunoreactivity. Our results support the hypothesis that there is injury of the nTS neurons in SIDS victims, even if the causes of this damage are still unknown. This neuronal damage may explain why adequate ventilation is often not maintained during hypoxia. Such histological findings have never been thought sufficient to explain SIDS, but the tissue findings could be an indication of the impairment of several pathophysiological mechanisms which may underlie brainstem dysfunction, affecting cardiorespiratory control.

Hypoxic response in newborn rat is attenuated by neurokinin-1 receptor blockade

Substance P (SP) is considered to be involved in the regulation of respiration, in particular when respiratory demands are increased, such as during hypoxic stress. In the present study we have investigated the effects of intracerebroventricular pre-treatment with the selective NK-1 receptor antagonist RP67580 on the respiratory response to hypoxia in 5-day-old rat pups. Basal respiration was not altered by RP67580. When subjected to hypoxia (10% O(2)), rat pups pre-treated with RP67580 were unable to sustain the increased respiratory frequency at 10 min. In situ hybridisation demonstrated increased expression of c-fos mRNA in several brainstem areas following hypoxia. This activation was blocked by the antagonist in the retrotrapezoid nucleus and the rostral ventrolateral medulla, areas known to be involved in the hypoxic ventilatory response. This study corroborates a role of endogenously released SP, mediated via NK-1 receptors, in the sustained response to hypoxia in 5-day-old rat pups and suggests that neurons in the rostral ventrolateral medulla are important in this function. It also represents a further example that neuropeptides are released under stressful conditions.

Serotonergic receptors in the midbrain correlated with physiological data on sleep apnea in SIDS victims

BACKGROUND

Recently it has been reported that serotonin and related matters are associated with the sudden infant death syndrome (SIDS), which is still the main cause of postneonatal infant death. To further explore this claim, the correlation between serotonin receptors in the brainstem and sleep apnea in SIDS victims was investigated.

MATERIALS AND METHODS

Among 27,000 infants studied prospectively to characterize their sleep-wake behavior, 38 infants died under 6 months of age including 26 cases of SIDS. All the infants had been recorded during one night in a pediatric sleep laboratory some 3-12 weeks before death. The frequency and duration of sleep apnea were analyzed. Brainstem material was collected and immunohistochemistry on 5-hydroxy tryptamine 1A (5HT1A) receptor was carried out. The density of 5HT1A receptor-positive neurons was measured quantitatively. Nonparametric analysis of the density of 5HT1A receptor-positive neurons was carried out between SIDS and non-SIDS cases. Correlation analyses were performed between the density of 5HT1A receptor-positive neurons and the data on sleep apnea.

RESULTS

There was no correlation between the pathological data on 5HT1A receptors and the physiological data on sleep apnea in SIDS victims.

CONCLUSIONS

No correlation between pathological findings of serotonin and physiological findings of sleep apnea were not in agreement with the association of sleep apnea in pathophysiology of SIDS.

Substance P in the midbrains of SIDS victims and its correlation with sleep apnea

BACKGROUND

Substance P (SP) is a neuropeptide transmitter found in sensory neurons of the central nervous system and related to pain sensation and respiratory regulation. Some reports claim an increase in SP in the brains of SIDS victims, so the correlation between SP and sleep apnea was investigated here.

MATERIALS AND METHODS

Among 27,000 infants studied prospectively to characterize their sleep-wake behavior, 38 infants died under 6 months of age, which included 26 cases of Sudden Infant Death Syndrome (SIDS). All the infants had been recorded during one night in a pediatric sleep laboratory some 3 to 12 weeks before death. The frequency and duration of sleep apnea were analyzed. Brainstem material was collected and immunohistochemistry for SP was carried out. The density of SP positive fibers was measured in the nucleus spinal and mesencephalic nervi trigemini and nucleus parabranchialis in the brainstem of abovementioned cases. Correlation analyses were carried out between the density of SP and the data of sleep apnea.

RESULTS

There was no SIDS specific correlation of SP through the above-listed parts of the midbrain with frequency and duration of sleep apnea.

CONCLUSIONS

There was no significant association between the SP findings and apnea data in SIDS; this is not in agreement with the association of apnea in pathophysiology of SIDS.

Alpha2-adrenergic receptor subtype alterations in the brainstem in the sudden infant death syndrome

BACKGROUND

The sudden infant death syndrome (SIDS) is still the main cause of postneonatal infant death. However, the causes and mechanisms of SIDS have never been completely elucidated. Catecholamines, via alpha2-adrenergic receptor (alpha2-AR) interactions, are known to influence brainstem autonomic and respiratory activity.

AIMS

To examine the catecholaminergic system abnormalities in SIDS victims, we investigated the alterations of alpha2-AR subtypes.

