Early developmental changes in [3H]nicotine binding in the human brainstem

Differential development of 5-HT receptor and the serotonin transporter binding in the human infant medulla

Tissue receptor autoradiography with 3H-lysergic acid diethylamide (3H-LSD), 3H-8-hydroxy-2-[di-N-propylamine] tetralin (3H-8-OH-DPAT), and 125I-RTI-55 was used to map the distribution and developmental profile of 5-HT(1A-1D) and 5-HT2 receptors, 5-HT1A receptors, and the serotonin (5-HT) transporter (SERT), respectively, to nuclei with cardiorespiratory function in the human medulla from midgestation to maturity. The distribution pattern of the 5-HT markers was heterogeneous, with variable densities of binding of each observed both in nuclei with and without 5-HT cell bodies. The highest density of binding for each marker was observed in the raphé nuclei, the site of the highest density of 5-HT cell bodies. A significant reduction in 5-HT receptor binding measured with 3H-LSD was observed between midgestation and infancy, and between infancy and maturity in multiple nuclei, but no changes were observed across infancy. A significant increase in 5-HT1A receptor binding density was observed across infancy in the hypoglossal nucleus (regression slope coefficient = 0.008 +/- 0.002, P = 0.02), and a marginally significant increase was observed in the raphé obscurus (regression slope coefficient = 0.061 +/- 0.026 [mean +/- SEM], P = 0.05). No significant age-related changes in SERT binding were observed at any time. With the exception of the hypoglossal nucleus, where 5-HT1A receptor binding increases while SERT binding remains stable, the medullary 5-HT markers analyzed in the study are essentially "in place" at birth. This study provides important baseline data that serve as a foundation for future work in pediatric 5-HT brainstem disorders, including sudden infant death syndrome.

Analyses of the potential oxygen transfer capability in placentae from infants succumbing to sudden infant death syndrome

BACKGROUND

Morphometric oxygen diffusive conductance (Dp) was estimated to assess the potential efficiency of oxygen transfer across the materno-fetal interface in placentae obtained from victims of sudden infant death syndrome (SIDS).

STUDY DESIGN

SIDS placentae were retrieved from archived storage and classified into normal birth weight (NBW, n=16), or small for gestational age (SGA, n=9) and compared against control placentae (n=40) or SGA (n=24) placentae. A combination of stereological techniques and physiological constants were used to estimate total Dp.

RESULTS

SIDS NBW cases showed a crucial reduction in fetal capillary surface area when compared with control placentae. SIDS SGA showed a number of deficiencies in basic volumetric and surface area parameters. Values for total and specific Dp in placentae in both SIDS groups were maintained at levels comparable with control and SGA cases, respectively.

CONCLUSION

Since more reductions were observed in SIDS SGA group, this suggests that factors responsible for these reductions maybe associated with SGA rather than being SIDS-specific factors.

Effect of prenatal nicotine exposure on biphasic hypoxic ventilatory response and protein kinase C expression in caudal brain stem of developing rats

Current evidence suggests that maternal smoking is associated with decreased respiratory drive and blunted hypoxic ventilatory response (HVR) in the newborn. The effect of prenatal nicotine exposure on overall changes in HVR has been studied; however, there is limited data on the effect of nicotine exposure on each component of biphasic HVR. To examine this issue, 5-day timed-pregnant Sprague-Dawley rats underwent surgical implantation of an osmotic minipump containing either normal saline (Con) or a solution of nicotine tartrate (Nic) to continuously deliver free nicotine at 6 mg.kg of maternal weight(-1).day(-1). Rat pups at postnatal days 5, 10, 15, and 20 underwent hypoxic challenges with 10% O(2) for 20 min using whole body plethysmography. At postnatal day 5, Nic was associated with attenuation of peak HVR; peak minute ventilaton increased 44.0 +/- 6.8% (SE) from baseline in Nic pups, whereas that of Con pups increased 62.9 +/- 5.1% (P < 0.05). Nic pups also had a reduction in the magnitude of ventilatory roll-off; minute ventilation at 15 min decreased 7.3 +/- 7.1% in Nic pups compared with 27.3 +/- 4.0% in Con pups (P < 0.05). No significant difference in HVR was noted at postnatal days 10, 15, and 20. Hypercapnic response was similar at all ages. We further investigated the effect of prenatal nicotine exposure on PKC expression in the caudal brain stem (CB) of developing rats. At postnatal day 5, Nic was associated with increased expression of PKC-beta and PKC-delta in CB, whereas other PKC isoforms were not affected. It is concluded that prenatal nicotine exposure is associated with modulation of biphasic HVR and a selective increase in the expression of PKC-beta and PKC-delta within the CB of developing rats.

Serotonergic brainstem abnormalities in Northern Plains Indians with the sudden infant death syndrome

The rate of the sudden infant death syndrome (SIDS) among American Indian infants in the Northern Plains is almost 6 times higher than in U.S. white infants. In a study of infant mortality among Northern Plains Indians, we tested the hypothesis that receptor binding abnormalities to the neurotransmitter serotonin (5-HT) in SIDS cases, compared with autopsied controls, occur in regions of the medulla oblongata that contain 5-HT neurons and that are critical for the regulation of cardiorespiration and central chemosensitivity during sleep, i.e. the medullary 5-HT system. Tritiated-lysergic acid diethylamide binding to 5-HT(1A-D) and 5-HT2 receptors was measured in 19 brainstem nuclei in 23 SIDS and 6 control infants using tissue receptor autoradiography. Binding in the arcuate nucleus, a part of the medullary 5-HT system along the ventral surface, in the SIDS infants (mean age-adjusted binding 7.1 +/- 0.8 fmol/mg tissue, n = 23) was significantly lower than in controls (mean age-adjusted binding 13.1 +/- 1.6 fmol/mg tissue, n = 5) (p = 0.003). Binding also demonstrated significant diagnosis x age interactions (p < 0.04) in 4 other nuclei that are components of the 5-HT system. These data suggest that medullary 5-HT dysfunction can lead to sleep-related, sudden death in affected SIDS infants, and confirm the same binding abnormalities reported by us in a larger dataset of non-American Indian SIDS and control infants. This study also links 5-HT abnormalities in the arcuate nucleus with exposure to adverse prenatal exposures, i.e. cigarette smoking (p = 0.011) and alcohol (p = 0.075), during the periconceptional period or throughout pregnancy. Prenatal exposure to cigarette smoke and/or alcohol may contribute to abnormal fetal medullary 5-HT development in SIDS infants.

