Synergistic effect of influenza a virus on endotoxin-induced mortality in rat pups: a potential model for sudden infant death syndrome

Peripheral Neuroplasticity of Respiratory Chemoreflexes, Induced by Prenatal Nicotinic Exposure: Implication for SIDS

Sudden Infant Death Syndrome (SIDS) occurs during sleep in seemingly healthy infants. Maternal cigarette smoking and hypoxemia during sleep are assumed to be the major causal factors. Depressed hypoxic ventilatory response (dHVR) is observed in infants with high risk of SIDS, and apneas (lethal ventilatory arrest) appear during the fatal episode of SIDS. Disturbance of the respiratory center has been proposed to be involved, but the pathogenesis of SIDS is still not fully understood. Peripherally, the carotid body is critical to generate HVR, and bronchopulmonary and superior laryngeal C-fibers (PCFs and SLCFs) are important for triggering central apneas; however, their roles in the pathogenesis of SIDS have not been explored until recently. There are three lines of recently accumulated evidence to show the disorders of peripheral sensory afferent-mediated respiratory chemoreflexes in rat pups with prenatal nicotinic exposure (a SIDS model) in which acute severe hypoxia leads to dHVR followed by lethal apneas. (1) The carotid body-mediated HVR is suppressed with a reduction of the number and sensitivity of glomus cells. (2) PCF-mediated apneic response is largely prolonged via increased PCF density, pulmonary IL-1β and serotonin (5-hydroxytryptamine, 5-HT) release, along with the enhanced expression of TRPV1, NK₁R, IL1RI and 5-HT₃R in pulmonary C-neurons to strengthen these neural responses to capsaicin, a selective stimulant to C-fibers. (3) SLCF-mediated apnea and capsaicin-induced currents in superior laryngeal C-neurons are augmented by upregulation of TRPV1 expression in these neurons. These results, along with hypoxic sensitization/stimulation of PCFs, gain insight into the mechanisms of prenatal nicotinic exposure-induced peripheral neuroplasticity responsible for dHVR and long-lasting apnea during hypoxia in rat pups. Therefore, in addition to the disturbance in the respiratory center, the disorders of peripheral sensory afferent-mediated chemoreflexes may also be involved in respiratory failure and death denoted in SIDS victims.

Mechanisms underlying a critical period of respiratory development in the rat

Twenty-five years ago, Filiano and Kinney (1994) proposed that a critical period of postnatal development constitutes one of the three risk factors for sudden infant death syndrome (SIDS). The underlying mechanism was poorly understood. In the last 17 years, much has been uncovered on this period in the rat. Against several expected trends of development, abrupt neurochemical, metabolic, ventilatory, and electrophysiological changes occur in the respiratory system at P12-13. This results in a transient synaptic imbalance with suppressed excitation and enhanced inhibition, and the response to acute hypoxia is the weakest at this time, both at the cellular and system's levels. The basis for the synaptic imbalance is likely to be contributed by a reduced expression of brain-derived neurotrophic factor (BDNF) and its TrkB receptors in multiple brain stem respiratory-related nuclei during the critical period. Exogenous BDNF or a TrkB agonist partially reverses the synaptic imbalance, whereas a TrkB antagonist accentuates the imbalance. A transient down-regulation of pituitary adenylate cyclase-activating polypeptide (PACAP) at P12 in respiratory-related nuclei also contributes to the vulnerability of this period. Carotid body denervation during this time or perinatal hyperoxia merely delays and sometimes prolongs, but not eliminate the critical period. The rationale for the necessity of the critical period in postnatal development is discussed.

Clinical and experimental aspects of breathing modulation by inflammation

Neuroinflammation is produced by local or systemic alterations and mediated mainly by glia, affecting the activity of various neural circuits including those involved in breathing rhythm generation and control. Several pathological conditions, such as sudden infant death syndrome, obstructive sleep apnea and asthma exert an inflammatory influence on breathing-related circuits. Consequently breathing (both resting and ventilatory responses to physiological challenges), is affected; e.g., responses to hypoxia and hypercapnia are compromised. Moreover, inflammation can induce long-lasting changes in breathing and affect adaptive plasticity; e.g., hypoxic acclimatization or long-term facilitation. Mediators of the influences of inflammation on breathing are most likely proinflammatory molecules such as cytokines and prostaglandins. The focus of this review is to summarize the available information concerning the modulation of the breathing function by inflammation and the cellular and molecular aspects of this process. I will consider: 1) some clinical and experimental conditions in which inflammation influences breathing; 2) the variety of experimental approaches used to understand this inflammatory modulation; 3) the likely cellular and molecular mechanisms.