SUBJECTS AND METHODS

We examined the developmental changes of alpha2-AR subtypes in the brainstem, especially in cardiorespiratory nuclei, in 21 SIDS victims and 17 age-matched controls by means of immunohistochemical methods. For statistical analysis, the chi2-test or Fisher's exact probability test was performed.

RESULTS

There was a significant decrease in alpha2A-AR immunoreactivity in the solitary nucleus and ventrolateral medulla (VLM) in the medulla oblongata in SIDS victims compared with in control cases, but there were no significant differences of the alpha2B and alpha2C-AR immunoreactivity in the brainstem between SIDS victims and controls.

CONCLUSION

Alpha2A-AR immunoreactivity was selectively decreased in the solitary nucleus and VLM in the medulla oblongata in SIDS victims, so there was no possibility that it was secondary to chronic hypoxia or repeated ischemia. It may be related to some impairment of the cardiorespiratory neuronal system. Therefore, SIDS victims may be vulnerable to asphyxia, hypoxia, and/or hypercapnia, and fail to exhibit brainstem responses.

Catecholaminergic neurons in the brain-stem and sleep apnea in SIDS victims

BACKGROUND

Tyrosine hydroxylase (TH) is a specific marker for catecholaminergic neurones. Some reports have demonstrated a decrease of TH in the Sudden Infant Death Syndrome (SIDS) compared with controls. To further investigate this, the correlation between TH and sleep apnea was investigated here.

MATERIALS AND METHODS

Among 27,000 infants studied prospectively to characterize their sleep-wake behavior, 38 infants died under 6 months of age. They included 26 cases of SIDS. All the infants had been recorded during one night in a pediatric sleep laboratory some 3 to 12 weeks before death. The frequency and the duration of sleep apnea were analyzed. The brain stem material was collected and subjected to immunohistochemical studies for TH. The density of TH-immunoreactive neurons was measured in the nucleus hypoglossus, nervus vagus dorsalis, solitary and ambiguous and the ventrolateral medulla (VLM) in the medulla oblongata. Correlation analyses were carried out between the density of TH-immunoreactive neurons and the data from the sleep apnea studies.

RESULTS

There was no SIDS specific correlation between TH-immunoreactive neurons in the nucleus hypoglossus, nervus vagus dorsalis, solitary and ambiguous and the ventrolateral medulla (VLM) in the medulla oblongata and the frequency and duration of sleep apnea.

CONCLUSIONS

No significant association between the pathological data and the physiological data refers to TH positive neurons in the medulla oblongata in SIDS victims.

Hormones and breathing

A number of hormones, including hypothalamic neuropeptides acting as neurotransmitters and neuromodulators in the CNS, are involved in the physiologic regulation of breathing and participate in adjustment of breathing in disease. In addition to central effects, some hormones also control breathing at peripheral chemoreceptors or have local effects on the lungs and airways. Estrogen and progesterone seem to protect from sleep-disordered breathing, whereas testosterone may predispose to it. Progesterone and thyroxine have long been known to stimulate respiration. More recently, several hormones such as corticotropin-releasing hormone and leptin have been suggested to act as respiratory stimulants. Somatostatin, dopamine, and neuropeptide Y have a depressing effect on breathing. Animal models and experimental human studies suggest that also many other hormones may be involved in respiratory control.

Developmental neurotransmitter pathology in the brainstem of sudden infant death syndrome: a review and sleep position

Developmental studies on neurotransmitters and their receptors in sudden infant death syndrome (SIDS) infants and controls are reviewed, including comparison between the prone and supine positions at death. In SIDS infants, there are an increase of glial fibrillary acidic protein (GFAP)-positive astrocytes in the brainstem, an increase of substance P (SP) in the medulla and pons, a decrease of tyrosine hydroxylase (TH)-positive catecholaminergic neurons in the ventrolateral medulla (VLM), and vagal nuclei in the medulla oblongata and basal ganglia, a decrease of tryptophan hydroxylase (TrH)-positive serotonergic neurons in the periaqueductal gray matter (PAG), and decreases of 5-hydroxytryptamine 1A (5-HT1A) and 5-HT2A receptor immunoreactivities in the VLM and vagal nuclei in the medulla oblongata. These findings may be the result of chronic or repeated hypoxia and at the same time suggest hypofunction or immaturity of cardiorespiratory regulation. In contrast, 5-HT1A and 5-HT2A receptor immunoreactivities are increased in the PAG of SIDS infants. These increased immunoreactivities may reflect delayed neuronal maturation or a developmental abnormality of the nocicetive reaction of cardiorespiratory and arousal control in SIDS. Also, there are no differences of brainstem gliosis and catecholaminergic neuron changes between the prone and supine positions. Therefore, these changes may be predisposing factors for SIDS.

