Peripheral chemoreceptors in congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS) is a rare disorder of unknown etiology, characterized by failure of the autonomic control of respiration. The primary defect is believed to involve central respiratory control; however, no specific lesion has been identified. We report two cases of CCHS (one female, 3 mo of age and one male 2 yr of age) in which there was detailed examination of the neural, muscular, and chemoreceptor components of respiratory control. Although no specific abnormalities were identified in the central nervous system (CNS) or muscles of respiration, striking changes were observed in arterial chemoreceptors, carotid bodies (CB), and airway chemoreceptors, neuroepithelial bodies (NEB). In both cases, CB were small (< 50% of control), with a marked decrease in the number of glomus cells identified by immunostaining for tyrosine hydroxylase and serotonin. Ultrastructural analysis of glomus cells in Case 1 showed a marked decrease in the frequency of dense core vesicles (< 20% of control), the storage site of amine and peptide neurotransmitters. Immunostaining for S100 protein, a marker of sustentacular or Type II cells, was increased up to twofold compared with controls. In the lung, the frequency and size of NEB immunostained for bombesin was increased twofold in both cases, suggesting compensatory hyperplasia of airway chemoreceptors. Since intact peripheral chemoreceptors are essential for respiratory control, especially the response to hypoxia, abnormalities in CB and NEB may contribute to the pathophysiology of CCHS and related conditions such as sudden infant death syndrome (SIDS).

Maternal smoking and pulmonary neuroendocrine cells in sudden infant death syndrome

BACKGROUND

Maternal smoking is a well-recognized risk factor for sudden infant death syndrome (SIDS), but the precise mechanism is unknown. We tested a hypothesis that maternal smoking affects pulmonary neuroendocrine cells (PNECs) and neuroepithelial bodies (NEBs), which are innervated PNEC clusters and presumed airway chemoreceptors.

METHODS

Lung sections from infants who died of SIDS and whose mothers smoked during pregnancy (n = 22), infants who died of SIDS and whose mothers were nonsmokers (n = 17), and age-matched control infants (n = 15) who died of other causes were immunostained for bombesin (a PNEC and NEB marker) and assessed morphometrically.

RESULTS

The frequency of PNEC (the percentage of airway epithelium immunoreactive for bombesin) was increased up to twofold in the lungs of infants who died of SIDS (7.7 +/- 0.4%) compared with controls (4.9 +/- 0.4%), as was the frequency (40 +/- 3.5 vs 23 +/- 3.7/cm2) and size (748 +/- 46.5 vs 491 +/- 25.8 microns2) of NEBs. In infants who died of SIDS and who were born to smoking mothers, PNEC frequency was increased significantly compared with that in those born to nonsmoking mothers, but the frequency and size of NEBs were not significantly different between the two groups.

CONCLUSION

Our findings suggest that maternal smoking potentiates hyperplasia of the PNEC system in the lungs of infants who die of SIDS and that a dysfunction of these cells may contribute to the pathophysiology of SIDS.

Fatal Bordetella pertussis infection: report of two cases with novel pathologic findings

We report two infants less than 2 months of age who died of Bordetella pertussis infection: one of primary B. pertussis infection and the other of secondary bronchopneumonia. We describe histopathologic findings in the lung, including transmission and immunoelectron microscopy, studies showing close association between B. pertussis organisms and ciliated cells. A novel finding in both cases was striking dilatation and inspissation of proteinaceous material in pancreatic ducts, reminiscent of changes described in cystic fibrosis. The possible mechanism for these changes may be related to cellular and molecular actions of pertussis toxin-a powerful inhibitor of G proteins and adenyl cyclase important in cellular signal transduction.