Selective vulnerability of cerebellar granule neuroblasts and their progeny to drugs with abuse liability

Cerebellar development is shaped by the interplay of genetic and numerous environmental factors. Recent evidence suggests that cerebellar maturation is acutely sensitive to substances with abuse liability including alcohol, opioids, and nicotine. Assuming substance abuse disrupts cerebellar maturation, a central question is: what are the basic mechanisms underlying potential drug-induced developmental defects? Evidence reviewed herein suggests that the maturation of granule neurons and their progeny are intrinsically affected by several classes of substances with abuse liability. Although drug abuse is also likely to target directly other cerebellar neuron and glial types, such as Purkinje cells and Bergmann glia, findings in isolated granule neurons suggest that they are often the principle target for drug actions. Developmental events that are selectively disrupted by drug abuse in granule neurons and/or their neuroblast precursors include proliferation, migration, differentiation (including neurite elaboration and synapse formation), and programmed cell death. Moreover, different classes of drugs act through distinct molecular mechanisms thereby disrupting unique aspects of development. For example, drug-induced perturbations in: (i) neurotransmitter biogenesis; (ii) ligand and ion-gated receptor function and their coupling to intracellular effectors; (iii) neurotrophic factor biogenesis and signaling; and (iv) intercellular adhesion are all likely to have significant effects in shaping developmental outcome. In addition to identifying therapeutic strategies for drug abuse intervention, understanding the mechanisms by which drugs affect cellular maturation is likely to provide a better understanding of the neurochemical events that normally shape central nervous system development.

Anatomic relationships of the human nucleus of the solitary tract in the medulla oblongata: a DiI labeling study

The nucleus of the solitary tract (nTS) is a major site of brainstem control of vital functions (e.g., cardiovascular reflexes and respiration). We examined anatomic relationships of the human nucleus of the solitary tract, using a bidirectional lipophilic fluorescent tracer 1-1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) in 10 postmortem human fetal midgestational medullae oblongatae. Labeling by diffusion of DiI from the nucleus of the solitary tract included: (1) neuropil of all future subdivisions of the nucleus of the solitary tract ipsilateral to the DiI crystal; (2) stellate cells in the caudal raphe at the junction of the nucleus raphe pallidus and the arcuate nucleus at the ventral medullary surface, as well as single fibers along the caudal raphe and the arcuate nucleus; (3) cells and fibers in other medullary areas related to autonomic and respiratory control, including the dorsal motor nucleus of the vagus, nucleus ambiguus complex/ventral respiratory group, rostral ventrolateral medulla (RVLM) and caudal ventrolateral medulla (CVLM), and medullary reticular formation. The pattern of connections of the nucleus of the solitary tract already established by midgestation in the human fetus is consistent with the pattern previously demonstrated in adult experimental animals. A major finding of the study is that of the stellate cells at the junction of nucleus raphe pallidus and the arcuate nucleus at the ventral medullary surface, which project to the nucleus of the solitary tract, and could be homologous to chemosensitive serotonergic neurons at the midline ventral medullary surface of experimental animals. This connection between the ventral caudal raphe and the nucleus of the solitary tract may participate in chemoreception and central regulation of cardiorespiratory reflexes during human perinatal development; it is, therefore, relevant to the study of sudden infant death syndrome (SIDS).

Higher expression of alpha7 nicotinic acetylcholine receptors in human fetal compared to adult brain

Neuronal nicotinic acetylcholine receptors are thought to be involved in regulation of several processes during neurogenesis of the brain. In this study the expression of the alpha7 nicotinic acetylcholine receptor subtype was investigated in human fetal (9-11 weeks of gestation), middle-aged (28-51 years) and aged (68-94 years) medulla oblongata, pons, frontal cortex, and cerebellum. The specific binding of the alpha7 receptor antagonist [(125)I]alpha-bungarotoxin was significantly higher in fetal than in both middle-aged and aged medulla oblongata and aged pons. No significant decrease in [(125)I]alpha-bungarotoxin binding sites was observed from fetal to adult cortex and cerebellum. The alpha7 mRNA expression was significantly higher in all fetal brain regions investigated, except for aged cortex, than in corresponding middle-aged and aged tissue. The high expression of alpha7 nicotinic acetylcholine receptors in fetal compared to adult brain supports the view that these receptors play an important role during brain development.

Altered arousal response in infants exposed to cigarette smoke

AIMS

A failure of the arousal mechanism is a key feature in the apnoea theory for sudden infant death syndrome (SIDS). In infants studied at an age when the incidence of SIDS is highest, we evaluated whether in utero smoke exposed infants have altered arousal response to standardised auditory stimuli, and/or sleep pattern, as recorded on overnight complex sleep polysomnography.

METHODS

A standardised sequence of audiology stimuli was applied binaurally to 20 in utero smoke and non-smoke exposed infants aged 8-12 weeks during a rapid eye movement (REM) and NREM epoch, in a controlled (temperature, position, pacifier use, noise) sleep environment. Infants were monitored for 10-12 hours using complex sleep polysomnography.

RESULTS

Five infants exposed to in utero tobacco smoke did not have behavioural arousal response, whereas all non-smoke exposed infants aroused during NREM (p = 0.016). There was, however, no difference in REM sleep, and the groups did not differ in routine overnight complex sleep polysomnography parameters.

CONCLUSION

At the age when the incidence of SIDS is at its peak, infants of smoking mothers are less rousable than those of non-smoking mothers in NREM sleep; this may partly explain why such infants are more at risk of SIDS.

Effects of maternal tobacco smoking, sleeping position, and sleep state on arousal in healthy term infants

OBJECTIVES

To investigate whether a history of maternal tobacco smoking affected the maturation of arousal responses and whether sleeping position and infant age alters these relations.

DESIGN

Healthy term infants (13 born to mothers who did not smoke and 11 to mothers who smoked during pregnancy) were studied using daytime polysomnography on three occasions: (a) two to three weeks after birth, (b) two to three months after birth, and (c) five to six months after birth. Multiple measurements of arousal threshold in response to air jet stimulation were made in both active sleep (AS) and quiet sleep (QS) when infants slept both prone and supine.

RESULTS

Maternal smoking significantly elevated arousal threshold in QS when infants slept supine at 2-3 months of age (p<0.05). Infants of smoking mothers also had fewer spontaneous arousals from QS at 2-3 months in both prone (p<0.05) and supine (p<0.001) sleeping positions. In infants of non-smoking mothers, arousal thresholds were elevated in the prone position in AS at 2-3 months (p<0.01) and QS at 2-3 weeks (p<0.05) and 2-3 months (p<0.001).

CONCLUSIONS

Maternal tobacco smoking significantly impairs both stimulus induced and spontaneous arousal from QS when infants sleep in the supine position, at the age when the incidence of sudden infant death syndrome is highest.

