Antenatal environmental stress and maturation of the breathing control, experimental data.

The nervous respiratory system undergoes postnatal maturation and yet still must be functional at birth. Any antenatal suboptimal environment could upset either its building prenatally and/or its maturation after birth. Here, we would like to briefly summarize some of the major stresses leading to clinical postnatal respiratory dysfunction that can occur during pregnancy, we then relate them to experimental models that have been developed in order to better understand the underlying mechanisms implicated in the respiratory dysfunctions observed in neonatal care units.

Maternal caffeine ingestion during gestation and lactation influences respiratory adaptation to acute alveolar hypoxia in newborn rats and adenosine A2A and GABA A receptor mRNA transcription.

Caffeine is a widely used psychostimulant freely crossing the placental barrier. At the doses usually absorbed, it acts as an antagonist of both A1 and A2A adenosine receptors. Pregnant women are generally not advised to limit their caffeine consumption and thus expose their progeny to the drug during the whole of gestation and lactation.

Prenatal diazepam exposure alters respiratory control system and GABAA and adenosine receptor gene expression in newborn rats.

In experimental animals, prenatal diazepam exposure has clearly been associated with behavioral disturbances. Its impact on newborn breathing has not been documented despite potential deleterious consequences for later brain development. We addressed this issue in neonatal rats (0-2 d) born from dams, which consumed 2 mg/kg/d diazepam via drinking fluid throughout gestation.

Consequences of prenatal exposure to diazepam on the respiratory parameters, respiratory network activity and gene expression of alpha1 and alpha2 subunits of GABA(A) receptor in newborn rat.

Diazepam (DZP) enhances GABA action at GABA(A) receptor. Chronic prenatal administration of DZP delays the appearance of neonatal reflexes. We examined whether maternal intake of DZP might affect respiratory control system in newborn rats (0-3 day-old).

Autonomic response and Fos expression in the NTS following intermittent vagal stimulation: importance of pulse frequency.

Chronic intermittent stimulation of the vagus nerve (VNS) is an approved adjunctive therapy of refractory epilepsy. Nevertheless, the circuits triggered by VNS under the variable conditions used in patients are not well understood. We analyzed the effect of increasing pulse frequency on physiological variables (intragastric pressure, cardiac and respiratory frequencies) and neuronal activation in the solitary tract nucleus (NTS), the entry level of peripheral vagal afferents, in the rat.

Effect of postnatal exposure to caffeine on the pattern of adenosine A1 receptor distribution in respiration-related nuclei of the rat brainstem.

Caffeine, which belongs to the methylxantine family of compounds, is commonly ingested in a range of beverages such as coffee, tea, and cola drinks. It is also used therapeutically and is frequently employed in the treatment of respiratory disturbances in human neonates. The aim of the present work has been to examine the ontogeny of the adenosine A1 receptor system in the brainstem of the newborn rat following postnatal treatment with caffeine to mimic the therapeutic administration of caffeine to premature human infants.

Rhythmic activity from transverse brainstem slice of neonatal rat is modulated by nitric oxide.

We investigated the role of nitric oxide (NO) in the modulation of respiratory-like activity recorded from hypoglossal rootlets in brainstem slices of neonatal rats (P0-P8). Sodium nitroprusside (SNP), S-Nitroso-N-acetyl-D,L-penicillamine (SNAP) and diethylamine-NO (DEA-NO), three NO-donors, reversibly increased hypoglossal burst amplitude with inconsistent effects on burst frequency. Similar effects were also obtained with the endogenous substrate of nitric oxide synthase (NOS), L-arginine, whereas the inactive enantiomer D-arginine had no effect.

Postnatal changes in the respiratory response of the conscious rat to serotonin 2A/2C receptor activation are reflected in the developmental pattern of fos expression in the brainstem.

The influence on the breathing pattern of the activation of serotonin receptors belonging to the subtypes 2(A) and 2(C) (5-HT(2A/2C)) has been assessed in newborn and adult conscious rats. Rats were given an acute intraperitoneal dose of the agonist DOI (1-(2.5-dimethoxy-4-iodophenyl)-2-aminopropane; 5 mg/kg).

