Armand Bianchi

Activity of dorsal respiratory group inspiratory neurons during laryngeal-induced fictive coughing and swallowing in decerebrate cats

Membrane potential changes and/or discharges from 36 inspiratory neurons were recorded intracellularly in the dorsal respiratory group (DRG; i.e., the ventrolateral subdivision of the nucleus tractus solitarii) in decerebrate, paralyzed, and ventilated cats. Electrical activities were recorded from both somata (n=10) and axons (n=26). Activities during quiet breathing were compared with those observed during fictive coughing and swallowing evoked by repetitive electrical stimulation of afferent fibers of the superior laryngeal nerve (SLN). These nonrespiratory behaviors were evident in paralyzed animals as characteristic discharge patterns of the phrenic, abdominal, and hypoglossal nerves. Twenty-six neurons exhibiting antidromic action potentials in response to electrical stimuli applied to the cervical (C3–5) spinal cord were classified as inspiratory bulbospinal neurons (IBSNs). These neurons were considered as premotoneurons. The remaining 10 inspiratory neurons (INAA) were not antidromically activated by electrical stimuli applied to either cervical spinal cord or ipsilateral cervical vagus. These neurons are thought to be propriobulbar neurons. We recorded the activity of 31 DRG inspiratory neurons (24 IBSNs and 7 I-NAA) during coughing. All but one (a late-recruited IBSN) discharged a burst of action potentials during the coughing-related phrenic nerve activity. Typically, ramp-like membrane depolarization trajectories and discharge frequencies during coughing were similar to those observed during inspiration. We recorded the activity of 33 DRG inspiratory neurons (23 IBSNs and 10 I-NAA) during swallowing. Most (28/33) neurons were briefly activated, i.e., discharged a burst of action potentials during swallowing, but peak discharge frequency decreased compared with that measured during inspiration. The membrane potentials of nine somata exhibited a brief bell-shaped depolarization during swallowing, the amplitude of which was similar to that observed during inspiration. These results suggest that some inspiratory premotoneurons and propriobulbar neurons of the DRG might be involved in nonrespiratory motor activities, even if clearly antagonistic to breathing (e.g., swallowing). We postulate the existence in the medulla oblongata of adult mammals of neurons exhibiting a “functional flexibility”.

Biopolymer hydrolysis and bacterial production under ambient hydrostatic pressure through a 2000 m water column in the NW Mediterranean

Kinetic parameters for aminopeptidase, phosphatase, and bacterial production rates were studied during spring and fall through a 2000 m water column in the NW Mediterranean. Bacterial production ranged from 60.4 ng at 30 m to 0.2 ng C l � 1 h � 1 at 2000 m. For both ectoenzymatic activities, the Km values ranged from 0.44 to 1.13mM for aminopeptidase activity and from 0.05 to 1.23mM for phosphatase activity. Depth profiles of the potential activity of aminopeptidase and phosphatase activity drastically decreased below depths of 100 m. At 1000 m, hydrolytic activities were one order of magnitude lower than the maximal rate measured in the surface layer. Despite this decrease, depthintegrated rates through the thickness of different water masses showed that the potential hydrolysis fluxes within the productive surface layer (10–200 m), through the twilight zone (200–1000 m depth), and through the deep water mass (1000–2000 m) were roughly the same order of magnitude. This study used the first assay for measuring ectoenzymatic activities of deep-sea microbial populations where pressure stresses were eliminated during sampling and incubation. The results showed that prokaryotic induced ectoenzymatic activities are affected by pressure conditions. Generally, aminopeptidase and phosphatase rates measured in samples maintained under in situ pressure conditions were 2.3 times higher than those measured in their decompressed counterparts. r 2002 Elsevier Science Ltd. All rights reserved.

