Vagal pulmonary afferents and central respiratory effects of 5-HT in newborn rats.

In decerebrate newborn rats, serotonin (5-HT) is a respiratory depressant via activation of 5-HT2 receptors, whereas it evokes respiratory stimulant effects when applied to the isolated brainstem obtained from the newborn rat. This discrepancy could be due to deafferentation in the in vitro preparation. The aim of our study was to analyse the role of vagal afferents in the modulation of central respiratory effects of 5-HT. In decerebrate cervically or abdominally bivagotomized newborn rats aged between 0 and 3 days, we recorded electrical activity from the diaphragm and from a hypoglossally innervated tongue muscle, as well as cardiac frequency (Fc), before and after application of 5-HT to the floor of the IVth ventricle. The effects of related agents (a 5-HT1A agonist, 8-OH DPAT, and a 5-HT2 agonist, DOI) were studied in cervically bivagotomized animals. For comparison, and to assess the spontaneous variability in inspiratory frequency (Fi) and Fc, sham groups were studied. Each group comprised ten newborn rats. In cervically bivagotomized newborn rats, 5-HT induces a significant increase in Fi, which is the opposite to that observed in decerebrate newborn rats with intact vagi. This respiratory effect is mediated in particular, via activation of 5-HT1A. By contrast, in abdominally bivagotomized newborn rats, a decrease in Fi was observed in response to 5-HT (as previously described in decerebrate animals with intact vagi). We conclude that pulmonary vagal afferents modulate the central respiratory action of 5-HT in decerebrate newborn rats, explaining the conflicting results between in vivo and in vitro experiments.

Central effects of 5-HT on respiratory rhythm in newborn rats in vivo.

The role of 5-HT in inducing apnoeas (a major element in sudden infant death syndrome) is controversial because while 5-HT is a respiratory depressant in vivo, it evokes respiratory analeptic effects when applied to the isolated brainstem of the newborn rat. In decerebrate newborn rats, the electrical activity of the diaphragm and that of a hypoglossally innervated tongue muscle, as well as the cardiac frequency (Fc), were recorded before and after the application of 5-HT and related agents to the floor of the IVth ventricle. To assess the spontaneous variability in inspiratory frequency (Fi) and Fc, a sham group was studied. A decrease in Fi was observed in response to 5-HT. This respiratory depressant effect was associated with an activation of the tongue muscle, but there was no change in Fc. Application of agonists elicited a small increase in Fi linked to activation of 5-HT1A receptors, and decreases in both Fi and the activity of the tongue muscle resulting predominantly from activation of 5-HT2 receptors. The decrease in Fi was much smaller in newborn rats than that reported in newborn kittens. Indeed, in newborn rats, we did not observe long-lasting apnoeas. Our results differ from those obtained from the newborn rat in vitro, inasmuch as in vivo 5-HT essentially depressed the respiratory rhythm generator. The role of the afferent system appears to be crucial in modulating the action of 5-HT.

Maturation of the mammalian respiratory system.

In this review, the maturational changes occurring in the mammalian respiratory network from fetal to adult ages are analyzed. Most of the data presented were obtained on rodents using in vitro approaches. In gestational day 18 (E18) fetuses, this network functions but is not yet able to sustain a stable respiratory activity, and most of the neonatal modulatory processes are not yet efficient. Respiratory motoneurons undergo relatively little cell death, and even if not yet fully mature at E18, they are capable of firing sustained bursts of potentials. Endogenous serotonin exerts a potent facilitation on the network and appears to be necessary for the respiratory rhythm to be expressed. In E20 fetuses and neonates, the respiratory activity has become quite stable. Inhibitory processes are not yet necessary for respiratory rhythmogenesis, and the rostral ventrolateral medulla (RVLM) contains inspiratory bursting pacemaker neurons that seem to constitute the kernel of the network. The activity of the network depends on CO2 and pH levels, via cholinergic relays, as well as being modulated at both the RVLM and motoneuronal levels by endogenous serotonin, substance P, and catecholamine mechanisms. In adults, the inhibitory processes become more important, but the RVLM is still a crucial area. The neonatal modulatory processes are likely to continue during adulthood, but they are difficult to investigate in vivo. In conclusion, 1) serotonin, which greatly facilitates the activity of the respiratory network at all developmental ages, may at least partly define its maturation; 2) the RVLM bursting pacemaker neurons may be the kernel of the network from E20 to adulthood, but their existence and their role in vivo need to be further confirmed in both neonatal and adult mammals.

