Sudden infant death syndrome: altered aminergic-cholinergic synaptic markers in hypothalamus

Hypothalamic volume and asymmetry in the pediatric population: a retrospective MRI study

This study investigated age- and sex-related changes in the volumetric development and asymmetry of the normal hypothalamus from birth to 18. Individuals aged 0-18 with MRI from 2012 to 2020 were selected for this retrospective study. Seven hundred individuals (369 [52.7%] Males) who had 3D-T1 sequences and were radiologically normal were included in the study. Hypothalamus volume was calculated using MRICloud automated segmentation pipelines. Hypothalamus asymmetry was calculated as the difference between right and left volumes divided by the mean (in percent). The measurement results of 23 age groups were analyzed with SPSS (ver.23). The mean hypothalamic volume in the first year of life reached 69% of the mean hypothalamic volume between 0 and 18 years (1119.01 ± 196.09 mm³), 88% in the second year. The mean volume of the hypothalamus without mammillary body increased in the five-age segment, while it increased in the six-age segment with mammillary body. Although the hypothalamus volumes of males were larger than females in all age groups, a significant difference was found between the age groups of 3-8 and 12-18 years (p < 0.05). In the pediatric brain, the hypothalamus was right-lateralized between 2.39% and 14.02%. The first 2 years of life were critical in the volumetric development of the hypothalamus. A segmental and logarithmic increase in the hypothalamus volume was demonstrated. In the pediatric brain, asymmetry and sexual dimorphism were detected in the hypothalamus. Information on normal hypothalamus structure and development facilitates the recognition of abnormal developmental trajectories.

The α7 and β2 nicotinic acetylcholine receptor subunits regulate apoptosis in the infant hippocampus, and in sudden infant death syndrome (SIDS)

Apoptosis is increased in the hippocampus of infants who died of sudden infant death syndrome (SIDS), yet it is not known via which mechanism this has occurred. Following existing support for a role of the α7 and β2 nicotinic acetylcholine receptor (nAChR) subunits in apoptotic regulation, we aimed to determine whether these subunits are altered in the SIDS hippocampus and if they are correlated with cell death markers of active caspase-3 (Casp-3) and TUNEL. Further analyses were run according to the presence of major SIDS risk factors related to hypoxia (bed-sharing and prone sleeping), infection (presence of an upper respiratory tract infection (URTI)), cigarette smoke exposure and gender. Immunohistochemical expression of the markers was studied in 4 regions of the hippocampus (Cornu Ammonis (CA)1, CA2, CA3, CA4) and subiculum amongst 52 infants (aged 1-7 months) who died suddenly and unexpectedly (SUDI) and for whom the cause of death was explained (eSUDI; n = 9), or not and characterised as SIDS I (n = 8) and SIDS II (n = 35) according to the San Diego diagnostic criteria. Results showed that SIDS II infants had widespread increases in TUNEL compared with eSUDI and SIDS I infants, as well as increased α7 and Casp-3 in CA2 compared to eSUDI infants, although these changes were predominant amongst infants who did not bed-share. Cigarette smoke exposure had minimal effects on the markers, while an URTI was associated with changes in all markers (after accounting for bed-sharing). Our findings support the role of nAChRs in regulating apoptosis in the SIDS hippocampus, and highlight the need for separate analysis according to risk factors.

The α3 and α4 nicotinic acetylcholine receptor (nAChR) subunits in the brainstem medulla of sudden infant death syndrome (SIDS)

SIDS occurs in early infancy and predominantly during a sleep period. Abnormalities in nicotine receptor binding and in the expression of the nicotinic acetylcholine receptor (nAChR) subunits α7 and β2 have been reported in the brainstem of SIDS infants. This study focuses on the α3 and α4 nAChR subunits as α3 is important for early postnatal survival while α4 is crucial for nicotine-elicited antinociception and sleep-wake cycle regulation. Tissue from the rostral medulla of infants who died with a known cause of death (eSUDI, n = 7), and from SIDS classified as SIDS I (n = 8) and SIDS II (n = 27), was immunohistochemically stained for the α3 and α4 nAChR subunits and quantified in 9 nuclei comparing amongst these groups. The association with risk factors of sex, cigarette smoke exposure, upper respiratory tract infection (URTI), prone sleeping and bedsharing was also evaluated. Results showed that only α4 changes (increase) were evident in SIDS, occurring in the hypoglossal and cuneate nuclei of SIDS II infants and the nucleus of the spinal trigeminal tract of SIDS I infants. Amongst the SIDS infants, cigarette smoke exposure was only associated with decreased α4 in cribriform fibre tracts, while sex and bedsharing were associated with increases in α3 in the dorsal motor nucleus of the vagus and solitary nucleus, respectively. Combined, these findings suggest that abnormalities in endogenous acetylcholine synthesis and regulation may underlie the altered α3 and α4 nAChR subunit expressions in the SIDS brainstem medulla since the changes were not related to cigarette smoke exposure.

