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1 Neurobiology Sector and INFM Unit, International School for Advanced Studies (SISSA), Trieste, Italy
Tongue muscles innervated by the hypoglossal nerves play a crucial role to ensure airway patency and milk suckling in the neonate. Using a slice preparation of the neonatal rat brain, we investigated the electrophysiological characteristics of hypoglossal motoneurones in the attempt to identify certain properties potentially capable of synchronizing motor commands to the tongue. Bath-applied DHPG, a selective agonist of group I metabotropic glutamate receptors (mGluRs), generated persistent, regular electrical oscillations (4–8 Hz) recorded from patch-clamped motoneurones. Under voltage clamp, oscillations were biphasic events, comprising large outward slow currents alternated with fast, repeated inward currents. Electrical oscillations had amplitude and period insensitive to cell membrane potential, and required intact glutamatergic transmission via AMPA receptors. Oscillations were mediated by subtype 1 receptors of group I mGluRs (mGluR1s), and were routinely observed during pharmacological block of glycinergic and GABAergic inhibition, although they could also be recorded in standard saline. Simultaneous recordings from pairs of motoneurones within the same hypoglossal nucleus demonstrated that oscillations were due to their strong electrical coupling and were blocked by the gap junction blocker carbenoxolone. Pacing of slow oscillations apparently depended on the operation of KATP channels in view of the block by tolbutamide or glibenclamide. Under current clamp, oscillations generated more regular spike firing of motoneurones and facilitated glutamatergic excitatory inputs. These data suggest that neonatal motoneurones of the nucleus hypoglossus possess a formerly undisclosed ability to express synchronous electrical oscillations, unveiled by activation of mGluR1s.
(Received 18 November 2004;
accepted after revision 15 December 2004;
first published online 20 December 2004)
Corresponding author A Nistri: Neurobiology Sector and INFM Unit, International School for Advanced Studies (SISSA), Trieste, Italy. Email: nistri{at}sissa.it
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  J. Y. Sebe, J. F. van Brederode, and A. J. Berger Inhibitory Synaptic Transmission Governs Inspiratory Motoneuron Synchronization J Neurophysiol, July 1, 2006; 96(1): 391 - 403. [Abstract] [Full Text] [PDF]
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 E. Sharifullina and A. Nistri Glutamate uptake block triggers deadly rhythmic bursting of neonatal rat hypoglossal motoneurons J. Physiol., April 15, 2006; 572(2): 407 - 423. [Abstract] [Full Text] [PDF]
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A. Nistri, K. Ostroumov, E. Sharifullina, and G. Taccola Tuning and playing a motor rhythm: how metabotropic glutamate receptors orchestrate generation of motor patterns in the mammalian central nervous system J. Physiol., April 15, 2006; 572(2): 323 - 334. [Abstract] [Full Text] [PDF]
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