Role of respiratory and non-respiratory neurones in the region of the NTS in the elaboration of the sneeze reflex in cat.

Extracellular recordings were made in the dorsal respiratory group (DRG) and adjacent reticular formation following single-shock stimulation of the anterior ethmoidal nerve (AEN) and during sneeze evoked by repetitive stimulation of the AEN in nembutal-anaesthetized, curarized and ventilated cats. These neurones were characterised according to (i) their activity during the respiratory cycle (as inspiratory augmenting or decrementing (I Aug or I Dec), expiratory augmenting or decrementing (E Aug or E Dec), silent or tonic), and (ii) their axonal projection (bulbospinal or non-bulbospinal-non-vagal (BS or NBS-NV)). Following single-shock stimulation of the AEN, most of the inspiratory neurones were transiently inhibited, whereas E Aug neurones were activated and E Dec neurones were activated and then inhibited. Silent neurones responded with a multispike or a paucispike pattern. Following repetitive stimulation of the AEN and during the resulting sneeze reflex, I Aug neurones increased their activity in parallel with the phrenic activity, I Dec neurones fired at the onset and at the end of the inspiration, E Dec and some silent neurones fired either during the compressive phase or after the expulsive phase, whereas E Aug and some silent neurones fired during the expulsive phase. We conclude that sneeze involves a reconfiguration of the central respiratory drive which uses, at least partly, the respiratory network to trigger a non-ventilatory defensive motor act.

An improved mechanical air puff stimulator that allows activation of a variety of endoepithelial receptors and is suitable for the study of reflexes in animals and humans.

Studies of endoepithelial-triggered reflexes, such as nasal respiratory reflexes, are difficult to carry out in humans without a non-traumatic and reliable stimulation device. The air puff stimulator described allows us to deliver air puffs of brief duration at various intensities, frequencies, and temperatures. The stimulation is non-traumatizing and non-nociceptive. We have successfully used it in animals as a source of specific stimuli to enable us to study central and peripheral neuronal responses evoked by activation of endonasal dynamically sensitive receptors. Immunohistochemical studies of the c-fos expression evoked during sneezing elicited by air puffs provided additional evidence for the specificity of this particular stimulation technique. We suggest that the use of such a non-traumatizing air puff stimulator could be extended to human studies. It might be particularly useful in developmental studies of endoepithelial-triggered reflexes such as those respiratory reflexes whose immaturity at birth can be life-threatening.

Central effects of 5-HT on activity of respiratory and hypoglossally innervated muscles in newborn kittens.

1. In decerebrate kittens (n = 29), electrical activity was studied in the 3rd intercartilaginous (inspiratory), the 9th internal intercostal (expiratory) and the hypoglossally innervated muscles (geniohyoid m. and sternohyoid m.) evoked by the application of 5-HT (n = 16) or related agents (5-HT1A agonist, 8-OH-DPAT (n = 6) and 5-HT2 agonist, DOI floor of the IVth ventricle. 2. The application of a control solution (n = 2) produced no significant changes either in minute inspiratory frequency (Fi) or in the electrical activity of the muscles studied. Except for these controls, only one trial with one dose of one drug was performed in a given kitten. 3. A dose-related decrease in Fi was observed in response to 5-HT. Low doses (50-500 nmol, n1 = 8) induced a long-lasting bradypnoea; high doses (5000-10,000 nmol, n2 = 8) induced prolonged periods of apnoea. 4. The apnoeas observed in tracheotomized (n = 3) or non-tracheotomized (n2 = 8) kittens were mainly of central origin and linked to the lengthening of expiratory time. The expiratory muscle activation came on with the reinforcement of the activity of hypoglossally innervated muscles. 5. Application of agonists showed that both the 5-HT-dependent modulation of Fi and the effects of 5-HT on the activity of the muscles studied resulted predominantly from activation of 5-HT2 receptors.