Neuropathological Developments in Sudden Infant Death Syndrome

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

Sudden Infant Death Syndrome - Role of Trigeminocardiac Reflex: A Review

Sudden infant death syndrome (SIDS) is an unexplained death in infants, which usually occurs during sleep. The cause of SIDS remains unknown and multifactorial. In this regard, the diving reflex (DR), a peripheral subtype of trigeminocardiac reflex (TCR), is also hypothesized as one of the possible mechanisms for this condition. The TCR is a well-established neurogenic reflex that manifests as bradycardia, hypotension, apnea, and gastric hypermotility. The TCR shares many similarities with the DR, which is a significant physiological adaptation to withstand hypoxia during apnea in many animal species including humans in clinical manifestation and mechanism of action. The DR is characterized by breath holding (apnea), bradycardia, and vasoconstriction, leading to increase in blood pressure. Several studies have described congenital anomalies of autonomic nervous system in the pathogenesis of SIDS such as hypoplasia, delayed neuronal maturation, or decreased neuronal density of arcuate nucleus, hypoplasia, and neuronal immaturity of the hypoglossal nucleus. The abnormalities of autonomic nervous system in SIDS may explain the role of TCR in this syndrome involving sympathetic and parasympathetic nervous system. We reviewed the available literature to identify the role of TCR in the etiopathogenesis of SIDS and the pathways and cellular mechanism involved in it. This synthesis will help to update our knowledge and improve our understanding about this mysterious, yet common condition and will open the door for further research in this field.

Decreased orexin (hypocretin) immunoreactivity in the hypothalamus and pontine nuclei in sudden infant death syndrome

Infants at risk of sudden infant death syndrome (SIDS) have been shown to have dysfunctional sleep and poor arousal thresholds. In animal studies, both these attributes have been linked to impaired signalling of the neuropeptide orexin. This study examined the immunoreactivity of orexin (OxA and OxB) in the tuberal hypothalamus (n = 27) and the pons (n = 15) of infants (1-10 months) who died from SIDS compared to age-matched non-SIDS infants. The percentage of orexin immunoreactive neurons and the total number of neurons were quantified in the dorsomedial, perifornical and lateral hypothalamus at three levels of the tuberal hypothalamus. In the pons, the area of orexin immunoreactive fibres were quantified in the locus coeruleus (LC), dorsal raphe (DR), laterodorsal tegmental (LDT), medial parabrachial, dorsal tegmental (DTg) and pontine nuclei (Pn) using automated methods. OxA and OxB were co-expressed in all hypothalamic and pontine nuclei examined. In SIDS infants, orexin immunoreactivity was decreased by up to 21 % within each of the three levels of the hypothalamus compared to non-SIDS (p ≤ 0.050). In the pons, a 40-50 % decrease in OxA occurred in the all pontine nuclei, while a similar decrease in OxB immunoreactivity was observed in the LC, LDT, DTg and Pn (p ≤ 0.025). No correlations were found between the decreased orexin immunoreactivity and previously identified risk factors for SIDS, including prone sleeping position and cigarette smoke exposure. This finding of reduced orexin immunoreactivity in SIDS infants may be associated with sleep dysfunction and impaired arousal.

Monoamine oxidase A gene polymorphism and the pathogenesis of sudden infant death syndrome

OBJECTIVES

To test the hypothesis that there is a significant association between functionally relevant allelic variants of the monoamine oxidase A (MAO-A) polymorphism and sudden infant death syndrome (SIDS).

STUDY DESIGN

In a case-control study of 142 cases of SIDS and 280 sex-matched control cases, the distribution of allelic and genotype variants of a promoter polymorphism of the MAO-A gene was examined using polymerase chain reaction locus amplification and fluorescence based fragment length analysis.