Concept mapping: an effective instructional strategy for diet therapy

Concept mapping is an instructional strategy that requires learners to identify, graphically display, and link key concepts in instructional reading material. Although proven effective in numerous disciplines as a means to promote critical thinking and self-directed learning, concept mapping has not been tested in diet therapy. The objective of this study was to implement concept mapping as a small-group, cooperative learning strategy in an upper-division diet therapy course and to evaluate student attitudes about the effect of concept mapping on knowledge, self-directed learning, problem-solving, and collaborative skills. Students in the first semester (n = 27) initially learned course material by lecture (4 weeks) followed by an integrated mapping/lecture format (12 weeks); the second semester (n = 25) used an integrated mapping lecture format for the full 16 weeks. At the end of both semesters, students completed a 10-item original survey questionnaire. Responses for first (n = 25) and second (n = 21) semesters were analyzed independently. Results indicated that a majority of students thought participation in concept mapping enhanced knowledge of diet therapy principles (n = 19 of 25; 18 of 21), self-directed learning (n = 14 of 25; 18 of 21), critical thinking (n = 21 of 25; 14 of 21), problem-solving (n = 22 of 25; 16 of 21), and collaboration (n = 24 of 25; 20 of 21) skills. When noncooperation of teammates was a factor, concept mapping was viewed as more frustrating and time consuming than lecture. This study demonstrated concept mapping as an effective learning strategy for diet therapy; it improves students' ability to engage in self-directed learning, critical thinking, collaboration, and creative problem solving. Results suggest that concept mapping is most effective when accompanied with comprehensive training, coordinated lectures, instructor guidance, and long-term practice.

Pulmonary neuroendocrine cells in neonatal rats with congenital diaphragmatic hernia

Lung hypoplasia and persistent pulmonary hypertension are the principal causes of high mortality and morbidity in infants with congenital diaphragmatic hernia (CDH). Amine- and peptide-producing pulmonary neuroendocrine cells (PNEC), widely distributed throughout the airway mucosa, are thought to play an important role in both pulmonary development and regulation of pulmonary vascular tone. Furthermore, recent studies show increased levels of calcitonin gene-related peptide (CGRP), a pulmonary vasodilator produced by PNEC, during chronic hypoxia. The article reports data on morphometric analysis of CGRP immunoreactive PNEC clusters (neuroepithelial bodies, NEB) in a rat model of CDH. CDH was induced in neonatal Sprague Dawley rats by oral administration of 2,4-dichloro-phenyl-p-nitrophenylether (Nitrofen; Rohm Haas, Philadelphia, PA) to the mother at 10 days of gestation. Sections of lungs from term neonatal rats with and without CDH and controls were immunostained for CGRP (marker of NEB) with specific antibody against rat CGRP. NEB size and number of NEB/area of lung were assessed using a semiautomatic image analysis system. In lungs of neonatal rats with CDH, the number of NEB per surface area of lung parenchyma was significantly increased compared with the age-matched controls. Although the mean size of NEB was larger in CDH, the differences were not significant. This is the first study of PNEC in CDH. Whether the phenomenon observed in this study results in altered NEB function including imbalance in vasoactive mediators requires further studies, especially in the human being.

Detection of calcitonin gene expression in human infant and monkey carotid body chief cells by in situ hybridization

Calcitonin mRNA was detected in human and monkey carotid bodies by in situ hybridization histochemistry, using a 35S-labeled oligonucleotide probe for human calcitonin. In both human and monkey carotid body, moderate to high hybridization signal for calcitonin mRNA was observed in all cases. The hybridization signal in the formalin-fixed, paraffin-embedded samples was comparable to that obtained from frozen paraformaldehyde-fixed tissue. Our observations extend the finding of calcitonin-like immunoreactivity in the carotid body chief cells and indicate that calcitonin is produced in the carotid body, probably in the chief cells.