Pharyngeal motoneurones: respiratory-related activity and responses to laryngeal afferents in the decerebrate cat

SummaryIn decerebrate, paralyzed and artificially ventilated cats, we recorded the discharge of 64 motor axons supplying the pharyngeal muscles. Filaments containing motor axons, with discharges related to the respiratory cycle (phrenic nerve activity), were teased from the pharyngeal branches of the vagus and glossopharyngeal nerves. Most units (n = 41) fired only during expiration and exhibited a steady, a decreasing or a late augmenting discharge pattern. These units were found only in vagal filaments. Twenty three units discharged during inspiration and exhibited a steady, a late augmenting or a tonic discharge pattern. The inspiratory-related units were present in both the vagus (n=13) and glossopharyngeal (n=10) nerves. Nineteen of 20 pharyngeal inspiratoryrelated units tested were activated at short latency (range 3.4 to 8.0 ms) by stimulation of afferents in the superior laryngeal nerve (SLN). In 13 of these, such stimulation also suppressed their spontaneous activity. SLN stimulation elicited in all 17 pharyngeal expiratory-related units tested a short latency (range 0 to 8 ms) reduction of activity, followed in 7 units by an increase in activity. SLN stimulation occasionally evoked single or rhythmic multifibre bursts in the vagal pharyngeal filaments. These bursts, involving expiratory-related units, likely correspond to the buccopharyngeal stage of swallowing.

Activity of respiratory laryngeal motoneurons during fictive coughing and swallowing

Abstract Membrane potential changes and discharges from 28 laryngeal motoneurons were recorded intracellularly in the caudal nucleus ambiguus of decerebrate, paralyzed and ventilated cats. Electrical activities were recorded from 17 expiratory laryngeal motoneurons (ELMs) with maximal depolarizing membrane potential in early expiration, and from 11 inspiratory laryngeal motoneurons (ILMs) with maximal depolarizing membrane potential in inspiration. Activities during breathing were compared with those observed during fictive coughing and swallowing evoked by electrical stimulation of the superior laryngeal nerves. These non-respiratory behaviors were evidenced in paralyzed animals by characteristic discharge patterns of the phrenic, abdominal nerves and pharyngeal branch of the vagus nerve. We recorded the activity of 11 ELMs and 5 ILMs during coughing in which ELMs, but not ILMs, exhibited increased membrane depolarization and discharge frequencies. Membrane depolarization and discharge frequencies of all ELMs were also significantly increased during swallowing. In addition, membrane depolarization of most ELMs (15/17) was preceded by a short-lasting hyperpolarization due to chloride-dependent inhibitory mechanisms occurring at the onset of swallowing. Out of 10 ILMs tested during swallowing, 7 exhibited membrane depolarization, preceded in 5 cases by a short-lasting hyperpolarization. Discharge frequencies of ILMs were significantly reduced during swallowing. The same pattern of phasic activities of ILMs and ELMs was observed during coughing and breathing, suggesting the involvement of similar excitatory pathways in both behaviors. These results imply that the duration of activation and the discharge frequency of neurons of the central generator for breathing that drive laryngeal motoneurons are enhanced during coughing. During swallowing, in addition to central excitatory mechanisms, laryngeal motoneurons are subjected to an initial inhibition of unknown origin. This inhibition probably contributes to the temporal organization of the swallowing motor sequence.

Patterns of membrane potentials and distributions of the medullary respiratory neurons in the decerebrate rat

