Nicole Larnicol

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). In the retrotrapezoid nucleus, a structure involved in respiratory rhythmogenesis and chemoreception, immunoreactivity was detected in hypoxic but not in hypercapnic cats. Neurons in the nucleus raphe pallidus preferentially expressed c-fos in response to hypercapnia. Labelled neurons were concentrated in the dorsal and gelatinosus subnuclei of the solitary tract following hypoxia and hypercapnia, respectively. Our data suggest that some neurons that express c-fos in hypoxic or hypercapnic cats may be involved in coordination of cardiovascular and respiratory function.

Somatotopy in the phrenic motor nucleus of the cat as revealed by retrograde transport of horseradish peroxidase

Cats received unilateral or bilateral horseradish peroxidase (HRP) injections into various portions of the diaphragm. In two experiments one of the cut cervical roots of the phrenic nerve was immersed in HRP. The phrenic motoneurons located in the fifth and occasionally the fourth cervical segment send their axons, via the upper phrenic root, to pars sternalis and pars costalis of the diaphragmatic dome whereas the neurons of the sixth segment innervate preferentially the dorsal portion both crura and dome. No evidence of contralateral innervation of the diaphragm was obtained.

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. Sneezes were elicited in anaesthetized adult cats by driving air puffs to the superior nasal meatus through a catheter. Additional cats were used as controls for anaesthesia and for catheter insertion into the nostril. In sneezing cats, immunoreactivity was evoked in projection areas of the ethmoidal afferents which innervate the superior nasal meatus, e.g. the subnuclei caudalis, interpolaris and in the interstitial islands of the trigeminal sensory complex. Immunoreactivity was also markedly enhanced in the areas devoted to respiratory control in the medulla (solitary complex, nucleus retroambiguus) and in the pontine parabrachial area. C-Fos expression was also evoked in the lateral aspect of the parvicellular reticular formation in sneezing cats. This area might be of major importance in the adaptation of the ventilatory system to expulsive functions.

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. For this purpose, we compared the subnuclear distribution of Fos-like immunoreactivity within the NTS following VNS at frequencies selected for their low (1 Hz) or high (10 Hz) therapeutic efficacy. In addition, NADPH diaphorase histochemistry was conducted in double-labeling experiments to check whether activated neurons may express nitric oxide (NO). We demonstrated that increasing pulse frequency had a major influence on the cardiorespiratory response to VNS and on the amount of activated neurons within NTS subdivisions engaged in cardiorespiratory control. These data, in line with clinical observations, suggested that within the range of therapeutic frequency, VNS may favor the regulation by vagal inputs of cortical activities within limbic areas involved in both epileptogenesis and cardiorespiratory afferent control. Furthermore, we did not find any evidence that anticonvulsant VNS might trigger NOergic neurons in the NTS.

Spinal localization of the intercostal motoneurones innervating the upper thoracic spaces

At the rostral level of the thorax, the intercostal muscles participate both in postural and respiratory functions to a variable degree depending upon the considered muscle: external intercostal, intercartilaginous, internal intercostal, and triangularis sterni. In order to determine if these physiological properties are related to a special organization at the spinal cord level, we have used the retrograde transport of horseradish peroxidase as a tool for studying the spinal distribution of intercostal motor cells in the adult cat. Results suggest that the intercostal motoneurones could be distributed, in the ventral grey horn, among two areas according to the respiratory or postural muscle specialization.

MATERNAL CAFFEINE INGESTION DURING GESTATION AND LACTATION INFLUENCES RESPIRATORY ADAPTATION TO ACUTE ALVEOLAR HYPOXIA IN NEWBORN RATS AND ADENOSINE A2A AND GABAA 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. The possibility that such caffeine exposure may have long-term consequences on brain development has led to several behavioral investigations on animal models. Despite the crucial role played by adenosine receptor systems in neonatal breathing control, few studies in vitro have been concerned with the consequences of maternal caffeine absorption on breathing, and none in the unrestrained intact animal. The present investigation analyzed the influence of caffeine exposure via placental and milk transfer on resting ventilation and on the response to moderate alveolar hypoxia of 0 to 2-day-old newborn rat (P0-P2) together with the possible underlying mechanisms. Dams absorbed caffeine (46+/-3 mg/kg/day) via drinking fluid (0.2 g/L) throughout gestation, in conditions mimicking moderate human consumption. Caffeine exposure did not significantly affect basal respiratory parameters. In contrast, it attenuated both the early increase and the secondary decrease in ventilation triggered by moderate alveolar hypoxia (11% O2 inhaled). The abolition of Fos protein expression evoked by hypoxia suggested that caffeine exposure may decrease the activity of O2-sensing peripheral chemoreceptor pathway. From real-time PCR data, those functional alterations were associated to increases in A2A adenosine receptor and alpha2 GABA(A) receptor subunit mRNAs in the medulla. This indicates that, even at moderate doses, maternal caffeine consumption may induce a series of subtle developmental alterations that may affect modulation of breathing control in the neonate in pathological situations such hypoxia.

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). In newborns, DOI elicited a long-lasting respiratory depression by decreasing both tidal volume and respiratory frequency. In adults, DOI retained a depressant influence, although attenuated, on tidal volume. In contrast, it elicited an increase in respiratory frequency. In separate subsets of newborn and adult rats, immunohistochemistry has been used to monitor c-fos expression induced by DOI in the medullary and pontine regions involved in respiratory control. Counts of immunoreactive neurons indicated a marked increase in the neuronal populations activated in the adult compared to the newborn rat. The response to both experimental factors (newborn vs. adult controls) and drug (injected vs. control age-matched rats) were more pronounced in mature animals. Among developmental changes in the pattern of labeling, DOI elicited Fos expression in the adult but not in the neonate in the ventrolateral subnucleus of the nucleus of the solitary tract, the parabrachial area and the Kölliker-Fuse nucleus. This finding suggested that changes in the respiratory response to DOI might at least partly depend on maturational events within networks involved in the modulation of respiratory timing.

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. Postganglionic neurons from parasympathetic origin could be labelled in the sphenopalatine ganglion. These neurons probably supply mucosal secretory glands. They are in the same size range as the bulk of neurons in the same ganglia.

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.

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-HT2 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-HT2A/2C receptors by the agonist 1-(2.5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), and we delineated central structures possibly involved in this response, using Fos expression as a marker of neuronal activation. We demonstrated that intraperitoneal injection of 5 mg/kg DOI produced a long-lasting decrease in respiratory frequency and tidal volume, which could be blocked by the antagonist ritanserin. Fos immunohistochemistry suggested that the rostral ventrolateral medulla and the lateral paragigantocellular nucleus might have a key role in the respiratory response to 5-HT2 receptor activation. In addition, double immunostaining for Fos and tyrosine hydroxylase suggested that the contribution of catecholaminergic neurons to this response might be modest and indirect.