RESULTS

There was a significantly differential distribution of allelic and genotype variants between females with SIDS and controls. Moreover, there was a significant association between SIDS in females and allelic and genotype variants, each related to a higher transcriptional activity at the MAO-A locus.

CONCLUSIONS

Our results suggest a role of MAO-A in female SIDS pathogenesis exerted by functionally relevant allelic and genotype variants of the MAO-A polymorphism. However, with the complex and inconsistent evidence available to date, the impact of the MAO-A promoter polymorphism on SIDS etiology remains unclear.

Endogenous inhibition of the trigeminally evoked neurotransmission to cardiac vagal neurons by muscarinic acetylcholine receptors

Stimulation of the nasal mucosa by airborne irritants or water evokes a pronounced bradycardia accompanied by peripheral vasoconstriction and apnea. The dive response, which includes the trigeminocardiac reflex, is among the most powerful autonomic responses. These responses slow the heart rate and reduce myocardial oxygen consumption. Although normally cardioprotective, exaggeration of this reflex can be detrimental and has been implicated in cardiorespiratory diseases, including sudden infant death syndrome (SIDS). An essential component of the diving response and trigeminocardiac reflex is activation of the parasympathetic cardiac vagal neurons (CVNs) in the nucleus ambiguus that control heart rate. This study examined the involvement of cholinergic receptors in trigeminally evoked excitatory postsynaptic currents in CVNs in an in vitro preparation from rats. CVNs were identified using a retrograde tracer injected into the fat pads at the base of the heart. Application of the acetylcholinesterase inhibitor neostigmine significantly decreased the amplitude of glutamatergic neurotransmission to CVNs on stimulation of trigeminal fibers. Whereas nicotine did not have any effect on the glutamatergic responses, the muscarinic acetylcholine receptor (mAChR) agonist bethanechol significantly decreased the excitatory neurotransmission. Atropine, an mAChR antagonist, facilitated these responses indicating this trigeminally evoked brain stem pathway in vitro is endogenously inhibited by mAChRs. Tropicamide, an m4 mAChR antagonist, prevented the inhibitory action of the muscarinic agonist bethanechol. These results indicate that the glutamatergic synaptic neurotransmission in the trigeminally evoked pathway to CVNs is endogenously inhibited in vitro by m4 mAChRs.

Arousal from sleep mechanisms in infants

Arousals from sleep allow sleep to continue in the face of stimuli that normally elicit responses during wakefulness and also permit awakening. Such an adaptive mechanism implies that any malfunction may have clinical importance. Inadequate control of arousal in infants and children is associated with a variety of sleep-related problems. An excessive propensity to arouse from sleep favors the development of repeated sleep disruptions and insomnia, with impairment of daytime alertness and performance. A lack of an adequate arousal response to a noxious nocturnal stimulus reduces an infant's chances of autoresuscitation, and thus survival, increasing the risk for Sudden Infant Death Syndrome (SIDS). The study of arousability is complicated by many factors including the definition of an arousal; the scoring methodology; the techniques used (spontaneous arousability versus arousal responses to endogenous or exogenous stimuli); and the confounding factors that complicate the determination of arousal thresholds by changing the sleeper's responses to a given stimulus such as prenatal drug, alcohol, or cigarette use. Infant age and previous sleep deprivation also modify thresholds. Other confounding factors include time of night, sleep stages, the sleeper's body position, and sleeping conditions. In this paper, we will review these different aspects for the study of arousals in infants and also report the importance of these studies for the understanding of the pathophysiology of some clinical conditions, particularly SIDS.

Medullary serotonin defects and respiratory dysfunction in sudden infant death syndrome

Sudden infant death syndrome (SIDS) is defined as the sudden and unexpected death of an infant less than 12 months of age that occurs during sleep and remains unexplained after a complete autopsy, death scene investigation, and review of the clinical history. It is the leading cause of postneonatal mortality in the developed world. The cause of SIDS is unknown, but is postulated to involve impairment of brainstem-mediated homeostatic control. Extensive evidence from animal studies indicates that serotonin (5-HT) neurons in the medulla oblongata play a role in the regulation of multiple aspects of respiratory and autonomic function. A subset of SIDS infants have several abnormalities in medullary markers of 5-HT function and genetic polymorphisms impacting the 5-HT system, informing the hypothesis that SIDS results from a defect in 5-HT brainstem-mediated control of respiratory (and autonomic) regulation. Here we review the evidence from postmortem human studies and animal studies to support this hypothesis and discuss how the pathogenesis of SIDS is likely to originate in utero during fetal development.