Interactive effects of maternal cigarette smoke, heat stress, hypoxia, and lipopolysaccharide on neonatal cardiorespiratory and cytokine responses

Maternal cigarette smoke (CS) exposure exhibits a strong epidemiological association with Sudden Infant Death Syndrome, but other environmental stressors, including infection, hyperthermia, and hypoxia, have also been postulated as important risk factors. This study examines whether maternal CS exposure causes maladaptations within homeostatic control networks by influencing the response to lipopolysaccharide, heat stress, and/or hypoxia in neonatal rats. Pregnant dams were exposed to CS or parallel sham treatments daily for the length of gestation. Offspring were studied at postnatal days 6-8 at ambient temperatures (T_a) of 33°C or 38°C. Within each group, rats were allocated to control, saline, or LPS (200 µg/kg) treatments. Cardiorespiratory patterns were examined using head-out plethysmography and ECG surface electrodes during normoxia and hypoxia (10% O₂). Serum cytokine concentrations were quantified from samples taken at the end of each experiment. Our results suggest maternal CS exposure does not alter minute ventilation (V̇e) or heart rate (HR) response to infection or high temperature, but independently increases apnea frequency. CS also primes the inflammatory system to elicit a stronger cytokine response to bacterial insult. High T_a independently depresses V̇e but augments the hypoxia-induced increase in V̇e Moreover, higher T_a increases HR during normoxia and hypoxia, and in the presence of an immune challenge, increases HR during normoxia, and reduces the increase normally associated with hypoxia. Thus, while most environmental risk factors increase the burden on the cardiorespiratory system in early life, hyperthermia and infection blunt the normal HR response to hypoxia, and gestational CS independently destabilizes breathing by increasing apneas.

Role of brain-derived neurotrophic factor in the excitatory-inhibitory imbalance during the critical period of postnatal respiratory development in the rat

The critical period of respiratory development in rats is a narrow window toward the end of the second postnatal week (P12–13), when abrupt neurochemical, electrophysiological, and ventilatory changes occur, when inhibition dominates over excitation, and when the animals’ response to hypoxia is the weakest. The goal of this study was to further test our hypothesis that a major mechanism underlying the synaptic imbalance during the critical period is a reduced expression of brain-derived neurotrophic factor (BDNF) and its TrkB receptors. Our aims were to determine (1) that the inhibitory dominance observed in hypoglossal motoneurons during the critical period was also demonstrable in a key respiratory chemosensor, NTS_VL; (2) if in vivo application of a TrkB agonist, 7,8-DHF, would prevent, but a TrkB antagonist, ANA-12, would accentuate the synaptic imbalance; and (3) if hypoxia would also heighten the imbalance. Our results indicate that (1) the synaptic imbalance was evident in the NTS_VL during the critical period; (2) intraperitoneal injections of 7,8-DHF prevented the synaptic imbalance during the critical period, whereas ANA-12 in vivo accentuated such an imbalance; and (3) acute hypoxia induced the weakest response in both the amplitude and frequency of sEPSCs during the critical period, but it increased the frequency of sIPSCs during the critical period. Thus, our findings are consistent with and strengthen our hypothesis that BDNF and TrkB play a significant role in inducing a synaptic imbalance during the critical period of respiratory development in the rat.

Animal models for assessment of infection and inflammation: contributions to elucidating the pathophysiology of sudden infant death syndrome

Sudden infant death syndrome (SIDS) is still not well understood. It is defined as the sudden and unexpected death of an infant without a definitive cause. There are numerous hypotheses about the etiology of SIDS but the exact cause or causes have never been pinpointed. Examination of theoretical pathologies might only be possible in animal models. Development of these models requires consideration of the environmental and/or developmental risk factors often associated with SIDS, as they need to explain how the risk factors could contribute to the cause of death. These models were initially developed in common laboratory animals to test various hypotheses to explain these infant deaths – guinea pig, piglet, mouse, neonatal rabbit, and neonatal rat. Currently, there are growing numbers of researchers using genetically altered animals to examine specific areas of interest. This review describes the different systems and models developed to examine the diverse hypotheses for the cause of SIDS and their potential for defining a causal mechanism or mechanisms.