Cell biology of pulmonary neuroepithelial bodies--validation of an in vitro model. I. Effects of hypoxia and Ca2+ ionophore on serotonin content and exocytosis of dense core vesicles

Pulmonary neuroendocrine (NE) cells including the innervated clusters of NE cells--neuroepithelial bodies (NEB)--are difficult to study because of their small numbers and diffuse distribution within the airway mucosa of the lung. We have previously reported a method for isolation and culture of NE cells from rabbit fetal using a combination of mechanical and enzymatic dissociation followed by gradient centrifugation. This method provides single cell suspension of mixed lung cells enriched in NE cells, particularly those originating from NEB. This study further validates our in vitro model by detailed morphologic characterization of cultured NEB cells using high resolution light microscopy, transmission and scanning electron microscopy, HPLC for detection of serotonin (5-HT), and molecular (Northern blot) analysis of mRNA encoding for 5-HT synthesizing enzymes, tryptophane hydroxylase, and aromatic L-amino acid decarboxylase. In addition the effects of hypoxia on NEB cells in vitro were investigated to define the role of these cells as possible airway chemoreceptors. Exposure of NEB cultures to hypoxia resulted in decreased intracellular content of 5-HT accompanied by increased exocytosis of dense core vesicles (DCV). The amount of 5-HT release correlated with the degree of hypoxia, suggesting modulation by ambient pO2 levels. The role of Ca2+ ions in exocytosis of DCV and 5-HT release from NEB cells was tested in experiments with Ca2+ ionophore (A23187). Exposure of cultures to 5 micrograms/ml of ionophore resulted in up to 40% reduction in 5-HT content of NEB cultures as well as increased exocytosis of DCV. Our overall findings are consistent with a view that NEB cells are chemosensory in nature and that Ca2+ signaling pathway is involved in stimulus-secretion coupling. Further refinements in cell separation and culture methodology are required before more detailed investigation of NEB cell membrane properties, signal transduction mechanisms, and intracellular signaling pathways can be carried out.

Localization of cholecystokinin-like and calcitonin-like peptides in infant carotid bodies: a light- and electron-microscopic immunohistochemical study

Previous immunohistochemical studies have identified several regulatory peptides in the carotid body chief cells in both humans and animals. These peptides, together with amines, may be important in the modulation of the chemoreflex by the carotid body. We report the localization and distribution of calcitonin and cholecystokinin-like (CCK) immunoreactivity in chief cells of human infant carotid body by light- and electron-microscopic immunohistochemical techniques. Consecutive sections immunostained with calcitonin and/or CCK antibodies revealed positively stained chief cells, both alone and in clusters, scattered throughout the carotid body lobule. Generally more chief cells were positive for calcitonin than for CCK. This was confirmed by quantitative analysis showing that the ratio of calcitonin to CCK immunoreactive cells was consistently > 2:1 in all cases studied. There was no apparent correlation between the immunoreactivity for the two peptides and the age, sex, or postmortem interval. Calcitonin-like and CCK-like immunoreactivities were localized electron-microscopically over the dense core granules of the chief cells. Calcitonin and CCK-like peptides in carotid body chief cells may act as neurotransmitters or neuromodulators involved in chemoreception.

A case report of double-orifice tricuspid valve

A heart specimen with double-orifice tricuspid valve is described. The tricuspid valve was divided into the anterior and posterior orifices by a bridge of leaflet tissue. The valve was stenotic because of the arcade deformity of the anterior papillary muscle to which the bridging leaflet tissue had short chordal insertions. The anterior orifice was regurgitant as a result of a deficient septal leaflet. Clinical correlation was obtained by magnetic resonance imaging of the specimen. The functional significance of the malformed valve was assessed by three-dimensional reconstruction of the two-dimensional magnetic resonance images.

Hyperplasia of bombesin-immunoreactive pulmonary neuroendocrine cells and neuroepithelial bodies in sudden infant death syndrome