Mechanisms of pathogenesis in the Sudden Infant Death Syndrome

The likely processes of the Sudden Infant Death Syndrome (SIDS) were identified many years ago (apnea, failed arousal, failed autoresuscitation, etc.). The neurophysiological basis of these processes and the neurophysiological reasons some infants die of SIDS and others do not are, however, only emerging now. We reviewed recent studies that have shed light on the way in which epidemiological risk factors, genetics, neurotransmitter receptor defects and neonatal cardiorespiratory reflex responses interact to lead to sudden death during sleep in a small number of normal appearing infants. As a result of this review and analysis, we hypothesize that the neurophysiological basis of SIDS resides in a persistence of fetal reflex responses into the neonatal period, amplification of inhibitory cardiorespiratory reflex responses and reduced excitatory cardiorespiratory reflex responses. The hypothesis we developed explores the ways in which multiple subtle abnormalities interact to lead to sudden death and emphasizes the difficulty of ante-mortem identification of infants at risk for SIDS, although identification of infants at risk remains an essential goal of SIDS research.

The relationship between neuronal plasticity and serotonergic neurons in the brainstem of SIDS victims

BACKGROUND

The sudden infant death syndrome (SIDS) is still the main cause of postneonatal infant death and its cause is still unknown. Recently, the medullary serotonergic network deficiency theory has been proposed and an association between SIDS and neuronal plasticity has also been suggested. The growth-associated phosphoprotein 43 (GAP43) is a marker of synaptic plasticity and is critical for normal development of the serotonergic innervation. Therefore, the characteristics of GAP43-positive elements and their association with serotonergic neurons were here investigated in the brainstem of SIDS victims.

MATERIALS AND METHODS

The materials of this study included 26 cases of SIDS and 12 control cases. The brainstem material was collected and the immunohistochemistry of GAP43 and tryptophan hydroxylase (TrypH) carried out. The density of GAP43-positive neurons and dendrites and of TrypH-positive neurons were measured quantitatively. Nonparametric analyses of GAP43 between SIDS and non-SIDS and correlation analyses between GAP43 and TrypH were performed.

RESULTS

No significant difference in GAP43-associated findings was found between SIDS and non-SIDS nor any significant correlation between GAP43-associated findings and TrypH-positive neurons.

CONCLUSIONS

The results of this study were not in agreement with the association of GAP43 with SIDS and with serotonergic innervation in SIDS.

The correlation between serotonergic neurons in the brainstem and sleep apnea in SIDS victims

BACKGROUND

In the Sudden Infant Death Syndrome (SIDS), a medullary serotonergic network deficiency theory has been proposed, amongst many other hypotheses. The correlation between serotonergic neurons or dendritic spines in the brainstem of SIDS and sleep apnea was investigated here.

MATERIALS AND METHODS

Twenty-seven thousand infants were studied prospectively to characterize their sleep-wake behavior. Of these, 38 infants died under 6 months of age, including 26 cases of SIDS. The frequency and duration of sleep apnea were analyzed. Brainstem material was collected and immunohistochemistry for tryptophan hydroxylase (TrypH) carried out. The density of TrypH-positive neurons was measured quantitatively. Correlation analyses were carried out between the TrypH-associated pathological data and the physiological data of sleep apnea.

RESULTS

One significant positive correlation between the density of TrypH-positive neurons in the dorsal raphe nucleus of the midbrain and the duration of central apnea (p=0.027) was found in SIDS victims.

CONCLUSIONS

Some of serotonergic facts could be involved in the pathophysiology of SIDS.