We analyzed the membrane potential of 161 respiratory neurons in the medulla of decerebrate rats which were paralyzed and ventilated. Three types of inspiratory (I) neurons were observed: those displaying progressive depolarization in inspiration (augmenting I neurons), those which gradually repolarized after maximal depolarization at the onset of inspiration (decrementing I neurons) and those exhibiting a plateau or bell-shaped membrane potential trajectory throughout inspiration (I-all neurons). Three types of expiratory (E) neurons were also encountered: those in which the membrane potential progressively depolarized (augmenting E neurons), those in which the membrane potential repolarized during the interval between phrenic bursts (decrementing E or post-I neurons) and those exhibiting a plateau or bell-shaped membrane potential trajectory throughout expiration (E-all neurons). Axonal projections of these medullary neurons were identified in the cranial nerves (n = 34), or in the spinal cord (n = 19) as revealed by antidromic stimulation and/or by reconstruction following horseradish peroxidase (HRP) labeling. The other 108 neurons were not antidromically activated (NAA) by the stimulations tested, or had their axons terminating inside the medulla as revealed by HRP labeling. All these respiratory neurons, except for 3 which were hypoglossal motoneurons, had their somata within the ventrolateral medulla, in the region of the nucleus ambiguus, homologous to the ventral respiratory group (VRG) of the cat. No dorsal respiratory group (DRG) was detected within the medulla of the rats. Due to this absence of a DRG, it is concluded that the neural organization of respiratory centers is quite different in cats and rats.

Discharge patterns of laryngeal motoneurones in the cat: an intracellular study.

In decerebrate cats, stable intracellular recordings were made from 37 laryngeal motoneurones, the membrane potentials of which varied in relation to respiration. These motoneurones were identified as laryngeal since all were antidromically activated by stimulation of the recurrent laryngeal nerve, but in two, the antidromic activity could only be elicited by vagal stimulation (vagotomized cats). The cell bodies were all located within the nucleus ambiguous. Sixteen cells were depolarized during the phrenic burst and were classified as inspiratory laryngeal motoneurones (ILM). They repolarized at end-inspiration and received two successive waves of postsynaptic inhibition during expiration: an early, strong one and a late (end-expiratory), weaker one. The decay of the first wave was related to the duration of postinspiratory phrenic activity. Twenty-one cells depolarized abruptly in early expiration followed by a more-or-less gradual repolarization. They were classified as expiratory laryngeal motoneurones (ELM). All ELM were strongly inhibited during inspiration. Some of them received weak inhibition during end expiratory phase. The rapid and large depolarization observed during early expiration (and consequent maximal discharge frequency) can be explained by two summating mechanisms: a postinhibitory rebound resulting from the removal of inhibition during inspiration, and an excitatory phenomenon of unknown origin. The amplitude of this excitatory phenomenon was largest in cats with the most residual (early expiratory) phrenic activity. To explain the hyperpolarizations occurring in ELM during late expiratory and inspiratory phases and those occurring in ILM during early expiration, we hypothesize that reciprocal inhibition exists between networks controlling ILM and ELM activities or between these motoneurones themselves.(ABSTRACT TRUNCATED AT 250 WORDS)

ARE THE POST-INSPIRATORY NEURONS IN THE DECEREBRATE RAT CRANIAL MOTONEURONS OR INTERNEURONS ?

We examined the membrane potentials of 63 respiratory neurons in the ventrolateral medulla of decerebrate rats, whose trajectories had the characteristics of the post-inspiratory neurons, i.e. exhibiting hyperpolarization during inspiration, rapid depolarization at end-inspiration and progressive repolarization with a decrementing pattern during the intervals between phrenic bursts. Synaptic responses of 6 post-inspiratory neurons which were tested by stimulation of cervical vagus or superior laryngeal nerves were excitatory. Eleven of these 63 post-inspiratory neurons were labeled by intracellular injection of horseradish peroxidase (HRP). Ten of these 11 labeled neurons were motoneurons since their axons exited the medulla after joining the roots of cranial nerves. However, only one of these motoneurons was antidromically activated by stimulation of the ipsilateral cervical vagus nerve. We assumed that most of the post-inspiratory medullary neurons of the present study were motoneurons, but not interneurons, although antidromic invasion was not possible after stimulation of the cervical vagus and superior laryngeal nerves. Two post-inspiratory neurons of this sample had bulbospinal axons, which were revealed by antidromical activation of spinal cord and HRP labeling, respectively. The axon of the labeled bulbospinal neuron had axonal collaterals which were distributed within the region of the nucleus ambiguous of the ipsilateral medulla. The functional significance of this type of post-inspiratory neuron is discussed.