The distribution and frequency of bombesin immunoreactive neuroendocrine (NE) cells including neuroepithelial bodies (NEB) was analyzed morphometrically in lung sections from 25 infants who died of sudden infant death syndrome (SIDS) and 25 control infants. The control group included infants age-matched to those with SIDS, as well as subjects ranging in age from early to late infancy, to define the postnatal development of pulmonary NE-cell system. Quantitative analysis was performed on lung sections immunostained with monoclonal antibody against bombesin and the contents of bombesin-like peptide in lung extracts were measured by a specific radioimmunoassay (RIA). In control infants, the frequency of NE cells was high at birth but decreased dramatically during the first year of life. In SIDS infants, the frequency of NE cells, the size of NEB, and the mean concentration of bombesin-like peptide detected by RIA were significantly increased compared to those values for age-matched controls. These findings suggest hyperplasia of bombesin-immunoreactive NE-cell system in the lungs of SIDS infants. Since NEB are thought to function as hypoxia-sensitive airway chemoreceptors and since these cells are prominent in the neonates but decline postnatally, we speculate that chronic hypoxia and/or developmental delay may be responsible for this alteration in the lungs of SIDS victims. Potential dysfunction of pulmonary NE-cell system, compounded by other abnormalities in the autonomic regulation of respiration may be of importance in the pathogenesis of SIDS.

Serotonin in the human infant carotid body

By immunocytochemistry serotonin was localized in the chief cells of the carotid body in human infants. Radioenzymatic measurement of the serotonin concentration revealed that it represents a significant proportion of the total amine content of the carotid body.

Sudden infant death syndrome: increased carotid-body dopamine and noradrenaline content

Carotid bodies from infants dying of sudden infant death syndrome contained significantly higher concentrations of dopamine (10-fold) and noradrenaline (3-fold) than those from age-matched control infants. Administration of dopamine inhibits respiration by direct action on the carotid body, and it is suggested that the elevated levels of endogenous catecholamines found in victims of sudden infant death syndrome may compromise the normal function of the carotid body, particularly the ventilatory response to hypoxia.

Ultrastructure of carotid bodies in sudden infant death syndrome

Recent studies have implicated an abnormality in carotid body structure and function in the pathogenesis of sudden infant death syndrome (SIDS). In the present investigation, the light and electron microscopic findings in carotid bodies from ten victims of SIDS were compared with those in six control infants and five infants dying of congenital heart disease. The cross-sectional area of carotid body chemoreceptor cells and the frequency, distribution, and size of neurosecretory granules were assessed morphometrically. The area of carotid body occupied by chemoreceptor cells (the functional area) was comparable in SIDS victims, control infants, and infants with congenital heart disease. By electron microscopy, the carotid body chief cells from all groups contained numerous electron-dense neurosecretory granules. Distribution, frequency, and size of neurosecretory granules in SIDS victims and control infants did not differ significantly. Morphology of carotid bodies from SIDS victims was found to be normal. The presence of neurosecretory granules in chemoreceptor cells of SIDS victims suggests that the cellular mechanism of neurotransmitter synthesis and storage is not altered.

The effect of LH-RH administration on LH release in the female rabbit

Intracarotid infusion of LH-RH to female rabbits stimulated a significant increase in plasma LH concentration in the jugular vein. This response varied with the reproductive state of the animal, with a greater release occurring in oestrous (spontaneous or oestrogen-induced) and non-receptive does than in pseudopregnant or ovariectomized animals. If ovariectomized rabbits were pretreated with oestrogen, the pituitary response to LH-RH was restored. These findings suggest that there is little change in pituitary sensitivity to LH-RH infusion between oestrous and non-receptive rabbits, although pseudopregnancy (high physiological levels of progesterone) or ovariectomy inhibit its ability to respond to a releasing-hormone stimulus.

The effects of prostaglandin and mating on release of LH in the female rabbit

The release of LH in response to prostaglandin (PG) treatment of female rabbits in various reproductive states was compared with the surge following mating. Intracarotid infusion of PGE-2 or PGF-2alpha (0-3--900 microgram/h) into non-receptive and pseudopregnant does resulted in small, 2--4-fold elevations in jugular vein LH concentration. Similar doses of PGF-2alpha in oestrogen-pretreated, oestrous does stimulated a 13-fold increase in plasma LH levels. Mating resulted in a much larger release of LH, as plasma levels increased approximately 60-fold from 1-1 +/- 0-2 (S.E.M.) ng/ml to 67-8 +/- 10-5 ng/ml. These results indicate that PG can stimulate the hypothalamic-hypophysial axis to release LH in non-receptive, pseudopregnant and oestrogen-pretreated, oestrous rabbits.