Biphasic effects of substance P on respiratory activity and respiration-related neurones in ventrolateral medulla in the neonatal rat brainstem in vitro

The effects of substance P (SP) on respiratory activity in the brainstem-spinal cord preparation from neonatal rats (0-4 days old) were investigated. The respiratory activity was recorded from C4 ventral roots and intracellularly from three types of respiration-related neurones, i.e. pre-inspiratory (or biphasic E), three subtypes of inspiratory; expiratory and tonic neurones in the ventrolateral medulla (VLM). After the onset of SP bath application (10 nM-1 microM) a dose-dependent decline of burst rate (by 48%) occurred, followed by a weaker dose-dependent increase (by 17.5%) in burst rate. The biphasic effect of SP on inspiratory burst rate was associated with sustained membrane depolarization (in a range of 0.5-13 mV) of respiration-related and tonic neurones. There were no significant changes in membrane resistance in any type of neurones when SP was applied alone or when synaptic transmission was blocked with tetrodotoxin (TTX). The initial depolarization was associated with an increase in inspiratory drive potential (by 25%) as well as in bursting time (by 65%) and membrane excitability in inspiratory and pre-inspiratory neurones, which corresponded to the decrease in burst rate (C4 activity). The spiking frequency of expiratory and tonic neurones was also increased (by 36 and 48%). This activation was followed by restoration of the synaptic drive potential and bursting time in inspiratory and to a less extent in pre-inspiratory neurones, which corresponded to the increase in burst rate. The discharge frequency of expiratory and tonic neurones also decreased to control values. This phase followed the peak membrane depolarization. At the peak depolarization, SP reduced the amplitude of the action potential by 4-8% in all types of neurones. Our results suggest that SP exerts a general excitatory effect on respiration-related neurones and synaptic coupling within the respiratory network in the VLM. The transient changes in neuronal activity in the VLM may underlie the biphasic effect of SP in the brainstem respiration activity recorded in C4 roots. However, the biphasic effect of SP on inspiratory burst rate seems to be also defined by the balance in activity of other SP-sensitive systems and neurones in the respiratory network in the brainstem and spinal cord, which can modify the activity of medullary respiratory rhythm generator.

Neurotransmitters and neuromodulators during early human development

BACKGROUND

Neurotransmitters such as monoamines appear in the embryo before the neurones are differentiated. They may have other functions than neurotransmission during embryogenesis such as differentiation and neuronal growth. For example, serotonin may act as a morphogen. A number of neuropeptides are expressed during ontogenesis, but their function has been difficult to establish. Maybe some of them remain as evolutionary residues. Fast-switching neurotransmitters like the excitatory amino acids and the more ionotropic receptors dominate in the human brain, but appear probably later during evolution as well as during ontogeny.

METHODS

The distribution of catecholamines during development has been analysed with a fluorescence method, while most of the other neurotransmitters have been mapped with immunohistochemical methods. The classical method to determine the physiological role of a neurotransmitter or modulator is to study the physiological effect of its antagonist, blocking the endogenous activity. By transgenic technique, the genes encoding for enzymes involved in the synthesis of neurotransmitters can be knocked-out.

MAJOR FINDINGS

Pharmacological blocking of endogenous activity has, for example, demonstrated that adenosine suppresses fetal respiration. Knocking out the dopamine beta-hydroxylase gene results in fetal death, suggesting that noradrenaline is essential for survival. Some neurotransmitters change their effect during embryogenesis, e.g. GABA which is excitatory in the embryo, but inhibitory after birth due to a switch from a high to low chloride content in the nerve cells. It is possible that this is of importance for the wiring of neuronal network in early life. NMDA receptors dominate in the foetus, while kainate and AMPA receptors appear later. At birth, there is a surge of neurotransmitters such as catecholamines, which may be of importance for the neonatal adaptation.

CONCLUSIONS

Neurotransmitters and modulators are not only important for the neural trafficking in the embryo, but also for the development of the neuronal circuits. Prenatal or neonatal stress (hypoxia), as well as various drugs, may disturb the wiring and cause long-term behavioural effects (fetal and neonatal programming).