A serotonin malfunction hypothesis by finding clear mutual relationships between several risk factors and symptoms associated with sudden infant death syndrome

In our recent study allele variants in the promoter of serotonin transporter (5-HTT) gene have been shown as a novel risk factor for sudden infant death syndrome (SIDS). L and XL alleles were more frequent and S allele was less frequent in SIDS victims compared to age-matched controls. Serotonin (5-HT) is suggested as a major agent that is closely involved in the etiology of SIDS. Although many risk factors of SIDS looked mutually unrelated each other, we found in literature many of them other than prone position to change 5-HT levels in the brain. Along with the genetic factors, environmental and temporal factors appear additively to lower the excitatory function of 5-HT to the respiratory center, and finally SIDS might occur. Now the pathophysiological mechanisms and symptoms of SIDS are explained by decreased levels of 5-HT.

Serotonin transporter gene variation is a risk factor for sudden infant death syndrome in the Japanese population

OBJECTIVE

Serotonin (5-HT) in the nervous system is a major factor in facilitation of the brain center for respiration. Variations in the promoter region of the 5-HT transporter (5-HTT) gene have been shown to potentially regulate 5-HT activity in the brain. Therefore, we aimed to identify the possibility that specific allele variants of the 5-HTT gene can be found as a genetic background for sudden infant death syndrome (SIDS).

METHODS

Polymorphisms in the 5' regulatory region of the 5-HTT gene were determined in genomic DNA obtained from 27 SIDS victims and 115 age-matched health control participants.

RESULTS

There were significant differences in genotype distribution and allele frequency of the 5-HTT promoter gene between SIDS victims and age-matched control participants. The L and XL alleles were more frequently found in SIDS victims than in age-matched control participants.

CONCLUSION

Efficiency in the transportation of 5-HTT with the L allele is known to be higher than that with the S allele. The excitatory function by 5-HT is considered to be lower in the respiratory center of individuals with the L allele compared with those with S allele. The XL allele variant has shown another novel biological risk factor for SIDS.

Choline acetyltransferase: the structure, distribution and pathologic changes in the central nervous system

Choline acetyltransferase (ChAT), the enzyme responsible for the biosynthesis of acetylcholine, is presently the most specific indicator for monitoring the functional state of cholinergic neurones in the central and peripheral nervous systems. ChAT is a single-strand globular protein. The enzyme is synthesized in the perikaryon of cholinergic neurones and transported to the nerve terminals probably by both slow and rapid axoplasmic flows. ChAT exists in at least two forms in cholinergic nerve terminals: (i) soluble; and (ii) non-ionically membrane-bound forms. Multiple mRNA species of ChAT (R-, N-and M-types) are transcribed from different promoter regions and produced by different splicing in the mouse, rat, and human. All transcripts encode the same ChAT protein in rodents, while in human M-type mRNA has the capability to generate both large and small forms of ChAT proteins and R-and N-types ChAT mRNA generate a small form, which corresponds to the rodent ChAT. The genomic structure of ChAT is unique compared with other enzymes for neurotransmitters. The first intron of the ChAT gene encompasses the open reading frame encoding another protein, vesicular acetylcholine transporter (VAChT), which is responsible for the transportation of acetylcholine from the cytoplasm into the synaptic vesicles. The expressions of ChAT and VAChT appear to be coordinately regulated by multiple regulatory elements in cholinergic neurones. Immunohistochemical and in situ hybridization studies have revealed the localization of cholinergic neurones in the central nervous system: the medial septal nucleus, the nucleus of the diagonal band of Broca, the basal nucleus of Meynert, the caudate nucleus, the putamen, the nucleus accumbens, the pedunculopontine tegmental nucleus, the laterodorsal tegmental nucleus, the medial habenular nucleus, the parabigeminal nucleus, some cranial nerve nuclei, and the anterior horn of the spinal cord. Focally distributed cholinergic neurones project fibers to many areas in the central nervous system and construct a complicated cholinergic network, playing an important role in neuropsychic activities, such as learning, memory, arousal, sleep and movement. Central cholinergic neurones are involved in several neurodegenerative diseases such as Alzheimer's disease and amyotrophic lateral sclerosis, in which disturbance of the central cholinergic system does not appear to be closely related to the etiology, but rather to the development of clinical symptoms. In addition, abnormalities of ChAT in the brain have been recently demonstrated in schizophrenia and sudden infant death syndrome.