Nicotine-induced alterations in the expression of nicotinic receptors in primary cultures from human prenatal brain

The nicotinic receptor proteins and gene transcripts for the different nicotinic receptor subunits exist in human prenatal brain already at 4-5 weeks of gestation. The early presence of nicotinic receptors suggests an important role for these receptors in modulating dendritic outgrowth, establishment of neuronal connections and synaptogenesis during development. When measurements of nicotinic receptors using [(3)H]epibatidine (labelling both the alpha3 and alpha4 subtype) and [(3)H]cytisine (labelling the alpha4 subtype) were performed in intact cells from the cortex, subcortical forebrain and mesencephalon (7.5-11 weeks of gestation), the highest specific binding for both ligands was detected in cells from mesencephalon, followed by subcortical forebrain and cortex. The effects of nicotine exposure were studied in primary cultures of prenatal brain (7.5-11 weeks of gestation). Treatment with nicotine (1-100 microM) for 3 days significantly increased the specific binding of [(3)H]epibatidine and [(3)H]cytisine in cortical cells but not in cells from subcortical forebrain and mesencephalon brain regions, indicating region-specific differences in the sensitivity to nicotine exposure. Relative quantification of mRNA showed that the expression of the nicotinic receptor subunits alpha3 and alpha7, but not alpha4, was increased in cortical cells after nicotine treatment. These findings support the assumption of a potential risk of disturbance in the functional role of nicotinic receptors during brain development as a consequence of maternal smoking during pregnancy.

Prenatal exposure to nicotine impairs protective responses of rat pups to hypoxia in an age-dependent manner

Experiments were carried out on rat pups to investigate the interaction between prenatal exposure to nicotine and postnatal age on protective responses that promote survival during exposure to hypoxia. From days 6 or 7 of gestation, pregnant rats received either nicotine (approximately 6 mg of nicotine tartrate/kg of body weight per day) or vehicle continuously via a 28-day osmotic minipump. On postnatal days 1--2, 5--6 and 10--11, the pups were exposed either to a single period of hypoxia produced by breathing an anoxic gas mixture (97% N(2) and 3% CO(2)) and their time to last gasp determined, or they were exposed repeatedly to hypoxia and their ability to autoresuscitate from primary apnea determined. Prenatal exposure to nicotine decreased the time to last gasp, but only in the 1--2-day-old animals. The total number of gasps was, however, increased in this age group due to the effect of nicotine on the gasping pattern. Furthermore, prenatal exposure to nicotine decreased the number of successful autoresuscitations and influenced the cardiorespiratory events preceding death in the 1--2- and 5--6-day-old pups but not in the 10--11-day-old pups. Thus, our experiments show that prenatal exposure to nicotine impairs protective responses of rat pups that may sustain life during exposure to hypoxia in an age-dependent manner.

Distribution of alpha 2-adrenergic receptor binding in the developing human brain stem

Rapid and dramatic changes occur in cardiorespiratory function during early human life. Catecholamines within select brain stem nuclei are implicated in the control of autonomic and respiratory function, including in the nucleus of the solitary tract and the dorsal motor nucleus of X. Animal and adult human studies have shown high binding to alpha 2-adrenergic receptors in these regions. To determine the developmental profile of brainstem alpha 2-adrenergic binding across early human life, we studied brain stems from five fetuses at midgestation, three newborns (37-38 postconceptional weeks), and six infants (44-61 postconceptional weeks). We used quantitative tissue receptor autoradiography with [3H]para-aminoclonidine as the radioligand and phentolamine as the displacer. In the fetal group, binding was high (63-93 fmol/mg tissue) in the nucleus of the solitary tract, dorsal motor nucleus of X, locus coeruleus, and reticular formation; it was low (< 32 fmol/mg tissue) in the principal inferior olive and basis pontis. Binding decreased in all regions with age: in infancy, the highest binding was in the intermediate range (32-62 fmol/mg tissue) and was localized to the nucleus of the solitary tract and dorsal motor nucleus of X. The most substantial decrease in binding (75%-85%) between the fetal and infant periods occurred in the pontine and medullary reticular formation and hypoglossal nucleus. Binding remained low in the principal inferior olive and basis pontis. The decreases in binding with age remained significant after quench correction. These data suggest that rapid and dramatic changes occur in early human life in the brain stem catecholaminergic system in regions related to cardiorespiratory control.

Heart rate response to transient chemoreceptor stimulation in term infants is modified by exposure to maternal smoking

Modulation of heart rate (HR) during transient hyperoxia, hypoxia, and hypercapnia was studied in 46 healthy term infants on 103 occasions (postnatal d 2 to 82). Twenty-three infants had smoking mothers (median, 11 cigarettes/d). Transient chemoreceptor stimuli (100% O(2), 15% O(2), or 3% CO(2)) were presented repeatedly during quiet sleep. Beat-by-beat HR and breath-by-breath ventilation were recorded continuously. The coherently averaged HR and ventilation responses to each stimulus were calculated for each infant at each age. Outcome variables (HR change from baseline to end of stimulation, maximum HR change, and time to half-maximum) were analyzed by ANOVA. Overall, HR declined during hyperoxia (median change, 4.2 beats/min) and rose during hypoxia (median change, 4.2 beats/min) and hypercapnia (median change, 4.6 beats/min). The percentage change in HR was positively correlated with the percentage change in ventilation (p < 0.001). Increasing number of cigarettes smoked by the mother was correlated with deeper HR declines and smaller HR rises (p = 0.02). For the population as a whole, the HR response lagged 3.8 s behind the ventilatory response during hyperoxia and hypoxia (p < 0.001), whereas during hypercapnia there was no significant lag. The lag in HR response in the smoke-exposed group was 2.5 s greater than that in the control group for all three stimuli (p = 0.001), and the difference increased with the number of cigarettes smoked by the mother (p < 0.01). Both pulmonary reflexes and the type of the chemoreceptor stimulus seemed to influence HR. Maternal smoking affected the magnitude and time-course of the HR response in a dose-dependent manner.

Neck extension and rotation in sudden infant death syndrome and other natural infant deaths

It has been hypothesized that some cases of sudden infant death syndrome (SIDS) are a result of neck extension and/or rotation that causes vertebral artery (VA) compression and brain stem ischemia. There is a paucity of relevant literature on this topic. Therefore, our aim was to compare neck rotation and extension in SIDS and other natural infant deaths. Cases of SIDS and other natural infant deaths within the San Diego SIDS Research Project database were analyzed retrospectively with respect to neck and body position as reported by the trained, experienced scene investigators and/or the caretakers who discovered the infants. Information was used from 246 SIDS cases and 56 cases of other natural deaths. Simultaneous neck extension and rotation was not reported in either group. When data regarding neutral/flexed/extended position and rotation of the neck were combined, no significant differences were found between the two groups (P = 0.94); 40% of the SIDS cases and 41% of the other natural death cases were found with the neck either extended or rotated (odds ratio [OR] 0.97, [reference group = neck either neutral or flexed, and not rotated], 95% confidence interval [CI] 0.45, 2.11). There were also no significant differences between the groups when neck rotation and neck extension were analyzed independent of one another. Neck rotation among cases found in the prone position was common and was not significantly different between the two groups (49% of 146 SIDS cases, 58% of 24 other natural death cases, P = 0.38, OR 0.68, 95% CI 0.28, 1.62). Neck rotation among infants found in the supine position occurred one-third as often in the SIDS group (9% of 33 cases) as in the other natural death group (29% of 14 cases); however, the difference was not significant (P = 0.17; OR 0.25, 95% CI 0.05, 1.31). Although our analysis does not exclude VA compression and brain stem ischemia in some cases of SIDS, we found no evidence to affirm its importance. This study demonstrates the importance of meticulous scene descriptions, including neck position.