Virus Infections and Sudden Death in Infancy: The Role of Interferon-γ

Respiratory infections have been implicated in sudden infant death syndrome (SIDS). As interferon-γ (IFN-γ) is a major response to virus infection, we examined (1) the frequency of single nucleotide polymorphism (SNP), IFNG T + 874A, in SIDS infants, their parents, and ethnic groups with different incidences of SIDS; (2) model systems with a monocytic cell line (THP-1) and human peripheral blood monocytes (PBMC) for effects of levels of IFN-γ on inflammatory responses to bacterial antigens identified in SIDS; (3) interactions between genetic and environmental factors on IFN-γ responses. IFNG T + 874A genotypes were determined for SIDS infants from three countries; families who had a SIDS death; populations with high (Indigenous Australian), medium (Caucasian), and low (Bangladeshi) SIDS incidences. The effect of IFN-γ on cytokine responses to endotoxin was examined in model systems with THP-1 cells and human PBMC. The IFN-γ responses to endotoxin and toxic shock syndrome toxin (TSST-1) were assessed in relation to genotype, gender, and reported smoking. There was a marginal association with IFNG T + 874A genotype and SIDS (p = 0.06). Indigenous Australians had significantly higher proportions of the IFNG T + 874A SNP (TT) associated with high responses of IFN-γ. THP-1 cells showed a dose dependent effect of IFN-γ on cytokine responses to endotoxin. For PBMC, IFN-γ enhanced interleukin (IL)-1β, IL-6, and tumor necrosis factor-α responses but reduced IL-8 and IL-10 responses. Active smoking had a suppressive effect on baseline levels of IFN-γ. There was no effect of gender or genotype on IFN-γ responses to bacterial antigens tested; however, significant differences were observed between genotypes in relation to smoking. The results indicate virus infections contribute to dysregulation of cytokine responses to bacterial antigens and studies on physiological effects of genetic factors must include controls for recent or concurrent infection and exposure to cigarette smoke.

Exploring the risk factors for sudden infant deaths and their role in inflammatory responses to infection

The risk factors for sudden infant death syndrome (SIDS) parallel those associated with susceptibility to or severity of infectious diseases. There is no evidence that a single infectious agent is associated with SIDS; the common thread appears to be induction of inflammatory responses to infections. In this review, interactions between genetic and environmental risk factors for SIDS are assessed in relation to the hypothesis that many infant deaths result from dysregulation of inflammatory responses to "minor" infections. Risk factors are assessed in relation to three important stages of infection: (1) bacterial colonization (frequency or density); (2) induction of temperature-dependent toxins; (3) induction or control of inflammatory responses. In this article, we review the interactions among risk factors for SIDS for their effects on induction or control of inflammatory responses. The risk factors studied are genetic factors (sex, cytokine gene polymorphisms among ethnic groups at high or low risk of SIDS); developmental stage (changes in cortisol and testosterone levels associated with 2- to 4-month age range); environmental factors (virus infection, exposure to cigarette smoke). These interactions help to explain differences in the incidences of SIDS observed between ethnic groups prior to public health campaigns to reduce these infant deaths.

Maternal nicotinic exposure produces a depressed hypoxic ventilatory response and subsequent death in postnatal rats

In this study, we asked whether a “full term” prenatal nicotinic exposure (fPNE, 6 mg·kg⁻¹·day⁻¹ nicotinic delivery) over the full gestation, compared to a traditional PNE (tPNE) over the last two‐thirds of the gestation, caused a higher mortality following a remarkable depressed hypoxic ventilatory response (dHVR) independent of brain and pulmonary edema and change in serum corticosterone. P12‐14 pups pretreated with tPNE, fPNE or their vehicle (tCtrl and fCtrl) were exposed to 5% O₂ for up to 60 min followed by harvesting the brain and lungs or anesthetized to collect blood for detecting arterial blood pH/gases and serum cotinine and corticosterone levels. We found that fPNE had little effect on baseline V_E and heart rate, but consistently induced a dHVR and prolonged apnea that were rarely observed after tPNE. The severity of the dHVR in PNE pups were closely correlated to an earlier appearance of lethal ventilatory arrest (the hypoxia‐induced mortality). PNE did not induce brain and pulmonary edema, but significantly increased serum corticosterone levels similarly in tPNE and fPNE pups. Moreover, the accumulated nicotinic dose given to the individual was significantly higher in fPNE than tPNE pups, though there was no difference in serum cotinine levels and arterial blood pH/gases between the two groups. Our results suggest that nicotinic exposure at the early stage of gestation achieved by fPNE, rather than tPNE, is critical in generating the dHVR and subsequent death occurring independently of brain/pulmonary edema and changes in arterial blood pH/gases and serum corticosterone.