Effect of enhanced geomagnetic activity on hypothermia and mortality in rats

The hypothesis was investigated that variability in the severity of limbic seizure-induced hypothermia in rats was affected by ambient geomagnetic activity. Data were obtained in support of this hypothesis. The depth of the hypothermia was significantly (P < 0.001) reduced if the ambient geomagnetic activity exceeded 35 nT to 40 nT. Mortality during the subsequent 5 days was increased when the geomagnetic activity was > 20 nT. The magnitude of the effect was comparable to the difference between exposure to light or to darkness during the 20 h after the induction of limbic seizures.

Development of the human hypothalamus

The hypothalamus has been claimed to be involved in a great number of physiological functions in development, such as sexual differentiation (gender, sexual orientation) and birth, as well as in various developmental disorders including mental retardation, sudden infant death syndrome (SIDS), Kallman's syndrome and Prader-Willi syndrome. In this review a number of hypothalamic nuclei have therefore been discussed with respect to their development in health and disease. The suprachiasmatic nucleus (SCN) is the clock of the brain and shows circadian and seasonal fluctuations in vasopressin-expressing cell numbers. The SCN also seems to be involved in reproduction, adding interest to the sex differences in shape of the vasopressin-containing SCN subnucleus and in its VIP cell number. In addition, differences in relation to sexual orientation can be seen in this perspective. The vasopressin and VIP neurons of the SCN develop mainly postnatally, but as premature children may have circadian temperature rhythms, a different SCN cell type is probably more mature at birth. The sexually dimorphic nucleus (SDN, intermediate nucleus, INAH-1) is twice as large in young male adults as in young females. At the moment of birth only 20% of the SDN cell number is present. From birth until two to four years of age cell numbers increase equally rapidly in both sexes. After this age cell numbers start to decrease in girls, creating the sex difference. The size of the SDN does not show any relationship to sexual orientation in men. The large neurosecretory cells of the supraoptic (SON) and paraventricular nucleus (PVN) project to the neurohypophysis, where they release vasopressin and oxytocin into the blood circulation. In the fetus these hormones play an active role in the birth process. Fetal oxytocin may initiate or accelerate the course of labor. Fetal vasopressin plays a role in the adaptation to stress--caused by the birth process--by redistribution of the fetal blood flow. Corticotropin-releasing hormone (CRH) neurons of the PVN play a central role in stress response. Thus fetal CRH neurons may play a role in the timing of the moment of birth. Recently, alterations have been described in peptidergic, aminergic and cholinergic transmitters in the hypothalamus in SIDS. Future research will have to establish whether these changes are part of the course of SIDS. A large proportion of the SON and PVN neurons also produce tyrosine hydroxylase (TH). In neonates the majority of TH-immunoreactive neurons colocalizes vasopressin, while in the adult the majority of TH-positive neurons colocalizes oxytocin.(ABSTRACT TRUNCATED AT 400 WORDS)

Synaptic neurochemistry of human striatum during development: changes in sudden infant death syndrome

There is evidence of abnormalities in the brain-stem monoamine-containing neurons in infants with sudden infant death syndrome (SIDS). By taking advantage of the rich innervation of the human basal ganglia by monoaminergic afferents from cell bodies in the brainstem, we studied the synaptic chemistry of catecholamine and associated neurons of the putamen obtained postmortem from 14 SIDS infants, eight age-matched control infants, and older control subjects of various ages. We found significantly lower concentrations of dopamine and higher homovanillic acid/DA ratios in samples from SIDS infants compared with age-matched control infants. Noradrenaline and 5-hydroxytryptamine were lower in SIDS compared with control subjects, but the difference did not reach statistical significance. There was no clear evidence that dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid were altered. Immunoblot analysis of striatal tissue showed that samples from infants with SIDS, which exhibited lower DA, also had lower tyrosine hydroxylase protein. Other transmitter-specific neuronal markers were also assessed, including enzymes associated with cholinergic and GABA-containing neurons. We found significantly decreased choline acetyltransferase activities. However, GABA, glutamate, or somatostatin concentrations or monoamine oxidase activities were unchanged in SIDS. We also noted age-dependent changes in brain weights and some synaptic markers by comparing the age-matched infants with older control subjects. Analysis of variance revealed that homovanillic acid, dihydroxyphenylacetic acid, and monoamine oxidase B activities were increased with age. DA and choline acetyltransferase were also found to be positively correlated in putamen. Our findings suggest developmental changes in some transmitter-specific neurons in SIDS that may result from apneic episodes or chronic hypoxia induced before death.