Medullary serotonergic network deficiency in the sudden infant death syndrome: review of a 15-year study of a single dataset

The sudden infant death syndrome (SIDS) is the leading cause of postneonatal infant mortality in the United States today, despite a dramatic 38% decrease in incidence due to a national risk reduction campaign advocating the supine sleep position. Our research in SIDS brainstems, beginning in 1985 and involving a single, large dataset, has become increasingly focused upon a specific neurotransmitter (serotonin) and specific territories (ventral medulla and regions of the medullary reticular formation that contain secrotonergic neurons). Based on this research, we propose that SIDS, or a subset of SIDS, is due to a developmental abnormality in a medullary network composed of (at least in part) rhombic lip-derived, serotonergic neurons, including in the caudal raphé and arcuate nucleus (putative human homologue of the cat respiratory chemosensitive fields); and this abnormality results in a failure of protective responses to life-threatening stressors (e.g. asphyxia, hypoxia, hypercapnia) during sleep as the infant passes through a critical period in homeostatic control. We call this the medullary serotonergic network deficiency hypothesis. We review the triple-risk model for SIDS, the development of the dataset using tissue autoradiography for analyzing neurotransmitter receptor binding; age-dependent baseline neurochemical findings in the human brainstem during early life; the evidence for serotonergic, rhombic lip, and ventral medullary deficits in at least some SIDS victim; possible mechanisms of sudden infant death related to these deficits; and potential causes of the deficits in the medullary serotonergic network in SIDS victims. We conclude with a summary of future directions in SIDS brainstem research.

Alpha2 receptor binding in the medulla oblongata in the sudden infant death syndrome

The sudden infant death syndrome (SIDS) is the leading cause of postnatal infant mortality in the United States. Its etiology remains unknown. We propose that SIDS, or a subset of SIDS, is due to a failure of autoresuscitation, a protective brainstem response to asphyxia or hypoxia, in a vulnerable infant during a critical developmental period. Gasping is an important component of autoresuscitation that is thought to be mediated by the "gasping center" in the lateral tegmentum of the medulla, a region homologous in its cytoarchitecture and chemical anatomy to the intermediate reticular zone (IRZ) in the human. Since we found that [3H]para-aminoclonidine ([3H]PAC) binding to alpha2-adrenergic receptors localizes to this region in human infants and, thereby provides a neurochemical marker for it, we tested the hypothesis that [3H]PAC binding to alpha2-adrenergic receptors is decreased in the IRZ in SIDS victims. Using quantitative tissue autoradiography with [3H]PAC as the radioligand and phentolamine as the displacer, we analyzed alpha2-receptor binding density in the IRZ, as well as in 7 additional sites for comparison, in 10 SIDS and 10 control medullae. There were no significant differences in alpha2 receptor binding in the IRZ, vagal nuclei, or other medullary sites examined between SIDS and control cases. These results suggest that the putative gasping defect in the IRZ in SIDS victims is not related to [3H]PAC binding to alpha2-adrenergic receptors.

Nicotinic acetylcholine receptors during prenatal development and brain pathology in human aging

Nicotinic acetylcholine receptor (nAChRs) proteins and gene transcripts are already present in human prenatal brain and spinal cord at 4-6 weeks gestation, and a clear age-related increase in number of nAChRs was apparent during first trimester. In pons, there was also a parallel increase in the alpha7 mRNA level with age. The highest specific binding of [3H]epibatidine and [3H]cytisine was detected in spinal cord, pons and medulla oblongata, and binding of [125I]alpha-bungarotoxin was highest in spinal cord, medulla oblongata and mesencephalon. From the late fetal stage brain nAChRs have been shown to fall with increasing age. During aging (between 40 and 100 years) high affinity nicotine binding in the frontal cortex decreases in parallel with glutamate NMDA receptor binding ([3H]MK801). In the hippocampal formation and entorhinal cortex nicotine binding also declines with age, in common with [125I]alpha-bungarotoxin in the entorhinal cortex, but NMDA receptor binding remains unchanged. These reductions in nicotine binding with age may predispose the neo- and archicortex to the loss of nAChRs observed in age-associated neurodegenerative conditions. By contrast no loss in nAChR binding with aging is observed in the thalamus and only after the 70th decade in the striatum, although in Alzheimer's disease, Parkinson's disease and Lewy body dementia deficits in nAChRs are observed in these areas and may be associated with specific disease-related processes.

Perinatal complications associated with maternal tobacco use

The use of tobacco products by pregnant women is associated with placenta previa, abruptio placentae, premature rupture of the membranes, preterm birth, intrauterine growth restriction and sudden infant death syndrome. Approximately 15-20% of women smoke during pregnancy. It has been suggested that smoking is responsible for 15% of all preterm births, 20-30% of all infants of low birthweight, and a 150% increase in overall perinatal mortality. Cigarette smoking is one of the most important and modifiable risk factors associated with adverse perinatal outcomes.

Sleep influences on homeostatic functions: implications for sudden infant death syndrome

The mechanisms underlying the sudden infant death syndrome (SIDS) appear to have origins in the fetal environment resulting in neural damage which later compromises responses to breathing or blood pressure challenges during sleep. The deficits appear to involve alterations in neurotransmitter receptors within regions involved in chemoreception and cardiovascular control. SIDS risk is enhanced by pre- and postnatal nicotine exposure, and possibly by hypoxic experiences. The prone sleeping position plays a significant role in risk, as do head positions that minimize facial escape from enclosed spaces; elevated body temperature may also be a factor. Compensatory mechanisms, including diminished gasping ability, relative failure to arouse to a safer state, or a failure to recruit respiratory efforts to overcome a blood pressure loss have been the object of recent research efforts. The findings suggest that the fatal event involves a neurally-compromised infant, circumstances that challenge vital physiology, most likely during sleep, at a particular developmental period.