Our results suggest that nicotinic exposure at the early stage of gestation achieved by “full term” prenatal nicotinic exposure (fPNE), rather than traditional prenatal nicotinic exposure (tPNE), is critical in generating the depressed hypoxic ventilatory response (dHVR) and subsequent death. The fPNE‐induced cardiorespiratory impairement is independent of brain/pulmonary edema and changes in arterial blood pH/gases and serum corticosterone.

Postnatal development of glycine receptor subunits α1, α2, α3, and β immunoreactivity in multiple brain stem respiratory-related nuclear groups of the rat

The respiratory system is immature at birth and significant development occurs postnatally. A critical period of respiratory development occurs in rats around postnatal days 12-13, when enhanced inhibition dominates over suppressed excitation. The mechanisms underlying the heightened inhibition are not fully understood. The present study tested our hypothesis that the inhibition is marked by a switch in glycine receptor subunits from neonatal to adult form around the critical period. An in-depth immunohistochemical and single neuron optical densitometric study was undertaken on four respiratory-related nuclear groups (the pre-Bötzinger complex, nucleus ambiguus, hypoglossal nucleus, and ventrolateral subnucleus of solitary tract nucleus), and a non-respiratory cuneate nucleus in P2-21 rats. Our data revealed that in the respiratory-related nuclear groups: (1) the expressions of GlyRα2 and GlyRα3 were relatively high at P2, but declined after 1-1½ weeks to their lowest levels at P21; (2) the expression of GlyRα1 increased with age and reached significance at P12; and (3) the expression of GlyRβ rose from P2 to P12 followed by a slight decline until P21. No distinct increase in GlyRα1 at P12 was noted in the cuneate nucleus. Thus, there is a switch in dominance of expression from neonatal GlyRα2/α3 to the adult GlyRα1 and a heightened expression of GlyRα1 around the critical period in all respiratory-related nuclear groups, thereby supporting enhanced inhibition at that time. The rise in the expression of GlyRβ around P12 indicates that it plays an important role in forming the mature heteropentameric glycine receptors in these brain stem nuclear groups.

Peripheral-central chemoreceptor interaction and the significance of a critical period in the development of respiratory control

Respiratory control entails coordinated activities of peripheral chemoreceptors (mainly the carotid bodies) and central chemosensors within the brain stem respiratory network. Candidates for central chemoreceptors include Phox2b-containing neurons of the retrotrapezoid nucleus, serotonergic neurons of the medullary raphé, and/or multiple sites within the brain stem. Extensive interconnections among respiratory-related nuclei enable central chemosensitive relay. Both peripheral and central respiratory centers are not mature at birth, but undergo considerable development during the first two postnatal weeks in rats. A critical period of respiratory development (∼P12-P13 in the rat) exists when abrupt neurochemical, metabolic, ventilatory, and electrophysiological changes occur. Environmental perturbations, including hypoxia, intermittent hypoxia, hypercapnia, and hyperoxia alter the development of the respiratory system. Carotid body denervation during the first two postnatal weeks in the rat profoundly affects the development and functions of central respiratory-related nuclei. Such denervation delays and prolongs the critical period, but does not eliminate it, suggesting that the critical period may be intrinsically and genetically determined.

Genetics of the sudden infant death syndrome

The sudden infant death syndrome (SIDS) is currently defined as "the sudden unexpected death of an infant less than 1 year of age with onset of the fatal episode apparently occurring during sleep, that remains unexplained after a thorough investigation". SIDS, whose etiology remains rather vague, is still the major cause of death among infants between 1 month and 1 year of age in industrialized countries with varying incidences in different populations. Herein, after touching on definitory approaches and several current hypotheses concerning SIDS etiology, we focus on the triple risk model of SIDS and discuss two large classes of genetic factors potentially contributing to or predisposing for the generation of a vulnerable infant that, when encountering an environmental trigger, may succumb to SIDS. We conclude by acknowledging that for the integration of the vast and complex genetic evidence concerning SIDS, a lot more research will be required and we briefly discuss the potential use of recently presented animal models for functional studies of SIDS pathology.

Breaking patterns of environmentally influenced disease for health risk reduction: immune perspectives

BACKGROUND

Diseases rarely, if ever, occur in isolation. Instead, most represent part of a more complex web or "pattern" of conditions that are connected via underlying biological mechanisms and processes, emerge across a lifetime, and have been identified with the aid of large medical databases.

