HYPOXIC RESPONSE OF HYPOGLOSSAL MOTONEURONS IN THE IN-VIVO CAT

1. In current and voltage clamp, the effects of hypoxia were studied o n resting and synaptic properties of hypoglossal motoneurones in barbi turate-anaesthetized adult cats. 2. Twenty-nine hypoglossal motoneuron es with a mean membrane potential of -55 mV responded rapidly to acute hypoxia with a persistent membrane depolarization of about +17 mV. Th is depolarization correlated with the development of a persistent inwa rd current of 0.3 nA at holding potentials close to resting membrane p otential. 3. Superior laryngeal nerve (SLN) stimulation-evoked EPSPs w ere reduced in amplitude by, on average, 46%, while IPSP amplitude was reduced by 31%. SLN stimulation-evoked EPSCs were reduced by 50-70%. 4. Extracellular application of adenosine (10 mM) hyperpolarized hypog lossal motoneurones by, on average, 5.6 mV, from a control value of -6 2 mV. SLN stimulation-evoked EPSPs decreased by 18% and IPSPs decrease d by 46% during adenosine application. 5. Extracellular application of the K-ATP channel blocker glibenclamide led to a blockade of a persis tent outward current and a significant increase of SLN stimulation-evo ked EPSCs. 6. We conclude that hypoglossal motoneurones have a very lo w tolerance to hypoxia. They appear to be under metabolic stress even in normoxia and their capacity to activate protective potassium curren ts is limited when compared with other brainstem neurones. This may he lp to explain the rapid disturbance of hypoglossal function during ene rgy depletion.