Development of thyrotropin-releasing hormone and norepinephrine potentiation of inspiratory-related hypoglossal motoneuron discharge in neonatal and juvenile mice in vitro

Abstract

1. The ontogeny of thyrotropin-releasing hormone (TRH) and norepinephrine (NE) potentiation of inspiratory-related hypoglossal (XII) motor nerve discharge was studied in medullary slices from P0–3, P7, and P11-14 mice that retain functional networks for respiration. 2. TRH, applied locally to the XII motor nucleus, had no effect on XII inspiratory burst amplitude in slices from P0–3 mice. By P7 there was significant potentiation of burst amplitude that increased more than three-fold by P11–14. NE applied to the XII nucleus produced significant potentiation in all age groups. Potentiation increased developmentally with the largest increase occurring between P0–3 and P7. 3. Thus catecholamine and TRH modulation of inspiratory-related XII nerve activity increases during the first two weeks of life; the potentiating effects of NE appear prior to those of TRH. 4. With rhythmically active, transverse medullary slices from mice up to 2 wk of age, it is now possible to study the development of XII motoneuron modulation as it relates to respiratory control of the upper airway.