OBJECTIVE

We have described how an understanding of patterns of disease may be used to develop new strategies for reducing the prevalence and risk of major immune-based illnesses and diseases influenced by environmental stimuli.

FINDINGS

Examples of recently defined patterns of diseases that begin in childhood include not only metabolic syndrome, with its characteristics of inflammatory dysregulation, but also allergic, autoimmune, recurrent infection, and other inflammatory patterns of disease. The recent identification of major immune-based disease patterns beginning in childhood suggests that the immune system may play an even more important role in determining health status and health care needs across a lifetime than was previously understood.

CONCLUSIONS

Focusing on patterns of disease, as opposed to individual conditions, offers two important venues for environmental health risk reduction. First, prevention of developmental immunotoxicity and pediatric immune dysfunction can be used to act against multiple diseases. Second, pattern-based treatment of entryway diseases can be tailored with the aim of disrupting the entire disease pattern and reducing the risk of later-life illnesses connected to underlying immune dysfunction. Disease-pattern-based evaluation, prevention, and treatment will require a change from the current approach for both immune safety testing and pediatric disease management.

The role of infection and inflammation in sudden infant death syndrome

Sudden Infant Death Syndrome (SIDS) is the most common cause of post-neonatal mortality in the developed world. The exact cause of SIDS is likely to be multifactorial involving a critical developmental period, a vulnerable infant, and one or more triggers. Many SIDS infants have a history of viral illness preceding death. Prone sleep position, one of the leading risk factors, can increase airway temperature, as well as stimulate bacterial colonization and bacterial toxin production. Markers of infection and inflammation are often found on autopsy along with microbial isolates. Although the causal link between infection and SIDS is not conclusive, there is evidence that an infectious insult could be a likely trigger of SIDS in some infants.

Is shock a key element in the pathology of sudden infant death syndrome (SIDS)?

In developed countries, sudden infant death syndrome (SIDS) is the most common cause of death for infants between 1 month and 1 year of age. The etiology of SIDS is likely to be multifactorial, and current paradigms often describe three overlapping elements of risk. Those elements are a critical developmental period, a vulnerable infant, and one or more exogenous stressors. In the triple-risk model, SIDS infants are described as having an underlying vulnerability in cardiorespiratory control in the central nervous system during a critical period when autonomic control is developing. This vulnerability might affect the response to exogenous stressors, including prone sleeping position, hypoxia, and increased carbon dioxide. In the common bacterial hypothesis and fatal triangle, the focus is on the stressors. In the first, a combination of common respiratory infections can cause SIDS in an infant during a developmentally vulnerable period. This theory also includes 3 factors of vulnerability: a genetic predisposition, a vulnerable developmental age, and infectious stressors. In the fatal triangle theory, infection, inflammation, and genetics each play a role in triggering a SIDS fatality. From our work in an animal model, we have found that rat pups die from a combination of infectious insults during a critical time of development. This is exacerbated by perinatal nicotine exposure, a condition shown to alter the autonomic response in exposed offspring. We are proposing that shock and cardiovascular collapse is a key element that links these theories.

Evidence for infection, inflammation and shock in sudden infant death: parallels between a neonatal rat model of sudden death and infants who died of sudden infant death syndrome

This study compared pathological findings from a neonatal rat model of sudden death with those from 40 sudden infant death syndrome (SIDS) infants collected at autopsy. In the rat model, influenza A virus was administered intranasally on postnatal day 10, and on day 12 a sublethal, intraperitoneal dose of Escherichia coli endotoxin; mortality was 80%. Tissue samples from the animals and infants were fixed in formaldehyde, embedded in paraffin, and sections stained with hematoxylin and eosin. Tissues from the SIDS specimens were additionally cultured for bacteria and viruses; post-mortem blood samples were evaluated for signs of inflammation. All sections were examined by a pediatric forensic pathologist familiar with SIDS pathology. Comparisons between the rat model and the human SIDS cases revealed that both exhibited gross and microscopic pathology related to organ shock, possibly associated with the presence of endotoxin. Uncompensated shock appeared to be a likely factor that caused death in both infants and rat pups. Response to a shock-inducing event might have played an important role in the events leading to death. The similarities between the neonatal rats and the human cases indicate that further research with the model might elucidate additional aspects of SIDS pathology.

Identifying infants at risk for sudden infant death syndrome

PURPOSE OF REVIEW

This review examines recent research relevant to the underlying pathophysiology and risk factors for sudden infant death syndrome.