Influence of maternal smoking on autonomic nervous system in healthy infants

To determine the influence of maternal smoking on autonomic nervous system in healthy infants, 36 infants were recorded polygraphically for one night. Their mothers were defined, according to their smoking frequency during pregnancy, as "nonsmokers" (no cigarettes smoked during pregnancy) or "smokers" (10 or more cigarettes per day). The infants had a median postnatal age of 10.5 wk (range 6 to 16 wk); 18 were born to nonsmokers, and 18 to smokers. During the whole night, spectral analyses of heart rate (HR) were evaluated as a function of sleep stages. Two major peaks were recognizable: a low-frequency component (LF) related to sympathetic and parasympathetic activities and a high-frequency component (HF) reflecting parasympathetic tonus. The ratio of LF/HF powers was calculated as an index of sympathovagal interaction. In REM sleep, "smokers" infants were characterized by significantly lower HF powers and normalized HF powers, and higher LF/HF ratios than "nonsmokers." The finding did not reach statistical significance in NREM sleep. In conclusion, maternal smoking induced changes in autonomic control and maturation in infants. These effects of cigarette smoke exposure can be added to those already reported and offer additional evidence for counseling mothers to stop smoking.

Prenatal exposure to cigarette smoking is associated with a decrease in arousal in infants

OBJECTIVE

Sudden infant death syndrome has been related to both exposure to prenatal cigarette smoke and impaired arousability from sleep. We evaluated whether healthy infants born to mothers who smoked during pregnancy had higher auditory arousal thresholds than those born to mothers who did not smoke and whether the effects of smoking occurred before birth.

STUDY DESIGN

Twenty-six newborns were studied with polygraphic recordings for 1 night: 13 were born to mothers who did not smoke, and 13 were born to mothers who smoked (>9 cigarettes per day). Other infants with a median postnatal age of 12 weeks were also studied, 21 born to nonsmoking mothers and 21 born to smoking mothers. White noise of increasing intensity was administered during rapid eye movement sleep to evaluate arousal and awakening thresholds.

RESULTS

More intense auditory stimuli were needed to induce arousals in newborns (P =.002) and infants (P =. 044) of smokers than in infants of nonsmokers. Behavioral awakening occurred significantly less frequently in the newborns of smokers (P =.002) than of nonsmokers.

CONCLUSIONS

Newborns and infants born to smoking mothers had higher arousal thresholds to auditory challenges than those born to nonsmoking mothers. The impact of exposure to cigarette smoke occurred before birth.

Increased airway smooth muscle in sudden infant death syndrome

The underlying pathophysiological mechanism behind death in the sudden infant death syndrome (SIDS) is uncertain. Although infants dying of SIDS frequently have a postmortem examination performed, no specific diagnostic pathology in any organ system has been identified. Previous theories relating to the cause of death in SIDS have included increased lower airway closure. We examined the airway morphometry of 57 infants who died of SIDS and compared these findings with those obtained from 21 age-matched infants who had died of non-SIDS causes. Airway wall dimensions, epithelial thickness, and the area of smooth muscle within the airway wall were measured. Airways from infants who died of SIDS showed a significantly higher proportion of airway smooth muscle than control airways when corrected for age and sex (p < 0.01). There was no significant difference between the groups for wall thickness or epithelial thickness. Increased airway smooth muscle in infants who have died of SIDS may contribute to excessive airway narrowing, raising the possibility that the cause of death in this condition is related to abnormalities in lower airway function.

Maternal nicotine depresses eupneic ventilation of neonatal rats

Maternal smoking is a risk factor for the sudden infant death syndrome (SIDS). We hypothesized that pre-natal exposure to nicotine would result in abnormalities of ventilatory activity in newborns. Neonatal rats which had been exposed to nicotine had significantly lower minute ventilation breathing air and hypoxic gas mixtures than did control animals. In both groups, anoxia elicited gasping which was equally effective in restoring eupnea. Maternal exposure to nicotine may result in a reduced metabolic rate and/or chronic hypoventilation in the newborn.

Perinatal nicotine exposure impairs ability of newborn rats to autoresuscitate from apnea during hypoxia

Failure to autoresuscitate by hypoxic gasping during prolonged sleep apnea has been suggested to play a role in sudden infant death. Furthermore, maternal smoking has been repeatedly shown to be a risk factor for sudden infant death. The present experiments were carried out on newborn rat pups to investigate the influence of perinatal exposure to nicotine (the primary pharmacological and addictive agent in tobacco) on their time to last gasp during a single hypoxic exposure and on their ability to autoresuscitate during repeated exposure to hypoxia. Pregnant rats received either nicotine (6 mg. kg-1. 24 h-1) or vehicle continuously from day 6 of gestation to days 5 or 6 postpartum via an osmotic minipump. On days 5 or 6 postpartum, pups were exposed either to a single period of hypoxia (97% N2-3% CO2) and their time to last gasp was determined, or they were exposed repeatedly to hypoxia and their ability to autoresuscitate from primary apnea was determined. Perinatal exposure to nicotine did not alter the time to last gasp, but it did impair the ability of pups to autoresuscitate from primary apnea. After vehicle, the pups were able to autoresuscitate from 18 +/- 1 (SD) periods of hypoxia, whereas, after nicotine, the pups were able to autoresuscitate from only 12 +/- 2 periods (P < 0.001) of hypoxia. Thus our data provide evidence that perinatal exposure to nicotine impairs the ability of newborn rats to autoresuscitate from primary apnea during repeated exposure to hypoxia, such as may occur during episodes of prolonged sleep apnea.

Postnatal changes of nicotinic acetylcholine receptor alpha 2, alpha 3, alpha 4, alpha 7 and beta 2 subunits genes expression in rat brain

Postnatal changes of nicotinic acetylcholine receptor (nAChR) alpha 2, alpha 3, alpha 4, alpha 7 and beta 2 subunits mRNAs were investigated in rat brain using ribonuclease protection assay. Multiple developmental patterns were observed: (1) transient expression during the first few postnatal weeks; alpha 2 in the hippocampus and brain stem, alpha 3 in the striatum, cerebellum and cortex, alpha 4 in the hippocampus, striatum and cerebellum, alpha 7 in the cerebellum and beta 2 in the striatum. (2) Constant expression across development; alpha 2 and alpha 3 in the thalamus, alpha 4 in the cortex, thalamus and brain stem, alpha 7 in the thalamus and brain stem and beta 2 in all brain regions except striatum. (3) Non-detection across development; alpha 2 in the cortex, striatum and cerebellum. (4) Increase with age; alpha 7 in the cortex and hippocampus. (5) Bell-shaped development; alpha 7 in the striatum. Postnatal changes of nAChR isoforms in different brain regions of rat were investigated by receptor binding assays. The developmental patterns of [3H]epibatidine and (-)-[3H]nicotine binding sites were similar to each other in each brain region, but different from that of [3H] alpha-bungarotoxin binding sites. No obvious correlation was observed between the developmental patterns of [3H] alpha-bungarotoxin, [3H]epibatidine and (-)-[3H]nicotine binding sites and corresponding subunits mRNAs. These results indicate that multiple mechanisms are involved in changes of gene expression of nAChRs subunits in the brain of developing rats.