Modulation of hypoglossal motoneuron excitability by NK1 receptor activation in neonatal mice in vitro

1. The effects of substance P (SP), acting at NK1 receptors, on the excitability and inspiratory activity of hypoglossal (XII) motoneurons (MNs) were investigated using rhythmically active medullary-slice preparations from neonatal mice (postnatal day 0-3). 2. Local application of the NK1 agonist [SAR(9),Met (O(2))(11)]-SP (SP(NK1)) produced a dose-dependent, spantide- (a non-specific NK receptor antagonist) and GR82334-(an NK1 antagonist) sensitive increase in inspiratory burst amplitude recorded from XII nerves. 3. Under current clamp, SP(NK1) significantly depolarized XII MNs, potentiated repetitive firing responses to injected currents and produced a leftward shift in the firing frequency-current relationships without affecting slope. 4. Under voltage clamp, SP(NK1) evoked an inward current and increased input resistance, but had no effect on inspiratory synaptic currents. SP(NK1) currents persisted in the presence of TTX, were GR82334 sensitive, were reduced with hyperpolarization and reversed near the expected E(K). 5. Effects of the alpha(1)-noradrenergic receptor agonist phenylephrine (PE) on repetitive firing behaviour were virtually identical to those of SP(NK1). Moreover, SP(NK1) currents were completely occluded by PE, suggesting that common intracellular pathways mediate the actions of NK1 and alpha(1)-noradrenergic receptors. In spite of the similar actions of SP(NK1) and PE on XII MN responses to somally injected current, alpha(1)-noradrenergic receptor activation potentiated inspiratory synaptic currents and was more than twice as effective in potentiating XII nerve inspiratory burst amplitude. 6. GR82334 reduced XII nerve inspiratory burst amplitude and generated a small outward current in XII MNs. These observations, together with the first immunohistochemical evidence in the newborn for SP immunopositive terminals in the vicinity of SP(NK1)-sensitive inspiratory XII MNs, support the endogenous modulation of XII MN excitability by SP. 7. In contrast to phrenic MNs (Ptak et al. 2000), blocking NMDA receptors with AP5 had no effect on the modulation of XII nerve activity by SP(NK1). 8. In conclusion, SP(NK1) modulates XII motoneuron responses to inspiratory drive primarily through inhibition of a resting, postsynaptic K+ leak conductance. The results establish the functional significance of SP in controlling upper airway tone during early postnatal life and indicate differential modulation of motoneurons controlling airway and pump muscles by SP.

Exposure to prenatal carbon monoxide and postnatal hyperthermia: short and long-term effects on neurochemicals and neuroglia in the developing brain

The effects of prenatal exposure to carbon monoxide (CO), a major component of cigarette smoke, was studied alone or in combination with postnatal hyperthermia, on the structural and neurochemical development of the postnatal brain at 1 and 8 weeks. Pregnant guinea pigs (n = 11) were exposed to 200 p.p.m CO for 10 h/day from midgestation until term (68 days), whereas control mothers (n = 10) breathed room air. On postnatal day 4, neonates from the control and CO-exposed pregnancies were exposed to hyperthermia (35 degrees C) for 75 min or remained at ambient (23 degrees C) temperature. Using semiquantitative immunohistochemical techniques the following neurotransmitter alterations were found in the medulla at 1 week: a decrease in met-enkephalin-immunoreactivity (IR) following postnatal hyperthermia and an increase in 5-hydroxytryptamine-IR following a combination of CO and hyperthermia. No alterations were observed in substance P- or tyrosine-hydroxylase-IR in any paradigm. At 8 weeks of age the combination of prenatal CO exposure followed by a brief hyperthermic stress postnatally resulted in lesions throughout the brain and an increase in glial fibrillary acidic protein-IR in the medulla. Such effects on brain development could be of relevance in cardiorespiratory control in the neonate and could have implications for the etiology of Sudden Infant Death Syndrome, where smoking and hyperthermia are major risk factors.

Chronic prenatal exposure to carbon monoxide results in a reduction in tyrosine hydroxylase-immunoreactivity and an increase in choline acetyltransferase-immunoreactivity in the fetal medulla: implications for Sudden Infant Death Syndrome

Maternal cigarette smoking during pregnancy is associated with a significantly increased risk of Sudden Infant Death Syndrome (SIDS). This study investigated the effects of prenatal exposure to carbon monoxide (CO), a major component of cigarette smoke, on the neuroglial and neurochemical development of the medulla in the fetal guinea pig. Pregnant guinea pigs were exposed to 200 p.p.m CO for 10 h per day from day 23-25 of gestation (term = 68 days) until day 61-63, at which time fetuses were removed and brains collected for analysis. Using immunohistochemistry and quantitative image analysis, examination of the medulla of CO-exposed fetuses revealed a significant decrease in tyrosine hydroxylase-immunoreactivity (TH-IR) in the nucleus tractus solitarius, dorsal motor nucleus of the vagus (DMV), area postrema, intermediate reticular nucleus, and the ventrolateral medulla (VLM), and a significant increase in choline acetyltransferase-immunoreactivity (ChAT-IR) in the DMV and hypoglossal nucleus compared with controls. There was no difference between groups in immunoreactivity for the m2 muscarinic acetylcholine receptor, substance P- or met-enkephalin in any of the medullary nuclei examined, nor was there evidence of reactive astrogliosis. The results show that prenatal exposure to CO affects cholinergic and catecholaminergic pathways in the medulla of the guinea pig fetus, particularly in cardiorespiratory centers, regions thought to be compromised in SIDS.