RECENT FINDINGS

Current research focuses on the linkage between known risk factors and vulnerability, genetic contributions, and the role of dysfunctional brainstem neurotransmission in the pathogenesis of this syndrome. While social inequalities, prematurity, maternal smoking, infant sleeping practices and sleep environment, arousal failures and environmental pollutants remain important risk factors, new evidence is emerging that certain genetic polymorphisms may contribute to vulnerability. New neuropathological studies have provided strong support for abnormal brainstem serotonergic function. Since serotonin influences a wide range of physiological systems including breathing, the cardiovascular system, temperature, and sleep-wake cycles, this finding strongly supports the hypothesis that sudden infant death syndrome is the result of dysregulation of the autonomic nervous system and provides biological plausibility for certain risk reduction strategies.

SUMMARY

Despite a putative diagnostic shift, sudden infant death syndrome remains the most common cause of death from 1 month to 1 year of age. Recent studies confirmed established risk factors and have suggested new genetic vulnerabilities. Finally, new evidence supports a key role for abnormalities in brainstem serotonin systems in the pathophysiology of this syndrome.

Sudden infant death syndrome, infection and inflammatory responses

Sudden infant death syndrome (SIDS) is sudden unexpected death in infancy for which there is no explanation after review of the history, a death scene investigation and a thorough autopsy. The use of common diagnostic criteria is a prerequisite for discussing the importance of infection, inflammatory responses and trigger mechanism in SIDS. Several observations of immune stimulation in the periphery and of interleukin-6 elevation in the cerebrospinal fluid of SIDS victims explain how infections can play a role in precipitating these deaths. Finally, these findings and important risk factors for SIDS are integrated in the concept of a vicious circle for understanding the death mechanism. The vicious circle is a concept to elucidate the interactions between unfavourable factors, including deficient auto-resuscitation, and how this could result in death.

Animal models of sudden unexplained death

The etiology of sudden infant death syndrome (SIDS) is unknown but thought to be multifactorial. Several animal models have been developed that induce death without pre-existing symptoms and with pathology similar to that seen in SIDS infants; however, the relevance of these animal models to the events leading to SIDS remains elusive, in part because animal models are as varied as the potential causes of SIDS. In addition, it is difficult to find an animal model that can accurately reflect the genetic, developmental and environmental risk factors for SIDS. Comparisons between species can prove difficult but animal models provide a useful tool for evaluating potential mechanisms related to sudden unexplained death. This review focuses on models developed to examine the association of infection and inflammation with mechanisms proposed to explain sudden unexplained death.

Alteration in regulation of inflammatory response to influenza a virus and endotoxin in suckling rat pups: a potential relationship to sudden infant death syndrome

Data increasingly implicate a possible role of immune and inflammatory responses to infection in sudden infant death syndrome (SIDS). We have previously described a dual challenge model that results in pathology, organ damage, vascular collapse and unexplained death similar to that seen in SIDS. In this study, we examined changes in inflammatory cytokine mRNA in the lung and liver and regulation of pathways associated with nitric oxide production. Our data suggest that priming of the immune system by mild viral infection disturbs normal inflammatory response to endotoxin. This results in an increased nitric oxide synthase production, most likely the cause of liver pathology and clotting abnormalities.

Is sudden infant death syndrome (SIDS) an autoimmune disorder of endogenous vasoactive neuropeptides?

Sudden infant death syndrome (SIDS) remains a perplexing diagnosis with conflicting laboratory investigation and lack of a biologically plausible aetiology. Investigations into the endogenous vasoactive neuropeptides, including pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are revealing the critical role these substances have in homeostasis including thermo- and cardiovascular regulation. For example, studies in PACAP receptor-deficient mice have revealed sudden neonatal death attributed to respiratory control defects, possibly due to mutations in genes encoding components of PACAP signalling pathways. PACAP and VIP belong to the secretin/glucagon superfamily of hormones and function as vasoactive neuropeptides. They act as hormones, neurotransmitters, immune modulators and neurotrophes. They are readily catalysed to small peptide fragments. They and their binding sites are immunogenic and are known to be associated with a range of autoimmune conditions. Vasoactive neuropeptides have a known role in thermoregulation and deficiency states are associated with higher neonatal death rates in rats. PACAP plays a significant role in carbohydrate and lipid metabolism and impairment of functioning has potentially serious consequences. It is postulated PACAP and VIP receptors in brain may become compromised through autoimmune phenomena resulting in cardio-respiratory dysfunction and death. This paper discusses the potential role of certain vasoactive neuropeptides in causing autoimmune responses in susceptible infants predisposing them to SIDS.