Pontine cholinergic respiratory depression in neonatal and young rats

We postulated that activation of pontine cholinergic mechanisms would cause respiratory depression in neonatal and young rats. Phrenic activity was recorded in decerebrate, paralyzed, ventilated and vagotomized rats of 4 to 22 days after birth. Small volumes (10-60 nl) of carbachol (44-88 mM) were injected into the medial portion of the rostral pons. The injection of carbachol, but not saline, decreased phrenic peak activity (83 +/- 6% of control) and respiratory frequency (64 +/- 9.5% of control) within 2 min following the injection in neonates and the depression lasted for less than 10 min. The site of injection in the pontine reticular formation was confirmed by histology. Results suggest that cholinergic mechanisms in the medial pons depress respiratory activity in the neonate.

Regional distribution of nicotinic receptors during prenatal development of human brain and spinal cord

The development of nicotinic acetylcholine receptors (nAChRs) in brains from human fetuses of 4-12 weeks gestational age was studied. The expression of nAChR subunit mRNAs was analyzed using reverse transcriptase-polymerase chain reaction. Expression of alpha 3, alpha 4, alpha 5, alpha 7, beta 2, beta 3 and beta 4 mRNA were all detected in the prenatal spinal cord, medulla oblongata, pons, cerebellum, mesencephalon, subcortical forebrain and cortex during first trimester development. Relative quantification of mRNA showed that the highest levels for alpha 3, alpha 4 and alpha 7 were expressed in the spinal cord, alpha 5 was most abundant in the cortex and beta 3 was highest in the cerebellum. beta 4 seemed to be equally distributed in all regions whereas beta 2 was high in the cortex and cerebellum. A comparison of expression of nAChR subunit mRNAs in the cortex and cerebellum of prenatal and aged (54-81 years) brain showed that mRNA levels for alpha 4, alpha 5, alpha 7, beta 2 and beta 4 were significantly higher in the prenatal cortex and cerebellum than in aged brain, whereas the level of alpha 3 transcript was similar, and beta 3 significantly higher in aged cortex. Specific binding of [3H]-epibatidine to prenatal brain membranes was detected as early as 4-5 weeks of gestation in the spinal cord, medulla oblongata, pons and subcortical forebrain. A positive correlation between gestational age and [3H]-epibatidine and [3H]-cytisine binding was found in several brain regions. The highest specific binding of [3H]-epibatidine and [3H]-cytisine was detected in the spinal cord, pons and medulla oblongata and the lowest in the cortex. Saturation analysis of [3H]-cytisine binding in both prenatal and aged brain were best fit by a model for a single site, whereas binding data for [3H]-epibatidine revealed two classes of binding sites. The early presence of nAChR proteins and gene transcripts shown in the present study suggests an important role for nAChRs in modulating dendritic outgrowth, establishment of neuronal connections and synaptogenesis during development.

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.

A case-control study of smoking and sudden infant death syndrome in the Scandinavian countries, 1992 to 1995. The Nordic Epidemiological SIDS Study

AIM

To establish whether smoking is an independent risk factor for sudden infant death syndrome (SIDS), if the effect is mainly due to prenatal or postnatal smoking, and the effect of smoking cessation.

METHODS

The analyses were based on data from the Nordic epidemiological SIDS study, a case-control study with 244 cases and 869 controls. Odds ratios were computed by conditional logistic regression analysis.

RESULTS

Smoking emerged as an independent risk factor for SIDS, and the effect was mainly mediated through maternal smoking in pregnancy (crude odds ratio 4.0 (95% confidence interval 2.9 to 5.6)). Maternal smoking showed a marked dose-response relation. There was no effect of paternal smoking if the mother did not smoke. Stopping or even reducing smoking was beneficial. SIDS cases exposed to tobacco smoke were breast fed for a shorter time than non-exposed cases, and feeding difficulties were also more common.

CONCLUSIONS

Smoking is an independent risk factor for SIDS and is mainly mediated through maternal smoking during pregnancy. Stopping smoking or smoking less may be beneficial in reducing the risk of SIDS.

Auditory arousal thresholds are higher when infants sleep in the prone position

OBJECTIVE

To evaluate the possibility that infants sleeping in the prone position have higher arousal thresholds to auditory challenges than when sleeping in the supine position.

STUDY DESIGN

Polygraphic recordings were performed for 1 night in 25 healthy infants with a median age of 9 weeks. The infants were exposed to white noises of increasing intensities while sleeping successively in the prone and supine positions, or vice versa. Arousal thresholds were defined by the auditory stimuli needed to induce polygraphic arousals.

RESULTS

Three infants were excluded from the study because they awoke while their position was being changed. For the 22 infants included in the analysis, more intense auditory stimuli were needed to arouse the infants in the prone position than those in the supine body position (p = 0.011). Arousal thresholds were higher in the prone than in the supine position in 15 infants; unchanged in 4 infants; and lower in the prone position in 3 infants (p = 0.007).

CONCLUSIONS

Infants show higher arousal thresholds to auditory challenges when sleeping in the prone position than when sleeping in the supine position. The finding could be relevant to mechanisms concerned with the reported association between sudden deaths and the prone sleeping position in infants.

Developmental changes in heterogeneous patterns of neurotransmitter receptor binding in the human interpeduncular nucleus

The interpeduncular nucleus (IPN) exhibits many complex features, including multiple subnuclei, widespread projections with the forebrain and brainstem, and neurotransmitter heterogeneity. Despite the putative importance of this nucleus, very little is known about its neurochemical development in the human. The human IPN is cytoarchitectonically simple, unlike the rat IPN, which displays considerable heterogeneity. In the following study, we hypothesized that the developing human IPN is neurochemically heterogeneous despite its cytological simplicity. The chemoarchitecture in this study was defined by neurotransmitter receptor binding patterns by using quantitative tissue autoradiography for the muscarinic, nicotinic, serotoninergic, opioid, and kainate receptors. We examined neurotransmitter receptor binding in the developing human IPN in a total of 15 cases. The midbrains of five midgestational fetuses (19-26 gestational weeks) and six infants (38-74 postconceptional weeks) were examined. The midbrain of one child (4 years) and three adults (20-68 years) were analyzed as indices of maturity. At all ages examined, high muscarinic binding was localized to the lateral subdivision of the IPN, high serotoninergic binding was localized to the dorsal IPN, and high opioid receptor binding was localized to the medial IPN. The developmental profile was unique for each radioligand. We report a heterogenous distribution of neurotransmitter receptor binding in the developing human IPN, which supports a complex role for it in human brain function.