Brainstem and hypothalamic areas activated by tissue hypoxia: Fos-like immunoreactivity induced by carbon monoxide inhalation in the rat.

Acute ambient hypoxia interacts with the ventilatory and cardiocirculatory control systems, via the concomitant activation of arterial chemoreceptors and tissue oxygen-sensing mechanisms. Whether these latter mechanisms may trigger a specific pathway had not yet been elucidated. We addressed this issue, mapping Fos expression in adult conscious rats subjected to tissue hypoxia elicited by carbon monoxide inhalation, under conditions of minimal activation of arterial chemoreceptors.

5-HT(2A/2C) receptor-mediated hypopnea in the newborn rat: relationship to Fos immunoreactivity.

Previous data derived from anesthetized, decerebrate, or in vitro preparations suggested that 5-HT(2) receptor activation might be responsible for respiratory dysfunction. Such a mechanism has not yet been documented in the intact animal, but might be of clinical relevance to the apneic spells of the premature infant. In the present investigation on conscious newborn rats we analyzed the respiratory response to the activation of 5-HT(2A/2C) receptors by the agonist 1-(2.

Postnatal changes in Fos-like immunoreactivity evoked by hypoxia in the rat brainstem and hypothalamus.

We have recently used Fos expression in adult rats to map neuronal populations activated in the brainstem and hypothalamus during the acute ventilatory response to moderate hypoxia (O(2) 11%). Although present at birth, this response evolves postnatally. The present investigation aimed at a better understanding of these maturational processes by delineating structures that might functionally develop after birth.

Brainstem and hypothalamic areas involved in respiratory chemoreflexes: a Fos study in adult rats.

The adaptation to hypoxia and hypercapnia requires the activation of several anatomical structures along the neuraxis. In this study, using Fos immunoreactivity, we sought to map neuronal populations involved in chemoreflex networks activated during the responses to moderate hypoxia (O(2) 11%), and hypercapnia (CO(2) 5%) in the brainstem and the hypothalamus of the rat. In the medulla, hypoxia elicited marked and significant staining in the nucleus of the solitary tract (NTS), and in parapyramidal neurons located near the ventral surface, whereas hypercapnia evoked significantly c-fos only near the ventral surface in paraolivar neurons.

Changes in Fos-like immunoreactivity evoked by maturation of the sneeze reflex triggered by nasal air puff stimulation in kittens.

The sneeze reflex is a valuable tool for exploring the maturation of the respiratory control in the newborn as it alters both inspiratory and expiratory activities. Air puff stimulation of the superior nasal meatus innervated by ethmoidal afferents consistently evokes sneeze in adult cats. Such stimulation evokes only a reinforcement of expiratory activities in newborn kittens.

C-Fos-like immunoreactivity in the cat brainstem evoked by sneeze-inducing air puff stimulation of the nasal mucosa.

Sneeze is one of the most important protective reflex of the respiratory tract. It is elicited from trigeminal peripheral fields and results in major changes in the discharge patterns of the medullary respiratory-related neurons. The pattern of c-Fos-like immunoreactivity evoked by sneezing was explored as a structural approach to the networks involved in this particular model of trigemino--respiratory interactions.

c-fos-like immunoreactivity in the cat's neuraxis following moderate hypoxia or hypercapnia.

The overall pattern of c-fos immunoreactivity was studied in the brainstem and spinal cord of cats subjected to moderate hypoxia or hypercapnia. In control cats (normoxic, normocapnic), c-fos was expressed mainly in pontine and periaqueductal grey but not in brainstem structures engaged in respiratory control nor in the spinal cord. Both hypoxia and hypercapnia induced c-fos expression in the parabrachial area (pneumotaxic center).

The sneeze: maturation of the reflex in kittens.

This is the first study to compare the influence of nasal afferent stimulation on inspiratory and expiratory muscle activity during sneezing, in kittens and adult cats. In kittens, we demonstrate that nasal afferent stimulation does not reinforce inspiratory activity prior to the expiratory thrust as it normally does in adult cats. These stimulations evoke an active expiration similar to but weaker than the expiratory thrusts observed under the same conditions during sneezing in adult cats.

A comparative HRP study of the neuronal supply to the inferior and superior nasal meatus in the cat.

