NEUROMODULATION OF HYPOGLOSSAL MOTONEURONS - CELLULAR AND DEVELOPMENTAL MECHANISMS

Hypoglossal motoneurons (HMs) in the caudal brainstem have a respirato ry-related activity pattern and contribute to control of upper airway resistance. In this review, we focus primarily on signalling mechanism s utilized by neurotransmitters to enhance HM excitability. In particu lar, we consider: (1) the membrane depolarization induced by a number of different putative transmitters [thyrotropin-releasing hormone (TRH ), serotonin (5-HT), norepinephrine (NE)]; and (2) the inhibition of a calcium-dependent spike afterhyperpolarization (AHP) by 5-HT and its effect on firing behavior. Potential functional consequences on HM beh avior of these different neurotransmitter effects is discussed. In add ition, we describe postnatal changes in transmitter effects and sugges t potential cellular mechanisms to explain those developmental changes . Most of the data discussed are derived from in vitro electrophysiolo gical recordings performed in preparations from neonatal and adult rat s. (C) 1997 Elsevier Science B.V.