Human neuronal nicotinic receptors

Nicotine is a very widely used drug of abuse, which exerts a number of neurovegetative, behavioural and psychological effects by interacting with neuronal nicotinic acetylcholine receptors (NAChRs). These receptors are distributed widely in human brain and ganglia, and form a family of ACh-gated ion channels of different subtypes, each of which has a specific pharmacology and physiology. As human NAChRs have been implicated in a number of human central nervous system disorders (including the neurodegenerative Alzheimer's disease, schizophrenia and epilepsy), they are suitable potential targets for rational drug therapy. Much of our current knowledge about the structure and function of NAChRs comes from studies carried out in other species, such as rodents and chicks, and information concerning human nicotinic receptors is still incomplete and scattered in the literature. Nevertheless, it is already evident that there are a number of differences in the anatomical distribution, physiology, pharmacology, and expression regulation of certain subtypes between the nicotinic systems of humans and other species. This review will attempt to survey the major achievements reached in the study of the structure and function of NAChRs by examining the molecular basis of their functional diversity viewed mainly from pharmacological and biochemical perspectives. It will also summarize our current knowledge concerning the structure and function of the NAChRs expressed by other species, and the newly discovered drugs used to classify their numerous subtypes. Finally, the role of NAChRs in behaviour and pathology will be considered.

Nicotinic and muscarinic cholinergic receptor binding in the human hippocampal formation during development and aging

High-affinity nicotine, alpha-bungarotoxin (alpha BT) and muscarinic receptor binding was measured in the human hippocampal formation in a series of 57 cases aged between 24 weeks gestation and 100 years. Changes in nicotine receptor binding during development and aging were more striking than differences in alpha BT and muscarinic binding. Nicotine binding was higher at the late foetal stage than at any other subsequent time in all areas investigated. In the hippocampus a fall in binding then occurred within the first six months of life, with little or no subsequent fall during aging, whereas in the entorhinal cortex and the presubiculum the major loss of nicotine binding occurred after the fourth decade. alpha BT binding was significantly elevated in the CA 1 region, but in no other region of the hippocampus, in the late foetus, and there was also a fall in alpha BT binding in the entorhinal cortex during aging from the second decade. The modest changes in total muscarinic binding, which appeared to reflect those in M1 and M3 + 4 rather than M2 binding, were a rise in the entorhinal cortex between the foetal stage and childhood and a tendency for receptors to fall with age in the hippocampus and subicular complex. These findings implicate mechanisms controlling the expression of nicotinic receptors to a greater extent than muscarinic receptors in postnatal development and aging in the human hippocampus.

The role of the cholinergic system in the development of the human cerebellum

High affinity (-)nicotine ([3H]nicotine), alpha-bungarotoxin ([125I]alpha-bungarotoxin) and muscarinic binding ([3H]N-methyl scopolamine) in the human cerebellum were compared between the foetal period (23-39 weeks gestation) and young adulthood (14-34 years) in an autoradiographic study. To estimate proportions of muscarinic receptor subtypes variable wash times and displacement with pirenzepine were employed. [3H]Nicotine binding and total muscarinic binding in foetuses exceeded that in young adults by a factor of 6 and 2 respectively in the dentate nucleus, and by a factor of 3 in white matter. [3H]Nicotine and muscarinic binding was also higher in the foetal external granule cell layer than in the internal granule cell layer of adult, [125I]alpha-Bungarotoxin binding was raised in the dentate nucleus of the foetus compared with the adult. The M2 subtype appeared to be the predominant muscarinic receptor in the cerebellum, however it tended to represent a lower proportion of the muscarinic binding in the foetus than the adult. All 3 receptor types were highest in the foetal brainstem where the M3 + M4 muscarinic subtypes appeared to predominate. The p75 nerve growth factor receptor, measured by immunocytochemistry, in common with cholinergic receptors, paralleled choline acetyltransferase activity which has previously been reported to be high in the cerebellum during late foetal development and to fall in adulthood.

Three-dimensional distribution of [3H]quinuclidinyl benzilate binding to muscarinic cholinergic receptors in the developing human brainstem

Acetylcholine has been implicated in brainstem mechanisms of cardiac and ventilatory control, arousal, rapid eye movement (REM) sleep, and cranial nerve motor activity. Virtually nothing is known about the developmental profiles of cholinergic perikarya, fibers, terminals, and/or receptors in the brainstems of human fetuses and infants. This study provides baseline information about the quantitative distribution of muscarinic cholinergic receptors in fetal and infant brainstems. Brainstem sections were analyzed from 6 fetuses (median age: 21.5 postconceptional weeks), 4 premature infants (median age: 26 postconceptional weeks), and 11 infants (median age: 53 postconceptional weeks). One child and three adult brainstems were examined as indices of maturity for comparison. The postmortem interval in all cases was less than or equal to 24 hours (median: 10 hours). Muscarinic receptors were localized by autoradiographic methods with the radiolabeled antagonist [3H]quinuclidinyl benzilate ([3H]QNB). Computer-based methods permitted quantitation of [3H]QNB binding in specific nuclei and three-dimensional reconstructions of binding patterns. By midgestation, muscarinic cholinergic receptor binding is already present and regionally distributed, with the highest binding levels in the interpeduncular nucleus, inferior colliculus, griseum pontis, nucleus of the solitary tract, motor cranial nerve nuclei, and reticular formation. During the last half of gestation, [3H]QNB binding decreases in most, but not all of the nuclei sampled. The most substantial decline occurs in the reticular formation of the medulla and pons, a change that is not fully explained by progressive myelination and lipid quenching. Binding levels remain essentially constant in the inferior olive and griseum pontis. Around the time of birth or shortly thereafter, the relative distribution of binding becomes similar to that in the adult, with the highest levels in the interpeduncular nucleus and griseum pontis, although binding levels are higher overall in the infant. In the rostral pontine reticular formation, paramedian bands of high muscarinic binding are present which do not correspond to a cytoarchitectonically defined nucleus. By analogy to animal studies, these bands may comprise a major cholinoreceptive region of the human rostral pontine reticular formation involved in REM sleep. In the human interpeduncular nucleus in all age periods examined, muscarinic binding localizes to the lateral portions bilaterally, indicative of a heterogeneous chemoarchitecture. Muscarinic binding is high in the arcuate nucleus, a component of the putative respiratory chemosensitive fields along the ventral surface of the infant medulla. This observation is consistent with the known effects of muscarinic agents on chemosensitivity and ventilatory responses applied to the ventral medullary surface in animal models. The nonuniform distribution of muscarinic binding in the caudorostral plane in individual brainstem nuclei, as illustrated by three-dimensional reconstructions, underscores the need for rigorous sampling at precisely matched levels in quantitative studies. This study provides basic information toward understanding the neurochemical basis of brainstem disorders involving dysfunction of autonomic and ventilatory control, arousal, and REM sleep in preterm and full-term newborns and infants and for developing cholinergic drugs for such disorders in the pediatric population.