[Exploratory study of amitriptyline resistance in depressed patients: results of WHO French collaborating center on depressions resistant to treatments]. / Etude exploratoire de la résistance à l'amitriptyline chez les déprimés : résultats du centre français collaborateur OMS sur les dépressions résistantes aux traitements.

A multicountry, multicentre double-blind study in a group of depressives, coordinated by the Mental Health Division of the World Health Association (WHO) has been done. The goal of the study is to determine whether the therapeutic effects of amitriptyline can be enhanced and potentiated by combining it with an antioxydant (gingko biloba). An exploratory study has preceded the main study which had the objective to estimate the proportion of non-response patient to amitriptyline. We report the results concerning the French center. 23 inpatients meet the ICD-10 criteria for depression (F32 and F33) and were treated during 6 weeks by amitriptyline with the initial daily dose of 50 mg until the maximum dose of 200 mg. The proportion of non-responsive patient to amitriptyline was 34.78 (95% confidence interval : 15.32 to 54.24%), all clinically deteriorated.

Activities of vagal receptors in the different phases of sneeze in cats.

We studied the activity of 50 slow-adapting receptors (SAR), 13 rapidly-adapting receptors (RAR) and 3 expiratory modulated receptors in the different phases of sneeze in tracheostomized and non-tracheostomized anaesthetized cats. SAR activity increased progressively during the first phase of the preparatory inspiration in parallel to integrated diaphragmatic activity. During the second phase of the preparatory inspiration, SAR increased their discharge frequency; higher threshold SAR and RAR were recruited. During the compressive phase, discharge of SAR kept stable or increased slightly in parallel to an increase in transpulmonary pressure, while expiratory modulated receptors were activated. During the expulsive phase, only RAR were activated. Increase in transpulmonary pressure at the end of the inspiration phase of sneeze shortened expiratory duration and increased the rate of rise of expiratory muscle activity. Increase in transpulmonary pressure at the end of the compressive phase further shortened expiratory duration. These results suggest: first, a facilitatory effect on the triggering of the second phase of the preparatory inspiration from SAR; second, a modulation of the early stage of expiration by SAR, RAR and expiratory modulated receptors during the compressive phase; third, a permissive effect on a rapid expulsive thrust by SAR which can be further limited by RAR; fourth, a facilitatory effect on the triggering of inspiratory activity that follows the expiratory thrust by RAR. Both SAR and RAR might participate in the occurrence of successive sneeze in an attack and in the increased frequency of sneezing. Our results suggest that complex convergent inputs from nasal and vagal receptors, which alter the respiratory rhythm and rhythmogenesis, modulate finely the sneeze reflex.

Central effects of 5-HT on respiratory and hypoglossal activities in the adult cat.

The activities of the diaphragmatic, internal intercostal and hypoglossal-innervated muscles were studied in adult decerebrate cats in response to 5-HT and related agents (8-OH-DPAT and DOI). The drugs were placed on the floor of the IVth ventricle. The mean respiratory frequency (Fi) increased (124-193% of the control value) within 3 min of the 5-HT application, and decreased thereafter (30-90%). The mean Ti and Te changed similarly, but opposite to Fi. With some delay, the hypoglossal-innervated muscles were tonically activated or exhibited increased activities. Methysergide pretreatment completely blocked the effect of 5-HT on all the respiratory parameters and the hypoglossal-innervated muscles activities. The responses to 8-OH-DPAT and DOI indicate that 5-HT modulates the respiratory frequency via activation of both 5-HT1A and 5-HT2 receptors. Nevertheless, the effect of 5-HT on both the expiratory and hypoglossal-innervated muscles seems to depend on 5-HT2 receptors activation only.

Influence of vagal afferents in the sneeze reflex in cats.

