1. alpha1-adrenergic receptor-induced slow rhythmicity in nonrespiratory cervical motoneurons of neonatal rat spinal cord
- Author
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Morin, Didier, Bonnot, Agnès, Ballion, Bérangère, Viala, Denise, Institut Mondor de Recherche Biomédicale (IMRB), and Institut National de la Santé et de la Recherche Médicale (INSERM)-IFR10-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)
- Subjects
MESH: Phenylephrine ,Hypoglossal Nerve ,Periodicity ,MESH: Periodicity ,Patch-Clamp Techniques ,Potassium Channels ,[SDV]Life Sciences [q-bio] ,MESH: Rats, Sprague-Dawley ,MESH: Animals, Newborn ,MESH: Dose-Response Relationship, Drug ,Membrane Potentials ,MESH: Spinal Cord ,Rats, Sprague-Dawley ,MESH: Respiratory Center ,Phenylephrine ,MESH: Pregnancy ,MESH: Vagus Nerve ,Pregnancy ,MESH: Animals ,Glossopharyngeal Nerve ,Motor Neurons ,Medulla Oblongata ,Axotomy ,Vagus Nerve ,MESH: Potassium Channels ,Spinal Cord ,MESH: Hypoglossal Nerve ,Female ,Spinal Nerve Roots ,Adrenergic alpha-Agonists ,MESH: Motor Neurons ,MESH: Spinal Nerve Roots ,MESH: Rats ,MESH: Axotomy ,Tetrodotoxin ,MESH: Medulla Oblongata ,Receptors, Adrenergic, alpha-1 ,MESH: Patch-Clamp Techniques ,MESH: Membrane Potentials ,Animals ,MESH: Glossopharyngeal Nerve ,Dose-Response Relationship, Drug ,Respiratory Center ,MESH: Tetrodotoxin ,Rats ,nervous system ,Animals, Newborn ,MESH: Adrenergic alpha-Agonists ,MESH: Female ,MESH: Receptors, Adrenergic, alpha-1 - Abstract
International audience; Previous studies have reported that the alpha1-adrenergic system can activate spinal rhythm generators belonging to the central respiratory network. In order to analyse alpha1-adrenergic effects on both cranial and spinal motoneuronal activity, phenylephrine (1-800 microM) was applied to in vitro preparations of neonatal rat brainstem-spinal cord. High concentration of phenylephrine superfusion exerted multiple effects on spinal cervical outputs (C2-C6), consisting of a lengthening of respiratory period and an increase in inspiratory burst duration. Furthermore, in 55% of cases a slow motor rhythm recorded from the same spinal outputs was superimposed on the inspiratory activity. However, this phenylephrine-induced slow motor rhythm generated at the spinal level was observed neither in inspiratory cranial nerves (glossopharyngeal, vagal and hypoglossal outputs) nor in phrenic nerves. Whole-cell patch-clamp recordings were carried out on cervical motoneurons (C4-C5), to determine first which motoneurons were involved in this slow rhythm, and secondly the cellular events underlying direct phenylephrine effects on motoneurons. In all types of motoneurons (inspiratory and nonrespiratory) phenylephrine induced a prolonged depolarization with an increase in neuronal excitability. However, only nonrespiratory motoneurons showed additional rhythmic membrane depolarizations (with spiking) occurring in phase with the slow motor rhythm recorded from the ventral root. Furthermore the tonic depolarization produced in all motoneurons results from an inward current [which persists in the presence of tetrodotoxin (TTX)] associated with a decrease in neuron input conductance, with a reversal potential varying as a Nernstian function of extracellular K+ concentration. Our results indicate that the alpha1-adrenoceptor activation: (i) affects both the central respiratory command (i.e. respiratory period and inspiratory burst duration) and spinal inspiratory outputs; (ii) induces slow spinal motor rhythmicity, which is unlikely to be related to the respiratory system; and (iii), increases motoneuronal excitability, probably through a decrease in postsynaptic leak K+ conductance.
- Published
- 2000