Substance P and central respiratory activity: a comparative in vitro study on foetal and newborn rat

Experiments were performed in vitro on foetal (embryonic days 18 to 21, E18-21) and newborn rat (postnatal days 0 to 3, P0-3) brainstem spinal cord preparations to analyse the perinatal developmental changes in the effects induced by substance P. Superfusion of the preparations with SP-containing artificial cerebrospinal fluid (aCSF) induced significant increase in the respiratory frequency of newborn rats (10-9 M), whereas concentration up to 10-7 M induced no change in foetal preparations. A whole cell patch clamp approach was used to record intracellularly from phrenic motoneurones. In newborn or E20-21 foetal rats SP-containing aCSF depolarised the phrenic motoneurones, increased their input resistance, reduced the rheobase current and shifted the frequency-intensity curves upward. In E18 foetal rats, no change was evoked by SP. A peptidase inhibitor mixture was used to block the enzymatic degradation of endogenous SP. This mixture was ineffective in changing the respiratory frequency in newborn and foetal preparations. In newborn rat phrenic motoneurones, the peptidase inhibitor mixture induced changes similar to those caused by SP but no change was induced in foetal rats. These results indicate that SP may modulate (i) the activity of the respiratory rhythm generator in newborn but not in foetal rats, and (ii) the activity of phrenic motoneurones at E20, E21 and in newborn rats but not at E18. Results obtained using the peptidase inhibitor mixture suggest that endogenous SP is probably not involved in the control of the respiratory rhythm in the prenatal period, but may influence the activity of the phrenic motoneurones after birth.

Maturation of the mammalian respiratory system

In this review, the maturational changes occurring in the mammalian respiratory network from fetal to adult ages are analyzed. Most of the data presented were obtained on rodents using in vitro approaches. In gestational day 18 (E18) fetuses, this network functions but is not yet able to sustain a stable respiratory activity, and most of the neonatal modulatory processes are not yet efficient. Respiratory motoneurons undergo relatively little cell death, and even if not yet fully mature at E18, they are capable of firing sustained bursts of potentials. Endogenous serotonin exerts a potent facilitation on the network and appears to be necessary for the respiratory rhythm to be expressed. In E20 fetuses and neonates, the respiratory activity has become quite stable. Inhibitory processes are not yet necessary for respiratory rhythmogenesis, and the rostral ventrolateral medulla (RVLM) contains inspiratory bursting pacemaker neurons that seem to constitute the kernel of the network. The activity of the network depends on CO2 and pH levels, via cholinergic relays, as well as being modulated at both the RVLM and motoneuronal levels by endogenous serotonin, substance P, and catecholamine mechanisms. In adults, the inhibitory processes become more important, but the RVLM is still a crucial area. The neonatal modulatory processes are likely to continue during adulthood, but they are difficult to investigate in vivo. In conclusion, 1) serotonin, which greatly facilitates the activity of the respiratory network at all developmental ages, may at least partly define its maturation; 2) the RVLM bursting pacemaker neurons may be the kernel of the network from E20 to adulthood, but their existence and their role in vivo need to be further confirmed in both neonatal and adult mammals.

Tritiated-naloxone binding to brainstem opioid receptors in the sudden infant death syndrome

The sudden infant death syndrome (SIDS) is defined as the sudden death of an infant under 1 year of age that remains unexplained after a thorough case investigation, including a complete autopsy. We hypothesized that SIDS is associated with altered 3H - naloxone binding to opioid receptors in brainstem nuclei related to respiratory and autonomic control. We analyzed 3H - naloxone binding in 21 regions in SIDS and control brainstems using quantitative tissue receptor autoradiography. Three groups were analyzed: SIDS (n = 45); acute controls (n = 14); and a chronic group with oxygenation disorders (n = 15). Opioid binding was heavily concentrated in the caudal nucleus of the solitary tract, nucleus parabrachialis medialis, spinal trigeminal nucleus, inferior olive, and interpeduncular nucleus in all cases analyzed (n = 74). The arcuate nucleus on the ventral medullary surface contained negligible binding in all cases (n = 74), and therefore binding was not measurable at this site. We found no significant differences among the three groups in the age-adjusted mean 3H - naloxone binding in 21 brainstem sites analyzed. The only differences we have found to date between SIDS and acute controls are decreases in 3H - quinuclidinyl benzilate binding to muscarinic cholinergic receptors and in 3H - kainate binding to kainate receptors in the arcuate nucleus in alternate sections of this same data set. The present study suggests that there is not a defect in opioid receptor binding in cardiorespiratory nuclei in SIDS brainstems.

