DEVELOPMENTAL MODULATION OF GLUTAMATERGIC INSPIRATORY DRIVE TO HYPOGLOSSAL MOTONEURONS

Proper function of hypoglossal motoneurons (XII MNs) innervating tongu e muscles is critical for respiratory control of the airway. Morpholog ical and electrophysiological properties of XII MNs change during post natal development, as do modulatory systems. Despite these changes, th e system producing respiratory movements must remain fully functional throughout life. Modulatory systems have therefore received considerab le attention since coordination of their development with a developing neuromuscular system may be critical for maintenance of continuous, e fficient breathing. Developmental modulation of XII inspiratory activi ty by three transmitter systems is examined. Thyrotropin-releasing hor mone (TRH) mediates an increase in MN input resistance (R-N) in juveni le but not neonate MNs, and this likely underlies the developmental in crease in TRH potentiation of inspiratory activity. Norepinephrine (NE ) potentiation of inspiratory activity, which in the neonate is produc ed in part by an alpha(1)-mediated increase in R-N, also increases pos tnatally. Effects of purinergic transmission on XII inspiratory activi ty remain constant during the first 2 weeks of postnatal development. Adenosine-triphosphate (ATP) produces tonic excitation and inspiratory potentiation that likely result from activation of postsynaptic P2 re ceptors. A secondary inhibitory effect likely results from hydrolysis of ATP to adenosine and activation of presynaptic A1 adenosine recepto rs. The functional relevance of these postnatal changes is discussed. (C) 1997 Elsevier Science B.V.