We studied the effects of bilateral vagotomy and step pulmonary inflations (5, 10, 15 mmHg, i.e., 0.66, 1.33, 2 kKPa) on sneeze reflex in ketamine-anaesthetized cats. Bilateral vagotomy lengthens the duration of preparatory inspiration and diminishes the amplitude of expiratory activities in sneeze. In contrast, 5 mmHg pulmonary inflation facilitates the sneeze. It shortens the inspiratory preparation and increases the frequency of sneeze attacks. At 10 mmHg pulmonary inflations, inspiration is inhibited and only expiratory thrust occurs. At 15 mmHg pulmonary inflations, vagal afferent stimulations inhibit the sneeze.

Nonvagal reflex apnea in the newborn kitten and during the early postnatal period.

The aim of this work was to study the nonvagal mechanisms which might induce apneic reflexes in kittens. Experiments were performed on spontaneously breathing animals (19 kittens at different postnatal ages). Animals were anesthetized (halothane) or decerebrated by transcollicular section of the brainstem. Weakly nociceptive cutaneous stimulations and various oral stimulations were administered in all animals. In 10 kittens, one of the lingual nerves was stimulated electrically. In 3 decerebrate kittens the effects of serotonin on respiratory activity and on muscles innervated by the hypoglossal nerve were studied. All the stimulations produced apneas of variable duration, and expiratory reinforcement was associated with activation of pretracheal muscles. Similar effects were observed after applying serotonin to the floor of the 4th ventricle. Thus serotonin may be involved in the mechanisms that cause some apneas.

[Motor and staged sensory conduction velocities of the ulnar nerve in normal subjects]. / Vitesses de conduction motrices et sensitives étagées du nerf ulnaire chez le sujet normal.

Normative data of ulnar motor and orthodromic sensitive conduction velocities are performed at different levels on 68 (19 to 49 year old) adult population which included 35 men and 33 women. In fact, 102 ulnar nerves are tested, 51 nerves for female population and male population respectively. For motor conduction velocities, the ulnar nerve is stimulated at five levels: at the wrist level, below elbow, at the elbow, above elbow, and at the axillary point; the motor responses were picked up on the hypothenar muscles (surface electrodes). For orthodromic sensitive conduction velocities, the fifth finger is stimulated and the electrical activities are picked up by surface electrodes which are placed at the same points. The difference between the conduction velocities values measured on the below elbow/wrist segment and the above elbow/wrist segment proved to be satisfactory for the possible detection of a compression of the ulnar nerve at the elbow.

Oral stimulations induce apnoea in newborn kittens.

The aim of the present work was to study oral trigeminal mechanisms which might induce apnoeic reflexes in adult cats and kittens at different postnatal ages. Various oral stimulations and electrical stimulations of the lingual nerve produced apnoeas whose duration decreased with age until three weeks of life. In addition, swallowing was only rarely observed before 5 days and then occurred with apnoea until the third week. Responses became similar to those observed in adults between weeks 3 and 4. Thus, in kittens, the nervous control which regulates coordination between breathing and swallowing appears to be immature at birth.

Influence of trigeminal nasal afferents on bulbar respiratory neuronal activity.

This study examined the influence of nasal trigeminal afferents, the anterior ethmoidal nerve (AEN) and posterior nasal nerves (PNN) on the spike discharges of respiratory-related neurons recorded in the ventral respiratory group (VRG) (2.6-3.5 mm lateral to the midline, from 1 mm rostral to 3 mm caudal to the obex and at depth of 2-4 mm below the dorsal surface). Electrical stimulations to the AEN and PNN were administered to 10 pentobarbital anaesthetized cats and to 8 ketamine anaesthetized, vagotomized, curarized and ventilated cats. Single shock stimulations of either nerve evoked transient and total inhibition of inspiratory activities. Expiratory-related neurons of the VRG presented three patterns of activity in response to stimulation:excitation, inhibition or inhibition followed by excitation. More generally, expiratory units are activated with a short latency. In the course of repetitive stimulation of the AEN and PNN we observed a prolongation of the spontaneous inspiratory discharge which presented transient, short inhibition in response to each shock. Most expiratory units presented a short activation which was synchronous with the transient inhibition of inspiratory activities. When repetitive stimulation provoked a sneeze-like response, we observed a progressive increase in the duration of transient inspiratory inhibition first, associated with a progressive reinforcement of transient expiratory activation. Secondarily, just before the expiratory thrust, we noted a stronger inhibition of the inspiratory activity which preceded a high-frequency (400 Hz) expiratory discharge. Nasal afferents exert a forceful excitatory effect on bulbospinal (BS) and non-bulbospinal-non-vagal (NBS-NV) expiratory cells of the VRG. The effects due to vagotomy and curarization are discussed.