Deficient hypoxia awakening response in infants of smoking mothers: possible relationship to sudden infant death syndrome

OBJECTIVE

To determine whether fetal exposure to cigarette smoke impairs postnatal chemoreceptor control of ventilation and hypercapnic and hypoxic awakening responses.

STUDY DESIGN

Smoking (n = 13) and nonsmoking (n = 34) women were recruited during pregnancy. Serum cotinine levels were measured to assess level of nicotine exposure. The infants were studied at 2 to 3 months of age for ventilatory and awakening responses to hypoxia (17%, 15% and 13% inspired O2) and hypercapnia 4%, 6%, and 8% inspired CO2). Continuous measures were analyzed with unpaired t tests and analysis of variance for repeated measures. Proportions of awakening and periodic breathing were analyzed by means of a comparison of proportions.

RESULTS

The infants of smokers had lower birth weights (3022 +/- 566 vs 3518 +/- 491 gm; p < or = 0.005) and were older at the time of study (10.4 +/- 2.8 vs 8.7 +/- 1.3 weeks; p < 0.01) than the control infants. Maternal cotinine levels were higher in smokers (97.8 +/- 107 ng/ml vs no cotinine; p < 0.0001). More infants of smokers failed to awaken with hypoxia than did control infants (54% vs 15%; p = 0.006). The ventilatory responses to hypoxia and hypercapnia were similar in the two groups. All infants awakened with hypercapnia, and there was no difference in the awakening threshold for carbon dioxide (50.3 +/- 4.5 vs 48.3 +/- 5.4 mm Hg; p = 0.28).

CONCLUSION

Infants of mothers who smoked during pregnancy have deficient hypoxic awakening responses, which may contribute to the increased risk of sudden infant death syndrome in infants of smoking mothers.

Developmental changes in [3H]kainate binding in human brainstem sites vulnerable to perinatal hypoxia-ischemia

The human brainstem is especially susceptible to hypoxia-ischemia in early life. To test the hypothesis that the period of vulnerability of the developing human brainstem to hypoxia-ischemia correlates with a transient elevation in kainate receptor binding, we compared the quantitative distribution of [3H]kainate binding in brainstem nuclei between four fetuses (19-26 gestational weeks), four infants (one to nine months), and three "mature" individuals (one child and two adults) without neurological disease. Quantitative tissues autoradiography was used. [3H]Kainate binding decreased in all brainstem regions from early life to maturity with the most significant decreases occurring in nuclei thought to be especially vulnerable to perinatal hypoxia-ischemia (e.g. principal inferior olive, griseum pontis, inferior colliculus and reticular core). The highest binding in the fetal and infant period was found primarily in the major cerebellar-relay nuclei. In the inferior olive and arcuate nucleus, binding increased from the fetal to the infant period, and then fell 50-61% to low mature levels. In the griseum pontis, binding decreased 60% between the fetal and mature periods. In the reticular formation, binding fell 67-78% from the fetal to mature period. These data support a correlation between the period of brainstem vulnerability to hypoxia-ischemia in early life to transient elevation in kainate binding, and are particularly relevant to the topographic brainstem patterns in perinatal hypoxia-ischemia of infantile olivary gliosis, pontosubicular necrosis and reticular core damage. Striking localization of [3H]kainate binding to rhombic lip derivatives further suggests that kainate receptors may be involved in the development and function of human brainstem-cerebellar circuitry.

A reexamination of the risk factors for the sudden infant death syndrome

OBJECTIVE

To determine which risk factors are specific for the sudden infant death syndrome (SIDS) rather than characteristic of postneonatal deaths in general.

STUDY POPULATION

The live births and infant death cohorts of the 1988 National Maternal and Infant Health Survey.

METHODS

Information on live births, deaths from SIDS, and postneonatal deaths from other causes was abstracted from the National Maternal and Infant Health Survey. To account for oversampling of certain populations, the data were weighted to reflect national counts. Risk factors were defined as black race, birth weight less than 1500 gm, birth weight less than 2500 gm, gestational age at birth less than 37 weeks, 5-minute Apgar score less than 7, male gender, more than two previous pregnancies, maternal age less than 20 years, maternal education level less than 12 years, multiple births, and maternal smoking during pregnancy. Odds ratios (ORs) and 95% confidence intervals (Cls) were calculated to compare the SIDS with the live births cohort, infants who died of other causes with the live births cohort, and SIDS with non-SIDS deaths. The population-attributable risk percentage was computed for risk factors independently associated with SIDS when compared with other postneonatal deaths.

RESULTS

For all characteristics other than a 5-minute Apgar score less than 7, the ORs comparing infants who died of SIDS with the live births cohort were significantly greater than 1.0. Similarly, ORs comparing infants who died of other causes with the live births cohort were also greater than 1.0, except for male gender. When the two infant death cohorts were compared, only maternal smoking during pregnancy and low maternal education level were significantly more common among the SIDS group. After we controlled for cigarette smoking, the adjusted OR for low maternal education level was not significantly greater than 1.0. However, even after control for low maternal education level, prenatal exposure to tobacco was significantly more common among the SIDS group than in infants dying of other causes (OR = 1.97; 95% Cl, 1.59 to 2.45). On the basis of an adjusted OR of 2.92 when the SIDS group was compared with the live births cohort, the population-attributable risk percentage for maternal smoking as a risk factor for SIDS was 30%.

CONCLUSION

Among characteristics generally thought to be risk factors, only maternal smoking during pregnancy was independently associated with SIDS. Data from this nationally representative sample indicate that if women refrained from smoking while pregnant, up to 30% of SIDS might be prevented.

Genetic and environmental aspects of the role of nicotinic receptors in neurodegenerative disorders: emphasis on Alzheimer's disease and Parkinson's disease

As neurodegenerative disorders are better characterized, the importance of genetic and environmental interactions is becoming more evident. Among the neurodegenerative disorders, Alzheimer's disease and Parkinson's disease are both characterized by large losses of nicotinic binding sites in brain. In addition, losses in nicotinic receptors occur during normal aging. Chronic administration of nicotine in man or experimental animals increases the number of nicotinic receptors in brain. Nicotine has been shown to possess some neuroprotective properties for both cholinergic and dopaminergic neurons. These neuroprotective properties, when better understood, may provide important information on normal aging and neurodegenerative disorder related neuronal cell death. Understanding the functional aspects of neuronal nicotinic receptor subtypes may lead to successful therapeutic treatments or disease preventative strategies for neurodegenerative disorders.