Chronic placental insufficiency in the fetal guinea pig affects neurochemical and neuroglial development but not neuronal numbers in the brainstem: a new method for combined stereology and immunohistochemistry

This study has examined the development of the brainstem in a suboptimal intrauterine environment induced via chronic placental insufficiency in the fetal guinea pig. Placental insufficiency was produced by unilateral ligation of the maternal uterine artery at mid-gestation (term = 66-68 days) resulting in the production of growth-retarded fetuses that are chronically hypoxic and malnourished. The structural and neurochemical development of brainstem nuclei either directly or indirectly related to cardiorespiratory control were analysed by using new stereological methods and immunohistochemistry. A technique was devised to enable the procedures to be performed on alternate frozen sections. There were no significant differences between control and growth-retarded fetuses in the total number of neurons, area of neuronal somata or volume of the hypoglossal nucleus. Quantitative densitometry was used to measure immunohistochemical staining in the brainstem of growth-retarded fetuses compared to controls and revealed a significant (P < 0.02) decrease in substance P(SP)-immunoreactivity in the spinal trigeminal nucleus and a significant (P < 0.05) increase in met-enkephalin-immunoreactivity in the hypoglossal nucleus. Counts of stained neurons demonstrated a significant increase in the density of SP-positive neurons in the nucleus tractus solitarius (P < 0.05) and of met-enkephalin-positive neurons in the ventral medullary reticular formation (P < 0.05). There was also a proliferation of astrocytes, as determined by immunoreactivity to glial fibrillary acidic protein in the dorsal motor nucleus of the vagus, nucleus tractus solitarius and more generally around blood vessels throughout the brainstem. Thus, these results have been shown that although chronic intrauterine deprivation does not alter neuronal numbers, at least in the hypoglossal nucleus, there is a proliferation of astrocytes, and the expression of neurotransmitters/neuromodulators is markedly effected in some of the nuclei involved with cardiorespiratory control.

Tachykinins and central respiratory activity: an in vitro study on the newborn rat

The newborn rat brainstem-spinal cord preparation was used to study the effects of tachykinins on the activity of the respiratory rhythm generator in vitro and to characterize the receptors involve. Substance P and tachykinin NK1 and NK3 receptor agonists induced a concentration-dependent increase in the respiratory frequency (10(-9)-10(-7) M), whereas the respiratory frequency was only slightly affected by the tachykinin NK2 receptor agonist. Pre-treatments with tachykinin NK1 receptor antagonists (SR140333, (S)1-¿2-[3-(3.4-dichlorophenyl) -1-(3-isopropoxyphenylacetyl)piperidin-n-3-yl]ethyl¿-4-ph eny l-1-azoniabicyclo [2,2,2]octane chloride; GR82334, pGlu-Ala- Asp-Pro-Asn-Lys-Phe-Tyr-(S-S)Pro-Leu(spiro-gamma-lactam)-Trp-NH2) reduced the substance P-induced increases in the respiratory frequency but the tachykinin NK2 receptor antagonist (SR48968, ((S)-N-methyl-N-[4-4-acetylamino-4-phenylpiperidine)-2-(3,4-dichlorop hen yl) butyl]benzamide); MEN 10376, Asp-Tyr-D-Trp-Val-D-Trp-Lys-NH2) had no effect; the increase in the respiratory frequency induced by the tachykinin NK3 receptor agonist was not affected by a pre-treatment with tachykinin NK1 and NK2 receptor antagonists. These result indicate that tachykinin NK1 and NK3 receptors may be involved in the control of the respiratory frequency.

Relationship of substance P and gliosis in medulla oblongata in neonatal sudden infant death syndrome

Substance P and glial fibrillary acidic protein (GFAP) immunohistochemistry was applied to the medulla of neonatal infants who died of sudden infant death syndrome (SIDS). A quantitative analysis of cells demonstrating immunoreactivity to GFAP and substance P in 15 neonatal SIDS cases revealed increased GFAP immunoreactivity in the reticular formation, the dorsal vagal nucleus, and the solitary nucleus and an increase in substance P immunoreactivity in the spinal trigeminal nucleus and the solitary nucleus as compared with that in age-matched controls. GFAP immunopositivity suggests astrogliosis which implies a pathologic insult to neurons in the area of astrogliosis. The failure of neurons in these sites to show enhanced substance P immunopositivity may indirectly indicate altered neurons. Further study of prenatal events may be of importance in clarifying the pathogenesis of neonatal SIDS.