[Postnatal development of central motor pathways. An electrophysiological study]. / Développement postnatal des voies motrices centrales. Etude électrophysiologique.

The percutaneous electrical stimulation of the brain and spinal cord has been used to study the central motor pathways in 19 healthy full-term newborns and in 19 infants. The evoked compound muscle action potential were recorded by bipolar surface electrodes fixed on the skin overlying the thenar eminence muscles and the tibialis anterior muscle. In full-term newborns, the responses of lower limb muscles to cortical stimulation are more difficult to obtain that those of upper limb muscles. At birth, the conduction velocity of central motor fibres along the spinal cord are around 10 m/s, 4 or 5 times lower that the lowest values published for adult subjects. Thus, as has been demonstrated in animals, there seems to exist in man a very clear dissociation between myelination of central motor pathways and that of peripheral motor fibres.

[Electrophysiological aspects of peripheral nervous system development]. / Aspects électrophysiologiques du développement du système nerveux périphérique.

Different aspects of the maturation of the peripheral nervous system have been studied in infants, essentially during the first year of postnatal life. Absolute refractory periods which enable indirect estimation of excitability have been measured in both nerve and muscle fibers. It appears that already at birth, the absolute refractory period is characteristic for a given group of nerve fibres. In each group of nerve fibres, the absolute refractory period is not correlated to conduction velocity (ie fibre diameter) and remains rather constant during development. However, the absolute refractory period of the most excitable fibres is smaller than the absolute refractory period of motor fibres independent of the subject's age. On the other hand, the absolute refractory period of muscle fibres is slightly higher in premature in comparison with full-term neonates and adults. The diameter growth of different categories of nerve, fibers (motor--IA--non nociceptive cutaneous) is assessed by measurement of conduction velocities. At each age the IA fibre conduction velocities are the highest. The marked difference which exists between length development and postnatal increase of the fibre diameter explains the particular evolution of conduction times.

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.

[Effect of acute administration of acamprosate on the risk of encephalopathy and on arterial pressure in patients with alcoholic cirrhosis]. / Effet de l'administration aiguë d'acamprosate sur le risque d'encéphalopathie et sur la pression artérielle chez les malades atteints de cirrhose alcoolique.

To evaluate the risk of hepatic encephalopathy and arterial hypotension in cirrhotic patients after acute administration of acamprosate, a GABA mimetic drug used in the weaned alcoholic, a randomized double-blind trial was conducted in 24 cirrhotic patients with low or moderate hepatic insufficiency (Pugh grade A or B). Twelve patients received 666 mg (2 tablets) of acamprosate and 12 received placebo. The 2 groups were similar before treatment, except for a male predominance in the acamprosate group. Tested parameters were the P100 latency of visual evoked potentials using a checkerboard pattern reversal as stimulus, the number connection test and the arterial blood pressure in upright and recumbent positions. The two first parameters were studied before and 2 hours after treatment. Blood pressure was recorded every half hour during 6 hours. No significant effect on the development of subclinical hepatic encephalopathy was noted. Nevertheless, even if some authors disagree with the GABA hypothesis of hepatic encephalopathy, it is possible that the dose was too low to induce subclinical hepatic encephalopathy. A study with more prolonged treatment could be necessary to be sure of the drug's safety in these patients. On the other hand, a transient decrease of diastolic arterial blood pressure was observed without significant systolic blood pressure modification. These results suggest that a moderate dose of acamprosate does not induce subclinical encephalopathy, but transient diastolic hypotension.