Neurons supplying the nasal mucosa in the cat were retrogradely labelled with horseradish peroxidase. Sensory trigeminal neurons to the inferior and superior nasal meati are somatotopically organized, according to the ophthalmic or maxillary origin of the afferents studied. Whatever their relative location, the cell bodies from nasal afferents were, on average, smaller than the overall cell population in the ganglion, in keeping with the high proportion of nasal receptors innervated by thin fibers.

Postnatal development of small and large dorsal root ganglion neurons in the cat. A study on cervical levels (C5-C6) and on phrenic afferents.

During feline postnatal development, the size of phrenic afferent neurons labelled by horseradish peroxidase was evaluated in comparison to that of the bulk of counterstained neurons located in the same cervical dorsal root ganglia (DRG) (C5-C6). From age 1 week to maturity, small and large cell components were individualized from experimental size distributions using a mathematical approach. The analysis of data in adult indicated a close correspondence between small cells and unmyelinated afferents and between large cells and myelinated afferents, respectively.

The cat cervical dorsal root ganglia: general cell-size characteristics and comparative study of neck muscle, neck cutaneous and phrenic afferents.

Sizes of neuronal somata in the cat cervical dorsal root ganglia were determined at different levels (C1-C8). The average value and class distribution of mean cell diameter were analyzed. The ganglia from C1 to C5 could be clearly distinguished from those at levels of brachial plexus afferents (C6-C8) with respect to cell size range, distribution and average.

Morphometrical study of the cat thoracic dorsal root ganglion cells in relation to muscular and cutaneous afferent innervation.

The sizes of neuronal somata in cat dorsal root ganglia were determined at the different thoracic segmental levels (T1-T13). The intersegmental variations in the average value and class distribution of diameters were analysed. The maximal and minimal average mean cell diameters were 51.

Identification of phrenic afferents to the external cuneate nucleus: a fluorescent double-labeling study in the cat.

In the cat, C5-C6 dorsal root ganglion cells related to phrenic afferents projecting directly to the ipsilateral external cuneate nucleus (ECN) were submitted to a double-labeling procedure using anterogradely transported Fast Blue and retrogradely transported Nuclear yellow. These afferents, certainly related to muscle spindles and/or Golgi tendon organs, are very few and terminate preferentially in the intermediate and rostral parts of the ECN. Our results confirm previous electrophysiological and histological studies on the participation of phrenic afferents to the spino-cuneo-cerebellar pathway ascending through the dorsal columns.

Identification of phrenic afferents in the dorsal columns: a fluorescent double-labeling study in the cat.

In this study in the cat, the tracer combination of the anterogradely transported Fast Blue and the retrogradely transported Nuclear Yellow was used to label dorsal root ganglion cells related to phrenic afferents running up through the ipsilateral dorsal column. These afferents are few; some of them leave the dorsal column near their segment of entry. Their localization in the dorsal column suggests that they are related to tendon and muscle receptors, which confirms previous electrophysiological studies.

An HRP study of the cat's spinal respiratory motoneurones during postnatal development.

The localization and morphology of spinal respiratory motoneurones (phrenic and intercostal) were studied in the cat by retrograde labelling using Horseradish Peroxidase (HRP), at different stages of postnatal development. At birth, the distribution of the phrenic and intercostal motoneurones in the cervical and thoracic ventral horn, respectively, is similar to that observed in adult animals. At birth, the phrenic and intercartilaginous motoneurone somata have respectively 60% and 40% of their adult volume, appearing much more developed than the motoneurones involved in the motor control of limbs.

Quantitative morphological changes in phrenic and intercostal motor columns and their respective spinal cord segments during postnatal development in the kitten.

In newborn kittens, the nervous control of breathing appears more mature than that of motricity which follows a cephalo-caudal evolution. In order to determine if the different postnatal evolutions of the respiratory and the motor function have an anatomical support at the spinal cord level, we made morphometric comparisons of the postnatal development of the spinal segments including motor columns sustaining both limb and respiratory movements (cervical and thoracic segments), with the postnatal development of segments containing only motoneurones involved in locomotion (lumbar segments). Furthermore, we used horseradish peroxidase to label cervical and thoracic groups of inspiratory motoneurones, i.