Regional distribution of substance P binding sites in the brainstem of the human newborn

The distribution of [3H]substance P ([3H]SP) binding sites in the brainstem of the human newborn was investigated in eleven cases (aged 1 h to 6 months) by in vitro quantitative receptor autoradiography. The binding of [3H]SP to newborn brainstem tissue was found to be saturable (for the eight cases examined, Kd and Bmax (M +/- S.E.M.) were 0.29 +/- 0.03 nM and 206 +/- 21 fmol/mg tissue, respectively). Competition studies showed unlabeled SP to be the most potent peptide for displacing [3H]SP binding from tissue sections. The desaturating effect of GTP on the specific binding of [3H]SP was also investigated, but was not found to be significant. Autoradiographic analysis showed that the neurokinin-1 (NK-1)/SP binding sites were widely but unevenly distributed, and that they varied with age. The highest densities of (NK-1)/SP binding sites were observed in the locus coeruleus, olivaris inferior nuclei, raphe magnus and obscurus nuclei, while low to moderate densities were observed in other brainstem structures. These findings support the idea that SP is involved in cardiovascular regulation, and that it may interact with the catecholaminergic and/or serotonergic system.

Sudden infant death syndrome — a ‘diagnosis’ in search of a disease

Although Sudden Infant Death Syndrome (SIDS) is the major cause of death in infants aged between 1 week and 1 year in Western countries, it is one of the most enigmatic conditions encountered in paediatric forensic practice. SIDS has been recognized since Biblical times, and yet the definition continues to be debated and the aetiology remains obscure. In addition, there are no accepted pathognomonic features at post-mortem and the diagnosis is still one of exclusion. Emery once asked whether the term 'SIDS' is in reality more of a 'diagnostic dustbin' into which are placed a variety of unrelated entities.(1) To a certain extent this is true, as it is now recognized that a range of disorders can result in the sudden and unexpected death of an infant in a cot. It is also likely that the aetiology of SIDS is heterogeneous and that the term SIDS is not so much a diagnosis but a term covering a variety of mechanisms which result in a common lethal outcome. There are a number of controversies in the SIDS field which complicate the use of the term and which confound the assessment of causes and mechanisms of sudden infant death.

Brain stem nuclei in sudden infant death syndrome (SIDS): volumes, neuronal numbers and positions

It has been suggested that the defect underlying the sudden infant death syndrome (SIDS) lies in brain stem nuclei involved in cardiac and respiratory function. However, most studies have not used rigorous quantitative techniques to assess brain stem nuclear volumes and neuronal numbers. We have measured the volume, neuronal numbers and position of brain stem nuclei in 11 SIDS and 11 aged-matched control infants. Using serial sagittal sections, nuclei involved in maintaining airway patency (hypoglossal, ambiguus and retroambiguus), heart rate (dorsal vagal) and generation of respiratory rhythm (ambiguus and dorsal vagal) were studied. No significant differences were found in nuclear volume increase with age, total neuronal number or nuclear position between SIDS and control cases. These findings support the hypothesis that the nervous system in SIDS may be normal until the final event that kills these infants.

Inverse relationship between beta-endorphin immunoreactivity in cerebrospinal fluid and nucleus tractus solitarius in sudden infant death

In nucleus tractus solitarius (NTS) beta-endorphin (BEND) induces bradycardia and respiratory depression which have been reported to precede death in sudden infant death (SID). Of SID victims, 50% have elevated levels of beta-endorphin immunoreactivity (BENDI) in the cerebrospinal fluid (CSF), and 50% had undetectable levels. We therefore investigated the relationship of BENDI in the CSF to BENDI levels in the NTS area. This study included SID victims (CSF from n = 47, brain stem from n = 16), borderline SID victims (CSF and brain stem from n = 2), sudden death in childhood (CSF and brain stem from n = 1), and controls (CSF from n = 32, brain stem from n = 11). BEND in CSF and NTS area, after extraction, was measured by radioimmunoassay. High performance liquid chromatography was used for closer identification of BENDI. We found that the SID victims divided into two subpopulations, one having a relatively high BENDI level in CSF and one having no detectable level (P < 0.01). Furthermore, an inverse relationship was found between BENDI level in CSF and BENDI level in NTS area in the SID victims (P < 0.05). We conclude that increased BENDI level in CSF is associated with low BENDI level in the NTS area in 50% of SID victims. The low BENDI level in the NTS area may be due to increased release of BEND.