Activity of respiratory-related oropharyngeal and laryngeal motoneurones during fictive vomiting in the decerebrate cat

Activities of respiratory laryngeal and oropharyngeal respiratory nerves were studied during fictive vomiting elicited by supradiaphragmatic vagus nerve stimulation in the decerebrate cat. Inspiratory laryngeal nerves were strongly inhibited throughout the retching and expulsion phase. Glossopharyngeal, hypoglossal and expiratory laryngeal nerves were coactivated with the phrenic and abdominal nerve bursts. The pharyngeal branch of the vagus nerve discharged during the phrenic and abdominal inter-burst of the retching phase, and was silent during the abdominal expulsion. These activities permit speculation about the role of upper airway muscles during vomiting.

Potent inhibition of both the acute and delayed emetic responses to cisplatin in piglets treated with GR205171, a novel highly selective tachykinin NK1 receptor antagonist

The effects of GR205171, a selective tachykinin NK1 receptor antagonist, were investigated on both the acute and delayed phases of cisplatin‐induced nausea‐like behaviour and vomiting in the conscious piglet. Animals receiving cisplatin (5.5 mg kg−1, i.v.) were observed for 60 h. Fifteen min prior to cisplatin infusion (T0−15 min), eight piglets acting as controls received an intravenous injection of saline solution (1 ml kg−1), whereas experimental animals received a single i.v. administration of GR205171 (1 ml kg−1) at a dose of 0.01 (n=8), 0.03 (n=8), 0.1 (n=8), 0.3 (n=16) or 1.0 (n=13) mg kg−1. In eight additional piglets, GR205171 (1 mg kg−1) was administered 15 min before the onset of the delayed phase (T16−15 min). A further five piglets received GR205171 (1 mg kg−1) every 6 h throughout the experiment. The latencies of the first emetic episode (EE) and nausea‐like behavioural episode (NE) increased in all experimental groups treated at T0−15 min, and the total number of both EE and NE during the 60 h was reduced in a dose‐dependent manner. In piglets treated at T0−15 min with GR205171 1 mg kg−1, eight out of 13 (62%) did not vomit throughout the experiment. Animals treated with GR205171 (1 mg kg−1) at T16−15 min exhibited an acute response to cisplatin but did not vomit during the delayed phase. The greatest inhibition of both nausea‐like behaviour and vomiting was observed in piglets receiving multiple injections of GR205171. These results demonstrate the long‐lasting anti‐emetic effects of GR205171, and confirm the key role of substance P within the emetic reflex.

Central distributions of the efferent and afferent components of the pharyngeal branches of the vagus and glossopharyngeal nerves: an HRP study in the cat

SummaryThe central distributions of efferent and afferent components of the pharyngeal branches of the vagus (PH-X) and glossopharyngeal (PH-IX) nerves in the cat were studied by soaking their central cut ends in a horseradish peroxidase (HRP) solution. HRP-labelled PH-X neurones were distributed ipsilaterally in the rostral part of the nucleus ambiguus (NA) and the retrofacial nucleus (RFN); HRP-labelled PH-IX neurones were found in the ipsilateral RFN and the bulbopontine lateral reticular formation (RF). Vagal pharyngeal neurones constituted a large population of brainstem motoneurones. The population of HRP-labelled glossopharyngeal neurones was divided into two components. Indeed, on the basis of their location and somal morphology, the most ventral cells were identified as cranial motoneurones and those scattered in the lateral RF as parasympathetic preganglionic neurones. Application of HRP to the PH-IX nerve resulted also in the labelling of fibres and terminals in the alaminar spinal trigeminal nucleus and the nucleus of the solitary tract (NTS). The afferent fibres entered the lateral medulla with the glossopharyngeal roots, ran dorsomedially, then turned caudally toward the NTS and the caudal part of the alaminar spinal trigeminal motor (V) nucleus. In the NTS, labelled fibres ran mainly along the solitary tract, projecting to terminals in the dorsal and dorsolateral nuclei of the NTS.