Cocaine and development: mechanisms of fetal toxicity and neonatal consequences of prenatal cocaine exposure

As cocaine use during pregnancy has become increasingly recognized, there also has been increased concern about the toxic and teratogenic properties of cocaine on the fetus. A significant literature exists describing the adverse fetal and neonatal outcomes associated with in utero cocaine exposure. However, specific causality by cocaine on outcome in the human is difficult to ascertain because of multiple confounding variables associated with substance abuse including social factors and polydrug use as well as difficulty in confirming timing, dose and frequency of cocaine exposure. Most literature suggests that prenatal cocaine exposure is associated with developmental risk to the fetus. What is currently unknown is the extent of risk, the additive and/or synergistic factors contributing to cocaine's toxicity and the reversibility of the injury. In this paper we review the pharmacologic properties of cocaine as related to a model of mechanisms for developmental injury secondary to cocaine exposure and the published literature on the adverse fetal and neonatal outcomes associated with cocaine use during pregnancy. Specific attention has been focused on the structural, neurobehavioral and respiratory control teratogenesis.

Brain banking and the human hypothalamus--factors to match for, pitfalls and potentials

The study of an increasing number of processes occurring in the human brain can be carried out on autopsy material. The availability of this material, whether fresh, frozen or fixed, makes it possible to develop methodologies for studying the neuroanatomical and neurochemical aspects of the human brain. It has also become possible in recent years to correlate functional changes with neurochemical changes and with neuroanatomical abnormalities in disease states. Some compounds and structures are damaged irreversibly within minutes after death and some brain components are known to disintegrate within seconds. This led to the widespread idea that autopsy material would not be suitable for basic research purposes and would not supply the necessary answers on the various fundamental questions regarding processes occurring in normal or diseased brain. However, from data published in recent years in which autopsy material has been routinely used, it becomes more and more evident that this is a misconception. There is an increasing number of reports based on the use of normal and pathological human brain tissue obtained by autopsies in spite of the fact that there is a worrying continuous decline in autopsy rate which causes serious concern among scientists world-wide (Anderson and Hill, 1989). It also became evident that when using the proper fixation procedures, sufficient structural integrity is retained in the tissue to allow morphological and morphometrical studies (Swaab and Uylings, 1988). Electron microscopic examination of synaptosomal preparations from post-mortem human brain showed them to be only slightly less pure than preparations from fresh tissue although there was some degree of damage (Hardy et al., 1982). Agonal state effects the stability of brain compounds and causes brain hypoxia. This again forms a tremendous difficulty for the study of human neurological and psychiatric diseases as one of the frequent causes of death is bronchopneumonia which leads to brain hypoxia and results in pronounced lactic acidosis. The Netherlands Brain Bank has succeeded to partly circumvent some of the serious problems encountered in providing human tissue for research by performing rapid autopsies with an average post-mortem delay of 2-4 h. This has become possible by a close collaboration of numerous nursing homes in Amsterdam and its vicinity and with the neuropathologists of the Free University in Amsterdam. We also measure the pH of the tissue as indicator of agonal state in order to reveal unsuitable specimens. The human hypothalamus contains various nuclei manifesting a wide variety of changes in different conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Maternal cocaine addiction. II: An animal model for the study of brainstem mechanisms operative in sudden infant death syndrome

Respiratory control abnormalities are mechanistic in Sudden Infant Death Syndrome (SIDS). In particular, arousal form sleep is an important component of respiratory regulation. Cocaine alters central neurotransmitter metabolism, particularly the monoamines. The locus coeruleus, the major Norepinephrine (NE) neuronal system, is involved in arousal from sleep related apnea and has extensive forebrain and brainstem projections. Thus, it is plausible that in utero cocaine exposure disrupts the normal maturation of transmitters and/or brain structures essential to sleep related respiratory regulation. Infants exposed to cocaine in utero may have an increased incidence of SIDS. We propose that cocaine use in pregnancy alters the normal maturation of centers and/or neurotransmitters involved in respiratory regulation thereby altering postnatal respiratory control. We hypothesize that the increased incidence of SIDS in cocaine exposed infants may be secondary to deficits in arousal. The study of prenatal brain development and of postnatal respiratory control in rabbit pups exposed to cocaine in utero will provide a useful model for the study of mechanisms operative in SIDS.

Neural maturational delay as a link in the chain of events leading to SIDS

Although numerous etiological or triggering factors have been suggested in sudden infant death syndrome (SIDS), the underlying mechanism of death is ultimately cardiac and/or respiratory in nature. As there is no evidence of lung or heart abnormalities, attention has focussed on the neural control of respiration and cardiac function. It is important to appreciate the methodological limitations involved in utilizing autopsy material and the criteria for selection of appropriate controls. This report reviews the pathological evidence for developmental delay in SIDS emphasizing delay of neural maturation of both myelination and synapses. Other abnormalities of the nervous system apparently associated with hypoxia-ischemia such as brainstem astrogliosis are also discussed. The occurrence of SIDS at a precise age together with our preliminary studies indicate that neural development delay is an important link in the chain of events leading to SIDS.